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Sonntag, 29. März 2015 - 17:39 Uhr

Astronomie-History - Kosmos 1943: Der Komet 1942g

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Aus dem CENAP-Archiv:

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Quelle: KOSMOS, CENAP-Archiv


Tags: Astronomie 

1590 Views

Sonntag, 29. März 2015 - 12:00 Uhr

Raumfahrt - Space-X auf der Suche nach neuen Verbrennungstechnologien, für bemannte Missionen zum Mars

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Elon Musk is shaking up both the car and space industries with his respective Tesla and SpaceX companies, and the irony is that while the former is totally upending the combustion engine for land transportation with zippy and stylish electric cars, the latter company has to not only embrace but to create new combustion technologies to get a manned mission to Mars as Musk not only dreams of doing, but is making happen.
Getting a small group of human beings to Mars and back is no easy task, we learned at the recent GPU Technology Conference in San Jose hosted graphics chip and accelerator maker Nvidia. One of the problems with such a mission is that you need a very large and efficient rocket engine to get the amount of material into orbit for the mission, explained Adam Lichtl, who is director of research at SpaceX and who with a team of a few dozen programmers is try to crack the particularly difficult task of better simulating the combustion inside of a rocket engine. You need a large engine to shorten the trip to Mars, too.
“One of the major problems is radiation exposure,” explained Lichtl. “To get to Mars, you need to align your launch with the correct window to an orbit given the amount of energy that your rocket can produce. Anyone who has played Kerbil Space Program has seen this is delta-v, which is the change in one orbit – say one around the Earth – and escaping that by giving yourself a delta-v and a different trajectory that will intersect with Mars. We need vehicles that can provide as much delta-v as possible in order to shorten that trip to Mars. In addition, there is a second major obstacle of actually staying on Mars – not just taking a robot or a rover or going on a suicide trip, but a real expedition to Mars – and that is infrastructure. When the pioneers went across the country to settle, they had to build their own cabins and they had to hunt for food. But they had air. It is a little bit more tricky on Mars.”
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Not only do you need a lot of stuff to get to Mars and sustain a colony there, but you also need a way to generate fuel on Mars to come back to Earth. All of these factors affect the design of the rocket engine.
The International Space Station weighs about 450 tons, and it took 36 Space Shuttle missions and five Proton rocket launches to heft its parts into space. The NASA Mars Design Reference Architecture wants to get about 300 tons of material into Earth orbit and assemble a vehicle for the Mars trip – and do it in three launches of 100 tons each. Building this vehicle and giving it fuel from Earth is relatively easy, but the rocket on the spacecraft has to be able to burn methane as a fuel, because this can be synthesized from water in the Martian soil and carbon dioxide in the Martian air relatively easily. (The current Merlin 1D engines used by SpaceX in its launch vehicles run on kerosene, which is a much denser and thrust-producing fuel, which is made through the distillation of oil.)
As if these were not problems enough, there is another really big issue. The computational fluid dynamics, or CFD, software that is used to simulate the movement of fluids and gases and their ignition inside of all kinds of engines is particularly bad at assisting in rocket engine design.
“Methane is a fairly simple hydrocarbon that is perfectly good as a fuel,” Lichtl said. “The challenge here is to design an engine that works efficiently with such a compound. But rocket engine CFD is hard. Really hard.”
And so, SpaceX is working with various academic research institutions and Sandia National Laboratories to come up with its very own CFD software, which will be used to create future – and beefier – versions of the company’s Merlin rocket engines suitable for the trip to Mars and able to burn methane as a fuel.
Lichtl is an interesting choice to head up the design of the rocket engines at SpaceX, which seems like a dream job if you ask me. While a graduate student at Carnegie Mellon University, Lichtl developed Monte Carlo and high-energy physics simulations, and then he worked at Brookhaven National Laboratory as a post-doc doing high-energy physics research. This was followed up by a stint of several years at Morgan Stanley as a quant and then as a strategist for the oil and gas and then base and precious metals desks at the financial services firm. Lichtl joined SpaceX as a principal propulsion engineer two years ago and has risen through the ranks to head up the Mars engine design effort.
Stephen Jones, who is the lead software engineer at SpaceX and a former engineer at Nvidia, is running the project to develop the company’s homegrown CFD software. This software has not yet been given a name, and the techniques that SpaceX has developed could ironically be used to improve all kinds of combustion engines – including those used in cars. (Elon Musk might not like that.)
Existing CFD Not Well Suited To Rockets
At its engine plant in Texas, SpaceX is trying out a number of different injectors and other parameters to squeeze the most performance out of its engines, and it runs tests every day. These tests are expensive and, more importantly, even if you design engines and do physical testing on them and layer them with all manner of sensors on the outside, you cannot see what is going on inside the engines as they run. It is far better to simulate all of the components of the engine and their fuels and narrow down the injector configurations through simulations and then do the design, manufacturing, and physical testing on just a few, optimal configurations.
“Another very important insight that can be gained with rocket engines is that of combustion instability, which is the coupling of pressure waves and chemical energy release. This is a phenomenon that has delayed many engine projects for many years. It is the bane of engine development. The engine starts to shake and either it shakes so violently it comes apart or you can’t put a payload on top of the vehicle because it will shake it too much.”
Automobile engine and turbine engine manufacturers have used CFD to radically improve the efficiency of these engines. But the timescales are much more confined and so are the areas where the combustion reaction is taking place. These engines have far less complex chemical reactions and physical processes to simulate than what is going on in a much larger rocket engine. So you can’t just take CFD software that was designed for an internal combustion engine like the one that Tesla is trying to remove from the roads over the next several decades and use it to simulate a rocket engine.
At the molecular scale in the fuel and oxidizers, reactions inside of a rocket engine take place at between 10-11 and 10-9 seconds, and flow fields (or advection) occur at between 10-7 and 10-6 seconds, and the acoustical vibrations and the chamber residence (when the fuel is actually burning in and being ejected by the rocket motor) occur at between 10-4 and 10-3 seconds. This is a very broad timescale to have to cover in a CFD simulation.
“The difference is that without GPU acceleration, and without the architecture and the techniques that we just described, it takes months on thousands of cores to run even the simplest of simulations.”
The physical size of the reactions that need to be simulated is also a problem that other combustion CFD programs do not have to cope with. At the one extreme, the combustion chamber of a rocket motor is around 1 meter or so long and at the other end the scale is what is called the Kolmogorov scale, at one micrometer, that controls the rate of viscous dissipation in a turbulent fluid and therefore determines the rate of combustion in the rocket engine. (Basically, the exploded fuel creates ever smaller eddies of chemically reacting fuel and oxidizer, starting with the injection at a large scale and ending with combustion at the Kolmogorov scale, where the extreme friction between these components creates the heat that ejects the material from the rocket, producing thrust.) That is a factor of 1 million scale that the simulation has to cope with on the physical level.
“If you think about subdividing any sort of CFD mesh by powers of two, over and over again, you need to subdivide it by about 20 times in order to span that kind of dynamic range in length scales,” says Lichtl. “If you were to uniformly populate a grid the size of a combustion chamber, we are talking about yottabytes of data. This is not feasible.”
What rocket designers do is what others who do simulation and modeling typically do, and that is either to have a coarse grained simulation with lots of features but pretty low resolution or a much smaller simulation, in terms of scales of time and space, but with a richer sense of what is going on.
“Why not have it both ways?,” Lichtl asks rhetotically. “The interesting thing about turbulence is that even though there is structure at all scales, it is not dense. You do not have to resolve down to the finest scales everywhere. It is really fractal in nature. This lower or fractal dimensionality allows us to concentrate computing resources where it is needed. You can think of this as a glorified compression algorithm.”
The trick is to do all of the mathematics on the compressed fractal data that describes the turbulent fluids without having to decompress that data, and to accomplish this, software engineers at SpaceX have come up with a technique called wavelets local fractal compression. This is done by using an adaptive grid for the simulation, splitting the difference between a structured grid at a certain scale and an unstructured grid that offers a non-uniform chopping of simulation space that is related to the scale of the features around it. Both of these are static and have to be configured before the simulation beginds, but what SpaceX has come up with is both dynamic and automatic.
To show off its CFD code, Jones showed a simulation of some fuel and oxidizer being exploded in a box, with shock waves bouncing the fluid around and causing a tremendous amount of fractal turbulence. (This simulation is so much better than a lava lamp. You can see it at this link starting at about 36 minutes into the presentation.) This simulation shows the density of the gases changing over a span of time covering microseconds:
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“If you actually did this as a fully dense calculation, this would require 300 million grid nodes,” said Jones. “We did this on a single GPU because we are only calculating it where it needs to be done and it figures it out for itself where that data needs to be.”
Jones did not divulge which GPU that SpaceX was using, but presumably it was a “Kepler” class Tesla GPU coprocessor and presumably it is making use of the dynamic parallelism features of that GPU to do this adaptive grid. (This is one of the key differentiators between the GPUs that GeForce graphics cards get and the Tesla server coprocessors that have this and other features and that command a premium price because of that.)
Here is the same simulation running on a single GPU that shows the ignition of the gas and the distribution of temperatures (starting at 37:45) as it explodes and the gas ricochets around:
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The yellow areas are the hottest spots in the explosion, and Jones said you can zoom in by a factor of 60,000X in this simulation and still see structures.
Lichtl says that people have tried to use wavelet compression before, and these particular simulations are based on work done by Jonathan Regele, a professor at the department of aerospace engineering at Iowa State University.
“The difference is that without GPU acceleration, and without the architecture and the techniques that we just described, it takes months on thousands of cores to run even the simplest of simulations. It is a very interesting approach but it doesn’t have industrial application without the hardware and the correct algorithms behind it. What the GPUs are doing here is enabling tremendous acceleration. I am grateful to SpaceX for allowing us to basically start from scratch on CFD and in many ways reinventing the wheel. People may say, ‘Why would you do that?’ The reason is that if you are a little bit wrong in a traditional CFD simulation, you are typically OK, you are close enough to the answer to make an engineering decision. With a combustion simulation, if you get it wrong, you have to deal with the vicious interplay of all of these different physical processes.”
To be more precise, if you get the temperature wrong in the simulation by a little, you get the kinetic energy of the gas wrong by a lot because there is an exponential relationship there.  If you get the pressure or viscosity of the fluid wrong by a little bit, you will see different effects in the nozzle than will happen in the real motor.
The other neat thing about its GPU-accelerated combustion CFD, says Lichtl, is that the software and hardware is really good at handling the chemical kinetic models that describe the backwards and forwards chemical reactions as fuel and oxidizer come together. Burning of hydrogen and oxygen is not a simple reaction that creates two water molecules from two hydrogen molecules and one oxygen molecule; rather, you have to simulate 23 possible reactions and 11 intermediate species of molecules to cover all the possible permutations. With the burning of methane with oxygen, there are 53 species of possible intermediate molecular species and 325 possible reactions.
“This is not to be taken lightly,” said Lichtl. “And having the ability to have a massively parallel system crunching this is invaluable. If you can reduce the number of grid points you have to keep active, you can use that otherwise wasted resource on something more valuable, like a chemical reaction calculation.”
This is precisely what SpaceX is doing with its own CFD code, which simulates the chemical reactions and turbulence of fuel being burned in a compressor chamber and ejects from a nozzle (at 43:00 in the presentation):
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This particular simulation is showing the acoustical properties of the burn, including the Mach disk and the trailing Mach diamonds, all generated from the physics of the SpaceX CFD model and, as you can see, pretty faithfully mirroring the actual burn of a Space Shuttle engine shown on the upper left. The gases are supersonic and clear as they exit the nozzle, but they hit the shock wave behind the nozzle, slow down and compress, and turn white.
While the homegrown SpaceX CFD code is still under development, the obvious thing to do is to scale it out by having it span multiple GPUs and then across a cluster of systems.
“The code is currently running on a single machine now, but the near-term goal is to parallelize it,” Lichtl confirmed to The Platform after his presentation.
Lichtl said that SpaceX did not have to wait until Nvidia delivers its NVLink GPU clustering interconnect to hook GPUs to each other to scale up the CFD application and that SpaceX can cluster over the PCI-Express bus for now. (He added that “NVLink would be great,” and like many customers running GPU-accelerated simulations, wishes that NVLink was already here.) SpaceX is also looking at various interconnects to link GPUs and CPUs together and is also exploring the use of the MPI protocol to have server nodes work in parallel running the CFD code.
One possible interim option ahead of NVLink might be to deploy the SpaceX CFD software on clusters built using IBM’s Power8 processors and using InfiniBand network interface cards that are tightly and efficiently coupled to the processor through IBM’s Coherent Accelerator Processor Interface, or CAPI. This is the architecture that the US Department of Energy has chosen for two of its largest supercomputers, nicknamed Summit and Sierra, that will be delivered in 2017. Those systems, as The Platform has previously reported when divulging the OpenPower roadmap put together by IBM, Nvidia, and Mellanox Technologies, will also sport a second generation NVLink for linking GPUs together and possibly 200 Gb/sec InfiniBand instead of the 100 Gb/sec speed in the contract. The thing is that Mellanox is already today shipping 100 Gb/sec ConnectX-4 network interface cards that can speak CAPI to the Power8 chip, radically lowering latency compared to 56 Gb/sec InfiniBand and offering nearly twice the bandwidth, too. There are plenty of OpenPower system makers who would love to get the SpaceX business, if the company decides to go down this route.
One important thing, Lichtl continued with his shopping list, was to have server nodes with lots and lots of GPUs.
Music to Nvidia’s ears, no doubt.
Quelle: GPU

Tags: Raumfahrt 

1913 Views

Sonntag, 29. März 2015 - 11:05 Uhr

Astronomie - IZw18: die Galaxie, die die Geschichte des Universums offenbart

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A map of ionized helium in the galaxy has just been published which indicates the presence of peculiar stars similar to the first that ever shone in the universe

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The first galaxies were formed some 13.3 billion years ago, mainly composed of hydrogen and helium, the primary elements that emerged from the Big Bang. Their study to date has been technically very challenging due to their great distance from us, but the observation of analogous galaxies in our vicinity has turned out to be an excellent shortcut.
"Dwarf galaxy IZw18 is the least abundant in metals (in astrophysics, elements heavier than hydrogen and helium) in the nearby universe, and one of the most akin to the primeval galaxies. Its study therefore allows us to catch glimpses of the conditions that prevailed in the primordial universe”, says Carolina Kehrig, researcher at the Institute of Astrophysics of Andalusia in charge of the study that analyses the properties of IZw18.
The study has found a very large region in this small galaxy of ionized helium, which tends to be more frequent in very distant galaxies with low presence of metals. The ionization of helium implies the presence of objects emitting a radiation intense enough to knock electrons off the helium atoms. "In this study we propose a new interpretation of the origin of this radiation in galaxy IZw18, a subject which is still enigmatic”, Kehrig says.
Using the PMAS integral field spectrograph of the 3.5 meter telescope at the Calar Alto Observatory (CAHA), researchers have obtained the first detailed map of this region of  IZw18 and have analyzed possible ionizing sources.
Conventional sources of ionization, such as Wolf-Rayet stars – very massive and with very violent stellar winds – or shocks generated by remnants of supernovae, cannot provide the energy necessary to explain the halo of ionized helium present on  IZw18, so researchers considered other possibilities.
"Our data point to the fact that extremely hot stars, such as supermassive stars with low metal content or massive stars practically devoid of metals may hold the key to the enigma of the excitement of helium on IZw18, even though the existence of these stars has not yet been confirmed by observations on any galaxy”, says Carolina Kehrig (IAA-CSIC).
We would be talking about very hot stars analogous to first generation stars (known as Population III stars) which, according to theoretical models, would be composed only of hydrogen and helium and could be hundreds of times more massive than the Sun. These stars are believed to have played a decisive role in the “reionization” of the universe, during which period the first stars and galaxies became visible and which is still little known.
This study shows how it is possible to extract information about the history of the universe within our own galactic vicinity. 
Quelle:Instituto de Astrofísica de Andalucía (IAA-CSIC)

Tags: Astronomie 

1760 Views

Samstag, 28. März 2015 - 23:00 Uhr

Raumfahrt - ESA IXV Raumgleiter zurück auf dem Trockenen

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ESA’s recovered IXV spaceplane arrived at the Port of Livorno in Italy yesterday and is set to be taken to Turin for final analysis.
Hardware will be removed for engineers to evaluate the reusability of components and the effects of heat, pressure and shock during the mission.
The Intermediate eXperimental Vehicle, IXV, was launched on a Vega rocket from Europe’s Spaceport in French Guiana on 11 February. Released into a suborbital trajectory, it flew autonomously, reentering and splashing down in the Pacific Ocean after 100 minutes.
IXV’s reentry from orbital speed and altitude is an important first for Europe and will drive the development of future reentry vehicles.
The results from the mission are offering new insights into the harsh conditions of reentry and the performance of the craft’s new features.
IXV is ESA’s first reentry testbed since the Atmospheric Reentry Demonstrator capsule in 1998, and added many new features. These included the spacecraft lifting capability for precision landing, flaps and thrusters for a fully controlled reentry, ceramic carbon-matrix composite heatshielding and more than 300 sensors and infrared cameras.
The vehicle responded to conditions so precisely and promptly that mission controllers commented that it was like watching a simulation.
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“We have gathered all the flight data and we are finding some very interesting readings,” notes project manager, Giorgio Tumino.
The results will allow ESA’s aerothermodynamics experts to check their reentry models against observed reality, meaning future reentry missions can be more precisely designed with narrower margins.
As well as contributing to future reentry missions, IXV results could lead to reusability of rocket stages and cheaper access to space.
The general public will have the opportunity to see IXV displayed at various events around Europe this year. Its final destination will be ESA’s ESTEC technology centre in the Netherlands.
Companies and research organisations involved in the craft’s design and construction will have access to mission data. After this, ESA intends to release data to other organisations from Member States in the programme.
ESA is forging ahead with plans for a reusable spacecraft for launch around 2020: Pride, or Programme for Reusable In-orbit Demonstrator for Europe, to be lofted into low orbit by the next-generation small launcher, Vega C.
Quelle: ESA

Tags: Raumfahrt 

1990 Views

Samstag, 28. März 2015 - 17:15 Uhr

Raumfahrt - Erfolgreicher Start von ISRO Polar Satellite Launch Vehicle (PSLV-C27) mit IRNSS-1D Satelliten

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2.03.2015

India will be launching its fourth navigational satellite as part of the Indian Regional Navigational Satellite System (IRNSS) on 9 March, which will be followed by a series of launches in what will be a busy year for the Indian Space Research Organisation (Isro). The satellite IRNSS-1D will be launched onboard Polar Satellite Launch Vehicle (PSLV-C27), the workhorse rocket of the Indian space agency, at 6.35pm from Satish Dhawan Space Centre in Sriharikota. IRNSS is an independent regional navigation satellite system being developed by India consisting of a constellation seven satellites. It is designed to provide accurate position information service to users in India as well as the region extending up to 1500 km from its boundary, which is its primary service area. . The IRNSS System is expected to provide a position accuracy of better than 20 metres in the primary service area. Three satellites are to be placed in suitable orbital slots in the geostationary orbit, a circular orbit 35,786km above the equator and the remaining four will be placed in geosynchronous orbits which are elliptical orbits designed to keep communication satellites within the view of ground stations. The system will provide two types of services including Standard Positioning Service (SPS) which is provided to all the users and Restricted Service (RS), which is an encrypted service provided only to the authorized users. Some of the applications provided by the IRNSS would be terrestrial, aerial and marine navigation, disaster management, vehicle tracking and fleet management, integration with mobile phones, precise timing, mapping and geodetic data capture, terrestrial navigation aid for hikers and travelers, visual and voice navigation for drivers. “With the launch of the fourth satellite, we will be able to start getting accurate positioning information on the ground and they will start evaluating the proof of concept of the navigation project involving the ground support system,” said the Isro spokesperson. “The final details of the launch countdown are still being looked at by senior officials,” he added. After the launch of a navigational satellite, its solar panels are deployed automatically, and Isro’s master control facility at Hassan, Karnataka, takes control of the satellite. The fifth IRNSS satellite is expected to be launched by September. The navigational system aims to reduce India’s dependence on foreign systems such as the US global positioning system and the Russian global navigation satellite system. The IRNSS launch will be followed by a commercial satellite launch aboard the PSLV and the GSAT-6 satellite launch aboard the GSLV-D6 with an indigenous cryogenic engine. Before the end of the year, the space agency will launch India’s first dedicated astronomical satellite, ASTROSAT.
Quelle: livemint
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Countdown to IRNSS 1D on March 7

The 59-hour countdown for the launch of IRNSS 1D satellite, which will help India kick-start functioning of indigenous navigation system on a par with the U.S.’ Global Positioning System (GPS), will commence at 7.35 am on March 7.
The launch is scheduled at the first launch pad of Satish Dhawan Space Centre at Sriharikota at 6.35 p.m. on March 9, a senior ISRO official told The Hindu .
Fourth satellite
IRNSS 1D is the fourth of the seven satellites to be launched to put in place India’s very own satellite navigation system, which will be established at a cost of Rs. 1,400 crore.
Though the launch would help the ISRO commence initial operations on the system, the formal commencement of the IRNSS function would be announced a few months later, as the satellite would have to take its final position.
Communication satellite
Following the IRNSS 1D, the ISRO is planning to launch a GSAT-6 communication satellite on board GSLV D-6 rocket with indigenous cryogenic engine by July.
“A foreign satellite on a commercial launch is planned in May onboard a PSLV and we plan to launch IRNSS 1E and Astrosat satellites before the end of this year,” he said.
Quelle: The Hindu
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ISRO proposes to launch 10 satellites every year
Taking a big step in space exploration, the Indian Space Research Organisation has proposed to launch 10 satellites every year beginning 2015, said S.K. Shivakumar, Director, ISRO Satellite Centre, Bengaluru, here on Sunday.
Speaking at the Science Day celebrations at Sona College of Technology, he said that currently five satellites are launched by India every year of which most of the satellites are for our own use. “We need to expand our space programme and hence, planned for 10 launches from this year,” he added.
He said that India had launched 72 satellites from 1975 till date and the 73{+r}{+d}satellite for navigation is scheduled for March 9 launch. The scientist behind the successful Mars Orbiter Mission said “solving technology challenges in each state, micro level planning, multi-level review and collaborative engineering efforts of all ISRO centres is the success behind our space programme.” He called upon each engineering student to contribute for the nation’s growth through their innovative skills and asked them to be technically updated.
“ISRO welcomes students from all engineering streams as tremendous opportunities are available,” he added. When a student asked why satellites were launched from foreign countries, he said that “it was to exhibit our calibre and strength to foreign nations.”
C. Valliappa, Chairman, Sona Group of Institutions, said that the college is carrying out research for supplying a component for Chandrayaan 2 mission to the ISRO.
He explained the institution’s contribution in supplying various components for ISRO’s earlier missions.
K. Karunakaran, Dean and coordinator for the event, V. Jayaprakash, Principal, C.V. Koushik, Director of Academics, and others spoke.
As part of the week-long Science Day celebrations, exhibitions, paper presentations, quiz and seminar on patent rights were conducted.
About 300 students displayed projects that focused on earthquake resistant building, energy from speed breakers, power generation through water flow in households, mobile security alert and others.
Quelle: The Hindu
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India will move closer to its own satellite navigation system with the launch of its fourth satellite tentatively slated for March 9, a senior official of the Indian space agency said on Monday.
“The launch is tentatively planned for March 9 evening around 6.35 p.m. However final green signal for the launch will be given days ahead of the satellite launch,” M.Y.S. Prasad, director, Satish Dhawan Space Centre, part of Indian Space Research Organisation (ISRO).
He said the satellite has been tested and mated with the rocket and the heat shield will be closed Monday.
“Full test will be done again Tuesday and the rocket will be moved to the second launch pad on March 4,” Prasad said.
According to him, the space agency’s Launch Authorisation Board (LAB) has to give the final nod for the rocket’s flight.
The LAB meeting is slated for March 6.
The 59 hour countdown is expected to begin on March 7 morning.
Weighing 1,425 kg, the fourth of the Indian Regional Navigation Satellite System (IRNSS) satellite-IRNSS-1D would be flown into space in an Indian rocket called Polar Satellite Launch Vehicle-XL.
After its successful launch and commissioning IRNSS-ID is expected to make India among select group of countries having its own satellite navigation system.
The satellite has a life span of around 10 years.
Currently India is knocking at the door step of an exclusive space club – navigation satellite system owing club – that has the US, Russia, China and Japan as members.
Though the full system comprises of nine satellites – seven in orbit and two on the ground as stand-by – the navigation services could be made operational with four satellites, ISRO officials had said earlier.
Each satellite costs around Rs.150 crore and the PSLV-XL version rocket would cost around Rs.130 crore. The seven rockets would involve an outlay of around Rs.910 crore.
The entire IRNSS constellation of seven satellites is planned to be completed by 2015.
The first satellite IRNSS-1A was launched in July 2013, the second IRNSS-1B in April 2014 and the third one October 16, 2014.
Once the regional navigation system is in place, India need not be dependent on others.
The IRNSS will provide two types of services — standard positioning service and restricted service. The former is provided to all users and the latter is an encrypted service for authorised users.
The IRNSS system comprises of two segments – the space and the ground. The space segment consists of seven satellites of which three will be in geostationary orbit and four in inclined geosynchronous orbit.
The ground segment consists of infrastructure for controlling, tracking and other facilities.
Quelle: BER
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Update: 5.03.2015
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ISRO defers satellite launch

The Indian Space Research Organisation has postponed the launch of IRNSS-1D, its fourth navigational satellite, from the Satish Dhawan Space Centre, Sriharikota, scheduled for March 9.
A technical anomaly detected during combined electrical checks of the satellite and the launcher on Tuesday led to the postponement. The flight on the PSLV-C27 launcher will take place after testing and clearing the anomaly, the space agency announced on its website on Wednesday.
Quelle: The Hindu
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Update: 24.03.2015
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Isro to Launch Fourth Navigational Satellite IRNSS-1D on Saturday

India's fourth navigation satellite will be launched on March 28 evening, the Indian space agency said on Monday.
According to Indian Space Research Organisation (Isro), the Indian rocket - Polar Satellite Launch Vehicle (PSLV-XL) - will blast off with the fourth satellite of the Indian Regional Navigation Satellite System (IRNSS) at 5.19 p.m. on March 28.
The 1,425 kg satellite is called IRNSS-1D and will be the first satellite to be put into orbit by an Indian rocket in 2015.
"The rocket has been moved to the launch pad or the umbilical tower. The rocket will be fixed to the umbilical tower," M.Y.S. Prasad, director of the Satish Dhawan Space Centre, told IANS over phone from Sriharikota.
India's only rocket port is located at Sriharikota in Andhra Pradesh around 80km from Chennai.
According to Prasad, after the rocket is connected to the umbilical tower system, checks would be carried out including full rocket and satellite checks.
Originally Isro had planned to launch the IRNSS-1D satellite on March 9.
But on March 4, Isro deferred the launch after it found that one of the telemetry transmitters in the IRNSS-1D was not working properly.
India has so far launched three regional navigational satellites as part of a constellation of seven satellites to provide accurate position information service to users across the country and the region, extending up to an area of 1,500km.
Though the full system comprises nine satellites - seven in orbit and two on the ground as stand-by - the navigation services could be made operational with four satellites, Isro officials had said.
Each satellite costs around Rs. 150 crores and the PSLV-XL version rocket costs around Rs. 130 crores. The seven rockets would involve an outlay of around Rs. 910 crores.
The entire IRNSS constellation of seven satellites is planned to be completed this year itself.
The first satellite IRNSS-1A was launched in July 2013, the second IRNSS-1B in April 2014 and the third on October 16, 2014.
Once the regional navigation system is in place, India need not be dependent on other platforms.
Meanwhile European space agency Arianespace is also getting ready to launch two Galileo satellites on March 27.
The two satellites would be launched jointly by a Soyuz rocket blasting off from French Guyana.
According to Arianespace, the Galileo programme is Europe's initiative for satellite navigation. Providing a highly accurate global positioning system under civilian control, it would consist of 30 satellites in total, along with European control centres and a worldwide network of sensor and uplink stations.
Quelle: NDTV

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Update: 26.03.2015
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Countdown Begins for Launch of IRNSS-1D
CHENNAI:  The countdown for the lift of an Indian rocket with the country's fourth navigation satellite as the sole passenger began at 5.49 am today, the ISRO said.
According to Indian Space Research Organisation (ISRO), the 59 and half hours countdown for the launch of rocket Polar Satellite Launch Vehicle (PSLV-27) carrying Indian Regional Navigation Satellite System-IRNSS-1D began in the Sriharikota rocket port in Andhra Pradesh.
The rocket is expected to blast off at 5.19 pm on March 28 to put into orbit the 1,425 kg IRNSS-1D satellite.
India has so far launched three regional navigational satellites as part of a constellation of seven satellites to provide accurate position information service to users across the country and the region, extending up to an area of 1,500 km.
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Isro to Launch Fourth Navigational Satellite IRNSS-1D on Saturday
Though the full system comprises of nine satellites - seven in orbit and two on the ground as stand-by - the navigation services could be made operational with four satellites, ISRO officials said.
Each satellite costs around Rs.150 crore and the PSLV-XL version rocket costs around Rs.130 crore. The seven rockets would involve an outlay of around Rs.910 crore.
The entire IRNSS constellation of seven satellites is planned to be completed this year itself.
The first satellite IRNSS-1A was launched in July 2013, the second IRNSS-1B in April 2014 and the third on October 16, 2014.
Once the regional navigation system is in place, India need not be dependent on other platforms.
Quelle: NDTV
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Update: 27.03.2015
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Quelle: ISRO
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Update: 28.03.2015 
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Launch of IRNSS-1D by PSLV-C27 on March 28, 2015
The launch of India’s fourth Navigation Satellite IRNSS-1D onboard PSLV-C27 in now scheduled at 1719 hrs IST in the evening on Saturday, March 28, 2015 from Satish Dhawan Space Centre, Sriharikota.
Quelle: ISRO
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Update: 17.15 MEZ
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Erolgreicher Start von PSLV-C27/IRNSS-1D Mission
The fourth satellite of IRNSS Constellation, IRNSS-1D was launched onboard PSLV-C27. The satellite is one among the seven of the IRNSS constellation of satellites slated to be launched to provide navigational services to the region. The satellite is placed in geosynchronous orbit.
Satellite
The satellite will help augmenting the satellite based navigation system of India which is currently under development. The navigational system so developed will be a regional one targeted towards South Asia. The satellite will provide navigation, tracking and mapping services.
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Quelle: ISRO


Tags: Raumfahrt 

1817 Views

Freitag, 27. März 2015 - 23:00 Uhr

Raumfahrt - Start von Soyuz VS11 mit 2 Galileo Satelliten

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7.02.2015

Inside its protective shipping container, one of the two Galileo satellites is unloaded from a Boeing 747 cargo aircraft at French Guiana.
Soyuz Flight VS11
The two Galileo satellite passengers for launch on Arianespace’s next Soyuz flight have now been delivered to French Guiana, enabling the start-up of payload preparations for this medium-lift mission.
Transported by a Boeing 747 cargo jetliner, the pair arrived overnight at Félix Eboué International Airport near the capital city of Cayenne – after which these satellites, protected inside their shipping containers, were unloaded and subsequently moved by road to the Spaceport early this morning.
OHB System built the two Galileo spacecraft in Bremen, Germany as prime contractor. Their navigation payloads, which will generate the precision positioning measurements and services to users worldwide, were supplied by Surrey Satellite Technology Ltd. in Guildford, UK.
The Galileo program is Europe’s initiative for satellite navigation, providing a highly accurate global positioning system under civilian control – to consist of 30 satellites in total, along with European control centers and a worldwide network of sensor and uplink stations.
To deliver highly accurate positioning for most places on Earth, the complete Galileo constellation will be distributed along three circular medium Earth orbit planes at an operational altitude of 23,222 km., inclined 56 deg. to the equator.
The network’s complete operational and ground infrastructure will be deployed during Galileo’s Full Operational Capability phase, which is managed and funded by the European Commission, with the European Space Agency delegated as the design and procurement agent on the Commission’s behalf.
The upcoming mission, designated Flight VS11 in Arianespace’s numbering system, will mark the company’s fourth launch to date with Galileo spacecraft. 
Quelle: arianespace
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Update: 15.02.2015
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Soyuz Flight VS11
The third and fourth Galileo Full Operational Capability (FOC) satellites are a confirmed “fit” for their Arianespace Soyuz launch in March, having made initial contact with the mission’s dual-payload dispenser in French Guiana.
This week’s activity – which is called the fit check – was completed over a two-day period inside the Spaceport’s S1A payload preparation building. The two satellites were installed separately, with the Flight Model #3 (FM3) spacecraft integrated on – and subsequently removed from – the dispenser on Monday. Flight Model #4 (FM4) underwent the same process the following day.
The payload dispenser for Galileo was developed by RUAG Space Sweden for Arianespace, and carries one satellite on each side. It will deploy the spacecraft during their Soyuz launch by firing a pyrotechnic separation system to release them in opposite directions at the orbital insertion point.
Final integration on the dispenser is to be performed during upcoming processing at the Spaceport, and will be followed by the completed unit’s installation on Soyuz.
This March 27 mission – designated Flight VS11 in Arianespace’s numbering system – will be the company’s fourth launch carrying spacecraft for the Galileo constellation, which is Europe’s initiative for a satellite-based navigation system. FM3 and FM4 were built by OHB System, with Surrey Satellite Technology Ltd. supplying their navigation payloads.
The Galileo network’s complete operational and ground infrastructure will be deployed during the Full Operational Capability phase, which is managed and funded by the European Commission. The European Space Agency has been delegated as the design and procurement agent on the Commission’s behalf. 
Quelle: arianespace
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Update: 6.03.2015
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Soyuz Flight VS11
The Soyuz launcher for Arianespace’s upcoming mission with two European Galileo navigation satellites is taking shape at the Spaceport for a March 27 liftoff from French Guiana.
During activity in the Spaceport’s Soyuz Launcher Integration Building, the medium-lift workhorse began to assume its iconic form with integration of the four first-stage strap-on boosters to the Block A core second stage.
The next step will be the mating of Soyuz’ Block I third stage to the launcher’s core, completing the basic build-up, and readying the vehicle for its rollout to the launch pad – where the payload will be mated.
Arianespace’s March 27 flight will be the 11th Soyuz flight from French Guiana since the launcher’s introduction at the Spaceport in October 2011.  It is designated Flight VS11 in Arianespace’s numbering system for its launcher family – which also includes the heavy-lift Ariane 5 and lightweight Vega.
For the upcoming Soyuz mission, Arianespace will loft the third and fourth Galileo Full Operational Capability (FOC) satellites to further expand the constellation for Europe’s space-based navigation system.  Flight VS11’s two satellites were built by OHB System, with Surrey Satellite Technology Ltd. supplying their navigation payloads. 
Galileo’s complete operational network and its ground infrastructure will be deployed during the program’s Full Operational Capability phase, which is managed and funded by the European Commission. The European Space Agency has been delegated as the design and procurement agent on the Commission’s behalf.  
Quelle: arianespace
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Update: 9.03.2015 
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Galileo Satelliten bereit für die Betankung zum Start
All the elements for this month’s Galileo launch are coming together at Europe’s Spaceport in French Guiana. As the two satellites undergo final testing and preparations, the first part of their Soyuz launcher has also been integrated.
Assembly of the Soyuz ST-B’s first two stages, plus its four first stage boosters, took place at the Spaceport’s Soyuz Launcher Integration Building last week. Assembly takes place on a horizontal basis, in the Russian manner.
The next step will be the addition of the third stage, then the main part of the launcher will be complete, ready to be transported to the Soyuz launch pad and moved to the vertical position.
The final fourth stage of the Soyuz is the reignitable Fregat, which will transport the two satellites to their final 23 222 km altitude medium Earth orbit. This will be attached to the Soyuz on the launch pad, once the satellites, their dispenser and launch fairing have been mounted on it.
Since the seventh and eighth Galileo satellites arrived in French Guiana last month, they have undergone several tests – including one System Compatibility Test Campaign each, where they are linked up to the rest of the global Galileo ground segment as if they are already ‘live’ in orbit.
The all-important ‘fit check’ was passed in the middle of February. The two satellites were installed separately onto their dual-launch dispenser, to check they fitted correctly.
This dispenser has the task of holding them in place atop the Fregat during the launch and flight to their final orbit, then releasing them. They will be installed together later this month, after the satellites have been fuelled.
Last week saw the finalisation of their hardware and software, and the charging of their batteries – on which the satellites will be reliant from the short but crucial period from their launch to the unfurling of their solar arrays in orbit.
The pair of satellites is now ready to be transferred to the Spaceport’s S5A fuelling facility, where they will receive the fuel to keep them controllable during their 12-year working lives.
After their fuelling and final check, the pair of satellites will be in launch configuration. After a final review they will then become available for Arianespace teams to carry out the final preparation, known as Combined Operations, leading to the launch day.
The launch of the seventh and eighth Galileo satellite will take place on Friday 27 March.
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Cutaway view of the Soyuz rocket fairing carrying a pair of Galileo satellites.
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Artist's view of the Soyuz rocket fairing carrying the first two Full Operational Capability satellites (SAT 5-6).
The pair will be launched together aboard a Soyuz rocket, joining the four Galileo satellites already in orbit. The launch is set for summer 2014, from Europe's Spaceport, French Guiana.
The definition, development and in-orbit validation phases of the Galileo programme were carried out by ESA and co-funded by ESA and the EU.
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Artist's view of the Soyuz rocket fairing carrying the first two Full Operational Capability satellites (SAT 5-6).
The pair will be launched together aboard a Soyuz rocket, joining the four Galileo satellites already in orbit. The launch is set for summer 2014, from Europe's Spaceport, French Guiana.
The definition, development and in-orbit validation phases of the Galileo programme were carried out by ESA and co-funded by ESA and the EU.
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Artist's view of the fifth and sixth Galileo satellites on their Fregat upper stage separating from the Soyuz upper stage, some 9 minutes and 23 seconds after launch. The Fregat flew them the rest of the way up to medium-Earth orbit. 
The first two Galileo Full Operational Capability satellites (satellites 5-6) were launched together aboard a Soyuz rocket from Europe's Spaceport in French Guiana on 22 August 2014, joining the four Galileo satellites already in orbit.
The definition, development and in-orbit validation phases of the Galileo programme were carried out by ESA and co-funded by ESA and the EU.
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The Fregat upper stage flew the fifth and sixth Galileo satellites most of the way up to medium-Earth orbit, having separated from the third stage of the Soyuz at 9 minutes and 23 seconds after launch.
The first two Galileo Full Operational Capability satellites (satellites 5-6) were launched together aboard a Soyuz rocket from Europe's Spaceport in French Guiana on 22 August 2014, joining the four Galileo satellites already in orbit.
The definition, development and in-orbit validation phases of the Galileo programme were carried out by ESA and co-funded by ESA and the EU.
Quelle: ESA
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Update: 15.03.2015
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Soyuz Flight VS11
Preparations for Arianespace’s next Soyuz flight are in full swing at multiple locations across the Spaceport, including a key integration step for the medium-lift launcher, plus the start-up of fueling for its Galileo satellite passengers.
Soyuz’ Block I third stage was mated to the vehicle’s core during activity today in the MIK Launcher Integration Building, concluding its basic build-up. Once the checkout process is completed, Soyuz will be transferred to the launch pad – where it will receive the two Galileo spacecraft and the Fregat upper stage, all of which are well into preparation phases of their own.
Payload fueling commenced earlier this week, with Flight Model #4 (FM4) – the fourth Galileo Full Operational Capability (FOC) satellite – receiving its propellant load in the Spaceport’s S5A fueling and integration hall. After its “sister” FM3 co-passenger undergoes this same process, the two will be integrated side-by-side on a dispenser for their shared ride aboard Soyuz on March 27.
The fueling process followed the finalization last week of FM3 and FM4’s hardware and software, as well as the charging of their batteries – which will be relied upon during the short period from launch to unfurling of these spacecraft’s solar arrays in orbit.
The Galileo program is Europe’s initiative for satellite navigation, providing a highly accurate global positioning system under civilian control – to consist of 30 satellites in total, along with European control centers and a worldwide network of sensor and uplink stations.
Galileo’s FOC phase – during which the network’s complete operational and ground infrastructure will be deployed – is managed and funded by the European Commission, with the European Space Agency delegated as the design and procurement agent on the Commission’s behalf.
The FM3 and FM4 spacecraft were built by OHB System in Bremen, Germany. Their navigation payloads, which will generate the precision positioning measurements and services to users worldwide, were supplied by Surrey Satellite Technology Ltd. in Guildford, UK.
This upcoming mission is designated Flight VS11 in Arianespace’s numbering system. It will be the company’s fourth launch carrying spacecraft for the Galileo constellation, as well as the 11th flight of a workhorse Soyuz from French Guiana since the 2011 introduction. 
Quelle: arianespace
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Update: 18.03.2015
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Getting ready for launch: Payload integration is underway for Soyuz’ Galileo passengers
Soyuz Flight VS11
The two Galileo navigation satellites for Arianespace’s upcoming medium-lift flight have “joined up” with their payload dispenser system – a key step in the preparations for this March 27 mission.
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One of Soyuz’ Galileo navigation satellite passengers is already installed on the payload dispenser system (seen in the background), as the second spacecraft is moved into position for its integration.
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During activity at the Spaceport’s S5A preparation hall in French Guiana, the Galileo Full Operational Capability (FOC) spacecraft were mounted on their two-sided dispenser system, readying them for integration on Soyuz’ Fregat upper stage and encapsulation in the payload fairing. These steps will create the “upper composite,” which is installed atop Soyuz once the workhorse vehicle is moved to its Spaceport launch zone.
Designated Soyuz Flight VS11 in Arianespace’s numbering system, Soyuz’ 11th launch from the Spaceport in French Guiana is planned for an evening liftoff on March 27 at precisely 6:46:18 p.m. local time.
On this mission, Arianespace’s medium-lift launcher will carry out a nearly 3-hour, 48-minute mission to place its Galileo passengers into a targeted circular orbit at an altitude of 23,522 km., inclined 55.04 degrees to the equator.
Soyuz Flight VS11’s passengers are the latest FOC satellites in the Galileo program, which will create a European-operated space-based navigation system. Providing a highly accurate global positioning system under civilian control, the complete Galileo constellation will consist of 30 satellites in total, along with European control centers and a worldwide network of sensor and uplink stations.
The European Commission is managing and funding Galileo’s FOC phase – during which the network’s complete operational and ground infrastructure will be deployed. The European Space Agency has been delegated as the design and procurement agent on the Commission’s behalf.
The FOC spacecraft to be lofted on Soyuz Flight VS11 were built by OHB System in Bremen, Germany, with their navigation payloads supplied by Surrey Satellite Technology Ltd. in Guildford, UK.
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Quelle: arianespace
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Update: 24.03.2015
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Final payload integration process begins for this week’s Arianespace Soyuz launch from the Spaceport with two Galileo spacecraft

Soyuz Flight VS11
The payload build-up has been completed in French Guiana for Arianespace’s medium-lift Soyuz mission on March 27, which is to orbit the third and fourth Full Operational Capability (FOC) satellites for Europe’s Galileo navigation system.
These latest preparations – which occurred in the Spaceport’s S3B clean room facility – involved installation of the two Galileo spacecraft with their dispenser system atop Soyuz’ Fregat upper stage, followed by encapsulation in the two-piece protective payload fairing.
The completed unit, called the “upper composite,” will be mated atop Soyuz after the workhorse vehicle’s rollout from the MIK integration building – where launcher assembly is handled – to the launch zone.
Scheduled for liftoff on March 27 at precisely 6:46:18 p.m. local time in French Guiana, Soyuz will carry out a nearly 3-hr., 48-min. mission from launch to separation of the two Galileo satellite passengers. Fregat – which is responsible for the final orbital maneuvers – will perform two burns separated by a three-hour-plus ballistic phase to reach the targeted deployment point.
Galileo is Europe’s initiative for satellite navigation. Its complete operational and ground structure will be deployed during the FOC phase, which is managed and funded by the European Commission, with the European Space Agency delegated as the design and procurement agent on the Commission’s behalf.
OHB System built the Galileo FOC satellites for launch by Soyuz, while Surrey Satellite Technology Ltd. supplied their navigation payloads.
The upcoming mission is designated Flight VS11 in Arianespace’s numbering system, and will mark the company’s fourth launch to date carrying Galileo spacecraft.
Quelle: arianespace
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Update: 26.03.2015
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Thousands of engineers have worked on the seventh and eighth navigation satellites of Europe’s Galileo constellation in recent years, but last Friday marked the very last time the spacecraft were glimpsed by human eyes. 
The team from ESA and builders OHB in the S3B building of Europe’s Spaceport in French Guiana looked on as the focus of their work disappeared from view.
The pair of satellites – already resting atop their Fregat upper stage and attached to their dispenser – was enclosed within the halves of the Soyuz rocket’s protective fairing.
This unit was moved yesterday to the launch site, where it will be lifted atop the first three stages of the Soyuz ST-B to complete the vehicle for Friday’s launch.
Last week saw the two satellites being fuelled in the Spaceport’s S5A preparation hall and then brought together atop the dispenser that will support them during the rigours of ascent.
The dispenser’s final task is to release them in opposite directions once their 22 522 km-altitude orbit is reached. The satellites themselves will then gradually lower themselves to their working 22 322 km orbit.
After fuelling, the satellites plus dispenser were moved to the S3B processing building, where their Fregat was already fuelled and waiting.
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The reignitable Fregat is as much a spacecraft as a rocket stage. Once the Soyuz reaches low orbit, Fregat will take over the task of hauling the satellites higher through a pair of burns.
The two Galileos and their dispenser altogether weigh more than one and a half tonnes, so the attachment operation took place with great care and precision.
Then the fairing halves were slowly slid into place around them and closed. Enclosed in this way, the satellites will be protected from the harsh slipstream and vibration of the first few moments of launch, when the Soyuz is still travelling through the thickest layers of atmosphere.
The fairing is due to be ejected 3 min 29 sec after liftoff.
Until liftoff, the satellites remain connected to the outside world via power and data links, allowing ESA’s Galileo team keep a check on their battery charging and the health of their atomic clocks.
The satellites stay switched off during launch, and will be activated automatically on separation from the dispenser. 
Launch is due at 21:46:18 GMT (22:46:18 CET, 18:46:18 local time) on 27 March. The satellites are scheduled for release upon reaching their set orbit 3 h 47 min 57 sec after launch.
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Quelle: ESA
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Soyuz Flight VS11
The next medium-lift Soyuz to be launched from French Guiana is now complete following the integration of its “upper composite” – which consists of two Galileo satellite passengers, their protective payload fairing and the Fregat upper stage.
This activity was performed at the Spaceport’s ELS launch complex. It began with the upper composite’s transfer yesterday from the S3B payload preparation facility to the launch pad on a special transporter, and was followed by its hoisting to the upper level of a purpose-built mobile gantry – which provides a protected environment for the vertical installation atop Soyuz.
Final checkout of the completed launch vehicle is now underway, leading up to the Arianespace liftoff that is planned on Friday, March 27 at precisely 6:46:18 p.m. local time in French Guiana.
The mission’s payload – a pair of Full Operational Capability (FOC) spacecraft that will further expand Europe’s Galileo global navigation satellite system – are to be deployed during a flight lasting approximately 3 hrs., 47 min.
OHB System built the two spacecraft in Bremen, Germany as prime contractor. Their navigation payloads, which will generate the precision positioning measurements and services to users worldwide, were supplied by Surrey Satellite Technology Ltd. in Guildford, UK.
Galileo’s FOC phase – during which the network’s complete operational and ground infrastructure will be deployed – is being managed and funded by the European Commission, with the European Space Agency delegated as the design and procurement agent on the Commission’s behalf. 
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Quelle: arianespace
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Update: 27.03.2015
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Quelle: arianespace
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Update: 23.00 MEZ: Erfolgreicher Start 
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Quelle: arianespace
 
 
 

Tags: Raumfahrt 

2031 Views

Freitag, 27. März 2015 - 11:00 Uhr

Raumfahrt - Grenzwerte und Signaturen relativistischer Raumfahrt

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While special relativity imposes an absolute speed limit at the speed of light, our Universe is not empty Minkowski spacetime. The constituents that fill the interstellar/intergalactic vacuum, including the cosmic microwave background photons, impose a lower speed limit on any object travelling at relativistic velocities. Scattering of cosmic microwave phtotons from an ultra-relativistic object may create radiation with a characteristic signature allowing the detection of such objects at large distances.

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Quelle: Cornell University Library
 

Tags: Raumfahrt 

3057 Views

Freitag, 27. März 2015 - 10:15 Uhr

Astronomie - Bislang bester Blick auf Staubwolke, die am Schwarzen Loch im Zentrum der Milchstraße vorbeizog

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Diese Collage zeigt die Bewegung der staubhaltigen Wolke G2, wie sie sich annähert und dann schließlich am supermassereichen Schwarzen Loch im Zentrum der Milchstraße vorbeizieht.
Neue Beobachtungen mit dem VLT der ESO haben gezeigt, dass die Wolke die nahe Begegnung mit dem Schwarzen Loch scheinbar überlebt hat und weiterhin aus einem kompakten Objekt besteht, das sich nicht wesentlich ausgedehnt hat.
In dieser Collage sind die Positionen der Wolke in den Jahren 2006, 2010, 2012 und im Februar, bzw. September 2014 von links nach rechts gezeigt. Die einzelnen Bilder der Wolke wurden farbig dargestellt, um die Bewegung der Wolke deutlich zu machen, hierbei bedeutet rot, dass sie sich entfernt und blau, dass sie sich der Erde annähert. Die Position des supermassereichen Schwarzen Lochs ist mit einem Kreuz markiert.
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Beobachtungen mit dem VLT bestätigen, dass G2 die Annäherung überstanden hat und ein kompaktes Objekt ist
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Im Mai 2014 kam sich die staubhaltige Gaswolke G2 dem supermassereichen Schwarzen Loch im Zentrum der Milchstraße so nah wie nie zuvor – und überstand dies offenbar unbeschadet. Die besten Messungen von diesem Objekt überhaupt, durchgeführt mit dem Very Large Telescope der ESO von einem Wissenschaftlerteam der Universität zu Köln, zeigen, dass G2 bei der Passage nicht wesentlich gestreckt wurde und nach wie vor sehr kompakt ist. Höchstwahrscheinlich handelt es sich um einen jungen Stern mit einem massereichen Kern, der noch immer Materie ansammelt. Das Schwarze Loch selbst hat bisher noch keinen Anstieg seiner Aktivität gezeigt.
Ein supermassereiches Schwarzes Loch mit einer Masse, die dem Viermillionenfachen der Masse der Sonne entspricht, befindet sich im Herz der Milchstraße. Umrundet wird es von einer kleinen Gruppe heller Sterne. Zusätzlich konnte in den letzten paar Jahren eine rätselhafte staubige Wolke mit dem Namen G2 verfolgt werden, die sich in Richtung auf das Schwarze Loch bewegt hat. Die größte Annäherung, was man auch als Peribothron bezeichnet, fand im Mai 2014 statt.
Angesichts der großen Gezeitenkräften in dieser Region starker Gravitation nahm man an, dass die Wolke auseinanderreißen und sich entlang ihrer Umlaufbahn zerstreuen würde. Ein Teil dieser Materie würde dann das Schwarze Loch füttern, was zu einem plötzlichen Aufleuchten oder anderen Hinweisen darauf führen sollte, dass dieses Monster gerade eine seiner seltenen Mahlzeiten genießt. Um diese seltenen Ereignisse beobachten zu können, wurde die Region im galaktischen Zentrum in den vergangenen Jahren von vielen Astronomengruppen mit großen Teleskopen überall auf der Welt sorgfältig systematisch untersucht.
Darunter befand sich auch das Team um Andreas Eckart von der Universität zu Köln, das die Region mit dem Very Large Telescope (VLT) der ESO [1] über viele Jahre hinweg beobachtete, einschließlich neuer Beobachtungen während der kritischen Phase zwischen Februar und September 2014, also kurz vor und nach dem Peribothron-Ereignis. Die Ergebnisse der neuen Beobachtungen stimmen mit denen früherer Beobachtungen am Keck-Teleskop auf Hawaii überein [2].
Die Aufnahmen im infraroten Licht, das vom leuchtenden Wasserstoff stammt, belegen, dass die Wolke sowohl vor als auch nach ihrer größten Annäherung an das Schwarze Loch kompakt war.
Das SINFONI-Instrument am VLT liefert nicht nur sehr scharfe Bilder, es zerlegt das Infrarotlicht auch in seine Spektralfarben und ermöglicht damit, die Geschwindigkeit der Wolke zu bestimmen [3]. Man fand heraus, dass sich die Wolke vor der größten Annäherung mit etwa zehn Millionen Kilometern pro Stunde von der Erde wegbewegte. Nachdem sie um das Schwarze Loch herumgeschwungen war, bewegte sie sich laut Messungen mit etwa zwölf Millionen Kilometern pro Stunde auf die Erde zu.
Florian Peissker, Doktorand an der Universität zu Köln, der einen Großteil der Messungen vornahm, erzählt: “Am Teleskop zu sein und dabei zuzuschauen, wie die Daten in Echtzeit ankommen, war eine faszinierende Erfahrung.“ Monica Valencia-S., Postdoktorandin und ebenfalls von der Universität zu Köln, die sich mit der anspruchsvollen Datenverarbeitung beschäftigte, fügt hinzu: „Es war sehr beeindruckend mitanzusehen, wie das Leuchten aus der Staubwolke vor und nach dem Punkt der größten Annäherung gleich dicht blieb.“
Obwohl frühere Beobachtungen nahelegten, dass G2 verzerrt wurde, lieferten die neuen Beobachtungen keine Belege dafür, dass die Wolke signifikant verschmiert wurde. Sie wurde weder sichtbar auseinandergezogen, noch verteilen sich die gemessenen Geschwindigkeiten breiter.
Zusätzlich zu den Beobachtungen mit dem SINFONI-Instrument hat das Team auch eine lange Beobachtungsreihe der Polarisation des Lichts, das aus der Region des supermassereichen Schwarzen Lochs stammt, mit dem NACO-Instruments am VLT angefertigt. Diese bisher besten Beobachtungen machen deutlich, dass das Verhalten der Materie, die in Richtung Schwarzes Loch gezogen wird, sehr stabil ist und – bislang – nicht durch angesaugte Materie aus der G2-Wolke gestört wurde.
Die Widerstandsfähigkeit der Staubwolke gegenüber den extremen gravitativen Gezeitenkräften so nahe am Schwarzen Loch legen sehr deutlich nahe, dass sie eher ein dichtes Objekt mit einem massereichen Kern umschließt, als dass es sich um eine lockere, freifliegende Wolke handelt. Diese These wird von der Tatsache unterstützt, dass ein Beweis dafür, dass das Monster im Zentrum mit Materie gefüttert wird, bisher fehlt, da dies zu einer Aufhellung und zunehmender Aktivität führen würde.
Andreas Eckart fasst die neuen Ergebnisse zusammen: „Wir haben uns die jüngsten Daten angesehen, speziell jene aus der Phase in 2014, als die größte Annäherung an das Schwarze Loch stattgefunden hat. Wir können keine signifikante Ausdehnung der Quelle bestätigen. Sie verhält sich zweifellos nicht wie eine kernlose Staubwolke. Wir gehen davon aus, dass es sich um einen jungen Stern handelt, der in Staub eingehüllt ist.“
Endnoten
[1] Hierbei handelt es sich um sehr schwierige Beobachtungen, da die Region hinter einer dichten Staubwolke versteckt ist, was eine Beobachtung im Infrarotbereich des Lichts notwendig macht. Zusätzlich geschehen solche Ereignisse sehr nahe am Schwarzen Loch, weshalb adaptive Optik angewendet werden muss, um Bilder zu bekommen, die scharf genug sind. Das Wissenschaftlerteam nutzte hierfür das SINFONI-Instrument  und das NACO-Instrument am Very Large Telescope der ESO, um das Verhalten der Region um das zentrale Schwarze Loch herum beobachten zu können.
[2] Die neuen Messungen mit dem VLT sind beide schärfer (da sie im Bereich kurzer Wellenlängen gemacht wurden) und beinhalten zusätzliche Geschwindigkeitsmessungen durch SINFONI und Polarisationsmessungen mit dem NACO-Instrument.
[3] Da sich die Staubwolke relativ zur Erde bewegt – vor dem Punkt der größten Annäherung mit dem Schwarzen Loch von der Erde weg und danach auf die Erde zu – verändert der Dopplereffekt die beobachtete Wellenlänge des Lichts. Diese Änderungen in der Wellenlänge können mit empfindlichen Spektrografen wie dem SINFONI-Instrument am VLT gemessen werden. Ebenso lässt sich die Streuung der Geschwindigkeiten der Materie messen, die zu erwarten wäre, wenn sich die Wolke entlang ihrer Umlaufbahn in erheblichem Ausmaß auseinanderziehen würde, wie in der Vergangenheit bereits berichtet wurde.
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Die Staubwolke G2 zieht am Schwarzen Loch im Zentrum der Milchstraße vorbei (beschriftet)
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Diese beschriftete Collage zeigt die Bewegung der staubhaltigen Wolke G2, wie sie sich annähert und dann schließlich am supermassereichen Schwarzen Loch im Zentrum der Milchstraße vorbeizieht.
Neue Beobachtungen mit dem VLT der ESO haben gezeigt, dass die Wolke die nahe Begegnung mit dem Schwarzen Loch scheinbar überlebt hat und weiterhin aus einem kompakten Objekt besteht, das sich nicht wesentlich ausgedehnt hat.
Die einzelnen Bilder der Wolke wurden farbig dargestellt, um die Bewegung der Wolke deutlich zu machen, hierbei bedeutet rot, dass sie sich entfernt und blau, dass sie sich der Erde annähert. Die Position des supermassereichen Schwarzen Lochs ist mit einem Kreuz markiert.
Quelle: ESO

Tags: Astronomie 

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Freitag, 27. März 2015 - 09:30 Uhr

Planet Erde - Wie zäh Leben sein kann, zeigt der Fund von Bärtierchen im Eis der Antarktis

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This undated image released by Bob Goldstein and Vicki Madden taken with an electron microscope, shows a micro-animal "tardigrade" also known as a water bear, at the UNC in Chapel Hill, N.C. In Jan. 2015, scientists found the DNA of a tardigrade in Antarctica's Lake Vostok, located in an area considered the most remote place on Earth. The mostly freshwater lake is buried under miles of ice, and hasn't been near open air for 15 million years, exciting astronomers who search for possible forms of life on other planets.
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Deep below the ice, far from the playful penguins and other animals that bring tourists to Antarctica, is a cold and barren world that by all indications should be completely void of life.
But recently, scientists researching melting ice watched a half-foot-long (15-centimeter) fish swim by. Not long after that, they saw shrimp-like creatures.
In even more remote places on the continent, areas that haven't been exposed to sunlight for millions of years, scientists found a surprise right out of an alien movie: the DNA of a microscopic creature that looks like a combination of a bear, manatee and centipede.
Life that is simultaneously normal and weird, simple and complex thrives in this extreme environment. To the scientists who brave the cold and remoteness to find life amid the ice, it's a source of surprise and wonder. For extreme life experts, it's a testimony to the power of evolution.
"It really shows how tenacious life is," said Reed Scherer, a micropaleontology professor at Northern Illinois University. "The possibilities are just beyond our prediction."
Scientists look at creatures found in harsh Antarctica and ask: If life can survive here, why not on Mars or one of the ice-covered moons of Jupiter and Saturn where water lurks beneath the frozen surface? Maybe we aren't alone.
Certainly not here.
"You don't have to be a rocket scientist to look around and see how extreme this environment is," biochemist Jenny Blamey said, pointing to the black granite rock covered by ice all around her on Deception Island. She wore a red parka with a black hood that was blown by the hard wind. While she spoke, her glasses fogged up and droplets of rain gathered on them.
"This is really like a desert, where you have extreme low temperatures," said Blamey, research director at the Biosciences Foundation in Chile who is studying the genetic material of microorganisms, essentially microbes that can't be seen.
Deception Island is a volcanic crater off the Antarctic Peninsula that used to be a refuge for whalers at the turn of the 20th century. It was evacuated many years ago after a handful of eruptions. Yet it is a garden compared to the spot where Ross Powell stopped to talk.
Powell had trekked across a separate part of the vast continent, hundreds of miles away from any buildings or research post, in a National Science Foundation mobile base camp. Speaking by satellite phone at the armpit edge of the Ross Ice Shelf in January, the professor from Northern Illinois University described what he and colleagues saw when they stuck a remote-controlled submarine a half mile under the ice to look at the leading underground edge of one of Antarctica's melting ice sheets.
It is an area of total darkness, 600 miles (1,000 kilometers) from the nearest ocean and with just 30 feet of liquid water under the ice. The water is 28 degrees Fahrenheit (minus 2 Celsius), but the saltiness keeps it from freezing.
Scientists turned on the cameras and were astonished to see a fish, thin and almost translucent, darting around and at times seeming to be playing peekaboo with the camera. Orange-shelled creatures called amphipods also drifted by.
When the scientists in the makeshift control room on the ice first saw the fish, they "started screaming and yelling and clapping," Powell said.
By the time a couple of days had passed, Scherer said the fish had become so common that "we got to the point of, 'Oh, there's another fish,' instead of, 'Oh my God! There's a fish!'"
As a joke, someone had brought a fish cage from New Zealand. But now it was no joke. The scientists tried to catch a fish using a giant net attached to the submarine's camera system and making leftovers out of bait from the previous night's supper.
They never caught a fish, but they did nab some of the amphipods. Still, Scherer, who loves seafood, wasn't tempted to nibble. "I thought they smelled kind of baity," he said.
Powell and Scherer are now trying to figure out where the animals came from and, even more importantly, where they get the food to survive.
The search for life has also taken scientists to Lake Vostok, considered the most remote place on Earth. The mostly freshwater lake is buried under 2.3 miles (3.7 kilometers) of ice, and hasn't been near open air for 15 million years.
A couple of years ago, scientists took water samples from the lake and tested them for traces of life. They found genetic sequences for 3,507 recognizable species as well as about 10,000 species not yet known to science, said Scott Rogers, a professor of microbiology at Bowling Green State University, who worked on the study.
"It seems like most of (the species) were alive recently" and not fossils from thousands of years ago, Rogers said.
About 94 percent of the species they could identify were bacterial, essentially simple microbial life. But there were also fungi and even a couple of genetic traces of microscopic animals. That included DNA from tardigrades, also known as water bears, the tiny creatures that look like one-eyed extraterrestrial grizzlies when seen under an electron microscope. There were even indications that elsewhere in the chilly lake there might be small fish.
These types of findings excite astronomers who search for possible forms of life on other planets. Just this month, astronomers found that Jupiter's giant moon Ganymede had water under the ice. So does Europa, another moon of Jupiter, and Enceladus, a moon of Saturn. And then there are exoplanets, those circling bodies outside our solar system.
When unexpected creatures are found under the ice, "you start to wonder if that couldn't happen on an icy moon or exoplanet," said Lisa Kaltenegger, an astronomer and director of the Institute for Pale Blue Dots at Cornell University.
Science doesn't have those cosmic answers yet, but the mysterious fish in the darkness of Antarctica may hold clues.
Quelle: PHYS-ORG

Tags: Planet Erde 

1954 Views

Donnerstag, 26. März 2015 - 23:46 Uhr

Luftfahrt

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Germanwings 4U9525 ehemals Lufthansa A-320 Mannheim D-AIPX



Tags: Luftfahrt 

1857 Views


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