Blogarchiv

Sonntag, 14. Juli 2013 - 15:30 Uhr

Luftfahrt - Erfolgreiche Landung von US Navy X-47B-Drohne auf Trägerschiff USS George H W Bush

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In a key development for the future of robotic flight, a pilotless US jet has landed aboard an aircraft carrier.

The US Navy X-47B drone touched down on the deck of the USS George H W Bush as it sailed off the coast of Virginia.

The bat-wing aircraft can deliver guided bombs from a range of 3,200km (1990 miles). It is the first drone to land on a ship at sea.

In May an unmanned aircraft launched from the same carrier but landed on a runway on the US mainland.

The plane was one of two test aircraft purpose-built by the aerospace giant Northrop Grumman, under a 2007 contract at a cost of about $1.4 bn.

In clear weather and light winds, the aircraft took off from the Patuxent River Naval Air Station in the US state of Maryland.

It headed for the ship which was operating in the Atlantic Ocean 112km off the coast of Virginia.

At 1740 GMT on Wednesday, the plane dropped its tail hook which then caught a cable across the carrier deck.

This arrested landing had been carried out before - but never at sea.

"It's not often that you get a chance to see the future, but that's what we got to do today," said Navy Secretary Ray Mabus, who witnessed the landing.

Museum piece

The X-47B is not intended for operational use. Both test planes will be sent to flight museums in Florida and Maryland, as the US military develops new models.

Officials plan to deploy unmanned reconnaissance and strike aircraft aboard carriers within the next three to six years.

The US Navy has asked for designs from Northrop, along with its rival manufacturers, Boeing, Lockheed Martin and General Atomics.

A future plane would be able to evade radar and fly over a target area for long periods of time,

For some the development has sparked calls for the military to clarify the chief purpose of drones.

Critics say the main strength of such aircraft is the ability to remain over a target area for a long period, searching for potential targets. They say that drones launched from land bases can perform that function as effectively as those based at sea.

Development questioned

"When it comes to operating an unmanned aircraft from carrier decks, the Navy seems to be ambivalent about the whole idea," Loren Thompson, a defence expert at the Lexington Institute think tank told the Associated Press.

He said the US navy needed to carry out a tough assessment to see what these new drones would bring to the fleet that could not be accomplished with manned aircraft or land-based drones.

The Obama administration has come under increasing criticism for using drones to carry out deadly missile attacks against suspected militants in Pakistan, Yemen, Afghanistan, and Iraq.

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Quelle: BBC


3012 Views

Samstag, 13. Juli 2013 - 23:55 Uhr

Raumfahrt - Spacewalk von ESA Astronaut Luca Parmitano (Luca Skywalker)

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These images were taken by ESA astronaut Luca Parmitano during his spacewalk, together with NASA's Chris Cassidy, 9 July 2013.
The spacewalk, the first for Luca and the fifth for Chris, lasted 6 hours 7 minutes.
This was the first of two Expedition 36 excursions to prepare the International Space Station for a new Russian module and perform additional installations on the station’s backbone.
The second spacewalk is scheduled for 16 July; Luca, working again with Chris Cassidy, will egress the Quest airlock at around 12:15 GMT (14:15 CEST).

Credits: ESA/NASA
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Blick auf Columbus-Modul der ISS
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Letzter Blick auf die Erde von Luca vor EVA-Ende
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Quelle: ESA

2942 Views

Samstag, 13. Juli 2013 - 22:34 Uhr

Luftfahrt - USAF erhält BOEING-KC-46-Tankflugzeuge

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A KC-46 conducts in-flight refueling on a B-2 bomber in this illustration. The first KC-46 is expected to fly in 2015. (Air Force illustration)

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WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- Boeing's announcement this past week that they have begun assembly of the first KC-46 wing spar is a significant event for the Air Force tanker program. It marks the start of assembly of the first KC-46 Engineering and Manufacturing Development aircraft.

"We are excited and pleased that KC-46 fabrication has begun. The Boeing team continues to make significant progress in the development of the Air Force's next tanker," said Maj. Gen. John Thompson, Program Executive Officer for Tankers at the Air Force Life Cycle Management Center. "The development effort is on track, detailed test planning is making good progress, and initial beddown, training and sustainment planning is underway."

The Air Force is about a third of the way into the KC-46 tanker development program. The Air Force contracted with Boeing in February 2011 to acquire 179 KC-46 Tankers to begin recapitalizing the more than 50-year-old KC-135 fleet. The initial delivery target is for 18 tankers by 2017. Production will then ramp up to deliver all 179 tankers by 2028.

The aircraft being produced at the Boeing factory in Everett, Washington is a commercial derivative design based on the Boeing 767-200ER passenger aircraft. When the aircraft comes off the Everett production line, it will be a 767-2C Provisioned Freighter that will eventually become a military-configured KC-46 tanker.

The first fully equipped KC-46 is slated to fly in early 2015.

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KC-46A TANKER


Mission
The KC-46A is intended to replace the U.S. Air Force's aging fleet of KC-135 Stratotankers which has been the primary refueling aircraft for more than 50 years. With more refueling capacity and enhanced capabilities, improved efficiency and increased capabilities for cargo and aeromedical evacuation, the KC-46A will provide aerial refueling support to the Air Force, Navy, Marine Corps as well as allied nation coalition force aircraft.

Features
The KC-46A will be able to refuel any fixed-wing receiver capable aircraft on any mission. This aircraft is equipped with a modernized KC-10 refueling boom integrated with proven fly-by-wire control system and delivering a fuel offload rate required for large aircraft. In addition, the hose and drogue system adds additional mission capability that is independently operable from the refueling boom system.

Two high-bypass turbofans, mounted under 34-degree swept wings, power the KC-46A to takeoff at gross weights up to 415,000 pounds. Nearly all internal fuel can be pumped through the boom, drogue and wing aerial refueling pods. The centerline drogue and wing aerial refueling pods are used to refuel aircraft fitted with probes. All aircraft will be configured for the installation of a multipoint refueling system.

MPRS configured aircraft will be capable of refueling two receiver aircraft simultaneously from special "pods" mounted under the wing. One crewmember known as the boom operator controls the boom, centerline drogue, and wing refueling pods during refueling operations. This new tanker utilizes an advanced KC-10 boom, a center mounted drogue and wing aerial refueling pods allowing it to refuel multiple types of receiver aircraft as well as foreign national aircraft on the same mission.

A cargo deck above the refueling system can accommodate a mix load of passengers, patients and cargo. The KC-46A can carry up to 18 463L cargo pallets. Seat tracks and the onboard cargo handling system make it possible to simultaneously carry palletized cargo, seats, and patient support pallets in a variety of combinations. The new tanker aircraft offers significantly increased cargo and aeromedical evacuation capabilities.

The aircrew compartment includes 15 permanent seats for aircrew which includes permanent seating for the aerial refueling operator and an aerial refueling instructor. Panoramic displays giving the ARO wing-tip to wing-tip situational awareness.

Background
The Boeing Company was awarded a contract for the Engineering and Manufacturing Development phase of the KC-46 program on Feb. 24, 2011. The initial flight of the KC-46A aircraft is scheduled for late calendar year 2014. The current contract, with options, provides the Air Mobility Command an inventory of 179 KC-46 tankers.

General Characteristics
Primary Function: Aerial refueling and airlift
Prime Contractor: The Boeing Company
Power Plant: 2 Pratt & Whitney 4062
Thrust: 62,000 lbs - Thrust per High-Bypass engine (sea-level standard day)
Wingspan: 157 feet, 8 inches (48.1 meters)
Length: 165 feet, 6 inches (50.5 meters)
Height: 52 feet, 10 inches (15.9 meters)
Maximum Takeoff Weight: 415,000 pounds (188,240 kilograms)
Fuel Capacity: 212,299 pounds (96,297 kilograms)
Maximum Transfer Fuel Load: 207,672 pounds (94,198 kilograms)
Maximum Cargo Capacity: 65,000 pounds (29,484 kilograms)
Pallet Positions: 18 pallet positions
Air Crew: 15 permanent seats for aircrew, including aeromedical evacuation aircrew
Passengers: 58 total (normal operations); up to 114 total (contingency operations
Aeromedical Evacuation: 58 patients (24 litters / 34 ambulatory) with the AE Patient Support Pallet configuration; 6 integral litters carried as part of normal aircraft configuration equipment


2921 Views

Samstag, 13. Juli 2013 - 17:51 Uhr

Raumfahrt - Saturn-Mond Dione im Focus von Cassini

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Buckling Under the Weight

This image, which is composed of data obtained by NASA's Cassini spacecraft, shows the topography of a mountain known as Janiculum Dorsa on the Saturnian moon Dione. Color denotes elevation, with red as the highest area and blue as the lowest.

Janiculum Dorsa is a 500-mile-long (800-kilometer-long) mountain and ranges in height from 0.6 to 1.2 miles (1 to 2 kilometers). An analysis of the topography data suggests the crust under the mountain puckers as much as 0.3 mile (0.5 kilometer). This bending of the crust suggests the icy crust was warm at some time in recent history. The best explanation for such behavior is the existence of a subsurface ocean under the mountain when it formed.

The data used to create this image were obtained from NASA's Cassini spacecraft on Oct. 11, 2005, and Oct. 17, 2010.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

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Quelle: NASA


3095 Views

Samstag, 13. Juli 2013 - 17:35 Uhr

Astronomie - Schönes Ende von einem Stern

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Composite image of planetary nebula NGC 2392.
Image Credit: 
X-ray: NASA/CXC/IAA-CSIC/N. Ruiz et al; Optical: NASA/STScI
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Stars like the Sun can become remarkably photogenic at the end of their life. A good example is NGC 2392, which is located about 4,200 light years from Earth. NGC 2392, nicknamed the "Eskimo Nebula", is what astronomers call a planetary nebula. This designation, however, is deceiving because planetary nebulas actually have nothing to do with planets. The term is simply a historic relic since these objects looked like planetary disks to astronomers in earlier times looking through small optical telescopes.

Instead, planetary nebulas form when a star uses up all of the hydrogen in its core -- an event our Sun will go through in about five billion years. When this happens, the star begins to cool and expand, increasing its radius by tens to hundreds of times its original size. Eventually, the outer layers of the star are carried away by a thick 50,000 kilometer per hour wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a much faster wind traveling six million kilometers per hour. The radiation from the hot star and the interaction of its fast wind with the slower wind creates the complex and filamentary shell of a planetary nebula. Eventually the remnant star will collapse to form a white dwarf star.

Now days, astronomers using space-based telescopes are able to observe planetary nebulas such as NGC 2392 in ways their scientific ancestors probably could never imagine. This composite image of NGC 2392 contains X-ray data from NASA's Chandra X-ray Observatory in purple showing the location of million-degree gas near the center of the planetary nebula. Data from the Hubble Space Telescope show – colored red, green, and blue – the intricate pattern of the outer layers of the star that have been ejected. The comet-shaped filaments form when the faster wind and radiation from the central star interact with cooler shells of dust and gas that were already ejected by the star.The observations of NGC 2392 were part of a study of three planetary nebulas with hot gas in their center. The Chandra data show that NGC 2392 has unusually high levels of X-ray emission compared to the other two. This leads researchers to deduce that there is an unseen companion to the hot central star in NGC 2392. The interaction between a pair of binary stars could explain the elevated X-ray emission found there. Meanwhile, the fainter X-ray emission observed in the two other planetary nebulas in the sample – IC 418 and NGC 6826 – is likely produced by shock fronts (like sonic booms) in the wind from the central star. A composite image of NGC 6826 was included in a gallery of planetary nebulas released in 2012.

Quelle: NASA


2953 Views

Samstag, 13. Juli 2013 - 15:00 Uhr

Raumfahrt - Dream Chaser ETA schließt erste Schlepptau Tests auf Dryden ab

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Sierra Nevada Corporation (SNC) have completed the opening salvo of tow tests on their Dream Chaser Engineering Test Article (ETA) at NASA’s Dryden Flight Research Center (DFRC). These opening test objective are being used to validate the performance of the spacecraft’s nose skid, brakes, tires and other systems.

SNC shipped the ETA to Dryden on the back of a truck, allowing Dream Chaser to join an illustrious list of vehicles that spent their early years testing their capabilities at the famous Californian facility.

Marking Dream Chaser’s arrival, NASA Administrator Charlie Bolden met with the SNC team and the ETA, noting the historical association with NASA lifting bodies and more famously Enterprise, following her series of Approach and Landing Tests (ALTs) in the 1970s, paving the way for her orbital sisters to learn how to land during the 30 year career of the Shuttle.

Dream Chaser – also known unofficially as “Eagle” – will also end her mission by landing on a runway, although there will be some key differences, especially during the actual touchdown.

The Dream Chaser is the only reusable lifting body vehicle in the running to transport American astronauts to Low Earth Orbit (LEO) destinations, such as the International Space Station (ISS). All the other commercial crew competitors are of the capsule design.

Thanks to its lifting body shape, the Dream Chaser will sport around one thousand miles of theoretical cross range.

With this capability, the vehicle can land on a runway from virtually any point in the orbit, and can land on a CONUS runway in no longer than six hours.

As such, SNC class the vehicle as capable of something they believe the ISS program considers particularly valuable, which is its “dissimilar redundancy” when compared to capsules.

With a similar, yet smaller, appearance to the Space Shuttle orbiters, Dream Chaser will closely follow in the footsteps of its big sisters during landing.

SNC have already stated that the Dream Chaser’s home landing strip will be the 15,000 ft long Shuttle Landing Facility (SLF) at the Kennedy Space Center (KSC), a runway physically marked by numerous orbiter landings over the history of the Space Shuttle Program (SSP).

The marriage between the SLF and a potential Commercial Crew provider holds extra synergy, following Space Florida’s opening talks with NASA to operate the famous runway.

For approach, Dream Chaser will be targeting a landing speed of 191 knots, after re-entering the atmosphere protected by a Thermal Protection System (TPS) that is similar to that on the Space Shuttle.

She will touch down on its two Main Landing Gear (MLG) just like the shuttle orbiters.

Click here for recent SNC Dream Chaser articles: http://www.nasaspaceflight.com/?s=SNC

However, there will be one major difference when the nose is pitched forward, given the Dream Chaser will not be using a traditional Nose Landing Gear (NLG) wheel for its rollout. Instead, and inbuilt skid strip will touch the concrete floor of the SLF.

SNC have previously noted to NASASpaceFlight.com that this system is a simple, light, safe option.

The company also added that there had been some issues with the analysis relating to the performance of tires in the space environment and this eliminates one of the tires – with the other two tires easier to control than the nose wheel if there’s a problem with one of them.

Although Concept Of Operations videos (L2 DCSS Section) show Dream Chaser was originally designed to utilize a front wheel, the Colorado company also noted they do not expect any issues, such as crosswind limitations, from using the skid during landing and rollout.

With Dream Chaser now into its test program at Dryden, engineers conducted the opening two tow tests to validate the performance of the spacecraft’s nose skid, brakes, tires and other systems.

The company has performed the tests at 10 and 20 mph – as a pickup truck pulled the Dream Chaser flight vehicle on Dryden’s concrete runways. The next tests will involve a tow at speeds of 40 and 60 mph tests later this month.

Range and taxi tow tests are standard for winged vehicles that touch down on a runway to prove the overall spacecraft handling post-landing.

Depending on how the testing proceeds, the first drop test is still expected to take place sometime later in the summer. However, serious doubts over Dream Chaser’s schedule remain, given SNC continue to avoid questions relating to testing schedules, since suffering from initial processing delays early this year.

The drop test will be conducted via the use of a helicopter, carried out early in the morning, in near darkness, before the Californian weather becomes too warm to fly the helicopter at the altitudes required for the testing.

The focus will then switch to the Dream Chaser Flight Test Vehicle (FTV), which is currently under construction.

(Images via SNC, L2 and NASA)

(With the shuttle fleet retired, NSF and L2 are providing full transition level coverage, available no where else on the internet, from Orion and SLS to ISS and Commercial Cargo/Crew, to European and Russian vehicles.

Quelle: NASA

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Update: 15.00

Sierra Nevada Corporation's Dream Chaser flight test vehicle is towed from its hangar at NASA's Dryden Flight Research Center in preparation for tow tests on a Dryden taxiway. The tow tests were part of ground tests in preparation for captive-carry and free-flight tests scheduled during the fall of 2013 at NASA Dryden. NASA / Ken Ulbrich May 30, 2013

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Sierra Nevada Corporation's Dream Chaser engineering test vehicle is towed across the ramp at NASA's Dryden Flight Research Center in preparation for tow tests on a Dryden taxiway. The tow tests were part of ground tests in preparation for captive-carry and free-flight tests scheduled during the fall of 2013 at NASA Dryden. NASA / Ken Ulbrich May 30, 2013 

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Sierra Nevada Corporation engineers and technicians prepare the firm's Dream Chaser engineering test vehicle for tow tests on a taxiway at NASA's Dryden Flight Research Center. The tow tests were part of ground tests in preparation for captive-carry and free-flight tests scheduled during the fall of 2013 at NASA Dryden. NASA / Ken Ulbrich June 27, 2013 

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Sierra Nevada Corporation engineers and technicians prepare the firm's Dream Chaser engineering test vehicle for tow tests on a taxiway at NASA's Dryden Flight Research Center. The tow tests were part of ground tests in preparation for captive-carry and free-flight tests scheduled during the fall of 2013 at NASA Dryden. NASA / Ken Ulbrich June 27, 2013 

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Quelle: NASA


3259 Views

Samstag, 13. Juli 2013 - 11:35 Uhr

Astronomie - Teile von Tscheljabinsk Meteorit unter dem Mikroskop

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Often referred to as the Chebarkul meteorite after the lake where many pieces were found, the space rock appears to be a standard "chondrite"

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Scientists have released microscopic images of fragments of the meteorite that hit central Russia in February.

A team from the Ural Federal University was able to analyse some of the dozens of samples as soon as they were found.

But the technique they used allowed them to assess the rock's chemical make-up at the microscopic level even as they snapped pictures of the fragments.

This will provide extra information on the space rock's formation and journey.

The fragments represent just a small portion of the remains of the 17m-diameter body that struck the Earth's atmosphere in a spectacular trail of light over the city of Chelyabinsk.

The team, led by Urals Federal University's Viktor Grokhovsky, determined right away that the overall chemistry of the meteorite was a familiar "chondrite".

"The fragments contain a standard number of minerals, including olivine, pyroxene, troilite and kamacite. These minerals that can be discovered only in outer space confirm the fragments' extraterrestrial nature," he told the Voice of Russia at the time.

But far more information was in the offing.

The way differing minerals are laid out gives clues as to their origin and their journey

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The team was using a scanning electron microscope, which fires a beam of electrons focused onto a tiny part of a sample, scanning around to see how the electrons are deflected and thereby building up a detailed picture of the sample's nanometre-scale bumps and valleys.

But that process causes the emission of a small amount of X-ray radiation - with the exact energy of the X-rays corresponding to the chemical element present in the focus of the electron beam.

This is where a silicon drift detector comes in - harvesting these X-rays and determining their energy. The result is a series of what are called X-ray maps - pictures of the same sample showing the presence and quantity of different elements.

It is this understanding of the minerals at a microscopic level that goes far beyond simply telling us what the meteorite is made of, said Simon Burgess of Oxford Instruments, which made the X-max silicon drift detector used by the team.

"For the researchers who are looking at this meteorite, it's going to be telling them information about which (mineral) phase is associated with which," he told BBC News.

"When they get into more detail beyond what the main chemistry of the meteorite is, they may be looking at processes in terms of how it formed, the temperature it formed at, what its history has been since its formation, possibly things about what happened to it during its impact with the Earth.

"A lot of that you cannot tell just by crushing it up and getting a 'bulk analysis'; you have to look at the chemistry of the individual parts and associations between the different minerals in the meteorite."

The X-max technology is in the running for the Royal Academy of Engineering's MacRobert Award, to be announced on Friday 19 July.

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The X-ray maps show the precise distribution of individual chemical elements

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Quelle: BBC


Tags: Tscheljabinsk Meteorit 

3120 Views

Freitag, 12. Juli 2013 - 14:30 Uhr

Astronomie - Rote Mondsichel am späten Abend am Westhimmel

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Fotos: ©-hjkc

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3137 Views

Freitag, 12. Juli 2013 - 13:00 Uhr

UFO-Forschung - Solar-Zeppelin wieder im Verkauf

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6.06.2013 / Update 11.06.2013

Die Jugend-Zeitschrift YPS legt in der aktuellen Ausgabe nach 30 Jahren wieder den Solar-Zeppelin bei, welcher schon in den 80igern für UFO-Alarm sorgte und bei drei großen Ufologen-Gruppen und ihren Promotern für "Mutterschiffe" sorgte, welche dort immer noch in ihren Märchen-Sammlungen zu finden sind.

Rückblick in die 80iger:

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Kaum waren die YPS-Hefte im Umlauf gab es UFO-Alarm über ganz Deutschland, nachfolgend zwei Beispiele aus der Presse (cenap-archiv)

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Fotos davon sorgten für wirre Deutungen bei den Ufologen-Gruppen und ihren Promotern, welche der Ufologen-Gemeinde die Solar-Zeppeline als Mutterschiffe der Außerirdischen verkauften und bis heute keine Identifizierung haben.

Update: 10.06.2013

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Nachfolgend Fotos vom Wochenende, an welchem wir zu Referenz-Zwecken ein Video sowie Fotos vom aktuellen YPS-Solar-Zeppelin anfertigten, um die verschiedenen Flugeigenschaften und Reflexionseffekte aufzuzeigen. Fotos: ©-hjkc

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Update 12.06.2013

 

 

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Update: 17.06.2013

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Update: 18.06.2013

 

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Bisher kam es bei der CENAP-UFO-Meldestelle in Mannheim (0621-701370)  zu nachfolgenden Meldungen welche auf den YPS-Solar-Zeppelin zurückzuführen war:

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08.06.2013 - Bremen

09.06.2013 - Kronberg

10.06.2013 - Schwäbisch-Gemünd

11.06.2013 - Nürnberg mit Foto vom 8.06.2013

12.06.2013 - Bad-Sulza

13.06.2013 - Neuschwanstein

14.06.2013 - Bissendorf

15.06.2013 - Schweich

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Darüber hinaus gab es Anrufe, bei denen man uns informierte, so einen Solar-Zeppelin fliegen zu lassen, als Hinweis Betreff etwaigen Meldungen.

CENAP-Mannheim, 19.06.2013

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Update: 11.07.2013

Herr Frank O. wurde von NDR an CENAP sowie GWUP weitergeleitet, um seine Beobachtung am Ostsee-Strand (7.07.2013) zu melden. Er sah mit weiteren Zeugen hoch am Himmel in der Nähe der Sonne "für Ihn kleine Rauchringe", die er auch auf Video festhalten konnte. Nach Video-Auswertung entpuppte sich dann vom Flugverhalten sowie Reflexionseffekt die "Flugkörper" als Solar-Zeppeline. Frams davon nachfolgend:

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Quelle: Video: Frank O.

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Hierzu können wir auch unsere Referenz-Aufnahmen auf YT empfehlen, auf welchen ebenfalls in großer Höhe diese Flugverhalten sowie Reflexionseffekte zu sehen sind:

http://www.youtube.com/watch?v=E_2aqa4lPhM

 

 

 

 


Tags: YPS Solar-Zeppelin UFO-Alarm 

3734 Views

Freitag, 12. Juli 2013 - 10:00 Uhr

Astronomie - Stellar Monster kollidieren nicht - keine Aussicht für eine spektakuläre Katastrophe

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This is the Tarantula Nebula (30 Doradus) in the Large Magellanic Cloud, imaged by the Hubble Space Telescope. It is here that stars with masses of 200-300 times that of our sun have recently been discovered.
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One might expect that collisions between the remains of monstrous stars, with masses reaching 200-300 times that of our Sun, would be among the most spectacular phenomena in the Universe. Perhaps they are, but we will unfortunately probably never have the chance to find out. Astrophysicists from the Astronomical Observatory of the Faculty of Physics at University of Warsaw have discovered that the first such collisions will not occur until billions of years from now.
For a long time, astronomers have believed that the biggest stars in the Universe do not exceed 150 solar masses. However, three years ago star clusters in the Magellanic Clouds were discovered to house "impossible" stars – tremendous monsters with masses between 200 and 300 times that of our own Sun. The discovery aroused great interest among astrophysicists, in particular those involved in the century-long search for gravitational waves. If such stellar monsters formed tight binary systems, collisions between their remnants could occur. The gravitational waves resulting from such an event would be powerful enough that even our current detectors could sense them – and at distances much larger than for typical stellar black holes. "But we cannot count on detecting any such spectacular collision," says Dr. Krzysztof Belczyński of the Astronomical Observatory of the Faculty of Physics at the University of Warsaw.
Dr. Belczyński's team discussed the latest results of their research with participants at the 10th Edoardo Amaldi Conference on Gravitational Waves, now being held in Warsaw in conjunction with the 20th International Conference on General Relativity and Gravitation (GR20/Amaldi10).
Stars with large masses may end their lives in two ways: their material can be blown into space or they can collapse under their own gravity into a black hole. A few months ago, astrophysicists led by Dr Norhasliza Yusof at the University of Kuala Lumpur demonstrated, using computer modelling, that some supermassive stars can form black holes. This means that the universe might indeed play host to binary systems of supermassive stars which later evolved or transformed into systems of two black holes with masses much larger than these typically observed for black holes.
Objects orbiting in tight binary systems composed of neutron stars or ordinary black holes lose their energy over time, leading to closer and closer orbits and finally a collision. Such a collision may have the astronomically observable effect of a powerful gamma-ray burst, and the explosion should also be accompanied by the emission of gravitational waves. However, up to now we have failed to observe these waves. Current detectors can only "see" the collison of typical black holes in the local Universe. The collision of black holes produced by supermassive stars would be something else entirely. Then, the gravitational waves should be strong enough that they might be detected in the near future.
But such a collision turns out not to be in the cards.
The components of common large star binary systems with masses of, say, 50, or even 100 solar masses, are formed at a distance from each other of at least several hundred or even several thousand solar radii. Such objects cannot be born closer together, because the resulting density of matter would collapse into one star and a binary system would not be created. Therefore, for an already formed binary system to collide, its components must somehow lose orbital energy. This happens due to the rapid evolution of one of the objects, which at a particular point begins to expand rapidly. The second component of the system then moves in the atmosphere of its companion and – as a result of interaction with it – quickly loses energy. As a consequence of this the orbit tightens in what is known as a common envelope event.
"In a supermassive binary star system, the situation is different," says Dr. Belczyński. "We know that the components of such a system must be formed at a relatively large distance from each other. We also know that supermassive stars do not expand, so there cannot be a common envelope phase. This means that there is no physical mechanism that would effectively cause the orbit to tighten!"
In this situation, the only process that allows for a gradual loss of energy by the remnants of supermassive stars in a binary system is the emission of gravitational waves. But the gravitational waves emitted by such a system of widely separated stars or black holes are very weak and the energy loss is slow.
"It will take many tens of billions of years, perhaps hundreds of billions of years, for the black holes to collide. That is many times longer than the amount of time which has passed since the Big Bang, so we stand practically no chance of detecting the gravitational waves from such a collision in the heavens. Unless...," Dr. Daniel Holz of the University of Chicago trails off in mid-sentence.
Exactly: unless the current models of stellar evolution and the formation of binary stars in dust clouds of matter are wrong. Then the observation of such a spectacular catastrophe in space would mean a spectacular disaster for contemporary astrophysical theories.
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Dr. Belczyński's research group was funded by a grant from the MASTER programme of the Foundation for Polish Science.
The Edoardo Amaldi Conference on Gravitational Waves is organised biannually under the auspices of the International Committee on Gravitational Waves. This year, the tenth conference (Amaldi10), taking place in Warsaw on 7-13 July, coupled with the 20th International Conference on the General Theory of Relativity and Gravitation (GR20). The joint conference GR20/Amaldi10 is an unprecedented event, which has attracted to Warsaw 900 of the most distinguished physicists and astronomers working on theories of quantum gravity and gravitational waves. This year's event is being organized by the Polish Society on Relativity and the Faculty of Physics at the University of Warsaw.
Physics and Astronomy first appeared at the University of Warsaw in 1816, under the then Faculty of Philosophy. In 1825 the Astronomical Observatory was established. Currently, the Faculty of Physics' Institutes include Experimental Physics, Theoretical Physics, Geophysics, Department of Mathematical Methods and an Astronomical Observatory. Research covers almost all areas of modern physics, on scales from the quantum to the cosmological. The Faculty's research and teaching staff includes more than 200 university teachers, of which close to 80 are employees with the title of professor. The Faculty of Physics, University of Warsaw, is attended by almost 1000 students and about 140 doctoral students.
The Polish Society on Relativity (PTR) consolidates the Polish relativistic community, promotes the achievements of Polish relativists worldwide and disseminates knowledge about the achievements of other communities in the field of relativity in Poland. The PTR's most important activities provide Polish undergraduates, doctoral students and young scientists the best possible conditions to help start their own research at the highest level in the modern fields of relativistic physics and the mathematics of space-time. Honorary members of the Society include the eminent physicists Professor Abhay Ashtekar and Professor Roger Penrose.
Quelle: Astronomical Observatory of the Faculty of Physics at the University of Warsaw 

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