Raumfahrt - Vier Satelliten der NASA-Magnetospheric Multiscale oder MMS, Mission bildeten engste Flugformation



On Oct. 15, 2015, the four spacecraft of NASA's Magnetospheric Multiscale, or MMS, mission entered the tightest flying formation ever achieved (shown here in an artist concept) – a pyramid shape, with each satellite just six miles from each other.
Credits: NASA's Goddard Space Flight Center
On Oct. 15, 2015, a NASA mission broke its own record: the four satellites of its Magnetospheric Multiscale mission are now flying at their smallest separation, the tightest multi-spacecraft formation ever flown in orbit. The four spacecraft are just six miles apart, flying in what's called a tetrahedral formation, with each spacecraft at the tip of a four-sided pyramid. The close formation is all the more impressive as the spacecraft speed along at up to 15,000 miles per hour and – with their booms extended – each spacecraft covers as much area as a professional baseball stadium.
This four-sided pyramid formation is imperative to achieve the science goals of the Magnetospheric Multiscale mission, known as MMS. MMS directly measures the space environment at the boundaries of Earth’s magnetic bubble, the magnetosphere, where the sun's constant stream of magnetized solar wind collides with Earth's own magnetic field. The tetrahedral formation allows the mission to track events in three dimensions. As it flies through these magnetic collisions, MMS can use its four spacecraft to determine how a given event moves in three dimensions or changes over time. If all four spacecraft moved in a line or a plane, MMS wouldn’t be able to observe the full 3D shape of a structure as it flies through.
“Moving MMS into this tight tetrahedron formation is a huge milestone for NASA,” said Tom Moore, MMS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “We are incredibly excited to be getting on with science analysis after all the testing we have done since our launch in March."
The MMS team finished its commissioning phase on Aug. 31, 2015, and is now officially in the first phase of its science mission to gather data on the electrical and magnetic properties of the space environment around Earth. MMS gathers data to study a phenomenon called magnetic reconnection, which occurs when the magnetic field surrounding Earth connects and disconnects from the magnetic field carried by the solar wind, reconfiguring the very shape of Earth's magnetic environment.  Magnetic reconnection can result in the explosive release of energy that can accelerate particles to incredible speeds – in some cases to nearly the speed of light. The MMS orbit is designed to carry the spacecraft directly though reconnection events. Reconnection is a common process throughout our universe; occurring in space near Earth, in the atmosphere of the sun and other stars, and in the vicinity of black holes and neutron stars.
“Its pyramid formation and time resolution will offer the first ever three-dimensional observations down to the smallest scales of reconnection,” said Moore.
When MMS first formed a tetrahedral shape in July 2015, the spacecraft were flying about 100 miles apart. Over the past few months, MMS gradually closed that spacing to just six miles. Another mission, ESA/NASA’s Cluster, had times in which two of its four spacecraft were that close, but MMS is the first mission to hold four spacecraft in such close proximity. To achieve this milestone, first the MMS spacecraft dropped down to 40 miles apart, then 15 and finally on Oct. 15 the spacing dropped to its closest point, just a little over six miles apart. After operating over that range, the MMS science team will then decide what spacing was optimal and return to that value.
MMS is the fourth NASA Solar Terrestrial Probes Program mission. The goal of the STP Program is to understand the fundamental physical processes of the space environment from the sun to Earth, other planets, and the extremes of the solar system boundary. Goddard built, integrated, and tested the four spacecraft and is responsible for overall mission management and mission operations. The Southwest Research Institute in San Antonio, Texas, leads the Instrument Suite Science Team, with the University of New Hampshire leading the Fields instrument suite and Goddard leading the plasma instrument suite with the Fast Plasma Investigation. Science operations planning and instrument command sequence development will be performed at the MMS Science Operations Center at the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder.
NASA's Magnetospheric Multiscale mission (shown here in an artist concept) flies through the borders of the magnetic fields around Earth to better understand how they connect and disconnect with similar magnetic fields coming from the sun. Such magnetic reconnection can explosively release energy and particles into near-Earth space.
Credits: NASA
Quelle: NASA
Update: 21.09.2016

NASA's MMS Achieves Closest-Ever Flying Formation

On Sept. 15, 2016, NASA’s Magnetospheric Multiscale, or MMS, mission achieved a new record: Its four spacecraft are flying only four-and-a-half miles apart, the closest separation ever of any multi-spacecraft formation. The previous record was first set by MMS in October 2015, when the spacecraft achieved a flying separation of just over six miles apart.

artist concept of MMS flying formation
This animation illustrates the four Magnetospheric Multiscale satellites' flying formation.
Credits: NASA's Goddard Space Flight Center/Joy Ng, producer


The four MMS spacecraft fly in a pyramid shape, with one satellite marking each corner. This shape, called a tetrahedron, allows MMS to capture three-dimensional observations of magnetic reconnection – critical for fully understanding this process. Magnetic reconnection happens when magnetic fields pinch off and explosively reconfigure, sending particles zooming in all directions. It’s thought to happen throughout the universe, and is one of the few ways that material is energized in space.


MMS’ new, closer formation will allow the spacecraft to measure magnetic reconnection at smaller scales, helping scientists understand this phenomenon on every level.

Quelle: NASA


Update: 9.02.2017


NASA Spacecraft Prepares to Fly to New Heights

On Feb. 9, 2017, NASA’s Magnetospheric Multiscale mission, known as MMS, began a three-month long journey into a new orbit. MMS flies in a highly elliptical orbit around Earth and the new orbit will take MMS twice as far out as it has previously flown. In the new orbit, which begins the second phase of its mission, MMS will continue to map out the fundamental characteristics of space around Earth, helping us understand this key region through which our satellites and astronauts travel. MMS will fly directly through regions – where giant explosions called magnetic reconnection occur – never before observed in high resolution.


Launched in March 2015, MMS uses four identical spacecraft to map magnetic reconnection – a process that occurs when magnetic fields collide and re-align explosively into new positions. NASA scientists and engineers fly MMS in an unprecedentedly close formation that allows the mission to travel through regions where the sun's magnetic fields interact with Earth's magnetic fields – but keeping four spacecraft in formation is far from easy. 


“This is one of the most complicated missions Goddard has ever done in terms of flight dynamics and maneuvers,” said Mark Woodard, MMS mission director at NASA’s Goddard Flight Space Center in Greenbelt, Maryland. “No one anywhere has done formation flying like this before.”

Over three months, the MMS spacecraft transitions from the dayside magnetopause, to a new, larger orbit on the nightside, as shown in this visualization.
Credits: NASA's Goddard Space Flight Center/Tom Bridgman, visualizer


To form a three-dimensional picture of reconnection, the mission flies four individual satellites in a pyramid formation called a tetrahedron. While a previous joint ESA (European Space Agency)/NASA mission flew in a similar formation, MMS is the first to fly in such an extremely tight formation – only four miles apart on average. Maintaining this close separation allows for high-resolution mapping but adds an extra dimension of challenge to flying MMS, which is already a complex undertaking.


Flying a spacecraft, as one would suspect, is nothing like driving a car. Instead of focusing on just two dimensions – left and right, forward and backwards – you also must consider up and down. Add on to that, keeping the four MMS spacecraft in the specific tetrahedral formation necessary for three-dimensional mapping, and you’ve got quite a challenge. And don’t forget to avoid any space debris and other spacecraft that might cross your path. Oh, and each spacecraft is spinning like a top, adding another layer to the dizzying complexity. 


“Typically, it takes about two weeks to go through the whole procedure of designing maneuvers,” said Trevor Williams, MMS flight dynamics lead at NASA Goddard. 


Williams leads a team of about a dozen engineers to make sure MMS’s orbit stays on track. During a normal week of operations, the maneuvers, which have been carefully crafted and calculated beforehand, are finalized in a meeting at the start of the week.


To calculate its location, MMS uses GPS, just like a smart phone. The only difference is this GPS receiver is far above Earth, higher than the GPS satellites sending out the signals. 


“We’re using GPS to do something it wasn’t designed for, but it works,” Woodard said.


Since GPS was designed with Earth-bound users in mind, signals are broadcast downwards, making it difficult to use from above. Fortunately, signals from GPS satellites are sent widely to blanket the entire planet and consequentially some from the far side of the planet sneak around Earth and continue up into space, where MMS can observe them. Using a special receiver that can pick up weak signals, MMS is able to stay in constant GPS contact. The spacecraft uses the GPS signals to automatically compute their location, which they send down to the flight control headquarters at Goddard. The engineers then use that positioning to design the maneuvers for the spacecraft’s orbits. 


While the orbit for each MMS spacecraft is almost identical, small adjustments need to be made to keep the spacecraft in a tight formation. The engineers also rely on reports from NASA’s Conjunction Assessment Risk Analysis, which identifies the locations of space debris and provides notification when objects, like an old communications satellite, might cross MMS’s path. While nothing yet has been at risk for colliding with MMS, the crew has a prepared backup plan – a dodge maneuver – should the need arise.


On scheduled Wednesdays, one or two per month, the commands are sent up to the spacecraft to adjust the tetrahedral formation and make any necessary orbit adjustments. These commands tell MMS to fire its thrusters in short bursts, propelling the spacecraft to its intended location.


Moving MMS is a slow process. Each spacecraft is equipped with thrusters that provide four pounds of thrust, but they also weigh nearly a ton each. The spacecraft all spin like tops, so the timing of each burst needs to be precisely synchronized to push the spacecraft in the right direction.


The next day, once the spacecraft are in their proper locations, a second round of commands are given to fire the thrusters in the opposite direction, to fix the spacecraft in formation. Without this command, the spacecraft would overshoot their intended positions and drift apart with no resisting forces to stop them.   


Unlike airplanes, which constantly fire their engines to keep in motion, the spacecraft rely on their momentum to carry them around their orbit. Only short bursts from their thrusters, lasting just a few minutes, are required to maintain their formation and make minor adjustments to the orbit.


“We spend 99.9 percent of the time coasting because we need to be sparing with the fuel,” Williams said. 


Launched with 904 pounds of fuel, the spacecraft have only used about 140 pounds in their first two years of operation. However, sending MMS into a wider orbit for its second phase will consume about half the remaining fuel – and there are no gas stations in space for refueling. The operations crew carefully plan each maneuver to minimize fuel consumption. Typical maneuvers take less than half a pound of fuel and the crew hopes their fuel conservation efforts will save MMS enough fuel to allow extended studies past the end of the primary mission.   


The new elliptical orbit will take MMS to within 600 miles above the surface of Earth at its closest approach, and out to about 40 percent of the distance to the moon. Previously, the spacecraft went out only one-fifth (20 percent) of the distance to the moon.


In the first phase of the mission, MMS investigated the sun-side of Earth’s magnetosphere, where the sun's magnetic field lines connect to Earth's magnetic field lines, allowing material and energy from the sun to funnel into near-Earth space. In the second phase, MMS will pass through the night side, where reconnection is thought to trigger auroras. 


In addition to helping us understand our own space environment, learning about the causes of magnetic reconnection sheds light on how this phenomenon occurs throughout the universe, from auroras on Earth, to flares on the surface of the sun, and even to areas surrounding black holes. 


While MMS will not maintain its tetrahedral formation as it moves to its new orbit, it will continue taking data on the environments it flies through. The operations crew expects MMS to reach its new orbit on May 4, 2017, at which point it will be back in formation and ready to collect new 3-D science data, as its elliptical orbit carries it through specific areas thought to be sites for magnetic reconnection.

Quelle: NASA




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