Friday, December 27, 2013

Satellites to sail to afterlife on Gossamer wings

Space debris; Cleaning up our orbit from decommissioned satellites is far more important than you might think. The potential threat to spacecraft from those heading to space to those already there, such as the ISS or other satellites is of major concern.

This has been seen as an important issue this past year and some great solutions have been developed. From the refueling of the satellites to extend their lives to Clean Space One, a satellite that escorts them to their deorbit and subsequent burning up in the atmosphere, there have been numerous concepts carried through to testing and planned implementation. Now we welcome a new entry to the mix.

Incorporating Solar Sails into the design of a satellite, holding off on deployment until they entered retirement, is the Gossamer Deorbit Sail. It works by increasing the Aerodynamic drag would then pulling the craft from its orbit and to its fiery end.

Retired or decommissioned Satellites today are capable causing mid-air collisions for up to a century, perhaps longer. The ESA has taken on this issue and is committed to cleaning up our orbits within the next 25 years. There are numerous levels and classifications of orbit from: Centric, & Altitude, to Inclination & Eccentricity and at least 5 more each which includes several grouping beneath it. Most of the ideas up until now have concentrated on removing the debris that is already up there, but this concept takes it a step further and proposes something that could be incorporated in to the satellite design to plan ahead for its eventual demise.

The Gossamer Deorbit Sail weighs 2 kilograms and compacts down to 15 x 15 x 25 centimeters. When it is deployed it extends to 5 x 5 meters. This size can bring down a satellite of up to 700 kilograms. The average satellite weighs 7.25 kilograms but the average communications satellite weighs, surprise 700 kilograms.

The sail takes care of more than just causing atmospheric drag, in low orbits, perhaps that would be enough, but to make the time frame involved more do-able, thrusters would be necessary. But then that would require ten times the equivalent mass in propellant. So these sails become solar sails. Up in the higher orbits the sail uses solar radiation pressure to descend along with an attitude control system.

So far the tests have been Earth bound but extensive. From thermal and vibration to vacuum tests, all has done extremely well. Next? The team is hoping that they will see a new extensive battery of tests conducted by the end of 2014 but this time in orbit. A demonstration satellite will be sent up on a piggy-back launch opportunity.

Once in orbit, the sail will be deployed and the following 2-3 weeks will be spent demonstrating its solar sailing propulsion. Next the sail will be rotated to increase the atmospheric drag and deorbit the satellite. It is expected that the death could take from 2 months to one year, approximately 1/100thof the usual timeframe expected.

The idea is a good one, better is that we are coming up with ideas and recognizing the need! It is a unfortunate that the people of Earth were incapable of planning ahead when satellites first flew, but great that now not only do we have the technology to put them up there, but also to bring them down, to clean up orbit. 

As we stand on the precipice about to leap into galactic travel, good that we learn first to clean up after ourselves!

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