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The Automated Transfer Vehicle

Published by Sigurd De Keyser on Tue Jan 17, 2006 5:49 pm
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By Klaus Schmidt and reviewed by Stephen Deisher, The Space Fellowship; With the Space Shuttle still not flying regularly, the Russian Progress supply ships are the only way to resupply the International Space Station. With that vehicle’s limited capacity of about 2.3 tons, the station crew is currently limited to two members. And as the Space Shuttle is slated for decommission in 2010 and therefore carrying mainly station modules for the further build-up, the international space community awaits the first launch of the European-build Automated Transfer Vehicle (ATV).

That resupply vehicle will carry up to 7667 kg of cargo and enable the ISS to support at least three humans. As NASA wants to increase the ISS crew to six persons in 2009, the ATV becomes a crucial element. Unfortunately, the first launch of the ATV is delayed by one year to mid-2007.

But now let’s take a deeper look into the ATV. The ATV will be launched from Kourou, French Guyana, on top of an Ariane 5. It is composed of a service and a cargo module. Mounted onto the frame of the service module are four solar arrays as the ATV is intended to be docked to the ISS for six months. After that time, they will still deliver 3800W to the ISS power grid. The ATV is powered by four 490 N strong engines, feeded by Monomethyl hydrazine fuel and Nitrogen tetroxide oxidizer. These main engines are also intended to regularly boost the ISS orbit.
The cargo module comprises compartments for unpressurised, propellants and liquids like water, and pressurised cargo. That cargo is not only food, clothing and other life-supporting things but also scientific cargo and racks.

After the launch, the ATV is put on a rendezvous course with the ISS. As the ATV is not only crucial to the ISS but also quite expensive regarding its heavy cargo and scientific payload it is designed more like a manned spacecraft than an expendable craft. For example, the flight computer three times redundant. It also would be not so nice to see 20 tons crashing into the ISS, when a single flight computer would crash. What then can happen we all know from the crash of a (much lighter) progress ferry into a Mir module in 1997. As the ATV docks with the Russian-build service module Svesda the ATV uses the same flight-proven docking components like the Progress crafts.

As the ATV remains docked to the ISS for six months it is also used as an extension to the ISS, so it has not only micro-meteoroid shielding but also a life support system. After six months, the ATV, loaded with trash, undocks with the ISS and reenters where it will burn up. That’s the main disadvantage of the craft. It has no reentry module, so it cannot bring back any scientific experiments and data. That will remain a major duty of the Space Shuttle until its retirement. After that, there will be three possibilities to recover cargo from the ISS.

Perhaps it will be possible to modify the ATV to incorporate a reentry module. The other options are the still to be developed Russian Kliper and American CEV crafts. Both should be available for not only carrying humans but also transporting cargo and getting cargo back to the earth. But that’s still far in the future and won’t happen until at least 2012.

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