WATCH your head if you鈥檙e out for a stroll next week: two experimental
spacecraft are due to return to Earth using no parachutes. The
shuttlecock-shaped ships, which will rely solely on air resistance to slow their
descent, will put an inflatable heat shield through its paces for the first
time.
Part of an experiment run by the European Space Agency, Daimler Chrysler
Aerospace (Dasa) and NPO Lavotchkin, a Russian company that makes tough
inflatable materials, the craft is due to be launched from Kazakhstan on 9
February.
The idea is to cut the cost of transporting cargoes into orbit by shrinking
the craft: using an inflatable heat shield and not stowing large parachutes, the
craft can be much smaller than usual. And by making the craft鈥檚 upper stages
smaller, they are also easier to send back to Earth for reuse. If things don鈥檛
go according to plan, the 1800-kilogram upper stage of the Soyuz rocket and the
110-kilogram payload could hit Earth at an alarming rate.
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Hopefully, a massive cone-shaped inflatable heat shield should decelerate the
craft when it opens out in stages
(see Diagram). This is used to protect the
craft from the intense heat as it enters the atmosphere and as a means of
creating sufficient drag to slow it to a safe 鈥渓anding鈥� speed of 50 kilometres
per hour.
The Inflatable Re-entry and Descent Technology (IRDT) is designed principally
to save space. By making it inflatable, however, space scientists can contain a
14-metre wide heat shield in a 0.7-metre space. According to Dieter Kassing,
project manager for the European Space Agencies, the cost per kilogram of
transporting cargo on the space shuttle is $20 000. 鈥淲e expect, at the
very least, to halve this cost, if not more,鈥� he says.
As the craft negotiates the Earth鈥檚 atmosphere, the first stage of the heat
shield is deployed, spreading an 8-metre diameter fan of air-filled shield on
one craft and a 2.4-metre fan on the second, smaller demonstrator.
While the nose takes the brunt of the thermal shock wave on entering the
atmosphere, as well as temperatures of more than 1000 掳C, the heat shield is
designed to withstand 500 掳C to protect its payload. While being flexible
enough to be inflatable, it must also be rigid enough to hold its shuttlecock
shape. The material that makes this possible was developed by NPO
Lavotchkin.
Once the craft have entered the atmosphere, the shield alone is insufficient
to slow it down so a second stage is deployed, virtually doubling the
circumference of each of them.
And according to a Dasa spokesman, recent drop tests show that these craft
should still function despite an impact without parachutes鈥攁nd even
suggest that a similar technique with a slower landing could eventually be used
for piloted missions.