FUTURE spacecraft could be shot into orbit from a giant flying air gun,
according to a US Air Force plan. The radical launch system would be fitted to
standard cargo planes in hours and could slash the cost of getting satellites
into space, its inventors say.
Launching satellites from the air saves rocket fuel and means you don鈥檛 need
to build expensive and cumbersome launch sites on the ground. The US already
uses Pegasus rockets slung beneath B-52 planes to put lightweight satellites
into orbit. But this system has its drawbacks. Rockets hooked beneath the
plane鈥檚 fuselage are limited in size by the aircraft鈥檚 undercarriage. And only
certain planes have strong enough wings to carry rockets beneath them. But there
are other drawbacks. 鈥淭he problem with Pegasus is they have a dedicated
aircraft,鈥� says Kenneth Hampsten, who heads a team that tests innovative
satellite launch systems at Kirtland Air Force Base in New Mexico. These planes
are costly to maintain and may not get used very often, he says.
Hampsten and his colleague John Walker propose installing a pneumatic rocket
launcher, similar to those used in submarines to launch intercontinental
ballistic missiles, in the cargo bay of a carrier plane and fitting customised
cargo doors at the rear. Using the whole cargo area in this way would allow
larger, heavier satellites to be carried without creating additional drag.
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With the plane at an altitude of 12,000 metres, cruising just below the speed
of sound, a giant compressed-gas launcher fires the rocket tail-first from the
back of the plane. After five seconds the rocket鈥檚 wings fold out to provide
lift, and the rocket performs a quarter roll to ensure it doesn鈥檛 hit the plane
when the boosters are ignited.
The retractable wings provide a tremendous amount of lift, allowing the
rocket to make a smooth transition from horizontal flight to its required
trajectory, says Hampsten. But as the atmosphere thins out and the wings become
less efficient, they are folded back into the rocket body to minimise drag.
Walker says the novel launch system and the new rocket, called Bladerunner,
have the potential to slash satellite launch costs from the $11,000 to
$44,000 per kilogram it costs today to under $6600 per kilogram.
With Pegasus rockets it costs around $33,000 to launch a kilogram of
payload, which is very expensive, says Dave Gibbon of Surrey Satellite
Technology. Cutting the cost of launching small satellites could encourage more
launches which could in turn bring the price down further.
Not only do air-launched systems like Bladerunner have a head start over
conventional launchers, they are also more efficient, says Hampsten. For
example, its rocket nozzle can be designed for a thin atmosphere rather than
having to work across a broad range of pressures like a rocket that lifts off
from the ground.
The pneumatic launcher wouldn鈥檛 need an expensive, dedicated aircraft,
because the whole system can be fitted into the cargo bay of a variety of
military planes like the C-17 and C-141 Starlifter, says Hampsten. The
conversion should take less than 24 hours. This should provide more flexibility
in how a fleet is used. 鈥淚t doesn鈥檛 require any new infrastructure and the
aircraft isn鈥檛 dedicated to this role,鈥� says Hampsten.
Though the idea has been patented, it may be some time before it becomes a
reality. Although the team have done computer models, they don鈥檛 have funds to
build a demonstration system. 鈥淲e need money,鈥� says Walker. 鈥淲e think that with
adequate resources we could fly a prototype vehicle within four years.鈥�
