Guy Norris/LOS ANGELES
NASA hopes to restart full scale free-flight drop tests of the X-38 crew return vehicle (CRV) as early as October, pending successful tests of a redesigned parafoil system in September.
The X-38 is being developed as a "life boat" for crews of the International Space Station and, according to NASA, could be the first new spacecraft built in the past two decades capable of carrying people to and from orbit. Built along the lifting body design lines established with the US Air Force's X-24A project in the 1970s, the X-38 is intended to glide from orbit and then deploy a steerable, parafoil parachute for its final descent. During initial drop tests in March at Edwards AFB, California, the parafoil unexpectedly twisted and ripped during deployment.
The incident forced a suspension of tests as NASA engineers sought a solution.
The agency completed trials of a subscale parafoil design at the US Army's Yuma Proving Ground in Arizona at the end of July with "excellent results", says X-38 and crew return project manager, John Muratore. The original problem was caused by "-significantly more wake effects behind the body than we anticipated". NASA had estimated that there should not be any wake effects "five body diameters back".
Muratore says, however, that "-we suspected that was the reason because the drogue chute didn't cause it to decelerate as fast as we expected, and the video showed the chute was distorted".
A team from Johnson Space Center in Texas investigated wake effects on a windtunnel model at Texas A&M University which showed that this caused the parafoil to twist. The motion caused the foil to half inflate, and simultaneously rip. "To eliminate the twist we built a geometric subscale parafoil and dropped it out of a helicopter at Yuma," says Muratore.
The redesigned parafoil, with several stages moved to new positions, inflated from the centre. NASA also thickened the rigging lines to help prevent a repeat of the incident.
Two tests on a full-scale 510m² (5,500ft²) parafoil will be made in mid-September using a Lockheed Martin C-130 as a launch platform. If these are successful, Muratore says the X-38 drop tests will restart at Edwards using the Boeing B-52 launch aircraft. Concurrent with the last Yuma tests, NASA will be delivering the next X-38 to Edwards. This vehicle, which is capable of manouvring, will be fitted with advanced electrical actuators .
Construction of the first space vehicle is "moving along", says Muratore, who adds that the cabin is "almost complete". The atmospheric test phase is expected to run through to around June 2000, with first space deployment scheduled in November 2000 from the Space Shuttle. The unpiloted test vehicle will descend to landing on earth after deployment. The X-38 CRV is targeted to begin operations aboard the International Space Station in 2003.
Source: Flight International
