X-38: Crew Return
January 1998: New
Technology Helps X-38 Team Overcome Parafoil Challenge
X-38 program has been discontinued. The following article is for
X-38 Crew Return Vehicle is an innovative new spacecraft designed
at JSC to validate technologies required for a future International
Space Station emergency crew return "lifeboat" which would be
delivered to the space station by the space shuttle.|
Developers of the X-38
prototype International Space Station crew return vehicle overcame
one of the toughest challenges faced by the team so far with the
recent successful pallet drop test of a stronger and more stable
The project is now on track
toward a drop test of the first unpiloted X-38 atmospheric test
vehicle at the Dryden Flight Research Center in early February,
said X-38 Project Manager John Muratore. The parafoil difficulties began for the X-38 team last summer as tests were under way of techniques
for reefing the parafoil to increase its stability and uniformity
during deployment. In a modification of a technique used in sport
parachuting, the team was testing a system called "Zero-Stage Reefing"
that holds the giant, rectangular X-38 parachute into a more round
shape for a few seconds after its deployment, making it more stable.
To the team's surprise,
during a pallet drop test of the new reefing system in October 1997
in Yuma, Ariz., the parafoil tore completely in half. The team went
back to the drawing board to find a method of measuring and reducing
stresses caused by the reefing and to strengthen the parafoil. But
no system for measuring such forces in the cloth of a parachute
Steve Fitzgerald of JSC's
Aeroscience Branch came to the rescue with a totally new method
for instrumenting the leading edge of the parafoil and measuring
the stresses it experienced. Fitzgerald worked with a Conroe company,
Invocon, Inc., that was developing tiny wireless data systems for
NASA under a Phase 3 Small Business Innovation Research grant. Working
with Fitzgerald, the company modified their systems to be used to
measure forces in the parachute's canopy.
Crew Return Vehicle in free flight after release from B-52 Mothership.|
No such instrumentation
had ever before been developed for a parachute, and the Invocon
system is now expected to find widespread use outside of NASA within
the parachute industry, Fitzgerald said. "The people involved with
parachute testing at the Army's Yuma Proving Ground are very interested,
as well as others," Fitzgerald said. "This is the first time anyone
has ever been able to do this, and that makes a lot of people involved
in parachute testing excited."
The team spent the fall
conducting a series of 20 subscale drop tests to measure forces
on the parafoil and modifications to the reefing system. "With Steve's
instrumentation, we were able to determine where and how much the
load was on the parafoil and to modify the reefing system to reduce
it," Muratore said.
As a result of the measurements,
the parafoil was strengthened as well. The parafoil's manufacturer,
Pioneer Aerospace, modified the parachute at its Columbia, Miss.,
facilities, replacing the material in the bottom of the parafoil
with a new material twice as strong as before.
The success of all of the
modifications was borne out in the first full-scale pallet drop
test of the new parafoil conducted Dec. 12, 1997, in Yuma. "It was
a beautiful test, and everything worked perfectly," Muratore said.
"The parafoil problems have definitely been the biggest challenge
we have faced so far in the project. But to find out these things
is why you do a lot of testing. You want to find out these problems
when you have a less expensive pallet underneath the parachute instead
of a full test vehicle."
Crew Return Vehicle on ground after first free flight.|
Following the planned February
test of the first X-38 atmospheric test vehicle, which was outfitted
at JSC and shipped to the Dryden Flight Research Center last summer,
unpiloted drop tests of three such vehicles will continue for the
next two years. The first vehicle already has been through a series
of captive carry flight tests, where it remained attached under
the wing of the NASA B-52 aircraft at Dryden. For the February test,
the vehicle will be dropped from an altitude of about 23,000 feet,
flying free for only a few seconds before the parafoil is deployed.
The drop tests will work
up to an altitude of about 50,000 feet and longer free-flight times
for the X-38 vehicles prior to deployment of the parafoil. The second
X-38 atmospheric test vehicle, which includes active flight control
surfaces, is already being outfitted at JSC in Bldg. 220. It is
scheduled to be shipped to Dryden in March and perform a drop test
in May. The airframe for the third atmospheric vehicle is currently
under construction in California. It also will be outfitted at JSC.
In addition, the parts
for an X-38 space test vehicle are already being fabricated by JSC's
Manufacturing, Materials and Process Technology Division. The nose
and forward part of the cabin for the X-38 space test vehicle, planned
to fly an unpiloted space test from a space shuttle mission in 2000,
have already been assembled in Building 220.