The X-38 was a joint project by NASA and ESA, developed at JSC. It was a prototype for the ISS's Crew Return Vehicle (CRV, in other word's ISS's lifeboat. Currently the only escape vehicle is a Soyuz which can only carry 3 passengers, which limits the numbers onboard the ISS to 3 (except when the shuttle is present). The X-38 would have allowed the ISS to have its full complement of 7 astronauts. On a longer time scale the X-38 was also to serve as the basis for the design of other crew return vehicles (CRVs) but it was never supposed to be a general purpose orbiter, for example the life support systems were only designed to function for 9 hours (although ESA was planning to use the experience gained during the X-38 project on more widely scoped projects). The project began in 1995 with an approximate budget of $500 million and was terminated by NASA on April 29, 2002.
Basic specs:
- Landing mass: ≤ 10 000kg
- Landing speed: ≤ 9.1 m/s (horizontally), ≤ 4.6 m/s vertically
- Landing accuracy: with a 9 km radius
- Length: 9.1m
- Width: 5.5m
- Cabin volume: 11.8m3
- Parafoil area: 7500 ft2
- Power source: batteries
A brief time line:
- October 1991-December 1996: The use of a parafoil as a means of autonomously recovering and landing a spacecraft is successfully tested as part of the Spacecraft Autoland project.
- Early 1995: In-house development study of the X-38 project begins at JSC.
- Summer 1995: The parafoil concept is extended to the X-38. The firsts tests using a 1/6 model show that the vehicle has good flight characteristics.
- Early 1996: Scaled Composites is awarded a contract to build 3 atmospheric test airframes,
- September 1996: The first airframe is delivered to JSC where it was equipped with avionics, computers systems etc... for flight tests.
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December 1996: A second airframe is delivered.
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July 30, 1997: First tests onboard a modified B-52. During these tests the X-38 remained attached to the B-52. There were 4 such captive tests that year, and 3 in 1998.
- March 12, 1998: First free flight test. These continued from 1998 to 2001 at progressively higher altitudes and faster speeds. The last test flight was on December 13, 2001.
- April 29 2002: NASA officially shelves the project.
Basic design
The X-38's configuration is what is known as a "lifting body", closely resembling the X-24A that was tested from 1969 to 1971. Roughly shaped like a very narrow glider aircraft it does not have any real wings, but does have vertical winglets. Although it would not generate enough lift to land safely, it would allow for some flight manoeuvres. Lift would have been provided by a large parafoil. In many ways a parafoil is similar to a parachute except that far more control is available. The parafoil was a key part of the X-38's design as it allows the vehicle to be slowed progressively, for a safe landing. The parafoil deploys in 5 stages, each stage further slowing down the vehicle.
Three 80% size prototypes were used: the V131, V132, and V131R (a modified V131). A fourth full-size prototype to be named V133 was also planned.
These 4 prototypes were all for atmospheric tests: a modified B-52 carried them to their desired altitude before releasing them. This was to test both the gliding phase of the vehicle's flight and the use of its parafoil. Another prototype, the V201 was to be built for space testing: it would have been carried into space by the space shuttle and released from the cargo bay. Construction of the V201 started in 1999 but was never finished. Initially the X-38 was a 100% NASA project, however in 1997 ESA and NASA agreed to make the project a joint one. ESA was to provide 15 major subsystems of the V201.
Mission profile
Had the X-38 ever been used, its use would have been as follows:
- Setup: The X-38 would be carried to space onboard the space shuttle. Once attached to node 3 of the ISS it would remain dormant for up to 3 years before any maintenance was necessary
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De-orbital and reentry: After separating from the ISS a rocket is fired to slow down the spacecraft and to begin reentry. After use the de-orbit module is jettisoned.
- Gliding phase: After re-entering the earth's atmosphere, the X-38 initially glides in a way similar to the space shuttle.
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Parafoil deployment and landing: At around 40,000 feet when the X-38 has slowed sufficiently, a large parafoil is deployed, allowing greater control and slowing the vehicle down to a speed suitable for landing. Instead of normal landing gear the X-38 use skids, which double as shock absorbers. Upon landing the skids fold up under the vehicle.
Use of the X-38 was simplified to the extreme, it would literally have been a case of jumping in and hitting the big red button. All other operations would have been fully automatic (with the possibility of manual overrides) as, because it was designed for use in emergencies, it was a distinct possibility that crew members might be injured and unable to pilot the X-38.
Space on a shoe string
One of the key aspects of the X-38's design was the use of standard parts, materials or technologies when possible. Of course this does not mean that old technology was being used, much of it had never been applied to spacecraft. For example the flight computer is currently used in commercial aircraft and the flight operating system is in use in many aerospace applications. The X-38's thermal tiles come from an existing NASA project and its primary navigation instruments are in use onboard Navy fighters.
Reusing existing technology has important effects on both the time required to design the X-38 and its cost. Previous research had indicated that $2 billion would be necessary to develop a vehicle serving the X-38's purpose whereas the X-38 was initially expected to cost only a quarter of that (although in the end it would have cost $700 million).
All this came to an end when NASA cancelled the project for budgetary reasons (surprise surprise), preferring to concentrate resources on the more versatile X-37. The X-38 was only 2 years from completing its test phase and was expected to enter active service by 2006. The X-38 would have been the basis for a design that could be easily modified for other purposes, in particular ESA was planning a version that would be launched atop an Ariane 5.
Sources:
http://www.dfrc.nasa.gov/Newsroom/X-Press/special_editions/X-38/stories/073101/new_future.html
http://www.fas.org/spp/guide/usa/launch/x-38.htm
http://www.dfrc.nasa.gov/Newsroom/FactSheets/FS-038-DFRC.html
http://esapub.esrin.esa.it/bulletin/bullet101/graf.pdf
http://www.dfrc.nasa.gov/Gallery/Photo/X-38/
http://www.nasaexplores.com/show2_articlea.php?id=01-026