29 December 2010

The Chrysler SERV: Thinking Out of the Box for Space Travel

Chrysler SERV ascends on its aerospike engine
By the late 1960s, the groundwork was being laid down that would eventually evolve in the Shuttle Transportation System that today is in the twilight of its career. The NASA-led studies that involved the major aerospace contractors of the day was divided into "phases" and at each phase candidate contractors had to demonstrate their concepts to the Manned Spacecraft Center (MSC) at the Johnson Space Center outside of Houston. Apollo was run out of the NASA headquarters in Washington, but the technical reach of a reusable spacecraft meant that NASA wanted the program leadership to be at a field center run by engineers- and at the time, only Houston and the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, had the technical expertise for such an undertaking. Not wanting to put its eggs in one basket, though, NASA established on 6 July 1970 the Alternate Space Shuttle Concepts (ASCC) study to evaluate alternative concepts and proposals to what was already under development in cooperation with the aerospace industry and the MSC in Houston. Given that the MSC had it hands full, program leadership of the ASCC was assigned to the MSFC in Huntsville. Over 29 configurations were studied and millions in funding were provided. A joint submission by Grumman/Boeing was evaluated, along with one from Lockheed and one from Chrysler, which at the time had a thriving space division that had been in business since 1962 building the first stages for the Saturn I rocket and Saturn IB rocket. Chrysler's ASSC proposal was the recipient of a $1.9 million study contract for what has to be one of the most unorthodox if not outright unique space shuttle concepts ever taken seriously by NASA. 

Schematic diagram of the Chrysler SERV
Chrysler's design was called the SERV- Single-stage Earth-orbital Reusable Vehicle- and it looked like nothing else under study at the time. It was a large conical vehicle that looked like a supersized Apollo command module. It was 65 feet high and 90 feet in diameter with a central payload bay 23 feet wide and 60 feet long. Liquid hydrogen and liquid oxygen tanks then surrounded the payload bay to fill the rest of the volume of the SERV. Its propulsion engine was highly innovative and developed with assistance from Rocketdyne- the SERV had a 12-module liquid oxygen/liquid hydrogen aerospike engine integral to the base of the SERV that was 87.4 feet in diameter and just over 8 feet long. The engine developed an astounding 5.4 million pounds of thrust (by comparison, each Space Shuttle Main Engine develops about 400,000 lbs of thrust at launch). Each of the 12 modules were interconnected and each had a set of turbine driven fuel pumps that could run as high as 120% to compensate for the failure of any pair of pumps in the 12 modules. The engines designed were so powerful, that the SERV's aerospike had to be throttled back to 20% just before reaching "max-Q"- the point of highest aerodynamic stress to prevent overstressing the SERV during its ascent to orbit. A series of doors could close over the aerospike modules to protect them during re-entry. 

SERV with the MURP spaceplane. Note the doors for the jet engines.
At launch, the SERV weighed in at approximately 4.5 million lbs and different modules could be attached to the top of the SERV- the most studied were an external extension to the payload bay and the other was what was called the MURP- Manned Upper Reusable Payload, which was a small orbiter design with flick-out wings on return to Earth. The MURP could carry up to ten astronauts. Launches would have taken place from large concrete pads as the SERV had its own landing legs to support its weight. To return to the Earth, the SERV would re-enter the same way as the Apollo command module did, with the blunt end first and protected by thermal tiles. But instead of a water landing, at an altitude of 25,000 feet, a set of intakes and exhaust ports opened and four banks of seven jet engines (that's right, twenty eight engines!) powered by JP-4 fuel would start up and provide deceleration and maneuver capability that would bring the SERV back home for a soft landing on its own landing legs. The planned landing site for the SERV would have been on the skid strip at Cape Canaveral adjacent to the Kennedy Space Center. 

Chrysler's space division would have built the SERV at the Michoud facility that today has been responsible for the Space Shuttle's external tank. A specially-modified transport ship would then take the completed SERV to the Kennedy Space Center. Chrysler estimated that each SERV would cost $350 million each. However, by the time the ASCC studies were winding down, the Chrysler SERV got little attention as the design submissions from Lockheed and Grumman/Boeing were decidedly much more "conventional" than the SERV- but the SERV is a fascinating exercise in aerospace development when preconceived notions are cast aside and an innovative solution is found to meet an exacting set of requirements! 

Source: Space Shuttle: The History of the National Space Transportation System- The First 100 Missions by Dennis R. Jenkins. Specialty Press, 2001, p123-125.

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