Chrysler SERV

History

In 1966 the US Air Force began a study effort exploring various crewed spacecraft and launchers, categorizing proposals into three classes based on reusability. Class I placed a spaceplane atop an existing or modified ICBM launcher; Class II added partial reusability; Class III was fully reusable. The USAF had worked on the Class I X-20 Dyna Soar, cancelled in December 1963, and was interested in the Lockheed Star Clipper Class II design, but the study effort produced no results as the Air Force reduced its involvement in crewed space programs.

Meanwhile, NASA was winding down Project Apollo and began exploring crewed missions for the 1970s and beyond, with a permanently crewed space station a favored concept. These plans assumed use of existing Saturn rockets, but the Saturn systems were not suited for constant supply and crew rotation. The idea of a simple, inexpensive crewed launcher, a "ferry and logistics vehicle," emerged from space station studies, first appearing in fiscal year 1967 budgets.

Design of a low-cost, reusable Space Transportation System began in earnest in December 1967, when George Mueller organized a one-day brainstorming session. He invited the USAF and kept the original USAF acronym "ILRV." Like the earlier USAF studies, a small vehicle was envisioned, but NASA's Space Task Force quickly decided to move directly to Class III designs.

Description

SERV had a large conical body with a rounded base, described by Chrysler as a "modified Apollo design. Both vehicles used blunt body re-entry profiles, which reduce heating by creating a large shock wave in front of a rounded surface. Tilting the vehicle relative to its direction of motion changes the shock wave pattern, producing lift for maneuvering up to about 100 NM on either side of its ballistic path. The cone was stepped, with the lower portion angled at about 30 degrees and the upper portion at about 45 degrees.

The vehicle was 96 ft across at its widest point and 83 ft tall. Most of the airframe was steel composite honeycomb. The base had screw-on ablative heat shield panels for easy replacement; upper portions, experiencing lower heating, were covered with metal shingles over quartz insulation. Four landing legs extended from the bottom, their feet forming part of the heat shield when retracted.

A twelve-module LH2/LOX aerospike engine was arranged around the base rim, covered by movable metal shields that adjusted for decreasing air pressure during ascent, forming an altitude-compensating nozzle. The engine was fed by four cross-linked turbopumps normally running at 75% capacity; if one failed, the remaining three could throttle to 100% to maintain full power. Total thrust was 7,454,000 lbf, about the same as the Saturn V's S-IC first stage.

Around the base were forty 20,000 lbf jet engines fired just before touchdown to slow descent, with movable doors for feed air. Two RL10 engines provided de-orbit thrust, and small LOX/LH2 engines handled on-orbit maneuvering.

Similar designs

SERV resembled the later McDonnell Douglas DC-X, but the DC-X was built for a military mission requiring greater re-entry maneuvering, leading to a long, skinny airframe that re-entered nose-first and generated more lift but faced higher heating. The Blue Origin Goddard spacecraft used the original SERV layout, as it did not need extended crossrange and returned to the blunt-base re-entry profile.