Shuttle Derived HLLV
Several Shuttle-derived vehicle (SDV) designs were envisioned in the 1980's for NASA and DOD heavy lift launch vehicle (HLLV) missions into the 21st century. Studies performed at the Marshall Center have included SRB-X, side mount and in-line boostered configurations, each an evolutive concept incorporating STS features to deliver 144,000-195,000 lb payloads into LEO or 10,000 lb into GEO. A three-stage multitank design sporting a cluster of eight 1.757 Mlb thrust engines on the first stage emerged as a favored HLLV. The second stage would be lofted by four 481,000 lb thrust SSME derivative engines and the third stage would have two of the derivatives. All stages would be drogue-parachuted to water touchdown for reuse.
This concept has come into vogue again in mid-2005 with the continuing search for a Shuttle replacement. ATK-Thiokol (the maker of the SRB) has proposed an inline heavy lift carrier equivalent to the Saturn-V. Four SSME engines would be at the base of a stretched external tank, flanked by two shuttle RSRM motors with a fifth segment added. Atop this would be an 8.7 m diameter Lox/LH2 stage, followed by a 10-m diameter payload fairing. Availability would be ten years after go-ahead.
The advantage of SDV designs is that the booster is known and reliable, and already man-rated. The infrastructure to build, launch and retrieve the Shuttle already exists and has significant political sway. A major downside of using Shuttle technology in a non-reusable booster is cost. The complexity, and hence per unit cost of the SSME is significantly higher than that of the competing RS-68, which is used in the Delta-IV.
The ATK-Thiokol proposal also includes a growth version for lifting heavier cargos using three RS-68 engines. Additional engines would be clustered for launching heavier loads such as those needed for Mars missions. Using these engines would require significant redesign of the external tank.
Robert Zubrin's 1991 Mars Direct study also proposed reusing Shuttle technology in his Ares concept. It would use shuttle Advanced Solid Rocket Boosters, a modified shuttle external tank for handling vertically-mounted payloads, and a new Lox/LH2 third stage for trans-Mars or trans-lunar injection of the payload. Ares would put 121 tonnes into a 300 km circular orbit , boost 59 tonnes toward the moon or 47 tonnes toward Mars. Without the upper stage 75 tonnes could be placed in low earth orbit.
Future designs for the CLV point to an inline configuration. Appearing on NBC's "Meet The Press" on 31 July 2005, NASA director Mike Griffin said that NASA will not "design a manned spacecraft that places the crew in a position where anything can fall on them." In the wake of the loss of Columbia and the continuing problem with foam shedding on STS-114, this seems like a good idea.
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