Between 1984 and 1995 the government investigated numerous concepts for the development of a replacement to the shuttle. Each of these concepts focused on the vehicle only and did not address the entire flight and ground systems. Major emphasis was placed on the reduction of flight element production costs and retained the support the design approach, starting with the rocket engines, then the vehicle, and then the ground facilities and support equipment required. It was recognized that operations experience was needed to evolve to a more operable approach for the future.
However, due to priorities at the launch operations center, personnel with hands-on experience were not actively involved in these advanced study efforts. In many cases the concept was targeted to replace shuttle; however, there was no definitive plan to bridge the gap from shuttle until the new program was certified as operational. Additionally, the lack of definition of a mission model in many cases led to the premature termination of each effort.
Shuttle-C was envisioned to fill the gap between shuttle and ALS5. Using an unmanned cargo carrier in place of the orbiter, Shuttle-C was compatible with existing shuttle infrastructure and offered a heavy-lift capability (up to 150K lbs. to low earth orbit) within a four year window. In the spring of 1989 a Shuttle-C Users Conference was sponsored at Huntsville, Alabama to enlighten the user community of system capabilities and determine a preliminary mission model. The then Space Station Freedom was targeted at that time as a potential user in the space station assembly sequence and the logistics resupply missions.
Shuttle-C, a partially reusable cargo vehicle, would capitalize on the existing Space Transportation System infrastructure at KSC and elsewhere to keep costs down. With its heavy lift capability -- anywhere from 100,000 to 170,000 pounds (45,360 to 77,112 kilograms) -- Shuttle-C could reduce by 50 percent the number of launches and length of assembly time for space station elements. It also could be used to carry into orbit scientific spacecraft. Among the candidate missions under study were two of the Great Observatories, AXAF and SIRTF. A cargo Shuttle could serve as a test bed for new Shuttle elements like the ASRM.
Several Shuttle-derived vehicle (SDV) designs have been envisioned for near-term 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 is emerging 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.
The technology requiring the greatest advances to realize the design is a reusable, long-life liquid oxygen/hydrocarbon fueled booster. The 5-6 yr development span would require associated selections of launch sites and the construction of launch facilities which would not interfere with STS operations.
In October 1987, NASA selected three contractors to perform the first of a two-phase systems definition study for Shuttle-C. The efforts focused on vehicle configuration details, including the cargo element's length and diameter, the number of liquid-fueled main engines, and an operations concept evaluation that included ground and flight support systems. A major purpose of the study was to determine whether Shuttle-C would be cost effective in supporting the space station. Using Shuttle-C could free the Space Shuttle for STS-unique missions, such as solar system exploration, astronomy, life sciences, space station crew rotation, and logistics and materials processing experiments. Shuttle-C also would be used to launch planetary missions and serve as a test bed for new Shuttle boosters.
The results of the Shuttle-C efforts were to be coordinated with other ongoing advanced launch systems studies to enable a joint steering group, composed of DOD and NASA senior managers. The purpose of the steering group was to formulate a national heavy-lift vehicle strategy that best accommodated both near-term requirements and longer term objectives for reducing space transportation operational costs.
Due to sharing the development costs, the space station community was not ready to commit to using the Shuttle-C. The message from other potential users was "build it and we will come"; however, no one was willing to step up and commit to Shuttle-C. With no clear definition of annual utilization the program was ultimately terminated.
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