After the Challenger accident, NASA believed there would be a need for a 14 per year shuttle launch rate. But such a rate would be unachievable given the existing orbiter flow times and the reduced number of orbiters available. The Shuttle-C (Cargo) would allow such a rate to be achieved. After Challenger, NASA studied development of a new unmanned Heavy Lift Launch Vehicle with the Air Force. In the discussions NASA insisted that any HLLV be a Shuttle Derived Vehicle. This led to the USAF pulling out of the shuttle program, and developing the Titan IV for the short term, and beginning a study of a new ALS Advanced Launch System for the long term. The USAF did not believe low-cost access to space was possible using man-rated systems. In the aftermath of the kerfuffle a Joint NASA-DoD-USAF steering group was set up to monitor development of the ALS and Shuttle-C. In August 1987 NASA Houston officially began Shuttle-C studies through assignment of a task team. In November 1987 nine-month study contracts were let to Martin-Marietta, United Space Boosters Inc, and Rockwell for definition of a Shuttle-Derived Vehicle. Phase I of the studies was to determine the optimum vehicle configuration, and Phase II was to completely define the selected vehicle. Concept studied included:
The Class I SDV was again found to be the best solution. It was estimated it could deliver payload to orbit at a cost of $4400/kg, as opposed to $1720 for the Delta II, $ 1800 for the Titan IV, or $ 3400 for the shuttle. As a result a Request for Proposal was issued for the Expendable Cargo Element - a payload fairing for the Shuttle-C to be mounted on the side of the external tank. This could accommodate 4.6 m x 22 m payloads weighing up to 47,000 kg and would be delivered into a 407 km / 28.5 deg orbit for docking with Space Station Freedom. The system could also deliver 52,000 kg to a 300 km / 28.5 deg orbit. The CE (Cargo Element) was equipped with 2 Space Shuttle Main Engines, and 2 Orbital Maneuvering System pods. The payload would either be released attached to the planned Orbital Maneuvering Vehicle transfer stage, or an OMV already in orbit would dock with the CE and take the payload away; or the OMS itself would be used to put the payload in its final orbit, release it, then retrofire to return the CE to earth.
In February 1988 the industrial team Rockwell - Martin Marietta - Boeing - Teledyne - Intermetrics - United Space Boosters was awarded follow-on18-month study contract NAS8-37144. During the course of the study NASA canceled the OMV, and the design had to be modified to handle in-orbit delivery and release of the payloads. The final report of the study envisioned two generations of Shuttle-C's. Generation 1 would be an expendable CE with a 4.6 m x 24.7 m cargo bay, using two SSME's, and capable of deliverying 45,000 kg to orbit. The CE would have an empty weight of 31,750 kg, using the shuttle thrust structure, and be fitted with shuttle engines and computers at the end of their useful lives. Three to four flights per year could be accomplished using the expendable approach, while NASA believed it had a requirement for 10 to 12 per year. Generation 2 would have a new-design recoverable CE, powered by 3 SSME's, and capable of delivering 77,000 kg in a 7.3 m x 29.3 m volume.
In early 1989 the study contract was extended by one year, including consideration of use of the Centaur G-Prime from the Titan IV as an upper stage. It was determined that the MPTA-098 structural article built in the 1970's for the SSME development program could be used as the Shuttle-C prototype. At the end of the study NASA decided that the development cost for Shuttle-C would be $ 1.8 billion. The Office for Technology Assessment estimated the cost as only $985 million, a rare case indeed where NASA made a high-ball estimate. Cost per launch would be $424 million for the Generation 1 design, or $9350 per kg. 14 Space Shuttles and 10 Shuttle-C's could be launched per year using existing Kennedy Space Center facilities. However such a rate would quickly exhaust the supply of surplus SSME engines. Therefore new-build engines would have to be purchased at a cost of $38 million each, or a total of $500 million per year. When this cost was taken into consideration, Shuttle-C was more expensive than the USAF Titan IV - therefore, NASA concluded, there was no reason to develop it. The decision was taken in 1990 to cancel Shuttle-C.
LEO Payload: 77,000 kg (169,000 lb) to a 400 km orbit at 28.00 degrees in 1985 dollars. Flyaway Unit Cost $: 84.970 million.
Stage Data - Shuttle C
Status: Study 1989.
Gross mass: 1,966,675 kg (4,335,776 lb).
Payload: 77,000 kg (169,000 lb).
Height: 56.00 m (183.00 ft).
Diameter: 8.70 m (28.50 ft).
Thrust: 20,299.20 kN (4,563,442 lbf).
Apogee: 400 km (240 mi).