5.6 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| RS-25 | 5/9 | https://en.wikipedia.org/wiki/RS-25 | reference | science, encyclopedia | 2026-05-05T13:21:33.138292+00:00 | kb-cron |
The history of the RS-25 traces back to the 1960s when NASA's Marshall Space Flight Center and Rocketdyne were conducting a series of studies on high-pressure engines, developed from the successful J-2 engine used on the S-II and S-IVB upper stages of the Saturn V rocket during the Apollo program. The studies were conducted under a program to upgrade the Saturn V engines, which produced a design for a 350,000 lbf (1,600 kN) upper-stage engine known as the HG-3. As funding levels for Apollo wound down the HG-3 was cancelled as well as the upgraded F-1 engines already being tested. It was the design for the HG-3 that would form the basis for the RS-25. Meanwhile, in 1967, the US Air Force funded a study into advanced rocket propulsion systems for use during Project Isinglass, with Rocketdyne asked to investigate aerospike engines and Pratt & Whitney (P&W) to research more efficient conventional de Laval nozzle-type engines. At the conclusion of the study, P&W put forward a proposal for a 250,000 lbf engine called the XLR-129, which used a two-position expanding nozzle to provide increased efficiency over a wide range of altitudes. In January 1969 NASA awarded contracts to General Dynamics, Lockheed, McDonnell Douglas, and North American Rockwell to initiate the early development of the Space Shuttle. As part of these 'Phase A' studies, the involved companies selected an upgraded version of the XLR-129, developing 415,000 lbf (1,850 kN), as the baseline engine for their designs. This design can be found on many of the planned Shuttle versions right up to the final decision. However, since NASA was interested in pushing the state of the art in every way they decided to select a much more advanced design in order to "force an advancement of rocket engine technology". They called for a new design based on a high-pressure combustion chamber running around 3,000 psi (21,000 kPa), which increases the performance of the engine. Development began in 1970, when NASA released a request for proposal for 'Phase B' main engine concept studies, requiring development of a throttleable, staged combustion, de Laval-type engine. The request was based on the then-current design of the Space Shuttle which featured two reusable stages, the orbiter and a crewed fly-back booster, and required one engine which would be able to power both vehicles via two different nozzles (12 booster engines with 550,000 lbf (2,400 kN) sea level thrust each and 3 orbiter engines with 632,000 lbf (2,810 kN) vacuum thrust each). Rocketdyne, P&W and Aerojet General were selected to receive funding although, given P&W's already-advanced development (demonstrating a working 350,000 lbf (1,600 kN) concept engine during the year) and Aerojet General's prior experience in developing the 1,500,000 lbf (6,700 kN) M-1 engine, Rocketdyne was forced to put a large amount of private money into the design process to allow the company to catch up to its competitors. By the time the contract was awarded, budgetary pressures meant that the shuttle's design had changed to its final orbiter, external tank, and two boosters configuration, and so the engine was only required to power the orbiter during ascent. During the year-long 'Phase B' study period, Rocketdyne was able to make use of their experience developing the HG-3 engine to design their SSME proposal, producing a prototype by January 1971. The engine made use of a new Rocketdyne-developed copper-zirconium alloy (called NARloy-Z) and was tested on February 12, 1971, producing a chamber pressure of 3,172 psi (21,870 kPa). The three participating companies submitted their engine development bids in April 1971, with Rocketdyne being awarded the contract on July 13, 1971—although work did not begin on engine development until March 31, 1972, due to a legal challenge from P&W. Following the awarding of the contract, a preliminary design review was carried out in September 1972, followed by a critical design review in September 1976 after which the engine's design was set and construction of the first set of flight-capable engines began. A final review of all the Space Shuttle's components, including the engines, was conducted in 1979. The design reviews operated in parallel with several test milestones, initial tests consisting of individual engine components which identified shortcomings with various areas of the design, including the HPFTP, HPOTP, valves, nozzle, and fuel pre-burners. The individual engine component tests were followed by the first test of a complete engine (0002) on March 16, 1977, after its final assembly line was established in the main Rocketdyne factory in Canoga Park, Los Angeles. NASA specified that, prior to the Shuttle's first flight, the engines must have undergone at least 65,000 seconds of testing, a milestone that was reached on March 23, 1980, with the engine having undergone 110,253 seconds of testing by the time of STS-1 both on test stands at Stennis Space Center and installed on the Main Propulsion Test Article (MPTA). The first set of engines (2005, 2006 and 2007) was delivered to Kennedy Space Center in 1979 and installed on Columbia, before being removed in 1980 for further testing and reinstalled on the orbiter. The engines, which were of the first manned orbital flight (FMOF) configuration and certified for operation at 100% rated power level (RPL), were operated in a twenty-second flight readiness firing on February 20, 1981, and, after inspection, declared ready for flight.
=== Space Shuttle program ===