RS-25
Country of origin | United States |
---|---|
First flight | April 12, 1981 43 years ago (STS-1) |
Manufacturer | Rocketdyne, Pratt & Whitney Rocketdyne, Aerojet Rocketdyne |
Associated LV | Space Shuttle Space Launch System |
Predecessor | HG-3 |
Status | Used on SLS after refurbishment |
Liquid-fuel engine | |
Propellant | Liquid oxygen / liquid hydrogen |
Mixture ratio | 6.03:1 |
Cycle | Fuel-rich dual-shaft staged combustion |
Configuration | |
Nozzle ratio | 78:1[1] |
Performance | |
Thrust, vacuum | 512,300 lbf (2.279 MN)[1] |
Thrust, sea-level | 418,000 lbf (1.86 MN)[1] |
Throttle range | 67–109% |
Thrust-to-weight ratio | 73.1[2] |
Chamber pressure | 2,994 psi (20.64 MPa)[1] |
Specific impulse, vacuum | 452.3 seconds (4.436 km/s)[1] |
Specific impulse, sea-level | 366 seconds (3.59 km/s)[1] |
Mass flow | 1,134.26 lb/s (514.49 kg/s) |
Dimensions | |
Length | 168 inches (4.3 m) |
Diameter | 96 inches (2.4 m) |
Dry weight | 7,004 pounds (3,177 kg)[2] |
References | |
References | [3][2] |
Notes | Data is for RS-25D at 109% of rated power level. |
The
Designed and manufactured in the United States by Rocketdyne (later Pratt & Whitney Rocketdyne and Aerojet Rocketdyne), the RS-25 burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing 1,859 kN (418,000 lbf) thrust at liftoff. Although RS-25 heritage traces back to the 1960s, its concerted development began in the 1970s with the first flight, STS-1, on April 12, 1981. The RS-25 has undergone upgrades over its operational history to improve the engine's reliability, safety, and maintenance load.
The engine produces a specific impulse (Isp) of 452 seconds (4.43 kN-sec/kg) in a vacuum, or 366 seconds (3.59 kN-sec/kg) at sea level, has a mass of approximately 3.5 tonnes (7,700 pounds), and is capable of throttling between 67% and 109% of its rated power level in one-percent increments. Components of the RS-25 operate at temperatures ranging from −253 to 3,300 °C (−400 to 6,000 °F).[1]
The Space Shuttle used a cluster of three RS-25 engines mounted at the stern of the
Four RS-25 engines are installed on each Space Launch System, housed in the engine section at the base of the core stage, and expended after use. The first four Space Launch System flights use modernized and refurbished engines built for the Space Shuttle program. Subsequent flights will make use of a simplified RS-25E engine called the Production Restart, which is under testing and development.
Components
The RS-25 engine consists of pumps, valves, and other components working in concert to produce
Once in the engine, the propellants flow through low-pressure fuel and oxidizer turbopumps (LPFTP and LPOTP), and from there into high-pressure turbopumps (HPFTP and HPOTP). From these HPTPs the propellants take different routes through the engine. The oxidizer is split into four separate paths: to the oxidizer heat exchanger, which then splits into the oxidizer tank pressurization and pogo suppression systems; to the low-pressure oxidizer turbopump (LPOTP); to the high-pressure oxidizer pre-burner, from which it is split into the HPFTP turbine and HPOTP before being reunited in the hot gas manifold and sent on to the main combustion chamber (MCC); or directly into the main combustion chamber (MCC) injectors.
Meanwhile, fuel flows through the main fuel valve into
Turbopumps
Oxidizer system
The low-pressure oxidizer turbopump (LPOTP) is an
Then, mounted before the HPOTP, is the pogo oscillation suppression system accumulator.[6] For use, it is pre-and post-charged with He and charged with gaseous O
2 from the heat exchanger, and, not having any membrane, it operates by continuously recirculating the charge gas. A number of baffles of various types are present inside the accumulator to control sloshing and turbulence, which is useful of itself and also to prevent the escape of gas into the low-pressure oxidizer duct to be ingested in the HPOTP.
The HPOTP consists of two single-stage
The HPOTP turbine and HPOTP pumps are mounted on a common shaft. Mixing of the fuel-rich hot gases in the turbine section and the liquid oxygen in the main pump can create a hazard and, to prevent this, the two sections are separated by a cavity that is continuously purged by the engine's helium supply during engine operation. Two seals minimize leakage into the cavity; one seal is located between the turbine section and the cavity, while the other is between the pump section and cavity. Loss of helium pressure in this cavity results in automatic engine shutdown.[4]
Fuel system
The low-pressure fuel turbopump (LPFTP) is an axial-flow pump driven by a two-stage turbine powered by gaseous hydrogen. It boosts the pressure of the liquid hydrogen from 30 to 276 psia (0.2 to 1.9 MPa) and supplies it to the high-pressure fuel turbopump (HPFTP). During engine operation, the pressure boost provided by the LPFTP permits the HPFTP to operate at high speeds without cavitating. The LPFTP operates at around 16,185 rpm, and is approximately 450 by 600 mm (18 by 24 in) in size. It is connected to the vehicle propellant ducting and is supported in a fixed position by being mounted to the launch vehicle's structure.[4]
The HPFTP is a three-stage centrifugal pump driven by a two-stage hot-gas turbine. It boosts the pressure of the liquid hydrogen from 1.9 to 45 MPa (276 to 6,515 psia), and operates at approximately 35,360 rpm with a power of 71,140 hp. The discharge flow from the turbopump is routed to, and through, the main valve and is then split into three flow paths. One path is through the jacket of the main combustion chamber, where the hydrogen is used to cool the chamber walls. It is then routed from the main combustion chamber to the LPFTP, where it is used to drive the LPFTP turbine. A small portion of the flow from the LPFTP is then directed to a common manifold from all three engines to form a single path to the liquid hydrogen tank to maintain pressurization. The remaining hydrogen passes between the inner and outer walls of the hot-gas manifold to cool it and is then discharged into the main combustion chamber. A second hydrogen flow path from the main fuel valve is through the engine nozzle (to cool the nozzle). It then joins the third flow path from the chamber coolant valve. This combined flow is then directed to the fuel and oxidizer pre-burners. The HPFTP is approximately 550 by 1,100 mm (22 by 43 in) in size and is attached to the hot-gas manifold by flanges.[4]
Powerhead
Preburners
The oxidizer and fuel pre-burners are
The speed of the HPOTP and HPFTP turbines depends on the position of the corresponding oxidizer and fuel pre-burner oxidizer valves. These valves are positioned by the engine controller, which uses them to throttle the flow of liquid oxygen to the pre-burners and, thus, control engine thrust. The oxidizer and fuel pre-burner oxidizer valves increase or decrease the liquid oxygen flow, thus increasing or decreasing pre-burner chamber pressure, HPOTP and HPFTP turbine speed, and liquid oxygen and gaseous hydrogen flow into the main combustion chamber, which increases or decreases engine thrust. The oxidizer and fuel pre-burner valves operate together to throttle the engine and maintain a constant 6.03:1 propellant mixture ratio.[3]
The main oxidizer and main fuel valves control the flow of liquid oxygen and liquid hydrogen into the engine and are controlled by each engine controller. When an engine is operating, the main valves are fully open.[4]
Main combustion chamber
The engine's main combustion chamber (MCC) receives fuel-rich hot gas from a hot-gas manifold cooling circuit. The gaseous hydrogen and liquid oxygen enter the chamber at the injector, which mixes the propellants. The mixture is ignited by the "Augmented Spark Igniter", an H2/O2 flame at the center of the injector head.[7] The main injector and dome assembly are welded to the hot-gas manifold, and the MCC is also bolted to the hot-gas manifold.[4] The MCC comprises a structural shell made of Inconel 718 which is lined with a copper-silver-zirconium alloy called NARloy-Z, developed specifically for the RS-25 in the 1970s. Around 390 channels are machined into the liner wall to carry liquid hydrogen through the liner to provide MCC cooling, as the temperature in the combustion chamber reaches 3300 °C (6000 °F) during flight – higher than the boiling point of iron.[8][9]
An alternative for the construction of RS-25 engines to be used in SLS missions is the use of advanced structural ceramics, such as
Nozzle
The engine's
Controller
Each engine is equipped with a main engine controller (MEC), an integrated computer which controls all of the engine's functions (through the use of valves) and monitors its performance. Built by
Two independent dual-CPU computers, A and B, form the controller; giving redundancy to the system. The failure of controller system A automatically leads to a switch-over to controller system B without impeding operational capabilities; the subsequent failure of controller system B would provide a graceful shutdown of the engine. Within each system (A and B), the two M68000s operate in
The controllers were designed to be tough enough to survive the forces of launch and proved to be extremely resilient to damage. During the investigation of the Challenger accident the two MECs (from engines 2020 and 2021), recovered from the seafloor, were delivered to Honeywell Aerospace for examination and analysis. One controller was broken open on one side, and both were severely corroded and damaged by marine life. Both units were disassembled and the memory units flushed with deionized water. After they were dried and vacuum baked, data from these units was retrieved for forensic examination.[18]
Main valves
To control the engine's output, the MEC operates five hydraulically actuated propellant valves on each engine; the oxidizer pre-burner oxidizer, fuel pre-burner oxidizer, main oxidizer, main fuel, and chamber coolant valves. In an emergency, the valves can be fully closed by using the engine's helium supply system as a backup actuation system.[4]
In the Space Shuttle, the main oxidizer and fuel bleed valves were used after shutdown to dump any residual propellant, with residual liquid oxygen venting through the engine and residual liquid hydrogen venting through the liquid hydrogen fill and drain valves. After the dump was completed, the valves closed and remained closed for the remainder of the mission.[4]
A coolant control valve is mounted on the combustion chamber coolant bypass duct of each engine. The engine controller regulates the amount of gaseous hydrogen allowed to bypass the nozzle coolant loop, thus controlling its temperature. The chamber coolant valve is 100% open before the engine start. During engine operation, it is 100% open for throttle settings of 100 to 109%. For throttle settings between 65 and 100%, its position ranged from 66.4 to 100%.[4]
Gimbal
External videos | |
---|---|
RS-25 gimbal test |
Each engine is installed with a
The low-pressure oxygen and low-pressure fuel turbopumps were mounted 180° apart on the orbiter's aft fuselage thrust structure. The lines from the low-pressure turbopumps to the high-pressure turbopumps contain flexible bellows that enable the low-pressure turbopumps to remain stationary while the rest of the engine is gimbaled for thrust vector control, and also to prevent damage to the pumps when loads were applied to them. The liquid-hydrogen line from the LPFTP to the HPFTP is insulated to prevent the formation of liquid air.[4]
Helium system
In addition to fuel and oxidizer systems, the launch vehicle's main propulsion system is also equipped with a helium system consisting of ten storage tanks in addition to various regulators, check valves, distribution lines, and control valves. The system is used in-flight to purge the engine and provides pressure for actuating engine valves within the propellant management system and during emergency shutdowns. During entry, on the Space Shuttle, any remaining helium was used to purge the engines during reentry and for repressurization.[4]
History
Development
The history of the RS-25 traces back to the 1960s when
Meanwhile, in 1967, the
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.[25] 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.[23] 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".[12][23] 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
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.[12] 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.[12][23]
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. 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
Space Shuttle program
Each Space Shuttle had three RS-25 engines, installed in the aft structure of the Space Shuttle orbiter in the Orbiter Processing Facility prior to the orbiter being transferred to the Vehicle Assembly Building. If necessary the engines could be changed on the pad. The engines, drawing propellant from the Space Shuttle external tank (ET) via the orbiter's main propulsion system (MPS), were ignited at T−6.6 seconds prior to liftoff (with each ignition staggered by 120 ms[26]), which allowed their performance to be checked prior to ignition of the Space Shuttle Solid Rocket Boosters (SRBs), which committed the shuttle to the launch.[27] At launch, the engines would be operating at 100% RPL, throttling up to 104.5% immediately following liftoff. The engines would maintain this power level until around T+40 seconds, where they would be throttled back to around 70% to reduce aerodynamic loads on the shuttle stack as it passed through the region of maximum dynamic pressure, or max. q.[note 1][23][26] The engines would then be throttled back up until around T+8 minutes, at which point they would be gradually throttled back down to 67% to prevent the stack exceeding 3 g of acceleration as it became progressively lighter due to propellant consumption. The engines were then shut down, a procedure known as main engine cutoff (MECO), at around T+8.5 minutes.[23]
After each flight the engines would be removed from the orbiter and transferred to the Space Shuttle Main Engine Processing Facility (SSMEPF), where they would be inspected and refurbished in preparation for reuse on a subsequent flight.
Upgrades
Over the course of the Space Shuttle program, the RS-25 went through a series of upgrades, including combustion chamber changes, improved welds and turbopump changes in an effort to improve the engine's performance and reliability and so reduce the amount of maintenance required after use. As a result, several versions of the RS-25 were used during the program:[9][23][25][26][31][32][33][34][35]
- FMOF (first manned orbital flight): Certified for 100% rated power level (RPL). Used for the orbital flight test missions STS-1 – STS-5 (engines 2005, 2006 and 2007).
- Phase I: Used for missions Challenger Disaster.
- Phase II (RS-25A): First flown on STS-26, the Phase II engine offered a number of safety upgrades and was certified for 104% RPL & 109% full power level (FPL) in the event of a contingency.
- Block I (RS-25B): First flown on STS-70, the Block I engines offered improved turbopumps featuring ceramic bearings, half as many rotating parts, and a new casting process reducing the number of welds. Block I improvements also included a new, two-duct powerhead (rather than the original design, which featured three ducts connected to the HPFTP and two to the HPOTP), which helped improve hot gas flow, and an improved engine heat exchanger.
- Block IA (RS-25B): First flown on STS-73, the Block IA engine offered main injector improvements.
- Block IIA (RS-25C): First flown on STS-89, the Block IIA engine was an interim model used whilst certain components of the Block II engine completed development. Changes included a new large throat main combustion chamber (which had originally been recommended by Rocketdyne in 1980), improved low-pressure turbopumps, and certification for 104.5% RPL to compensate for a 2 seconds (0.020 km/s) reduction in specific impulse (original plans called for the engine to be certified to 106% for heavy International Space Station payloads, but this was not required and would have reduced engine service life). A slightly modified version first flew on STS-96.
- Block II (RS-25D): First flown on STS-104, the Block II upgrade included all of the Block IIA improvements plus a new high-pressure fuel turbopump. This model was ground-tested to 111% FPL in the event of a contingency abort, and certified for 109% FPL for use during an intact abort.
- RS-25E: It will be used on the Space Launch System for future Artemis program missions beginning with Artemis 5, as the RS-25D stock is intentionally being used up. Unlike previous versions, this engine is designed to be expendable.[5] The powerhead is almost completely redesigned (as of September 2023[update] the specific design changes from the -25D have not been announced), and intended to incorporate various cost-saving measures and innovations in manufacturing. The first testing engine, E10001, passed all its qualifications and tests at NASA's Stennis Space Center, and demonstrated both a 113% FPL and a 30% increase in thrust.[36]
Engine throttle/output
The most obvious effects of the upgrades the RS-25 received through the Space Shuttle program were the improvements in engine throttle. Whilst the FMOF engine had a maximum output of 100% RPL, Block II engines could throttle as high as 109% or 111% in an emergency, with usual flight performance being 104.5%. Existing engines used on the Space Launch System are throttled to 109% power during normal flight, while new RS-25 engines produced for the Space Launch System are to be run at 111% throttle,[37] with 113% power being tested.[38][39] These increases in throttle level made a significant difference to the thrust produced by the engine:[6][26]
Of RPL (%) |
Thrust | ||
---|---|---|---|
Sea level | Vacuum | ||
Minimum power level (MPL) | 67 | 1,406 kN (316,100 lbf) | |
Rated power level (RPL) | 100 | 1,670 kN (380,000 lbf) | 2,090 kN (470,000 lbf) |
Nominal power level (NPL) | 104.5 | 1,750 kN (390,000 lbf) | 2,170 kN (490,000 lbf) |
Full power level (FPL) | 109 | 1,860 kN (420,000 lbf) | 2,280 kN (510,000 lbf) |
SLS Production Restart | 111 | 2,320 kN (521,000 lbf) | |
Production Restart Abort | 113 | 1,887 kN (424,000 lbf) | 2,362 kN (531,000 lbf) |
Specifying power levels over 100% may seem nonsensical, but there was a logic behind it. The 100% level does not mean the maximum physical power level attainable, rather it was a specification decided on during engine development—the expected rated power level. When later studies indicated the engine could operate safely at levels above 100%, these higher levels became standard. Maintaining the original relationship of power level to physical thrust helped reduce confusion, as it created an unvarying fixed relationship so that test data (or operational data from past or future missions) can be easily compared. If the power level was increased, and that new value was said to be 100%, then all previous data and documentation would either require changing or cross-checking against what physical thrust corresponded to 100% power level on that date.[12] Engine power level affects engine reliability, with studies indicating the probability of an engine failure increasing rapidly with power levels over 104.5%, which was why power levels above 104.5% were retained for contingency use only.[31]
Incidents
During the course of the Space Shuttle program, a total of 46 RS-25 engines were used (with one extra RS-25D being built but never used). During the 135 missions, for a total of 405 individual engine-missions,[29] Pratt & Whitney Rocketdyne reports a 99.95% reliability rate, with the only in-flight SSME failure occurring during Space Shuttle Challenger's STS-51-F mission.[3] The engines, however, did suffer from a number of pad failures (redundant set launch sequencer aborts, or RSLSs) and other issues during the course of the program:
- STS-41-D Discovery – No. 3 engine caused an RSLS shutdown at T−4 seconds due to loss of redundant control on main engine valve, stack rolled back and engine replaced.[40]
- STS-51-F Challenger – No. 2 engine caused an RSLS shutdown at T−3 seconds due to a coolant valve malfunction.[41][42]
- STS-55 Columbia – No. 3 engine caused an RSLS shutdown at T−3 seconds due to a leak in its liquid-oxygen preburner check valve.[43]
- STS-51 Discovery – No. 2 engine caused an RSLS shut down at T−3 seconds due to a faulty hydrogen fuel sensor.[44]
- STS-68 Endeavour – No. 3 engine (2032) caused an RSLS shutdown at T−1.9 seconds when a temperature sensor in its HPOTP exceeded its redline.[45]
- STS-93 Columbia – An Orbiter Project AC1 Phase A electrical wiring short occurred at T+5 seconds causing an under voltage which disqualified SSME 1A and SSME 3B controllers but required no engine shut down. In addition, a 0.1-inch diameter, 1-inch long gold-plated pin, used to plug an oxidizer post orifice (an inappropriate SSME corrective action eliminated from the fleet by redesign) came loose inside an engine's main injector and impacted the engine nozzle inner surface, rupturing three hydrogen cooling lines. The resulting three breaches caused a leak resulting in a premature engine shutdown, when four external tank LO2 sensors flashed dry resulting in low-level cutoff of the main engines and a slightly early main engine cut-off with a 16 ft/s (4.9 m/s) underspeed, and an 8 nautical mile lower altitude.[46]
Constellation
During the period preceding final Space Shuttle retirement, various plans for the remaining engines were proposed, ranging from them all being kept by NASA, to them all being given away (or sold for US$400,000–800,000 each) to various institutions such as museums and universities.[47] This policy followed changes to the planned configurations of the Constellation program's Ares V cargo-launch vehicle and Ares I crew-launch vehicle rockets, which had been planned to use the RS-25 in their first and second stages respectively.[48] While these configurations had initially seemed worthwhile, as they would use then-current technology following the shuttle's retirement in 2010, the plan had several drawbacks:[48]
- The engines would not be reusable, as they would be permanently attached to the discarded stages.
- Each engine would have to undergo a test firing prior to installation and launch, with refurbishment required following the test.
- It would be expensive, time-consuming, and weight-intensive to convert the ground-started RS-25D to an air-started version for the Ares I second stage.
Following several design changes to the Ares I and Ares V rockets, the RS-25 was to be replaced with a single
Space Launch System
On 14 September 2011, following the retirement of the Space Shuttle, NASA announced that it would be developing a new launch vehicle, known as the Space Launch System (SLS), to replace the shuttle fleet.[50] The design for the SLS features the RS-25 as part of its core stage, with different versions of the rocket being equipped with between three and five engines.[51][52] The initial flights of the new launch vehicle are making use of previously flown Block II RS-25D engines, with NASA keeping such engines in a "purged safe" environment at Stennis Space Center, "along with all of the ground systems required to maintain them."[53][54] For Artemis 1, the RS-25D units with serial numbers E2045, E2056, E2058, and E2060 from all three orbiters were used.[55] They were installed on the core stage by November 6, 2019.[56] For Artemis 2, the units with serial numbers E2047, E2059, E2062, and E2063 will be used.[57] They were installed on the core stage by September 25, 2023.[58]
In addition to the RS-25Ds, the SLS program makes use of the Main Propulsion Systems (MPS, the "plumbing" feeding the engines) from the three remaining shuttle orbiters for testing purposes (having been removed as part of the orbiters' decommissioning), with the first two launches (Artemis 1 and Artemis 2) originally predicted to make use of the MPS hardware from Space Shuttles Atlantis and Endeavour in their core stages.[52][54][59] The SLS's propellants are supplied to the engines from the rocket's core stage, which consists of a modified Space Shuttle external tank with the MPS plumbing and engines at its aft, and an interstage structure at the top.[5]
For the first two Artemis missions, the engines are installed on the SLS core stage in Building 103 of the Michoud Assembly Facility;[60] they will be installed in the Space Station Processing Facility at Kennedy beginning with Artemis 3.[61][62]
Once the remaining RS-25Ds are exhausted, they are to be replaced with a cheaper, expendable version designated the RS-25E.[5] In 2023, Aerojet Rocketdyne reported reductions in manufacturing time and labour requirements during manufacturing of new-production RS-25 engines, such as a 15% reduction in fabrication time for the powerhead and a 22-month reduction in the time needed to produce a main combustion chamber.[63]
On 1 May 2020, NASA awarded a contract extension to manufacture 18 additional RS-25 engines, with associated services, for $1.79 billion, bringing the total SLS contract value to almost $3.5 billion.[64]
On 29 August 2022, Artemis 1 was delayed by a problem with engineering sensors on RS-25D #3 (serial number E2058) erroneously reporting that it hadn't chilled down to its ideal operating temperature.[65]
On 16 November 2022, Artemis 1 launched from Kennedy Space Center Launch Complex 39B, the first time the RS-25 engine had flown since the Space Shuttle's final flight, STS-135, on 21 July 2011.[66]
Engine tests
In 2015, a test campaign was conducted to determine RS-25 engine performance with a new engine controller unit, under lower liquid-oxygen temperatures, with greater inlet pressure due to the taller SLS core-stage liquid-oxygen tank and higher vehicle acceleration; and with more nozzle heating due to the four-engine configuration and its position in-plane with the SLS booster exhaust nozzles. New ablative heat-shield insulation was to be tested as well.
Following these tests, four more engines were scheduled to enter a new test cycle.
On February 28, 2019, NASA conducted a 510-second test burn of a developmental RS-25 at 113 percent of its originally designed thrust for more than 430 seconds, about four times longer than any prior test at this thrust level.[75]
On January 16, 2021, the RS-25 engines were fired again, during a hot-fire test as part of the Artemis program. The test was originally scheduled as an 8-minute test but was terminated at the 67th second due to intentionally conservative test parameters being breached in the hydraulic system of Engine 2's (serial number E2056) Core Stage Auxiliary Power Unit (CAPU) during the thrust vector control (TVC) system test. Engine 2's CAPU was shut down automatically, although if this issue had occurred during flight, it would not have caused an abort, as the remaining CAPUs are capable of powering the TVC systems of all four engines.[76] The engine also suffered a different "Major Component Failure", in the engine control system, that was caused by instrumentation failure. This would have triggered an abort of the launch countdown during an actual launch attempt.[77]
On March 18, 2021, the four RS-25 core-stage engines were once again fired as part of the second SLS core stage hot-fire test, which lasted the full duration of 500 seconds,[78] successfully certifying the Artemis 1 core stage for flight.
On December 14, 2022, a single development RS-25E, serial number E10001, attempted a 500-second hot-fire test. The test aborted at T+209.5 due to test systems subsequently interpreting signals from a group of improperly configured accelerometers during the hot fire as exceeding acceptable vibration limits.[79] Tests of the engine continued in 2023; on February 8, 2023, it was fired for 500 seconds at 111% power, fitted with a new-production nozzle.[80] Subsequent tests included a 600-second test at 111% power on February 22,[81] a 520-second test at 113% power on March 8,[82] a 600-second test at 113% power on March 21,[83] a 500-second, 113% power level test on April 5,[84] a 720-second fire that tested the engine's thrust vectoring gimbal system on April 26,[85] a 630-second test on May 10,[86] and five more 500-second, 113% power level tests without gimbaling on May 23,[39] June 1,[87] June 8,[88] June 15,[89] and June 22.[90][36]
The RS-25E developmental unit E0525, with significant inclusion of new components including a redesigned nozzle, hydraulic actuators, flex ducts and turbopumps, was hot fire tested to 111% power levels for 550 seconds in the first in a series of certification tests beginning October 17, 2023.[91][92][93] It was tested to 113% power levels for 500 seconds on November 15,[94][95] and to 113% for 650 seconds with gimbaling on November 29, 2023,[96] to 113% for 500 seconds on January 17, 2024,[97][98][99] January 23,[100][101] and January 29,[102][103] to 113% for 550 seconds on February 23,[104][105] to 111% for 615 seconds on February 29,[106] and to 113% for 600 seconds on March 6[107][108][109] and 500 seconds on March 22[110] and 27,[111] and April 3.[112]
XS-1
On May 24, 2017,
On January 22, 2020, Boeing announced its departure from the XS-1 program, leaving no role for the AR-22.[116]
See also
Notes
- ^ The level of throttle was initially set to 65%, but, following review of early flight performance, this was increased to a minimum of 67% to reduce fatigue on the MPS. The throttle lever was dynamically calculated based on initial launch performance, generally being reduced to a level around 70%.
References
This article incorporates public domain material from websites or documents of the
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- ^ a b c Wade, Mark. "SSME". Encyclopedia Astronautica. Archived from the original on December 28, 2016. Retrieved December 28, 2017.
- ^ a b c "Space Shuttle Main Engine" (PDF). Pratt & Whitney Rocketdyne. 2005. Archived from the original (PDF) on February 8, 2012. Retrieved November 23, 2011.
- ^ a b c d e f g h i j k l m n o p United Space Alliance (December 15, 2008). "2.16 Main Propulsion System (MPS)". Shuttle Crew Operations Manual (PDF) (Technical report). NASA. pp. 577–618. USA007587. Archived (PDF) from the original on April 11, 2023. Retrieved May 23, 2023.
- ^ a b c d Bergin, Chris (September 14, 2011). "SLS finally announced by NASA – Forward path taking shape". NASASpaceflight.com. Archived from the original on March 22, 2023. Retrieved December 14, 2011.
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External links
- Spherical panoramas of RS-25D in SSME Processing Facility prior to shipping to Stennis Space Center
- Lawrence J. Thomson Collection, The University of Alabama in Huntsville Archives and Special Collections Files of Lawrence J. Thomson, chief engineer for the SSME from 1971 to 1986
- Historic American Engineering Record (HAER) No. TX-116-I, "Space Transportation System, Space Shuttle Main Engine, Lyndon B. Johnson Space Center, 2101 NASA Parkway, Houston, Harris County, TX", 20 photos, 2 measured drawings, 8 photo caption pages