History of the Space Shuttle Main Engine (SSME) - Rocketdyne RS-25

  Overview

           



SSME powerhead component arrangement



Combustor and nozzle




Design Evolution
The Space Shuttle Main Engine (SSME) was designed and developed by Pratt & Whitney Rocketdyne under contract to the NASA Marshall Space Flight Center. The work on the engine began in 1972. In the six years of development between the start of testing and the first flight, numerous SSME hardware redesigns took place. Also in following long SSME history, all of the major components were continued modified and improved.

Baseline SSME

The first configuration was the baseline SSME design for the first five flights of the Space Shuttle. These first Shuttle flights were intended to be the checkout phase of Space Shuttle operations.
The engine power level was limited to 100%, or about 470,000 pounds vacuum thrust.

Full Power Level or Phase-I SSME
A Full Power Level or Phase-I configuration was introduced into the flight program. This configuration flew from STS-6 (1983) until STS-33 (1986). One hundred forty-seven design changes were made including changes to the powerhead and, perhaps most significantly, to the four turbopumps.The program restricted engine operation in flight to 104% thrust or less and put a long term plan in place to achieve the higher operating power levels.

Phase-II SSME
Following the 1986 Challenger disaster, the entire Space Shuttle Program was re-assessed. The Phase-II configuration was first flown on the flight mission STS-26R (1988). The new configuration included powerhead and duct changes. Significant durability improvements to high pressure turbopump blades and bearings were part of the redesign.

Block-I/IA SSME

The Block-I SSME introduced several upgrades to the engine, improving reliability and safety. The Phase-I+ powerhead was included in the Block- and -IA SSME configurations and implemented a two-duct fuel-side hot-gas manifold which improved the high pressure fuel turbine discharge pressure distribution resulting in more uniform introduction of hot-gas products to the main injector, thus improving performance. The redesigned powerhead had 52 fewer piece-parts and 74 fewer welds. A new single-tube heat exchanger (HEX) replaced the bifurcated configuration. Baffles in the main injector were removed, which resulted in an efficiency gain in the engine as well as a producibility gain in the main injector. The baffles had been in place to damp out potential combustion instabilities,
The Block-I SSME incorporated a completely new HPOTP. A heavier allowable weight permitted a much stronger, stiffer rotor system, as well as more robust pump and turbine housings. Advances in casting technologies permitted the incorporation of finegrained castings in the Block-I HPOTP, which allowed the elimination of 293 welds within the turbopump.
Block-IA incorporated all of the Block-I features plus modifications to faceplate coolant holes in the main injector for increased performance. Block-IA flew for the first time on STS-73 (1995).

Block-IA SSME

The Block-IIA SSME implemented the Large Throat Main Combustion Chamber (LTMCC) which had been touted as the single most important SSME reliability improvement. The LTMCC increased the main chamber throat area by approximately 12% allowing the engine to operate at the same thrust level but at greatly reduced system pressures and temperatures. The new LTMCC had new features in addition to a larger throat size. Inlet and outlet manifolds were changed from welded forgings to integral castings. The cast manifolds eliminated 46 welds, including 28 criticality welds. For most engine components, operation at 109% thrust with a LTMCC is enveloped by operation at 104% thrust with a standard throat MCC. Block-IIA engines were introduced on STS-89 (1998) and flew until full implementation of the Block-II engines.

Block-II SSME
The Block-II SSME added to the Block-IIA design an advanced High Pressure Fuel Turbopump along with miscellaneous minor changes in order to incorporate the new turbopump into the engine. The redesigned HPFTP incorporated improvements similar to those on the Block-I HPOTP. The new HPFTP had no welds and utilized silicon nitride rolling elements in both of its bearings. It also incorporated robust, thick-walled turbine and pump housings.
 
  Baseline Phase-1 Phase-II Block-I Block-IA Block-IIA Block-II

 

  Main improvements  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------->

 

  • Powerhead
  • HPFTP
  • HPOTP
  • LPFTP
  • LPOTP
  • Nozzle
  • Avionics
  • MCC
  • HPFTP
  • HPOTP
  • Avionics
  • Powerhead
    (two ducts)
  • HPOTP-AT
  • Main Injector
  • LTMCC
  • LPFTP
  • LPOTP
  • Avionics
  • Spark Igniter
  • HPFTP-AT
  • Health
     Management
    System

 

SSME Characteristics*

 

  RS-24 ? RS-25 RS-25A RS-25B RS-25B RS-25C RS-25D RS-25E

Baseline

Phase-I

Phase-II

Block-I

Block-IA

Block-IIA

Block-II

Block-III (?)

Engine type used

15

60

171

10

17

49

83

 0

First Flight

STS-1

STS-6

STS-26R

STS-70

STS-73

STS-89

STS-110

SLS

Fuel Main Turbopump

HPFTP

HPFTP

HPFTP

HPFTP

HPFTP

HPFTP

HPFTP-AT

HPFTP-AT

Oxidizer Main Turbopump

HPOTP

HPOTP

HPOTP

HPOTP-AT

HPOTP-AT

HPOTP-AT

HPOTP-AT

HPOTP-AT

Combustor

MCC

MCC

MCC

MCC

MCC

LTMCC

LTMCC

LTMCC

Nozzle Exp. Ratio

77.5

77.5

77.5

77.5

77.5

69.0

69.0

69.0

Spezific Impulse (s) s.l./vac

362.4

454.4

363.2

455.2

361.5

453.5

364.8

452.9

 364.8

452.9

366.3

452.3

366

452

 

 

Chamber
Pressure (psia)

65%

1945

?

?

1857

1857

 -

 -

 -

67%

-

-

-

-

-

 ?

?

 

100%

2995

?

3006

?

?

?

?

 

104%

-

3140

3126

2971

2971

-

-

-

104.5%

-

 -

-

 -

 -

2885

2871

 

109%

(3258)

(3291)

(3276)

(3114)

(3114)

3008

2994

 

Flow Rate (lb/s)

65%

695

670

672

673

673

-

-

-

67%

-

-

-

-

-

699

698

 

100%

1060

1032

1031

1038

1038

1041

1039

 

104%

-

1075

1080

1079

1079

-

-

-

104.5

-

-

-

-

-

1088

1086

 

109%

(1152)

(1125)

(1129)

(1130)

(1130)

 1134

1133

 

Thrust (klb) s.l/vac

65%

251.9

315.8

243.4

305.0

242.9

304.8

245.5

304.8

244.6

305.0

-

-

-

-

-

-

67%

-

-

-

-

-

-

-

-

-

-

256.0

316.1

255.5

315.5

 

 

100%

384.2

481.5

375.0

470.0

372.7

467.6

378.6

470.0

376.9

470.0

381.3

470.8

380.1

469.448

 

 

104%

-

-

390.4

489.3

390.4

489.8

393.7

488.8

392.0

488.8

-

-

-

-

-

-

104.5%

-

-

-

-

-

-

-

-

-

-

398.4

491.9

397.4

490.847

 

 

109%

(417.5)

(523.5)

(408.6)

(512.1)

(408.1)

(512.0)

(412.2)

(511.8)

 (412.5)

(514.0 )

415.4

512.9

414.8

 512.271

 

 

 

* A difficult task to find the right data; therefore partly calculated

 

SSME MPTA
(with nozzle exp. ratio 35.0)

 SSME Baseline

 SSME Phase-I

 SSME Phase-II

SSME Block-I SSME Block-IA

 SSME Block-IIA
(
coolant pipes with red cover)

SSME Block-II
(
coolant pipes with red cover)

ME SLS


 


 


 


 


 


 

 
 


 


 

   
HPFTP HPFTP HPFTP HPFTP HPFTP HPFTP

HPFTP-AT

HPFTP-AT

HPOTP HPOTP HPOTP HPOTP-AT HPOTP-AT HPOTP-AT HPOTP-AT

HPOTP-AT

MCC

MCC

MCC

MCC

MCC

LTMCCC

LTMC

LTMCC