Pratt & Whitney Rocketdyne J-2X
J-2X is a distinct LOX/LH2 gas-generator upper-stage engine developed by NASA and Pratt & Whitney Rocketdyne for the Ares I/Ares V and later SLS exploration architecture. NASA documents a primary-mode vacuum thrust of about 294,000 lbf (1,308 kN), 448 s vacuum specific impulse, approximately 4.7 m length, 3.0 m diameter, and roughly 2.5 t dry mass; these are development requirements and test-article specifications, not a claim of operational flight status.
Identity
- Aliases
- J-2XJ2XPratt & Whitney Rocketdyne J-2X
- Domains
- spaceflight
- Identity Level
- variant
- Kind
- liquid-rocket-engine
- Name
- Pratt & Whitney Rocketdyne J-2X
- Status
- historical
Details
- Description
- J-2X is a distinct LOX/LH2 gas-generator upper-stage engine developed by NASA and Pratt & Whitney Rocketdyne for the Ares I/Ares V and later SLS exploration architecture. NASA documents a primary-mode vacuum thrust of about 294,000 lbf (1,308 kN), 448 s vacuum specific impulse, approximately 4.7 m length, 3.0 m diameter, and roughly 2.5 t dry mass; these are development requirements and test-article specifications, not a claim of operational flight status.
- Developers
- Dry Mass Kg
- 2,516
- Length M
- 4.699
- Lineage
- Note
- J-2X incorporated J-2S tap-off-cycle heritage and lessons while remaining a separate development engine.
- Related Propulsion System
- Relationship
- technology-derived-from
- Sources
- Note
- NASA identifies the heritage J-2S tap-off-cycle engine as a technical basis for the later J-2X engine.
- Publisher
- NASA Technical Reports Server
- Title
- The J-2X fuel turbopump: Design, development, and test
- Note
- NASA documents J-2X heritage and its separate upper-stage development program.
- Publisher
- NASA Technical Reports Server
- Title
- The J-2X Upper Stage Engine: From Heritage to Hardware
- Propellants
- liquid oxygenliquid hydrogen
- Rocket Specs
- Cycle
- gas generator
- Vacuum Specific Impulse S
- 448
- Vacuum Thrust Kn
- 1,308
Links
Assets & Meta
- Creation Time
- August 6, 2026 at 18:32:33 UTC
- Updated Time
- August 21, 2026 at 11:22:53 UTC
- Image
- Download
Other
- Diameter M
- 3.048
- Sources
- Note
- NASA identifies J-2X as a distinct next-generation upper-stage engine, describes its SLS role and testing, and distinguishes it as a redesign of the heritage J-2.
- Publisher
- NASA
- Title
- J-2X Engine Ready for Higher Level of Tests
- Note
- NASA technical history documents J-2X as an evolved J-2 variant selected for Ares upper stages, with distinct performance and development requirements.
- Publisher
- NASA Technical Reports Server
- Title
- The J-2X Upper Stage Engine: From Heritage to Hardware
- Note
- NASA records J-2X development by Pratt & Whitney Rocketdyne for the SLS upper stage; current lifecycle is left unknown rather than inferred from historical development pages.
- Publisher
- NASA
- Title
- J-2X Engine Ready For Second Test Series
- Note
- NASA technical documentation identifies the LOX/LH2 gas-generator cycle and 294,000 pounds of vacuum thrust in primary operating mode.
- Publisher
- NASA Technical Reports Server
- Title
- From Paper to Production to Test: An Update on the J-2X Engine for Exploration
- Accessed Date
- 2026-08-20
- Note
- NASA technical presentation lists 448 s vacuum specific impulse, 5,535 lb dry weight, and 120 in diameter by 185 in length for the J-2X design.
- Publisher
- NASA Technical Reports Server
- Title
- The J-2X Upper Stage Engine: From Design to Hardware
- Accessed Date
- 2026-08-21
- Note
- NASA identifies Marshall Space Flight Center engineers as managing J-2X development.
- Publisher
- NASA
- Title
- NASA Test Stand Passes Review for Next-Generation Rocket Engine Testing
- Accessed Date
- 2026-08-21
- Note
- NASA records that the Ares I upper-stage development effort, including J-2X subsystems, concluded when the Constellation Program was canceled; this supports historical rather than active lifecycle status.
- Publisher
- NASA Technical Reports Server
- Title
- Ares I Upper Stage Subsystems Design and Development