SLS upper stage proposals reveal increasing payload-to-destination options
With less than a year to go before the inaugural flight of NASA’s Orion crew capsule and just over four years until the debut of the SLS rocket in 2017, work on the massive Heavy Lift Vehicle continues with ongoing proposals and studies targeting the vehicle’s upper stage.
Expanding SLS capabilities:
As the Space Launch System (SLS) rocket continues to track toward its debut launch in December 2017, engineers responsible for the rocket’s design upgrades beyond its initial test-vehicle configuration are turning their eyes toward the rocket’s proposed multi-use capabilities.
With the wide-range of proposed mission running the gamut from trips to the International Space Station in Low Earth Orbit (LEO) to crewed missions to asteroids in the inner solar, a key determiner in exactly how much payload SLS will be capable of delivering to these targets is its upper stage.
Currently, that upper stage is slated to be the iCPS (interim Cryogenic Propulsion Stage) with a hydrogen/oxygen burning single RL-10 B2 engine.
But for the first time, SLS engineers have revealed a proposed new Large Upper Stage that would not only increase SLS’s payload delivery capabilities to already-defined targets, but also enable SLS to support missions to the outer solar system.
Specifically, and excitingly, these newly identified (from the Boeing perspective) targets include the Jovian moon Europa, the Saturnian moon Titan, and the planet Uranus.
As stated by Boeing in the “SLS Capabilities with a New Large Upper Stage” presentation, available for download on L2, “The SLS is the most powerful rocket ever built and provides a critical heavy-lift launch capability enabling diverse deep space missions.
“A new 8.4m Large Upper Stage (LUS), as a follow on to the interim Cryogenic Propulsion Stage (iCPS), can provide significant increases in SLS payload injection capability.”
Under Boeing’s proposal, the new LUS would be constructed at the Michoud Assembly Facility in Louisiana on the same 8.4m tooling mechanism as the SLS Core stage – thus eliminating the need for the development of new machining equipment.
Examining the new LUS performance marks:
Under Boeing’s proposal, the new LUS would be 8.4m in diameter. Working in conjunction with the twin Five Segment Boosters (FSBs) and the 4-engine core stage of the SLS, the new LUS’s performance marks are all based on delivering the payload to a final 130x130nm (nautical mile) LEO orbit prior to a LUS-performed departure burn to points anywhere from the moon to Uranus.
According to Boeing, “Because of increased thrust and higher propellant loading, increased payload injection capability can be achieved with the LUS” to points beyond Low Earth Orbit.
Specially, Boeing lists 5 BEO (Beyond Earth Orbit) destinations and the deliverable payload mass projections of SLS with the new LUS variants to these destinations.
Specifically, those five destinations are: the moon, Mars, Europa, Titan, and Uranus.
Furthermore, three LUS variants are presented for review. “The three versions of the LUS presented are identical except for the engines, thrust vector control (TVC), feedlines, and thrust structure,” notes the Boeing presentation.
“A variety of propellant loads were evaluated, but for this presentation, LUS usable propellant was set to 105mt (231,483 lbs). Tank size and propellant loads are identical for all three LUS variants.”
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The three LUS versions are based on three engine options, which include: (1) a four RL10 C2 engine version, (2) a dual MB-60 engine version, and (3) a single J2X engine version.
Baseline SLS configuration – the iCPS upper stage:
Under the current baseline SLS configuration, the Delta-IV-derived 5m, single-RL-10 B2 engine iCPS, interim Cryogenic Propulsion Stage, upper stage would be capable of delivering the following payload masses to the five Boeing destinations.
For this analysis, the 4-engine core stage (total loaded weight at liftoff: 2,387,000 lbs) and twin FSB (total loaded weight at liftoff: 3,215,600 lbs) design is maintained (total vehicle liftoff weight less the iCPS and payload: 5,602,600 lbs).
The iCPS would carry 27.1mt (metric tons) of usable propellant and shroud the SLS payload in a 5m fairing.
Total engine thrust from the iCPS would be 24,750 lbf (in a vacuum) with a total deliverable payload mass to LEO (final 100x975nmi) of 70mt.
From there, the iCPS would be capable of sending 24mt through a Trans-Lunar Injection (TLI) burn to the moon and 20.2mt through a Trans-Mars Injection (TMI) burn to Mars.
For missions beyond Mars, the iCPS would only be capable of sending (with a 5m payload fairing) 2.9mt to Europa, 1.8mt to Titan, and only 0.13mt to Uranus.
The new LUS capabilities:
With these clearly defined capabilities for the iCPS, Boeing set out to study realistic potential upgrades and improvements to SLS’s upper stage performance marks.
According to the Boeing presentation, “The SLS’s payload capability improves significantly by the addition of a new 8.4m Large Upper Stage.
“Payload increases 60 percent to TLI (39mt vs 24mt) and 50 percent to LEO (105mt vs 70mt) vs. the Block 1 vehicle.”
Four engine configuration:
With Boeing’s proposal, the first option for the new LUS would see a 4-RL 10C2 engine design with a final LEO initial orbital destination target of 130x130nm.
This LUS would be capable of carrying an 8.4m payload fairing and a useable propellant load of 105mt.
Total engine thrust (all four engines combined) would be 99,000 lbf – with each engine producing 24,750 lbf).
Total payload mass to LEO would be 93.1mt.
Beyond that, this 4-engine LUS would be capable of delivering 38.1mt through a TLI to the moon and 31.7mt through a TMI to Mars.
For missions beyond Mars, this LUS would, like the iCPS, use a 5m payload fairing.
Unlike its iCPS counterpart, this 4-engine LUS would be capable of sending 8.1mt to Europa, 5.7mt to Titan, and 1.7mt to Uranus.
This LUS design would use a 2 MB60 engine LUS design with a final LEO initial orbital destination target of 130x130nm.
This 2-engine LUS would be capable of carrying an 8.4m payload fairing and a useable propellant load of 105mt.
Total engine thrust (both engines combined) would be 120,000 lbf – with each engine producing 60,000 lbf).
Total payload mass to LEO would be 97mt.
Beyond that, this 2-engine LUS would be capable of delivering 39.7mt through a TLI to the moon and 32.6mt through a TMI to Mars – the best of any of the four upper stage variants (iCPS included).
For missions beyond Mars, this LUS would, like the iCPS and 4-engine LUS, use a 5m payload fairing. It would be capable of sending 8.5mt to Europa, 6.0mt to Titan, and 2.0mt to Uranus – the best of any of the four upper stage variants (iCPS included).
Under this proposed LUS design, Boeing’s presentation shows a J2X engine LUS design with a final LEO initial orbital destination target of 130x130nm.
This single-engine LUS would be capable of carrying an 8.4m payload fairing and a useable propellant load of 105mt.
Total engine thrust would be 294,000 lbf.
Total payload mass to LEO would be 105.2mt – the best of any of the four upper stage variants (iCPS included).
Beyond that, this single-engine LUS would be capable of delivering 38.5mt through a TLI to the moon and 31.6mt through a TMI to Mars – a decrease from the 2-engine LUS variant.
For missions beyond Mars, this LUS would, like all other proposed or baselined upper stages, use a 5m payload fairing. It would be capable of sending 7.1mt to Europa, 4.6mt to Titan, and 0.5mt to Uranus – the least amount of deliverable payload capacity of any proposed LUS variant (but still greater than the baselined iCPS).
While it is unclear whether any of these proposed LUS variants will come to fruition in future designs/upgrades for SLS, investment in future exploration options and versatility of the SLS is paramount to the realization of its promised deliverables.
As Boeing states, “The SLS provides a critical heavy-lift launch capability enabling diverse deep space missions.”
With a capability to launch large scientific payloads farther and faster into the solar system than ever before, the “added payload to destination that can be provided by a new Large Upper Stage would be an enhancement for future science, astronomy, and Human spaceflight missions” of the SLS.
(Images: Via L2 content from L2’s SLS specific L2 section, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site. Other images via NASA, Boeing)
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