Latest configuration of EUS for the Space Launch System (Credit: NASA, Boeing)

by Marcel F. Williams

Boeing's development of the EUS (Exploration Upper Stage) for the Space Launch Systems super heavy lift configuration (Core stage/2 SRBs, EUS) should also enable the SLS to be deployed as a simpler two stage rocket.

SLS Block I and Block IB (Credit: NASA)

The SLS core stage plus and EUS upper stage should be capable of deploying more than 30 tonnes of payload to low Earth orbit. In this article, I refer to this SLS variant as the SLS-C.

Notional SLS-C (SLS core stage plus EUS upper stage) capable of deploying a CST-100 crew module plus nearly 17 tonnes of payload or more than 30 tonnes of payload to LEO (After NASA/Boeing).

Utilizing the SLS-C as a much more frequently launched crew launch vehicle could significantly reduce the cost of its super heavy lift variant. The SLS-C would also be more environmentally friendly since it won't produce the CO2 and the black carbon (soot) created by hydrocarbon fueled rockets (methane and RP-1). Black carbon is also deleterious to the Earth's ozone layer.

Deploying Boeing's crewed CST-100 Starliner would allow the SLS-C to deploy the 13 tonne spacecraft with nearly 17 tonnes of additional payload to LEO. So an SLS-C should be capable of deploying a crew plus satellites to LEO. And since orbiting propellant producing water depots are now being developed by Blue Origin, a crew plus nearly 17 tonnes of water could also be deployed to LEO. The SLS-C could also be routinely used to deploy 30 tonnes of water to orbiting space stations or propellant manufacturing water depots at LEO.

Notional Mega orbital habitat deployed to LEO with-- a single-- SLS super heavy lift launch. The EUS hydrogen tank derived space habitats are attached to a spent SLS core stage retrofitted by robots or astronauts with airlocks. Combined with the spent core stage, the Mega habitat provides more than 4000 cubic meters of volume; more than four times the total volume of the ISS. Solar panels and radiators are viewed laterally. One CST-100 Starliner his attached to an airlock while the other has detached before heading back to the Earth's surface.

But if commercial space stations are deployed to LEO then the EUS upper stages could be retrofitted for other commercial purposes. This could be done by astronauts or by robots teleoperated from the Earth's surface or by astronauts and robots working together in space.

Flexcraft could be crewed or teleoperated from Earth to retrofit spent SLS core stages or spent EUS upper stages for a variety of commercial uses (Credit NASA).

The EUS hydrogen tank in particular will be 8.4 meters in diameter and 7.5 meters tall. And such a substantially spacious tank could be used for a large variety of commercial purposes that could allow-- each spent EUS-- to generate hundreds of millions of dollars in savings annually.

X-ray of the EUS showing the large 8.4 meter in diameter hydrogen tank and the small oxygen tank (Credit NASA/Boeing).

An EUS retrofitted near a commercial space station with airlocks, pump connectors, or solar powered cryocoolers could be used for:

Water storage: Both the spent hydrogen and oxygen tanks of the EUS could be modified to store nearly 300 tonnes of water. Water can be used by commercial space stations for drinking, food processing, the the production of air, and to enhance radiation shielding. Propellant depots can convert water into hydrogen and oxygen propellant for spacecraft destined for beyond LEO cis-lunar and interplanetary missions.

Large habitat module: Retrofitted with an airlock, the empty hydrogen tank could be pressurized and attached to a small or large habitat, adding a huge amount of additional habitat area: 7.5 meters high and 8.4 meters in diameter. Such a substantial increase in space could be used for microgravity recreation or used to add three or four 2.5 meter high habitat levels.

Sewage storage: Waste water from commercial space stations can be stored and later reprocessed into potable water.

LOX storage: During the production of LOX/LH2 propellant through electrolysis at an orbiting depot, 25% of the oxygen is wasted. Retrofitted with a pump connectors and cryocooler, the spent EUS hydrogen tank could be used to store more than 200 tonnes of excess oxygen saving more than a billion dollars in additional launch cost from Earth.

Micogravity lettuce farm: a large variety of edible lettuce can be grown under microgravity conditions. A spent EUS would allow substantially more area for growing food.

Microgravity Mushroom farms: mushrooms can be grown in microgravity and when exposed to UV light than can be enriched with vitamin D. Growing mushrooms within spacious EUS hydrogen tank could help to reduce the cost of shipping food from the Earth's surface.

Artificial gravity aquaculture: attached to two thruster modules, the EUS hydrogen tank could be filled with water or seawater and used to raise brine shrimp, fish, or oysters.

Micrometeorite and radiation shielding: A spent US transferred to the lunar gateway or other cis-lunar Lagrange point areas for utilization could still have value after its no longer used for habitats, water, sewage, or oxygen storage. If the EUS is simply crushed and grounded up into fragments by solar powered machines in orbit, the high density fragments could be used to enhance the radiation shielding for habitats beyond the Earth's magnetosphere while also enhancing micrometeorite protection.

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