Copyright 2022 Robert Clark
The SLS was planned to have a large upper stage called the Exploration Upper Stage(EUS). This would take the SLS Block 1 to the SLS Block 1B, needed for a single flight lunar architecture. However, the multi-billion dollar cost for development of a large upper stage from scratch means it’s unlikely to be funded.
NASA is proposing a solution using the Starship making separate flights. But this plan takes 6 flights total or likely more of the Superheavy/Starship for the Starship to fly to the Moon to act as a lander. One look at this plan makes it apparent it’s unworkable:
Actually, it’s likely to be more complex than portrayed in the figure, needing 8 to 16 refueling flights. This is what SpaceX submitted to NASA in proposing the plan, requiring 6 months to complete the Starship refueling:
SpaceX CEO Elon Musk details orbital refueling plans for Starship Moon lander. By Eric Ralph Posted on August 12, 2021
First, SpaceX will launch a custom variant of Starship that was redacted in the GAO decision document but confirmed by NASA to be a propellant storage (or depot) ship last year. Second, after the depot Starship is in a stable orbit, SpaceX’s NASA HLS proposal reportedly states that the company would begin a series of 14 tanker launches spread over almost six months – each of which would dock with the depot and gradually fill its tanks.
In response to GAO revealing that SpaceX proposed as many as 16 launches – including 14 refuelings – spaced ~12 days apart for every Starship Moon lander mission, Musk says that a need for “16 flights is extremely unlikely.” Instead, assuming each Starship tanker is able to deliver a full 150 tons of payload (propellant) into orbit after a few years of design maturation, Musk believes that it’s unlikely to take more than eight tanker launches to refuel the depot ship – or a total of ten launches including the depot and lander.
Everyone, remember the Apollo missions where we could get to the Moon in a single flight? In fact, this would be doable with the SLS given a large upper stage. Then the suggestion is for the ESA to provide a Ariane 5 or 6 as the upper stage for the SLS. It would save on costs to NASA by ESA paying for the modifications needed for the Ariane core.
As it is now ESA is involved in a small role in the Artemis lunar program by providing the service module to the Orion capsule. But it would now be playing a major role by providing the key upper stage for the SLS.
The argument might be made that the height of the Ariane 5/6 is beyond the limitations set forth by NASA for the EUS. However, if you look at the ca. 30 m height of Ariane 5 core compared to the 14 m height of the interim cryogenic upper stage now on the SLS, this would put the total vehicle height only a couple of meters beyond the height that had already been planned for the SLS Block 1B anyway:
See discussion here:
Budget Moon Flights: Ariane 5 as SLS upper stage, page 2.
Coming up: ESA also could provide a low cost lander for the Artemis program.
Here’s the Silverbird Astronautics estimates for the payload capacity using the Ariane 5 as the upper stage. The vacuum Isp used for the Ariane 5 is taken as 462 s since it it known by the example of the RL10 engine that a hydrogen engine can have its vacuum Isp raised to this level by a nozzle extension. Specifications shown below, with the 5-segment SRB data estimated by 25% scale up of the Space Shuttle SRB’s data.
And the results for the LEO payload:
The estimated payload for TLI is found by putting -1.0 in for the hyperbolic C3 value for “Escape trajectory” field. This is a number that indicates it’s just below escape velocity for a free return trajectory around the Moon in case the mission has to be aborted.
So both the LEO payload of 150 tons and the TLI payload of 60 tons are above even the Block 2 payload capacity that would use advanced carbon fiber casing for the SRB’s.
Input data taken from: