SpaceX’s Moon Starship is a brilliant step towards reusable Mars rockets

SpaceX’s newly-announced Moon Starship is a fairly radical departure from the Mars-focused, fully-reusable vehicle the company has been pursuing for years. Unintuitively, that may be the perfect half-step towards truly reusable Mars rockets.

On April 30th, NASA announced that SpaceX had won $135 million to design and build a highly-customized variant of its reusable Starship spacecraft with the intention of launching a handful of space agency astronauts to the Moon in the mid-2020s. Whether or not that initial seed translates into enough funding to seriously design and build the ship SpaceX has shown off in new renders, it has already broken the ice, so to speak, between the US federal government (or at least NASA) and the company’s ambitious next-generation launch vehicle.

With a substantial amount of money now on the table for SpaceX to begin initial work on its Moon Starship, it’s worth analyzing just how different it is from the Starship the company is working on today.

First and foremost, perhaps the most obvious difference between SpaceX’s ‘base’ Starship and its lunar variant is the rocket’s hull. In the case of the Moonbound ship, SpaceX appears to have returned to a fully-painted vehicle for unknown reasons. More likely than not, that white paint is likely motivated by the fact that proposed NASA Moon landers must (obviously) be capable of landing and safely returning their astronaut cargo back into lunar orbit.

To do that, those landers must be able to sit on the surface of the Moon after landing for at least several days, with longer stays being even better. For Starship, this means that the vehicle must likely be able to keep its cryogenic liquid methane and oxygen propellant from warming up and turning into gas, thus preventing it from igniting its main Raptor engines. White paint is at least a bit more reflective (and thus insulating) compared to Starship’s shiny steel hull but it could also hint at the use of more extensive insulation then sealed off with paint.

This ties into perhaps the most significant functional change to the rocket. While visible in a render of the craft after landing on the Moon, a separate render just before touchdown fully revealed not only the addition of large vacuum-optimized retrothrusters – but a major strategic shift in how Lunar Starship will attempt to land on the Moon.

In short, it appears that SpaceX does not plan on propulsively landing Lunar Starship on the Moon under the power of its main Raptor engines. Instead, three triple-thruster clusters – likely relying on the same methane and oxygen propellant as Raptor – will fire up shortly before touchdown to gently land Starship on the Moon. This approach has significant benefits: the Moon’s gravity is so low (~1/8th of Earth’s) that using even just one engine as powerful as Raptor to land would be incredibly difficult – a single engine could theoretically lift a fully-fueled Starship thanks to low lunar gravity.

Additionally, powerful Raptor engines – even if they could be used to land – would likely dig huge craters in the Moon’s powder-like surface during a landing burn, making it more difficult astronauts to leave the ship to explore their surroundings. However, it also means that SpaceX must design and certify an entirely new kind of vacuum-optimized rocket engine – likely using gas propellant and fed by high-pressure tanks – for an extremely critical part of operations. If those landing engines were to fail, Starship would very likely crash on the Moon, marooning, wounding, or even condemning the astronauts aboard it.

Beyond new thrusters, a radically different landing strategy, and a painted (and possibly insulated) steel hull, Lunar Starship also features what looks like the tip of a Crew Dragon spacecraft in place of its nose, likely including Draco thrusters and a docking port. SpaceX has also copied the concept of Crew Dragon’s trunk section, installing a curved solar array that wraps around a large portion of Starship’s conical nose. Lunar Starship also offers what looks like the first official glimpse into a new style of Starship landing legs, prototypes of which are already installed on Starship SN4.

Simplicity first (ish)

Additionally, SpaceX has chosen to entirely exclude a windward heat shield from Lunar Starship, as NASA’s plan is (rather painfully) to launch astronauts to the Moon with SLS and carry them to lunar orbit and back to Earth on Orion. Starship also appears to be missing its complex and extensive habitation module and massive gallery window. All that absent hardware is almost certainly meant to dramatically simplify Starship to the point that even NASA would consider funding its development. Incredibly, that strategy appears to have worked and it’s possible that we could see Lunar Starships flying to the Moon as early as 2022.

While a stop at the Moon is decidedly one-way and requires a bit of a one-off Starship variant, what SpaceX has really done is found a way to get NASA to help fund the development of its fully-reusable next-generation launch system. Even if NASA’s Artemis program dies, flounders, or goes nowhere, SpaceX will likely still benefit significantly, much in the same way that NASA’s assistance developing Cargo Dragon and Falcon 9 was a huge boon for the company.

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