Why the SLS mega rocket can’t be repurposed like SpaceX

The massive SLS rocket proved to work. It successfully lifted off on November 16th, sending the Orion spacecraft to the Moon. But unlike the SpaceX Falcon 9, the SLS cannot be reused. It’s not a coincidence.

She finally took off. “She” is the Space Launch System (SLS) rocket, which finally made its maiden flight on November 16, 2022 after months of delay. It is with this launcher that humanity will return to the Moon in the 2020s. But it will not be with the rocket that has just left Earth: in fact, it has become unusable.

This is one of the characteristics of the SLS: it was not manufactured in the same model as the SpaceX launchers, with a reusable first stage (a feature that can also be found elsewhere, such as the New Glenn launcher by Blue Origin). This means that each SLS is single use, just like Ariane. Most rockets in the world work this way.

This lack of recovery is seen in this diagram from the European Space Agency, published on November 15th. It can be seen that the two side thrusters are ejected two minutes after takeoff, followed by the main stage after eight minutes. At no point is the possibility of recovering them mentioned – the same, incidentally, for the second floor.

The US space agency says the same thing: after they burned the propellant […]thrusters are jettisoned, lightening the load for the rest of the spaceflight “. According to NASA, the thrusters fall into the Atlantic Ocean, 225 km off the coast of Florida, while the main stage ends in the Pacific, between Hawaii and California.

When we know the success found by SpaceX with its recovery policy, it inevitably calls.

After all, when the American company operates the Falcon 9, the main stage automatically returns to Earth and refuels several times. The same goes for the Falcon Heavy and its two side thrusters (which are actually parts of the Falcon 9’s launchers). That way, SpaceX can chain shots together and lower its costs, as it doesn’t have to rebuild a rocket from scratch.

All fuel must be used to send to the Moon

For this question, NASA provided an explanation on its official website: including such a capability would logically require reserving some of the fuel (or adding some) to ensure the controlled return of the main stage to Earth. However, the SLS uses its power to maximize the payload the rocket can send to the Moon. 🇧🇷

Adding fuel would affect the overall mass of the SLS. Ditto if it were necessary to provide a cut propulsion system for this type of mission. It would also be necessary to provide a landing foot if you want the stage to be placed correctly with the vertical. Again, this adds volume and complexity (and risk of failure).

The main floor (in orange) isn’t tiny. A considerable amount of fuel would be required for a controlled return to Earth. // Source: NASA/Joel Kowsky (cropped photo)

Another element deserves to be considered. It’s one thing to judge NASA’s choices for the SLS today with SpaceX’s success in mind. Another is to place oneself in the context of the time, when the American mega-rocket project was formalized. And when SpaceX had not yet proven the relevance of this model.

The SLS project was formalized in September 2011, following in the wake of the Saturn V rocket from the time of the Apollo missions (it was also not reusable). Certainly, at the time, SpaceX already existed. Several of its rockets successfully took off and delivered payloads into orbit. It wasn’t until April 2014 that the center stage of a Falcon 9 could be salvaged for the first time.

During these two and a half years, the design of the SLS progressed in parallel, which increasingly fixed its final design. Furthermore, the project had already absorbed significant resources. As for SpaceX, it still took a few years to reach the stage where this recovery becomes a routine operation. SLS was almost complete.

At the turn of 2010, who could imagine the size of the upheaval that the era of reusable launchers for the space sector would be? “New Space” players like SpaceX and Blue Origin, no doubt. But among the already existing organizations, this matter was obviously not yet such an obvious and critical matter.

SpaceX Falcon 9
SpaceX’s first success in recovery dates back to 2014. But at the time, NASA had already launched the development of the SLS a few years ago. // Source: SpaceX

Would it have been possible to redirect SLS development along the way, assuming that integrating such a capability would be useful for the Artemis program? As it wasn’t initially designed for that, it took the risk of starting from scratch, or almost. With a rocket that already cost nearly $27.5 billion, multiplying budget overruns, the pill would have been hard to swallow.

In addition to funding issues, these design changes would likely further delay the start of the Artemis mission – just to conduct a test campaign to validate the recovery of the SLS first stage. It means exposing yourself to delaying the return of astronauts to the Moon for a few years. And, by extension, the start of a mission to Mars. Is this reasonable when China is also moving forward and has big ambitions in this area?

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The Tiawen-1 landing pad.  // Source: CNSA (cropped photo)

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