Starship HLS - Why Hydrogen might be the smart option?

With much interest in the HLS Starship as the moon lander for the Artemis programme, today we explore what a realistic Delta V budget is and why Hydrolox might be the fuel of choice

[snakevenom]

Something I think you glossed over was the refueling. You don't have the payload be the propellants. Your extend the tanks giving you overall more propellant which greatly increases Delta V.

With current iteration of Starship I calculated the propellant transfer capacity to 200t and 300t to V2

[CKalitin]

Like Blue's Moon Lander vs. Starship it's about vehicle optimization vs. long-term architecture optimization. This is why all rockets don't 100% optimize for performance, their goal isn't performance, but rather in Starship's near-term case, landing on the Moon and launching Starlink satellites. Completely optimal performance is a suboptimal strategy to achieve Starship's goals as it is more expensive and slower. Interesting to model this out though.

[snakevenom]

It isn't clear whether aluminum is better for rockets than steel. While aluminum is lighter, you also need a LOT more of it for the same results. For an example, the tanks. Most rockets contain an inner tank and the walls of the ship is more aluminum. This greatly increases your mass. While with Steel you don't need to have a seperate tank and skin. It's strong enough to work as both. Andy Lapsa said the payload between Aluminum, Carbon Composite and Stainless is pretty much the same. The only real difference between the three is cost and ease of use which Steel wins by a wide margin.

Hydrogen also cannot share a common bulkhead like Methalox does. This increases the mass as well since you would need to stretch the ship even more or reduce payload even more to add the dome halves.

[wingsley]

Hydrolox is the rocket engine / rocket fuel of choice for crewed lunar landers and orbital and cislunar vehicles. The only issue I can see with your assumptions: People-in-the-know are still hedging their bets on how many refueling sorties the current Starship and its HLS variant (using methalox) would need to leave Earth orbit and travel to the Moon. Some estimate 8 refueling sorties, others say 15. Don't be surprised if its anywhere in this range; maybe 10 to 12.

Here's an idea: if we get to the point where an HLS Starship is ready to go to the Moon, when it is launched, it could be fitted with built-in hydrolox engines only and the external bottom skirt of the Starship could be fitted with several disposable graphite-epoxy solid rocket boosters like the ones used by United Launch Alliance on its Vulcan rocket. Once the Starship is up into Earth orbit, the SRB's would no longer be needed, and they could be jettisoned just like with Vulcan. Then, it could be hydrolox all the way.

[miguellopez]

An issue with hydrogen for starships mission profile is long mission times, the hydrogen will boil off significantly by the time it gets to mars or from the moon back to earth.

[aowen]

Given the amount of water/ice that is indicated to be all over the moon (Chinese apparently even found it in normal regolith) then maybe Hydrogen is the way to go longer term.
In terms of changing SS to Alu, not going to happen any time soon so Methane will be SX choice.
If BO get their act together then maybe it would give then an advantage in a area where the competition field is still wide open.

[Electrohawk_CopperCompass]

Regardless of fuel, an Al Moon Lander makes sense... or any upper stage that isn't expected to come back to Earth or to Mars. The heat of re-entry will always require steel.

[iamsick]

At that point i think nuclear would make more sense.

[EveryoneWhoUsesThisTV]

I think in situ fuel mining will never be an issue personally.
Having worked in the mining industry I think astronauts have zero chance of mining and processing anything of significance on the moon or Mars using lightweight portable equipment.
By the time we have the ability to do in situ fuel harvesting, we won't really need it for fuel.

SpaceX won't do anything special for the HLS mission because it's such a low priority. :(
Artemis is just pork barrels to replace the former Space Shuttle pork barrels, it exists to distribute funds for political reasons.
The motivation to do a crewed moon mission with no base building is likewise a political 'beat China' bunch of nonsense.
NASA would never have planned a crewed moon mission with no base building if it was left up to them.

Starship isn't built for moon trips, and they won't rebuild the architecture just for Artemis which so few people care :)

[marksinclair]

Very compelling, nice work.
Does this eliminate the need for SLS? Can’t another expendable 20t payload “HLS” pre-deliver Orion+service module to LLO?
Or could you upsize this, or perhaps deliver another depot to LLO, and then do HLS propulsive return to LEO and land using Dragon? Eliminating both SLS and Orion....
I suppose these options apply to the current Starship/HLS as well.
Anyway, reducing the number of tankers to LEO is good, but not as good as more tankers and no Artemis……

[stocky]

I'd really like to see other companies make use of the super heavy booster. If NASA was to develop something to use the SHB I would expect to see a 3 stage system with the two upper stages being hydrolox with no refueling. Have one launch to send a lunar lander of some sort and a second launch to take the astronauts using the already flight tested Orion capsule. The Saturn C-8 supposedly would have had a mass approaching 4800 Tonnes and a lunar injection capacity of 74 Tonnes. With the super heavy booster you should be able to at least match this capability with a 3 stage system with no refueling (Maybe)

[alanday]

Aluminum may work on paper, depending on its thickness or composite. But will it be resistant to micro impacts?

[ericmatthews]

I think that Starship V2 making up a payload to orbit deficiency of 50 tons is going to be a huge challenge for SpaceX. Especially considering that Starship dry mass is still increasing as they are still searching for a successful design. This payload deficiency will increase the number of launches in a campaign for a deep space mission to a ridiculous level - taking months. I simply don't like the operational and logistic complexity of orbital refueling. Apollo didn't need to do this, and each Saturn V had half the liftoff thrust of Super Heavy/Starship.  

Starship seems inefficient for modern technology.