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Comment by russdill | Hacker News Reader

Many of these risks don't apply to the lunar variant. The lunar variant won't be launching people from earth and won't be returning to earth. No re-entry, no landing flip, etc.

As far as descent, it will do final touchdown with smaller engines higher up to avoid kicking up rocks. During landing, I think pretty much any one of the 6 raptor engines can be used to abort.

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They somewhat apply because the lunar variant still needs to be fueled up in LEO with ~ 6 additional launches , all in relatively quick succession.

This seems unfeasible without rapid reuse actually working.

True enough, they can't be throwing away tankers for each refuel.

At the price NASA is willing to pay, they can. The tankers are only a few million dollars in raw materials.

In my opinion the way to think about SuperHeavy+Starship is a scaled up stainless steel Falcon 9. Currently Falcon 9's first stage booster (usually) lands and is quickly/cheaply refurbished/reused, while the second stage is completely thrown away except for partially successful attempts at fairing recovery. They've used this partially reusable system to do a large number of launches quite cost effectively.

In SH+SS, the "Starship" part is the second stage, with the revolutionary goal that it can deliver a payload to orbit and then skydive back to earth and propulsively land itself. That has major risks and is unlikely to succeed the first number of attempts, with the loss of the stage and the 6 raptor engines.

The "Superheavy" portion is very much equivalent to a scaled-up F9 booster, and the risks to landing it should be much lower (Elon's crazy catch ideas notwithstanding).

tl;dr I think Starship system can mostly work if it's partially reusable to a similar extent as F9. Losing a half-dozen second stages to do a full orbital refueling for a Moon or Mars mission should still be a fraction of the cost of a single SLS launch, and they can continue working on full reusability while performing missions and cashing checks.

Fairing recovery has been abandoned.

Fairing recovery is not abandoned, they decided to fish them out of the water after a soft landing instead of catching them with a net.

Ah yes, right you are, it is the catching that they have abandoned. Thank you for the correction.

Why do you think they would need to do those launches in quick succession? If the lunar lander starship is parked in orbit without a crew it can be refuelled over any convenient period of time. Once it's fuelled just send up the crew in a dragon capsule and off you go. The dragon would probably make a good lifeboat if you brought it along for the ride somehow.

They may have solved the LOX boiloff problem, but perhaps not.

Even if they need to refuel quickly, why not launch 6 starships for that mission? They’re planning to build lots of them aren’t they?

As long as the crewed starship is fuelled in orbit not too long after the last tanker ship launched, then the amount of boiloff will be negligible.

I suspect Spacex will develop cooling systems to re-liquefy any gaseous propellants as this will be more of a concern for the ~6 month mission to Mars.

Wikipedia[1] cites a 2010 study that gives a boiloff rate of 0.1% per day for hydrolox. Not sure if it would be less for pure LOX. Methane would remain stable so I wonder if there's a way you could balance the fuel load so that you can deliver only methane on some of the trips and then all the LOX in one trip to avoid having it hang around in orbit.

[1] https://en.wikipedia.org/wiki/Propellant_depot#Feasibility_o...

Oxygen is the vast majority of the propellant mass, I'm afraid. Methalox is CH4+2O2->CO2+2H2O, so you need 4 Oxygen atoms for every Carbon atom (with Hydrogen being a rounding error).

Dragon is 4.4 meters (14.4 feet) tall and 3.66 meters (12 feet) in diameter. Starship fairing payload envelope is 22m tall and 8m in diameter. More than 3 dragons would comfortably fit inside.

I think the idea is that the fueled-up Starship in LEO would have already have most the payload inside since it launched. The only thing it would be lacking is the astronauts, so they can come in a much smaller vehicle.

That said, this contract has astronauts boarding Starship in lunar orbit, not Earth orbit.

This contract is to take astronauts from lunar orbit to the lunar surface. They get from Earth to lunar orbit with SLS/Orion.

Good one, you almost had me until 'SLS'.

As stupid as it is, that is the contract.

That just confirms that they can launch and fuel the starship lander on their own schedule.

Also it does not need to be the same tanker to do the resupply. The plan is to make 2 starships per week. There should be plenty available to continue refuelling missions if one is not available.

Re-entry is required for the ship that will refuel the lunar lander. So yes the re-entry portion is required for the system to work.

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