What if Starship can't work as currently envisaged?

[thespacecow]

Do we really need to start another thread when there's already a thread for it: What if Starship fails? Possible Plan B's for SpaceX

And no, Elon didn't give up on Mars, Peter Thiel is wrong. Elon corrected him here. Do not ask for context since it's deeply political which would blow up this thread (which may not be a bad idea tbh).

[hkultala]

IMO, SpaceX overreached in trying to solve too many new problems simultaneously.

They are solving many of them successively, over different prototype vehicles.

This is the same error Lockheed Martin made 30 years ago with the Venture Star SSTO programme, which failed completely.  The next step after Falcon 9 to build a "BFR" (originally supposedly standing for Big Falcon Rocket) should have been exactly that.  Solve only three problems:
1) Upscale to building the most powerful first stage ever

Why?

There is very little commercial need for very expensive super-heavy booster.

2) Make this massive booster stage reusable with a new catch system

Flights of super-heavy rockets are still too expensive with expandable upper stage.

3) Design new methane based engines and build experience with them

For what purpose?

If not going to FFSC cycle, or fuel production at Mars, methane does not give much improvement over kerosene.

What is won by very slightly higher ISP is lost on worse propellant density (worse T/W ratio and bigger tanks)

In Raptor, FFSC is the big thing, not methane.

If they had done only this, they would be near success already, with huge potential from a reliable reusable heavy lift booster.

Wrong. There is near-zero market use case for very expensive super-heavy rocket.

The reusable second stage was always where all the gremlins lurked.

... but it is the thing that makes a super-game rocket make any sense. Without reusable second stage, the super-heavy rocket would just be way too expensive.

What they REALLY should have done is the exact opposite:

making a reusable second stage, at much smaller size.

And then later scaled this up into a super-heavy rocket.


They originally wanted to make even bigger rocket for their Mars missions. But they understood that that would be too big and not commercially viable for commercial near-earth missions, so scaled it down into the current 9m diameter starship-rocket. With full reusability, this 9m rocket is still viable for near-earth missions, and it's still big enough for manned mars missions.

The elephant in the room always has been thermal protection for the second stage.  Either the TPS would be light but fragile ceramic tiles or perhaps heavy metallic tiles with active evaporative cooling system which would be complex, heavy and reduce payload mass.

"reduced payload mass" is not a real problem. It's a tradeoff everybody should understand (but you clearly do not, because you think it is some big problem).

It's real problem only a problem for direct launches to high-energy trajectories without refueling, because then it can make the payload zero.

There might never be an ideal solution to this problem and the developmental time could be long.

There very rarely are magic solutions that removes all negative penalties/tradeoffs. And there is no need to be. Having reduced payload for fully reusable second stage is totally acceptable.

The stated goal of crewed missions to Mars added many other major challenges, on orbit refuelling

On-orbit refueling of ISS is already been done. It's not a totally new problem but a solved one.

And they do not need this to use Starship to launch commerical payload to LEO. And because Starship is fully reusable, it can still be commercially viable (cheaper than much smaller expendable or partially expendable rockets).

They can make money selling Starship launches to LEO while they are developing a solution to this problem.

, the requirement for landing legs

Landing legs are not a problem, they have them for F9/FH first stage already.

, and maintenance of cryogenic fuels for months in transit requiring active cooling.

This is a real new problem.

But they do not need this to use Starship to launch commerical payload to LEO. And because Starship is fully reusable, it can still be commercially viable (cheaper than much smaller expendable or partially expendable rockets).

They can make money selling Starship launches to LEO while they are developing a solution to this problem.

None of these problems are simple,

Many of these "problems" have existing clearly working solutions, and many of these problems are not problem for profitable LEO use of Starship while developing the solutions to them

[Vultur]

There are several possibilities depending on what part is the killer problem.

I'd argue that Super Heavy is already developed past the point where "it will never be able to launch anything" is plausible. So the simplest, but also most limited, fallback would be a pure Starlink V3 launcher - expendable upper stage on top of a Super Heavy. That would work for Starlink but not for HLS or Mars.

Beyond that, it depends on where the problem is.

The Raptor engine itself seems ok, but there could be fundamental problems with the integration into the vehicle in Starship v2. That could presumably be redesigned.

If the TPS cannot be made reliable enough ... well, HLS could probably be done with expendable tankers, it'd just be more expensive, but that would rule out the Mars plan.

OTOH, a total TPS redesign (transpiration cooling everywhere?) is a possibility.

--

I don't think SpaceX will give up on the general concept/category of "super heavy rocket with some kind of Raptor/Raptor derivative engine". But significant redesign is possible.

[Chris Bergin]

Do we really need to start another thread when there's already a thread for it: What if Starship fails? Possible Plan B's for SpaceX

And no, Elon didn't give up on Mars, Peter Thiel is wrong. Elon corrected him here. Do not ask for context since it's deeply political which would blow up this thread (which may not be a bad idea tbh).

That thread's last post is five years ago. Different situation now.

[spacenut]

I have heard that Musk talked about adding 2 more engines to the booster center because there was room.  Then, stretch the tanks on the booster to make up for the two engines use.  Wasn't much of a stretch from what I remember.  This should allow a slightly more robust Starship.  Would this help with staging higher to help Starship get to orbit? 

I think maybe to get big payloads to orbit, just until they get the harmonics fixed, they should abandon the TPS and fins and launch Starlink satellites, and expend the second stage.  Make it work first to orbit cheaper, then work on the TPS and fins.  With expendable upper stage, someone figured a 200-260 ton payload could be launched. 

Someone also mentioned abandoning the COPVs and use electric pumps.  Batteries for these pumps could be recharged with solar panels, which are going to be used on Starship anyway on it's trip to Mars.  This might be tried, but may take a little more time to implement. 

Also, If the Lunar Starship can get to orbit without TPS, fins, etc, the problem becomes refueling.  Expendable tankers would take more payload, but may cost more to refuel. 

Hopefully they can get the problems worked out quickly with version Raptor 3 and get to orbit. 

It makes me think Shuttle might have been cheaper to operate if they had reusable side boosters and maybe used kerolox engines on the Shuttle to be able to have a smaller expendable tank.  Still only got about 20-25 tons of usefull payload to orbit.  The reusable side boosters could have done that alone with an expendable upper stage.  So, space planes and maybe even Starship really cut down on payload capability. 

[Riccardo11]

Three facts, based on known information.

1. The super-heavy booster works, and reusability has already been achieved. While, in theory, replacing Raptor 2 with Raptor 3 engines could break the booster, I consider this extremely unlikely.

2. The Starship v1 had no unsolvable flaws. They did a full test flight and the ship landed in one piece.

3. Raptor 2 has been used both in the Booster as well as in Starship v2. The former works, the latter doesn't.

Based on these facts, I find it very difficult to imagine a situation in which Starship (the booster and the ship combined) cannot work due to an unsolvable engineering challenge. Even if Starship v2 is unsuccessful, they could always revert to v1, albeit at the cost of payload/performance.

[spacenut]

The thrust of R1 was 185 tons, R2 was/is 230 tons, and R3 is 280 tons.    I know each increased the thrust. 

Is too much thrust on the Starship a problem?  Also, can the Raptor throttle down to the lower thrust but just burn longer to get the job done? 

[dondar]

Firstly, just to get it out of the way, this is hypothetical. I think Starship will eventually be made to work as currently planned (two stage, fully reusable, methalox, etc).

But let's say it can't be made to work. Full and rapid reuse eats all the payload. Or the vehicle can't be made robust enough for economic reuse and acceptable reliability.

What would you change about the design in order to arrive at a vehicle which comes closest to achieving the program goals?

"can not be made to work" is too hypothetical construct.
There two  natural barriers in engineering projects of any kind.
1. (unmanageable) design complexity,
2. Physics.
I should mention here that the complexity is not always driven by physics of course.

And of course there are always two connected social barriers:
1. financing,
2. Quality of available force.

For example hard weight restrictions in DC-X pushed engineers to very complex tank designs(see physics), and the failure to produce these tanks (see  unmanageable complexity) led to the death of the project.
Whatever failure mode is activated first the kill switch is always unmanageable complexity. And the working solution is always serious project simplification.

So the answer is "falling down to Falcon".

SpaceX will continue to exploit  Falcon and probably they will try to design superheavy rocket  with (half) expendable second stage.

[steveleach]

Are you asking what they should do if it simply isn't viable to create a fully reusable launch vehicle? Or just whether anyone has come up with a better design for a full-reusable upper stage?

If the former, presumably the next best alternative would be to mass-produce the cheapest possible expendable upper stage.

If the latter, presumably the answer depends on exactly what part(s) of the Starship design is irreparably flawed.

[spacenut]

Well, it got into orbit with vs 1 Raptors, but had problems returning which could have been worked out.  So that tells me there is too much thrust on the Starship with vs. 2 Raptors.  Any opinions.  Should they reduce the Starship by one engine or could they throttle down.  I know increased thrust means more payload. 

So, is it the design on R2 or the increased thrust?

[sdsds]

[...] So that tells me there is too much thrust on the Starship with vs. 2 Raptors. 

There is no solid evidence supporting that speculation.

More generally we know large reusable upper stages are possible because NASA conducted 133 successful  STS orbiter reentries.

[Robotbeat]

Thing is, V3 Starship solves the problems we’ve seen so far with V2, and the COPV thing is likely a quality control issue, which can be solved as QC issues usually are solved.

There is nothing fundamentally unworkable about Starship. But if you want to know what I think about ways to improve Starship… well I think a discardable (and recoverable) fairing is worth it and allows even larger (by volume) payloads, say 15m in diameter and 50m tall. Or smaller and with much greater efficiency as you’re not pushing the heavy heat-shielded fairing to low orbit or beyond.

I’d also like to see downrange recovery of the booster eventually with a stretched booster. This is logistically complicated to make worthwhile (you’d need to send back multiple boosters on a boat to be worthwhile, with transfer at sea), but I think may be worth it.

[Kaputnik]

Are you asking what they should do if it simply isn't viable to create a fully reusable launch vehicle? Or just whether anyone has come up with a better design for a full-reusable upper stage?

If the former, presumably the next best alternative would be to mass-produce the cheapest possible expendable upper stage.

If the latter, presumably the answer depends on exactly what part(s) of the Starship design is irreparably flawed.

I think it's possible to design and operate a fully reusable vehicle. It breaks no laws of physics to do so.

But, specifically, a two stage vehicle with a RTLS booster and an upper stage with ~5.5km/s delta V (IIRC that's what's needed to go from Mars surface through TEI), with minimal/no refurb between flights, with a meaningful payload and acceptable (man rated) reliability and safety?

That's certainly not a given. Just like reusable SSTO isn't a given.

So I'm exploring some of the options that would allow Starship to fulfill its requirements. There's obviously a lot of scope to stage higher and faster, for example.

[Robotbeat]

5.5km/s delta-v isn’t even that hard. It’s nowhere near the same class of problem as a SSTO RLV. A SSTO requires 3 times the mass fraction (using methalox… but it’s actually harder for hydrolox due to hydrogen’s low density). And actually, it probably IS feasible to do SSTO RLV with hydrocarbon fuel.

I mean, you literally just watched 2STO RLV with RTLS on one of the previous starship flights. Recovery of first stage and a booster splashdown that probably would’ve worked with legs.  I just don’t see why people think there are showstoppers hidden somewhere even when the thing basically already happened. Is it literally just a complete inability to see even slightly beyond what has already happened, inability to think from engineering principles? Like, oh, to do full orbital requires 1% more delta-v or whatever, therefore I can’t extrapolate about whether it can be done or not?

I just don’t understand this kind of refusal to acknowledge something can be done unless it’s already being done. Certainly no one who thinks like this has ever attempted to actually invent or build something new.

[Twark_Main]

First, just an aside, in a recent NYT interview, Peter Thiel incidentally let slip that Elon Musk told him in 2024 that he had given up on Mars.  If true, this is huge, and removes the incentive to develop a reusable upper stage ASAP, which is where all the problems lie.

IMO, SpaceX overreached in trying to...

Just so this doesn't get misinterpreted (which it seems like it immediately was), Thiel claimed (based on Thiel's extrapolation, not anything Musk explicitly said) that Musk gave up on Mars as an escape from terrestrial politics. Thiel didn't say Musk gave it up because he thought it was technically infeasible.

https://archive.is/HTIF6

[Politics is] toxic for all the people who get involved in different ways. There is a political dimension of getting “Back to the Future.” You can’t — this is a conversation I had with Elon back in 2024, and we had all these conversations. I had the seasteading version with Elon where I said: If Trump doesn’t win, I want to just leave the country. And then Elon said: There’s nowhere to go. There’s nowhere to go.

And then you always think of the right arguments to make later. It was about two hours after we had dinner and I was home that I thought of: Wow, Elon, you don’t believe in going to Mars anymore. 2024 is the year where Elon stopped believing in Mars — not as a silly science tech project, but as a political project. Mars was supposed to be a political project; it was building an alternative. And in 2024 Elon came to believe that if you went to Mars, the socialist U.S. government, the woke A.I. would follow you to Mars.

Really though, this whole thread is absurd.  "If you assume they can't make it work, then how can they make it work?" is a nonsense question.

[Twark_Main]

To me what Starship looks like is just a platform to test rocket engines.  In the movie industry, it’s a Macguffin.  Just a plot device, but never the main part of the story. Skunkworks did this carp.

It’s all about the rocket engines and only the rocket engines.  HLS as a vehicle has not materialized in hardware. 

So I ask myself, why… and all I can surmise is that SX folks wanted to just establish engine performance and manufacturing production capabilities.

It's so funny to me how people still don't understand the concept of iterative development.

SpaceX can tell people till they're blue in the face, but fundamentally if you don't get it then you don't get it. 

[steveleach]

To me what Starship looks like is just a platform to test rocket engines.  In the movie industry, it’s a Macguffin.  Just a plot device, but never the main part of the story. Skunkworks did this carp.

It’s all about the rocket engines and only the rocket engines.  HLS as a vehicle has not materialized in hardware. 

So I ask myself, why… and all I can surmise is that SX folks wanted to just establish engine performance and manufacturing production capabilities.

It's so funny to me how people still don't understand the concept of iterative development.

SpaceX can tell people till they're blue in the face, but fundamentally if you don't get it then you don't get it. 

Purveyors of misinformation have a tendency to purvey misinformation in their writing.

[OTV Booster]

If the current Starship/SuperHeavy system were somehow intrinsically flawed, the next best approach would be to take the best LPRE the world has ever seen (Raptor 3), design a massive reusable booster with the SL version of that engine, and use that booster as a flying test stand to work out what's required for a fully reusable upper stage.

No, that's not identical to the current plan because it drops the the requirement that the Ship can return from Mars to Earth without refilling. Having a single-stage Ship designed to get from the Mars surface to low Mars orbit still allows eventual Mars settlement, albeit more slowly than will happen with the current Ship design.

I assume you mean return mars to earth without mars orbital refueling. Mars orbital refueling looks to be one of the possible options until propellant ISRU is up and running.


IMO the chances of a successful prepositioned robotic ISRU plant are somewhere between nil and zip. Just too many hard 'we ain't never done this before' choke points. This leaves the first and probably second crewed missions depending on earth supplied propellant.


All the propellant can be landed or land only enough for the ship to mate up with an orbital depot. Either would work but my money is on a depot, which makes mars orbit refueling a currently planed core capability.

[OTV Booster]

If they can't make it work, at some point (when money becomes an issue) they will have to stop trying and scrap the program.  I don't see a middle ground with this outfit.  Here's hoping they make it work.

 - Ed Kyle

The hard limit seems to be that the system doesn't work unless the Ship has enough delta V to get from the Martian surface back to earth. So whilst we can discuss drop tanks, extra stages, etc, this fundamental requirement always remains. Like you say, no middle ground.

If they wanted to shelve the Mars plan, they would have all sorts of options open. They have, after all, developed the world's highest performance engine. There's a great launcher in there somewhere.

The hard limit you point out may not be there. See previous post for an argument for a depot on mars orbit.


Once ISRU is up and running the best of the many cargo ships not expected to return can be used as tankers to feed the depot. The depot use that starts as a way to supply return propellant from earth can carry on with a martian propellant source if necessary.

[steveleach]

If the current Starship/SuperHeavy system were somehow intrinsically flawed, the next best approach would be to take the best LPRE the world has ever seen (Raptor 3), design a massive reusable booster with the SL version of that engine, and use that booster as a flying test stand to work out what's required for a fully reusable upper stage.

No, that's not identical to the current plan because it drops the the requirement that the Ship can return from Mars to Earth without refilling. Having a single-stage Ship designed to get from the Mars surface to low Mars orbit still allows eventual Mars settlement, albeit more slowly than will happen with the current Ship design.

I assume you mean return mars to earth without mars orbital refueling. Mars orbital refueling looks to be one of the possible options until propellant ISRU is up and running.


IMO the chances of a successful prepositioned robotic ISRU plant are somewhere between nil and zip. Just too many hard 'we ain't never done this before' choke points. This leaves the first and probably second crewed missions depending on earth supplied propellant.


All the propellant can be landed or land only enough for the ship to mate up with an orbital depot. Either would work but my money is on a depot, which makes mars orbit refueling a currently planed core capability.

This is why the alternative-to-Starship will depend entirely on what exactly isn't working.

If orbital refuelling and aerocapture are working, but interplanetary-velocity EDL isn't viable for some reason, then you probably end up with a multi-vehicle architecture.

If refuelling fundamentally doesn't work then you go with a many-stage approach.

But for SpaceX to achieve its goals (Occupy Mars) then all these things need to work, and that means Starship works.