Author Topic: Starship performance expendable mode in LEO with over 200 T fully reusable mode?  (Read 8509 times)

Online DanClemmensen

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I do very much like the idea of SpaceX bidding version of SS itself as an orbiting space station.  I do think a space station is intended to stay in space, not consistently be going back & forth from the surface, so all the instruments one may want to jam into a Starship based space station would maybe bump into the mass limit if you had to launch it all in one launch.
If you intend to launch an SS-based station with large habitable volume, it may be more reasonable to just launch two or more SS instead of one with a custom form-factor. If you never intend to use the Raptors after you get to your orbit, you can perhaps convert the tankage into more habitable space. I think this was examined and rejected in the past, but the economics have changed, because you could send up the material and tooling to do the conversion in a standard cargo SS. I think this trick will require a considerably larger access hatch than the standard IDSS docking port, But the tanks can stay in vacuum until the big items are moved in.

Note that a 9m diameter cylinder with (say) 35m of habitable length has a much higher habitable volume than an airbus A380.

Offline oldAtlas_Eguy

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I do very much like the idea of SpaceX bidding version of SS itself as an orbiting space station.  I do think a space station is intended to stay in space, not consistently be going back & forth from the surface, so all the instruments one may want to jam into a Starship based space station would maybe bump into the mass limit if you had to launch it all in one launch.
If you intend to launch an SS-based station with large habitable volume, it may be more reasonable to just launch two or more SS instead of one with a custom form-factor. If you never intend to use the Raptors after you get to your orbit, you can perhaps convert the tankage into more habitable space. I think this was examined and rejected in the past, but the economics have changed, because you could send up the material and tooling to do the conversion in a standard cargo SS. I think this trick will require a considerably larger access hatch than the standard IDSS docking port, But the tanks can stay in vacuum until the big items are moved in.

Note that a 9m diameter cylinder with (say) 35m of habitable length has a much higher habitable volume than an airbus A380.
A complete conversion of the tanks a normal length SS has ~2.000m^3 volume. A stretched by 10 m SS would have ~2,800m^3 volume.

ADDED - A little bit of warning is that watch out for wandering off to far from the thread topic. This includes myself.
« Last Edit: 07/27/2023 05:04 pm by oldAtlas_Eguy »

Offline ZachF

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300 tonne expended payload capacity + orbital refueling = sample return missions to just about everywhere with a ~300 tonne hypergolic mission stack.

Possibilities are amazing once you start mathing them out.
« Last Edit: 07/28/2023 01:12 pm by ZachF »
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Offline UKobserver

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300 tonne expended payload capacity + orbital refueling = sample return missions to just about everywhere with a ~300 tonne hypergolic mission stack.

Possibilities are amazing once you start mathing them out.

It is definitely useful to know what tonnage the Starship system could launch fully expended.

I am certain that wealthy individuals, governments and international partnerships will eventually take advantage of this fully expended capability to enable previously impossible, extremely high energy missions. As suggested above, imagine launching with a 200/300-tonne (mostly propellant) 3rd stage/payload, fully refuelling the Starship (2nd stage) in LEO from a depot and then burning to depletion before deploying the 3rd stage/payload to continue from there under its own power. That could enable some phenomenal missions.

SpaceX could offer Transporter type missions to Jupiter, Saturn, Uranus and Neptune, allowing projects from all over the world to book volume/mass on those missions without having to cover the whole cost. That could encourage an explosion of research as, in addition to the cost savings, it would make launch booking and scheduling a simple and transparent commercial transaction between each project team and SpaceX, with no need for any bureaucracy beyond national approval of each project and it’s overall budget/launch proposal at the start of each project.

Offline UKobserver

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Remains to be seen.
Because of the very long roundtrip time, the financial benefits of reusability don't only get reduced, they get deferred.

Unlike a tanker, a Mars ship will only be used 10 times or so, and the financial benefit deferred by 20 years.

Also, faster trips reduce payload and increase fuel requirements, resulting in more tanker flights.

Since stainless ships are so cheap, it really may make sense to not bother returning them. 

The unequivocal statements about reuse and super-fast return trajectories predate the transition to stainless IIRC.

The comments about whether to return Mars Starships to earth or not also provoke some interesting thoughts.

Deferred savings is a concept that I had not considered. The ship will not return for at least ~two years, and maybe ~4, so any investment made in allowing it to do so will only result in savings that far down the line, by which time making Starships may well be cheaper, reducing these potential savings.

Refurbishment also needs to be factored in, particularly if the Starship will carry people on its second flight, as that makes thorough inspection and re-certification essential, further reducing the savings when compared to just building and testing a new human-rated Starship.

Consider also that these hoped-for and deferred “savings” (compared to just building replacement Starships) depend on making a considerable additional up front capital investment, namely building out a big enough ISRU and launch infrastructure on Mars capable of generating enough fuel, and having enough pad space, to relaunch/return EVERY ship that arrives at Mars.

Of course, they have no choice but to build at least a minimally capable ISRU and relaunch infrastructure in order to be able to return human crews to earth from Mars, but presumably the size and expense of that (in terms of mass/material/equipment delivered to Mars to build it) would only be a fraction of the cost of the equipment/plant needed to enable the return of EVERY ship arriving at Mars.

SpaceX may therefore conclude that the cost of building a much larger ISRU plant negates any savings made from being able to re-use a larger proportion of the ships that land at Mars.

Finally, consider how significantly the designs of Falcon 9 and Starship have evolved in the last few years. It is entirely feasible that a Starship returning from Mars will be obsolete after just one or two roundtrip missions. They may become incompatible with redesigned launch infrastructure and/or newer designs of boosters that would be expected to launch them. Alternatively design flaws may have been identified in the design of that vintage, making SpaceX loathe to reuse an older, flawed model, when a newer, safer, more capable one is available.

If SpaceX thinks this is likely to be the case, and that they may only get a couple of uses out of each Mars Starship, then that completely changes the business case for building all the additional ISRU infrastructure needed to get them back. It becomes yet another reason to just simply leave them on Mars for repurposing into other things in due course.

Obsolescence will be less of an issue for boosters, tankers and earth-based cargo Starships, as they will make new flights as quickly as SpaceX can turn them around, burning through their designed lifespans/fatigue life much more rapidly and giving SpaceX a larger return on their re-use investment before the design can evolve enough to render them obsolete and see them retired or expended in one final hurrah.

TLDR; I do not think it will be worth it financially for SpaceX to attempt to return EVERY Starship from Mars. I think they will return only the minimum needed to get crews safely home and to bring geological samples back for study. I suspect the rest will remain on Mars for eventual repurposing/harvesting of materials/cannibalising for components. Whereas they will squeeze as many flights as they can out of the earth-based fleet, as that could save/earn them a lot of money.

Offline steveleach

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SpaceX are aiming to get a million people to Mars, and are planning fleets of a thousand or so ships leaving every 26 months.

I'm sure they could just build 40 ships a month (not including tankers), but I really don't think that's their vision.

Offline meekGee

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SpaceX are aiming to get a million people to Mars, and are planning fleets of a thousand or so ships leaving every 26 months.

I'm sure they could just build 40 ships a month (not including tankers), but I really don't think that's their vision.
The argument applies equally well at any volume - 4 or 4000 ships.

Even if you reuse, you still need to make a huge amount of them, and as pointed out, the problem escalates.  You don't get to just reduce your effort by 10x.

Also, those millions of people need a lot of ISRU activity, whose two main requirements are power, and a place to store the thousands of materials you'll be synthesizing, so until such time that you can just as easily make industrial stainless tanks on Mars, you don't want to send them back.

Send the engines if you want - they pack well.

I think the reuse and therefore super-fast transits thinking is from when Starships were going to be crazy carbon fiber constructions, not liberty-class style ships.
« Last Edit: 07/29/2023 01:27 am by meekGee »
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Offline steveleach

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SpaceX are aiming to get a million people to Mars, and are planning fleets of a thousand or so ships leaving every 26 months.

I'm sure they could just build 40 ships a month (not including tankers), but I really don't think that's their vision.
The argument applies equally well at any volume - 4 or 4000 ships.

Even if you reuse, you still need to make a huge amount of them, and as pointed out, the problem escalates.  You don't get to just reduce your effort by 10x.

Also, those millions of people need a lot of ISRU activity, whose two main requirements are power, and a place to store the thousands of materials you'll be synthesizing, so until such time that you can just as easily make industrial stainless tanks on Mars, you don't want to send them back.

Send the engines if you want - they pack well.

I think the reuse and therefore super-fast transits thinking is from when Starships were going to be crazy carbon fiber constructions, not liberty-class style ships.
We're wandering off topic, so I've started a new thread for this at https://forum.nasaspaceflight.com/index.php?topic=59286.0

Offline MarkBogdani

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Any new information anyone? The 250-300 tons expendable is an information earlier than this post for over 200 tons reusable. So it means futher improvements had in payload mass, and also the quotes have been expendable only the booster or the ship but not for both of them.

Any information, or calculations?

Or were I can ask this question for some aproximate calculations for the fully expendable?

Tags: rocket SpaceX 
 

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