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I'm having difficulty understanding how/if Starship and/or Super Heavy could be used to deliver crew to LEO.

Is it expected to deliver astronauts to the ISS Crew-Dragon-style, but without the 2nd stage; that is, "FSTO"? (as opposed to SSTO)

If no, can the Super Heavy be made into an SSTO spaceship, capable of ISS docking and vertical landing?

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    $\begingroup$ Several issues: what you are calling "FSTO" seems to be what is generally called SSTO. Second, the Crew Dragon is not SSTO, so it's unclear how that can be "Crew-Dragon-style". Third, the second half of your question jumps to asking about the Superheavy, which is the booster. Also, SSTO capabilities of Starship have been asked about before, does space.stackexchange.com/a/39275/15771 answer your questions? (And aside from all that, Starship is not currently planned to be used in ISS operations.) $\endgroup$
    – Christopher James Huff
    Commented Apr 10, 2021 at 22:26
  • $\begingroup$ @ChristopherJamesHuff I like the newly-coined "First Stage to Orbit" or FSTO. :-) Concern about Dragon and other terminology been addressed by adjusting the wording slightly. I've been quite puzzled by the same question that the OP asks so I hope an answer can be posted. $\endgroup$
    – uhoh
    Commented Apr 11, 2021 at 0:07
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    $\begingroup$ What could "Crew-Dragon-style" even mean in this context? A SSTO crew transfer vehicle wouldn't have any more in common with Crew Dragon than any other spacecraft. The question's basically saying "like Crew Dragon, except different in almost every detail". $\endgroup$
    – Christopher James Huff
    Commented Apr 11, 2021 at 12:43
  • $\begingroup$ @ChristopherJamesHuff no it is not basically saying that, it's saying what's written in the post. My guess is that it simply means "capsule style" where it docs, opens a hole, and people crawl through. $\endgroup$
    – uhoh
    Commented Apr 11, 2021 at 20:10
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    $\begingroup$ I wonder if OP is not using “SSTO” for “Second Stage To Orbit” when most people use it for “Single Stage To Orbit” which is nearly exactly the opposite? That would explain part of the confusion... $\endgroup$
    – jcaron
    Commented Apr 12, 2021 at 8:05

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Is Starship planned to fly directly to the ISS without first stage?
Is it expected to deliver astronauts to the ISS Crew-Dragon-style, but without the 2nd stage; that is, "FSTO"?

No. Starship will be launched on top of Super Heavy. There is no plans for a SSTO Starship on Earth to carry crew/cargo to orbit.

Is it even possible?

Is regards to whether Starship could do SSTO on Earth, Musk said "It technically could, but wouldn’t have enough mass margin for a heat shield, landing propellant or legs, so not reusable"

You would have to launch Starship without recovery equipment to do SSTO; meaning no recovery, which for crew transportation to LEO; is problematic to say the the least.

If no, can the Super Heavy be made into an SSTO spaceship, capable of ISS docking and vertical landing?

Probably not. The mass margins of a reusable Super Heavy are going to be similar to that of a reusable Starship; because same engines, tanking, heatshield and launch profile. With scale you can have somewhat better margins, but not by much. To go a bit more in depth for Starship; if we assume a ∆V requirement of ~8600m/s to get to LEO, we'll need a dry mass/total mass fraction of ~8-8.5% (this is very sensitive to ISP and total gravity losses). Starship SN-20 as it stands has a dry mass of 100-110 tons. Add in landing propellant of 10 tons and you've already hit a mass fraction of 8.7% (unable to get to orbit) with 0 payload.

The mass margins just aren't there for a reusable single stage methalox full flow staged combustion cycle rocket.

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  • $\begingroup$ Thanks for straightening this all out. I didn't really have a clear picture of what could or couldn't be done. $\endgroup$
    – uhoh
    Commented Apr 11, 2021 at 20:11
  • $\begingroup$ I like your answer very much, but I've also used it as an example in meta; Shall we make it explicit site policy that screenshots of text ≠ readable text? I think it's most helpful to leave this answer as-is while things are being worked out there, but long term perhaps adding the block quotes (for screen readers and searchability) will be better. $\endgroup$
    – uhoh
    Commented Jul 16, 2021 at 22:59
  • $\begingroup$ Downvoted for lack of accessibility. Thanks for pointing out this answer, @uhoh. $\endgroup$
    – David Hammen
    Commented Jul 23, 2021 at 16:06
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Is it expected to deliver astronauts to the ISS Crew-Dragon-style, but without the 2nd stage; that is, "FSTO"? (as opposed to SSTO)

Starship cannot get to orbit in any meaningful way without Super Heavy. Theoretically, it would be possible to get to LEO without any payload and by removing all recovery hardware, the body flaps, the landing legs, the heat shield, the header tanks, and the extra fuel for landing. However, doing so wouldn't make any sense.

You need Super Heavy to do anything meaningful … such as bringing crew to the ISS.

If no, can the Super Heavy be made into an SSTO spaceship, capable of ISS docking and vertical landing?

Super Heavy is the booster. It can't get to orbit. And if by some miracle a Super Heavy magically gets transported into orbit, then it can't get back: it has no heat shield, no way to shed its velocity, no way to survive reentry from orbital velocity.

It doesn't really make sense to compare Starship to capsule-based systems such as Dragon, Soyuz, Starliner, Orion, or Apollo. You should compare it to the Space Shuttle.

Starship works very much like the Space Shuttle in that it "merges" the traditionally separate second stage and crew vehicle into a single vehicle. There are only two stages: Super Heavy, which is the booster, and Starship, which is both the second stage and the "capsule". Unlike the Space Shuttle, it will not throw away its tanks.

Starship docked to the ISS will look pretty ridiculous, though:Starship docked to the ISS[Source: SpaceX]

Starship's pressurized volume is comparable in size to the pressurized volume of the entire ISS – this means that a single Starship launch will bring as much habitable space into orbit as 12.5 years of construction on the ISS!

However, note that despite the renders on the SpaceX website, there are currently no plans to actually use Starship to launch to the ISS. Also, it is going to be a long time until Starship gets crew-rated as well as certified for ISS proximity operations.

In fact, it is questionable whether that even makes sense: why go through all the hassle of docking to the ISS, unloading all the crew and cargo and the experiments, install all the experiments on the ISS, then after 6 months un-install all the experiments, load everything back into Starship, etc. when Starship is so big and so cheap that you can just use it as the space station?

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    $\begingroup$ I'm shuddering at the amount of integration work that would be necessary to get that combination approved. Docking loads alone would be quite the beast. $\endgroup$
    – Tristan
    Commented Apr 12, 2021 at 17:45
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    $\begingroup$ It's not even obvious to me who is docking to whom :-D $\endgroup$
    – Jörg W Mittag
    Commented Apr 12, 2021 at 18:27
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    $\begingroup$ I think it becomes a mutual affair at some point $\endgroup$
    – Tristan
    Commented Apr 12, 2021 at 18:29
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I can think of one reason to try to get a Starship Booster into orbit, even stripped of heat tiles, landing legs etc.

Such a large hull in orbit could act as a high-capacity supertanker for Starship missions to the Moon and beyond.

It could be topped off at a different cadence to Lunar Starship missions - say taking surplus fuel from Starship Starlink launches and such before they return to earth.

Once full, it would be able to tank (multiple) Starships bound for beyond orbit missions.

Or, once refuelled, re-mount a Mars Starship on the non-flamey end and send the whole caboodle to the Red Planet so that there would be a tanking station in orbit there as well.

A fully fuelled Booster/Starship stack travelling to Mars orbit would allow Starship to descend to the surface with only sufficient fuel load-out to return to the orbiting Booster tanker for refuelling for the journey home.

So, if it is technically possible to get a Booster into orbit, sans legs, tiles, and fins, it might have significant utility once there.

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    $\begingroup$ A fully fueled Booster/Starship stack travelling to Mars orbit will need numerous refueling for both Super heavy and Starship. SH is planned to have 30 sea level Raptors which is big waste for Mars transit. Using less vacuum type Raptors will be much more efficient. If you want send supertanker to Mars orbit, why simply not use Super heavy to launch Starship super tanker without legs, fins and TPS, which stay in Mars orbit. Same like with planned Moon Starship supertanker, if you connect volume of all tanks with payload bay volume you can get even more capacity for propellant than SH has. $\endgroup$
    – David Cage
    Commented Jul 16, 2021 at 19:52
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    $\begingroup$ Edit : Sending Starship supertanker to Mars orbit may still require some refueling in LEO after Super heavy launch it into orbit. But hard to say how many if you don't know exactly how much you can save with no needing legs, fins and TPS and not needing propellant for landing on Mars. $\endgroup$
    – David Cage
    Commented Jul 16, 2021 at 20:34
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    $\begingroup$ related: How could Starship “deep space variants” improve payload performance by “orders of magnitude” (Elon Musk)? $\endgroup$
    – uhoh
    Commented Jul 16, 2021 at 22:10
  • $\begingroup$ On top of not having vacuum-optimized engines, a Superheavy booster would be extremely overbuilt as an orbital boost stage. You're looking at a huge amount of engine and structure mass that's not needed for that purpose. It also lacks the header tanks for long-term propellant storage, or the delta-v to get itself into Mars orbit, let alone get there with enough propellant for Starship to return. And even if you somehow got it there, Starship is being designed for 100-150 t of landing payload: even if that was all propellant, it wouldn't be enough to get back to Mars orbit. $\endgroup$
    – Christopher James Huff
    Commented Jul 23, 2021 at 23:57
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No way to make the booster go into orbit unless you remove starship and still make it fly correctly, you would also lose alot of fuel during launch. A better option is just have a very large starship with no flaps or heat shield and use that as a fuel depot. Wouldn't have to change the design of the booster then.

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