Ars technica: “ SpaceX releases a Payload User’s Guide for its Starship rocket”

[ecarfan]

I don’t know if this topic would be better placed in an existing thread, so @Grendal feel free to move it.

SpaceX releases a Payload User’s Guide for its Starship rocket

When “the first and second stages reserve enough fuel to return to Earth. In this configuration, the rocket can deliver more than 100 metric tons to low-Earth orbit and 21 tons to geostationary transfer orbit...The killer application, however, is the potential to refuel Starship in low-Earth orbit with other Starships, enabling transportation deeper into the Solar System for 100 tons or more.”

I think we already had this basic information, so I suspect that SpaceX publicly released the Starship “Payload User’s Guide” to put pressure on NASA and Congress to more seriously consider Starship for future missions. Of course Starship has yet to reach orbit, so this is classic Elon over-confidence!

“The user's guide also provides information about the size of the payload fairing in the cargo configuration of the vehicle, with a width of 8 meters and an extended volume capable of encompassing payloads as long as 22 meters. This would be, by far, the largest usable payload volume for any rocket that exists today or is in development.”

The Shuttle payload bay was 18.3 x 4.6 meters. And of course the rockets flying today provide nothing comparable to that. Starship’s cargo capacity will be extraordinary.

But first it has to reach orbit!

 

[Grendal]

If it's fully reusable then it will drive costs down significantly even if it ends up less than what Elon hopes. Given time, it will be improved just as the Falcon 9 improved. Elon and SpaceX just has to do it once or twice and then everything changes. It's interesting that the big trick here is the rocket and not the engines. Usually you build the engine and the rocket design is a natural result of what the engines need. In this case, you need to build the reusable rocket able to do all the things it needs to do in the environments it will encounter. The payload will be the end result of what the finalized rocket design becomes. As we've seen, it's been through four to six iterations so far. I have no doubt Elon and SpaceX will get there. They are narrowing it down.

So I agree that this is more of a political move than a real "payload user's guide." NASA or the military will hopefully throw some more money at SpaceX to help with the development. The current NASA administration likes to hear about big goals.

 

[ecarfan]

Elon and SpaceX just has to do it once or twice and then everything changes.

Agreed, as soon as Starship achieves orbit and successfully returns to its LZ that will really impact NASA’s plans.

It would be fantastic if SpaceX can make that happen this year. We all need some good news to boost our spirits!

 

[bxr140]

Most interesting for me is the very modest 21T to GTO relative to active and in-development launchers that are much smaller. That's a 5x-7x ratio to Starships LEO capacity, where most other systems are ~2-3x. Certainly if the price and launcher availability are there it won't matter much, but its interesting that Starship is much better suited for LEO than GTO.

Speculating here: Certainly there's a delta-v vs. mass capability element, but the 'low' GTO capability suggests that Starship may also need fuel to drop out of GTO before actually hitting the atmosphere.

Approximate GTO/LEO capabilities, for reference:
Delta Heavy: 14/29
Ariane 5/6: 11/21
Blue: 13/45
Vulcan: 18/37

 

[ecarfan]

the 'low' GTO capability suggests that Starship may also need fuel to drop out of GTO before actually hitting the atmosphere.

Thanks, I think you have zeroed in on an important issue. Of course all the other launchers you listed are not concerned about re-entry from orbit since they are discarded/trashed/not reusable.

Once we know the advertised price of a Starship launch to LEO/GTO than the launcher comparisons will get really interesting!

 

[Grendal]

It's interesting that Starship is much better suited for LEO than GTO.

Speculating here: Certainly there's a delta-v vs. mass capability element, but the 'low' GTO capability suggests that Starship may also need fuel to drop out of GTO before actually hitting the atmosphere.

Very possible. Keep in mind that Starship is supposed to be refueled in orbit. Once refueled it is then supposed to go and do whatever is needed in the solar system. So that is another major hurdle for Starship: making In Orbit Refueling a reality and easy.

 

[larmor]

How does the starship payload capacity and dimensions compare to the space shuttle?

 

[ecarfan]

How does the starship payload capacity and dimensions compare to the space shuttle?

From my post of yesterday...

“The user's guide also provides information about the size of the payload fairing in the cargo configuration of the vehicle, with a width of 8 meters and an extended volume capable of encompassing payloads as long as 22 meters. This would be, by far, the largest usable payload volume for any rocket that exists today or is in development.”

The Shuttle payload bay was 18.3 x 4.6 meters. And of course the rockets flying today provide nothing comparable to that. Starship’s cargo capacity will be extraordinary.

 

[bxr140]

Thanks, I think you have zeroed in on an important issue. Of course all the other launchers you listed are not concerned about re-entry from orbit since they are discarded/trashed/not reusable.

You missed the nuance.

Starship is 100-150T capacity to LEO. That's basically ~3-5x capacity of existing and pipeline launchers and that already factors in the fact that Starship is reusable and must maintain capability (propellant, thermal, etc.) to re-enter. So at least on the first order one would expect similar 3-5x capability over the other launchers, but in fact that number is only 1.X.

While a small difference in those ratios could be accepted, there's got to be some additional variable beyond the already normalized re-entry aspect to make the GTO ratio so different than the LEO ratio. Having to carry propellant to first drop from GTO to LEO before dropping from LEO into the atmosphere is the only thing I can think of that would make such a huge difference.

The obvious follow-on implication is that all starship flights (lunar, martian, etc.) must first enter LEO before returning to earth. That's different than Apollo, which dumped right into earth's atmosphere from translunar. I'm not sure that's what's been advertised for starship though...?

Keep in mind that Starship is supposed to be refueled in orbit.

For sure. The 21T is non-refueled capability and so is apples-to-apples with the other launchers.

 

[Cosmacelf]

Given starship reusability, it really doesn't matter what it's GTO payload is. Fuel costs just don't matter, it is vehicle costs that matter and Starship will be far, far less than anything else since it'll be reusable.

BTW, cute cameo on last night's Westworld Season 3, episode 4, we saw two falcon nine cores landing and one taking off in the distance while a main character casually strolls by. Given this takes place 40 years from now, those must have been ULA rockets

 

[bxr140]

Given starship reusability, it really doesn't matter what it's GTO payload is. Fuel costs just don't matter, it is vehicle costs that matter and Starship will be far, far less than anything else since it'll be reusable.

Yeah, covered that already.

The technical discrepancy still remains and it would be very interesting to understand the major driver, be it some nuance of Starship (like the mission profile) or some nuance with the person identifying the technical discrepancy.

 

[Grendal]

This is the closest thread for this piece. It all about the payload and getting it somewhere though.
U.S. Transportation Command to study use of SpaceX rockets to move cargo around the world - SpaceNews

 

[hmcgregoraz]

I wonder if this large diff between LEO and GTO would make it worth while for the Geo sat to have essentially it's own third stage to take it from Leo to GTO or even straight to Geo.

 

[bxr140]

I wonder if this large diff between LEO and GTO would make it worth while for the Geo sat to have essentially it's own third stage to take it from Leo to GTO or even straight to Geo.

GEOs already use their onboard propulsion system to go from GTO to GSO. The main roadblock with dropping the satellite off in LEO would be the significantly higher propulsion load (and all the corollary design impacts) on the satellite because of the significantly higher ∆V required to go from LEO to GSO. As it stands, a biprop GEO uses ~half its propulsion load to get from GTO to GSO (much of that is making the inclination turn). Also, electric propulsion would be untenable from LEO to GSO (true GTO to GSO on EP is already 6 months or so, often EP GEO's get injected into a super synch orbit with more energy than GTO to cut down the transfer time), and EP is generally where the industry is headed.

It is conceivable that a high thrust kick stage could be added between Starship and a GEO sat such that Starship can just go to LEO and back (regardless if the satellite has chemical or electric propulsion). But...I don't think we know enough about the seemingly 'less than expected' Starship to GTO performance to really play that one out much farther and ,if we're honest, Starship-to-GTO capability is still way higher than anything else, and nobody's going to be building a Starship-only GEO for probably the better part of a decade...so this is all kind of a moot point anyway.