Author Topic: Should Starship have a third stage for single-launch high-energy trajectories?  (Read 72584 times)

Online Twark_Main

  • Senior Member
  • *****
  • Posts: 3621
  • Technically we ALL live in space
  • Liked: 1878
  • Likes Given: 1187
Could a fully fuelled F9 2nd stage (without the need for fairings) not fit inside the Starship cargo bay? What trajectories can you achieve with say a 10 ton payload if you have a fully fuelled F9 2nd stage in LEO?

Please correct me if I'm wrong, but as far as I know, for a third stage packing Starship, wouldn't the best maneuver involve refueling the ship in LEO, burning to a highly eccentric orbit, and dropping the third stage off for a massive Oberth burn while the Starship returns to Earth?

And then for more delta-v you can refuel two Starships in LEO, burn to the highly eccentric orbit, dump all fuel from Starship 1 into Starship 2, then burn Starship 2 into an even higher orbit, then execute the final Oberth slam. Continue in the obvious manner with 3 or more vehicles. I call this maneuver the "Tanker Slam."

I wrote a calculator here to calculate performance for exactly this type of refueling ladder. The spreadsheet supports fleets of up to 5 vehicles (4 tankers + 1 mission Starship, which can have a different mass than the tankers).

« Last Edit: 06/11/2021 07:35 am by Twark_Main »
"The search for a universal design which suits all sites, people, and situations is obviously impossible. What is possible is well designed examples of the application of universal principles." ~~ David Holmgren

Offline joek

  • Senior Member
  • *****
  • Posts: 4869
  • Liked: 2782
  • Likes Given: 1096
That's why they think the minimum reasonable cost for Starship will be as much as the F9, but not below that.
Not sure who this amorphous "they" is you are referring to. Certainly there are skeptics, but using F9 costs are simply wrong when comparing to SS as it assumes a linear (or worse case, no) progression. In any case, this discussion belongs in other threads in the SpaceX Reusability or somewhere else in this (current) section.

Offline soyuzu

  • Full Member
  • **
  • Posts: 271
  • Liked: 403
  • Likes Given: 215
...
There is a limit for every rocket, Starship included, and adding a third stage can break that limit.

Agree. But that is not an SS issue, it is a payload issue. As payload owner, you have 100-150t delivered to LEO to play with. Knock yourself out (and stop throwing shade at SS because it does not satisfy all payload owner desires).

I don’t think so, just as SpaceX provides equipment handling Methalox at LC-39A for Nova-C (and results in a delay), SpaceX would also be included in the process of integrating a third stage to Starship.

Offline Alberto-Girardi



Also, Starship suffer from high empty mass, even a stripped down expendable version will weights 40t, which is not very efficient when the payload mass is on the order of several tons.

where did you get the 40 t mass? I'm not saying it is wrong.
Ad gloriam humanitatis - For the Glory of Humanity
I want to become an Aerospace Engineer!

Offline Pipcard

  • Full Member
  • ****
  • Posts: 622
  • Liked: 275
  • Likes Given: 130
That's why they think the minimum reasonable cost for Starship will be as much as the F9, but not below that.
Not sure who this amorphous "they" is you are referring to.
If you want me to be more specific, I will say that it is a particular community of people (which I am a part of) who play Kerbal Space Program with the Real Solar System and Realism Overhaul mods (which as you can tell, make the game much more realistic but not as much as professional simulation software), and sometimes like to discuss real-world spaceflight history and current events. The zeitgeist over there right now is one of skepticism about Starship and how it's only practical as an LEO tug unless it has a high energy upper stage.
« Last Edit: 06/11/2021 07:49 am by Pipcard »

Offline soyuzu

  • Full Member
  • **
  • Posts: 271
  • Liked: 403
  • Likes Given: 215


Also, Starship suffer from high empty mass, even a stripped down expendable version will weights 40t, which is not very efficient when the payload mass is on the order of several tons.

where did you get the 40 t mass? I'm not saying it is wrong.

https://twitter.com/elonmusk/status/1111798912141017089?s=21

And it seems to agree with previous analysis on this forum.
« Last Edit: 06/11/2021 07:36 am by soyuzu »

Offline joek

  • Senior Member
  • *****
  • Posts: 4869
  • Liked: 2782
  • Likes Given: 1096
I don’t think so, just as SpaceX provides equipment handling Methalox at LC-39A for Nova-C (and results in a delay), SpaceX would also be included in the process of integrating a third stage to Starship.
From SpaceX SS perspective, it would be payload. No more and no less than any other. Yes, SpaceX would be involved in the process (it is their LV). It would no more be a "third stage" than any number of other payloads which include their own propulsion. Plenty of examples of those launched on a variety of LV's.

Offline joek

  • Senior Member
  • *****
  • Posts: 4869
  • Liked: 2782
  • Likes Given: 1096
It's a particular community of people (which I am a part of) who play Kerbal Space Program with the Real Solar System and Realism Overhaul mods (which as you can tell, make the game much more realistic but not as much as professional simulation software), and sometimes like to discuss real-world spaceflight history and current events. The zeitgeist over there right now is one of skepticism about Starship and how it's only practical as an LEO tug unless it has a high energy upper stage.
High energy upper stage for what? Current conops include cislunar and Mars with standard SS. Again, you have 100-150t to LEO to work with as payload owner. Why does SS need an intrinsic capability beyond that? Those missions are going to be few and far between for the foreseeable future. This attitude that, because SS cannot alone solve all high C3 needs is a canard.

Offline Alberto-Girardi

The graphs are interesting (it will be intersting to see them updated with centaur  V performances),  and a fully fueled SS, like pointed out by soyuzu, can't reach  Pluto with appreciable payload, even for a fly by (note that this is in case of no gravitational assist.).

It all depends on SS cost. If there are a lot of mission to high energy trajectories (which I don't expect soon) a lot of SS will be expanded, and probably those flights will be at loss, that will be offsetted by "normal" launches. But stripping down a SS will take further developemente, and the cost could turn out higher that integrating a kickstage.
Ad gloriam humanitatis - For the Glory of Humanity
I want to become an Aerospace Engineer!

Offline Pipcard

  • Full Member
  • ****
  • Posts: 622
  • Liked: 275
  • Likes Given: 130
It's a particular community of people (which I am a part of) who play Kerbal Space Program with the Real Solar System and Realism Overhaul mods (which as you can tell, make the game much more realistic but not as much as professional simulation software), and sometimes like to discuss real-world spaceflight history and current events. The zeitgeist over there right now is one of skepticism about Starship and how it's only practical as an LEO tug unless it has a high energy upper stage.
High energy upper stage for what? Current conops include cislunar and Mars with standard SS. Again, you have 100-150t to LEO to work with as payload owner. Why does SS need an intrinsic capability beyond that? Those missions are going to be few and far between for the foreseeable future. This attitude that, because SS cannot alone solve all high C3 needs is a canard.
Actually, even if most payloads to go the Moon and Mars and not to Mercury or Jupiter, they still want to minimize the number of refueling launches (ideally wanting single-launch missions) because of aforementioned doubts about Starship's costs as well as doubts surrounding launch cadence/rapid reuse, and because "cryogenic orbital refueling hasn't been tested and proven yet."
« Last Edit: 06/11/2021 08:27 am by Pipcard »

Offline ETurner

  • Full Member
  • ***
  • Posts: 359
  • Liked: 374
  • Likes Given: 387
Can’t we just say that “Starship can carry a third stage as payload”?
This sidesteps the semantic controversy and gives impressive delta V numbers for final, conventional-size payloads.
« Last Edit: 06/11/2021 10:26 am by ETurner »

Online sferrin

  • Full Member
  • ****
  • Posts: 724
  • Utah
  • Liked: 913
  • Likes Given: 773
Can’t we just say that “Starship can carry a third stage as payload”?
This sidesteps the semantic controversy and gives impressive delta V numbers for final, conventional-size payloads.


This.  Just do what the Shuttle did. 
"DARPA Hard"  It ain't what it use to be.

Offline DreamyPickle

  • Full Member
  • ****
  • Posts: 955
  • Home
  • Liked: 921
  • Likes Given: 205
The cost of an expendable version of starship is extremely unclear: even if refueling is as cheap as hoped for you are still expending the vehicle and the Raptors that power it. Can't see this selling for less that $100M.

Adding a third stage would require expensive GSE upgrades depending on the stage. A falcon upper stage would require kerosene fuel but at least everything can be done in-house. A Centaur requires hydrolox and is extremely unlikely to be sold by ULA. Flying the EUS is about as likely. As for hypergolic upper stages nobody seems to sell them in the US, one would have to be developed from scratch. Nobody seems to be selling good vacuum-optimized hypergolic engines either.

The cheapest and easiest option for a high-energy trajectory would probably still be the stripped-down Starship, perhaps with an additional STAR motor for small payloads. Those require zero support and can easily fit inside Starship mass and volume.

My answer to the question in the topic would be NO: SpaceX shouldn't invest in supporting third stages. They can win all likely payload contracts with just refueling.
« Last Edit: 06/11/2021 11:27 am by DreamyPickle »

Offline volker2020

  • Full Member
  • ***
  • Posts: 312
  • Frankfurt, Germany
  • Liked: 323
  • Likes Given: 832
The cost of an expendable version of starship is extremely unclear: even if refueling is as cheap as hoped for you are still expending the vehicle and the Raptors that power it. Can't see this selling for less that $100M.
...

I see no way that a throw away Starship would anywhere near that expensive (even considering including R&D). Pure production cost will be tops 15M, using a best case scenario I more or less end up with around 7M.
Assumptions here, no heat shield, no flaps, no landing gear, simple F9 derived cold gas thrusters, minimal electronics. It is unbelievable what impact mass production has on production costs.

Offline rakaydos

  • Senior Member
  • *****
  • Posts: 2825
  • Liked: 1869
  • Likes Given: 69
The cost of an expendable version of starship is extremely unclear: even if refueling is as cheap as hoped for you are still expending the vehicle and the Raptors that power it. Can't see this selling for less that $100M.


The aspirational numbers are 2 million to refly, and 5 mil to build a new ship, including all 6 raptors on the upper stage and all the fin actuators. SpaceX is aiming to get the cost of each raptor down to half a million dollars or less, or about twice what a merlin currently costs them.

This sounds crazy to someone used to pork- funded, 8-engines-a-year traditional aerospace prices. SpaceX isnt like that.

Offline hplan

  • Member
  • Posts: 83
  • Michigan, USA
  • Liked: 76
  • Likes Given: 13
The cost of an expendable version of starship is extremely unclear: even if refueling is as cheap as hoped for you are still expending the vehicle and the Raptors that power it. Can't see this selling for less that $100M.


The aspirational numbers are 2 million to refly, and 5 mil to build a new ship, including all 6 raptors on the upper stage and all the fin actuators. SpaceX is aiming to get the cost of each raptor down to half a million dollars or less, or about twice what a merlin currently costs them.

This sounds crazy to someone used to pork- funded, 8-engines-a-year traditional aerospace prices. SpaceX isnt like that.

When Musk gives eye-popping numbers like "2 million marginal cost" per flight, one has to remember that that's not the total cost, that's the marginal cost. You still have to add fixed costs.

For example, suppose the Starship development program costs $1.5 billion per year. (Estimate based on 4 years for the Lunar Starship program with a total cost of $6 billion.)

If SpaceX launches 12 times in a year, that's $125 million in fixed costs per launch. Even if SpaceX manages 100 launches in a year, that's $15 million per launch in fixed costs.

Now, maybe development costs shouldn't be considered part of fixed costs. But assuming development is ongoing and they don't lay off much of the development staff, the amount of revenue they'd need in order not to go broke would be $15 million per launch plus marginal costs.

In any case, one must be careful not to confuse marginal costs and total costs. The great value of marginal costs, and the reason Musk thinks that way IMHO, is that total cost approaches that marginal cost when the number of reflights is high and the number of flights per year gets huge, well into the 1000s of flights per year.
« Last Edit: 06/11/2021 01:07 pm by hplan »

Offline rakaydos

  • Senior Member
  • *****
  • Posts: 2825
  • Liked: 1869
  • Likes Given: 69
The cost of an expendable version of starship is extremely unclear: even if refueling is as cheap as hoped for you are still expending the vehicle and the Raptors that power it. Can't see this selling for less that $100M.


The aspirational numbers are 2 million to refly, and 5 mil to build a new ship, including all 6 raptors on the upper stage and all the fin actuators. SpaceX is aiming to get the cost of each raptor down to half a million dollars or less, or about twice what a merlin currently costs them.

This sounds crazy to someone used to pork- funded, 8-engines-a-year traditional aerospace prices. SpaceX isnt like that.

When Musk gives eye-popping numbers like "2 million marginal cost" per flight, one has to remember that that's not the total cost, that's the marginal cost. You still have to add fixed costs.

For example, suppose the Starship development program costs $1.5 billion per year. (Estimate based on 4 years for the Lunar Starship program with a total cost of $6 billion.)

If SpaceX launches 12 times in a year, that's $125 million in fixed costs per launch. Even if SpaceX manages 100 launches in a year, that's $15 million per launch in fixed costs.

Now, maybe development costs shouldn't be considered part of fixed costs. But assuming development is ongoing and they don't lay off much of the development staff, the amount of revenue they'd need in order not to go broke would be $15 million per launch plus marginal costs.

In any case, one must be careful not to confuse marginal costs and fixed costs. The great value of marginal costs, and the reason Musk thinks that way IMHO, is that total cost approaches that marginal cost when the number of reflights is high and the number of flights per year gets huge, well into the 1000s of flights per year.
While true, when looking at "the cost of expending" (and thus replacing) any given launch, marginal prices are where to look. it wont be that cheap, but it will be at least that much more expensive. (not much, relatively speaking, in this case)

Offline DreamyPickle

  • Full Member
  • ****
  • Posts: 955
  • Home
  • Liked: 921
  • Likes Given: 205
The aspirational $2M launch price is for flying a reused vehicle to LEO and back. An expendable custom version will be much more expensive and you need to add something like 6-8x marginal price just for the refueling flights.

Offline rakaydos

  • Senior Member
  • *****
  • Posts: 2825
  • Liked: 1869
  • Likes Given: 69
The aspirational $2M launch price is for flying a reused vehicle to LEO and back. An expendable custom version will be much more expensive and you need to add something like 6-8x marginal price just for the refueling flights.

Why customize the expendable version? just expend a normal one for cheaper.

Heck, let's throw in a second expendable, so you refuel mid escape burn.
10 million for expended ships. 32 million for refueling flights, plus 4 million to launch the expended ships. Double everything, because these are asperational numbers. Still under 100 million dollars.

Offline DreamyPickle

  • Full Member
  • ****
  • Posts: 955
  • Home
  • Liked: 921
  • Likes Given: 205
Where did you get the $5M figure for an expended starship coming off the line? This would be extremely cheap even for an aircraft of similar size. It seems "more aspirational" than $2M/flight.

Assuming an expendable starship is comparable to existing expendable stages seems more reasonable. And it's enough to support the point that expending the second stage is cheaper than adding an entirely unrelated third stage.

 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1