Author Topic: Should Starship have a third stage for single-launch high-energy trajectories?  (Read 70237 times)

Offline rakaydos

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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.

https://twitter.com/elonmusk/status/1094793664809689089
Tweet Content  This will sound implausible, but I think there’s a path to build Starship / Super Heavy for less than Falcon 9

and

March 5th 2020 Updates:  Boca Chica, Starship and Raptor progress

Lots of info from interviewing Elon at BC in this great article:

https://arstechnica.com/science/2020/03/inside-elon-musks-plan-to-build-one-starship-a-week-and-settle-mars/

Some choice quotes below, lots more detail & background in the article:

Quote
All told, the company added 252 people to its South Texas Launch Site on that Sunday and Monday. It doubled the workforce, just like that, to more than 500 workers.

“It’s what you might call the thrust puck— there’s an inverted cone where we mount the three sea-level engines.”
“It’s such a dumb design. It’s one of the dumbest things on the whole rocket because it’s heavy, expensive, and unreliable.”

SpaceX is designing its factory here to build a Starship every 72 hours.

As of Saturday, since manufacturing operations began in Boca Chica about 11 months ago, the company has built 50 barrels. But the process is accelerating. The company can now make two barrels a day, and it aims to reach a production cadence of four barrels a day.
 
The current process for building a pressure dome takes about a week

Musk has challenged his team to find ways to go faster, to cut production time, and to improve weld qualities. […] And they think they’re close to a solution for dome welding with a tool called a “knuckle seamer.”

SpaceX’s stretch goal is to build one to two Starships a week, this year, and to pare back construction costs to as low as $5 million each.

After this [20km hop], Musk has set an aspirational goal of flying an orbital mission— maybe with SN5 or SN6, he really doesn’t know—before the end of 2020.

“Like, we’re on Raptor engine 23 or something, Maybe 24. It’s lighter, cheaper, better in almost every way than Raptor version one, which sucked and blew up, basically. One of about six or seven Raptors that blew up, I’ve lost count.”

Offline ETurner

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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.
Here’s a cutaway diagram of an aircraft of comparable size. It’s immensely more complicated than Starship:
https://www.flickr.com/photos/27417638@N07/7421912866/in/set-72157630241248940

Raptors are the most complex parts, but are cheap by aircraft-engine standards -- the list price for a single turbofan engine is about $30 million.
https://en.wikipedia.org/wiki/General_Electric_GE90
« Last Edit: 06/11/2021 07:39 pm by ETurner »

Offline RotoSequence

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I don't think the marginal cost of Starship operations has anything to do with theoretical delta-V capabilities of launch vehicle and payload combinations  ???

Offline Twark_Main

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An expendable custom version will be much more expensive

Not really.

The build instructions are the same as the expendable custom version of Falcon 9 that we've all seen -- SpaceX just "forgets" to add parts like legs and fins. For Starship they can also "forget" to add the heat shield.
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Offline Twark_Main

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I don't think the marginal cost of Starship operations has anything to do with theoretical delta-V capabilities of launch vehicle and payload combinations  ???

The question is "should Starship have a third stage?"

Hard to answer that question without comparing it to other strategies for sending payloads on high-energy trajectories.
"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 Alberto-Girardi

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.

IMO we can forget about hypergolics due to toxicity (higher costs) and low Isp. I think we can also delete kerosene-based upper stages, because of low Isp. As you say getting a Centaur or a EUS will be difficult. But if using a 3 stage turns out to be better ULA may prefer to partially join their competitor instead of risking to lose nearly everything.
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Offline groundbound

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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.

One additional point you missed is opportunity cost. Especially in the first few years, the number of annual launches will not be infinite. If there are any other launch customers on the manifest, conducting a refueling program of 8 launches or more may push other customers later in the schedule.

I can believe that they will get thousands of launches per year some day, but there are operational issues that will take a long program of continual improvements to get there.

Even so, the winds of the economic forces involve blow very heavily against one-off special solutions.

Offline Coastal Ron

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I don't think the marginal cost of Starship operations has anything to do with theoretical delta-V capabilities of launch vehicle and payload combinations  ???

The question is "should Starship have a third stage?"

Hard to answer that question without comparing it to other strategies for sending payloads on high-energy trajectories.

Exactly.

The simple solution is to use modular "boosters" or "tugs" that can be ganged as needed to provide the energy required. The Starship (or other launchers too) would launch the booster/tugs before the payload is launched, then they all meet up in orbit.

No need for a special Starship, just use a regular one.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline 1

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None of y'all are thinking like Spacex.

SpaceX would be perfectly happy to develope a third stage if someone else pays them to do so. Less so otherwise; I'd imagine.

And let's not forget that if Spacex does indeed achieve it's primary goals, it could potentially offer some very exotic launch options, such as refeuling an expendable starship and then doing the final departure burn from Martian orbit.

Anyway, back in the the real world, I would very much hesitate to say that they "should" do anything that does not at least indirectly help them obtain their primary goal; which is Mars and not anything higher energy.


Offline Twark_Main

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None of y'all are thinking like Spacex.

SpaceX would be perfectly happy to develope a third stage if someone else pays them to do so. Less so otherwise; I'd imagine.

And if there's a cheaper way where SpaceX doesn't have to develop the third stage to achieve the same performance, they'll do that and just take the money. :D

And let's not forget that if Spacex does indeed achieve it's primary goals, it could potentially offer some very exotic launch options, such as refeuling an expendable starship and then doing the final departure burn from Martian orbit.

Has anyone done the math on this? ISTM that Mars launch is at a disadvantage due to Oberth losses, because Mars has a shallower gravity well and at 1.5 AU it's higher in the Sun's gravity well.

Anyway, back in the the real world, I would very much hesitate to say that they "should" do anything that does not at least indirectly help them obtain their primary goal; which is Mars and not anything higher energy.

True, but we can say that SpaceX definitely won't do it if there's a cheaper way to get the same C3.
« Last Edit: 06/12/2021 07:52 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 RotoSequence

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What percentage of the launch market involves payloads that would actually benefit from a third stage for high energy trajectories, anyway? I don't imagine its a number big enough to justify much in the way of investment in dedicated high energy stages specifically for Starship.

Offline joek

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What percentage of the launch market involves payloads that would actually benefit from a third stage for high energy trajectories, anyway? I don't imagine its a number big enough to justify much in the way of investment in dedicated high energy stages specifically for Starship.

A very small percentage; they are all nationally funded science missions. One reason I pushed back in a previous post to the assertion that SS needs a native high energy stage.

p.s. Ed Kyle's https://www.spacelaunchreport.com/ has a breakdown; have not run the numbers to determine %, but obviously low for deep space (high C3).
« Last Edit: 06/12/2021 08:47 am by joek »

Offline Robotbeat

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It’s hard to beat a Star motor for this sort of thing.
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Offline Twark_Main

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Just by lightening Starship to 40 tonnes (per Musk's tweet), it can kick a 20 tonne payload with a delta-v of 11.3 km/s, or 5 tonnes at 12.4 km/s. If the charts posted by Pipcard are accurate, this has superior performance in both axes (C3 and payload) vs a Centaur or F9 second stage.
« Last Edit: 06/12/2021 04:20 pm 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 DreamyPickle

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One "real" high-energy payload Europa Clipper: it's currently set to launch of Falcon Heavy but due to performance limitations the trip will take several years longer than a direct trajectory on SLS. The SLS was rejected for issues of vibration and uncertain availability but cutting years of travel time and gravity assists is something that makes a large difference.

Here's a paper with SLS capabilities to the outer solar system: https://baas.aas.org/pub/2021n4i451/release/1 including stuff like extra upper stange on top of the EUS. They are far higher than an expendable Falcon Heavy.

If the math of that graph posted higher up the thread is correct then a fully refueled starship is enough for 20 tons direct to Saturn but performance collapses to zero for a direct launch to Neptune.

Offline wannamoonbase

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It’s hard to beat a Star motor for this sort of thing.

Agreed, there are plenty of solid fueled upper stages that would do just nicely.

It would be a heck of a thing if the kick stage cost more than the Starship flight to LEO.

Liquid Hydrogen is the ultimate high energy fuel, I think there could be a market for SpaceX to have a liquid hydrogen cargo service and on orbit depot.  That could really open up some great deep space missions for Neptune, Uranus orbiters etc.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline spacenut

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What about a large array of Ion engines fueled up with argon or krypton gas to take a payload to deep space.  It might take longer to build up speed, but with almost continuous acceleration, it will get there?  Just launch it out of a cargo Starship.

Or, refuel a cargo Starship in LEO, then swing around the moon, and launch a probe with a solid kick stage or an Ion engine. 

Offline wannamoonbase

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What about a large array of Ion engines fueled up with argon or krypton gas to take a payload to deep space.  It might take longer to build up speed, but with almost continuous acceleration, it will get there?  Just launch it out of a cargo Starship.

Or, refuel a cargo Starship in LEO, then swing around the moon, and launch a probe with a solid kick stage or an Ion engine. 

Why do so much work to send 100 tons of Starship just to get to the moon to deploy a spacecraft with a kick stage?

Keep the 100 tons in LEO.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline spacenut

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What about a large array of Ion engines fueled up with argon or krypton gas to take a payload to deep space.  It might take longer to build up speed, but with almost continuous acceleration, it will get there?  Just launch it out of a cargo Starship.

Or, refuel a cargo Starship in LEO, then swing around the moon, and launch a probe with a solid kick stage or an Ion engine. 

Why do so much work to send 100 tons of Starship just to get to the moon to deploy a spacecraft with a kick stage?

Keep the 100 tons in LEO.

Depends on the mass of the payload.  Leaving the moon area would take less delta V than leaving LEO.  The Starship could return to earth after deploying a deep space probe swinging by the moon. 

Also, a solid upper stage might have vibration issues like the SLS, or too many G forces on acceleration. 
« Last Edit: 06/12/2021 02:08 pm by spacenut »

Offline Twark_Main

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If it's a Raptor-based kick stage using methalox, it can be launched empty (=larger size possible) and filled on-orbit. "Just" add fill lines from the main tanks.

If any plan is going to work, it'll be that one IMO.
« Last Edit: 06/12/2021 04:28 pm 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

 

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