Author Topic: After Starship: speculation on ITS, SeaDragonX, other next generation rockets  (Read 114587 times)

Offline Tywin

But anyway, I suspect SpaceX will be tweaking Starship/SuperHeavy for the next decade or two at least. And I do think they'll consider a carbon fiber Starship again eventually.
SpaceX will never go back to CF for future SH/SS systems as they have learned their lesson on that. The TPS requirements for CF more than outweigh the mass advantage over stainless steel. A CF SH/SS will have a higher dry mass than a stainless steel one due to all the TPS needed on the CF one.

Never is a big word...with the investment are making in CF for other industries, is possible the price of this materials, go really down in a future...
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Offline frederickm17

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Personally I don't see SpaceX going to space-to-space designs unless they start using a propulsion system that restricts them from landing. The delta-v advantage of aerobraking is so great that it's going to take a lot for SpaceX to give it up, and once you're designing the ship for aerobraking it's pointless to stop at aerocapture without going for a landing. That doesn't rule out future designs involving magnetoshell aerocapture and either nuclear or anti-matter propulsion, but until those or similar technologies mature SpaceX is likely to stick with surface-to-surface.

As for larger Starship successors, I think that's an obvious next step but I wouldn't be surprised at all if SpaceX sticks to 30-40 engine clusters for the foreseeable future. One of the strengths of Starship, and Falcon, is the engine commonality with both upper and lower stages using the same engine. The catch with this approach is that if you combine it with a reusable upper stage and propulsive landing the minimum thrust per engine becomes as important as the maximum.

Once you're constrained by the requirement to throttle low enough for landing (especially an empty upper stage) while maintaining engine commonality between upper and lower stages, going with clusters of small engines becomes your only viable choice.

I agree SpaceX probably wont be involved in space-to-space vehicles. I was thinking very long term in the process of becoming a spacefaring civilization and what that will require. A significant colony on any body other than earth will require a ship that can carry more than ~100 people.

In the mean time, SpaceX have cornered the market for reusable ships that will be the workhorses for taking cargo and people to space and back. SpaceX should continue to push that tech forward, and Starship is doing exactly that. Starship has been designed from the beginning to be a "ferry" between earth and space, as well as the transport to other locations in the solar system, which is SpaceX's stated purpose, and Starship's design is using the most advanced technology currently available. I don't think we will see a next generation ship for quite a long time, as there is a lot that can be done to perfect Starship and make it the most reliable it can be by achieving a synergy between the current tech and the constraints of physics. I would be surprised if we saw a significant departure from this architecture until there is a major breakthrough in engine technology.
« Last Edit: 08/24/2019 10:06 pm by frederickm17 »

Offline rakaydos

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I'm liking the suggestion of Antiproton capture transfer ship with magnetic aerocapture.

Park it in a Van Allen belt between synod's to refuel, bring it out before loading it with cargo.

Offline Oli

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Personally I don't see SpaceX going to space-to-space designs unless they start using a propulsion system that restricts them from landing. The delta-v advantage of aerobraking is so great that it's going to take a lot for SpaceX to give it up, and once you're designing the ship for aerobraking it's pointless to stop at aerocapture without going for a landing. That doesn't rule out future designs involving magnetoshell aerocapture and either nuclear or anti-matter propulsion, but until those or similar technologies mature SpaceX is likely to stick with surface-to-surface.

I'm not aware of any reusable TPS that can handle reentry from Mars. Refueling in Mars orbit or nuclear thermal are good alternatives to aerocapture.

Offline livingjw

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Personally I don't see SpaceX going to space-to-space designs unless they start using a propulsion system that restricts them from landing. The delta-v advantage of aerobraking is so great that it's going to take a lot for SpaceX to give it up, and once you're designing the ship for aerobraking it's pointless to stop at aerocapture without going for a landing. That doesn't rule out future designs involving magnetoshell aerocapture and either nuclear or anti-matter propulsion, but until those or similar technologies mature SpaceX is likely to stick with surface-to-surface.

I'm not aware of any reusable TPS that can handle reentry from Mars. Refueling in Mars orbit or nuclear thermal are good alternatives to aerocapture.

Active cooling could.

John

Offline Lemurion

Personally I don't see SpaceX going to space-to-space designs unless they start using a propulsion system that restricts them from landing. The delta-v advantage of aerobraking is so great that it's going to take a lot for SpaceX to give it up, and once you're designing the ship for aerobraking it's pointless to stop at aerocapture without going for a landing. That doesn't rule out future designs involving magnetoshell aerocapture and either nuclear or anti-matter propulsion, but until those or similar technologies mature SpaceX is likely to stick with surface-to-surface.

I'm not aware of any reusable TPS that can handle reentry from Mars. Refueling in Mars orbit or nuclear thermal are good alternatives to aerocapture.

Starship's design is based on developing reusable TPS for reentry from Mars. It's a design requirement that it be able to handle direct entry on Mars and then return for a direct Earth reentry without significant refurbishment. Once you take that off the table you're no longer talking about successors to Starship, you're talking about alternatives that are required because the original idea didn't work; that's a completely different conversation.


Offline M.E.T.

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SS is optimized for very cheap access to LEO. Once they have operational, refuelable SS’s on both Earth and Mars, travel to orbit and back from either planet will be relatively cheap. It is the trip between the two planets that requires significantly more velocity, fuel and presents greater heat shield challenges upon arrival.

So how how about building large solar powered laser systems in orbit around Earth and Mars, and then building a large interplanetary laser sail craft to cycle between the two? This craft could be large enough to have a rotating ring for artificial gravity and enough radiation shielding to make the trip perfectly safe for even long durations.

And since the lasers at the two ends provide both acceleration and deceleration, aerobraking is not required at interplanetary velocities.

Starships dock with the sailing ship in orbit and ferry people up and down, with only fuel costs incurred and very little heat shield wear.

Seems like it might be a next step worth considering, once Starships are operational from both planets.
« Last Edit: 08/25/2019 01:15 am by M.E.T. »

Offline laszlo

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In the mean time, SpaceX have cornered the market for reusable ships that will be the workhorses for taking cargo and people to space and back...

Hardly. They have demonstrated technically successful first stage re-use (if you ignore FH cores), with the jury still out on financial success until enough re-use occurs to demonstrate that. They've dabbled with capsule re-use and are experimenting with fairings. They're deliberately expending all second stages.

SpaceX has managed some interesting technical achievements for sure, but they have no more cornered the market than Boeing did with the technologically advanced 247D in the 1930s. That's the problem with next-generation designs -  they may be coming from the competition who's been learning valuable lessons from the pathfinders. In spite of all the high tech features of the DC3 having been pioneered in the 247, the DC3 came from Douglas, not Boeing.

Offline Robotbeat

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In the mean time, SpaceX have cornered the market for reusable ships that will be the workhorses for taking cargo and people to space and back...

Hardly. They have demonstrated technically successful first stage re-use (if you ignore FH cores), with the jury still out on financial success until enough re-use occurs to demonstrate that. ...
Financial success already proven. They're able to achieve a launch rate that would've required a vast increase in factory investment. And they recently won a *Pegasus* class mission for like $50m.
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Offline Lemurion

In the mean time, SpaceX have cornered the market for reusable ships that will be the workhorses for taking cargo and people to space and back...

Hardly. They have demonstrated technically successful first stage re-use (if you ignore FH cores), with the jury still out on financial success until enough re-use occurs to demonstrate that. They've dabbled with capsule re-use and are experimenting with fairings. They're deliberately expending all second stages.

SpaceX has managed some interesting technical achievements for sure, but they have no more cornered the market than Boeing did with the technologically advanced 247D in the 1930s. That's the problem with next-generation designs -  they may be coming from the competition who's been learning valuable lessons from the pathfinders. In spite of all the high tech features of the DC3 having been pioneered in the 247, the DC3 came from Douglas, not Boeing.

I'd say that given SpaceX's approach of optimizing for cost it's very likely indeed that they have managed to make first stage reuse financially successful even if they have yet to fully amortize the costs of developing it. The company is already on record as saying that refurbishment costs less than building a new booster, and SpaceX was able to absorb much of the cost of experiments by using boosters that had already achieved mission success. There's also the fact that most of the upgrades came in the form of increased performance, which enables greater payload capacity in expendable mode as well as reusability.

As for Starship; should it fly on schedule it's going to revolutionize spaceflight and nobody has anything even approximately comparable on the drawing boards. Given the lead time on most rockets, SpaceX should be good for at least a decade before anyone else gets even close to Starship.

Offline frederickm17

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In the mean time, SpaceX have cornered the market for reusable ships that will be the workhorses for taking cargo and people to space and back...

Hardly. They have demonstrated technically successful first stage re-use (if you ignore FH cores), with the jury still out on financial success until enough re-use occurs to demonstrate that. They've dabbled with capsule re-use and are experimenting with fairings. They're deliberately expending all second stages.

SpaceX has managed some interesting technical achievements for sure, but they have no more cornered the market than Boeing did with the technologically advanced 247D in the 1930s. That's the problem with next-generation designs -  they may be coming from the competition who's been learning valuable lessons from the pathfinders. In spite of all the high tech features of the DC3 having been pioneered in the 247, the DC3 came from Douglas, not Boeing.

I may have been slightly over eager with that statement, but perhaps not...I would say that Spacex's successes in reusability go beyond interesting technical achievements. At this point in time, no other company or government can offer anything that resembles the reusability of F9. I would consider that market cornered for now. Fairing experimentation has resulted in successful fairing recovery. Second stage reusability was considered but axed in favor of focusing on the next generation fully reusability vehicle. Regardless, OT...

Offline meekGee

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In the mean time, SpaceX have cornered the market for reusable ships that will be the workhorses for taking cargo and people to space and back...

Hardly. They have demonstrated technically successful first stage re-use (if you ignore FH cores), with the jury still out on financial success until enough re-use occurs to demonstrate that. They've dabbled with capsule re-use and are experimenting with fairings. They're deliberately expending all second stages.

SpaceX has managed some interesting technical achievements for sure, but they have no more cornered the market than Boeing did with the technologically advanced 247D in the 1930s. That's the problem with next-generation designs -  they may be coming from the competition who's been learning valuable lessons from the pathfinders. In spite of all the high tech features of the DC3 having been pioneered in the 247, the DC3 came from Douglas, not Boeing.

I may have been slightly over eager with that statement, but perhaps not...I would say that Spacex's successes in reusability go beyond interesting technical achievements. At this point in time, no other company or government can offer anything that resembles the reusability of F9. I would consider that market cornered for now. Fairing experimentation has resulted in successful fairing recovery. Second stage reusability was considered but axed in favor of focusing on the next generation fully reusability vehicle. Regardless, OT...

If refurbishing a core costs anything similar to fabricating a new one, what is this money being spent on?  Where are the people and machinery and space where this money is spent?

I didn't get the impression that SpaceX has that much capability in Florida...

"Proven" is the wrong goal here.  They're clearly turning the cores around with minimal work, and some people don't want to believe it.  Luckily, they don't have to "prove" it to anyone.


Edit: continued on rapid reusability thread:
https://forum.nasaspaceflight.com/index.php?topic=48280.msg1983745.msg#1983745
« Last Edit: 08/25/2019 02:37 am by meekGee »
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Offline speedevil

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Personally I don't see SpaceX going to space-to-space designs unless they start using a propulsion system that restricts them from landing. The delta-v advantage of aerobraking is so great that it's going to take a lot for SpaceX to give it up, and once you're designing the ship for aerobraking it's pointless to stop at aerocapture without going for a landing. That doesn't rule out future designs involving magnetoshell aerocapture and either nuclear or anti-matter propulsion, but until those or similar technologies mature SpaceX is likely to stick with surface-to-surface.

I'm not aware of any reusable TPS that can handle reentry from Mars. Refueling in Mars orbit or nuclear thermal are good alternatives to aerocapture.

A few moments play with NASAs trajectory browser confirms my memory that transits from Mars can reenter at basically the same velocity as returns from the moon
11.3km/s is common with returns of about 8 months.

Lunar free return is 11.1km/s or so.

Mars entry velocity is considerably lower, and in many cases considerably lower than LEO. (at least for slow transits)


Offline ZachF

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With the 4-6 tankers required for every BLEO SS flight, perhaps the Space Elevator crowd should  focus on systems to deliver Methane.  By redefining the problem, there may be solutions that are not practical with other types of up-mass.  Methane, at least, wants to rise the first few kilometers.
It only takes 4-6 tankers for fast transits to Mars. Can do GTO flights directly. And deep space missions with fewer rankings at lower speed.

This is a bit old, but I paper mathed out some of the performance of Starship based on the number of refills, and a 140t to LEO capability (200t for tanker variant). It should be close to something like this:

0 Refills:
~140t to LEO
~70t to Polar (with dogleg from Cape)
~25t to GTO-1800
~15t to GTO-1500

1 Refill:
~130t to GTO-1800
~110t to GTO-1500
~85t to TLI
~30t to LLO

2 Refills
~140t to GTO-1800
~140t to GTO-1500
~140t to TLI
~100t to LLO
~35t to direct GEO

3 Refills
140t to LLO
100t to direct GEO

4 Refills
140t to direct GEO

5 Refills
~140t to Mars
~70t to Lunar surface

Getting the full 140t to the lunar surface requires refueling in a higher EEO.

If you assume a $15m cost per launch SS tramples everything to every orbit. Is a $120m Ariane 6.4 going to survive if the Starship system can deliver 100 tonnes directly to GEO for $60m?
« Last Edit: 08/25/2019 12:34 pm by ZachF »
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Offline ZachF

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With the 4-6 tankers required for every BLEO SS flight, perhaps the Space Elevator crowd should  focus on systems to deliver Methane.  By redefining the problem, there may be solutions that are not practical with other types of up-mass.  Methane, at least, wants to rise the first few kilometers.
It only takes 4-6 tankers for fast transits to Mars. Can do GTO flights directly. And deep space missions with fewer rankings at lower speed.

On the retanking point I have a simple question : how long it takes to make 4-6 tanking missions ?
Somewhere between twenty minutes and a month.

Twenty minutes is probably achievable if you have enough tankers on hand, and can launch them all at once, and then do rapid rendevous and transfer at propellant transfer rates equal to how fast they fill on the ground.
(I consider this very unlikely).
A month lets you do it with one minimally refurbished tanker, able to launch at best once a day as the tanker comes overhead, with some missed launches and a weeks stand-down.

The easiest thing to do would be just to fill up the first tanker and have it waiting up there fully loaded for you if you want to minimize time.
« Last Edit: 08/25/2019 01:07 pm by ZachF »
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Offline DJPledger

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But anyway, I suspect SpaceX will be tweaking Starship/SuperHeavy for the next decade or two at least. And I do think they'll consider a carbon fiber Starship again eventually.
SpaceX will never go back to CF for future SH/SS systems as they have learned their lesson on that. The TPS requirements for CF more than outweigh the mass advantage over stainless steel. A CF SH/SS will have a higher dry mass than a stainless steel one due to all the TPS needed on the CF one.
Never is a big word...with the investment are making in CF for other industries, is possible the price of this materials, go really down in a future...
SpaceX have realized that CF is not worth the hassle and expense and that it is far cheaper and quicker to build SH/SS out of stainless steel than CF. Stainless steel beats CF on all counts, quicker to build, lot quicker and cheaper to fix mistakes, much lower TPS requirements, and cheaper labour (stainless steel welders and sheet metal workers have lower pay than CF workers as stainless steel is much less specialized than CF). Also much lower tooling costs for stainless steel v CF.

All future SpaceX launch systems after the 9m dia. SH/SS system are highly likely to be made out of stainless steel.

Offline joek

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Never is a big word...with the investment are making in CF for other industries, is possible the price of this materials, go really down in a future...

True, but "possible" and "future" in the same sentence are equally questionable.  Certainly SpaceX keeps "possible" and "future" in mind.  And as we have seen, they explored CF to the point of building significant facilities and fabricating significant test articles--and then abandoned it, likely at no small cost.

That speaks volumes.   Obviously CF is not something they are willing to bet the business on here-and-now or for the foreseeable future.   That said, safe bet that should CF become more cost effective for their needs, it will be in SpaceX's mix of options.

Offline meekGee

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But anyway, I suspect SpaceX will be tweaking Starship/SuperHeavy for the next decade or two at least. And I do think they'll consider a carbon fiber Starship again eventually.
SpaceX will never go back to CF for future SH/SS systems as they have learned their lesson on that. The TPS requirements for CF more than outweigh the mass advantage over stainless steel. A CF SH/SS will have a higher dry mass than a stainless steel one due to all the TPS needed on the CF one.

Never is a big word...with the investment are making in CF for other industries, is possible the price of this materials, go really down in a future...
They went there (CF) and then turned away. They turned away for reasons other than cost. Why would they revisit it if the cost went down?

Stainless is about robustness and resilience. CF is finicky and fragile. CF is much more susceptible to complex failures like internal delamination, that can be caused by fatigue, or changes to the resins due to long term radiation and themal effects, especially in vacuum.

The realization that stainless is also mass-competitive in the larger picture was a master stroke. I think there are zero regrets about this decision.

If I had two ships to choose from on the way back from Mars I'd board the stainless one.
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Offline AC in NC

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Stainless is about robustness and resilience. CF is finicky and fragile. CF is much more susceptible to complex failures like internal delamination, that can be caused by fatigue, or changes to the resins due to long term radiation and themal effects, especially in vacuum.

The realization that stainless is also mass-competitive in the larger picture was a master stroke. I think there are zero regrets about this decision.

After AMOS-6, the thought of CF is frankly frightening.  I cannot imagine trying to build out the hardware needed counting on CF to hold up long term.

Reuse -> Scale -> Stainless is such an exciting breakthrough.  The possibilities of stainless seem limitless.

Offline spacenut

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Right now, anything over 12m in diameter can't be moved by intracoastal waterways in the US as that is the maximum width they can carry.  Sea maybe.  Still 12m is almost double the capacity of a 9m diameter rocket.  So if Starship can do 100 tons to LEO, a 12m one should do 200 tons. 

I think 12m would be the next step.  Would they use 80 some odd Raptors?  Probably not, but may upscale a Raptor to double the thrust or more in order to build a bigger rocket.  I don't see this happening for another 10 years, but stranger things have happened.   

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