Quote from: Robotbeat on 08/23/2019 12:44 pmBut 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.
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.
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.
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.
Quote from: Lemurion on 08/24/2019 06:14 pmPersonally 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.
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...
Quote from: frederickm17 on 08/24/2019 09:19 pmIn 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. ...
Quote from: frederickm17 on 08/24/2019 09:19 pmIn 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.
Quote from: laszlo on 08/25/2019 01:14 amQuote from: frederickm17 on 08/24/2019 09:19 pmIn 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...
Quote from: AJW on 08/24/2019 03:53 amWith 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.
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.
Quote from: BZHSpace on 08/24/2019 09:32 amQuote from: Robotbeat on 08/24/2019 05:13 amQuote from: AJW on 08/24/2019 03:53 amWith 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.
Quote from: Robotbeat on 08/24/2019 05:13 amQuote from: AJW on 08/24/2019 03:53 amWith 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 ?
Quote from: DJPledger on 08/23/2019 08:50 pmQuote from: Robotbeat on 08/23/2019 12:44 pmBut 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...
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...
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.