Author Topic: MCT Speculation and Discussion Thread 4  (Read 566621 times)

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2320 on: 06/15/2016 04:55 PM »
How about the reusable RaptorVac S2 first, likely 5+ meters, with a later Falcon-Raptor high performance S1 to replace the F9 Merlin cores? That eliminates duplicious ground systems and possibly having 2 launchers.

Musk is saying MCT will launch for Mars in 2022 if everything works right. I don't see any time to develop a ~5 meter Raptor booster before that...
Unless they've already started building it.

But I agree the 2022 date for MCT (which we assume is basically the full MCT, right?) does make such a stage less likely (ESPECIALLY a booster).
« Last Edit: 06/15/2016 04:55 PM by Robotbeat »
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Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2321 on: 06/16/2016 01:15 PM »
I think it's pretty clear that they have started building Raptor. They might have started building a ~5m upper stage for it since that could go on FH pretty easily and maybe even on F9.

But building a Falcon Heavy replacement booster, before FH even flies? I don't think so. MCT has a pretty clearly defined set of goals including super heavy lift, and building another heavy lift booster doesn't help achieve those in the very tight timeframe Musk is shooting for.

Offline JamesH65

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Re: MCT Speculation and Discussion Thread 4
« Reply #2322 on: 06/16/2016 01:51 PM »
I think it's pretty clear that they have started building Raptor. They might have started building a ~5m upper stage for it since that could go on FH pretty easily and maybe even on F9.

But building a Falcon Heavy replacement booster, before FH even flies? I don't think so. MCT has a pretty clearly defined set of goals including super heavy lift, and building another heavy lift booster doesn't help achieve those in the very tight timeframe Musk is shooting for.

It's quite common to be designing and test building your next version of <whatever> before the current version hits the market...Especially true of things that have a long development time.

Online MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2323 on: 06/16/2016 02:31 PM »
IAC 2016 PLENARIES AND HIGHLIGHT LECTURES

Tuesday September 27
13:30-14:30 CDT = 14:30-15:30 EDT
Colonizing Mars -- A deep technical presentation on the space transport architecture needed to colonize Mars (SpaceX late breaking)

Is this in addition to the previously known Friday 8:30-10:30 CDT = 9:30-11:30 EDT session?

Looks like they have a session on "The Saturn system as a natural laboratory to investigate the emergence of biology" from 8:30 - 9:30 Friday now.

Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2324 on: 06/16/2016 02:34 PM »
I'm not so sure the engines can't be protruding through a heatshield (more or less like a Falcon 9 first stage), assuming they have sufficient propellent to run at least some of the engines with enough power to use the supersonic retropropulsion effect to push the shock wave far enough out to reduce aero heating. For Mars decent that is probably easier since the atmosphere is thinner in the first place (less need for a heat shield), for Earth this may be more difficult.

Even if you cant the engines around the heatshield (more like Crew Dragon than Falcon 9 first stage), if you drop off the cargo as one giant module, you still have a problem, since you just dropped your (Mars) heat shield you need a second, more massive (at least you could save mass on the Martian one) Earth heat shield, which is above your engine nacelles. Alternatively you might put your engines far up the side of the vehicle to be above the Earth return heat shield, but now you need to shield the sides of the cargo from the engine exhaust and so on.

Vacuum nozzles cannot take the heat loads or the aero loads to do this during interplanetary entries. I don't think Falcon stage 1 nozzles could either. Falcon reenters at Mach 5. MCT will enter at Mach 25, with 25 times the energy dispersion and 125 times the heat load. Even if you push the shockwave away the plasma prevents any real radiative cooling. Retracting the vac bells can help with aero loads, but I don't believe they will survive the heat loads without an ablative shield.

SpaceX's approach with Dragon is to poke the engines around the heatshield and use very underexpanded but short and sturdy nozzles. That's good for reentry and landing, but terrible for high ISP in vacuum. The only way I can see to get high ISP with engines that can perform EDL is to move the engines behind the heatshield (or the shield in front of the engines). That gets complex in a hurry, many times more so than RL-10B nozzle extension, and I can't wait to see how they plan to solve all the movement-related issues.

Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2325 on: 06/16/2016 02:53 PM »
I think it's pretty clear that they have started building Raptor. They might have started building a ~5m upper stage for it since that could go on FH pretty easily and maybe even on F9.

But building a Falcon Heavy replacement booster, before FH even flies? I don't think so. MCT has a pretty clearly defined set of goals including super heavy lift, and building another heavy lift booster doesn't help achieve those in the very tight timeframe Musk is shooting for.

It's quite common to be designing and test building your next version of <whatever> before the current version hits the market...Especially true of things that have a long development time.

This would be developing and testing TWO versions ahead, since they have clearly been working on BFR for a while also. I don't see any reason to build a booster that will at best marginally outperform Heavy and will be superseded by BFR within ~2 years unless they plan to fly it concurrently with BFR... which seems unlikely.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2326 on: 06/16/2016 03:15 PM »
This would be developing and testing TWO versions ahead, since they have clearly been working on BFR for a while also. I don't see any reason to build a booster that will at best marginally outperform Heavy and will be superseded by BFR within ~2 years unless they plan to fly it concurrently with BFR... which seems unlikely.

They may want to fly BFR only to equatorial destinations. Which is most but not all of Falcon payloads. They will want to go fully reusable on all their flights. They may want to switch to all methane and Raptor. That would need a new first stage replacing Falcon. Not a priority but in the pipeline, I suspect. Especially if they build a wider upper stage.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2327 on: 06/16/2016 06:29 PM »
On MCT speculation, I'm sure I read quotes by Musk saying he advocates fast transit times 102 or 100 days or something.  Anyone know a source of such statement(s) or do I have a false memory?
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2328 on: 06/16/2016 06:38 PM »
On MCT speculation, I'm sure I read quotes by Musk saying he advocates fast transit times 102 or 100 days or something.  Anyone know a source of such statement(s) or do I have a false memory?

I think he mentions 3-month transits in this recent interview:

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2329 on: 06/16/2016 06:55 PM »
Is that supposed to be a drawing of Musk, because it looks terrible if it is.

Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2330 on: 06/16/2016 07:02 PM »
They may want to fly BFR only to equatorial destinations. Which is most but not all of Falcon payloads.

If they only launch out of Boca Chica, perhaps. If they hit anywhere near their reusability and cost targets for BFR/BFS it should be cheaper to launch (over the life of the vehicle) than Falcon is now, with 10x the performance. I think all GTO and BEO payloads will fly on BFR/BFS. Virtually all other payloads are small enough for Falcon 9 to easily RTLS, up to 15 to 20t to LEO with a reusable Raptor US. The slice of market that a 9-Raptor booster fits is very small and is firmly wedged between F9 and BFR.

Quote
They will want to go fully reusable on all their flights.
Which would be possible with a Raptor upper stage on F9 or FH, although Raptor might be easier to reuse than Merlin since methane burns cleaner. The only real case for a ~5m booster that I can see is if kerolox turns out to be a significant pain to reuse compared to methalox, or if its a USEFUL part of the MCT architecture.

Quote
They may want to switch to all methane and Raptor. That would need a new first stage replacing Falcon. Not a priority but in the pipeline, I suspect. Especially if they build a wider upper stage.
Flying a mix of kerolox and methalox is entirely viable long term IMO. Almost every launch provider has used higher energy fuels for upper stages for years, so these aren't new problems. Handling RP-1 is probably easier than LCH4.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2331 on: 06/16/2016 07:58 PM »
They may want to switch to all methane and Raptor. That would need a new first stage replacing Falcon. Not a priority but in the pipeline, I suspect. Especially if they build a wider upper stage.
Flying a mix of kerolox and methalox is entirely viable long term IMO. Almost every launch provider has used higher energy fuels for upper stages for years, so these aren't new problems. Handling RP-1 is probably easier than LCH4.

I agree that a mix of kerolox and methanlox is viable. But building only one type of main engine, the Raptor, has its advantages. It is possible they want to switch completely, especially now that Raptor is not that huge.

If they want to serve all orbits, they would need a west coast launch pad.

If a competitor like ULA or Blue Origin builds a fully reusable system that has a lower launch cost than BFR/MCT they may need that methane first stage too.


Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2332 on: 06/16/2016 08:40 PM »
A switch to only producing Raptor is possible if Falcon is switched to using 5 Raptor engines on first stage AND the Raptor has a very deep throttle capability allowing it to land on the center engine.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2333 on: 06/16/2016 08:46 PM »
A switch to only producing Raptor is possible if Falcon is switched to using 5 Raptor engines on first stage AND the Raptor has a very deep throttle capability allowing it to land on the center engine.
But you really might as well use a wider tank and go for more engines, like 7 or 9, to get at least FH performance. Still substantially less work than BFR to turnaround, but also allows full RTLS (no droneship needed) for almost all commercial payloads.
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Online Doesitfloat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2334 on: 06/16/2016 08:50 PM »
If they keep the Merlin based Falcon family of rockets. and they add the raptor based completely reusable rocket.
 Spacex would have 2 independent rocket systems.
Then all launches (US) could be Spacex. ;)

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2335 on: 06/16/2016 09:03 PM »
But you really might as well use a wider tank and go for more engines, like 7 or 9, to get at least FH performance. Still substantially less work than BFR to turnaround, but also allows full RTLS (no droneship needed) for almost all commercial payloads.

I always liked the idea of 7. It allows an equal spacing of all engines. It may not reach full Falcon Heavy capacity but for everything too big there would be BFR.

Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2336 on: 06/16/2016 10:08 PM »
5 Raptors won't fit under a 3.7m Falcon (need about 4.5m), and anything bigger won't be able to use all the Falcon infrastructure. Unlike a 5m US, a 5m booster would be rather hard to transport except via ship. In a lot of ways, it would have BFR heritage instead of Falcon's.

It's certainly a possibility, but I just don't see the need when F9 (or FH) can RTLS anything not worth launching BFR for.

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2337 on: 06/18/2016 01:52 AM »
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2338 on: 06/18/2016 03:01 PM »
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?

Unknown as nobody has done any.  {EDIT: see refutations in following posts}
Hydrolox would be the toughest mainly because of hydrogen's tiny atoms finding leaks really well and its need for really low temperature.
Hypergolic might be the easiest...until you accidentally started it up.
« Last Edit: 06/18/2016 04:55 PM by philw1776 »
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Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2339 on: 06/18/2016 03:13 PM »
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?

Unknown as nobody has done any.
Hydrolox would be the toughest mainly because of hydrogen's tiny atoms finding leaks really well and its need for really low temperature.
Hypergolic might be the easiest...until you accidentally started it up.

ISS is refueled by Progress.

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