Author Topic: Mars Precursor Vehicle  (Read 8736 times)

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #20 on: 06/26/2017 03:39 PM »
How come?  Won't any modifications be made in a backward compatible way?

Since a hypothetical MPV is not defined yet, any interface (mechanical or otherwise) is free to be designed so that it does not interfere with current TEL components for the current US.



It then would be constrained to the same diameter, length and common bulkhead location as the existing second stage.

Offline meekGee

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Re: Mars Precursor Vehicle
« Reply #21 on: 06/26/2017 04:06 PM »
How come?  Won't any modifications be made in a backward compatible way?

Since a hypothetical MPV is not defined yet, any interface (mechanical or otherwise) is free to be designed so that it does not interfere with current TEL components for the current US.



It then would be constrained to the same diameter, length and common bulkhead location as the existing second stage.

If they use the current TEL upper section, then yes, of course.

But if they replace the TEL upper section to accommodate an MPV, that new upper section can be made to still support the existing U/S.  Actually if the two are different sizes, it makes it easier, since the different functional bits of the interface occupy different areas.



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Offline meekGee

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Re: Mars Precursor Vehicle
« Reply #22 on: 06/26/2017 04:08 PM »
For a company that has innovation in its blood, running another fuel up the T/E is peanuts. It's not even a deep cryogen and if the US has no Helium tanks, even better.

For a (hypothetical) company that is used to think in terms of "minimizing change to existing assets/technology" - yeah, it's a high visibility issue.

SpaceX was never shy about changing things.  See the F9 1.1 and 1.2 arguments...

This kind of rhetoric is used a lot to justify any pet idea of a poster; "SpaceX will do this because it's the New Space way!"
So I might as well use it too:
To me, postponing ITS in order to make incremental improvements to Falcon, which a RUS would do, is less 'SpaceX-y' than just going full bore straight to ITS asap.  They'll learn more from ITS failures than RUS failures.

(Replying to a post from the general RUS thread:)

Well SpaceX hasn't started with a 9-engine cryo-propellant reusable top-of-its class booster, right?

It was F1 with an ablative engine, then F1 with a regenerative engine, then F9 1.0, then after only 6 flights it was F9 1.1 and reusability development, then  1.2 with cryo, reusability implementation, and some recovery-based learning, now we're seeing a transition to blocks 4 and 5 (is it 1.3?) which implement lessons learned and more "second round" improvements (e.g. new legs)...

SpaceX has ferocious goals, but to date they pursued them using a gradual implementation.  (!!!)

BFR/BFS was a departure from this pattern.

I do agree with your point though that any "midway step" is also a detour - so it's not a no-brainer.

In order to justify itself, the interim stage must have either A) value in and of itself (like being a reusable commercial constellation sat launcher) or B) have such a low cost-of-failure that overall, it's worth failing in "small scale".
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Offline envy887

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Re: Mars Precursor Vehicle
« Reply #23 on: 06/26/2017 04:14 PM »
RUS, the thing that I am vehemently against, is either a stock stage with methane or a wider one with methane that operates like the existing stage.  There is no point to these configurations.

An mini BFS/ITS as MG describes has some merit but......

a.  It would only operate out of LC-39A
b.  SLC-40 and/or Boco Chica have be up and running smoothly to keep the cash coming
c.  It would be after FH and Dragon 2 are flying smoothly. 
d.  DOD is not going to use F9 or FH for vertically integrated payloads
e.  It won't happen for 2020 because of c & d, unless LC-39B is used.

Actually, I am wrong about a.  It can't operated from 39A.  A mini BFS/ITS would be incompatible with the existing TEL. It would be too disruptive for the existing FH and it would interfere with manned Dragon 2 flights.  Both these are priorities for Spacex.  It would need to go to another pad.

Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #24 on: 06/26/2017 04:16 PM »
Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

They did not place the current HIF in the proper location to allow for this. It is right at the base of the pad incline.

Offline envy887

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Re: Mars Precursor Vehicle
« Reply #25 on: 06/26/2017 04:16 PM »
e.  It won't happen for 2020 because of c & d, unless LC-39B is used.

LC-39B is the SLS pad. Do you know or suspect that something bad will happen to this plan?

It is a multi user pad

Would this be a new HIF and TEL at 39B, or modify a MLP and crawler and use the VAB?

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #26 on: 06/26/2017 04:18 PM »

Would this be a new HIF and TEL at 39B, or modify a MLP and crawler and use the VAB?

whatever works

Offline envy887

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Re: Mars Precursor Vehicle
« Reply #27 on: 06/26/2017 04:22 PM »
Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

They did not place the current HIF in the proper location to allow for this. It is right at the base of the pad incline.

How about a pass-though  with a Y split to the south side. One fork for storing the existing TEL while the new one passes through, and the other fork leading to a new HIF south of the current one?

Offline envy887

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Re: Mars Precursor Vehicle
« Reply #28 on: 06/26/2017 04:22 PM »

Would this be a new HIF and TEL at 39B, or modify a MLP and crawler and use the VAB?

whatever works

So there's no first order issues preventing either option?

Offline JasonAW3

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Re: Mars Precursor Vehicle
« Reply #29 on: 06/26/2017 04:29 PM »

Would this be a new HIF and TEL at 39B, or modify a MLP and crawler and use the VAB?

whatever works

      In theory, couldn't they build a erector specifically for the subscale ITS and booster?  While expensive, I'm not totally certain that there are any technical reasons that it couldn't be done.

      I can see how expensive it would be, but couldn't that be written off as developmental expenses?
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Offline Jim

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Re: Mars Precursor Vehicle
« Reply #30 on: 06/26/2017 04:44 PM »
Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

They did not place the current HIF in the proper location to allow for this. It is right at the base of the pad incline.

How about a pass-though  with a Y split to the south side. One fork for storing the existing TEL while the new one passes through, and the other fork leading to a new HIF south of the current one?

That stops existing launches.  The south end of the HIF is a clean room

Offline envy887

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Re: Mars Precursor Vehicle
« Reply #31 on: 06/26/2017 04:54 PM »
Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

They did not place the current HIF in the proper location to allow for this. It is right at the base of the pad incline.

How about a pass-though  with a Y split to the south side. One fork for storing the existing TEL while the new one passes through, and the other fork leading to a new HIF south of the current one?

That stops existing launches.  The south end of the HIF is a clean room

So they would have to widen the ramp and allow the new TEL to split off part way down the incline. Some dirt and concrete work, but not on the level of what they are doing at Boca Chica.

Speaking of Boca Chica, it could be dedicated to this type of vehicle. It's higher performance would be useful for the GTO/lunar/interplanetary missions which are the only reason the launch facility exists.

Online Zed_Noir

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Re: Mars Precursor Vehicle
« Reply #32 on: 06/26/2017 07:43 PM »
Can meekGee's Mars Precursor Vehicle be use as a mid size Lunar lander? Presumably with Lunar orbital refueling.

Offline envy887

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Re: Mars Precursor Vehicle
« Reply #33 on: 06/26/2017 08:32 PM »
Can meekGee's Mars Precursor Vehicle be use as a mid size Lunar lander? Presumably with Lunar orbital refueling.

In theory, sure. There would be some challenges with thermal management, comms, power, etc. The usual trivialities of spaceflight :D

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #34 on: 06/26/2017 10:00 PM »
Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

They did not place the current HIF in the proper location to allow for this. It is right at the base of the pad incline.

How about a pass-though  with a Y split to the south side. One fork for storing the existing TEL while the new one passes through, and the other fork leading to a new HIF south of the current one?

That stops existing launches.  The south end of the HIF is a clean room

So they would have to widen the ramp and allow the new TEL to split off part way down the incline. Some dirt and concrete work, but not on the level of what they are doing at Boca Chica.

NASA isn't going to allow that

Offline watermod

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Re: Mars Precursor Vehicle
« Reply #35 on: 06/26/2017 10:17 PM »
The trouble with a small precursor to ITS is that it doesn't benefit from the mass/volume equation in the same way, making EDL quite a different thing. Additionally, keeping cryogenic fluids cold on a trip to Mars would be much harder. I think a smaller-than-ITS Mars ship would just about work for a flags and footprints mission, but a tiny craft isn't a goer. Fine for LEO, good as an alternative to SLS locally, but that's it.

What about using a Metal-Organic-Framework material instead of a cryogenic tank?

https://en.wikipedia.org/wiki/Metal-organic_framework

I don't know about oxygen but am told the materials can be designed to hold more methane or more hydrogen then a liquid tank of the same size.





Offline Bob Shaw

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Re: Mars Precursor Vehicle
« Reply #36 on: 06/26/2017 10:37 PM »

The trouble with a small precursor to ITS is that it doesn't benefit from the mass/volume equation in the same way, making EDL quite a different thing. Additionally, keeping cryogenic fluids cold on a trip to Mars would be much harder.

You have this backwards. Smaller vehicles have a much BETTER mass/area ratio for EDL, and big vehicles are harder to get through entry. This (and not launch vehicle capability) is why MSL is the largest thing to land on Mars to date.

The cryo problem is about the same either way.


Read my post again. I was pointing out that a mini-ITS wouldn't behave like the big chap during EDL, not specifying the difference. I also don't agree with you about the cryogenic sustainability issue being the same for a small, low-volume vehicle as a large, low surface area one - relatively speaking, the small ship suffers more heating, and must work harder to remain cool.

Offline MATTBLAK

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Re: Mars Precursor Vehicle
« Reply #37 on: 06/26/2017 10:50 PM »
Scaled-up Dragon - about 7 meters in diameter across the base? Or slightly larger even than that? I'm thinking something that would fit inside an 8.4 meter SLS style payload fairing. Or a similar sized fairing on another BFR.

No. Dragon doesn't scale up very well, and SpaceX is moving to BFS-style entry so I can't see them building anything new that doesn't move in that direction.

The trouble with a small precursor to ITS is that it doesn't benefit from the mass/volume equation in the same way, making EDL quite a different thing. Additionally, keeping cryogenic fluids cold on a trip to Mars would be much harder.

You have this backwards. Smaller vehicles have a much BETTER mass/area ratio for EDL, and big vehicles are harder to get through entry. This (and not launch vehicle capability) is why MSL is the largest thing to land on Mars to date.

The cryo problem is about the same either way.

...
I don't know why you expect a reusable upper stage on top of Falcon Heavy to have a 70 ton payload, that is higher than the maximum for a fully-expendable Falcon Heavy stack. I'd expect that the performance gain from switching to Raptor will be much less that what is lost in attempting to make it reusable and the difference will have to made up from using a larger booster.

It's also very dubious that they would build a special stage only for a few flights as it sort of defeats the purpose of reusability. Maybe if they somehow manage to build it to the same diameter as the early ITS and still fit it on the Heavy?

Perhaps a Falcon Heavy + Reusable Upper Stage could be cheaper to operate than a Falcon 9 + Expendable Upper Stages. This would require very fast and cheap refurbishment of multiple boosters.

With aggressive ITS-like mass fractions and full Raptor specs FH could do about 70t fully reusable. The biggest difference isn't that Raptor is so much better, but that the F9 upper stage is woefully undersized for FH. A 6m stage massing 300+ tonnes wet would allow FH to accelerate slower (less throttling losses) and stage sooner (easier recovery) while still putting far more mass in orbit. But 60-65 tonnes fully reusable is probably a better target, to allow for mass overruns and performance shortfalls.

It doesn't have to be strictly cheaper per launch than F9: if the larger payload allows constellation deployment in fewer launches, it would be worth operating if the total cost is less.
I was only advocating the Dragon shape - internally, it would be quite different. But I suppose developing such a big, derivative vehicle would cost most of what ITS is going to anyway, so....  Probably best if the Zubrin/Baker 'tuna can' Hab & semi-blunt biconic ERV 'Mars Direct' vehicles were done in the traditional manner, if done at all. Perhaps Zubrin could persuade the rather wealthy Jeff Bezos to launch his designs on the 'New Glenn' when it appears... ;) Twinned launches of the NG should roughly fit the Mars Direct mass estimates.
« Last Edit: 06/28/2017 10:59 AM by MATTBLAK »
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Offline DreamyPickle

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Re: Mars Precursor Vehicle
« Reply #38 on: 06/27/2017 01:14 AM »
I think the concerns about ground support are overblown for several reasons:

* The changes for a methane upper stage are much less than those for the full BFS. Remember how their intro video showed stacking the second stage right on the pad with a crane?
* Flying with different upper stages has been done before. The Atlas V is flying with multiple fairing diameters right now.
* They might be able to afford taking 39A out for a few months, and Boca Chica is being built in the same timeframe.

The biggest problem I see is building the business case. SpaceX is not very open about their costs but I'd guess the current upper stage is <10M per flight, and this is partially because it shares so much with the first stage booster. The fairing is not included in that but they've stated they are close to figuring out recovery for that.

In order for a methane upper stage to make sense it needs to cost much less than 10M per flight, including the design phase. The only way this could make is if the stage is fully reusable and has a larger diameter and mass (to preserve payload capacity). Has anyone done any simulations on how much a Falcon Heavy could lift in fully reusable mode with a different and larger upper stage?

I still think it's more likely that they'll just jump to a full methane-only rocket of uniform diameter instead of worrying around cross-compatibility.

Offline envy887

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Re: Mars Precursor Vehicle
« Reply #39 on: 06/27/2017 01:50 AM »
Is it not possible to add a second HIF and TEL to 39A without interrupting FH and Crew?

They did not place the current HIF in the proper location to allow for this. It is right at the base of the pad incline.

How about a pass-though  with a Y split to the south side. One fork for storing the existing TEL while the new one passes through, and the other fork leading to a new HIF south of the current one?

That stops existing launches.  The south end of the HIF is a clean room

So they would have to widen the ramp and allow the new TEL to split off part way down the incline. Some dirt and concrete work, but not on the level of what they are doing at Boca Chica.

NASA isn't going to allow that

NASA let them build a HIF right on the crawlerway. Why wouldn't they allow improvements to the pad?

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