Author Topic: Mars Precursor Vehicle  (Read 7811 times)

Online meekGee

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Mars Precursor Vehicle
« on: 06/26/2017 07:13 AM »
There's a lot of arguing over in the SpaceX general forum about a "Raptor Upper Stage", with some people correctly pointing out that RUS gives limited benefits if all we're doing is replacing a Merlin with a Raptor and changing fuel types.

But there's something a lot more ambitious they can do, which coincidentally will also provide a RUS...

Since ITS won't be built tomorrow, SpaceX could benefit from A) risk mitigation and B) early access to Mars which has lineage to ITS architecture (instead of RD, which is a dead end).

So - build a "Mars Precursor Vehicle" that acts like BFS - it's a second stage, but can also be a refuelable Mars vehicle.

It launches on FH, but with a RUS instead of the current Merlin, can take maybe 70 tons to orbit.

Now this stage can be used (in one variation) to launch satellites and be fully reusable, or (in a second configuration) do Mars missions.

SpaceX gets to test (in earth orbit)
- Raptor
- Composite tanks
- Autogenous pressurization
- Refueling

And then test on a Mars mission:
- long duration interplanetary flight
- EDL

---

Basically with a modest development effort, we can have Mars missions with a departure mass of say 3x the payload of FH/RUS.

I am perfectly happy with that as a "stop gap" until ITS, or mini-ITS, or whatever comes afterwards.

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Online guckyfan

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Re: Mars Precursor Vehicle
« Reply #1 on: 06/26/2017 08:14 AM »
This is the only setup that could possibly be ready to go to Mars in 2020 instead of RedDragon.

Should it not be able to do a Mars landing even without refuelling? Though refuelling would greatly increase payload.

Offline DreamyPickle

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Re: Mars Precursor Vehicle
« Reply #2 on: 06/26/2017 08:24 AM »
Another key feature a new upper stage should have is a non-detachable fairing, because if you want to land a payload on Mars you can't expose it during entry. But perhaps it might still be detached and recovered separately in LEO missions?

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.

Online meekGee

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Re: Mars Precursor Vehicle
« Reply #3 on: 06/26/2017 09:30 AM »
Another key feature a new upper stage should have is a non-detachable fairing, because if you want to land a payload on Mars you can't expose it during entry. But perhaps it might still be detached and recovered separately in LEO missions?

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.
Let's dial it down to 40-50 tons even.  This is a larger vehicle, 5m diameter, it should carry more fuel, and carry significantly more than today's (tomorrow's) FH.

I don't think it'll fly just a few times.  I think as a reusable deployer (with cargo bay instead of fairing) it will be a workhorse untill BFR or SFR get deployed several years later.

Of all intermediate steps, this one makes the most sense to me.
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Offline Bob Shaw

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Re: Mars Precursor Vehicle
« Reply #4 on: 06/26/2017 10:06 AM »
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.

Offline MATTBLAK

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Re: Mars Precursor Vehicle
« Reply #5 on: 06/26/2017 10:50 AM »
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.
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Offline MATTBLAK

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Re: Mars Precursor Vehicle
« Reply #6 on: 06/26/2017 11:03 AM »
...I'm thinking of a 'Mars Direct' based concept - based that is on the soon to be fully-proven form factor of the crewed 'Dragon 2.0'. Several versions of the same hull - Mars Transit, EDL & Surface Habitat, and an Ascent version that refuels after landing via ISRU: it climbs to Martian orbit where another ERV Dragon is attached to an Earth Return propulsion stage and an expendable, attached extra Habitat augmentation module. The Propulsion stage - either hypergolic or LOX/CH4 pushes the Dragon & Hab Earthwards and is ejected after TEI. Shortly before Earth interface, the Hab is jettisoned and the Dragon does either a direct entry to the Earth's surface for a propulsive landing, or aerocaptures into Earth orbit for a 'taxi' rendezvous to return the crew to Earth.

Basing the above ideas on variations of the Zubrin Direct or the NASA 'Semi-Direct' architectures.
« Last Edit: 06/26/2017 11:04 AM by MATTBLAK »
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Online envy887

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Re: Mars Precursor Vehicle
« Reply #7 on: 06/26/2017 12:15 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.

Offline Robotbeat

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Re: Mars Precursor Vehicle
« Reply #8 on: 06/26/2017 12:21 PM »
I've personally been using RUS interchangeably with a mini BFS.
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Online envy887

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Re: Mars Precursor Vehicle
« Reply #9 on: 06/26/2017 12:31 PM »
I've personally been using RUS interchangeably with a mini BFS.

This is not the only possible interpretation, but it's the only one that's plausible to me.

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #10 on: 06/26/2017 02:03 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-41 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.

Online meekGee

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Re: Mars Precursor Vehicle
« Reply #11 on: 06/26/2017 02:03 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.
Correct, it wouldn't be an efficient Mars vehicle as BFS would be - you need size.

But it'd be better than RD or anything else, it'd be enormous compared to any current or planned Mars missions  and you can test basics even when the system is very different.  You validate your model, not the actual end design.

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Online meekGee

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Re: Mars Precursor Vehicle
« Reply #12 on: 06/26/2017 02:06 PM »
I've personally been using RUS interchangeably with a mini BFS.
I know, and I did the same, but that was the reason for some of the RUS arguments.  Some people are talking about a 3.6 m engine replacement RUS with no Mars ambitions, and I felt this is sufficiently different that it merits it's own thread.
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Online meekGee

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Re: Mars Precursor Vehicle
« Reply #13 on: 06/26/2017 02:22 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-41 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.
I don't know if "vehemently", but I don't see those other two options as likely at all.

Mostly because if SpaceX were thinking about them, they would naturally migrate the design towards this.

Timing wise, I wouldn't be surprised if they aimed at 2020, but hit 2022.  Lots of factors here, including pad availability, other missions, funding, etc.

This is assuming of course that FH is successful operationally and they like flying it. If not, then it's a while new ballgame.

What the big IAC plan was missing was steps. I appreciated the audacity, and maybe "bigger is easier", but in the grand scheme of things this MPV can give them a lot of knowledge for considerably​ less effort, and might actually accelerate the schedule for ITS compared to what it would have ended up being in reality.

My guess is we won't hear about any of it until FH flies.
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Offline Jim

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Re: Mars Precursor Vehicle
« Reply #14 on: 06/26/2017 02:29 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.

Offline jpo234

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Re: Mars Precursor Vehicle
« Reply #15 on: 06/26/2017 03:06 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?

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #16 on: 06/26/2017 03:08 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

Online Semmel

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Re: Mars Precursor Vehicle
« Reply #17 on: 06/26/2017 03:17 PM »
d.  DOD is not going to use F9 or FH for vertically integrated payloads

That is interesting. I would be inclined to believe that SpaceX does not want to develop vertical integration for the Falcon family, but that they would do it if DOD asks. However I have never heard before that DOD does not WANT SpaceX to develop that capability. Thats a pretty strong statement. Do they simply put all VI payloads on Atlas and Delta?

Offline Jim

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Re: Mars Precursor Vehicle
« Reply #18 on: 06/26/2017 03:23 PM »
d.  DOD is not going to use F9 or FH for vertically integrated payloads

That is interesting. I would be inclined to believe that SpaceX does not want to develop vertical integration for the Falcon family, but that they would do it if DOD asks. However I have never heard before that DOD does not WANT SpaceX to develop that capability. Thats a pretty strong statement. Do they simply put all VI payloads on Atlas and Delta?

No, I am saying that for  mini BFS/ITS to happen, DOD would not use F9 or FH for vertically integrated payloads.

If LC-39A is modified for mini BFS/ITS, it is likely incompatible with stock F9 or FH and hence not DOD vertically integrated payloads.

Online meekGee

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Re: Mars Precursor Vehicle
« Reply #19 on: 06/26/2017 03:33 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.

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