Author Topic: How SpaceX may get crew to Mars by 2020.  (Read 14382 times)

Offline Nathan2go

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #120 on: 04/30/2017 02:19 AM »
Let's say I have a reusable methalox vehicle ... I want to deploy the ISRU unit ... then re-stow the unit back inside and take it back to orbit. ...
Doable?
Probably not.  The NIMF (Nuclear thermal rocket using Indigenous Mars Fuel), which Zubrin discusses in "The Case for Mars", would be great for that.  The "fuel" (really propellant) was simple liquid CO2, which is super easy to get on Mars.  With an Isp of only 260s though, it will be challenging to build an SSTO that has good payload capability, and it certainly can not fly non-stop from Mars surface to Earth.

If you want to make chemical fuel (e.g. methalox or  CO/O2), then that takes a lot of energy.  Zubrin and NASA DRM-5 assume the fuel plant will have nuclear power and will be remotely located and non-retrievable (i.e. no radiation shielding).  If you like the solar option, then plan to invest a lot of man-hours setting up the PV panels, even robotically, plus many months to collect enough energy.

An additional problem is that for Methalox (which is a much better propellant combo than CO/O2, with Isp=380s), you also need hydrogen.  Zubrin and NASA DRM-5 assuming you'll bring a load of LH2, just enough for one mission.  Maybe it's also possible to dig for perma-frost, then melt and electrolyze the water to make hydrogen (i.e. more man-power).

I think Methalox propellant production on Mars is something that happens at a permanent base, not an austere landing site for a temporary stopover.
« Last Edit: 04/30/2017 02:24 AM by Nathan2go »

Offline Lar

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #121 on: 04/30/2017 02:24 AM »
I asked this over on the main Missions to Mars thread, but perhaps there will be insights here as well....

I've read a lot of studies on Martian ISRU, but I haven't seen many clear figures on what's realistic for a reusable ISRU unit.

Let's say I have a reusable methalox vehicle which can deliver up to 40 tonnes of payload to the Martian surface in a 10 meter long, 4 meter wide cross section. I want to deploy the ISRU unit out of the cargo bay and onto the surface (potentially using a robotic arm), use it to refuel my vehicle's tanks, then re-stow the unit back inside and take it back to orbit. Once in orbit, the vehicle will transfer excess propellant to a tanker before re-entering, landing at a new location, and starting over.

The number of useful cycles varies with the dry mass of the ISRU unit. That is, a heavier ISRU unit needs to be able to survive more autonomous refueling cycles than a lighter one.

Doable?

Not sure this is on topic here either but why would you want to do this? Why wouldn't you deliver an ISRU unit and leave it there, running? If you want to do multiple sites, deliver multiple units.

Picking things up and taking them back to orbit isn't how you colonise things.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline sevenperforce

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #122 on: 04/30/2017 04:04 PM »
How did this become a thread about some weirdly shaped ITS variant? What's wrong with just using the regular ITS shape?

I guess it's better than what this thread was about immediately before that.

Carry on.
Size? The regular ITS cannot be launched on Falcon 9 or Falcon Heavy; a smaller one with bisymmetry rather than trisymmetry could.

Offline sevenperforce

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #123 on: 04/30/2017 04:07 PM »
I asked this over on the main Missions to Mars thread, but perhaps there will be insights here as well....

I've read a lot of studies on Martian ISRU, but I haven't seen many clear figures on what's realistic for a reusable ISRU unit.

Let's say I have a reusable methalox vehicle which can deliver up to 40 tonnes of payload to the Martian surface in a 10 meter long, 4 meter wide cross section. I want to deploy the ISRU unit out of the cargo bay and onto the surface (potentially using a robotic arm), use it to refuel my vehicle's tanks, then re-stow the unit back inside and take it back to orbit. Once in orbit, the vehicle will transfer excess propellant to a tanker before re-entering, landing at a new location, and starting over.

The number of useful cycles varies with the dry mass of the ISRU unit. That is, a heavier ISRU unit needs to be able to survive more autonomous refueling cycles than a lighter one.

Doable?

Not sure this is on topic here either but why would you want to do this? Why wouldn't you deliver an ISRU unit and leave it there, running? If you want to do multiple sites, deliver multiple units.

Picking things up and taking them back to orbit isn't how you colonise things.
Orbital propellant transfer seems much simpler, in principle, than trying to land a ship and refuel on the surface from a fixed depot. Too many variables with the latter. If you have a dedicated ship that is refueling itself via ISRU on the surface and then meeting other vehicles in orbit, they can always be sure of having enough fuel to get back into orbit before they ever commit to EDL.

Offline Robotbeat

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #124 on: 04/30/2017 04:18 PM »
How did this become a thread about some weirdly shaped ITS variant? What's wrong with just using the regular ITS shape?

I guess it's better than what this thread was about immediately before that.

Carry on.
Size? The regular ITS cannot be launched on Falcon 9 or Falcon Heavy; a smaller one with bisymmetry rather than trisymmetry could.
Dont know why it'd need bisymmetry. The reason ITS has trisymmetry is for the landing legs. Just two landing legs wouldn't work very well!

I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).
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Offline RonM

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #125 on: 04/30/2017 04:59 PM »
I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).

How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.

Offline sevenperforce

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #126 on: 04/30/2017 06:11 PM »
I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).

How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.
The problem is the amount of fuel you'd need to take.

My preferred architecture is to send a large, fluffy expandable hab, packed with supplies, with its own propulsion bus. Send the lander, which has its own propulsion and its heat shield, alongside. After TMI, the two rendezvous for the outgoing trip.

Immediately before entry, all the consumables and all but the barest margin of propellant is transferred from the hab's propulsion bus to the lander, and the lander does an aerocapture-to-circularization while the propulsion bus does a propulsive orbital insertion with the fluffy hab. They rendezvous and transfer propellant and consumables back to the propulsion bus, with the lander carrying only the fuel it needs for a minimum-weight EDL and SSTO. Once that is complete, they rendezvous, transfer propellant back to the lander for the homeward journey, and the propulsion bus is discarded while the lander sends the hab homeward.

Offline Robotbeat

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #127 on: 04/30/2017 06:18 PM »
I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).

How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.
Pretty small if you had one or two cargo ITSes beforehand and/or in parallel carrying power and ISRU equipment. I'm thinking like 3 total mini-ITSes: 2 cargo and one crew. 30-45 tons of payload each.
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Offline RonM

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #128 on: 04/30/2017 06:50 PM »
I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).

How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.
Pretty small if you had one or two cargo ITSes beforehand and/or in parallel carrying power and ISRU equipment. I'm thinking like 3 total mini-ITSes: 2 cargo and one crew. 30-45 tons of payload each.

That's a good way to get the initial base started while still working on the full-size ITS.

No reason for Congress to fund the colonization of Mars, but they might chip in some cash for the mini-ITS as long as NASA astronauts get to do the flag-and-footprints thing. Then SpaceX can use the new Mars infrastructure and start working on their colonization plans.

Offline sevenperforce

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #129 on: 05/01/2017 01:57 PM »
Wings for Earth good, wings for Mars meh...
Wings (or any winged-like shape) make the lander fluffier on entry, which means terminal velocity is lower, which means you don't need as much propellant for landing. Which means you can afford to bring along your fuel for ascent. Which means you have abort modes and don't need to carry a rover for transfer to an MAV.

All-around a very good choice.

Would you give it any lifting body characteristics at all? Earth and Mars entries both will require a lot of -ΔV from aerodynamic drag, though the flight profiles will have to be very different. On Earth, the ability to glide offers ability for airplane-like landing (with skids possibly better than wheels), while on Mars the ever increasing angle of attack at low altitude to maintain lift as V bleeds off could requires some modicum of aerodynamic profile that does generate that lift.

In that this is likely an experiment to obtain data, I imagine that what flies may not look like the final design. I know you believe they may have been working on this for longer than most think, but still, it has to be pretty prototypical in nature. If so, I have to wonder if they have strayed from pure cylindricality. If it does have the mini-raptor that you believe it might, does it have a larger diameter to accommodate the lower density CH4?  (IDNT it can be longer due to bending loads on total LV.) What kind of overall design do you think it might be? Would any landing legs be like F9-S1 or like ITS? If it cannot land on Vac engine, will it have Super Dracos, fore or aft? Do you have a TPS plate to shield the main nozzle, jettison the nozzle, jettison most of the nozzle and use the remnant as a SL engine? How do you envision the thing?
The lander needs thrusters for the landing, since it cannot land on even a mini Raptor Vac. The ITS is supposed to have ten-tonne RCS thrusters, so these would work very well as landing engines. If you use winglike extensions to drive down terminal velocity, you can place the landing thrusters biaxially in the wings and land this way:




Let's say I have a reusable methalox vehicle ... I want to deploy the ISRU unit ... then re-stow the unit back inside and take it back to orbit. ...
Doable?
If you want to make chemical fuel (e.g. methalox or  CO/O2), then that takes a lot of energy.  Zubrin and NASA DRM-5 assume the fuel plant will have nuclear power and will be remotely located and non-retrievable (i.e. no radiation shielding).  If you like the solar option, then plan to invest a lot of man-hours setting up the PV panels, even robotically, plus many months to collect enough energy.

An additional problem is that for Methalox (which is a much better propellant combo than CO/O2, with Isp=380s), you also need hydrogen.  Zubrin and NASA DRM-5 assuming you'll bring a load of LH2, just enough for one mission.  Maybe it's also possible to dig for perma-frost, then melt and electrolyze the water to make hydrogen (i.e. more man-power).
Yeah, methalox ISRU plans typically involve two or more rovers that dig up regolith, dump it into a (fixed) hopper, and then process the regolith to extract water. Water content in plain Martian soil is fairly high, high enough to crack into hydrogen.

Coming up with a way to do that all in a reusable package is...challenging.

You'd need to have your air collection and propellant processing systems bolted into your payload bay, and then you'd need your soil collection and water extraction module (CEM) to be lifted out of the payload bay and dropped on the ground on a Canadarm-type system. The CEM, in turn, must deploy a rover or two to dig up soil and dump it into the hopper, crush and heat the soil, condense the steam, and pump it up a hose into the onboard processing system. After many, many such cycles, the rover(s) need(s) to return and reattach to the CEM, which is then lifted back into the payload bay by the fixed arm so that the whole craft can return to orbit to fuel another vehicle.

I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).

How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.
Pretty small if you had one or two cargo ITSes beforehand and/or in parallel carrying power and ISRU equipment. I'm thinking like 3 total mini-ITSes: 2 cargo and one crew. 30-45 tons of payload each.
If you do two vehicles stripped of all but 3-4 seats each, then you could have a total of around 260 cubic meters of space. It's that open activity space that you really need for an extended mission. You could also take along a BEAM or two on the outgoing journey to carry extra pressurized payload, then discard it in Martian orbit once you've used the consumables.

Docked nose-to-nose, you could even spin them up very gently to simulate Martian gravity.

Offline TomH

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #130 on: 05/02/2017 06:21 AM »
The ITS is supposed to have ten-tonne RCS thrusters, so these would work very well as landing engines. If you use winglike extensions to drive down terminal velocity, you can place the landing thrusters biaxially in the wings and land this way:

Are you going to land it that way on both Earth and Mars?

Offline su27k

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #131 on: 05/02/2017 08:06 AM »
I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).

How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.
Pretty small if you had one or two cargo ITSes beforehand and/or in parallel carrying power and ISRU equipment. I'm thinking like 3 total mini-ITSes: 2 cargo and one crew. 30-45 tons of payload each.

That's a good way to get the initial base started while still working on the full-size ITS.

No reason for Congress to fund the colonization of Mars, but they might chip in some cash for the mini-ITS as long as NASA astronauts get to do the flag-and-footprints thing. Then SpaceX can use the new Mars infrastructure and start working on their colonization plans.

I don't think SpaceX will seek NASA funding for mini-ITS (if there is such a thing), they'll just pitch the full ITS plan. Whether it's for colonization or flag-footprints doesn't matter to congress, what matters is how much. The full ITS plan cost of $10B is very cheap if you consider it's for 8 to 10 years and as a public-private partnership SpaceX would be expected to pick up at least 1/3 of the cost. The annual cost to NASA would be lower than the current Commercial Crew funding, congress doesn't even need to cancel SLS/Orion.

If SpaceX is indeed interested in mini-ITS, I think they'll seek funding from USAF's EELV Launch Service Agreement program (continuation of their Raptor contract), they can sell it as their version of ACES.

Offline sevenperforce

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #132 on: 05/02/2017 02:59 PM »
The ITS is supposed to have ten-tonne RCS thrusters, so these would work very well as landing engines. If you use winglike extensions to drive down terminal velocity, you can place the landing thrusters biaxially in the wings and land this way:

Are you going to land it that way on both Earth and Mars?
Absolutely. The landing thrusters are set to permit aggressive propulsive landings on Earth with margin for downmass, so in the much lower Martian gravity, they have LOTS of power. The mini-ITS could refill its propellant tanks from a tanker in Martian orbit, then perform EDL, landing on its thrusters with more than enough fuel for a direct ascent return to Earth. You only need a fuel fraction of 68% for Martian SSTO and 84% for direct ascent to Earth entry with EDL reserves.

Offline GWH

Re: How SpaceX may get crew to Mars by 2020.
« Reply #133 on: 05/03/2017 08:30 PM »
My thoughts on a SpaceX accelerated timeline of a manned mission to Mars, it's a little long so be patient.
For SpaceX to accomplish the whole task in a 2020 or even 2022 timeframe alone I think there would be  just too much for them to take on themselves.  What would be more feasible I feel is taking on the launch, and landing hardware and leave the transit and surface habitats to someone else so those aspects can be developed on their path and not as one fully integrated system.
The Dragon 2 is nearing completion of its development, and should be able to function in deep space and able to land crew on Mars.  As such I think it would be an integral part of the transportation system .

The missing component for SpaceX is a long duration upper stage capable of landing large masses and volume on Mars, and as described by Robotbeat a miniature version of the ITS Spaceship could accomplish this with Raptor propulsion and carbon fiber construction.  Personally I don't feel there is sufficient evidence to suggests that this will fly in the next year, but think it could be developed in short order as a crash program.  For the suggested mission architecture below this stage I'd suggest would come in two variants: a 5m Falcon Heavy Upper stage Replacement with a traditional fairing, and an integrated fairing biconic vehicle with a hinged or disposable nose cone.  The Upper stage replacement may not be reusable, but the biconic vehicle certainly would.  In terms of appearance it would very much look like a scaled down ITS spaceship.

Surface and transit habitats I think would best be provided by those already engaged in the NextSTEP program, perhaps in a competition format.  The use of a traditional fairing would be specific to allow for expendables such as Bigelow. As at least some of the development in this area is underway, one would hope it could be accelerated.

Dragon 2 would be used as an Earth Ascent capsule for crew, dock in orbit to a refueled methalox Upper Stage+ Transit hab, and then be used as Mars Descent vehicle.  A 2nd Dragon 2 on Mars would be carried as a payload on a Mini-ITS spaceship landed, the MITS  to be used as the ascent booster for the Dragon Capsule.  This same ascent capsule can then dock with the space habitat and in turn be used to return crew to Earth surface. An alternative to the MITS booster would be a hypergolic fueled propulsive trunk based stage for the Dragon, this would be capable as a lunar lander/ascent stage but may be an unnecessary step.

In this scheme ISRU would be used to optionally recover the landers, however the ascent vehicle would need to allow for sufficient store propellant to ascend.  A second tanker or L2 staging may be required, about 40mT of landed prop, & Dragon Capsule should be sufficient for the ascent vehicle.  ISRU wouldn't be a driving force for return due to unknowns in development.

Proposed timeline (which looks a little ludicrous typing it out):
Tomorrow: Provide funding for development of Raptor US/MiniITS spaceship. Provide funding to get the habitat programs accelerated.
2018: Red Dragon to Mars - throw some funding to this and accelerate the program by any means necessary to gain the required EDL data and test of the lander. 
2018: Dragon to orbit moon - test out the crewed systems in deep space
2018/9: Testing of habitat prototype 1 by docking to ISS
2019: Test flights of MITS spaceship, including an unmanned landing and ascent from lunar surface
2019: Test flight of MITS spaceship and habitat on lunar flyby?
2020: Launch fleet of MITS landers: one habitat, one ascent vehicle, and one propellant tanker to refuel transit hab in orbit
2020: Crewed transit hab to depart to Mars later in the window. 
2021: The MITS landers and tanker arrive first, and building off the data from the 2020 Dragon lander and a little luck.  After confirmation of success (or failure) of surface habitat landing and deployment the go/no-go is given to the crewed transit hab to either continue on a free return trajectory OR inject to low Mars orbit.  The Dragon 2 capsule now lands the crew in the vicinity of the hab and ascent vehicles.
 
Time line after this would be follow up missions and development and testing of the ITS proper.
Thoughts?  I think it's more than a little crazy to say the least, but at least allows for a minimal amount of testing in the correct environment.

Offline TomH

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #134 on: 05/03/2017 10:42 PM »
GWH,

I'm not seeing the value of taking capsules to the surface and back if if Robotbeat's mini-ITS also exists. If you feel like you must have it, why not leave it in LMO with extra CH4 and O2 for re-propping the OTS via MOR and prior to TEI?

Depending on length of stay, that prop may need to arrive after the landing and prior to Mars launch, due to boil off concerns.

In transit boil off prevention needs to be better addressed as well.
« Last Edit: 05/03/2017 10:51 PM by TomH »

Offline GWH

Re: How SpaceX may get crew to Mars by 2020.
« Reply #135 on: 05/04/2017 12:08 AM »
The value in the capsule is primarily in that it is a standalone crew transportation vehicle, and one that will be proven out by the time of this theoretical mission.  That vehicle is just another payload as far as the booster, or ascent stage is concerned.
A fully integrated crew carrying lander like the ITS spaceship, or a downsized derivative, required that as the stage is being developed ALL the crewed features & systems need to be developed with it.  This also can't be tested landing on Mars by 2018 unless it is already well underway to flight at that date. I disagree here with Robotbeat that a Raptor Upper stage will be tested on the first FH, proof in the very standard looking interstage on the core we've seen.

So the idea is to keep the functions and system separate, the upper stage/lander is for carrying payloads only whether that cargo is a habitat or a crew vehicle.  You also benefit a little by having a separate and dissimilar system where crew can temporarily evacuate to, such as an event like an ammonia leak from the coolant system like what happened in the ISS. An uncrewed lander can get away with a more risky landing, such as the 3 engine suicide burn employed by the F9 on GTO missions.

This way, at least the way I see it, the habitat, upper stage/lander, and then crew lander & ascent vehicle can all be developed on their own separate paths, as non contiguous tasks.  I also think any efforts beyond a bare bones cargo carrying mini-ITS spacecraft are over and above what is needed and an even larger diversion from the ITS than the hodge-podge architecture of Dragon 2, Cygnus/Bigelow/Other transit hab, and mini-ITS cargo vehicle I've described.

Regarding your point on boil off on the surface, yes that may be an issue and mean that the ascent vehicle needs to be based entirely off a hypergolic + Super Draco derived stage.  A pricey adder, although would be very useful in the long run to enable Dragon landers to destinations without an atmosphere.
The in transit issues will need to be addressed for the ITS as well, and as such this would be a test run of the methods used there.

Offline MATTBLAK

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Re: How SpaceX may get crew to Mars by 2020.
« Reply #136 on: 05/05/2017 11:36 PM »
I've wondered how feasible a Draco system modified to use LOX and hydrazine would be? Or even hydrazine and very high-pressure gaseous oxygen - though with the right pressure/temperature combo, O2 would become liquid anyways. Modification for the Dracos would likely be a sparkplug type ignition system. Creating the LOX or O2 would be a relatively simple ISRU procedure of sucking in the Martian CO2 and 'cracking' it to get the oxygen.

The vacuum specific impulse of LOX/UDMH should be about 330 seconds - which aint too bad. If the Dragon Ascent vehicle didn't have to carry down the ascent oxidizer to the surface first time around, this would be a mass-saving. If there wasn't enough internal volume for all the propellants; perhaps the Ascent Dragon could be equipped with conformal tanks. We should probably assume that the Ascent Dragon would be a single-use vehicle that would climb to Martian orbit to meet another Dragon Earth Return Vehicle that is attached to a transit Hab module.
« Last Edit: 05/05/2017 11:38 PM by MATTBLAK »
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Offline GWH

Re: How SpaceX may get crew to Mars by 2020.
« Reply #137 on: 05/06/2017 06:20 AM »
What if they simply used a shortened F9 upper stage?  Maybe a second bulk head so they can seriously insulate the RP1 from freezing coupled with active heating?  Would that be totally crazy? For the bare minimum 4.1 km/s dV and with a 6.4mT D2 + 1mT payload, 2.5mT tank mass (total stage dry mass 3mT) that requires a total of 25mT prop, 7.5mT of which is RP1, and total required tank length is 2m.

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