Author Topic: SpaceX to the moon: mission profiles  (Read 37371 times)

Offline MikeAtkinson

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Re: SpaceX to the moon: mission profiles
« Reply #20 on: 03/22/2016 09:54 pm »
Getting 2 km/s out of such low-impulse engines requires a propellant mass fraction of 57%, which means an empty Dragon V2 (with a dry mass of 4.2 tonnes) would need at least 5.6 tonnes of propellant in order to get off the surface of the moon, 370% of its current fuel capacity.

That 4.2 tonnes is probably just the mass of the capsule, to that you need to add astronauts, moon suits, ECLSS consumables + margin, tools and equipment, mass for the extra tankage and bigger SuperDracos and propellant margin and residuals, and the trunk. So probably more like 8 tonnes which will need over 10 tonnes of propellant.

Dragon V2 is not designed for extended use without the trunk, which provides both power and cooling. Both of these might be might be problematic on the Lunar surface, due to Sun angle and reflected heat.

I think the best solution is to turn the trunk into a true service module, landing and ascent stage, but that is likely to mass even more.

Then EOR + propellant transfer. Second stage does TLI and then acts as a crasher stage. Landing by service module engine, ascent by service module engine to LLO, where it meets up with another second stage with propellant as its payload, propellant transfer to the service module then TEI and powered landing on Earth.

Significant enhancements to the second stage would be required and a completely new service module, but no major modifications to Dragon V2 (no outer mold line changes like would be needed for a larger nozzle SuperDraco).

I think however SpaceX will wait until MCT, the BFS should be able to do a moon mission with plenty of margin.

Offline IainMcClatchie

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Re: SpaceX to the moon: mission profiles
« Reply #21 on: 03/22/2016 11:58 pm »
Consider the following:

Elon Musk proposes the following to Hillary or Donald (I don't want to touch which one in this forum):
* Boots on the moon with NASA badges on the shoulders and no Russian vehicles or speakers during the 2020 re-election campaign, for $5 billion.  This is way cheaper than even a small military foray.
* Major, sustained distraction from foreign policy nightmares by a team that has demonstrated ongoing ability to capture and keep the American public's attention.
* Executed by a NewSpace company (free enterprise and all that).
* Clears away all the old government SLS crap, appears decisive, and yet provides plenty of jobs in CA, TX, and FL.  Also can be seen to validate the Commercial Crew initiative if under a Democratic administration.
* Will be visibly different than Apollo:
   * high-def landing and relaunch video via preplaced unmanned lander
   * landing video of and from the lunar crasher stage.  People love watching stuff go boom.
   * Lots of downlink bandwidth via three lunar orbiting relays
   * GoPros on practically everything, dedicated production staff similar to an NFL game, lots of earnest engineers explaining how it works (SpaceX has to get better at this).
   * bigger and better looking hardware that looks like an Apple product
   * more people on the surface at one time.  Three will do.
   * obviously practice with the hardware for Mars landing, so there is a future.  This means inflating stuff and driving around.

Offline wannamoonbase

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Re: SpaceX to the moon: mission profiles
« Reply #22 on: 03/23/2016 02:20 am »
Consider the following:

Elon Musk proposes the following to Hillary or Donald (I don't want to touch which one in this forum):
* Boots on the moon with NASA badges on the shoulders and no Russian vehicles or speakers during the 2020 re-election campaign, for $5 billion.  This is way cheaper than even a small military foray.
* Major, sustained distraction from foreign policy nightmares by a team that has demonstrated ongoing ability to capture and keep the American public's attention.
* Executed by a NewSpace company (free enterprise and all that).
* Clears away all the old government SLS crap, appears decisive, and yet provides plenty of jobs in CA, TX, and FL.  Also can be seen to validate the Commercial Crew initiative if under a Democratic administration.
* Will be visibly different than Apollo:
   * high-def landing and relaunch video via preplaced unmanned lander
   * landing video of and from the lunar crasher stage.  People love watching stuff go boom.
   * Lots of downlink bandwidth via three lunar orbiting relays
   * GoPros on practically everything, dedicated production staff similar to an NFL game, lots of earnest engineers explaining how it works (SpaceX has to get better at this).
   * bigger and better looking hardware that looks like an Apple product
   * more people on the surface at one time.  Three will do.
   * obviously practice with the hardware for Mars landing, so there is a future.  This means inflating stuff and driving around.

Nice ideas, but lets see if whomever the POTUS is and congress can agree on anything at all first.

I'm hopeful the next POTUS dumps the flat and lame asteroide mission thing and aims straight to the moon.  Orion, SLS, commercial capabilities. 

But again they branches of government need to work at a primitive level first.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline JamesH65

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Re: SpaceX to the moon: mission profiles
« Reply #23 on: 03/23/2016 08:56 am »
Consider the following:

Elon Musk proposes the following to Hillary or Donald (I don't want to touch which one in this forum):
* Boots on the moon with NASA badges on the shoulders and no Russian vehicles or speakers during the 2020 re-election campaign, for $5 billion.  This is way cheaper than even a small military foray.
* Major, sustained distraction from foreign policy nightmares by a team that has demonstrated ongoing ability to capture and keep the American public's attention.
* Executed by a NewSpace company (free enterprise and all that).
* Clears away all the old government SLS crap, appears decisive, and yet provides plenty of jobs in CA, TX, and FL.  Also can be seen to validate the Commercial Crew initiative if under a Democratic administration.
* Will be visibly different than Apollo:
   * high-def landing and relaunch video via preplaced unmanned lander
   * landing video of and from the lunar crasher stage.  People love watching stuff go boom.
   * Lots of downlink bandwidth via three lunar orbiting relays
   * GoPros on practically everything, dedicated production staff similar to an NFL game, lots of earnest engineers explaining how it works (SpaceX has to get better at this).
   * bigger and better looking hardware that looks like an Apple product
   * more people on the surface at one time.  Three will do.
   * obviously practice with the hardware for Mars landing, so there is a future.  This means inflating stuff and driving around.

Nice ideas, but lets see if whomever the POTUS is and congress can agree on anything at all first.

I'm hopeful the next POTUS dumps the flat and lame asteroide mission thing and aims straight to the moon.  Orion, SLS, commercial capabilities. 

But again they branches of government need to work at a primitive level first.

Asteroid mission is scientifically more interesting I suspect.

Offline stoker5432

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Re: SpaceX to the moon: mission profiles
« Reply #24 on: 03/23/2016 03:06 pm »
2. ISS to EML-1; crasher-stage direct ascent. Single Falcon 9 launch takes crew and Dragon V2 to ISS; docks. Falcon Heavy lifts Lunar Dragon to the ISS; crew and consumables transfer; Falcon Heavy transfers to EML-1 and then burns crasher-stage to drop a Lunar Dragon with additional fuel on the lunar surface. Lunar Dragon makes ascent and transfer to ISS and crew returns to earth via docked Dragon V2.

This mission profile looks like a winner to me for the manned part of the mission. Here's why:

1. Cheapest combination of launch vehicles: Falcon 9R and Falcon Heavy Expendable
2. Unused seats on Commercial Crew spacecraft (possible subsidizing)
3. Possible replacement of crasher stage and refueling of lunar dragon for future missions. ISS robotic arms courtd also prove useful in this operation. (possibly moving to Falcon Heavy reusable)
4. Various present and future docking options: ISS, spacecraft to spacecraft, Bigelow
5. Other options for earth to LEO crew delivery that can be substituted for both the spacecraft and launch vehicle.


« Last Edit: 03/23/2016 03:11 pm by stoker5432 »

Offline sevenperforce

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Re: SpaceX to the moon: mission profiles
« Reply #25 on: 03/23/2016 04:58 pm »
2. ISS to EML-1; crasher-stage direct ascent. Single Falcon 9 launch takes crew and Dragon V2 to ISS; docks. Falcon Heavy lifts Lunar Dragon to the ISS; crew and consumables transfer; Falcon Heavy transfers to EML-1 and then burns crasher-stage to drop a Lunar Dragon with additional fuel on the lunar surface. Lunar Dragon makes ascent and transfer to ISS and crew returns to earth via docked Dragon V2.

This mission profile looks like a winner to me for the manned part of the mission. Here's why:

1. Cheapest combination of launch vehicles: Falcon 9R and Falcon Heavy Expendable
2. Unused seats on Commercial Crew spacecraft (possible subsidizing)
3. Possible replacement of crasher stage and refueling of lunar dragon for future missions. ISS robotic arms courtd also prove useful in this operation. (possibly moving to Falcon Heavy reusable)
4. Various present and future docking options: ISS, spacecraft to spacecraft, Bigelow
5. Other options for earth to LEO crew delivery that can be substituted for both the spacecraft and launch vehicle.
Yeah, it's nice. The biggest drawback here is that it requires the largest dV for the lander. Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.

Offline stoker5432

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Re: SpaceX to the moon: mission profiles
« Reply #26 on: 03/23/2016 06:10 pm »
Yeah, it's nice. The biggest drawback here is that it requires the largest dV for the lander. Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.

Yes if your only talking about dV and not cost, but I'm assuming the profile you gave was still plausible for a useful manned mission. Was I incorrect in this assumption?

Offline the_other_Doug

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Re: SpaceX to the moon: mission profiles
« Reply #27 on: 03/23/2016 07:00 pm »
Yeah, it's nice. The biggest drawback here is that it requires the largest dV for the lander. Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.

Yes if your only talking about dV and not cost, but I'm assuming the profile you gave was still plausible for a useful manned mission. Was I incorrect in this assumption?

Oh, it's plausible.  It's something of a flags-and-footprints mission, in that it requires more launches, and more equipment, than the two launches proposed to do more than what Apollo managed to accomplish.

Not that this is a bad idea.  If it can be done for a tenth of Apollo's cost, and provide an architecture with enough re-usable elements to also reduce ongoing equipment costs, then we have a transport capability that, depending on what you want to do with it, could be considered semi-affordable.

I think, though, that it makes more sense to wait a few years, let NASA set up an Orion-serviced way station in high lunar orbit, and use that for your reusable lander resupply shop.  The delta-V requirements to get to the lunar surface from HLO and back are much lower than those quoted for LLO, aerocapture and LEO, right?

So, you could start out with needing three or four FH launches to set things up, and after that you would launch two FH's for every expedition.  But both would be used to refurbish a reusable lander that just shuttled from HLO to the lunar surface, and to provide a return vehicle from HLO back to Earth.

It's not a bad idea to test out some of those systems with a more limited flags-and-footprints set of missions, but you want to make certain you're not throwing a ton of money into dead-end technology that won't be useful once you get the cislunar way station set up -- much less into technology that doesn't serve to support the main goal of putting a colony on Mars.

To my knowledge, SpaceX has not yet seen a business case for attempting crewed lunar landings.  This could change, of course -- this is SpaceX, after all.

I'd love to see it, but I guess I'm not holding my breath.
-Doug  (With my shield, not yet upon it)

Offline sevenperforce

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Re: SpaceX to the moon: mission profiles
« Reply #28 on: 03/23/2016 07:03 pm »
Yeah, it's nice. The biggest drawback here is that it requires the largest dV for the lander. Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.

Yes if your only talking about dV and not cost, but I'm assuming the profile you gave was still plausible for a useful manned mission. Was I incorrect in this assumption?
No, it's plausible; it just greatly limits payload since so much of your landing vehicle has to be fuel. And FHE might have trouble getting enough mass to the lunar surface with any remaining payload.

If I get a chance I'll put together a comprehensive diagram of the exact dV and FHE payload numbers to and from each Earth-Lunar node. There are some helpful tricks along the way...for example, if you take a highly-eccentric Hohmann transfer just past EML-1, you can "fall through" into the lunar gravity well without needing to circularize, saving you about 500 m/s of dV. But you can't efficiently enter lunar orbit from this node; it's only useful if you are willing to drop straight to the surface and suicide burn away the 2.24 km/s impact speed. Also, Hohmann transfer from a 100 km parking orbit to any lunar node saves you noteworthy dV over transfer from the ISS thanks to old Oberth.

The only Earth Orbit Assembly I could see being feasible would be mating a crew capsule to a Falcon upper stage at the ISS using Canadarm, because it's something they could conceivably test as a nonessential part of a routine mission. Dock the capsule with the Falcon 9 upper stage still attached, then use Canadarm to remove it and replace it a couple of times. If that's simple enough, then it would be reasonable to launch the unmanned, loaded Lunar Dragon and the manned Dragon V2 to the ISS on a couple of F9Rs and then launch an empty FHE to the ISS to be mated to the Lunar Dragon as a transfer vehicle.

Offline stoker5432

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Re: SpaceX to the moon: mission profiles
« Reply #29 on: 03/23/2016 08:40 pm »
I like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.
« Last Edit: 03/23/2016 08:43 pm by stoker5432 »

Offline sevenperforce

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Re: SpaceX to the moon: mission profiles
« Reply #30 on: 03/23/2016 08:49 pm »
I think, though, that it makes more sense to wait a few years, let NASA set up an Orion-serviced way station in high lunar orbit, and use that for your reusable lander resupply shop.  The delta-V requirements to get to the lunar surface from HLO and back are much lower than those quoted for LLO, aerocapture and LEO, right?
Getting from LLO to an Earth aerocapture trajectory is actually really, really cheap. You can do a highly eccentric Hohmann transfer to EML-1, slide through, and essentially free fall to the high-velocity re-entry at an angle of your choosing with just a couple of RCS puffs. There is a good bit of dV spent circularizing that you can avoid if you do this sort of maneuver.

Regardless, SpaceX's major advantage disappears if you wait for a cislunar station. The Falcon family has very poor BLEO performance. The advantage exists if and only if SpaceX can boast lunar capability now, despite the low performance of their platforms.

Offline sevenperforce

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Re: SpaceX to the moon: mission profiles
« Reply #31 on: 03/23/2016 08:53 pm »
I like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.
It would take a lot of work, but not necessarily any more work than it would take to build a single-function Dragon-derived lunar lander. The major issue would be installing an auxiliary fuel tank inside the cabin without introducing significant risk. You end up with a significantly smaller payload, but the advantage of only needing a single vehicle for both the Moon and Earth cannot be overstated.

Offline stoker5432

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Re: SpaceX to the moon: mission profiles
« Reply #32 on: 03/23/2016 08:58 pm »
You need the trunk. Why don't you put the extra propellant there?

Offline sevenperforce

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Re: SpaceX to the moon: mission profiles
« Reply #33 on: 03/23/2016 09:04 pm »
You need the trunk. Why don't you put the extra propellant there?
You can use batteries; that's what the LM did. Landing on the trunk requires a second set of landing legs and an extended egress system, and is riskier due to the high center of mass.

Offline MikeAtkinson

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Re: SpaceX to the moon: mission profiles
« Reply #34 on: 03/23/2016 09:09 pm »
I like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.
It would take a lot of work, but not necessarily any more work than it would take to build a single-function Dragon-derived lunar lander. The major issue would be installing an auxiliary fuel tank inside the cabin without introducing significant risk. You end up with a significantly smaller payload, but the advantage of only needing a single vehicle for both the Moon and Earth cannot be overstated.

Won't work.

The final mass of the Dragon 2 after ascent will be about 8 tonnes, needing about 10 tonnes of propellant. This extra propellant will take up essentially the whole of the cabin.

This 8 tonnes includes the trunk as Dragon can only survive a short time without the power and cooling provided by the trunk. Also fuel margin and residuals, extra tank(s) and predestination system. Also crew, ECLSS supplies, etc.

Offline IainMcClatchie

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Re: SpaceX to the moon: mission profiles
« Reply #35 on: 03/23/2016 09:15 pm »
Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.

So with your Lunar Dragon + Return Dragon mission, we can compare the delta-V needed for both Dragons after they've both achieved LLO.
* Lunar Dragon needs 1.9 km/s down and 1.9 km/s back up.  That's 3.8 km/s.
* Return Dragon needs something like 0.9 km/s to get from LLO to aerobraking return.  That's a lot less.

If I understand correctly, you are thinking that Lunar Dragon gets the extra delta-V by not having a heat shield and having better Isp from bigger engine bells... and then just much bigger tanks.  Since both are postulated to lift off with the same Falcon Heavy launcher, the return Dragon is going to have a bunch of extra payload capacity compared to the Lunar Dragon.

It seems to me you are going to want to put a few tonnes of stuff on the return Dragon and then transfer that stuff to the Lunar Dragon in LLO before descent.  Would it make sense for the return Dragon to carry the Lunar Dragon's extra-big fuel tanks, and plonk them ON TOP of the Lunar Dragon?  They'll be mostly empty once it lands, so the center-of-mass problem isn't so bad.

Having a nice diagram which makes it easy to understand how to allocate delta-V would be great.  Something like this, which I'm sure you've seen:

Offline Andy Smith

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Re: SpaceX to the moon: mission profiles
« Reply #36 on: 03/23/2016 09:24 pm »
Assuming one reusable tanker was built (enlarged second stage tanks with Pica, launched by FHR), then refuelling a depot at LEO is achievable, multiple fuelling runs just cost fuel. Later on, refuelling the tanker itself from the depot, means the now fully loaded tanker could travel to EML-2 and refuel a second depot before returning to Earth.

Second stages for lunar missions could be refuelled twice (LEO and EML-2) and carry at least 25 tons to the lunar surface - not quite so much of a hover slam when carrying that payload.

The depot could be an F9 first stage, modified for refuelling capability. A first stage is just about ssto capable with no payload, then following fuelling it could be used as a depot, or take itself to EML-2. For decommissioning, or maintenance, the "depot" would have enough delta v to slow down and land without needing heat shielding (ssto in reverse).

Almost fully reusable infrastructure could make the costs of achieving lunar missions very very low

Offline nadreck

Re: SpaceX to the moon: mission profiles
« Reply #37 on: 03/23/2016 10:14 pm »

Regardless, SpaceX's major advantage disappears if you wait for a cislunar station. The Falcon family has very poor BLEO performance. The advantage exists if and only if SpaceX can boast lunar capability now, despite the low performance of their platforms.

The FH is projected to have better TLI performance than any current vehicle. But there is no advantage to SpaceX to building any sort of lunar capacity with the current Falcon Upper stage. Without being commissioned for a mission like this that requires it, they have no reason to keeping RP-1 from freezing for more than 12 hours, they have no reason to transfer RP-1, they have no reason to make a dragon with that much ΔV, no reason to work towards long term ECLSS before the MCT, and they have no reason to make an ascent vehicle before the MCT.

So if someone commissions them in the very short term, it would be that organizations imperative (and therefore funds) that drove it.  However, if SpaceX wants to test elements of its eventual Mars capability and if they actually go through with developing at Raptor based FH upper stage then, maybe, I can see them working with a partner with lunar ambitions towards a manned excursion/base.  In that circumstance some SpaceX ambition might drive giving the partner some cost advantages as SpaceX proves capability. In all other circumstances, except using the Dragon as a lander without ascent capability, I expect the only driver for SpaceX would be that it was a contract that furthers their business aims, but not one that tests anything useful to be incorporated on future Mars expeditions. In the meantime SpaceX can and will work on unmanned lunar projects, possibly even a communications constellation.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline CuddlyRocket

Re: SpaceX to the moon: mission profiles
« Reply #38 on: 03/23/2016 11:32 pm »
I don't think SpaceX will be going to the Moon until after the BFR/MCT has been developed. A system capable of getting to Mars and back will in all likelihood be capable of going to the Moon and back (perhaps with some modifications). I expect SpaceX would be willing to utilise the system on lunar missions - they would be useful test flights - and especially if someone else is paying!

I would imagine that if SpaceX can go to the moon now, with existing platforms, they would jump at the opportunity to test the tech and operations needed for Mars.

But SpaceX can't go to the Moon with existing platforms - Falcon/Dragon - or at least not without extensive modifications, the development of which will take both financial and engineering resources away from developing BFR/MCT, delaying the latter. Plus there's little overlap between the tech proposed to be used for, and the operations of, Falcon/Dragon lunar and BFR/MCT Mars missions.

Quote
The moon is a lot closer than Mars, and if they can use non-mission-critical legs of lunar missions to test technology like orbital propellant transfer, repeat rendezvous, uncrasher stages, hoverslam landings, and so forth, they can get to Mars that much earlier.

You don't need to use lunar missions for most (all?) of this; it can be done in LEO. But more importantly, you're not testing the BFR/MCT; you're testing similar equipment on other spacecraft. As an analogy, testing and flying the Airbus A-320, A-340 etc didn't reduce the testing required for the A-380.

Quote
And as far as the bill is concerned...if SpaceX can offer a return to the moon 5-8 years earlier than the closest competitors, I am sure someone high-ranking at NASA would at least consider it.

Probably. But possibly they might consider it better to wait for the BFR/MCT. After all, they don't need to beat the closest competitors by 5-8 years. One year would suffice for bragging rights.

Offline Zed_Noir

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Re: SpaceX to the moon: mission profiles
« Reply #39 on: 03/23/2016 11:48 pm »
I like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.
It would take a lot of work, but not necessarily any more work than it would take to build a single-function Dragon-derived lunar lander. The major issue would be installing an auxiliary fuel tank inside the cabin without introducing significant risk. You end up with a significantly smaller payload, but the advantage of only needing a single vehicle for both the Moon and Earth cannot be overstated.

Won't work.

The final mass of the Dragon 2 after ascent will be about 8 tonnes, needing about 10 tonnes of propellant. This extra propellant will take up essentially the whole of the cabin.

This 8 tonnes includes the trunk as Dragon can only survive a short time without the power and cooling provided by the trunk. Also fuel margin and residuals, extra tank(s) and predestination system. Also crew, ECLSS supplies, etc.

How about having an external prop module with the trunk functions mounted on the Dragon's nose. Along with an austere trunk discarded prior to landing on the Moon. Presuming you can land the Dragon with a module on top. To land this LEGO stack on the Moon will need to stacked another prop module as a pop off crasher stage.

Again presuming you can land the Dragon with a module on top. The modifications on the Dragon will be external prop lines and trunk function interfaces with the prop module through the docking hatch.

 

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