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Right. SpaceX doesn't have a craft capable of lunar orbit rendezvous https://en.wikipedia.org/wiki/Lunar_orbit_rendezvous https://en.wikipedia.org/wiki/Lunar_

Right. SpaceX doesn't have a craft capable of lunar orbit rendezvous https://en.wikipedia.org/wiki/Lunar_orbit_rendezvous https://en.wikipedia.org/wiki/Lunar_orbit_rendezvous so they would need to return to the Earth directly from the surface of the moon https://en.wikipedia.org/wiki/Direct_ascent https://en.wikipedia.org/wiki/Direct_ascent Direct ascent requires a much larger initial launch mass, i.e., a larger rocket than has ever been built. Since it took the massive Saturn V to complete the Apollo missions using lunar rendezvous, and SpaceX's Falcon Heavy is smaller, I don't think they are even close to having the ability to land on the moon and return. (And that's assuming there's not other insurmountable factors preventing Dragon from landing on the moon and taking off, which there probably are.) Hopefully someone with more knowledge can chime in.

XorNot 10y ago
SpaceX for a landing mission wouldn't try and build a larger rocket, they'd definitely argue to just do multiple launches instead. Fuel tankering is within their area of interest for Mars.
- ChuckMcM 10y ago
  I believe this (mating tanks given multiple missions) is what they were considering. Imagine you have your reusable falcon 9 boost into orbit a 'fuel only' second stage. Land the first stage, put another one on it, and send it up again. Once you have your 'boost pack' up in orbit, presumably docking with each other into a single unit, you launch your crew which attaches to the 'tug' that takes them to the moon. ULA has a great writeup of how you might do this if you have on orbit refueling capabilities. And on the one hand it seems like total science fiction but on the other, Elon is talking about next year.
  - yellowapple 10y ago
    This can be applied to much more than just fuel, mind you. Interplanetary manned vehicles might very well end up looking like space stations, with a bunch of modules docked together in order to provide the necessary creature comforts to sustain a crew for months on end. In fact, a permanently-in-orbit transfer vehicle might make sense here; have this vehicle run the actual Earth<->Mars transfers, then just shuttle in fuel/supplies/crew on each Earth arrival. Either way, a Falcon-like reusable launch system makes plenty of sense here in terms of making this sort of thing possible.
    - pheldagryph 10y ago
      > a permanently-in-orbit transfer vehicle might make sense here Buzz Aldrin is a big proponent of this approach: https://buzzaldrin.com/space-vision/rocket_science/aldrin-mars-cycler/ https://buzzaldrin.com/space-vision/rocket_science/aldrin-ma...
  - skookumchuck 10y ago
    Jet fighters routinely use so much fuel taking off that the first thing they do after gaining altitude is refuel. Rockets can use the same idea.
    - ChuckMcM 10y ago
      Yes but as the ULA whitepaper pointed out there are some challenges to doing so in orbit. For one, the lack of gravity makes it hard to pump fuel. You can spin the tanker to achieve fuel settling but now you are both spinning bodies. Then there is handling cryogenic propellants in space, you get nominal bleed off from warming and again ULA had a really interesting design of an internal combustion engine using the bleed off of Hydrogen and Oxygen as a chiller pump. But suffice it to say, its not as easy as it is flying a jet behind a slow re-purposed jetliner, and doing that is already difficult.
      - skookumchuck 10y ago
        > the lack of gravity makes it hard to pump fuel Evidently this problem is solved, because liquid fuel rockets have been working fine in space since the 60s. (Liquid fuel rockets have their propellants pumped into the chamber.) > nominal bleed off from warming Launch the tanker just beforehand. There won't be time for the fuel to bleed off.
        NickNameNick 10y ago
        Liquid fuel rockets use Surface tension against the slosh baffles to hold fuel in partially full fuel tanks in place. Ullage motors are used to settle the fuel at the bottom of the tanks, so the main motor pumps can get to it. Once the main motor starts providing acceleration, the ullage motors are no longer required. For cross tanking, keeping the ullage motors running for long enough to transfer all the fuel, without the main motors running might be prohibitive. https://en.wikipedia.org/wiki/Ullage_motor https://en.wikipedia.org/wiki/Ullage_motor
        skookumchuck 10y ago
pinewurst 10y ago
That's not to say that LOR is impossible with a smaller payload. Saturn V enabled a large, complex, redundant set of vehicles. The never successfully launched Soviet N1/L3 with half the TLI payload also used LOR but with much lighter vehicles and a smaller crew.
CydeWeys 10y ago
> Right. SpaceX doesn't have a craft capable of lunar orbit rendezvous Why not? Their Dragon capsules can dock with the ISS; why wouldn't they be able to dock with each, possibly with some kind of adapter? You can imagine one Dragon and a trunk docking with another upper stage that's all fuel tank, heading to the Moon, undocking in orbit, landing, ascending, and rendezvousing in orbit to return home. The total dv requirements of landing on the Moon and ascending again starting from low Moon orbit is 4 km/s. I haven't done the math, but I suspect that you can put together a workable mission using two Falcon Heavy launches. Now, granted, they don't have all the exact pieces put together quite yet, but I suspect they've been thinking about it.
- robszumski 10y ago
  A lot of the devil here is in the details. You need long term life support that Dragon hasn't proven yet. Deep space communications on the transmit and receive side. Abort scenarios for most or all phases of flight. All of this is untested and requires a huge amount of engineering and manufacturing work. Since this will likely share the same design as the NASA-contracted capsules, these systems will need to pass muster with them. And they don't cut corners.
  - CydeWeys 10y ago
    Minor quibble: you don't need deep space communications. The Moon is laughably close. I am quite confident that we can easily make contact with the existing unmodified Dragon capsules by using something like one of these bad boys: https://www.nasa.gov/sites/default/files/goldstone.jpg https://www.nasa.gov/sites/default/files/goldstone.jpg Of course it's laughably overkill for the purpose -- amateur radio operators using much smaller equipment can already send and receive signals to each other by bouncing them off the Moon, which has four times the signal attenuation owing to the doubled distance plus a good deal more in losses from the poor reflectivity of the Moon to radio waves.
Retric 10y ago
SpaceX is already docking with the space station which is similar difficulty as launching from the moon and docking in lunar orbit. The problem is getting a rocket with enough fuel on the surface of the moon without damaging it, not the docking in orbit. Which is even easier than doing the same thing from the surface of Mars. The only advantage of Mars is you don't need to burn fuel slowing down but that's more than offset by a significantly deeper gravity well. On the upside, they can land an un-manned assent vehicle on the surface of Moon / Mars before sending people there. Which can significantly increase your odds of getting back. PS: Yes, NASA did get to the moon and back several times, but they also took a massive chunk of US GDP to do so. https://en.wikipedia.org/wiki/Budget_of_NASA#/media/File:NASA-Budget-Federal.svg https://en.wikipedia.org/wiki/Budget_of_NASA#/media/File:NAS...
- jessriedel 10y ago
  I don't think either of us know much about this, but I do know that docking with the ISS to unload supplies requires completely different equipment than doing a rendezvous between a lunar lander and a lunar orbiter for Earth return. (That's why I didn't say merely "docking".) The only craft SpaceX has that can land on Earth or the Moon is Dragon. I am pretty sure Dragon does not have enough delta-v to do a full propulsive landing on the moon (no aerobraking available) and then return to orbit. And they definitely don't have the tech to re-fuel in lunar orbit for the return to Earth. None of this equipment exists. Not to mention that this would be a totally new lunar strategy, since the Apollo mission returned to earth in the lunar orbiter (Command Module) rather than re-fueling and returning in the lunar lander.
  - Retric 10y ago
    Yea, I am not a rocket guy. However, the minimum delta V to land on the moon is ~1.72 km/s, and you need another 1.72 km/s to get back into orbit + some safety factor ~2.2-2.4 km/s. By comparison it takes ~8km/s to get from LEO to low moon orbit and back to earth. Though you can reduce this by how hard to hit the earth's atmosphere. So, having fuel to land and take off from the moon is not that much worse than getting to the moon and back.
gozur88 10y ago
They'll be able to do LOR in the Dragon 2, which would be ready in time. I question whether they have enough endurance for a lunar landing mission, though, and they would still have to develop a lander.

XorNot 10y ago

SpaceX for a landing mission wouldn't try and build a larger rocket, they'd definitely argue to just do multiple launches instead. Fuel tankering is within their area of interest for Mars.

ChuckMcM 10y ago
I believe this (mating tanks given multiple missions) is what they were considering. Imagine you have your reusable falcon 9 boost into orbit a 'fuel only' second stage. Land the first stage, put another one on it, and send it up again. Once you have your 'boost pack' up in orbit, presumably docking with each other into a single unit, you launch your crew which attaches to the 'tug' that takes them to the moon. ULA has a great writeup of how you might do this if you have on orbit refueling capabilities. And on the one hand it seems like total science fiction but on the other, Elon is talking about next year.
- yellowapple 10y ago
  This can be applied to much more than just fuel, mind you. Interplanetary manned vehicles might very well end up looking like space stations, with a bunch of modules docked together in order to provide the necessary creature comforts to sustain a crew for months on end. In fact, a permanently-in-orbit transfer vehicle might make sense here; have this vehicle run the actual Earth<->Mars transfers, then just shuttle in fuel/supplies/crew on each Earth arrival. Either way, a Falcon-like reusable launch system makes plenty of sense here in terms of making this sort of thing possible.
  - pheldagryph 10y ago
    > a permanently-in-orbit transfer vehicle might make sense here Buzz Aldrin is a big proponent of this approach: https://buzzaldrin.com/space-vision/rocket_science/aldrin-mars-cycler/ https://buzzaldrin.com/space-vision/rocket_science/aldrin-ma...
- skookumchuck 10y ago
  Jet fighters routinely use so much fuel taking off that the first thing they do after gaining altitude is refuel. Rockets can use the same idea.
  - ChuckMcM 10y ago
    Yes but as the ULA whitepaper pointed out there are some challenges to doing so in orbit. For one, the lack of gravity makes it hard to pump fuel. You can spin the tanker to achieve fuel settling but now you are both spinning bodies. Then there is handling cryogenic propellants in space, you get nominal bleed off from warming and again ULA had a really interesting design of an internal combustion engine using the bleed off of Hydrogen and Oxygen as a chiller pump. But suffice it to say, its not as easy as it is flying a jet behind a slow re-purposed jetliner, and doing that is already difficult.
    - skookumchuck 10y ago
      > the lack of gravity makes it hard to pump fuel Evidently this problem is solved, because liquid fuel rockets have been working fine in space since the 60s. (Liquid fuel rockets have their propellants pumped into the chamber.) > nominal bleed off from warming Launch the tanker just beforehand. There won't be time for the fuel to bleed off.
      - NickNameNick 10y ago
        Liquid fuel rockets use Surface tension against the slosh baffles to hold fuel in partially full fuel tanks in place. Ullage motors are used to settle the fuel at the bottom of the tanks, so the main motor pumps can get to it. Once the main motor starts providing acceleration, the ullage motors are no longer required. For cross tanking, keeping the ullage motors running for long enough to transfer all the fuel, without the main motors running might be prohibitive. https://en.wikipedia.org/wiki/Ullage_motor https://en.wikipedia.org/wiki/Ullage_motor
        skookumchuck 10y ago

pinewurst 10y ago

That's not to say that LOR is impossible with a smaller payload. Saturn V enabled a large, complex, redundant set of vehicles. The never successfully launched Soviet N1/L3 with half the TLI payload also used LOR but with much lighter vehicles and a smaller crew.

CydeWeys 10y ago

> Right. SpaceX doesn't have a craft capable of lunar orbit rendezvous Why not? Their Dragon capsules can dock with the ISS; why wouldn't they be able to dock with each, possibly with some kind of adapter? You can imagine one Dragon and a trunk docking with another upper stage that's all fuel tank, heading to the Moon, undocking in orbit, landing, ascending, and rendezvousing in orbit to return home. The total dv requirements of landing on the Moon and ascending again starting from low Moon orbit is 4 km/s. I haven't done the math, but I suspect that you can put together a workable mission using two Falcon Heavy launches. Now, granted, they don't have all the exact pieces put together quite yet, but I suspect they've been thinking about it.

robszumski 10y ago
A lot of the devil here is in the details. You need long term life support that Dragon hasn't proven yet. Deep space communications on the transmit and receive side. Abort scenarios for most or all phases of flight. All of this is untested and requires a huge amount of engineering and manufacturing work. Since this will likely share the same design as the NASA-contracted capsules, these systems will need to pass muster with them. And they don't cut corners.
- CydeWeys 10y ago
  Minor quibble: you don't need deep space communications. The Moon is laughably close. I am quite confident that we can easily make contact with the existing unmodified Dragon capsules by using something like one of these bad boys: https://www.nasa.gov/sites/default/files/goldstone.jpg https://www.nasa.gov/sites/default/files/goldstone.jpg Of course it's laughably overkill for the purpose -- amateur radio operators using much smaller equipment can already send and receive signals to each other by bouncing them off the Moon, which has four times the signal attenuation owing to the doubled distance plus a good deal more in losses from the poor reflectivity of the Moon to radio waves.

Retric 10y ago

SpaceX is already docking with the space station which is similar difficulty as launching from the moon and docking in lunar orbit. The problem is getting a rocket with enough fuel on the surface of the moon without damaging it, not the docking in orbit. Which is even easier than doing the same thing from the surface of Mars. The only advantage of Mars is you don't need to burn fuel slowing down but that's more than offset by a significantly deeper gravity well. On the upside, they can land an un-manned assent vehicle on the surface of Moon / Mars before sending people there. Which can significantly increase your odds of getting back. PS: Yes, NASA did get to the moon and back several times, but they also took a massive chunk of US GDP to do so. https://en.wikipedia.org/wiki/Budget_of_NASA#/media/File:NASA-Budget-Federal.svg https://en.wikipedia.org/wiki/Budget_of_NASA#/media/File:NAS...

jessriedel 10y ago
I don't think either of us know much about this, but I do know that docking with the ISS to unload supplies requires completely different equipment than doing a rendezvous between a lunar lander and a lunar orbiter for Earth return. (That's why I didn't say merely "docking".) The only craft SpaceX has that can land on Earth or the Moon is Dragon. I am pretty sure Dragon does not have enough delta-v to do a full propulsive landing on the moon (no aerobraking available) and then return to orbit. And they definitely don't have the tech to re-fuel in lunar orbit for the return to Earth. None of this equipment exists. Not to mention that this would be a totally new lunar strategy, since the Apollo mission returned to earth in the lunar orbiter (Command Module) rather than re-fueling and returning in the lunar lander.
- Retric 10y ago
  Yea, I am not a rocket guy. However, the minimum delta V to land on the moon is ~1.72 km/s, and you need another 1.72 km/s to get back into orbit + some safety factor ~2.2-2.4 km/s. By comparison it takes ~8km/s to get from LEO to low moon orbit and back to earth. Though you can reduce this by how hard to hit the earth's atmosphere. So, having fuel to land and take off from the moon is not that much worse than getting to the moon and back.

gozur88 10y ago

They'll be able to do LOR in the Dragon 2, which would be ready in time. I question whether they have enough endurance for a lunar landing mission, though, and they would still have to develop a lander.