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You want to get all the exploding done before you launch the rocket with crew aboard. Saturn V could lift 140 tonnes to low earth orbit. Falcon Heavy can lift

by twic 6y ago

You want to get all the exploding done before you launch the rocket with crew aboard. Saturn V could lift 140 tonnes to low earth orbit. Falcon Heavy can lift 54 tonnes to low earth orbit. I think that means it could get a mission to the moon as long as it weighed 38% of what Apollo did. That doesn't sound like a fun trip. Unless you assemble the moon ship in earth orbit first. Falcon Heavy can launch Orion on its own, or the European Service Module that it requires. I imagine it could launch a lunar lander too. You would also need a booster to send the combination to the moon - the Saturn final stage that did that weighed 100 tonnes, twice what Falcon Heavy can launch. So, maybe you launch an empty booster, and send up a couple of tankers to fuel it on orbit? It's a lot of launches, and a lot of work to do in orbit. That's not impossible (and is cool as hell), but there would be a lot of work to do to make it possible.

inetknght 6y ago
> Saturn V could lift 140 tonnes to low earth orbit. Falcon Heavy can lift 54 tonnes to low earth orbit. I think that means it could get a mission to the moon as long as it weighed 38% of what Apollo did. That doesn't sound like a fun trip. While I haven't yet seen anything concrete, SpaceX's definitely wants to have orbital refueling. If I recall, that's actually one of SpaceX's requirements for Starship. Orbital refueling would mean that lift capacity to LEO doesn't translate directly the range beyond LEO.
- chasd00 6y ago
  orbital refueling makes a lot of sense, do you know if there are plans to manufacture the fuel in orbit? That would be somewhat good practice for producing fuel on Mars. At lease they would know not to forget anything, no making a quick trip to Home Depot while in orbit.
  - chrisjc 6y ago
    I've heard about approaches for manufacturing fuel on the Moon, but I can't imagine how you might manufacture it in earth's orbit. What are the leading ideas around this approach? edit: i know we can launch more fuel into orbit, and I really emphasize the "manufacturing" in orbit part.
    - twic 6y ago
      Collect a water-ice asteroid or cometary nucleus or some such, park it in orbit, and electrolyse it. I'm not aware of a less outlandish plan! Now, if you want oxidiser, you could skim air off the top of the earth's atmosphere. I have no idea if that has been considered outside of science fiction [1], though. [1] okay, here they're skimming nitrogen, but: https://en.wikipedia.org/wiki/Fallen_Angels_(science_fiction_novel) https://en.wikipedia.org/wiki/Fallen_Angels_(science_fiction...
      - Turing_Machine 6y ago
        If you were electrolyzing water ice, wouldn't you get both hydrogen (fuel) and oxygen (oxidizer), by definition?
        deleted 6y ago
        [deleted]
        twic 6y ago
        Yes. But if you only wanted oxidiser, you could skip the awkward "capture a cometary nucleus" step by scooping air. Since oxygen is much heavier than hydrogen, this could save you a lot in mass launched from the Earth.
        m4rtink 6y ago
        Also if you had enough power (solar or possibly nuclear) you could use the captured gases directly for slightly inefficient propulsion by heating them NERVA style or accelerating them by a modifiedion engine. I remember some concepts for very low altitude satellites that compensate for drag by running a solar powered ion ramjet. :)
    - Someone 6y ago
      The main problem would be getting the necessary atoms to your factory. It likely would be easier to construct fuel on earth or on the moon and send it up. (If your rocket exploded the ‘BOOM’ might be a bit louder if its cargo were rocket fuel instead of raw materials for rocket fuel, but the practical difference would be zero) Your best bet would be to use mass that’s present in space, but unfortunately (1), there isn’t that much in orbit. In theory, one could scope up cosmic dust, tiny meteorites, and old satellites in orbit. It would be a challenge to scale that up, though. https://en.wikipedia.org/wiki/Stardust_(spacecraft) https://en.wikipedia.org/wiki/Stardust_(spacecraft) didn’t catch kilograms of stuff, even though it explicitly went for a comet. Capturing a larger meteorite would work, but larger meteorites are harder to catch. If you’re extremely ambitious, build a solar powered particle accelerator in space, use it to create electrons, neutrons and protons (https://en.m.wikipedia.org/wiki/Matter_creation https://en.m.wikipedia.org/wiki/Matter_creation), turn those into atoms, and build fuel from those (apart from the practical problem of scaling that up, there are ‘a few’ Ph.D’s to be earned there.) (1) or fortunately, as having lots of mass there would make space flight dangerous (https://en.wikipedia.org/wiki/Space_debris https://en.wikipedia.org/wiki/Space_debris)
  - rtsil 6y ago
    Manufacturing fuel in orbit requires sending the plant in orbit, extracting the raw materials, packaging them then bringing them up there and also involves sending a ship every time a maintenance is needed, unlike Mars where the raw material (water, CO2) are already nearby. ISRU (in situ resource utilization) is the best way to go, i.e. you bring the plant to Mars but at least you use the local raw materials.
avmich 6y ago
> Saturn V could lift 140 tonnes to low earth orbit. Just to be pedantic, remember, that the only thing Saturn-V brought to LEO and left there was Skylab, with mass 77 tons. Other than that you counting parts of Saturn-V itself as part of payload, which is inconsistent - you don't count mass of Falcon-9 second stage as part of payload, for example, even though it gets to orbit. Saturn-V is better characterized by the mass it leaves on translunar orbit, which is 48,6 tons. For LEO it's awkwardly lopsided with mass of 3rd stage and remaining fuel. In other words, if you have a 140 tons satellite, you couldn't get it to LEO with Saturn-V. So the comparison is wrong.
- twic 6y ago
  Good points. I think the reason this is complicated is that the Apollo missions included one stage, the S-IVB, which was used twice, for getting into low earth orbit, and for departing for the moon. You have to count some fraction of that as mass lifted to orbit, but i don't know how much.
rbanffy 6y ago
> Falcon Heavy can lift 54 tonnes to low earth orbit. I think that means it could get a mission to the moon as long as it weighed 38% of what Apollo did You can launch the lander first, park it in lunar orbit, then launch the crew on a second Falcon Heavy, each having 38% of an Apollo worth of mass. With a little more creativity, you can launch the ascent vehicle on another Falcon Heavy and land it before the other two so that astronauts can rest assured that, unless they kill themselves during the landing, there is a ride back up waiting for them. With that you can have 3 separate chronograms and each mission is simplified in relation to a single Apollo. If you are unhappy with the mass budget, you can launch yet another series of missions with supplies and equipment to be landed before the ascent vehicles are landed. And, since in this case whatever lands doesn't even need to be pressurized, or delicate, landing it should be much easier too. Now we are at 1.52 Apollo masses per mission. It took 4 launches to get there but, still, it's a lot of stuff for our astronauts to work with. Also, if any one launch fails, you can always try again.
- m4rtink 6y ago
  One think to note is that if you use cryogenic proplants for your lander or lunar tug, you might face issues with fuel and oxidizer boiling off over time (unless you go for very good isolation or use active cooling, both rather heavy), reducing your time window to have everything launched & used. You can opt for hypergolic propellants that won't boil off, but you sacrifice performance and make ground handling more expensive and dangerous due to these being highly toxic.
  - rbanffy 6y ago
    You can use cryogenics for the landers and depots that don't stay parked in lunar orbit for long, but any assets with long shelf life should use hypergolics. And now my mission profile has two different landing modules, one using cryogenics, one using hypergolics. Oh well... We can always go hypergolic if the mass budget is not a big issue.
- nradov 6y ago
  Requiring the astronauts to execute a cross country EVA from the lander to the ascent vehicle seems like a huge risk. What if they land just slightly too far away?

by twic 6y ago

inetknght 6y ago

> Saturn V could lift 140 tonnes to low earth orbit. Falcon Heavy can lift 54 tonnes to low earth orbit. I think that means it could get a mission to the moon as long as it weighed 38% of what Apollo did. That doesn't sound like a fun trip. While I haven't yet seen anything concrete, SpaceX's definitely wants to have orbital refueling. If I recall, that's actually one of SpaceX's requirements for Starship. Orbital refueling would mean that lift capacity to LEO doesn't translate directly the range beyond LEO.

chasd00 6y ago
orbital refueling makes a lot of sense, do you know if there are plans to manufacture the fuel in orbit? That would be somewhat good practice for producing fuel on Mars. At lease they would know not to forget anything, no making a quick trip to Home Depot while in orbit.
- chrisjc 6y ago
  I've heard about approaches for manufacturing fuel on the Moon, but I can't imagine how you might manufacture it in earth's orbit. What are the leading ideas around this approach? edit: i know we can launch more fuel into orbit, and I really emphasize the "manufacturing" in orbit part.
  - twic 6y ago
    Collect a water-ice asteroid or cometary nucleus or some such, park it in orbit, and electrolyse it. I'm not aware of a less outlandish plan! Now, if you want oxidiser, you could skim air off the top of the earth's atmosphere. I have no idea if that has been considered outside of science fiction [1], though. [1] okay, here they're skimming nitrogen, but: https://en.wikipedia.org/wiki/Fallen_Angels_(science_fiction_novel) https://en.wikipedia.org/wiki/Fallen_Angels_(science_fiction...
    - Turing_Machine 6y ago
      If you were electrolyzing water ice, wouldn't you get both hydrogen (fuel) and oxygen (oxidizer), by definition?
      - deleted 6y ago
        [deleted]
      - twic 6y ago
        Yes. But if you only wanted oxidiser, you could skip the awkward "capture a cometary nucleus" step by scooping air. Since oxygen is much heavier than hydrogen, this could save you a lot in mass launched from the Earth.
        m4rtink 6y ago
        Also if you had enough power (solar or possibly nuclear) you could use the captured gases directly for slightly inefficient propulsion by heating them NERVA style or accelerating them by a modifiedion engine. I remember some concepts for very low altitude satellites that compensate for drag by running a solar powered ion ramjet. :)
  - Someone 6y ago
    The main problem would be getting the necessary atoms to your factory. It likely would be easier to construct fuel on earth or on the moon and send it up. (If your rocket exploded the ‘BOOM’ might be a bit louder if its cargo were rocket fuel instead of raw materials for rocket fuel, but the practical difference would be zero) Your best bet would be to use mass that’s present in space, but unfortunately (1), there isn’t that much in orbit. In theory, one could scope up cosmic dust, tiny meteorites, and old satellites in orbit. It would be a challenge to scale that up, though. https://en.wikipedia.org/wiki/Stardust_(spacecraft) https://en.wikipedia.org/wiki/Stardust_(spacecraft) didn’t catch kilograms of stuff, even though it explicitly went for a comet. Capturing a larger meteorite would work, but larger meteorites are harder to catch. If you’re extremely ambitious, build a solar powered particle accelerator in space, use it to create electrons, neutrons and protons (https://en.m.wikipedia.org/wiki/Matter_creation https://en.m.wikipedia.org/wiki/Matter_creation), turn those into atoms, and build fuel from those (apart from the practical problem of scaling that up, there are ‘a few’ Ph.D’s to be earned there.) (1) or fortunately, as having lots of mass there would make space flight dangerous (https://en.wikipedia.org/wiki/Space_debris https://en.wikipedia.org/wiki/Space_debris)
- rtsil 6y ago
  Manufacturing fuel in orbit requires sending the plant in orbit, extracting the raw materials, packaging them then bringing them up there and also involves sending a ship every time a maintenance is needed, unlike Mars where the raw material (water, CO2) are already nearby. ISRU (in situ resource utilization) is the best way to go, i.e. you bring the plant to Mars but at least you use the local raw materials.

avmich 6y ago

> Saturn V could lift 140 tonnes to low earth orbit. Just to be pedantic, remember, that the only thing Saturn-V brought to LEO and left there was Skylab, with mass 77 tons. Other than that you counting parts of Saturn-V itself as part of payload, which is inconsistent - you don't count mass of Falcon-9 second stage as part of payload, for example, even though it gets to orbit. Saturn-V is better characterized by the mass it leaves on translunar orbit, which is 48,6 tons. For LEO it's awkwardly lopsided with mass of 3rd stage and remaining fuel. In other words, if you have a 140 tons satellite, you couldn't get it to LEO with Saturn-V. So the comparison is wrong.

twic 6y ago
Good points. I think the reason this is complicated is that the Apollo missions included one stage, the S-IVB, which was used twice, for getting into low earth orbit, and for departing for the moon. You have to count some fraction of that as mass lifted to orbit, but i don't know how much.

rbanffy 6y ago

> Falcon Heavy can lift 54 tonnes to low earth orbit. I think that means it could get a mission to the moon as long as it weighed 38% of what Apollo did You can launch the lander first, park it in lunar orbit, then launch the crew on a second Falcon Heavy, each having 38% of an Apollo worth of mass. With a little more creativity, you can launch the ascent vehicle on another Falcon Heavy and land it before the other two so that astronauts can rest assured that, unless they kill themselves during the landing, there is a ride back up waiting for them. With that you can have 3 separate chronograms and each mission is simplified in relation to a single Apollo. If you are unhappy with the mass budget, you can launch yet another series of missions with supplies and equipment to be landed before the ascent vehicles are landed. And, since in this case whatever lands doesn't even need to be pressurized, or delicate, landing it should be much easier too. Now we are at 1.52 Apollo masses per mission. It took 4 launches to get there but, still, it's a lot of stuff for our astronauts to work with. Also, if any one launch fails, you can always try again.

m4rtink 6y ago
One think to note is that if you use cryogenic proplants for your lander or lunar tug, you might face issues with fuel and oxidizer boiling off over time (unless you go for very good isolation or use active cooling, both rather heavy), reducing your time window to have everything launched & used. You can opt for hypergolic propellants that won't boil off, but you sacrifice performance and make ground handling more expensive and dangerous due to these being highly toxic.
- rbanffy 6y ago
  You can use cryogenics for the landers and depots that don't stay parked in lunar orbit for long, but any assets with long shelf life should use hypergolics. And now my mission profile has two different landing modules, one using cryogenics, one using hypergolics. Oh well... We can always go hypergolic if the mass budget is not a big issue.
nradov 6y ago
Requiring the astronauts to execute a cross country EVA from the lander to the ascent vehicle seems like a huge risk. What if they land just slightly too far away?