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For Mars probably solar. The ISS's panels provide that much. Any time you're looking at electric propulsion your power plant is going to be a big fraction of

For Mars probably solar. The ISS's panels provide that much. Any time you're looking at electric propulsion your power plant is going to be a big fraction of your vehicle weight.

sp332 9y ago
The current prototype weighs 500 pounds (226 kg) so it could just accelerate itself at 1/400 g. After 100 hours it could be moving at 8,500 m/s but that's not including cargo or solar panels.
- Someone 9y ago
  The Voyagers do around twice that at the moment. So, (very much ballpark, and ignoring all additional weight for fuel, etc.), would that mean this could reach three times their speed in a month, and, after that, catch up with one of them in 15 years or so? If so, is it feasible to build one with enough fuel to accelerate for a year or so? If so, where’s the billionaire willing to spend a few quid on a machine that goes out to photograph one of the Voyagers from close up while it zooms by, or even bring one of them back to earth before the century is over?
  - Symmetry 9y ago
    So, getting up to 25.5 km/s with a rocket with an exhaust velocity of 30 km/s means you need the wet weight to be 2.33 times the dry weight. Last I checked [1] you can get 77 W/kg with photovoltaics so you need you'll need 1402 kg of those in addition to the 226 kg of engine for a total of 1626 kg. Round that up to 2200 kg for structure and tankage and so on for a total we mass of 5126 kg where 2926 kg of that is fuel. You're using that at 5.4/30000=.00018 kg/s for a total of 16255555 seconds of acceleration or about six months. So six months instead of one but basically yes. [1]http://hopefullyintersting.blogspot.com/2015/03/rockets-electric-propulsion.html http://hopefullyintersting.blogspot.com/2015/03/rockets-elec... EDIT: Of course, as it accelerates it'll get further away from the sun leading to less power from the solar panels and a slower acceleration.
    - sp332 9y ago
      Xenon is apparently pretty expensive, like $1,200/kg. Just running it for 100 hours at 0.00018 kg/s will cost $76,800 for the propellant. Plus 10,200 kWh of electricity!
      - jandrese 9y ago
        For a deep space probe that fuel cost is not a showstopper. That's well down in the weeds compared to the cost of launching it to orbit and manning the tracking stations and buying airtime on the Deep Space Network.
      - Symmetry 9y ago
        That's cheap! The launch'll set you back about $100m so another $3.5m for propellant isn't going to be worth worrying about. At some point we'll be wanting to start finding more fuel for our rockets at our destinations. There are ways we know how to do this for oxygen, hydrogen, and methane but getting more xenon on Mars or Titan just isn't doable. So at that point I expect people to switch over to Argon which doesn't ionize quite as easily but can be found all over the solar system.
        sp332 9y ago
        Or we could set up a Xenon distillery at Jupiter, where it's more abundant :)
        Symmetry 9y ago
        I don't envy whoever would have to haul it up that gravity well.
  - robotresearcher 9y ago
    Before doing more estimates, it's probably worth adding in the mass of a plausible payload i.e. the scientific instruments that are the purpose of the spacecraft.

For Mars probably solar. The ISS's panels provide that much. Any time you're looking at electric propulsion your power plant is going to be a big fraction of your vehicle weight.

sp332 9y ago

The current prototype weighs 500 pounds (226 kg) so it could just accelerate itself at 1/400 g. After 100 hours it could be moving at 8,500 m/s but that's not including cargo or solar panels.

Someone 9y ago
The Voyagers do around twice that at the moment. So, (very much ballpark, and ignoring all additional weight for fuel, etc.), would that mean this could reach three times their speed in a month, and, after that, catch up with one of them in 15 years or so? If so, is it feasible to build one with enough fuel to accelerate for a year or so? If so, where’s the billionaire willing to spend a few quid on a machine that goes out to photograph one of the Voyagers from close up while it zooms by, or even bring one of them back to earth before the century is over?
- Symmetry 9y ago
  So, getting up to 25.5 km/s with a rocket with an exhaust velocity of 30 km/s means you need the wet weight to be 2.33 times the dry weight. Last I checked [1] you can get 77 W/kg with photovoltaics so you need you'll need 1402 kg of those in addition to the 226 kg of engine for a total of 1626 kg. Round that up to 2200 kg for structure and tankage and so on for a total we mass of 5126 kg where 2926 kg of that is fuel. You're using that at 5.4/30000=.00018 kg/s for a total of 16255555 seconds of acceleration or about six months. So six months instead of one but basically yes. [1]http://hopefullyintersting.blogspot.com/2015/03/rockets-electric-propulsion.html http://hopefullyintersting.blogspot.com/2015/03/rockets-elec... EDIT: Of course, as it accelerates it'll get further away from the sun leading to less power from the solar panels and a slower acceleration.
  - sp332 9y ago
    Xenon is apparently pretty expensive, like $1,200/kg. Just running it for 100 hours at 0.00018 kg/s will cost $76,800 for the propellant. Plus 10,200 kWh of electricity!
    - jandrese 9y ago
      For a deep space probe that fuel cost is not a showstopper. That's well down in the weeds compared to the cost of launching it to orbit and manning the tracking stations and buying airtime on the Deep Space Network.
    - Symmetry 9y ago
      That's cheap! The launch'll set you back about $100m so another $3.5m for propellant isn't going to be worth worrying about. At some point we'll be wanting to start finding more fuel for our rockets at our destinations. There are ways we know how to do this for oxygen, hydrogen, and methane but getting more xenon on Mars or Titan just isn't doable. So at that point I expect people to switch over to Argon which doesn't ionize quite as easily but can be found all over the solar system.
      - sp332 9y ago
        Or we could set up a Xenon distillery at Jupiter, where it's more abundant :)
        Symmetry 9y ago
        I don't envy whoever would have to haul it up that gravity well.
- robotresearcher 9y ago
  Before doing more estimates, it's probably worth adding in the mass of a plausible payload i.e. the scientific instruments that are the purpose of the spacecraft.