Space Access: Henry Spencer on Affordable Spaceflight Beyond LEO

Henry Spencer
“Affordable Spaceflight Beyond LEO: Alternative Approaches, Paths Not Taken”

If you look at destination points beyond LEO, the moon is the obvious destination…

  • Relatively close
  • Interesting place to explore
  • Resources available

L1 and L2 points

  • a bit further away, longer travel time
  • Other than satellite maintence and refueling, not much interest in these regions


  • Much further away
  • Phobos and Deimos are closer to LEO in terms of Delta V than the moon
  • But, it takes longer and your return windows are longer due to orbit


  • Rendezvous with an asteroid, spend some time there, then jump off as it gets near Earth
  • Can do human missions with relative easy adapations of hardware
  • Suitable asteroids – one every year or two

Issues with Asteroid Missions

  • Patience
  • Radiation from cosmic rays and potentially fatal solar flares – need a storm shelter area
  • Large crew quarters – inflatable habitats might solve the problem
  • Tougher heat shield
  • Liquid hydrogen fuel – boil off issues

Lunar Missions

  • LEO refeuling capability
  • Not many changes required for moon vs. deep space
  • Colder environment
  • Continuous sunlight mostly
  • Shadows can last longer
  • Radiation issues – mostly with van Allen belt passage
  • Solar flares
  • Communications and navigational issues – detailed changes

Best Approaches

  • Long-terrm viewpoint focused on transportation services, multiple destinations and understanding methods and destinations will change
  • Focus on Mars could lead to a tightly focused, dead-end program that goes to the most interesting place possible before political support dies
  • Focus on affordable operations costs so you can fly over and over again
  • Evolutionary approach focused on technology that can be adapated for many missions – not revolutionary giant leap
  • If you’re focused on orbital assembly, then heavy lift doesn’t make a lot of sense

Earth to Orbit Issues

  • Base in LEO
  • Resonant orbits for first-orbit rendezvous
  • Tugs for altitude matching
  • Expendable tether as an upper stage and for de-orbiting the vehicle

Orbital Assembly

  • Decouples launch from departure
  • No weight growth problems
  • No follow-on mission problems
  • Using more launches is good
  • Requires semi-storage fuels – may not be able to use liquid hydrogen
  • Trade-off of additional launches for lower development costs

Moon Exploration Issues

  • High Delta V requirement
  • No atmosphere to help with descent
  • Critical navigation and piloting – time critical
  • Reusable vehicles – don’t want to throw away the spacecraft every time
  • No easy place to put an orbital base – low lunar orbits not stable
  • Lunar Lagrange point is a bit distant – awkward for lunar operations

Lunar Surface Operations

  • Lunar surface is difficult environment
  • Engineers overly optimistic about extracting resources from the soil
  • Equipment and processes will need debugging