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

Mars

• 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

Asteroids

• 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