Advanced propulsion for future of space exploration (Event write-up part 1)

Edgar Choueiri of Princeton was presenting at the D.C. Philosopher's club. To start with context, he provided a logarithmic scale map of the universe that was just a bit out of date given NASA's recent announcement of 1200 more solar systems likely to hold planets. On the map he noted that traveling from D.C. to Boston is less distance than getting to space. Thus as prep for going to Mars, traveling to the International Space Station is like Columbus dipping his toe in the Atlantic.  GPS satellites are a bit further out and geostationary satellites past that. Our Deep Space probes, Voyager 1, Voyager 2 are approaching Heliopause the edge of the solar system. They're traveling at 14k / sec which means it would take them 74,000 years to get to the nearest star. By comparison radio communications from Earth have now hit about 10,000 stars.

First question, how do we get a space station to geostationary orbit? Answer: Not chemical rockets but space elevator. You would need a cable 36,000 km long tethered to an asteroid. Very stable because the gravitational potential keeps it taut. The cable would need a strength of 70 giga pascals or 100* the strength of steel. A carbon nanotube can get to 100-110 giga pascals. However, the record length of nanotubes is 18.5 centimeters of nanotube which is an improvement over microns a few years ago. The point of the space elevator is saving money. It gets the per kilogram cost to low-earth orbit down from $10k to $20k to between $200-$400. For the farther out Geostationary orbit, the per kilogram cost cost would drop from around $100,000 to around $2,000 – $4,000. The most logical place to put the space elevator would be at the equator. Interestingly enough, space debris isn't really a problem due to the extremely small cross section of a nano-tube. Obviously the transport itself would have a much larger profile, but it would also have the ability to manipulate its rate of ascent or descent and detect debris, so it would be a manageable problem. I found this an unsurprising answer, although I've heard a lot of debate about the viability of space elevators and Dr. Choueiri's focus seemed more to be rocketry rather than proving the viability of the tubes. However, given the greater detail, I don't have time to write-up the more advanced propulsion mechanisms, and thus will finish my summary tomorrow.