Radar

The Launch Loop and the Space Elevator are both long and skinny, and need to move out of the way of large space debris. The space elevator moves radially, and the launch loop moves up and down. In both cases, it does not matter where along the line of the system that an impact might occur; we are moving the whole line, the less the better. So, we need high radial accuracy for impactor trajectories, and little axial accuracy. That suggests an asymmetrical radar emitter and receiver, very wide and not so tall for the space elevator, tall and not so wide for the launch loop.

Launch Loop

Space Elevator

The space elevator will have an array of radars in a circle around the space elevator ribbon on the top of the 50km platform. We are not concerned with material that is going to miss - that will have a large horizontal angular velocity when viewed from the radar. We are much more concerned with small material which is likely to hit the ribbon - it will not change incoming angle much.

From the high platform, we can see debris coming from thousands of kilometers away. Assume that we can see through 30km altitude atmosphere (1.5% of sea level atmosphere) and that we are using Ka band radar at 34GHz (the police radar band, not many police in the mid Pacific!). Assume we are looking for objects in circular orbits; while many actual orbits will be elliptical, they tend to decay towards circular. The analysis does not change much for elliptical tracks, anyway.

MORE LATER

• http://www.esa.int/esapub/bulletin/bullet109/chapter16_bul109.pdf

• http://www.fhr.fgan.de/fhr/fhr_c589_en.html

• http://orbitaldebris.jsc.nasa.gov/measure/optical.html