For the obvious reasons, I invariably get too busy to blog exactly when things get interesting...
One of the results of the Space Elevator Feasibility Condition is a lower bound on the power density of Space Elevator vehicles.
Power density is a measure for how powerful a motor system is in respect to its mass. In the case of a Space Elevator climber, the system mass must include the motor, the PV array, any cooling systems, and structure mass used to aid locomotion – basically everything but the cargo hold.
For a Carbon Nanotube tether that is 30 MYuri strong, and a characteristic time constant (CTC) of 1 year (Confused? Curious? Read the paper!) the Feasibility Condition requires that the climbers will have a power density of at least 1.0 kWatt/kg.
So where do the competition requirements stand in respect to this?
It is easy to show that when moving straight up, the power density of the climber is directly proportional to its speed (mgv/m), and so a 5 m/s speed in 1 g gravity corresponds to 50 Watt/kg, or about 5% of a real Space Elevator climber.
So how difficult is it to improve this performance by a factor of 20?
Not impossibly so.
The climbers built by the teams are designed to be rugged, and even at 5 m/s are having to deal with significant wind resistance. Even though they are designed to be lightweight, the actual panels on a Space Elevator climber will be much lighter. In space, lacking wind, and lacking cooling air, the PV panels will look more like Saran Wrap or Aluminum Foil than like real “panels”.
The PV panel shown below was manufactured by DLR in Germany, with the intent to be used in space. It is so thin and large (see the people in the back for scale) that it will never survive even the lightest winds on Earth and can fit into the little box at the center (from which it was deployed). In space, however, it would be the ideal building block for a Space Elevator climber, and even today this panel performs at several times the power density we need for a Space Elevator climber.
One of the nice things about this panel is that it is designed for Solar radiation, which means that after the initial laser-boosted stages of the climb, the climber can make the rest of the way (about 80% of it) using sunshine alone, which makes it easy to drive several climbers simultaneously.
Electric motors that operate at the kWatt/kg range exist today (though they are not super efficient), but ironically, the same CNTs that make tethers stronger, stand a very good chance of reducing the weight of electric motors by replacing the metallic windings that are in them.
So to conclude – on the power side of the feasibility condition, the building blocks are there – the solid state lasers, the PV receivers, the advanced motors and power electronics. Not ready to be assembled within a year, of course, but certainly within reach in the 10-year outlook.