Chair Force Engineer

Friday, August 21, 2009


The fun in a James Bond movie lies in the way it can take the classic James Bond formula and put a fresh twist on it. Example: in most Bond movies, Agent 007 saves the world and gets the girl by the end. In 1965's Thunderball, James Bond and the girl are seemingly stranded in a raft in the middle of the ocean after a climactic battle aboard a yacht. Never fear, as Agent 007 always has a gadget from Q-branch to come to the rescue. In this case, he inflates a balloon tethered to himself and his damsel. On cue, a modified B-17 swoops in and snares the hero and heroine using a cable-catcher on the aircraft's nose.

What does this escapist Bond-fantasy have to do with spaceflight? Well, it's a flashy way of demonstrating the technique of midair recovery for spacecraft. After much trial-and-error, it was perfected for snatching re-entering film canisters, descending under parachute. Mid-air recovery is one thing for tiny film capsules. It's quite another matter to attempt it with a manned capsule, or a recoverable engine module. Yet Bigelow Aerospace wants to try the former, and United Launch Alliance is proposing the latter.

In principle it's not difficult, but it creates challenges for the aircraft involved. In the case of large objects descending under parachute, the suspended load mustn't be carried too far off-center, or it will create a situation where the aircraft is fighting a steep bank. It also creates an asymmetric drag force, greatly impeding the aircraft's top speed and adding pitch and yaw tendencies. The aircraft selected for the mission will need to be capable of flying with the payload mass of the object being captured. Even still, the aircrew will notice an immediate loss in altitude and airspeed when the capture is made, as well as a downward pitching moment.

The size of the aircraft making the grab is important. Just as airplanes like the C-119 were unaffected by catching tiny film canisters, a larger airplane will be required to snag larger capsules. I can't give some kind of first-order guess as to which airplanes would be suitable for the midair recovery mission, but the Bigelow trade study will definitely give us an answer.

While avoiding a water landing is desirable, it's still a necessary contingency to plan for. In the event of an abort from existing launch sites, the spacecraft will splash down in coastal waters. A flotilla will still remain on standby, even if midair recovery is the preferred option. If a flotilla is required for launch aborts, it's worth keeping around in case midair recovery fails.

Midair recovery for booster engines is a good idea, because exposure to saltwater could be fatal to any attempts at engine re-use. It's certainly worthy of study for manned capsules, because it spares the astronauts the possibility of being exposed to frigid Atlantic waters which could potentially sink the capsule before the astronauts could be rescued. But the launch abort issue ensures that the recovery flotilla isn't going away anytime soon.