Friday, September 5, 2008

A Solution to the Launch Problem? Maybe.

If you want to really blow the doors off space development, read on. This might be it.

Transportation from Earth to orbit, space launch, is extremely expensive ($2K - 20K per kg) and dangerous (a few percent failure rate). This is what makes everything we do in space so ridiculously expensive. The fundamental reason for this difficulty is the extremely high temperatures, large forces, and fast decision making required to ride a tower of flame to orbital velocity (~28,000 km/hr).

Floating to Space by experimentalist John Powell lays out a solution that just might work; at a tiny fraction of the cost of alternatives. The basic idea is to use three types of lighter-than-air ships. The first travels from Earth to about 120,000 feet. Research balloons do this all the time, no problem. The second lives permanently at about 120,000 feet. Research balloons have stayed this high for long periods of time, but permanence requires on-site maintenance and Powell seems to understand more-or-less how to do this. More important, he has demonstrated some of the key capabilities in ground test. The last vehicle is a km-scale, inflatable, hypersonic flying wing that uses electric thrusters to achieve orbital velocity over a period of days. This is the hard part.

I don't know how to figure out if this works, but I intend to learn. It might be easier than many a launcher development we have already achieved. The key is that the atmosphere doesn't end at 100 km, it extends much further although it is very diffuse. The vehicle's enormous size allows aerodynamic forces generated by a diffuse atmosphere to provide lift. This lift allows very slow acceleration into orbit. Slow acceleration allows use of extremely efficient electric propulsion. Deorbit is relatively easy - pitch the vehicle up to expose its enormous cross section to atmospheric forces. This will decelerate the vehicle enough in a diffuse atmosphere that reentry heating is minor. The orbital vehicle then docks with the station at about 120,000 ft. Unlike today's rockets, there are no high temperatures, no enormous forces, and time is measured in hours not milliseconds. This just might be relatively easy to do. Maybe.

Powell's book is written for the lay public. Although he lays out the approach and the known problems, there is not enough detail to make a technical evaluation. The good news is that Powell is very open about his failures as well as his successes. He meticulously describes the dozens of balloon launches JP Aerospace, his company, has attempted with an entertaining description of the many accidents and problems. In addition, there is an entire section of the book devoted to the challenges that must be overcome. To my mind the most difficult and critical is reducing the orbital vehicle's drag -- or perhaps providing more thrust. Current materials, vehicle designs, and engines are insufficient.

America is spending nearly a billion dollars per shuttle flight. Flights after 2010, if funded, will cost two billion dollars apiece. For a fraction of one shuttle launch we could find out if Powell's vision will work. If it does, for far less than NASA's new launcher, we might well drop the cost of launch by a factor or 10 or more. Maybe much more. This would allow space solar power, lunar and martian bases, space settlement, asteroid mining and a thousand other applications to bloom. The wealth, power, and knowledge to be gained are immense.

If Powell is close to right, we need to do this. Now.

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