Rocketman has a post on the X-Prize and related subjects that’s worth reading, but there are a couple problems with it.

This is the most egregious:

The difference in energy required for a vehicle to reach the 100 mile altitude necessary to achieve orbit is ~25 times greater than the energy necessary to reach an altitude of 50 miles (I leave it as an exercise for the readers to figure out the difference in energy necessary between 62.5 and 100 miles).

This makes no sense at all. The difference in altitude between 50 and a hundred miles is, well, fifty miles. It’s merely doubled, so it makes no sense that it would be twenty five times the energy.

The problem of course, is that there are two components to energy–the specific potential energy as represented by the altitude (approximated as gravity times the altitude), and the kinetic energy, corresponding to the velocity (half the velocity squared). By ignoring the latter, this statement comes out completely garbled (and the exercise left for the readers is utterly meaningless, and would be frustrating to any who attempted it). Energy is a combination of both altitude and velocity, and the big problem in getting into orbit isn’t the former, but the latter.

Orbit is harder because it has go faster, not because it has to go higher. X-Prize is probably achievable at Mach three or four (say, a couple thousand miles an hour), and getting to a hundred miles wouldn’t require much more energy. Orbit requires seventeen thousand miles an hour–that’s the real killer.

He makes another point that’s more arguable (as opposed to physical nonsense), and I’ll argue it, as I did in last night’s post and today’s Fox column.

The statement that the “‘harsh environment’ of space was less harsh than that imposed by the ocean on the submersible” is just silly. Deep Rover operates in the ocean at a maximum depth of 1000 meters (3280 ft). At that depth, you are surrounded by water that is at ~40 degrees F and ~120 PSI. In space you are in a vacuum and your vehicle is exposed to direct solar energy that heats up one side of the vehicle and the vacuum of space that cools off the other.

The temperature extremes that exist in space create some difficult engineering problems because of the differences in thermal contraction and expansion that occurs between dissimilar materials. I have had to deal with these problems in my designs, and it is not trivial to engineer effective solutions.

Unlike vehicles that operate in salt water, the choice of materials that can be used in space is extremely limited. Most common materials get brittle at cold temperatures, and they also outgas in a vacuum, which changes their material properties. Some materials have problems with salt water, but there are many common materials that can be used under the conditions Deep Rover operates at.

But the biggest difference between a submersible and a spacecraft is that submersibles do not have to fly. You can afford to have relatively large factors of safety and, if necessary, redundant components in a submersible because weight is not a big issue. Also, spacecraft are subjected to tremendous dynamic and acoustic vibrations during launch, vibrations submersible never see. Designing and testing components to handle the vibrations of launch is again not a trivial problem (I speak from experience on this as well).

No matter what Maryniak would like to believe, space is an extremely harsh environment to design for. It also is not cheap to test components to determine how they will handle that environment. You cannot just sail out to deep water and drop your vehicle in the ocean to test it like you can with a submersible. Environmental chambers with liquid nitrogen ?cold walls,? large halogen lamps and huge vacuum pumps are needed to conduct these tests. And even the largest of these chambers is incapable of testing a complete launch vehicle, so components have to be tested individually.

They’re both harsh environments–but they’re different kinds of harsh. The marine environment is extremely corrosive, and it’s much more difficult, from a structural standpoint, to deal with many atmospheres of positive pressure (the deep sea) than a single atmosphere of negative pressure (the vacuum of space). Yes, space has radiation and temperature extremes that the ocean doesn’t, but both environments are harsh. For example, the choice of materials that can operate in salt water are limited as well.

Many of the implications of expensive launch are subtle, but they validate Gregg’s (and my) point.

Every objection that he has would be obviated by cheap launch, a point with which even he agrees at the end. If launch were cheap, you could afford heavier satellites, because the additional mass wouldn’t be so expensive. If launch were cheap, you could afford more redundancy. Cheap launch systems will have relatively smooth rides (because they’ll have to in order to be reliable and affordably reusable) so the launch environment won’t be an issue. Cheap launch implies affordable test facilities on orbit, so the components can be tested more easily.

So I’m not sure what his point is in arguing with Gregg on this issue.