Category Archives: Technology and Society

Orbits And Suborbits

I’ve updated yesterday’s piece at Ricochet to clarify, for those in comments. I’ve probably discussed this here before, but…

Per discussion in comments, there seems to be some confusion about the difference between high-altitude flight, suborbital flight, and orbital flight. As John Walker points out, orbital flight requires a minimum speed to sustain the orbit, but while that is necessary, it is not a sufficient condition. In fact, a flight can be suborbital with the same speed (energy) as an orbital flight. The best, or at least, most rigorous way to define a “suborbit” is an orbit that intersects the atmosphere and/or surface of the planet. So if you launched straight up at orbital velocity, it would still be a suborbit, because it would (after an hour or two, I haven’t done the math) fall back to the ground. So John’s numbers in terms of comparative energy are roughly correct for the particular vehicles being discussed here (XCOR Lynx and VG SpaceShipTwo), they can’t be generalized for any suborbital vehicle (e.g., a sounding rocket isn’t orbital, but it goes much higher than those passenger vehicles, often hundreds of kilometers in altitude).

The speed necessary to achieve orbit is partly a function of the mass of the body being orbited, but it is also a function of its diameter, and whether or not it has an atmosphere. If the earth were a point mass, an object tossed out at an altitude equivalent to the earth radius (that is ground level) would have very little velocity, but it would have a lot of potential energy. It would fall, gain speed, whip around the center and come back up to the person who had tossed it. That is, it would orbit. So even for the relatively low-energy suborbital vehicles discussed in this post, the reason that they’re not orbital is simply that the planet gets in the way.

One other interesting point is that, under the definition above, subsonic “parabolic” aircraft flights in the atmosphere, to offer half a minute or so of weightlessness (offered by the Zero G company), are suborbital flights, in terms of their trajectory. I put “parabolic” in quotes because in actuality, if properly flown, they are really elliptical sections, as all orbits and suborbits are. The parabola is just a close approximation if you assume a flat earth, which is a valid assumption for the short distances involved. Galileo did his original artillery tables based on flat earth, which is why beginning physics students model cannonball problems as parabolas, but modern long-range artillery has to account for the earth curvature, and it does calculate as elliptical trajectories.

Finally, one more extension. Ignoring the atmosphere, every artillery shell fired, every ball thrown or hit, every long jumper, every person who simply hops up into the air, is in a suborbit. The primary distinction for the vehicles discussed is that they are in a suborbit that reaches a specific altitude (at least a hundred kilometers to officially be in “space”), and leaves the atmosphere.

Clear as mud?

What Happened To My Suborbital Ride?

I have some thoughts and links on the 10th anniversary celebration, over at Ricochet:

Basically, the late Jim Benson of SpaceDev (now part of the Sierra Nevada corporation, which finally seems to have given up on its own plans to use a hybrid motor for its Dream Chaser vehicle) sold Burt Rutan a bill of goods with the hybrid, with claims of simplicity and safety. In fact, as many of us told him at the time, he’d have been a lot better off purchasing a liquid engine from XCOR, but they didn’t have a sufficient track record at the time for him to think they could meet the deadline to win the prize. Then, once they’d (sort of) succeeded in flying something into space, they continued on with what they thought they knew. They’ve been in a sunk-cost trap ever since, unable to get themselves out of the hybrid-propulsion rut.

As I’ve long noted, the delays in the arrival of commercial spaceflight have been a combination of people who knew what to do not having money, and the people how had money not understanding the problem, and being too arrogant to listen to the veterans. Only now is the crucial combination of money and know how finally coming together.

As I note there, I stopped by XCOR in the morning before the event. Looks like they’re making good progress in bringing the spacecraft together.

James Lileks

Internet copyright criminal:

YouTube had detected that I was using a 30-year old performance now owned by Sony, and thus I was VIOLATING EVERYTHING HELD SACRED or words to that effect. One had to marvel at a system that could detect such things, especially since the impression one gets from reading YouTube comments is that the service is aimed at a unique species of chimp that is making the transition from flinging its feces as a means of expressing disagreement to typing words which occasionally add up to an actual sentence.

It’s possible someone would have watched the video, and thought: Interesting piece, this Mahler thing. Even though I have heard but two minutes I believe I have grasped the totality of the work, and will refrain from seeking out the entire movement. Surely more could only add up to less. And thus Sony would be deprived of 23 cents in royalty.

Well, I didn’t own the copyright, and while I could claim Fair Use under the guise of using Mahler’s early use of his own Judaic heritage to score slo-mo goose-stepping spark plugs as means of examining the composer’s nominal acceptance of Christianity to ward off the anti-semitism of fin de siecle Vienna, ahhh, to hell with it.

And yes, before you ask, I am indeed behind on my Lileks.

Dreamchaser And Stratolaunch

I didn’t mention this earlier in the week, but SNC is teaming with StratoLaunch to get a subscale version into orbit. If it’s 75% scale, I figure that’s about 40% of the current interior volume, which lines up with their claim of being able to carry two or three passengers (the full-scale system is designed for seven). The big advantage of such a system would be single-orbit rendezvous, and runway landing, so if it happens, there’d certainly be a market niche for it.