I Have Just One Question

…about tonight’s debate.

Has Kerry learned his lesson yet, or will it still be possible to get hammered by playing the simple drinking game of taking a sip of wine every time he says the word “Vietnam”?

[Friday morning update]

OK, credit where credit’s due. By my count, he referred to his service only three times, and used the actual word “Vietnam” once. Maybe he is learning. However, ultimately, while Bush could have done better, Kerry finished himself off with the “global test,” and the notion that the US can’t be trusted with nukes. It’s the same old nuclear freeze mentality from the eighties. He appealed to his party’s left to hold the base, and he’s lost the center.

My Theory

Which is mine.

The fact that the roll problem seems to get worse as the burn progresses could be a result of:

  1. higher acceleration as the vehicle gets lighter
  2. less atmosphere as altitude increases, with correspondingly less aerodynamic control
  3. increasing thrust asymmetries as the nozzle erodes

I’m guessing that it’s a combination of all of the above and that the vehicle doesn’t have enough RCS control authority to muscle past the (unplanned) thrust asymmetries. The pilot is probably fighting to keep the nose pointed forward, and as Brett Buck suggested, yaw and pitch moments are getting coupled into roll.

If so, this is a problem that could be solved with a better engine nozzle design, thrust vector control on the main propulsion (a more expensive fix), more powerful RCS jets, or all of the above.

As I said previously, though, this shouldn’t necessarily prevent them from winning the prize, as is.

says it was caused by a “known deficiency”:

The unplanned corkscrew maneuver Wednesday was characterized as a “spin-stabilized” roll. Rutan said there

First Leg Successful

Sorry for not posting sooner, but my DSL connection’s been flaky all morning.

I’m concerned about that roll we saw during ascent. I was very concerned when it seemed to be accelerating, but it looks like he got it under control after engine shutdown. I wouldn’t fly again until I understood what caused that. I’m pretty sure that I wouldn’t want to ride a vehicle that did that, though others’ mileage may vary.

It was a little irritating to listen to John Pike on Fox. On the one hand, he actually did seem to be cheering them on, but he’s out of date on current events. He told the Fox hosts that DaVinci was planning to fly in the next few days, when they’ve announced that they’re delayed several weeks. It would be nice if media people could get some other names in their space rolodexes than John’s.

Maybe more thoughts later.

[Update]

Bruce Hoult (in comments to this post thinks that it’s being caused by swirl in the oxidizer flow of the engine. I doubt that. Brett Buck has a different, and more plausible to me (and more disturbing, if correct) diagnosis over at sci.space.policy:

…the problem appeared to be a coupling from yaw
to roll – definitely had a significant yaw angle, and the effective dihedral
is extraordinarily high with this design – a lot like the lifting bodies
that had similar control issues. Maybe that resulted from a yaw thrust
vector misalignment, maybe just plain old roll/yaw coupling issues at high
speeds. But it seems very unlikely to be something that can easily be fixed.

If he’s right, it doesn’t mean that SS1 can’t win the X-Prize, since it’s had two successful flights with the problem. It may mean that they may have to go back to the drawing board for SS2, and that the technology’s not quite as in the bag as Mr. Branson thinks. As I said, safety issues aside, I think that the market for a rolling ascent is more limited than for one that’s smoother and more controlled.

[Another update, after further reflection on Mr. Pike]

He also blew it when being asked why people find this so exciting, whereas they don’t seem to care about NASA. He repeated the old cliche about how NASA has managed the seemingly impossible feat of making spaceflight boring, but his (mis)diagnosis was that this was exciting because we could identify with the pilot, whereas NASA had reduced emphasis on showcasing the astronauts since the 1960s.

No, John. People find this exciting, because it offers a promise that they can go themselves.

[Update at 12:45]

A commenter points out that Mike Melvill says that he screwed up. He doesn’t say exactly what he did wrong.

Anyway, that’s good news, because it means that they don’t have to do any analysis to figure it out, and pilot error is easily fixable, either by making the pilot smarter, or by using a different pilot. I was surprised to see Melvill fly this time–I had the impression that he’s gotten his ride in June, and was satisfied to let someone else do it. Now, will he be the pilot on the second flight?

[5 PM EDT update]

Derek Lyons asks if the space community has already lost interest in this.

I don’t think so. I’ll bet that a lot fewer people came up from LA, because they’d already done it once, and the entry price increased quite a bit over the last one. I do think that there’s a sense that it’s got enough momentum now, and they are content to watch on the web (combined with the fact that, truth be told, like sporting events, the view is much better from home). I’ll bet that once it becomes a real race, like the Ansari Cup, there will be big crowds, and it will be crowds of people who weren’t necessarily interested in space.

The most important gauge of public interest isn’t how many people physically show up to events like this, but how many marketing deals, and investment agreements get signed, and how much continuing buzz it gets in the major media.

Biting Commentary about Infinity…and Beyond!