Triboelectrification trouble
Published on Oct 27, 2009 at 2:40 pm.
4 Comments.
Filed under rockets.
Well, the launch did not go as hoped for this morning. Last night, the forecast was for only about a 40% chance of the launch getting off. This morning, when I got up to head over to the space center, I saw stars! Things were definitely looking good! Then, as we headed to the launch site, I saw some clouds. Weather was moving in. Still, it looked like we’d get the thing off if everything went according to schedule. Well, it didn’t.
First of all, they were running a bit late. The announcer said that there were no particular problems. However, running late delayed the launch until clouds arrived. Weather aircraft were studying the clouds and balloons took a look at higher levels. Then, there was a delay due to high altitude winds. Next, a cover over a sensor near the top of the rocket got stuck. Finally, that came free. Then, the aircraft found the clouds just a bit too much. Finally, the weather cooperated. The winds were OK, there was a break in the clouds. The countdown started again. Suddenly, with about two and a half minutes to launch, the countdown stopped. The call was that a freighter had entered the exclusion zone offshore! (I may have my delays confused. I wrote this off of memory. See Ed’s comment.) At first, they were saying that it would take 90 minutes to clear the zone. It took far less time than that, but they had to reset the countdown. By the time they were ready to try again, the clouds had come back. Then, there was a window in the clouds but it was too windy. Finally, the wind died down, but the clouds were back. Finally, they scrubbed the launc for the day. We’ll go back in the morning to try again. I would definitely like to see the launch, but it appears that trying to change travel plans to stay another day would push the cost of the trip far beyond my travel allowance.
So, what’s the deal with the clouds? Naturally, those of us observing would like to have few clouds so that we could see the rocket arch across the sky. But, the bigger problem is something called triboelectrification. That’s a really fancy word that comes from Greek roots meaning electrification from rubbing. You may be familiar with it as “static electricity.” In fact, that is more like what they would have said years ago. Of course, it isn’t really static, since the rocket is moving, and it is the motion through the clouds that causes the problem.
What happens is that the rocket, as it passes through the clouds, pushes water droplets out of the way. The interaction between the rocket and the droplets results in charge being transfered between the two, leaving one positive and the other negative. It is like rubbing your feet along the carpet on dry days. You become electrically charged. I remember always being told that it was friction doing the work to build the static charge. But, as I understand it, chemical reactions, rather than friction, do the dirty work. The rubbing past one another simply exposes more surface area to the action.
The end result, of course, is that the rocket becomes eletrically charged, and so does a tube of vapor along the path of the rocket. That electric charge can interfere with signals between the rocket and the ground. For an unmanned test flight like this, where the whole idea of the flight is to provide flight data for analysis, then interfering with telemetry is bad. But, the interference also goes the other way. It can interfere with signals from the ground to the rocket. If the rocket were to go out of control, then the range safety officer has to be able to send a signal to destroy the rocket. So, if there are too thick of clouds over the launch pad, then the launch doesn’t happen. That was the problem most of this morning.
I got some good photos of the rocket on the pad, but my netbook lacks the tools to resize the to upload, so you’ll have to wait until I get home. Hopefully, I’ll have photos of the launch tomorrow!
Astroprof
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Ed Davies on October 27, 2009 at 4:56 pm: 2
“Suddenly, with about two and a half minutes to launch, the countdown stopped. The call was that a freighter had entered the exclusion zone offshore!”
My recollection was slightly different so I’ve just checked on SpaceflightNow [1]: the abort at T-2:39 was for weather. It happened at about 13:47Z and SpaceflightNow gave the reason at 13:50Z.
I have to say I was a bit surprised that the weather forecast could be good for the next four minutes then change enough in the next minute and a half to call an abort. It shows how close they were running things, I suppose.
The delay for the freighter happened a bit earlier, at 13:33Z, while they were still holding at T-4:00.
[1] http://spaceflightnow.com/ares1x/status.html
Astroprof on October 27, 2009 at 5:15 pm: 3
OK, I may have had my delays confused. I was going off of memory since I didn’t have the foresight to take notes on the delays. It was my first launch! Then the delay might have come as they were polling before restarting the countdown. It was rather frustrating with delays the whole morning. It was hot, humid, and the bugs were biting, so the multitude of delays just ran together in my mind. Next time, I’ll take notes as it happens! Thanks for correcting that.
Ed Davies on October 28, 2009 at 9:20 am: 4
Yes, very understandable. I just thought it would be nice to make the record accurate.
Good luck with seeing a launch today.