Shuttle Weather
Published on Aug 28, 2006 at 3:40 pm.
No Comments.
Filed under NASA, space shuttle.
Space Shuttle Atlantis has been sitting at the launch pad, ready to go. Unfortunately, the weather hasn’t been cooperative. There have been concerns over a lightning strike at the lauch pad this past week, and now over a possible hurricane. Right now, Ernesto is a tropical storm, but is is projected to regain hurricane strength and slide up the Florida coast. What is this? Does Florida have a giant hurricane magnet or something? It seems that you can expect a hurricane to hit Florida every year.
I thought that I might say a few words about these things. First, despite media reports to the contrary, Atlantis was not struck by lightning. Rather, the launch pad was struck. NASA is well aware that lighting and rockets don’t mix well. Despite damage that could result to the orbiter itself, those solid rockets are filled with highly flamable material, and should they be ignited, there is no way to stop them. That would be the end of the shuttle if one were to be ignited by a lightning strike. So, there are lightning rods and grounding cables all over the place. The idea is that if lightning were to strike, these things would carry the electric current away from critical systems. A number of years ago, an Atlas rocket was destroyed after a lightning strike during liftoff.
Of greater concern, though, than the damage due to a direct hit would be damage due to EMP (electromagnetic pulse). While the grounding rods and cables should keep the bulk of the current away from the spacecraft, it doesn’t stop all of it. There will always be some leakage. The more powerful the lightning strike, the more leakage. This was a particularly powerful strike. Worse, with powerful currents, you can get induced fields and currents even where the lightning’s current didn’t go itself. So, there is concern that this very poweful strike may have sent current and voltage spikes all sorts of places. Modern electronics doesn’t do well with such things. So, they had to check out the orbiter and make sure that all wiring, sensors, and computers were undamaged. Incidentally, the Saturn V carrying Apollo 12 was struck by lightning during liftoff. The computers reset, and the rocket kept going. That is a tribute to how tough those things were.
Well, after carefully going over the orbiter, it seems to be OK. But, now we’ve got a hurricane to deal with. Besides wind that might blow the shuttle over, there will be more lightning. So, you really don’t want the spacecraft sitting out on the launch pad in a hurricane. Ernesto might not strengthen, it might strengthen and then get weeker, or it might turn and miss Cape Canaveral completely. Or, it might strengthen into a hurricane and go right over the Kennedy Space Center. So, it is prudent to move the craft to safety. It will be several days until the storm gets there, if it does, so there is a bit of time to decide.
Moving the shuttle involves a Transporter/Crawler moving into position under the mobile launch platform, and lifting the platform, with shuttle sitting on top, up off of the ground. 
The crawler then carries the platform several miles back to the Vehicle Assembly Building, where the spacecraft should be safe. This is a several hour process, and it can’t be done in high winds. So, a decision must be made well before the storm arrives. NASA will likely make the call Tuesday morning.
If Atlantis is rolled back to safety, it will be the 17th time that a shuttle has had to have a rollback, and the fifth time on account of a tropical storm or hurricane. The last time that a shuttle was moved to shelter from a hurricane was September 4, 1996, when Atlantis was moved due to a threat from Hurricane Fran. In fact, Atlantis was moved one other time to escape a storm, on July 10, 1996, with Hurricane Bertha.
So, I guess that we’ll see what happens with the storm. Moving the shuttle, though, seriously delays launch, since once it gets back to the launch pad, all the preparations done to this point have to be done again. It isn’t a decision that NASA makes lightly. But, it is better to delay a launch than to lose a shuttle.
-Astroprof
(Images courtesy of NASA)
