I wondered if this was a good time to begin feeling a bit excited and optimistic about the outcome of the day’s expedition, but when I did, it started to give me a headache, so I stopped. ~ Douglas Adams and Mark Carwardine, Last Chance to See
As we began packing in earnest yesterday, balancing the shorts that might make Florida’s heat and humidity less oppressive with the long pants required to go out to the launch pad with the press corps for the photo op, we got pretty excited. We had met the crew and seen Atlantis roll over from the Orbiter Processing Facility to the Vehicle Assembly building, where it was then mated to the external fuel tank and solid rocket boosters (see above for the video we shot). This mission is tangible to us.
Then, we decided to check the weather forecast. Yikes. The Space Coast is expecting isolated and scattered thunderstorms all week. The media are already doomsayers: headlines threaten delay.
But we don’t want our excitement and optimism to take a hit. Sure, Kathy Winters, NASA’s weather guru, is saying there is only a 30 percent chance that weather will allow for Friday’s launch. Luckily, there are launch windows on Saturday and Sunday, and we already had planned to stay that long. (The shuttle can’t launch July 11-15 because of a conflict with a Delta 4 rocket launch at Kennedy Space Center.)
In order for Atlantis to liftoff, the weather has to meet basic launch commit criteria, and those criteria are somewhat complicated but clear and reasonable. Ad the weather criteria ensure good viewing when the launch actually is a go.
The temperature this time of year isn’t a problem. Of course, it’s well above low temperature safety limits (click HERE for an article by a former ICBM test director that points out, prior to the Challenger accident, NASA had no launch temperature criteria) of 41 degrees for the 24-hour average and the 33-degree 24-hour low. It also looks as if the temperature will not be above the 99 degrees that represents the limit at the other end of the thermometer. We’re glad for that, given how sweltering the swampy Kennedy Space Center can feel.
Wind is another factor. Filling the external fuel tank can’t begin if the wind is expected to exceed 42 knots during the next three hours. The peak allowable wind speed at launch varies according to direction, anywhere from 19 to 34 knots at 60 feet altitude. And winds higher up need to be taken into account too.
Because the external fuel tank gets filled will highly flammable liquids, tanking won’t begin if there’s a “greater than 20 percent chance of lightning within 5 nautical miles of the launch pad during the first hour.” If NASA sees a lightning strike and the cloud that produced it is within 10 miles of the pad, tanking waits for 30 minutes or until the cloud moves off. If the fuel doesn’t get into the tank in time for all the other tasks to occur before the launch window opens, the launch date will be changed. Last time, for Endeavour’s launch, tanking was delayed because of lightning, but they hurried things up and got back on schedule. After tanking, launch itself is a no-go “if lightning has been detected within 10 nautical miles of the pad or the planned flight path within 30 minutes prior to launch.”
One thing that’s nice about going to see a launch is that it never rains. If it’s raining at the pad at launch time or anywhere in the flight path, liftoff is scrubbed. No one gets wet at a successful space shuttle launch.
And it’s also rarely cloudy, though Endeavour disappeared into the clouds relatively quickly last time, leaving Space Coast spectators without a view of the solid rocket booster separation. Various launch commit criteria for clouds ensure a pretty good view. Cloud cover is the main concern for Friday’s scheduled launch.
Another, overarching weather issue that the launch director and safety officer must consider is that a Return to Launch Site (RTLS) abort must be possible. There’s a short period after the orbiter clears the service structure that, if necessary, it can return to Kennedy Space Center.
And it’s not just Florida’s weather that matters. One of the Trans-Oceanic Abort Landing (TAL) sites must have good enough weather for an emergency landing. They don’t all have to be sunny and dry, but Moron (Spain), Zaragoza (Spain), or Istres (France) has to be ready if an abort is necessary between about 2:30 to 8:30 minutes into the flight.
And the forecast has to be good for Edwards Air Force Base, too, because that’s a first-day Primary Landing Site. Of course, the weather in Southern California is the least of our worries as we head from there across the country this week.
So, as we were packing, we started thinking about the weather and got a bit of a headache. But the weather is something over which we have no control. Besides, NASA is unlikely to decide now—before our flight—whether the weather is going to be okay on Friday. Kathy Winters will recalculate the odds as the week goes along and has scheduled updates at NASA-TV press briefings on Wednesday and Thursday mornings. Just in case, we may pack an umbrella as a talisman to ward off bad weather.