I was up last night at 1:00 AM ET (which isn’t so bad when you’re actually in PT) watching and listening to the space shuttle tanking operations. So I was there (live) when the first report of hydrogen leak issues reappeared, and as they tried assorted work-arounds which I was certain wouldn’t work. I went to bed about a half-hour later.
Remember March 2009: Discovery had the same leak issues. They replaced seals and refitted the connectors, and the problem didn’t return. But they never identified a cause for the problem. That was never found.
Well, now they have a month to thoroughly dig into the problem. I’m confident the root cause will finally be understood and resolved.
Meanwhile, I’ve heard news agencies reporting that this delay to July is required because of “solar flares” or “increased solar activity.” That’s pure crap. For the interested, here’s what’s going on.
It’s easy to think about an orbit as being in the sun half the time, in the shadow of the Earth half the time. But, as usual, reality isn’t that simple. There are many factors: the tilt of your orbit with respect to the Earth, the tilt of the Earth with respect to the sun … even the launch time plays into it. These factors boil down to the beta angle — it’s the angle between your orbit and the incoming sunlight. The higher the beta angle, the more time you’re spending in sunlight on every orbit.
If you’re in low-Earth orbit and in the sun much more than you’re not, then you’re going to start accumulating heat. You just won’t be able to shed it quickly enough in the little time you’re in Earth’s shadow. And of course, if you’re headed for the moon, you’re in the sun ALL the time.
Most spacecraft in this situation operate in a “passive thermal roll” — they slowly spin around their flight axis, so that all parts have the opportunity to dissipate heat in the spacecraft’s shadow. (This is often called “rotisserie mode” for obvious reasons.)
The International Space Station has huge cooling fins (they’re the shiny gold-colored things extending off the structures) to help it shed excess heat. But if a shuttle orbiter is docked, it can’t do a thermal control roll, it’s not connected to the station’s cooling system (too much plumbing work involved), and it will start storing up heat. You’d think in the cold of space that heat would be your friend, but too much heat in places you don’t want it can damage delicate components.
So when the ISS beta angle exceeds 60 degrees … which happens a few times a year … shuttle orbiters cannot be docked there. This situation occurs in early July and will last a couple weeks.
Meanwhile, back at Pad 37, the Lunar Reconnaissance Orbiter and LCROSS probe have the range all to themselves for the rest of the week. They’ll need it, with high likelihood of afternoon thunderstorms right around the desired launch times.