Small Fish, Big Pond

Excellent video of the space shuttle Atlantis making it’s last jump into space.

One slow day at work we watched a NASA feed of a shuttle launch from T-5mins to fuel tank separation (~+8min). One co-worker is a walking encyclopeida of the shuttle and it’s systems so it was like being on a tour of the launch process.

If you notice at launch, water (350,000 gallons in 41 seconds) floods the pad. It’s not to cool things off, it’s added sound suppression because the shockwaves from the engines were actually damaging the Solid Rocket Boosters and Shuttle wings.

The shuttle is clamped down to the pad and won’t launch until the explosive bolts blow and the clamps let go. Hence the impression that the shuttle leaps off the pad. The Saturn Rockets that flew the Apollo missions worked the same way. Astronauts often have colorful ways to describe the feeling of going from rumbling on the pad to instant high-G acceleration.

The shuttle launches “Downrange”. Although it seems it’s going straight up the shuttle is really rolling onto it’s back as it launches; because it’s lateral speed around the earth that sends it to orbit, not necessarily altitude alone.

At an altitude of about 35,000ft the shuttle hits Max Q which is where the speed and air density create the maximum dynamic pressure and stress on the shuttle. After this point speed increases but due to low air density the stresses on the shuttle lower making it a major milestone in the launch.
The Challenger disaster happened around Max Q; when stress on the structure was at it’s peak the SRB mount broke causing the SRB to turn into the fuel tank. As the fuel tank broke up the orbiter veered out of position and the aerodynamic forces at Max Q caused the orbiter to disintegrate (it didn’t actually “explode”).

As the shuttle launches if you listen to the NASA sound feed you’ll hear Ground Control announce the passing of certain Abort Modes.
-First is Return To Launch Site (RTLS). The shuttle would ride until the SRBs burn out (they’re like bottle rockets and can’t be stopped once they’re lit), then shut off main engines, jettison the 3/4 full fuel tank and glide back to Florida.
-Next is Transoceanic Abort Landing (TAL). Upto about +8mins the shuttle can abort, run out the SRBs and main engines then land in Europe about 25 minutes after launch (beat that Concord!). Weather conditions need to be good at Florida and at least one of the three Europe landing sites. Prep at the sites begins 2 days in advance of launch.
-Abort Once Around (AOA) is rare. It’s when the shuttle has too much speed to make Europe but not enough for a stable orbit. The Shuttle would return to a Florida landing 90mins after launch.
-Last is Abort to Orbit (ATO). Basically orbit can be attained, but possibly not as high as they wanted. But it does give the opportunity to think things through and either come up with a solution or find a way down. It’s only been invoked once, the Challenger had one of it’s main engines shutdown during launch but made it to orbit. The mission was salvaged and it landed safely.