When shuttle Atlantis blasted off for the Hubble Telescope on Monday, she headed straight east off the launch pad, rolling to an azimuth of 90 deg. The shuttle was taking maximum advantage of Earth’s rotation to gain speed — saving propellant so she could make Hubble’s 350-mile altitude. Here is a brief discussion of those considerations as outlined in Air & Space Smithsonian magazine. The author is Michael Klesius, an editor at the magazine.
The space shuttle Atlantis rises from the launch pad at 2:01 EDT, May 11, 2009, carrying the crew of STS-125 on a final servicing mission to the Hubble Space Telescope. It’s clear from the tilt of the orbiter’s flight path that this is a mission to the telescope, which circles the planet at 28.5 degrees inclined to the Equator. This is the most easterly route available from Cape Canaveral, which lies 28.5 degrees north of the Equator. Compare it with a launch image from two years ago when Atlantis carried the crew of STS-117 to an orbit inclined 51.6 degrees to the Equator, which takes the vehicle northeast along the coast, and allows it to chase down the International Space Station (ISS). “It’s straight east out of the Cape—90-degree azimuth—to achieve a 28.5-degree inclination,” writes former astronaut Tom Jones in an email. His fourth and last mission was aboard Atlantis in 2001. He explains that the orbiter, whose belly faces north as it stands on the pad, has to roll quite a bit farther at the beginning of its ascent to embark on the 51.6-degree trajectory for an ISS mission. “On ISS missions, the big swing from your head pointing south to your head pointing northeast (and then gradually toward the ocean as you pitch over) is quite noticeable as the vehicle pivots (total of 90+52=142 degrees). For the launch today, the crew only rolled 90 degrees to pick up the easterly azimuth.” This, along with the fact that Hubble orbits at a greater altitude than the ISS, is why a second shuttle must be prepared as a rescue mission—if debris were to damage the first orbiter on ascent, the pilots couldn’t shift over to 51.6 degrees and take refuge aboard the ISS. “A plane change is very expensive in terms of fuel,” says Jones. “The shuttle can alter its plane on launch—by steering—by at most a degree or two. Gravity is tough!”
Thanks to Michael for the generous quotes.
I just watched Meghan McArthur grapple the massive, 13-ton telescope on Wed. afternoon.