By Sherry Jacobson
When it works the way it’s supposed to, re-entering Earth’s atmosphere is a quiet, even humbling experience for crew members aboard a U.S. space shuttle.
The long work of a shuttle mission is behind them, their objectives have been accomplished, and it’s time to go home.
Crew members are reduced to attentive passengers as computers glide the shuttle into Earth’s gravitational pull at speeds of up to 20,000 mph. Friction heats the exterior to 3,000 degrees Fahrenheit.
But inside, all is calm and quiet.
“It’s amazing, you’re in this fireball, but the thermal protection system is keeping it nice and cool inside,” Curt Brown, a former shuttle pilot who flew six shuttle missions for NASA, said Saturday.
“You’re weightless in orbit, and as you enter the atmosphere, it starts slowing you down, the drag,” he said. “You’ll feel a little deceleration from that drag hitting the outside of the orbiter. As you hit more and more air, you’ll get more and more drag.
“It’s very comfortable, it’s not very hard to withstand or anything,” said Mr. Brown, now a first officer with American Airlines.
Astronaut Richard J. Hieb recalls mainly the peacefulness of the descent. He flew on Discovery in 1991, the maiden voyage of Endeavour in 1992, and Columbia in 1994.
“All of my entries were very smooth. Of course, you know if something goes wrong, something terrible is going to happen,” Mr. Hieb said. “The ride itself is astonishingly smooth and very quiet.”
Looking out the back window, the astronauts can see the plume of plasma, “as you come through the atmosphere, ripping air apart,” he said. The air becomes ionized, making it visible as plasma.
During the supersonic phase of re-entry, the crew sits upright, with computers handling the guidance, navigation and control of the flight. Once the shuttle slows to subsonic speed, the commanders take over control of the flight briefly before landing.
“They’re pretty fully occupied once you get down to subsonic speeds,” said Mr. Hieb, who is still an astronaut.
The g-forces on landing are much less than those “going uphill,” or taking off, he said, when the astronauts lie on their backs.
Despite the supersonic speeds of landing – more than 18 times the speed of sound – the astronauts feel only about 1.5 to 2 g’s of force, which comes on gradually. The crew members can move comfortably in their seats, Mr. Hieb said.
However, because they’re coming out of weightlessness, crew members can feel the effects more intensely. “On one entry, I was holding a camcorder. Pretty soon, it felt like it weighed a thousand pounds,” he said.
Crewmembers engage in mental, not physical, activity during the re-entry stage in which Columbia broke apart.
“Generally what’s happening is you’re just monitoring,” said James Bagian, who was a mission specialist on Columbia for a 1991 mission. “The pilot, the commander and a mission specialist would be on the flight deck, monitoring the computer displays.”
The commander would usually retake manual control of the shuttle only for the final few minutes before landing, he said.
The rest of the shuttle personnel would be back in the midbay, essentially biding their time. “Typically, there’s not a lot for them to do at that point – just listening to radio chatter and sitting there, waiting to land,” Dr. Bagian said.
“It could have been that whatever failed, failed so abruptly that there wouldn’t have been any time for the crew to react,” he said. Columbia’s fuel cells were in the midbody, so once that part broke away from the rest of the shuttle, the flight deck would have lost all power, he said.
The crew was probably doing what they had trained to do hundreds of times in simulation.
“At that altitude, you don’t hear too much yet,” Dr. Bagian said. “You’re not in the thick part of the atmosphere. You get some air-rush noise, like the air around your car when you’re driving, but that mostly comes later.
“You’re decelerating rapidly. Imagine putting on the brakes fairly hard in your car – except the sensation doesn’t go away after a second, the way it would in a car. It keeps going for minutes. You’re pressed against the straps.”
It’s one of the sensations astronauts can’t really train for on Earth: the first minutes after a lengthy stretch of zero gravity, when bodies readjust to gravity.
NASA conditions astronauts for that moment of re-entry by tilting its flight simulators forward so astronauts hang inside their protective straps, said Dr. Bagian, who is now director of the Department of Veterans Affairs’ National Center for Patient Safety.
“Forty minutes before, you were weightless. Now suddenly, things weigh something,” he said. “Your checklist sits in your lap instead of floating around.”
Turns slow things down
The shuttle nose tilts up during re-entry, but the shuttle makes S-turns on its final path to Earth to bleed off excess speed before landing. The shuttle banks as it turns, and astronauts get to see the Earth a few times before landing.
“It was a very clear day, so I’m sure they were looking down at Earth,” Dr. Bagian said of the Columbia crew. “It’s not like being in space. The day before, they were 200 miles high. Now they’re down to 40 miles high.”
Charles “Sam” Gemar, a mission specialist on a 1994 Columbia mission, said it was probably too soon in Columbia’s descent for the crew to celebrate mission’s end.
“The crew is fairly focused on monitoring,” he said. “It’s still very businesslike on the flight deck. The most critical phase of that flight is not done. It’s not over until you’re off that vehicle.
“There’s no revelry yet. You recognize the awesome responsibility you have.”
Staff writers Joshua Benton, Katie Fairbank and Aline McKenzie contributed to this report.