NASA's new space capsule has a mind of its own.
- By Michael Klesius
- Air & Space magazine, September 2007
(Page 5 of 5)
FLYING ORION is an excercise in computer-astronaut harmony. Skip Hatfield gives the following general scenario of what it would be like to sit in Orion’s cockpit and pilot an orbital flight.
“On the ride uphill, it’s primarily automated,” he says, noting that it’s similar in that regard to the shuttle. “The crew will be monitoring the displays, looking for malfunctions. They’ll be able to select certain actions if needed.”
If a problem is serious enough, the first option is an auto abort system. His group is working on the contingencies for the manual overrides that everyone hopes will never be needed. During descent, the crew will reconfigure the displays to mimic their launch setups, providing an artificial horizon and data on vehicle orientation, speed, rate of descent, heat shield performance, and so on. Should the
astronauts need to override the system, they will be able to fly a manual descent with the stick.
Despite all the automation, Hatfield makes the distinction that the crewmembers, not ground controllers, will operate the vehicle. Even in unmanned cargo configurations, NASA’s vision leans toward that of a deep space probe, in which Orion monitors itself for prolonged periods but can still accept commands from the ground.
Because the physics of reentry haven’t changed, neither has the shape of crew return vehicles. They still have a circular, convex base covered by a heat shield. For most of the flight, the service module will protect the shield, separating just before reentry. On lunar and Mars returns, it will be shed in a maneuver known as a skip reentry. “And no, that’s not named after me,” says Hatfield. “It’s like a stone skipping on water.” At the low point of the maneuver, the service module will separate and burn up in the atmosphere. Meanwhile, the crew vehicle will travel several hundred miles downrange, its reaction control system maintaining the proper orientation for final entry, unobstructed by the service module. “We still don’t fully have the right [heat shield] material yet,” says Horowitz. “But it will be ablative.” In other words, it will mimic the Mercury, Gemini, and Apollo shields, which burned off during reentry.
The shuttle reenters from orbit at about 25,000 feet per second (fps), its leading edges heating up to about 3,000 degrees Fahrenheit—hot enough to melt steel.
When the Apollo modules reached Earth’s atmosphere after a three-day trip from the moon, they were moving at about 30,000 fps. Orion’s velocity will match this on its own lunar return.
But returning from Mars, it will be moving close to 35,000 fps. That speed, about 6.6 miles per second, would take you from Washington, D.C., to New York City in less than 30 seconds. “You’re talking hot,” says Horowitz, referencing a number that starts at more than 4,800 degrees
Fahrenheit. NASA obtained relevant information in January 2006, during the return of Stardust, an unmanned probe that reentered Earth’s atmosphere at about eight miles a second, or 41,967 fps, the highest Earth reentry speed any spacecraft ever attained. Its heat shield offers the best candidate—an advanced combination of carbon and rayon—for Orion’s shield.
But Stardust was less than three feet across. Manufacturing a similar ablator to cover Orion, which is five times larger, might require engineers to join blocks of the material. The seams would need special protection.
Finally, unlike Apollo-era modules and reminiscent of a long-standing Russian procedure, Orion will return to Earth on dry land. In abort mode, it will still be able to splash down in any ocean. But a ground landing is attractive because it eliminates the expense of using Navy ships for recovery. Orion will deploy three reusable parachutes, same as Apollo. Airbags will open just before impact to soften the landing. Orion then will be home, ready to make history nine more times.
“I watched the first Saturn Vs launch as a kid,” Horowitz says. “I was in sixth grade for the first moon landing. I figured, Oh man, by the time I get there this’ll all be over.”
Space veterans like Horowitz share a feeling that what they are doing will bridge the glories of Apollo and an equally exciting future. “What you see here is a vehicle that will be flown by the next generation of explorers,” Horowitz says.
Orion’s first pilots are likely in NASA programs now, the future commanders still just junior astronauts. In the same way, the brains of their spacecraft are now being prepared, so when machine and man are both ready they can explore the solar system together, one launch at a time.