As the space shuttle Atlantis passed overhead last week on its extended science mission, several of the astronauts wore Wristmac watches that can display data taken from an Apple Macintosh Portable computer that is on board.
When it was time to snap photographs of a particular feature on Earth or in the cosmos, the Wristmacs sounded an alarm and displayed a two-line message reminding the astronaut of his or her particular chore.
If schedules were changed, an event as common in space as on the ground, NASA officials at the Johnson Space Center in Houston could transfer updated files to the orbiting Mac Portable from Earth-based Macintoshes via fax modem, said Debra Muratore, a NASA engineer. Ms. Muratore is manager of a project designed to find the best methods to let astronauts operate computers in the microgravity of an orbiting space station.
The shuttle mission, STS-43, was especially interesting for personal computer buffs because it used several commercial products and programs that can be found at the corner computer store. Also, by finding ways to make computers easier to operate in space, researchers might discover ways to make personal computers easier to operate on the ground.
tTC Issues tested overhead were as diverse as file compression, the sound cues issued by a computer, the optimum size of a trackball, electronic mapping and transferring paper documentation to computer storage for hypertext retrieval.
A decision was made several years ago to choose a standard personal computer for astronauts, one that was versatile enough to handle such flight chores as calculating trajectories and escape sequences and keeping inventory, as well as processing data for any scientific experiments on board.
Early in the shuttle program, NASA selected a portable computer made by Grid Systems Inc., which is now a subsidiary of Tandy Corp. Because NASA is NASA, they couldn't just call it a portable PC; it became the PGSC, for Payload and General Support Computer.
On Earth, the PGSC is known as the Grid 1530, a rugged, 14-pound portable based on the 80386 microprocessor. It is likely to be the standard PC on shuttles for several years to come.
"We felt it was advisable to come up with a standard for payload and crew, so that if there were an equipment failure, we could swap it out easily and have ready access to another machine," said Stanley M. Blackmer, who is in charge of command and data systems for NASA's Payload Integration Engineering Office.
Several modifications were made to adapt the Grid to life in space. For one thing, Mr. Blackmer said, it is heavily adorned with Velcro to keep it from floating off.
Mr. Blackmer explained that the shuttle uses a 28-volt power system, as against the 12-volt standard in the United States, so the computer's power supply was adapted.
The standard gas plasma screen was replaced by an electroluminescent display; the gas plasma screen was easy to read but overheated quickly, and astronauts rejected the replacement liquid crystal display as hard to read.A fan was installed inside the computer to dissipate heat, since there is little convection in microgravity.
The Grid's modem was replaced with a special unit, since there are no regular phone lines aboard the shuttle. The astro modem on the Grid is connected to one of the craft's two air-ground communications loops, so files can be exchanged with Houston or Cape Canaveral.
Because of the placement of communications satellites, data links are lost for 15 to 20 minutes during each 90-minute revolution around the planet.
Data are transferred at the relatively slow rate of two kilobits a second, but Mr. Blackmer said much faster speeds would soon be possible.
The only other standard personal computer to leave Earth is the Macintosh Portable, which made its second flight; the first was on STS-41 in October.
Researchers had long ago determined that a so-called graphical user interface would be the preferred design for software used ++ aboard the proposed space station. Such software is typically operated by using a pointing device, like a mouse.
The trouble with mice, of course, is that they tend to float away in weightlessness. Ms. Muratore's project is to identify suitable replacements. Potential devices are flown first aboard the KC-135 parabolic test plane, which plunges to simulate weightless conditions.
Astronauts aboard STS-41 last year tested both the built-in trackball on the Mac Portable and a commercially available cursor-movement device called the Felix. Neither one made the grade.
"The major problem was that it was too loose in its socket," Ms. Muratore said. "The ball would float and the cursor would mistarget, causing a lot of errors."
"The Felix didn't do well in either one G or zero G," Ms. Muratore noted. One G is equivalent to Earth gravity.
Astronauts on the latest mission conducted both objective and subjective tests on four devices, including a modified version of the Mac Portable trackball. Logitech Inc., maker of the trackball, redesigned the housing to make it more precise.