The Space Shuttle, Modernized

By James W. Ramsey | November 1, 1999
Send Feedback

The space shuttle cockpit is getting a facelift. The U.S. National Aeronautics and Space Administration’s (NASA’s) four shuttles have flown 95 missions since 1981, equipped with 1970s/80s avionics technology. Now they are catching up with many of the commercial, corporate, and military aircraft that fly closer to earth with glass cockpit technology.

The Space Shuttle Atlantis is the first orbiter to receive new upgrades, which have been installed and currently are being tested in anticipation of a scheduled December 1999 launch date. That launch will deliver the third stage of equipment for the International Space Station. The other three orbiter vehicles—Endeavor, Discovery and Columbia—will be upgraded during regularly scheduled maintenance periods over the next two years.

Boeing Reusable Space Systems is the prime contractor for the upgrades. It works for the United Space Alliance, a Boeing/Lockheed Martin joint venture that conducts space flight operations under contract to NASA.

Honeywell Space Systems, in Phoenix, Ariz., designed and is producing the multifunction electronic display system (MEDS), a key element of the shuttle upgrade. Deliveries of MEDS units for Atlantis were completed in late 1997, and Honeywell completed MEDS hardware and spare parts delivery for the other orbiter upgrades last August. Installation on the last of the four shuttles is scheduled for September 2001.

Before installation on Atlantis, MEDS was tested at NASA’s Shuttle Avionics Integration Laboratory (SAIL) at the Johnson Space Center (JSC), Houston, Texas. Pilots/astronauts also "fly" with MEDS in a fixed-base simulator at JSC and on NASA’s astronaut training aircraft.

Honeywell’s MEDS features the first space-qualified, flat-panel, multifunction, liquid crystal displays (LCDs). They replace the orbiter’s electro-mechanical and cathode ray tube (CRT) displays, providing two and three-dimensional color graphic and video capabilities. From these multifunction displays (MFDs), shuttle crews gain primary flight information and other data.

The shuttle upgrade program includes a host of other improvements to enhance safety and reduce workload (see sidebar, this page). Guiding these goals are automation and improved situational awareness through data processing, communications, navigation and power subassemblies. Some upgrades, now only on the technological horizon, will not be incorporated until 2005.

Adapted from the 777

In the late 1980s and early 90s, NASA decided shuttle cockpit instrumentation was getting difficult to maintain and needed a major upgrade, according to Vic Revelle, Honeywell technical director for the MEDS program. In 1991, the avionics provider began design efforts to take a commercial airliner display and, with some modifications, provide for the space environment.

"We recommended putting the 777 jetliner display system in the space shuttle," Revelle says. The shuttle’s LCD displays use "exactly the same piece of glass" as the 777, and it comes off the same assembly line, he adds.

The glass cockpit technology in the shuttle should look quite familiar to the NASA pilots who fly modern military fighters. "It’s basically the same product," says Steve Hopkins, Honeywell’s MEDS program manager, of the military cockpits, "but brought up to speed in a space environment—to stand vibration and radioactivity."

One of the major differences in the shuttle is the electronics behind the display. Revelle explains that each multifunction display unit (MDU) has an R3000 processor that interprets and manages the graphics, along with the unit’s video. To interconnect all MEDS units, the subsystem uses four Mil-Std 1553 databuses for redundancy.

MEDS distributes processing to individual displays, instead of having one computer process for all cockpit displays. This allows for redundancy, Revelle says. "If one display fails, you can quickly transfer information from the failed display to another one, with no loss of time."

In addition to 11 MDUs in the shuttle, MEDS has four integrated display processors (IDPs) that contain 386DX computers and a 300-megabyte hard disc. The processor selects data from the four analog-to-digital converters (ADCs), from keyboard inputs and from the shuttle’s general-purpose computers. The four IDPs process flight data and send display data to the MDUs. The IDPs also contain all the interface electronics necessary to communicate with the displays and the shuttle’s main computer.

There are nine MDUs in the shuttle cockpit and two in the aft flight deck. The aft computers allow crew members to make keyboard inputs similar to those of the pilot and commander in the cockpit, explains Bill Gregory, a former astronaut who recently joined Honeywell’s Space System’s business development unit.

Pilot’s Perspective

"NASA initially has decided to use the displays in a familiar format to provide crewmembers a smooth transition from the older, round-dial gauges to the glass cockpit," Gregory says. Prior to MEDS, shuttle pilots used the standard CRTs "with very basic graphics for the landing phase of the space flight."

With the MEDS upgrade, the shuttle’s three monochromatic CRTs are being replaced along with the steam gauges. For a smooth transition, the CRTs are being replaced one-for-one. Pilots will use the new MDUs—located in front of the pilot and commander—for the same basic functions they had used the CRTs, only the MEDS displays also can be used to bring up much more data, says Gregory.

"You have to understand, the vehicles only fly a couple of times a year, the crews only once every few years," he explains. "When the entire fleet is outfitted and everyone is trained on the glass cockpit, we can exploit the full capabilities MEDS has to offer," adds Gregory, who piloted space shuttle mission STS-67 in 1995 and also helped evaluate MEDS from a pilot’s perspective.

Most astronauts entering the space shuttle for the first time, find the experience to be a step backwards. "The flight instruments are very reminiscent of the 60s and 70s technology," Gregory says. "When MEDS was first being developed…the shuttle pilots were older pilots…used to the steam gauges.

"Today, new shuttle commanders and pilots are used to the glass cockpits of the F-15s, F-16s and F/A-18s, which they have flown either as operational or test pilots. This [upgrade] is bringing them back to what is familiar to them."

Demanding Environment

In developing MEDS, the unique demands of the space environment particularly challenged Honeywell engineers, Revelle says. One example is the cockpit’s glass; the LCD screens in the shuttle are similar to those in the Boeing 777, with one significant difference.

"If for some reason a display breaks on a commercial airliner, the glass is going to fall on the cockpit floor," Revelle explains. "However, in the space shuttle, it will float around in the cabin and the astronauts could breathe glass. That is not an acceptable condition, so we have applied a polyester sheet in front of the glass to prevent any glass breaking from floating around.

"And we have added some extra coating material to the sheet," Hopkins notes. "We have a very good anti-reflection surface on our display—it is just as readable in a dark room as it is in full sunlight."

Radiation is the other space concern. "Single event latch-up" is a big concern at the subcomponent and transistor level, and requires special circuitry design," Revelle explains. To minimize negative effects, "power is reduced to the device, the latch-up goes away, then power is restored very quickly, and the device starts working properly again." He says that by using this "circumvention circuitry," in most cases, "the pilots would not even note an event occurred.

"Another technique to combat this radiation problem," Revelle says, "is to limit circuitry that would not allow a device to draw enough current to destroy itself, but enough to operate properly."

Receive the latest avionics news right to your inbox