We Fly The Space Shuttle (Simulator, That Is)

Back in the early '80s, I applied for the "Journalist in Space" program and was advised I'd made the first cut, which narrowed the field from something like 20,000 applicants to about 2,000. Unfortunately, when teacher Christa McAuliffe was lost in the explosion of Challenger in 1986, that was the end of all programs to fly a civilian into space. Later, I wrote to NASA twice, requesting a chance to fly the Space Shuttle simulator, and was turned down both times because of the heavy flight schedule. NASA was busy training pilots for the real thing, and there was little time remaining for journalists.

About a year ago, however, I met former astronaut Robert "Hoot" Gibson, and mentioned my dream of perhaps someday flying the Space Shuttle simulator. Gibson is a not-so-old pro in the astronaut business. In addition to making five flights in the shuttle and spending over a month in space, Gibson was chief of the astronaut office in the mid-'90s, and he felt there might be a chance for my flight, now that the shuttle program was winding down.

There's only one motion-based Shuttle simulator, and it's at NASA's Johnson Space Center in Houston, Texas. Though NASA is no longer training new crews, the agency keeps the sim up and running for recurrency training and emergency-procedure practice. My opportunity to fly what may be the ultimate simulator came in late June. Editor Jessica Ambats and I traveled to Houston, and astronaut Gibson flew down from his home in Tennessee to oversee my experience and make certain I didn't break anything.

In Houston, Gibson introduced me to Flight Director Paul Dye. Like Gibson, Dye is a confirmed aviation nut. In addition to serving as flight director on 37 shuttle flights, he's a member of EAA with a Van's RV-8 completed and an RV-3 under construction. He agreed to monitor my efforts on the Shuttle simulator and was the perfect host at NASA. Dye is probably one of the most knowledgeable and proficient sim aviators at NASA, and his advice and counsel was invaluable.

Gibson explained that the sim is very accurate in reproducing the response of the actual Space Shuttle, and he should know. Like all other astronauts who train as pilots, Gibson is a former military fighter pilot with thousands of hours in jet fighters. He's made literally thousands of approaches in the full-motion base simulator and in NASA's highly modified Gulfstream G-2s, better known as the Shuttle Training Aircraft (inevitably, the STA). NASA operates four of the 1970s-era jets, all heavily modified to simulate the Shuttle's brick-like glidepath during the last 35,000 feet of approach.

The Shuttle is unquestionably the world's least efficient, most expensive and fastest glider. It's also the most complicated machine ever built, a quarter-million pounds empty, containing some 2.5 million parts. The simulator doesn't quite match that level of complexity, but it does an excellent job of reproducing real in-flight response in a ground-bound cockpit.

The flight deck is familiar yet foreign, with eight flat-panel, PFD/MFD displays that offer graphical presentations of many standard aviation parameters---airspeed, altitude, attitude, heading, rate of climb, plus a number of other instruments you probably wouldn't recognize. Still, there's enough that's friendly so that those of us confined to the bottom 10 miles of sky don't feel lost.

Climbing into either of the pilot seats is exactly that, a climb, and I was doing it in comfortable street clothes with the cockpit conveniently straight and level as opposed to lying on its back. It's hard to imagine how difficult the task would be wearing a full David Clark pressure suit with the aircraft pointed vertically up.

The pilot flies the Shuttle with a short-throw, fly-by-wire hand controller mounted on a pedestal. It looks fairly conventional, but it has at least one function you may not recognize. It incorporates a third direction of travel in addition to pitch and roll. In space, without the benefit of an atmosphere, the Shuttle can be maneuvered thru its yaw axis, and the pilot commands thrusters to accomplish a lateral yaw roll by simply twisting the stick. This fires thrusters that rotate the spacecraft as if it were balanced on the head of a pin. Pretty obviously, that function isn't operative during an approach to landing.

Launch From Cape Canaveral
Everyone aboard the Shuttle is a passenger during the launch, as the entire process---liftoff to orbit---is computer controlled. Flight director Paul Dye nevertheless gave us a taste of the launch. The first step in a simulated launch is to rotate the sim to the aforementioned vertical position. This is, after all, a motion-based simulator, so we were given an idea of the real starting position, lying on our backs.

The simulator re-creates the experience of launch fairly accurately, though Gibson comments that the vibration of an actual launch is more violent than the sim experience. Considering that the sim is primarily an electric device with hydraulic assist, repeated shaking wouldn't be conducive to long life.

You feel the rumble of the engines seven seconds before launch, and when the countdown reaches zero and the explosive bolts release the Shuttle, the launch becomes a numbers game, and all the numbers are BIG. You can watch the tower begin to flash by as the 4.4 million-pound "stack" starts its climb with the assistance of about 7.5 million pounds of thrust. (The stack consists of the orbiter itself, two solid rocket boosters---SRBs---and the huge external tank.) Gibson commented that the real Shuttle comes off the ground with what seems like a tidal wave of power. Acceleration is reminiscent of riding the thrust of a giant rubber band, subjecting the crew to an eventual three G's of vertical acceleration. Meanwhile, the massive thrust of five rocket engines creates a level of vibration similar to a giant, berserk paint-shaking machine.

Eight seconds into the flight, the Shuttle begins a roll program, rotating onto its back and climbing away from Florida as if its tail were on fire, which, by the way, it is. The Shuttle's flight path becomes as much horizontal as vertical as it climbs higher, accelerating and gaining altitude almost exponentially. Zero airspeed to Mach 1.00 takes less than 60 seconds, and you can watch as the speed and altitude climb at an increasing rate. As you monitor the digital readout, you'll see numbers you've never seen before.

At two minutes, the Shuttle is passing through Mach 4 and is already climbing through 150,000 feet. At this point, the spacecraft is burning about 60,000 gallons of fuel a minute. Looking out the side windows, you'll see the flash of the SRBs shutting down and separating from the stack. The SRBs parachute down and land in the Atlantic where they're retrieved for use on a future launch. Now, the Shuttle is flying on its three main engines, still burning fuel from the giant external tank.

At five minutes, I glance out the small, left window to see what I'm told is the outline of the Chesapeake Bay drifting by below. The simulator's depictions of Earth aren't very realistic, but they don't need to be, as astronaut trainees have little use for the outside display. Considerations of IFR and VFR become irrelevant in an aircraft designed to operate outside the atmosphere.

At just under nine minutes after launch and 75 miles altitude (roughly 400,000 feet), the main engines shut down and the orange tank is ejected at the equivalent of Mach 25, typically 75 miles up, and the Shuttle continues to coast uphill at 500 feet per second to orbit. In total, the Shuttle's climb to altitude requires some 45 minutes, and all but the first nine minutes is without power. Once established in orbit, the Shuttle circles the Earth every hour-and-a-half in a typical orbit at 180 miles.

Return To Earth
At the conclusion of the orbital flight, the Shuttle begins the reentry process in what most pilots would consider an unusual manner. For several good reasons, the spacecraft typically flies in space upside down and backward with reference to the Earth.

The most important reason is that flying backward with the engines in the rear provides the crew with maximum protection from micrometeorites and space debris. Second, all the windows on the Shuttle are on the top of the fuselage, and since there's no up or down in space, it's logical to fly inverted to orient the windows toward Earth. Third, those 34,000 heat-shielding silica tiles on the belly of the aircraft help protect the crew from the heat of the sun, no longer filtered through the atmosphere. In the direct light of the sun in orbit, OAT in space can rise to 121 degrees C (250 degrees F).

The deorbit process begins with a three-minute burn of the orbital maneuvering system (OMS) engines, slowing orbital velocity by about 200 mph. This slows orbital velocity to a mere 17,000 mph, not enough to keep the spacecraft in orbit, and the Shuttle slowly begins to descend. To manage the reentry, the computer maneuvers the spacecraft through a half somersault to fly belly down, nose forward, the equivalent of straight and level. (The commander or pilot can fly the full reentry if necessary, but most of the time, the computer will do a more accurate job.)

As the spacecraft begins its fall back into the atmosphere, the computer gradually brings the nose up to a 40-degree angle of attack to let the ceramic tiles on the belly absorb the heat of reentry. The speed slowly bleeds off as the aircraft begins to encounter thicker air. The wings gradually assume more lift, and the computer commands a series of four aero-braking turns at up to 70 degrees of bank to slow the spacecraft and continue the descent, meanwhile maintaining the 40-degree pitch attitude. These turns are intended to help dissipate speed without overheating the tiles, subjected to temperatures of 1,500 degrees C during reentry. After the final aero-braking turn, the computer levels the wings and lowers the nose, and what was once a spacecraft becomes an aircraft once again.

If you guessed the Shuttle makes a terrible glider, you guessed right. Most pilots had better hope they never come close to experiencing the glide characteristics of a Space Shuttle. My Mooney and most other general aviation aircraft come downhill power-off at about a 10 to one L/D, 10 feet forward for every foot of descent. When I earned my glider rating 30 years ago, I flew a Czechoslovakian Blanik L13 trainer that offered a glide ratio of roughly 28 to one. The most efficient high-performance sailplanes record L/Ds as high as 70 to one.

In contrast, the Shuttle's glide at high altitude is barely distinguishable from that of a set of car keys. The spacecraft experiences a variable glide ratio, because it operates in variable levels of air density. It's a spacecraft in space and a conventional aircraft in air (duh!), so its glide characteristics change as the air becomes thicker. At hypersonic velocities in the upper atmosphere, above about Mach 5 and 200,000 feet, the Shuttle glides at a 1:1 ratio, one foot of forward travel for each foot of descent, about the same as a Steinway. That increases to 2:1 at supersonic velocities and improves to about 4.5:1 when you're on final approach.

In contrast to the extreme nose-up attitude of reentry, the world's largest glider must assume a nose-down pitch for the last 50,000 feet of descent. During this phase of the Shuttle's approach, it's dropping out of the sky at 10,000 fpm. Pilot error makes an undershoot possible, but the computer flies the airplane down to about 50,000 feet before the commander or pilot assumes control. In theory, the pilot takes over just before the shuttle reaches the HAC (heading alignment cone) that's located about 50,000 feet above the Kennedy Space Center. In other words, the computer doesn't guide the Shuttle directly to the threshold of Kennedy's three-mile-long runway but to a cone of airspace high above the Cape. From there, the pilot flies the aircraft around an arcing pattern to final approach.

Flying the approach is simplified somewhat by the HUD (head-up display) that overlays the windshield. The HUD allows you to look through the display at the runway and still receive visual cues of the approach. The HUD presents the pilot with a round, green flight-path marker representing the Shuttle, and a guidance diamond. Theoretically, if you fly the flight-path marker on top of the guidance diamond at all times, the STS will slide right down final to a squeaker landing. It says here.

Follow the HUD precisely, and it will arc you around to final approach at 12,000 feet, six miles out, about a minute from touchdown. A 20-degree glideslope is seven times as steep as a normal ILS, so if you try to fly the approach visually without the help of the HUD, you'll be challenged, to say the least. In the Shuttle, you'll be dropping out of the sky at 1,000 feet every six seconds, a pretty ferocious descent rate. In his capacity as unofficial Shuttle sim test pilot, Dye has flown many pure VFR approaches to Edwards AFB where the dry lake precedes the actual runway, and Dye has learned to do it reasonably well. For the rest of us, don't try this at home.

As you descend through 2,000 feet at roughly 300 knots glide speed, a pair of triangles begins to rise from the bottom, one on each side of the HUD, and Gibson suggested I'd better not let them get ahead of me. "That's your flare indicator," he explained. "If you don't catch the rising triangles and begin your flare before they reach the middle of the HUD, you're going to be low, and of course, you don't have any power to recover."

I learned that lesson on my fifth approach. I flew my first three approaches to the Kennedy Space Center and managed to plant the airplane on the runway all three times, though not necessarily with style or grace. One of the parameters NASA uses to evaluate a pilot's ability to land the shuttle is gear G-load at touchdown. I received a print-out of my landing results at the conclusion of two hours in the sim and noted that the max allowable sink rate was 9.0 fps, or 540 fpm. My worst effort was about 8.1 fps, barely within tolerance. My best effort of the five successful touchdowns was 3.5 fps---not bad, but no cigar.

On my second approach to Edwards, however, I blew it completely. I missed the rise of the flare indicators and wound up too low with no way to recover. I landed short, and the simulator simply locked up. Gibson, always the ultimate diplomat, laughed and reminded me that landing short at Edwards is no major sin, as the runway is fronted by several miles of flat lake bed.

You typically come across the fence at 220-230 knots, but again, the speed is masked slightly if you're flying the HUD. Just as with an airliner, the nonflying pilot calls out radar altitude as the commander eases the Shuttle down to the runway. The goal is to touch down 2,500 feet down the runway. At touchdown, the nose is still high above the runway. During initial flight tests in the late '70s, pilot John Young experimented with holding the nose off as long as possible to maximize aerodynamic braking. Eventually, it was decided to lower the nose earlier to minimize the load on the nose gear. The runway at Kennedy is three miles long, and the one at Edwards five miles in length, not counting the lake bed, so there's a little fudge factor if you're long. Just don't be short.

After all three wheels are on the asphalt, the pilot deploys the drag chute and applies the brakes to "maintain the center line, so the media will have a photogenic subject," said Gibson. Just as with the real aircraft, there's a certain let down when you're stopped on the runway at Kennedy or Edwards. But at least, in the sim, you have the satisfaction of knowing you just landed a near-exact replica of the world's fastest and highest-flying spacecraft.