SpaceShipOne and Me:
We Make a Couple of Digital Trips to Space in the SS1 Simulator

Text by Budd Davisson, Flight Journal, 2004

I've had a lot of high points in my rather twisted career, but none are higher than standing there on the ramp in a cold desert morning watching Mike Melvill shove it up NASA's nose. For years I've been crossing Burt's path when flying one of his prototypes or chairing a design conference or any of a number of sport aviation activities in which we were both involved. However, when I was invited out to be part of the crowd when he announced the SpaceShipOne program, that already had 20 flights on White Knight, there was absolutely no doubt that all of us knew we were standing in the presence of sheer genius. This was a man history would remember. And what made it all so cool, is that he's one of us. Sorta. I'm going to shut off now, or the intro will be longer than the article that follows, but let it be known that the times I've spent around Burt, Mike and Mike's wife , Sally, are right up there with the most important times of my life.

You’d have to live in the last grass hut at the end of the longest dirt road in Tasmania not to know and appreciate what Burt Rutan and his SCALED Composites team have accomplished in their Tier One space program. Fortunately, some of the networks, notably the Discovery Channel, have produced some of the most interesting, profoundly emotional and technically correct coverage seen in years.

So, you may ask, what can we, the small editorial staff of a magazine devoted to the aviation adventure, contribute to SpaceShipOne coverage that hasn’t already been detailed to death by others? How about putting our reader’s at the controls of SSI as one of us gives a pilot’s-eye view of a truly history-making aircraft while we fly the SS1 simulator?
The Man: Burt Rutan in the motor bay of SpaceShipOne

For those of us engrossed in sport aviation, Burt Rutan feels as if he has just always been there. His life story has now taken its rightful place in the annals of history, but my own involvement with him began in the early ‘70’s when he was working for Jim Bede of BD-5 fame in Newton, Kansas. I was sitting in an office with Les Birvin (Bede’s test pilot) and Jim Bede, when a tall, excited guy burst through the door.
“I’ve got it, I’ve got it,” he said, as he threw some papers and napkins on the desk. His energy was so high, that if the lights had been off, he was probably giving off blue sparks. He had just returned from a trip, but prior to his departure an idyll conversation had taken place about what it would take to keep an airplane in the air indefinitely. On that trip Burt’s brain wouldn’t leave the subject alone and he came back with tons of thoughts and calculations.As I remember, it involved using CDS cells to drive electric motors.

Today, thirty years later, Burt Rutan is still giving off sparks and his achievements have kept stacking up until it’s obvious that history will eventually count him among the most important influences in aviation. He and I have zigzagged back and forth across each other’s paths constantly during his odyssey. Ditto for Mike Melvill and his oh-so-patient and brave wife, Sally. For that reason, like so many others they have touched, the Tier One program meant a lot to me personally.

I dropped Burt a note asking if I could come out and fly the simulator in an effort to understand what kind of craft Mike and the other SCALED pilots had to cope with. Just describing what they’ve done is one thing, but to truly understand it, I felt I needed to sit at the controls and experience it. Well, not really experience it, since I’d be sitting in a hangar in the Mojave Desert, not perched on a cone of flaming rubber 62 miles straight up. Burt immediately answered my e-mail with “Sure come on out.” And so began my quest to become a virtual astronaut.

The door to the best video game on the planet!

First it should be understood that you don’t buy a simulator for a revolutionary form of spacecraft off the shelf. Like everything else the SCALED team did, along with designing and building their own launch aircraft (White Knight), they designed and built their own simulator right down to writing all of the required computer code.

I spent quite a bit of time getting a cockpit checkout sitting in the launch ship, White Knight, from Steve Losey, the crew chief, so when I crawled into the SS-1 simulator I was at least familiar with the general layout, since the two cockpits are practically identical.

The simulator itself is a composite (what else?) eggshell suspended in a web of steel supports. Next to the door is a white line labeled “If you aren’t at least this tall, you can’t ride this ride.” Above the door, a similar sign says, “Keep arms and legs inside the spaceship at all times.” Humor has always been key to the entire Rutan operation.

The seemingly odd arrangement of the windows, which is dictated as much by structural demands as ergonomics, gives sight angles probably 10-15 degrees either side of straight ahead, but straight ahead you’re looking at the back of the nose hatch. In fact, the control panel (the TONU), rudder pedals and about everything from the pilot’s knees on down is jettisoned along with the nose hatch giving free access straight ahead. But, when flying you can’t see squat right in front of you.

The camera is about where your eyes would be. The TONU system sticks up between your legs and the rudder pedals are on either side of it with the nose windows behind those. A Dynon nav system is on the top cabin bow as a back-up.

When you wrestle your way into the centrally mounted pilot’s seat you’re struck by the seeming simplicity of everything. You’d expect a massive array of system controls and computers but other than a couple of rudimentary control panels, including the environmental control system panel and some switches including those for launch arming on the fuselage frame above you, basically all you have is the stick, rudders and a rectangular box (the TONU) that sticks up between your legs.

The TONU (Tier One Navigation Unit) IS the airplane. Every bit of avionics, instrumentation and system monitoring is in that black box. It’s a CRT probably a foot wide by 18 inches tall that is split into two pages, top and bottom. The presentation on the top half is the flight direction system and the bottom half is a multi-page presentation that can be scrolled through to view a wild array of information about what the craft is doing and how the systems are functioning.

The page that is usually displayed on the bottom during flight is a horizontal situation map that continually shows the pilot where he is in relation to Mojave Air (now Space) Port and what he needs to do to make it back to the airport. Remember, this is a glider and going around after a bad approach isn’t an option. Maybe that’s what the One in SpaceShipOne means: you get one shot at landing it, so you’d better be on the ball.

The heart of SpaceShipOne: the TONU all-knowing system. The flight data is on the top half and the bottom half can be scrolled through about a dozen screens that tell you different parameters about the various systems.

The top half, the flight systems presentation, is dominated by a big artificial horizon, a variation of the same type of instrument seen on the panel of practically every airplane built in the last sixty years. It has to be remembered that SS-1 is hand-flown. In this day of computerized everything, Rutan’s guys went into space the same way Lindbergh crossed the Atlantic, by hand. Even though the highly computerized TONU is giving the pilot all the information he needs to fly the right profile, it is the pilot who actually controls the craft.

The artificial horizon differs in one major way from the normal general aviation version: it is capable of full 360 degree movement in all directions, which allows the pilot to command straight up and straight down attitudes.

The other critical flight information is displayed on the same screen as the artificial horizon, e.g. in the upper left corner you have indicated airspeed (actually, equivalent indicated airspeed, which is IAS corrected for compressibility effects) while the altitude and rate of climb is prominently displayed in the upper right.

A cross in the lower right displays the yaw and pitch trim position as well as stick and rudder position. In a quick glance you can instantly tell where the airplane is going and how well it’s doing as well as monitor what position the controls are in.

My first flight was a gliding drop from 50,000 feet and it was a real eye opener. Stick almost full back (the gray mark on the bottom of the cross), a short count down and the airplane falls free. Whoa! Instantly it dropped the left wing 20-30 degrees, then, as I was thinking about correcting, it rocked into a bank the other way. Then left again. It was classic Dutch roll where an airplane, with no input from the pilot, rolls uncontrollably from one bank angle to another. It’s not only disconcerting, but the natural instinct is to stop it, but it didn’t take long before I realized almost everything I did made it worse. Sometimes much worse. At one point I was in a ninety degree bank. Not cool!

White Knight with SS1 and Mike Melvill on the way to make history.

While fighting the rolls with the ailerons (actually elevons) and trying to coordinate with the rudder I discovered another characteristic of the airplane: it has a HUGE roll/yaw couple. Get the nose just a little to one side and the wing drops almost violently in that direction. This was further compounded by the rudder pedal pressure: to eliminate the possibility of a pilot accidentally inducing yaw by resting a foot on the pedal, the rudders are spring loaded to neutral. And I mean REALLY spring loaded. It took all the strength I had in one leg to push the rudder all the way down.

So, I’m chasing level flight while trying to maintain a reasonable speed. We’re dropping like a stone and it suddenly dawns on me that I have to try to find the airport. The navigation map has an airplane icon (me and SS1) and a buggy whip type of line attached to that icon. It curls around, continually changing as it shows the pilot which direction he has to turn from any given position to arrive abeam the airport on downwind at 8,500 feet.

With a little coaching from Jim Tighe, SCALED’s chief aerodynamicist, I managed to get within sight of the airport. By that time we were down to around 30,000 feet and the airplane was beginning to act more and more like a regular airplane. By 20,000 feet, there was nothing at all unusual about the airplane and holding 130 knots KEAS (Knots Equivalent Air Speed) for the approach was no big deal. What was a big deal was trying to keep track of the airport through the tiny windows. There it is, oops lost it, I’ll catch it in the next window.

The nose section and its locking ring. This is the portion they unlock and blow off, should the pilot decide to bail out. The TONU and rudder pedals go out with it.

Each window on the simulator has it’s own CRT and it’s amazing how real the entire visual system feels. I totally forgot this was a simulator. These guys ought to forget about space and start building arcade games. They’d clean up.

Several weeks earlier, I had been at Mojave and watched Mike land after qualifying as an astronaut so I knew I’d be making a curving approach, which is the way I land my own airplane anyway. I also knew it would be a high approach, but when I was at 4,000 feet on short final and Jim Tighe says to hold off putting the gear down to make sure we have the runway made, it drove home the point that this thing glides like an anvil. Plus, the gear doors are ready-made speed brakes.

On that first approach I totally forgot about the blind spot ahead because I was curving toward centerline, while watching out of the foremost windows and I fell good about the profile. Then I intercepted centerline and lost the runway entirely. It didn’t dawn on me until the second flight to lean sideways out of the seat to maintain some contact with the edge of the runway. I leveled too high, so didn’t see the edges of the runway again until too late. I wound up skidding through the dirt 25 feet to the left of the runway. Fortunately both the simulator and me survived without a scratch. Now it was time to go for space.

The most important controls for the pilot reside on a simple looking, flat console under his left arm. At the very front is a huge knob for the yaw trim and in watching flight movies later, I noticed Mike flew a lot of the flight with a hand on that knob. Especially during launch.

Three, two one, I’m dropped. The guards on both switches were already up. I hit the left arming switch, then hit the right one. In the sim I didn’t have the 2 G kick in the butt the real pilots felt but instantly the airspeed started climbing. As it did, an icon was projected on a vertical line through the TONU: that was the target. Keep the nose on that icon and the airplane would get maximum altitude out of the rocket motor burn.

The airplane is rocking left and right and I’m struggling, really struggling, to maintain a level attitude while putting the nose on the icon. The pitch trim switches on the top of the control stick became very handy at that point. As I fought to hold attitude, I glanced at the altitude read-out and had to grin—it showed me blasting through 200,000 feet with a climb rate of 150,000 fpm. That’s 1700 mph straight up!

In what seemed like seconds the rolling tendency died away as the atmosphere fell behind and the controls got increasingly lazy with no air to push against. It was fascinating to watch the interplay between “true” and “indicated” airspeed on the TONU. Indicated airspeed is actually a measure of how densely packed air molecules are. Even in light planes at altitudes as low as 8,000 feet the indicated airspeed lags the true airspeed by as much as 10-20 mph because the air has thinned out. The molecules are further apart so they aren’t hitting the pitot tube as often as at lower altitudes. All of the aerodynamic and structural effects of flight are grossly affected by this phenomenon. To put loads (G’s) on an airplane, the airplane needs air to push against, so the thinner the air, the lower the structural loads become.

The famous anti-gravity ping-pong ball. when the string wrinkles, you know you are a long way from home.

As the atmosphere fell behind, I watched true Mach numbers hovering around 1.0-1.5 while the airspeed was winding down through 40 knots, to 30 knots, then zero, With no air to generate forces on it’s control surfaces, as far as SS1 was concerned, it wasn’t seeing any more activity than it would sitting on the ramp regardless of how it was tumbling around.

Since the normal control surfaces weren’t working, SS1 started a lazy sort of roll, which was actually some motion left over from earlier because it was just floating. When Mike experienced the high rotation rolls going up hill on the first X-prize flight, he later commented that if it had started spinning later, after he had left the atmosphere, he would have had more problems. That was because in the atmosphere the aerodynamic controls would eventually arrest the roll, but out of the atmosphere he’d have to rely on the relatively low power of the RCS, the reaction control system.

Out of the atmosphere the controls consist of compressed air thruster nozzles molded into the top and sides of the nose and the top and bottom of each wing tip. When the control stick was pushed to the limit, it hit a microswitch that triggered the thruster on that side.

In a zero G environment, you’re not so much concerned with the rate at which a control change takes place as much as you are the acceleration. Once you start it moving, it’ll continue accelerating so all you really want to do is nudge it one way or the other. This requires nothing more than a gentle tap with the stick to get the effect you want. It was an interesting and thoroughly controllable control experience and almost relaxing after the intense, constantly-working-your-butt-off ride up.

As we approached apogee, as indicated by the rate of climb, Jim Siebold, one of the SCALED test pilots who had taken over coaching me, called for feather deployment. I pulled a large lever under my left arm up to unlock the feather, waited until the TONU told me it was unlocked, then pulled the feather lever.

The feathering concept works in combination with Rutan’s thoughts about weight. For its size, the SS1 is extremely light and comparing it to something like the Space Shuttle or X-15 is like comparing a ping-pong ball with a rifle bullet. The other airplanes are slick and extremely heavy for their size. They are dense, which results in what’s known as a high ballistic coefficient: gravity can speed them up easily and, because of their clean shape, they’ll hang on to their speed even as the atmosphere gets thicker. This is where aerodynamic heating becomes a problem and this was something Rutan avoided in the SS1

He not only wanted to keep the ballistic coefficient down but he wanted the ping pong ball to have extremely high drag so the second it senses any atmosphere at all, it would start slowing down. In feather mode the airplane literally breaks in half as the tail cants up, which presents an extremely high drag profile to the increasing atmosphere. By keeping it slow from the beginning, reentry problems are greatly eased.

Another benefit of the feather mode is that the airplane more or less self-aligns like a badminton birdie and automatically assumes the right attitude to hit the atmosphere. The X-15, like the Shuttle, was extremely critical to having both the flight path and the relative angle of the airplane accurate within two or three degrees or it was in trouble. In fact, one did break up on re-entry when the angles were wrong.

In the SS1, once in feather, the airplane is so stable and self-aligning that the pilot doesn’t have a thing to do but wait until it’s down to around 60,000 feet, when he puts it back in glider mode and he starts worrying about finding the airport.

The foregoing is a brilliant concept. It removes the single most terrifying and critical part of space flight. The SS1 never sees indicated re-entry speeds higher than about 130 knots even though mach numbers are approaching 3.2 so it never gets hot. Its thermal protection is a coat of proprietary resin of some kind that’s a tenth of an inch thick. Contrast that to the Shuttle’s cumbersome tile system.

In the simulator I had none of the rumbling noise during reentry that Mike reported as being “scary,” so it was a no-sweat ride down. At 60,000 feet I went back into feather mode and flew it back down. The Dutch roll gets less and less and, once I figured out the navigation display and could find the airport, life was good. I topped 350,000 feet twice and both times got the airplane back on the runway. So, I guess that makes me a virtual astronaut.

My everlasting impression of the entire Tier One program and the SS1 is how brilliantly simple everything is. The SS1 control system, for instance, is nothing more than push rods just like a normal airplane. The horizontal tail surfaces give both pitch and roll and the horizontal stabilizer is electrically trimmable and the airplane can be flown with one side completely inoperative since the spacecraft has redundancy in all of its systems.

On a personal note, even though Burt is a terrifically friendly, humorous, easily approached individual I have to be honest and admit that he intimidates the hell out of me. Even though I’m an aeronautical engineer (primarily structures) by training and an experienced pilot, without meaning to, his very presence is a continual reminder of where the rest of us fit in the intellectual food chain. He’s up there in the rarified atmosphere peopled by only a few true geniuses, while the rest of us are down here slogging along in the muck of mental mediocrity.

The really scary part about Burt Rutan is that I think we’ve only seen the tip of a gigantic iceberg and he’s just now hitting his stride. The next ten years are really going to be exciting. As he is fond of saying, “Things are looking up…way up.”

The core of the rocketmotor is a perforated log of hard rubber, which is nearly pure carbon. When this is ignited in the presence of liquid oxygen, you get a white hot , high speed burn. the light lines are electrical circuit wire wrapped around the rocket. If there is a breech, it will burn a wire and shut down the oxygen pumps and the fire goes out.
Going to space on burned tires
By now everyone knows that the SS1’s rocket motor burns rubber, but we thought we’d expand on that a little.

Technically the motor, which was designed and patented by Rutan and SCALED, is what’s known as a “hybrid” motor because it’s neither pure solid nor pure liquid fueled. The solid fuel core is a log made of Hydroxy-Terminated Polybutabiene (HTTB), which is nothing more than synthetic rubber. The fuel log is 20” in diameter with approximately 4” walls with 4” partitions cutting through the center creating four pie-shaped cavities full length.

And the music comes out here.
The front of the carbon fiber motor is bolted to a flange that is bonded into the back of the composite liquid fuel tank. The liquid part of the fuel combination is Nitrous Oxide, which dentists use to put their patients to sleep (laughing gas) and turns the lowly Honda street car in to a roaring tiger (Nitrous Oxide injection). The bulkhead between the tank and the rocket has a valve in it surrounded by a ring of small rocket motors that act as ignitors.

Both NO2 and HTTB are totally stable in their natural state and won’t react with one another, which is one of the real safety features of the hybrid concept. However, use the ignitor motors to get the rubber burning, then pump in NO2 under pressure as a super-oxidizer and you have a serious flame going. The expanding gas is accelerated through the nozzle and instantly you have thrust.

The motor is wrapped in electrical wire, which is a safety system: if a hole appears in the rocket case, it burns a wire in half, which shuts the valve and just that fast, the rocket shuts off. Like everything else in SS1, the propulsion is brilliant in its simplicity.

For lots more pilot reports like this one go to PILOT REPORTS