I just had the extreme pleasure of speaking
with Mike Melville yesterday, the pilot of Space Ship One's first
two flights above the Kerman line of 100 km MSL, and with his wife.
He gave a 45 minute presentation to the Aircraft Owners and Pilots
Association conference in Long Beach on Thursday, and got a several-minute
standing ovation. I was able to speak with him for a short while
after his talk.
Since he was speaking to pilots, he didn't have to translate for the
"general public" or pull many punches. He spent almost
half of his time going over the flight controls and the entire cockpit
layout inside of Space Ship One, explaining how it is flown.
I think this is the first time this has been explained publicly in such
detail, and it was amazing.
There are actually four separate flight
regimes, and each is flown differently. Just after launch, it flies
like a Piper Cub, using a joystick and rudder pedals with mechanical
linkages to the controls (no hydraulic assists). When it goes
supersonic, the aerodynamic forces are too high to be able to move the
stick, and the controls are subject to flutter. They use an
electrically powered trim system, flown using the "top hat"
switch on the joystick and a couple of grips on the arm rest of the
pilot's seat. (There are backup switches to the left of the
instrument panel, which had to be used on one flight.) This moves
the entire horizontal stabilizers, not just the elevons on the trailing
edges.
Eventually, they get high enough and the
air gets thin enough that they can again use manual controls, although the
response is totally different than lower down. But that goes away as
they exit the atmosphere; the Reaction Control System nozzles are then
used for maneuvering in space. Coming back down, the pilot has to
reverse the sequence. There is no automated switchover of control
systems; the pilot has to remember to move from one system to the next at
the right times.
The rudder pedals are not linked.
Each controls one of the two vertical stabilizer rudders separately.
You can push both rudder pedals at the same time, and get a fairly
effective speed brake, with both rudders canted outward. Push both
fully forward and they engage the wheel brakes. But these are not
very effective and are only really useful for steering input during
rollout. The real brake is on the nose skid: a piece of maple wood,
with the grain aligned down the centerline of the airplane. He said
it was the most effective braking material they could find.
We talked about G forces on Tuesday... He says that he gets hit with
about 3Gs kicking him backwards as soon as he lights the rocket
motor. He's supersonic within about 9 seconds later. But he
immediately starts to pull up into an almost vertical climb. So he
also gets over 4.3Gs pushing him down into his seat just from that
maneuver. The combined force is "very stressful" and Mike
says it's "important not to black out" at that point. He's
going 1880 knots straight up within 70 seconds.
On re-entry, the aircraft goes from being
absolutely silent while in space to
generating a deafening roar as it hits the atmosphere again. He's
going about Mach 3.2 by that time, and has to survive about 5.5Gs for over
30 seconds, and lesser G forces for longer than that, as it slows back
down. It sounds really intense, both as he explains it and on the
radio.
A couple of interesting side notes: Space Ship One has a standard
"N" registration number; but it is licensed as an experimental
"glider". Apparently there was a huge bureaucratic hassle
trying to license it as a rocket powered spacecraft, which they just
sidestepped by calling it a glider. I asked him if it had a yaw
string; he laughed and said that would have burned off. By the way,
the registration number is N328KF, where 328K is the number of Feet in
100km. (White Knight is N318SL - Burt Rutan's 318th design.)
Mike says that the flight director system, called a "TONU” (“Tier
One Navigation Unit"), was developed completely in-house by a couple
of 28-year-old programmers, and is absolutely fantastic to fly.
That's why they don't need a yaw string. But I had heard over the
radio that Brian Binnie had re-booted the TONU just before the landing
approach during the X2 flight, and it took quite a while for it to come
back up.
I asked Mike what that was about. He
says that during re-entry, the TONU loses its GPS lock. So it keeps
trying to go back to catch up, re-interpolate and compensate for the
missing data, and this keeps it a little behind in its actual position
calculations. The pilot has no straight-ahead vision at all, so they
have a real issue landing: they can't see the runway! The way they
do it is to fly directly down the runway at 9000 feet; then they do a
(military style) break and fly a full 360 degree pattern right to the
landing. The TONU gives the pilot a "blue line" to follow
and a target airspeed (which produces a given rate of descent). If
the pilot follows the blue line, right to the break point and through the
two 180 degree turns, it will put him right onto the runway at what ever
touchdown point he selects. But the TONU has to be absolutely
current when this is going on. So at something above 15,000 feet
they reboot the TONU and get it re-synched with the GPS satellites again
before setting up for the landing!
He also talked in detail about the rocket
motor, and had photos of its insides after firing. The nozzle throat
actually ablates as the motor burns, enlarging the interior throat
diameter as the burn progresses. He described the problem they had
on the June 21 flight: The rocket motor nozzle was skewed by about
˝ degree to one side. This generated a surprisingly high lateral
torque trying to turn the aircraft. If it had been up or down pitch
rather than lateral, the controls could have handled it; but the lateral
yawing forces were too great for Mike to compensate as the atmosphere
thinned. The result was that he was pretty far off course.
Mike says he reached apogee, rolled the spacecraft over, and was surprised
to see the Palmdale VOR directly beneath him. That was 30 miles away
from Mojave and a long glide home. He says its amazing how fast a
relatively small deviation can produce large distances when you're going
Mach 3!
For one of the static burn tests, they had
fire and safety crews all standing a mile away, ready to duck if anything
went wrong. In the middle of the test, Mike and Burt Rutan walked up
to the front of the motor assembly and felt the pressure vessel that
contains the N2O. Mike knew he was going to have this same thing
strapped onto his back soon, anyway, and he wanted to know how much it
vibrated, how hot it got, and how loud it was. It was deafening,
literally. It turns out that, with the nozzles they use at high
altitudes, it's actually not that noisy inside the spacecraft. But
he still wears hearing protection.
Scaled Composites seem to have fabricated quite a bit of the rocket motor
themselves, including the N2O tank (which is also the structural core of
the spacecraft) and the nozzle casings. It would be interesting to
hear from Michael's friend exactly what parts SpaceDev designed and
what they manufactured.
I took lots more notes. Very interesting stuff.
|
