September 26, 2004 notes
Since I got involved with the X-Prize, Peter Diamandis has
been talking to me about his other project, http://www.nogravity.com/ . Like most people, he was
hitting me up to invest in his company, but I said that I would rather be a
customer than an investor (where possible, this is a better way to support
companies). It took two years for it to go from "We are going to be
starting flights in a couple months!" to actually getting the airplane to
Dallas, but today I took all of the Armadillo crew and some of my partners from
Id Software up on a chartered flight, "beta testing" the experience.
It was awesome!
We had 14 people, so it was only a little over half the full
capacity, giving us plenty of room to bounce around. Doing the martian
(1/3) and lunar (1/6) gravity parabolas is a really good idea, as it lets
people get a little used to the movement before completely floating
around. Many people thought the lunar gravity parabolas were the best
We did a total of 17 parabolas, the normal 15 and two extras
at the end. At least half the people thought that was plenty (or two too
many), but a bunch of us were like "Ten more parabolas!"
Nobody puked, although we did have one person staring
solemnly at his barf bag at one point, and a few people had to go sit down for
a bit. They gave recommendations for prescription medication that a
couple people went and got filled, but the rest of us just took over the counter
dramamine pills that they provided. One of the crew mentioned a
promotional flight they had recently flown with a bunch of unmedicated
journalists that had been hitting the cocktail bar, resulting in fully one
third of them losing it.
The time went by so quickly that you completely forgot half
the things you planned on trying. A couple of us were doing low gravity
judo throws, and I took a shot at the worlds first flying armbar in zero
gravity (didn't work out too well). Most of us that were doing fairly aggressive
bouncing around landed on our heads at least once, so I have some concern that
they will eventually have someone test the liability waiver.
The bottom line is that I highly recommend the experience, and
I am almost certainly going to do it again at some point. Peter said most
of their bookings are for corporate incentive programs, which is probably the
most fun way to do it, but grabbing a friend and getting tickets for one of the
passenger flights that will be starting soon out of Florida would still be
memorable. The current individual price is $3k.
The take home lesson is that we need to add a lot of cabin
volume to our first consumer suborbital spacecraft. Adding an extra
63" by 12' of cabin volume will only cost us about 250 pounds. You
won't get much more total zero-g than on the parabolas, but it will be
contiguous, and combined with the view, the boost burn, the reentry
acceleration, and the exclusivity, I do think it is going to be a ride worth
$100k. Zero-G is almost certain to stir up a lot of excitement about
manned space flight in general.
We tried two more
engine configuration changes -- adding 20 more screens above the cold pack
monolith, and supporting the monolith with a cross of square bar stock above a
heavy perf plate, which was the way we used to build them before getting the
water jet cut support plates. Neither
change made in difference, it was still rough at full throttle.
On the theory that
the flameholder might be getting extinguished, we tried injecting hydrogen
between the packs. No difference.
Finally, we tried
an idea of John Carr's -- injecting nitrogen into the liquid above the
spreading plate to give it some compressibility. I almost didn't go for this, because I couldn't imagine it
helping, but, much to my surprise, we made two smooth runs at different pressures
with this change. On Tuesday we will
see if just making a gas accumulator at the engine inlet fixes it as well, and
try the fix on one of the other engines we still have sitting around fully
assembled. Years ago, we tried some
accumulators on 90% peroxide engines and it seemed like they made things worse,
but that just might be the key here.
James has all the
jet vane hardware ready to go on the new 12" motor, so if the experiments
on Tuesday work out, we should be welding the big motor together next
weekend. We got both new 450 gallon
tanks fitted with cone mounts, so on Tuesday we will also be drilling and
taping those for the cones. We are
still waiting on our machined manway and a repaired differential pressure
transducer before we can have everything in flight shape.
Lox Engine Work
fired the lox engine with our water cooled chamber, but we really shouldn't
have. We tore an o-ring when we were
putting it together, so it had a pretty big spray of water coming out the
bottom. We fired it anyway, and it ran
nicely for 30 seconds, but it did burn through on the side with the leak, at
about the height where we usually see a hot spot. It was probably mostly due to the water leak, but it also made us
want to fix our uneven combustion.
We built a new
fuel injector that fit below the lox vaporizer, injecting fuel from the outside
into a short tunnel twice the diameter of the oxygen sonic choke, so it would
have a short area to mix very vigorously before expanding into the main
I have had a cryo
ball valve on order for a while now, but we decided to just clean and use one of
the vented stainless steel ball valves we have on hand so we could log valve
position properly. We did a bunch of
tests with liquid nitrogen, and sure enough, after throttling on and off a
number of times, the ball valve did freeze closed. We wrapped some heat tape around it, but the kind I had on hand
didn't seem very aggressive. We also
have a manual valve in line, so we went ahead and used it for our lox tests.
We only had time
to do a chamberless test of the new fuel injector, but it looked very hot and
symetric, so we expect the uncooled chamber run on Tuesday to work well. The ball valve did freeze closed again for a
little while after starting and stopping it a few times. Im going to change to a beefier actuator
and try and find some fire-breathing heat tape.
Russ and I are
machining a new cooled chamber that we may have ready for testing next
Saturday. We are going to mill channels
in the internal section instead of relying on an annular gap, and we are going
to weld the entire thing together so it doesn't need o-rings at all. Since the throat didn't melt out on the test
this week, we are going to try another one with straight sides before we worry
about making a throat-fitting saddle.
We have started
looking at all the things we need to do to build a lox vehicle. We are going to continue pursuing the lox
work, but I'm glad we are finally seeing the monoprop engines running well
again, because I still think that is a better combination for suborbital
work. We'll probably use lox for later
orbital work now, because there hasn't been any visible progress on the 98%
peroxide availability front.