October 30 and November 3, 2001 Meeting Notes
Pure Silver Foam
Our pure silver foam blocks finally made it in, and we did
several test stand runs with it.
I tried to use a new laptop for the testing, but WinME seems
to leave one of the serial control lines in a different state than Win98, so it
was leaving the test stand solenoid on all the time. I switched back to the old laptop for today, and I will
We now have a lexan shield for the test stand that covers
the engines. Im not very worried about
our monoprop engines, but I think it is a good measure for when we do our
The silver foam is in half inch thick blocks, with 60 pores
per inch. It is a fairly rigid, slightly
crumbly sintered metal deal. We asked
for 80 PPI, but they informed us that they tried a few times and couldnt get
that working, so we settled for 60 PPI.
The first test we ran, with three lightly compressed blocks
separated by control rings in the engine did not provide enough back pressure,
and the run was wet. Compressing a
fourth block into the engine made it mostly clear, but it still clouded up
some, and when we opened the engine back up, the bottom block had severely
deformed, and the nozzle had a lot of silver plating on it.
We had been cautioned by Mark Henry, the lead propulsion engineer
for Beal, that pure silver foam was going to be too soft, and it looks like he
The control ring plates do seem to be doing their job, so we
assembled new packs for all four engines using mostly our existing silver
plated nickel foam. We left one
pre-compressed pure silver foam brick at the top, so we can see how that holds
up long term.
The current engine sets are made up with a double layer of
coarse perforated metal for the base plate (we need to get thicker stainless
base plates for the small motors), eight plated discs, a control ring, eight
more plated discs, another control ring, then a pure silver block that gets
compressed down as the cover is tightened down.
We are probably going to put twenty gallons of peroxide
through our engine sets in the next couple weeks, so we will be able to see if
the control rings are the key to longevity.
We did another short-form lander hop with the new engines. I used new laptop for this, which avoids any
chance of the S3 graphics-driver crash we had last week during testing. We had it on a single tether, but the two
gallon hop flew fine. However, the
flight computer hung after it bounced down on the ground. Telemetry was lost in the midst of the
settling bounce, and when we opened the box up, the LEDs were not lit on the
Power cycling brought the computer back up, but I didnt
want to fly it again until we had done something to try to address the
problem. We are assuming that shock is
twisting the PC104 stack, which can cause all sorts of bus failures. I have a very rugged versa-tainer to move
all the PC104 boards to, but it will mean moving away from the 802.11 card to a
separate wireless Ethernet device, and a lot of other changes. I am going to see about doing that over the
We still wanted to run the engines some more to see how the
control rings hold up, so it was suggested that we have a couple of the guys
stand on the lander so it cant possibly take off, and run the engines through
a load of peroxide. We would find out
some of the human factors involved with our piloted flights, like what the
noise level and fumes are like right next to all the engines.
Joseph and Russ were in the chem. Suits, so they stood on
opposite sides of the lander. They had
goggles, ear protection, and filter masks on.
Phil stood by with the hose. After
firing each of the attitude engines separately, I throttled the central engine
up, eventually going to full throttle.
With only 300 psi in the tank, and a total weight of 550 pounds, it definitely
wasnt going to take off (although we did leave the tether on, just in case
someone jumped off). It did manage to
slide the vehicle along the ground a little bit, mostly pivoting on Josephs
side, because he weighs over 100 pounds more than Russ.
They reported that the initial pulses of the attitude
engines when I was testing them individually felt completely smooth. The noise level was not a problem at
all. There wasnt any problem with
peroxide fumes, but these are all almost brand new cat packs, so that will
likely get worse with wear. They could
feel a lot of hot air coming up from the ground, but nothing dangerous. The ride did get rougher when the attitude
engines were working to level the platform dynamically and the engine got throttled
up, but it wasnt at a jarring level.
After the flight, we noticed two interesting things: at 75% throttle, there were pulsations in
the tank pressure telemetry, showing that the feed system wasnt choking the
engine well enough at that point. That
is reasonable, because a 1/2" ball valve would be more appropriate for an
engine a couple time larger than our current one.
The other thing we saw was that the central engine exhaust had
eroded some of the landing pads on the inside, depositing some melted bits on
the chem. suits and vehicle. We had
never seen this before, because it probably required a couple seconds at high
throttle right on the ground, while all of our previous flights lifted off before
it could happen.
The new twin-tank, seated-pilot-under-a-roll-bar vehicle
frame is taking shape. Unfortunately,
the only tanks that we can get a matching pair of at the moment are heavy hoop
wrapped aluminum NGV tanks. We have
access to five different pure-carbon tanks, but all of them are different
We will fly it originally with these tanks, then if we want
to save 100 pounds, I can get some tanks made to spec.
The FAA denied our request for a standing 5000 waiver over
my 100 acre property out of town. Im
pretty sure we will be able to work it out after making a few more trips up and
down the bureaucracy (the waiver got passed between four different people
before someone finally said no), but if we are reduced to applying for
one-shot waivers with a 30 day turnaround for every test flight, it is going to
have a significant impact on our development speed.
was unwilling to sell us recovery parachutes for our unusual application due to
liability concerns. They had the ideal
chutes for our next couple vehicles, but we will have to find something
equivalent elsewhere. They did provide
some information about their systems: the drawing rockets are 294 total NS with
a 1.1 second burn time, are attached to the chute with two angled cables, and dont
have any fins or guide rod.
We got a new book on parachute recovery systems, which makes
for some interesting reading. For high
mach, high altitude deployment, towed ram air ballutes get the highest
marks. A complete parachute recovery
system for an X-Prize class vehicle is looking more complex than I had
originally thought, probably involving three chutes (not counting backups): a
small supersonic chute to get it below mach one, then a drogue to get it bellow
300 mph, then a reefed main chute. We
spent a while discussing various dive break options that might be able to get
the vehicle to a 300 mph terminal speed, as well as having the ability to
reduce the peak reentry G loads by varying the extension, and possibly
providing some steering during descent by non-uniform extension. For the past couple weeks we have also been
semi-seriously considering building a roton, which neatly solves all the