August 10, 2003 Notes
Russian Space Suit
We bought a used Russian space suit on Ebay. Our plan has always been to have a
pressurized cabin, but an extra layer of safety is probably justified if we can
get this working without too much trouble.
It has a few holes that will need patching, but most of the material
looks in good shape. We will have to
fabricate some adapters to go from the Russian fittings to AN fittings, but
that shouldn’t be a problem. The big issue
is that the gloves are missing, even though the offer explicitly had them. The seller claims they were sent in a
separate box, but it has been several additional days, and it hasn’t arrived
yet. Hopefully, he just forgot to
include them, and they are on the way from Russia now, and we aren’t actually
being ripped off…
http://media.armadilloaerospace.com/2003_08_09/suit.jpg
http://media.armadilloaerospace.com/2003_08_09/russInSuit.jpg
Related to this, we did some cabin airflow tests on
Saturday. In 100+ degree Dallas
weather, being inside the cabin even with the hatch open for very long gets
uncomfortable pretty quick, which we notice when doing electronics work inside. Now that we have a tank of breathing air and
various flow meters, we are able to start testing our plan of using open loop
air venting to provide both breathing air and cooling. We ran a hose from the air bottle into the
cabin, and closed everything else up.
We didn’t actually seal it to the point that it pressurized, but it was
reduced to venting the air past a few known places. With 1 CFM of air flowing out the hose at your face, you don’t
have any trouble breathing, but the cabin does continue to rise in temperature
due to body heat. You could deal with
it for an X-Prize flight, but it will probably be better to increase flow until
a comfortable steady state is reached. We
will probably do some more precise tests with thermometers, timer, circulating
fans, and increased flow rates next week.
Small Vehicle Work
I finally got around to flashing the bios on our AMPRO PC104
flight computer. The only issue we have
had with it is that booting from the integral compact flash drive was
problematic, never booting on the first power-on, and requiring a voodoo
operation of rapidly power cycling it so it acted like a warm boot. That problem seemed to be getting worse,
sometimes taking multiple tries to get it to boot, which is extra annoying without
a video display attached. The bios
update did fix this issue.
We did a water test on the small vehicle to check everything
out, since it has been sitting around for over four months now. Everything is working perfectly, and we
should be good to go as soon as we get some 90% peroxide. Don Stark’s concentrator has been having a
lot of teething problems, but we still expect an initial shipment any time now.
Also on the topic of peroxide, FMC actually agreed to sell
something to us! They were willing to
sell us rocket grade peroxide in 50% concentration for our static tests of the
mixed monoprop combination. There are
significant conditions: it can’t be
used for concentrating, and it is only for static engine tests, but we hope
this is a good foot-in-the-door. Using
the extremely high purity grade peroxide will let us factor out poisoning from
the peroxide stabilizers as an issue during our testing.
Big Vehicle Work
We got a larger Sea Catch release that will be strong enough
for holding the vehicle under drogue during reentry. Unfortunately, I broke a 5/16” tap while preparing it for servo
actuation. Hopefully we can get it out
with a tap extractor. We will be using
the small Sea Catch for releasing the spring cannon that punts out the drogue,
while the big one holds the drogue-to-main connector until it is time to
release the main. A nice aspect of the
Sea Catches is that we can run a completely manual cable pull to them, so a
pilot could yank them open even if all the power was gone. When we add the redundant recovery system,
we will also have to have a release on the main chute to allow it to be cut
away before firing the backup system.
http://media.armadilloaerospace.com/2003_08_09/bigSeaCatch.jpg
The helicopter drop test showed us that the vehicle could
tip almost all the way back up after landing, which resulted in bending the
support studs the vehicle normally sits on (and stuffing dirt in an engine
bell). We also found that hoisting the
vehicle up by the cabin or nose was problematic, because it couldn’t be allowed
to tip up on the studs, or they would bend.
This seems to be a good rule of thumb: if you are ever worried about
bending something while moving the vehicle around the shop or transporting it,
it probably isn’t strong enough for our landing mode.
We built braced extensions under each engine mount by
welding 12” square, ¼” thick plates on the side, with 1” x 1.5” x 0.125” wall rectangular
aluminum structural tubing braces and 1.5” square by 2” long aluminum blocks as
the corner feet. We trimmed down the
stainless studs to just under the engine plates, so it only added about 15
pounds, but the vehicle is now strong enough to tip up and just let it drag
along the floor on the legs. We think
the aluminum will be ok by the engines, but we will find out with some long
duration static tests. Worst case, we
may need to add a little bit of insulation to it.
http://media.armadilloaerospace.com/2003_08_09/bracedLegs.jpg
http://media.armadilloaerospace.com/2003_08_09/upright.jpg
We decided that having chamber pressure transducers on each
engine is a worthwhile addition, especially for the mixed monoprop engines, so
we can tell if an engine is giving out during flight, and so we can make sure
that there is stable chamber pressure in all engines at cracked throttle before
throttling up for liftoff. Russ welded ¼”
swagelock fittings into the 2” throat engine bells, and I ordered four more PX176-1KS5V
pressure transducers from Omega. I also
tested the 1 micron porous metal pressure snubbers from McMaster for this
application. I was afraid that that
tiny of a snubber would cause the pressure readings to lag a human-noticeable
amount, but in the 100+ psi range, it still seems to track plenty fast. The biggest pain was running more wires down
the side of the rocket. We were going
to need more anyway for redundant parachute actuators, so we went ahead and ran
35 more lines down the side.
The minimum requirements for a nominal flight of our vehicle
is 35 lines – five each (two for bi-directional actuation power, plus three for
potentiometer feedback) for the four engine valves, the master cutoff valve,
the drogue cannon release, and the drogue-to-main release. We need 12 more lines for four pressure
transducers, and 15 more for the main chute cutaway servo and the backup drogue
and main servos. We might also add a servo
tank vent valve at some point. Sharing
a single common power and ground line to the base of the vehicle could save a
lot of wires, but I prefer to do all splitting in the cabin. We will probably be epoxying the wires
against the tank next week.
http://media.armadilloaerospace.com/2003_08_09/pressurePorts.jpg
http://media.armadilloaerospace.com/2003_08_09/wiring.jpg
Phil finished the work on our main parachute storage and
packing box. The bottom matches the
curve of the tank, and we built a matching packing box with a foam-filled
bottom so the chute can be pressure / vacuum packed if necessary. The box has right at 1 cubic foot of volume,
which we are afraid may not be enough, so we may need to extend the sides past
the level of the engine plates.
http://media.armadilloaerospace.com/2003_08_09/conformalBox.jpg
http://media.armadilloaerospace.com/2003_08_09/packingBox.jpg
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