January 15 and 19, 2002 Meeting Notes
The next screen pack test engine is almost ready to fire:
This has a 0.25 throat and a 1.1 diameter by 2 long catalyst
pack, which we will be filling with alternated stainless and pure silver
screens. I also finally got around to
measuring our other catalyst packs for documentation: Juan Lozanos motor has a 2 diameter by 1.9 deep catalyst pack
for a 0.56 throat, but it was designed to be expandable to a 0.73 throat with
the same pack. Our foam attitude motors
have a 0.5 throat and a 1.65 diameter by 1.2 deep catalyst pack. We havent fired Juans motor very much, but
when we took it apart there was a fair amount of silver plating dust that was
coming off. His plated screens
definitely react much quicker than the pure silver screens, but we are still concerned
about lifetime and batch to batch variability with plated screens. If we can make a pure silver screen based
pack work, it will probably be a simpler (but heavier) configuration.
The new test engine has a heavyweight aft section, which
includes an NPT port, so we will finally start collecting chamber pressure to
compare some different pack options.
After we have done that, we will probably do some very brief biprop
firings in a heat-soak mode. I am
curious to see if we can make anything auto-ignite with 70% concentration
peroxide, because that would drop the flame temperature enough that we could
use an uncooled plated TZM chamber. The
Isp would only be around 200, but it could be a very cheap combination with
The new engine also has a 0.010 relief cut on the bottom to
help retain the 0.025 thick copper gasket.
We will remember to re-torque the bolts after the first hot fire. We still have threads in the brass for this
nozzle section, but if we use it with a flight nozzle, it will have a flange
with stainless nuts
We are getting rather frustrated with our foam pack
engines. All of them were loose enough
to rattle today, even though they had only been on two flights since they were
repacked. We added a few more discs to the
attitude engines, and they worked fine, but our first short peroxide test of
the full up lander had the main engine never clearing up. We opened it up and saw such appalling
stripping in the center of the foam discs that we wondered if our peroxide was
over 90% concentration. We pulled out
the hydrometer that we bought a year ago (and never even tried out), but it
showed right at 1.4 g/cc as it should.
We think that there must have been one poorly plated sheet of foam. We added some more discs and got it to run
ok. We need to stop messing with our
engines to make real progress on the vehicles.
We will probably see if we can make a unified screen catalyst
pack for the rotor tip engines and the attitude engines on the lander. We are going to see if we can live with the
sizes of pre-cut stainless discs available from McMaster for the smaller
engines, because the stainless is such a pain to cut. For larger engines, we may just cut them by hand with offset grip
shears, or have them water jet cut.
I am going to try moving the injector pressure drop from the
spreading plate to a separate jet before the engine to allow it to be changed
without disassembling the whole engine.
We have emptied out our third drum of peroxide.
We did finally get the lander ready to lift off again after
the false starts with the engines, but we didnt have a good day.
The only new things for this flight were the use of the
1000mW Esteem wireless units on both sides, and the use of an anti-static wrist
strap when using the joystick (there is a belief that static may have caused
the joystick reset on the last crash).
The vehicle started tipping over after liftoff, and on coming
back down it kicked off two of the foam pads and bent one of the legs. We noticed that one of the engines wasnt
canted properly, and we had seen this twist-and-tip behavior before when the
cants were wrong. I later configured
the simulator with that setup and was able to replicate the behavior. The flight control is supposed to pay much
more attention to the non-roll axis, but when the roll gets far enough out of
bounds it still starts trying to correct it.
I am going to change that so if the other axis are more than 10 degrees
or so off, it completely ignores roll control.
We have kicked the pads off on landing too many times now,
so we are going to modify the legs to positively retain the foam instead of
relying on adhesive. We have used
adhesives of various quality (the one used today wasnt so good), but even when
we had good bonds, we have ripped the foam under the bond on bad landings. We are going to try out putting aluminum
skid plates under the foam, and secure those to the top plate with sliding
bolts going through the foam. A bit of
skidding on a landing with sideways velocity will be better than instantly
We are also going to shorten the legs, except for the one in
front of the pilot. The vehicle is just
too heavy now for long legs in single shear.
We had several successful flights of the short form lander, which was
much narrower than this will be, so we think it will be a good trade.
We are probably going to try again on Tuesday.
Rotor Vehicle Design
We spent a while discussing our options for the tip rotor
powered vehicle. The current thinking
is to have fixed, steeply pitched blades on a gimbaled hub with two linear
actuators for the computer to control.
If it tests out ok, we are looking at rotor-on-top, ascending without
aerodynamic stability, then descending with stability in the same
orientation. The descent wont be an
autorotation at those blade pitches, more like a drop with thin dive brakes
extended. We really dont know how
challenging the unstable control will be from a control systems
standpoint. The time rates will be a
lot more lenient than the pure rocket vehicles, because the rotor adds a lot of
gyroscopic stability, but the required actuation forces may still be very
significant for a gimbal. We have considered
many options to stay stable both ways, but that involves either swapping ends
at apogee and changing blade pitch, or deploying a fairly significant
aerodynamic modifier for half the flight, which would have to be on the ascent
phase for a rotor-on-top vehicle.
Rotor-on-bottom offers some efficiency advantages, but makes a powered
landing without a top over difficult. Even
death-swoop maneuvers got some consideration.
I have ordered a big set of extruded rotor blades, and I am
starting to assemble all the needed bearings and linkages for us to start
testing. After we have the rotor making
solid lift on the test stand, we will probably attach it to the top of the
current lander. We could optionally
make short flights using the attitude engines for correction until the gimbal
I am working on a unification of several of the software
programs we use. The simulator,
remotePilot, graphLog, and gpsView are all going to become a single program
with much better capabilities. There are
currently two or three different instances of a 3D rendered view and scrolling
graphs, all with different options. I
will also be logging more data over the telemetry, so we can try filtering our
accelerometer signals. I will probably
make the change after we get the laser altimeter integrated, where we would
have to change the telemetry format anyway.