January 3, 2007 notes:
We found that one of Pixels gimbal
linear actuators was broken in the last crash.
The anti-rotation block was broken into several pieces, giving a large
amount of lash and allowing the actuator end to freely twist. We have temporarily replaced it with a spare Electrak, but I have been worried for a while that even our
actuators are really too wimpy for 3000+ lbf motors. I have ordered two Ultramotion
Bug linear actuators as replacements, which should be several times
stronger. At almost $1000 each, they are
also several times as expensive, even counting our replacement motors.
The saddle is done for Pixel. We will be doing the upcoming tethered flight
test with it in place, but empty. After
that, we will probably strap a dummy on for future flights. I doubt we will do any untethered,
manned flights with this vehicle class, but I am pretty curious how much affect
leaning induced CG movement has on the control system, so there is a decent
chance someone will get on with it attached to both hanging crane tethers and
ground rocket anchors. Carrying a dummy
as our payload for the Lunar Lander Challenge next year will also be fun.
The first test hemispheres of 5383 alloy are in, and should
be welded up and hydrotested within a week. We negotiated a firm spec with AMS Industries
for this order (24 hemispheres), so the tolerances should be closer than on our
We have found a supplier for 5059 (Alustar)
alloy in the gauges we use, and it isnt all that expensive, but the minimum
order is enough for 18 spheres, which is a bit much for us at the moment. We still need to do some trade studies to
examine the performance tradeoffs in different operating pressure / weight
tradeoffs before we place a large material order. A nice power point on Alustar:
The regen engine development has
been a bit slower than we hoped, but we think it is almost wrapped up.
The welded injector face shown in last months update didnt
work out for two separate reasons: the angled spot faces for the injector
elements went deep enough to get below the weld depth and make a leak path, and
the fact that the flange and lox manifold werent completely parallel after
assembly and welding made the chamber pocket uneven enough with the flange that
the o-ring couldnt seal there.
I figured out how to modify the design to avoid any buried
welds and still leave the injector face as a single monolithic part. The new design does require welding things
together in a specific order, and some of the welds are hidden by other pieces
after assembly (but they are still only propellant to air welds, not propellant
to propellant). The first try at this
did have a weld problem that couldnt be fixed, so I added pockets around all
the mating points on the next try to make the welds easier to do. Designing for consistent manufacturability is
a big deal for us now, because we are going to be flying vehicles with at least
four engines this year, and we are looking at possible orbital vehicles with 64
or more modules.
I would really like to follow up on the coaxial injector
design, which would have a lot of manufacturing benefits, but it could be an
unknown time sink, and we want to get back to doing flights ASAP.
The big worry for the regen
engines is the startup sequence, since there is a lot of post-valve volume in
the cooling jacket that needs to fill before anything comes out of the injector
elements. It also turns out that we dont
have clearance under the Quads to mount the fuel valve directly to the lower
fuel manifold, so we had to add an extension pipe, which adds more post-valve
volume to fill before the engine will start.
The upgrade to this engine uses a tear drop corner to the
bottom fuel manifold, similar to the lox manifold, to avoid the fuel pipe dog
leg in that picture.
Since we have had our testing at both the shop and my local
land shut down, we have to drive a significant distance to do an engine test. We dont have any permanent facilities for
static tests now, so we set up for a horizontal firing off the trailer hitch at
half operating pressure so we dont jump the wheel chocks.
As expected, ignition didnt work with the existing
settings, since main flow fuel didnt reach the chamber in the 1000 msec allotted from valve motion start to igniter
shutoff. Operating at only 200 psi was certainly not helping. The non-start left a big puddle of alcohol in
the engine, which the helium purge couldnt clear out at that angle, so we had
to stick a rag in and mop it out by hand.
I extended the igniter running time to 1500 msec,
but it still didnt light. We tried
again with a longer lox pre-chill, and got a mild hard start. The graphite chamber was cracked, and a
couple welds were broken on the injector and jacket bottom.
It turns out that the longer lox pre-chill had allowed
enough of a lox puddle to accumulate in the horizontal engine that some of it
ran back into the film cooling holes, and combustion was able to start inside
the injector, probably with some left-over alcohol, when the igniter started. We never had this problem on our shop test
stand, because it was angled down at least ten degrees.
I was tempted to just remove the film cooling holes on the new
injector, since we may not need film cooling at all now. The graphite is slightly porous, so some fuel
will seep through to the chamber from the cooling jacket during operation
(which is also why we cant put the fuel valve post-cooling-jacket), giving
some degree of transpiration cooling, which probably provides enough of a rich
zone to avoid worries about oxidizing streaks on the graphite. I am trying not to fall into the trap of
chasing performance that we really dont need, so we are keeping the known
good design for the time being.
We decided that we are just going to try and fly the vehicle
with the new engine, leaving it a vertical firing and avoiding the problem. If we can get the crane, we are going to try
for a flight this weekend. Our launch
permit amendment for doing untethered flights at OKSP
is still being processed. The initial
application is just for flights like the lunar lander
challenge, but we want to do 4000 flights there as well.
I had concerns that letting the igniter run for too long
could melt the aluminum housing, but we did some tests with runs over five
seconds without a problem (combustion efficiency is really really
bad, but who cares?), so I have extended the igniter run time to three seconds,
which should be plenty of time. Im not
thrilled with the extra delay, especially since when we run at higher pressures
the engine will start earlier, leaving it cooking the ground and legs for a
couple seconds before liftoff. We might
adjust the time based on tank pressure.
Im sure everyone that follows the Armadillo updates is
already aware, but Blue Origin finally posted some public information about their
first test flight:
They have experimental permit number 1, we have number 2. We did the first permitted flights at XPC
shortly before their first test flight.
It will be interesting to see how the relative test flights go in the
coming year. We operate at a higher
tempo, but their experimental permit already allows them to go up to higher
I have zero inside information about Blue Origin, so my
comments are strictly from the peanut gallery here. Its HUUUUGE!
I honestly think they are making a mistake doing a development vehicle
that big, because it is going to cause much more anguish when it eventually crashes. While bigger doesnt always mean more
expensive, over broad ranges there is a strong correlation, and at least for
suborbital tourism, I still dont think bigger is actually better. I am in the demographic of potential space
tourism customers, and I would rather have my rocket flight in a smaller
vehicle than be stuffed in the space tourism bus with a half dozen other
wealthy strangers. When we saw the
weight listed in the papers filed with the FAA, I thought that the only reason
to build a suborbital vehicle that large would be if you intended to also boost
upper stages for orbital work, but it doesnt look like the shown design would
be appropriate for that. Maybe it is a
subscale version of an SSTO, or a nearly-SSTO upper stage intended to be
boosted by an even larger straight-up-straight-down VTVL (my preferred RLV path
I still think peroxide has some good advantages, and I
assume that an operation of their scale didnt have the same difficulty dealing
with FMC that we did (at least I would expect they went that way instead of
running their own concentrator). Flying
a monoprop vehicle and later transitioning to biprop is eminently sensible. Fixed (?) landing gear is sensible. Im still not sold on pumps, which they are advertising
for engineers to work on for future vehicles.
It looks like they are spending a lot of money, which will be hard to
recoup if the market is competitive. Of
course, while being profitable is nice, Jeff Bezos
doesnt exactly have to worry about it if he doesnt want to, and he can
proceed as slow and steady as he feels like.
I would love to pick over all the technical decisions some
time (hint hint!).
Also on that note, for the Blue Origin folks that read these
updates: if you have finally stepped out
of your cone-of-silence, you should join the Personal Spaceflight Federation,
so we can all have a unified front in dealing with the regulators, insurance companies,
and so on.