Jun 19, 2001 Meeting Notes
Analog Fiber Optic Gyros
Larger porous sheet metal
Ice pack cooling vests
0.8 second motorized ½ ball valve
70% semiconductor grade hydrogen peroxide
Re-gear the 1.3 second motorized valve to 0.8 seconds
More 568-216 Teflon O-rings for bottle manifolds
O-ring cord stock for large diameter motor O-rings (not
offered in Teflon, so I am getting silicone)
We fired the new 50 lb thrust motor with the externally
threaded closures tonight, but we ran into some problems.
The initial push-tests worked fine, but when we fired the
motor it only had a few valid samples, then all the samples started reading
over 300 lbs (on a 100 lb load cell).
We may have broken a leg of the strain gauge bridge by banging into the
load cell on the initial startup.
Tonight Ill pull everything apart and check it against our 500 lb load
The other thing that happened was that the new attempt to
internally thread the catalyst pack retaining plate into the motor didnt work
out. The initial burst actually
stripped the threads, and the retainer was cocked down for the rest of the run.
New Motor Designs
We are going to try using the perforated metal for the
injector plate and the catalyst pack retaining plate. Clamping it between flanges will probably work, but we may try
some tongue and grove machining to help it stay put. There are also a couple local companies that do chemical etching
that may be appropriate for some of our plates.
We are considering increasing the diameter some, because 50
pounds out of the same size that we were using for 15 pounds does put the flow
through the catalyst retaining plate closer to the nozzle velocity than it
The engine length can be cut down a lot, because we know
that we dont need more than 15 foam discs thickness.
Higher Performance Propulsion
While I am occasionally tempted by the nitrous / ethane combination,
I still think that catalyzed hydrogen peroxide is the oxidizer of choice,
largely because of the great simplification of using it for attitude control
Our current manned vehicle propulsion system is set up so we
will easily be able to convert the main lifting engine to either a biprop or
hybrid configuration to nearly double our Isp, and leave the attitude control
engines exactly the way they are.
In biprop form, my preferred design would probably use
isopropyl alcohol instead of kerosene.
There is a slight loss of Isp, but there are several advantages:
Cooler combustion temperatures, which can be reduced as low
as desired (with reduced performance) by watering the alcohol.
XCOR makes a good argument for using alcohol based on the
fact that kerosene will contaminate plumbing, requiring very thorough cleaning
if it might ever touch oxidizer, while alcohol will completely evaporate away.
Ignition! reports that the heat flux to the chamber walls
can be reduced 50% by mixing 1% silicone oil into the alcohol, because it acts
as a continuously deposited ablative layer on the inside of the chamber and
Hypergolic ignition could be experimented with by mixing 15%
manganous acetate with the alcohol.
For hybrids, just about any old grain will work, with
polyethylene and HTPB being the common choices.
The big problem with any higher performance motor is that
cooling becomes a significant issue, especially since we are looking at 60+
second burn times for future vehicles.
While peroxide is a very good coolant, I have some
reservations about doing regenerative cooling with it in a motor that will be
doing restarts, because when the engine shuts down, I am pretty sure that heat
soak will rapidly cook off the peroxide in the cooling tubes. If the engine valve is before the cooling
passages, that will probably cause the peroxide by the nozzle to blow the
peroxide around the chamber into the catalyst pack, causing an unexpected burst
from the engine. If the engine valve is
after the cooling passages, it would probably cause the entire tank to go off. I would not want to consider dedicated purge
Hybrids probably wont need much in the way of chamber wall
protection, as long as the grain isnt burned completely away, and they should
have some degree of automatic film cooling of the nozzle if the grain extends
all the way down, so they should have things a bit easier.
There are four major materials directions for us to
Graphite nozzle and phenolic chamber liner. Your basic experimental rocketry
combination. Long burning motors with
graphite nozzles have been reported to cause problems with heat conducting
through the graphite to the casing or retaining hardware.
Cooled copper, either regenerative or simple water jacket. If a simple water jacket with a reservoir worked
without having boundary layer boiling problems, that might be a nice solution,
but I dont think we are up to making a proper regeneratively cooled engine. Adding heat-sink style fins to the chamber
and nozzle inside a large water jacket might be helpful
Silica-phenolic ablative nozzle / chamber as used in several
noteworthy projects ( http://members.home.net/danmoser/
), and have given lifetimes of over 240 seconds with hot burning lox / kerosene
An Iridium / Rhenium nozzle / chamber from http://www.ultramet.com is probably very high
dollar (I am waiting for a quote), but would be the best solution it just wouldnt
care about the temperature, and there wouldnt be a worry about wearing it out
or having a burn-through.
I have been able to convince myself either way on the hybrid
/ biprop question in the past, but I think I have finally come down
conclusively on the hybrid side for our upcoming phase of development.
In the long term, cooled or Ir/Re biprop will be the way to
go, because it will have better testability characteristics, will be easier to
refuel, and will have a small Isp advantage, but in the near term, I think an
ablative hybrid solution wins due to simplicity and crash safety. If a vehicle comes down hard and breaks some
plumbing, having a lump of plastic covered in peroxide is just a hell of a lot
better than having a pool of peroxide and alcohol.
New Vehicle Design
Flying people is annoying for a high performance vehicle
A standing pilot on top of 2 diameter tanks would be good
packaging, but could only tolerate a couple Gs of acceleration.
A supine pilot makes a very non axisymmetric shape. You might be able to put them in a 2 by 4
capsule and use a pair of propellant tanks underneath them, but the airframe
and nosecone would be strange shaped.
Putting them in a conventional circular cross section
results in a much wider vehicle than you would really want for a single person. Even a spherical tank of 4diameter would
hold a lot more propellant than you need for a 100 km ride for one person.
If you go with a 4 diameter cabin, you might as well leave
room to stack three passengers, because you are going to be biting the drag
anyway, and your propellant tanks are going to be large enough.
Another option is to fill out the side volume beside the
passengers by using two 12 to 16 diameter propellant tanks on either side of
If we go with a hybrid main engine, the chamber length may
get quite long with a single port. The normal approach is to go to a multi-port
grain at that point, but that involves additional issues with a supporting web,
and we may be able to use the extra length in a useful way.
We want to have passive aerodynamic stability on the vehicle. Fins would be highly stressed, and a failure
would be catastrophic. A simple tubular
airframe can be stable even without fins if the CG is far enough forward. If half the vehicle length is the relatively
thin hybrid chamber, but it is enclosed in the same diameter airframe as the
cabin / peroxide tanks above it, the vehicle should be stable. There would be lots of wasted volume in
the bottom half of the vehicle, but the mass and drag would probably be at
least as good as having four stout fins, and the construction would be much easier
and more robust.
The attitude thrusters would be sideways firing at the
bottom of the vehicle, and would have a nice long lever arm to act on.
The only downside is that it would probably not be reasonable
to vertically land such a top-heavy vehicle, unless you deployed wide landing
gear, and gear deployment scares me.
The next vehicle after the manned VTVL will probably be a
demonstrator of this configuration. We
will take the propulsion system from the manned VTVL, enclose it in a 12
diameter by 10 airframe and fly it to test sideways firing attitude thrusters,
high mach flight conditions, and recovery options. It should be quite a good performer even as a monoprop, with a
mass ratio of 2 and reasonable aerodynamics.
If we add a hybrid grain, we may need to begin getting familiar with the
big launch sites to fly it.