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December 1, 2001 Meeting Notes

December 1, 2001 Meeting Notes


In attendance:


John Carmack

Phil Eaton

Russ Blink

Bob Norwood

Joseph LaGrave


New Manned Vehicle


We did a full up test fit of the new vehicle frame today, installing all the plumbing we could without the two tanks that aren’t here yet.


We did a drop test from a foot off the ground with Russ seated in the vehicle, and it bent a bit at one of the braces, so Bob is going to add some more strengthening to the frame before we fly it. We also turned it upside down in all possible landing positions with Russ seated inside it:




Landing this way would be bad news all around, but there is a lot more protection for the pilot than in the previous vehicle.


Ready to go, but for the tanks:





The electronics box has had a couple minor changes. The last time we flew, we accidentally left the electronics box on, so when I looked at it days later, the battery had been completely drained down and ruined. I replaced the main electronics battery with one nearly twice the size, which we had needed to do since we added the standalone 802.11b module and more pc104 boards. Our current draw is right at two amps with everything on, so we should have about two and a half hours of life with the new battery. The solenoid / motor battery is 3.3 amp hours, which never gets even a fraction discharged, but it still needs to be pretty beefy to source the nearly 20 amps that the actuators need. To make sure we don’t run it down again, I put a big, bright power light on the box top.



Molybdenum Nozzles


We have argued the cases for different ablative / cooled / exotic material nozzles for our hybrid motors for a long time, but I am looking into another potential option now.


Molybdenum is a step down the exotic materials list from the iridium - rhenium nozzles that we have talked about, but it may still be useful for us. Moly alloys can retain good strength to 3000 deg F, which while a lot lower than rhenium, may still be good enough for us. The combustion temperature of a peroxide – polyethylene hybrid is around 4000 deg F, but if you run the grain all the way down to the nozzle instead of leaving a post-combustion chamber, then you get a lot of film cooling, which may keep the nozzle under 3000.


Moly is reported to be a pain to work with, but you can still turn it on a lathe, and there are welding methods for it, which makes it a lot nicer than rhenium. Like rhenium, it does oxidize at elevated temperatures, so it will need to have a protective coating applied. I believe that any of the platinum group metals would do, but I have found some definite references to ruthenium plating on molybdenum. www.artisanplating.com offers plating of many PGM for consumer uses.


I have requested a quote for some bar stock from www.csm-moly.com , which we will make some test nozzles out of, and some information on larger scale fabrication options.



Rotary Rocket


We have started pursuing a new direction in conjunction with our current work. It originally came out of nailing down all the difficulties in doing parachute recovery from outside the atmosphere – once you start talking about putting controllable dive brakes on a vehicle, it is worth considering some other mechanical additions to the vehicle. The original HMX Roton concept http://www-im.lcs.mit.edu/roton/roton_paper.html has a lot going for it, and while Rotary’s SSTO design was extremely ambitious, it seems that there are dramatic simplifications that can be made by sacrificing flexibility and performance down to the suborbital level.


We are basically looking at making a tiny monoprop roton.


There are three key advantages that we see:


It may be possible to fly to 100 km using only monoprop peroxide with a rotary design, which would be a big win in development and test. You get significant atmospheric augmentation up through 50,000’ or so, and after that you get extremely high chamber pressure on the lifting rockets even with light tanks. I don’t know enough yet about prop drag to properly simulate this, but it sounds in the right ballpark. Jeff Greason of XCOR mentioned to us that there is a significant EPA marker at 5000 pounds of peroxide, so that becomes one of the gating design factors for us. We would almost certainly not undertake development of a biprop roton, which would be significantly more challenging.


A rotor can help solve the suborbital recovery in several different ways. At the least, it can act as an already deployed drag break to orient and slow the vehicle down to subsonic speeds for a normal parachute descent, even if the blades are completely stalled. If the pitch is adjustable, autorotation can get you down to a pretty reasonable rate of descent (30-60 fps straight down, slower if you have ground speed), and you may be able to flare for a soft touchdown. A small amount of reserve propellant could allow a powered soft landing after autorotation.


It may be easier to deal with the FAA if you have a vehicle that gets its lift from a rotor instead of a rocket. This may turn out to be an important consideration.



I’m sure we can make one fly, because there are at least two existence proofs of peroxide powered helicopters – the Rotary Rocket ATV, and the Firebird: www.intora-firebird.com . It is much more debatable if you can fly straight up at over 500 mph with one, then transition to supersonic ascent, then reenter at mach 4 or so. The fastest helicopters only climb around 60 mph, but prop planes can exceed 500 mph (horizontally), so that part seems reasonable with an appropriate power to weight ratio, but everything after that would be unknown territory.


There are tons of design choices – rotor at top or bottom, fixed or adjustable pitch blade, powered landing or parachute landing or flared autorotate landing, rotating shaft or rotating hub, swiveling tip engines or separate rotate / lift engines, engines on props or separate extensions, etc. I believe that it is possible to get attitude control by pulsing the engines as they rotate, sort of like an in-plane helicopter style cyclic, but our first vehicle will use our existing attitude control engines, with the drive prop just replacing the main lifting engine.


We have a bunch of shafts, bearings, clamps, motors, and gears now, and we have started assembling some different configurations. The old stand-up lander frame is getting turned into our rotary test stand, which we will probably have something spinning around under in a month or so. Once we have that going well, we will attach a prop to it and get some lift measurements, then fly it in a vehicle.





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