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Oct 24 meeting notes

Location: Long Range Systems

 

In attendance:

 

John Carmack

Phil Eaton

Russ Blink

Darin Smith

 

Next meeting at Norwood Autocraft, unless notified.

 

I was at the Space Frontier Conference last week, and did a few things related to the project.

 

I got to meet a couple of the ERPS guys, but circumstances conspired to prevent any substantive discussion time.

 

I had a long talk with Jeff Greason of XCOR (ex Rotary Rocket people), and he shared some thoughts on peroxide.  He isn't particularly fond of it, but he has worked with it and could grudgingly admit that it might be the right choice for us.  He likes biprop motors, but their trick motors (with electronic ignition) have five times the complexity of our simple ones.

 

His big piece of advice was just that peroxide lulls you into a state of complacency, and it is all too easy to get casual with it when you need to stay alert.  He had seen people go from full PVC suits to walking around with an open jug in one hand without even safety glasses.  He had also seen someone almost lose their eyebrows when an open container went off.

 

He also convinced me that a blow off valve really isn't much of a safety benefit.  With rocket concentrations, there isn't any such thing as decomposition slow enough for a blow off valve to help.  If anything in the tank catalytically decomposes from a tiny impurity, it will set the whole thing off with thermal decomposition.

 

The big win at the conference was talking to the JPA people and finding out that one of their sponsors (http://www.magnetometer.com) makes EXACTLY the part we need for our attitude sensor!  I am getting a sample soon, and JPA has already made an A/D board and bench tested it, so that removes a major uncertainty from our plans.  I will write up some GUI software for it to share back with them.

 

I didn't have much to bring to the meeting this week, but Phil and Russ had been busy.

 

We have found the perfect cart for the fill system, but it is backordered.

 

We have a 12vdc vacuum pump for the fill system.

 

We had the nickel metallic foam plated with silver, and Russ finished our first experimental engine.

 

I brought our now neatly organized collection of fittings, and left them with Russ and Phil.  We have already run out of -4 female / female fittings.

 

Darin has some output from the accelerometer, but it needs more work.

 

The big news is that we fired our own engine tonight!

 

It wasn't a very scientific test, because we were only committing to doing the peroxide compatibility testing, but we decided to go ahead with the firing.  We didn't have the load cell on, so we don't have real data, but we generated some good impressions.

 

We had three small jars of distilled peroxide, with less than a pint in each.  We don't know the exact concentration, but it is probably in the 80% range.

 

We had two pairs of gloves and goggles, so the two other people stood away and checked procedures.

 

We had the test stand on the other side of a solid concrete wall, and we watched it through a mirror we pulled off the bathroom wall.

 

We hooked everything up and ran a load of water through without any hitches in our procedure.  Hopefully this is the last week where we are hooking and unhooking the fill station, we should have the integrated cart soon.

 

First we just loaded up a bit of peroxide and let it sit in the tank while we watched for any pressure increases.  We could hear some bubbling, but it settled down and we didn't get any pressure rise.

 

We should drip some peroxide directly on the big O-ring in the bottle neck and make sure it is viton instead of rubber.

 

During the first fill, we had one minor incident.  We disconnected the vacuum line from the pump, intending to put it into an empty water jug in case someone opened the wrong valve, but vacuum started leaking out.  All of these valves and solenoids are directional, and this one has to be oriented to prevent nitrogen pressure from flowing out to the vacuum pump. Our plan is to have a catch tank always connected to the vacuum pump, but we might want to add another check valve on the vacuum side.  A big lesson that has been repeated many times is that we need more check valves than we expected.  For the tests, we just left the vacuum line connected to the pump.

 

When we fired it, it coughed and spit for a second or two with a plume of uncatalyzed peroxide, then made a bit of a roar just before it ran out and vented all the gas.   We had a long foaming puddle behind the nozzle.

 

When we drew the vacuum again, we got a bit of smoke and smell from the vacuum pump's muffler as it digested some peroxide drops left in the fill system.  This is almost certainly not a good thing, another reason why we need our catch tank in line.

 

We loaded the remaining 2/3 of our peroxide in and set up for another run. This time, we pulsed the launch valve open and closed to pre-heat the catalyst pack before dumping everything out.  It was very different this time.  The heating pulse was only a quarter second or so, but the exhaust was clear before it was over.  When we opened the launch valve the second time, it was absolutely perfect.  It roared for three seconds or so with a completely invisible exhaust plume.

 

We were quite surprised.  The first run was about how we were expecting things to go, based on our readings of the literature.  Seeing the awesomely clean second run was unexpected.  We knew we had a lot of water left in the system before the first firing, but the difference was striking.  We will need to do more tests to see if the high quality second run was just due to not having any water in the system, or if the residual heat from the first run was a primary factor.  There was nearly ten minutes between the firings, but I'm sure the motor was still warm.

 

This plated metallic foam catalyst seems to be a Very Good Thing.  Bob had given us a roll that had been used by a rocket dragster many years ago, but a funny coincidence occurred as we were getting it silver plated.  Russ and Phil ran into a guy that had samples of the same stuff in his briefcase, and it turns out we have a lot of options to experiment and pursue in this direction.  They were also given some information about baking the silver plating onto the foam if we had trouble with it coming off.

 

The catalyst pack was made by hand cutting disks of the foam and stacking them until it was about four inches high.  The pack was inserted into the engine by hand, without any compression, unlike silver screen packs.  Five cm is usually quoted as a good catalyst depth, so we expected it to be more than sufficiently catalyzed.  The pack still flowed easily enough to blow through.  We might try just rolling up the foam for a pack instead of cutting disks.

 

We ran a full load of water through after the last firing, then disassembled and washed everything.

 

I am a little concerned that the launch valve we are using may not even be able to flow 100lb of thrust.  The engine we ran today was a good bit larger than the one Juan rated at 100lb thrust, but it still took two or three seconds (I wish we had been logging!) to blow out only a couple pints of peroxide, which is well below that thrust level.  We have a higher flowing valve, but it is a momentary solenoid, which means we would need a flight battery and that it would close when power runs out, which is not good.  We may need to find a larger latching valve before flying the dumb rocket.

 

Phil got a little peroxide itch when he moved the vacuum pump, because he accidentally grabbed the suction point that had been whetted on the second fill.  It washed off fine.  This corroborates the opinion that you only get peroxide on you after you think you are done and have taken off your gear.

 

When we pulled the motor apart, we found that the nozzle side catalyst retaining plate had cracked during the firing.  We need to experiment with different materials and hole patterns.

 

The foam discs hold a pretty fair amount of liquid in them, so an incautious person picking up an engine after a peroxide firing could dump a lot out.

 

After we finished with the motor, we parted out all the plumbing and solenoids we will need to assemble the first VTVL platform.  If we share the tank with the dumb rocket, it should come in under $1000.

 

Going forward:

 

Russ is going to make a small engine in the 10lb thrust range, representative of what we will use in the VTVL platform.

 

I really, really need to start bringing the camera.

 

I need to get us a cheap laptop we can leave with the fill stand, so I don't have to remember to bring mine all the time.

 

Russ wants to turn a custom bottle fitting so we can dump the heavy NOS manifold at the bottle.  That will also improve our flow rate for the big motors somewhat, but I think the launch valve is still the killer.

 

We need to do several instrumented full tank runs on the stand with the bigger engines to make sure we are going to launch the dumb rocket fast enough to be stable.

 

Our biggest unknown now is how well pulse width modulation will work on the small engines.

 

We need a good peroxide source to start doing serious engine development and testing.  I would really prefer that we not distill any ourselves.

 

We are supposed to be able to get unstabilized 70% peroxide from a local source, but there may be a lead time.  That would be down on Isp, but if we can still fully catalyze it, I certainly don't have a problem using it. Lower chamber temperatures won't hurt.

 

FMC is going to be here on Thursday to tell us what we need to do to our site to get a drum of 90% from them delivered.

 

Russ knows exactly what we need to drive the solenoids from a microcontroller.  I am ordering more solenoids for the VTVL platform, so we should be able to test PWM soon.

 

We have appointed Neil (in his absence…) to build the flight rocket.  I would like to launch it next month at Windom on a certified motor to test stability with a tank loaded with water before we run it on a peroxide motor.

 

Tripoli experimental launches apparently won't allow liquid engines, so we are going to have to get our own launch insurance.  I am bumping the priority of creating a corporate entity for this purpose.  We need a name pretty soon.

 





 






 
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