Wednesday, March 05, 2008

Data and Plans

Based on a lot of discussion with the chemists on Arocket its clear that the potasium catalyst was about 1/7th as active as the sodium catalyst I’d designed for. So we need to rerun the test when we get our sodium permangenate. We have it on order from two different sources. I finally reduced the data from my test and I got zero thermocouple data. I need to work on that. We hope to rerun the test on the 14th.

Here is that data I did get.Peroxide_3_1

Several things to note. first off my pressure regulator is not healthy. Its hitting the correct final pressure, but it is not happy doing so. Second according to the CV calcs I did the 1/2 inch valve should have about 10 PSI drop at full flow, it clealry had 150 PSI of drop. This could be because chamber pressure did not come up due to incomplete decomposition, but in that case I would have expected a larger injector drop due to too high of flow. Toward this end I spent the last two nights fabricating a fast 1” ball valve controller, I’m waiting for one more McMaster part and I’ll test it Thursday night. 

We are currently fleshing out the details of our 90 second test vehicle. We made baffles and parts for welding the tanks together. I’ll provide pictures when the tank starts going together. The last parts should be back from the Water Jet Cutters Friday. We are going to use AN fittings for all the plumbing smaller than 3/4 and probably sanitary fittings for the larger plumbing.  We have one area where the two Pauls do not yet agree, we can’t decide if we are going to use attitude thrustors or jet vanes. For the monoprop the jetvanes are clearly a win, but our longer term plans include making the vehicle a bi/tri prop by adding fuel to the peroxide and getting more performance. The bi/triprop  is a bit warm for jetvanes. It probably means we need to use some kind of exotic refrectory metal or ceramic. The bi/tri prop is the  current path to the 180 second prize.

For the Monoprop the safety system will be easy, we will add one small normally closed  valve to the liquid catalyst. As you can see in the video the thrust stops abruptly when the catalyst is all gone. (You can also see this in the chamber pressure trace above)  The bi/tri prop is more problematic as one might expect the biprop to keep going even if you turn off the catalyst.  If all goes well we expect a compete monoprop vehicle in about 6 weeks. We have all the long lead parts in hand. The current design is really really simple

I’ve glossed over a whole bunch of work… cat pack research, small thrustor chambers, learning about peroxide chemistry,high temperature ball bearings,  big servos, off the shelf source  thrust chambers, work on the helicopter, etc.. etc…

I’ll present the details of the 90 second monoprop vehicle design at Space Access. We will be at Space Access for all three days.If you are a space fanatic, and enjoy hanging out with three sigma nerds you can’t beat space access. 


David said...

Do you know what your flowrate was at that pressure drop across the 1/2" valve? Do you think you'll have trouble with throttle control if you switch to a 1" valve?

Paul said...

I only know what the calculated flow rates were supposed to be.
My flow sheet says I should have 6 to 8 PSI across the valve and 45PSI across the injector. I choose the 1/2 in valve so I would have good throttling. The 1 inch will be harder to throttle. I may actually settle on a 3/4 inch or a 1" with some triangle flow modifiers. Flow rate was 30gpm
1/2 CV was 18 to 26 so I expected
a low pressure drop. There is a big disconnect between measured data and theory here.

John Carmack said...

A half inch ball valve should be good for a 500 pound thrust motor, it probably isn't big enough for your vehicle. A one inch valve will be a bit much, I would go with a 3/4.

Don't completely discount jet vanes even for a biprop. Graphite is flight proven, although it won't last forever. You would also have to move the vane motors much farther away from the engine for thermal reasons.

As I said before, attitude thrusters around a big engine is my least favorite attitude control system. I would chose a gimbal and roll thrusters first.

Paul said...

My 1" valve will very easily turn into a 3/4" valve. The drive and mounts are identical. I never said which Paul was in favor of which system. ;-) I'm leaning toward jet vanes, my son likes the idea that you can hang the vehicle on gimbals and work out the gains and rates with the thrusters while the system hangs in bearings.

heroineworshipper said...

That servo is the kind of thing which goes up in price even as electronics get cheaper. At 45,000 yen, it's going to take a lot more dollars next week than this week.