Tuesday, December 21, 2010

Way out of the box presure system...

Another out there concept... this won't work with the muiulti segment tank of the last wild idea, but will work for a single tank.

In a H2O2 rocket 80% of the propellant volume is H2O2, so you need to pay more attention to the H2O2 side than the fuel side.

Leave a small space at the top of the H2O2 tank. In this space put a solid silver screen/catalyst hung from a thermally compatible string. Unwind the string into the tank letting the silver decompose the H2O2 pressurizing the tank, raise and lower the catalyst to control pressure.

Fuel is pressurized with a bladder from the gas in the main oxidizer tank.

Main propellant valve is a simple burst disk.

16 comments:

Doug Jones said...

You might get better control with a pressure building circuit like a cryogen dewar. Liquid line from bottom of tank, control valve, then cat pack, with check valve to carry the oxygen & vapor to the top of the tank.

Open the valve and you get a modest flow of liquid into the cat pack (driven by the hydrostatic head), decomposition, then the gas rises up the pipe into the top of the tank, bootstrapping the pressure. Close the valve to stop raising pressure.

Stevo Harrington said...

Paul,
If you used a peristaltic pump in the configuration that Doug suggests, you could have nice linear control of the tank pressure. Otherwise there might not be enough driving pressure for good control.
You could also bleed the line in between the cat pac and the check valve to pressurize the tank.

Steve

Paul Breed said...

With a normal cat pack pressure drop I think one might need a small pump.
If you used a large area cat pack like you might "dip", the captured volume when valve turned off would be too much to control.

Paul Breed said...

How much pressure can a peristatic pump handle?

What peristatic pump material is peroxide compatible?

Ray Alderman said...

Paul - this would require tanks that could handle high pressure, so why do this instead of pressurizing on the ground? Are your plans with pressure driven motors (instead of pump driven ones) requiring a spare nitrogen tank to supply the high ullage pressure?

Bob Steinke said...

I've thought some about self-pressurizing schemes for peroxide tanks. The peristaltic pump/cat pack/check valve design that Doug and Steve described is the best I've been able to think of too.

You can get viton peristaltic pump hose for peroxide compatibility.

I think peristaltic pumps can pump to a few tens of psi, but you won't need fast flow through the cat pack so the pressure drop might not be too bad.

For your size you would be looking at something at the scale of a medical drug delivery pump, but you would probably have to build your own for lightness. And it still might not be lighter than just doubling your tank volume and doing blowdown.

Andrew Platzer said...

Do you need to keep a constant pressure or does it need to vary? If it's constant, what about a simple mechanical system, say a lid that opens up as the pressure drops allowing the H2O2 to hit a catalyst screen. Then as the pressure builds, the lid is closed again.

Dan Solvin said...

Don't care much for the peristaltic approach, as the tubing is going to be really stiff at 300psi+, and it could easily burst under a mechanical roller. How about a simple stepper motor driven needle valve at the tank bottom, with a check valve at the inlet, then a catpack and a tube at the outlet going to the top of the tank?

Dan Solvin said...

Which is basically what Doug said...

heroineworshipper said...

You need a turbopump.

Martijn Meijering said...

You may be familiar with these already, but your post reminded me of the following papers:

Self Pressurizing HTP Feed Systems
https://e-reports-ext.llnl.gov/pdf/236904.pdf

Your solution is mentioned in the introduction, but he goes on to explore more complicated systems.

http://www.dunnspace.com/self_pressurized_rockets.htm

Paul Breed said...

Martin, thanks for the ref, I'd read most of Mr Whitheads stuff, but some how missed that one. The 2nd article I'd seen.

As for using a peristaltic pump, the pump would be in the tank at tank pressure, not ambient so it would only have to pump against the cat pack drop not the full pressure.

Rocket Dude said...

Peristaltic pumps rated to 100 psi are COTS items

http://www.stenner.com/prod-pumplist.htm

I really don't think its worth the hassle though....

Martijn Meijering said...

How about using (undecomposed) nitrous oxide for pressurising the peroxide? Either mixed with it or in a separate vessel, perhaps using a regulator? It's not much heavier than gaseous nitrogen, its container can be lightweight compared to nitrogen and you can use the pressurant as a propellant in blow down mode at the end of the burn.

Martijn Meijering said...

The nitrous oxide could also be used for RCS (either as cold gas or as a monopropellant) and for a torch igniter using a standard Shell 405 catalyst. See the following paper for related work on a small nitrous oxide - propane rocket:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA393448&Location=U2&doc=GetTRDoc.pdf

Martijn Meijering said...

Some more wild ideas about nitrous oxide:

If you use gaseous catalysed nitrous + fuel as a bipropellant torch igniter, you no longer need a catalyst for the peroxide, which means you no longer have to worry about the purple menace, inconsistent cat packs, cat pack poisoning and about melting your cat packs at high peroxide concentrations and therefore high decomposition temperatures. Does this mean you could put lots of stabilisers into it, thus making it much safer to handle?

Such a torch igniter used alone might also be useful for safe stage separation.

If you need to keep the nitrous warm while it evaporates, you could embed it in the peroxide, perhaps with cooling (warming?) fins. This way you wouldn't risk overheating and triggering decomposition of the nitrous. Maybe the fins could do double duty as slosh baffles? Using heat pipe spreader plates maybe?

The nitrous as pressurant for storable oxidisers could also work in combination with pistonless pumps.

I hope there isn't some big drawback I'm overlooking, because there seem to be a whole bunch of advantages.