Tuesday, September 28, 2010

A few ideas and loose ends

This week I learned that the NASA Nanosat prize is funded, (I thought it was a proposal not a funded prize.) So this clearly puts a bulls eye on a project target. This process starts with a notional vehicle and works backwards from the last stage. With a 1Kg payload I think that I can build a three stage launcher with a gross liftoff mass of less than 1000lbs.
To do something on this scale every gram matters. I'm starting to designbthe best 3rd stage I can and works backwards... (If you do a good enough job you only need two stages)

One needs:
Efficent light high expansion motor. Working on small motors via the DMLS project.

Really light tanks.....I've purchased all the large beverage containers I can find and am weighing and pressure testing them. So far the best tank is a 2l soda bottle. 100+PSI and mass ratio of > 40. A single soda bottle is not really enough. Any scheme to group them together is heavier than the bottle. So I'm looking at maybe fabricating my own tanks. The idea H2O2 tank would be mylar lined (mylar is another version of PET like in soda bottles) with chemically compatible resins and kevlar. Normal Epoxy and normal Carbon fiber are not happy with H2O2. All the tanks at this scale are up against minimum gage issues so whatever pressure you get in the tank will be more than really needed. In concept these seem very similar to the H2O2 tanks shown by Richard Speck of Micro-space at the 2007 LLC. I've got most of the materials to try this on the way. The biggest unknown issue is how to build the liner. If I can make the process in patent #3661675work that would be ideal.

Really light valves and actuators... probably all based on brushless model airplane servos. one can get lighter brushed parts, but must trade against the requirement to put them in a pressure box and the smallest brushless ones seem to be a win.

Guidance.... more on that later...

Regulation... This one is hard because the regulatory framework that applies to orbital launches is tailored toward something like a big Atlas. My current concept is to make the 2nd and 3rd stages really light and fluffy. Almost all plastic, including the valves and plumbing. Only the thrust chamber will be non-plastic. The first stage will probably be metal. The concept is to launch off shore so that thrid party safety from the first stage is constrained by physics and the 2nd and 3rd stages are too light to survive reentry. The real trick will be proving that and path taken by the 2nd stage will either burn up or land within the 1st stage constrained by physics zone. IE if it shoots straight back down its not going so fast so it might burn up. If it flies perfectly by the end of its burn then its going to fast to survive reentry. The question is what happens between these two zones. My nominal vehicle meets all of the amateur limits except the no orbit allowed rule. IE less than 200Klb/sec and orbital altitude less than 150km. (Rules say you only need to go around once.) more rambling to follow as I figure things out.

Anyone in SoCal with access to a 14" diameter 20" long vacuum oven that I could use to try the process described in the patent above would be really helpful.


George Katz said...

Hi Paul,

It was interesting to read about the possibility of using soda bottles as tanks. We use them regularly in our water rockets, but splice two of them together so you get a neck at both ends. You can stack them this way. We then wrap them in a couple of layers of fiberglass.

Even though these might be a little heavy for your needs, at least the data below may prove useful as a baseline reference.

Here is some more info on their capacity, weight and burst pressures:


The ones we use hold at least 300psi.

You can keep splicing them for more capacity as needed. Doing it this way gives you the PET liner you mentioned.

You could certainly get better performance by replacing the fiberglass with CF and only use minimal epoxy resin.

- George

Paul Breed said...

I'm really hesitant about using glues with peroxide.

Anonymous said...

I look forward to see this rocket!

somegeek said...

There is a group in BC that played around with carbon fiber wrapped soda bottles.

A few years ago they pressurized one up to 1150 psi and using just the pressurized water got it up over 1200 ft.


David said...

A project again - yes. Good to see a target to aim for. I'll be watching.

Stevo Harrington said...

You can make a tank liner by powder coating an aluminum or plaster form, thereby creating a polyester liner, which you could cover with FRP. Then you could dissolve away the form with caustic or water.

Monroe said...

Have you looked much at the water rocket fellas? I saw one in particular that got 1000psi in a pop bottle that was hand wrapped in carbon fiber web. Google world record water rocket or something like that.

Anonymous said...

Why not UHMWPE fiber? If you could slightly melt it with the LDPE, you'd have a PE-PE composite with no glues.

Cameron said...

If you really like PET bottles as tanks, it may be possible you could make custom long ones. My imagination of the process is something like:

Find someone with a surplus/out-of-service 2L extrusion blow molder. (May not be that hard these days.) Set it up a bit higher than usual, if needed, since your "mold" will be long.

If you're really lucky, they'll also have a number of worn-out 2L molds sitting around. Cut the top off one, the bottom off another, and weld the cut end together. (Or, heck, just epoxy them: you're not making more than a few right now.) Don't worry about the water channels; you're only making one at a time. This you can probably use just like a regular mold, though maybe you have to close it by hand.

You can also make a "mold", I imagine, with a pipe and two two-piece hemispherical caps, one of which has a 2L-sized hole in the center. This is a bit tricker in extraction; hopefully the pipe is smooth enough you can slide the bottle out the ends. If not, I suppose you can always cut it in half also, like a traditional blow mold.

Then you do it like normal; extruder drops a thick tube of PET down your mold, the bottom squeezes it shut, stick the blower in the top, blow, and release.

It requires a bit more machinery than composites, but there are hundreds of vendors around the country, and you might be able to find one that'd help you out. It's vaguely possible to do at home, I suppose, but without careful monitoring of heat and flow, the results would probably be... uneven.

It would take a good bit of legwork, I think. And may be a bit unrealistic. But think how easy and cheap it would be for mass production!