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.

Wednesday, September 22, 2010

More Printed Motor news...

The DMLS machine that is most common is an EOS270. The company that makes these machines has recently started adding some new materials. The new Material I'm most interested is Aluminum for chambers, and maybe Inconel 718 for a possible turbo pump.

I'd gotten some chamber quotes a year or so ago and it was still too expensive. When I had GPI quote my design again this year it was half of what last years quote was and I ordered the part on the spot. (In Stainless) GPI was also very helpful in making geometry suggestions that woul d improve the quality of the resultant part.

After placing this order I thought I'd do some more price research and sent the same file to Morris Tech to quote. The response from Morris was very competitive and its clear that this industry is seeing significant price declines. (Neither vendor knows what the other quoted) I hope its a sustainable trend and not a bloody battle to bankruptcy.

I really don't like beating vendors against each other because any long term relationship needs to be win-win and you can't do that by abusing your vendors. While it might be tempting to beat vendors prices against each other, its not some thing I do.

I also asked both Morris and GPI about the availability of Aluminum.
GPI indicated that they would soon be running Aluminum and Morris indicated that they had already run some Aluminum parts and that in the next few weeks they would be running some more aluminum test parts.

Since I was doing interesting stuff as an individual inventor not a big corporation Morris offered me the chance to add a single part to the Aluminum test run for approximately their direct cost. Its an offer I can't refuse. So I will soon have small DMLS chambers in two materials!

The Aluminum Motor is actually a bit bigger than the stainless motor as it needs to be cooled the whole length with a stainless cat pack support thermally isolated from the cooled aluminum chamber as a sleeve inside.

So if you need DMLS parts there are at least two really awesome DMLS vendors in the U.S.


Saturday, September 18, 2010

Why the motor has horns.

If you look at this post from July. You will see how the finished motor will look. Rather then spend lots of $$ making the simple upper section I only had the lower part printed with DMLS. The upper section where the cat pack will go is fabricated in the normal way from a sanitary fitting. It will and then be welded to the motor bottom.

The horns sticking out the side are the fuel feed. The fuel goes in the curved part and a 8-32 Set screw with a orifice drilled in it goes down the straight section. Then the end of the straight section gets plugged. You can buy predrilled orfices in 8-32 set screws from Mcmaster Car.

Here is a picture of all the bits before welding:

The two small parts are the machined elbows to connect the vertical feed tubes with the Chamber top.

Wednesday, September 15, 2010

Sunday, September 12, 2010

Pressure Fed Upper Stage.

I've been doing some calculations on what an upper stage for the 1Kg Nanosat launcher would look like. One of the interesting twists is that if the motor only has to run in vacuum then it's ISP is almost independent of chamber pressure. So for any small launcher you are going to have minimum gauge problems long before you hit the minimum optimum tank wall thickness. This opens the possibility for tanks with things like 3L soda bottles and PVC valves. It makes me wonder why Space X went with the turbo pump 2nd stage for the F9. a lot of complexity for very little gain? Maybe just because they had one that was approximately the right size.

Wednesday, September 08, 2010

Some progress...

This weekend I worked on cleaning up my Garage.
I cleared the floor, two junk Tables and a cart. Everything I cleaned up now has a place. I still have piles on one bench and one cabinet. When those are done I need to start the task of going through all the storage containers, drawers etc.. and purge stuff I'm never going to use. A little bit more room would be really helpful. All in all I feel a lot better about the garage after putting three full days into it.

My Son and some of his friends went to burning man so just as I start to get a handle on the garage the truck comes back from Burning man filling the garage with dust covered stuff..... they have been working evenings getting it cleaned up so I can't really complain.

I tried to fill the porosity of my printed motor with some solder and I just could not get good penetration. It didn't stick to the stainless even using some fairly aggressive acid flux. As a result I redid my printed motor design for the DMLS process and had it quoted by GPI prototype. Their price was about 4X the Shapeways price, but the part is thinner and needs a lot less welding. (Its also about 2/3 of what I though it would be.) I ordered it Tuesday, so we should get it some time in the next two weeks. The parts on the DMLS "showcase" always look incredible. I asked them to give me the best possible price so please give it to be raw off the machine. It will be interesting to see the raw finish.

Sunday, September 05, 2010

An Orbital Vehicle Part 1

What does it take to build an orbital vehicle?
My interest is in something really small say a nano sat launcher. This is going to require more performance than a larger rocket as air drag has so much more effect. I'll start with John Whiteheads paper. For a LOX Hydrocarbon stage to get to a 200Km orbit he says we need ~9500 m/sec Delta V and for a 1T vehicle. This paper claims this was a simple analysis, and I always like to cross check. From the Falcon 1 Users guide table 2-1 we get the following:

2nd stage:

1200lb empty

8900 lb propellant

400kg (880lb) payload

317s ISP

Using the rocket equation I get 5173 m/sec DV

1st stage:

3000 lb empty

47380 propellant

10980 lb Payload(The 2nd stage)

300 s ISP

Using the rocket equation I get 4353 m/sec DV

Total DV 9526 m/sec

Extrapolating in the "How Small" paper we get about 9250 for a Falcon 1 sized vehicle. So I have a source to give me some target numbers and have independently verified that the numbers are not wildly off. So we need to design a vehicle with 9700 m/sec of Dv to go orbital.

The 180 sec LLC vehicles needed 1765m/sec DV. So orbit is a whole bunch harder. We could use the LLC L1 level of technology and stage 5 times this would weight 750K lbs. Clearly we need to do better. All but the first state will run in vacuum, they don't need to throttle, we don't need landing gear, so we should be able to do a lot better. My initial spread sheet says its quite possible with a three stage H2O2/Hydrocarbon vehicle. To do it in 2 stages would require developing a lightweight pump or making the vehicle really big. I'm going to refine my inital guess and publish it in the next week or so.

Wednesday, September 01, 2010

Keeping a neat Shop...

My review at my first ever "real" engineering job said something like:

"Paul Moves his assigned projects directly to the desired result with exceptional speed and skill leaving a trail of destruction in his wake."

This was a job where we built real prototype hardware controlled by electronics and
some of the earliest embedded computers. (6502 anyone?). I got the Job done but I left a wake of debris behind. Not much has changed. My rocket shop occupies a two car garage and a 8x10' office at my home. I find the continuous mess and inability to find things is probably the biggest frustration in my life.

I intellectually realize that I'm whining about my own personal shortcomings and should just gut it out and clean up my space. In my life I've never achieved that for any period of time measured in units longer than an hour. So I'm asking my readers if anyone has successfully overcome the this particular demon? I'm open to suggestions?

Its really a two part problem

Part One I have way to much stuff crammed in too small a space. So it needs a Major organizational redo. ( I can actually envision someday solving this part of the problem.)

Part Two once everything is organized how does one maintain cleaned up?
The Failure Scenario goes something like: Come home from work, family is going to have dinner in an hour so I go out to garage and start machining a pressure test plug, then dinner is called and I go in and eat... not to return to that project for a few days. This is complicated by the fact that I often have half a dozen partially finished projects in work at one time and I work on the different projects as I'm inspired to do so. This is not a complete failure as I actually do finish a significant percentage of what I start. (It may take 12 calendar months on a project that is only one real week of work)

Some specific questions for comment:

How do you handle partially finished projects in a way that you can efficiently task switch without leaving piles of half done all over the shop?

How do you decide when to throw something out?
Our current rule is if it is not a tool and has not been touched in (Replacement Cost /25) months it goes in the trash. If the value is over $250 it goes in the ebay pile... (The Ebay pile may someday actually make its way onto ebay)

How often do you redo your storage systems.....
How much dynamic range to you leave for expansion?
IE I have a drawer for AN male elbows. When I create the drawer its 25% full, a year later its over full and won't close so it sits on top the pile....

Has anyone ever tried to hire someone to clean up/ maintain their shop?
How did that work? How did you find such a person?
In So Cal one can find lots of low skill labor that will follow directions, but I think I really need someone that knows the difference between a drill bit and a mill bit, a servo and a valve etc...

Do you think it would be possible to hire a Science/Tech interested high school student to work on this without leaving them emotionally scared for life?