Friday, February 22, 2019

Creating new things in the real world, Musk, Tesla Spacex etc....

I'm a space geek, much of my social interaction is with other space geeks.
A lot of these people worship what Spacex and Elon have accomplished.

At the same time I've been more and more convinced that Tesla is going to fail.
This causes some significant personal cognitive dissonance.

The following is my attempt to work this out ...

Making a new thing is hard. You will fail, over and over again, you will fail.
Edison tried thousands of light bulb filaments before he found one that worked.

One of the really cool things about spacex is that they let you see them fail.
The blooper reel of landing attempts is outstanding.
Attempting to do something new and hard will have failures.
Trying something new in engineering or in business will have failures.

Because of Spacex:
  • We now know that first stage reuse can make sense.
  • We now know that the iterate fast model of engineering works for at least some of the  aerospace world.
  • Supersonic retro propulsion works.
  • You can (given the right engineering team ) built rockets for a tiny fraction of what the big aerospace primes charge.
All of this is new information in the world due to Spacex efforts.
Everything above this line is engineering....

We still don't really  know that the Spacex way will work in a business sense.
Recent layoffs and recent failed funding raise make this more questionable than it was 12 months ago. (Its clear that  the business case for the large aerospace primes, does not  work absent billions in direct government subsidies)

From an engineering stand point Spacex has been somewhat innovative....
SpaceX  have either surpassed or are approaching 50% of the total world wide launches.
In my opinion (if ancillary things like tesla don't take it out) Spacex will survive long term and the world will be a better place because of that. (see my earlier dialog on why space matters).

The space business has been run for a long time by cost plus contractors working for governments.
This is not a place where innovation thrives.

The Car business on the other had has been a brutally competitive market with microscopic  margins fought over by  efficient international behemoths. Its a hard brutal world.

Tesla managed to crack open that market and with the S and X, they  delivered  a well received  high end quality product that changed the perception of the world. Now every one of those behemoths is planning an EV. Just having a shot at this is a huge achievement...

Some how the engineer Elon that allows us to see spacex failures, has been unable to admit to the world that their are also business failures. By any unbiased measure Solar City was weeks from failing when Tesla bought it.  This burdens Tesla with a millstone that makes the difficult task of breaking into the brutally competitive car market even harder.

Watching the Engineer Elon do magic things at spacex I greatly admire  what he/they have accomplished.   Watching the Business Man Elon commit what looks very much like Fraud to save a failing business I do not admire.  Business ethics matter and used to matter to Elon (see his several year old  tweet about debts and personal responsibility for Solar City Debits) 

Some how the pressure to not have the business fail has pushed pushed Elon to do things that cross the ethical line in a way that has caused me to loose my respect for Business Man Elon...

The Big ones :
  • Solar City Purchase and fraudulent Solar roof presentation.
  • Model 3 production guarantees on the eve of big Tesla Bond Raise.
  • Screwing over his devoted customer base with the crappy quality M3 and things like not refunding deposits.
  • The $420 Funding secured Tweet and subsequent response.
  • The flipping the Bird at the SEC taunting tweets.
  • The recent guidance on Tesla that just does not pass the smell test.
  • The Fraudulent Guarantees in the Buffalo Solar city Factory morass.
  • Treatment of personnel (At both Spacex and Tesla) You can only run in start up panic mode for so long before it destroys people. I have many space friends that have left Spacex because of the relentless pressure.
It is my opinion that Tesla is very close to failing and will fail in the next 24 months.
It is my hope that this does not destroy Spacex. Elon has generated significant personal liabilities in his Tesla dealings, and if Tesla fails the only real Asset Elons owns is spacex. Spacex will be a very different and less dynamic place when its owned by plaintive s lawyers rather than Elon.

I find the whole affair sad.  I wish Elon had stuck to Spacex and just focused there.

I know that some of my followers that see the Spacex brilliance  and subscribe toe the "Saint Elon can do anything" view will rush in to defend Tesla.
I don't want to rehash that argument here. lets us just agree to disagree and we will know who is correct in 18 months or so.










Saturday, December 22, 2018

Low Low Low cost liquid thrust chambers...


The very premise of what I’m trying to do is low cost as a primary design goal.
One has to question ALL of ones assumptions…
I personally fired the first ever 3D printed Regenerativly cooled liquid rocket engine.
ever fired in the world (2009)
I’ve done a lot of work in that space. The 3D aluminum costs are coming down….
Its cool high tech and in many ways awesome. Its also the single most expensive hardware component on my rocket by a factor of 3. For the long term business case to work I need to get the single 6” 24 foot tube cost ready to fly under $2K.  A die cast aluminum inner with a saddle jacket outer made from injection molded saddle and thin wall extruded aluminum outer is a rocket motor with a cost of under $200.00   So for the next generation of motors I’m going to abandon the 3D printed motors…
The first rocket motor I designed my self, and the 2nd liquid rocket motor I ever fired was saddle jacket, and  this generation will be as well. (113 Sec Fireing) 

 I’ll use machined aluminum done on my CNC lathe /mill as a stand in for di-cast aluminum. And the Saddle will either be machined aluminum or possibly machined polyethylene as a stand in for injection molded. 






Saturday, December 15, 2018

Fusion360 cad beg...

I'm tryingto convert from Rhino to fusion 360.

The following was done in rhino, I'm trying to learn how to do the same in fusion...

I can easily draw this in fusion a Extruded cylinder with a hole in it.

I Can also draw my o-ring groove in fusion....



In Rhino I next draw two spheres.....(Blue and green)



Then I generate the line where the spheres intersect the cylinder.
(Inner intersection lines have been removed for clarity)
(I did this twice and the blue/green colors swapped  sorry for the confusion)


I then use the sweep2 command in Rhino to make a solid from o-ring profile and the two "Rails"
This is correctly tangent to the cylinder surface and has the correct o-ring breaks, radis etc...


Then subtract the solid and I have my o-ring grove.

So my fundamental fusion 360 issues....
I can't draw the spheres based on points, only dimensions. The lower dimension is easy to derive its the hole radius +the oring offset. The outer sphere is a lot harder as the oring groove sides are not straight and while I can place a point in the appropriate place fusion won't let me draw a sphere to the point. That problem I could work around with some triganometry, but the 2nd problem I can't seem to solve. I need to create a pair of lines to sweep the pattern, these lines need to be the intersection of a sphere and the cylinder. I can't seem to create this geometry no matter how I try.

Advice welcome.





Monday, November 19, 2018

0.018" matters...

I had a batch of end caps machined for the Carbon tube tank.
This was 4" outer, 0.035 metal liner 0.009  poly bag, and 0.004 gap.
This was all carefully measured and tested, it works well...

I thought I could reuse these end caps in the 4" 035 wall tube, alas I neglected to account for the bag.
The 0.009 on both sides or 0.0018 in diameter is enough that the caps don't seal correctly.....
Grumble Grumble....
I could line the aluminum tube with the bag and continue....


Not a huge deal, but I thought I had enough for 3 sets of flight hardware, now I have zero...
I need to machine new ones...

So even with the loose fit, I thought I'd assemble the tank and  hydro test one.
The end cap retention failed at 420PSI. The cap retaining screws failed in shear.
In hind sight I did not use enough screws, according to the screw stress calculations they should have failed at 390 psi.


So all in all its nice to actually be building and assembling hardware again.

So Mariellen's garden got its first dose of hydro test water, in about 4 years.

Wednesday morning update...
Rebuilt the test tank, used more screws, hydro ed
to 600 PSI without failure.






Thursday, November 15, 2018

Fill Drain how to make safe...

One way to fill a tank... (and how I've filled every rocket tank to date)
Is just put a removable fitting on the top of the tank and pour in the propellant.
Its real hard to make a system lighter than just a single AN cap.

This has several problems...
  • It does not scale, in a Otrag vehilce you might have 128+ tanks to fill.
  • On a biprop vehicle, once one of the propellants is loaded loading the other propellant becomes a hazard.
  • Its very difficult to precisely fill to exact levels.
  • It does not help you drain after an abort scenario.

    So I'd like to do remote fill and drain on the vehicle without adding a bunch of weight...
    Here is one possible scheme that can be done with a single tank penetration.










At the expense of wasign some propellant it ensures the system is filled to a precise level (the level of the bottom of the dip tube, and only requires one tank penetration.

It has the added advaltage that if you use the valve RV1 to vent the tank in an in flight abort, it does nto vent the all the propellant, only the pressurization gas.... With Lox its not an issue to dump propellant while in the air, with H2O2 dumping in the air can start a large area brush fire.








Tuesday, November 13, 2018

Random misc stuff...

Lots of little things....

It looks like the Fuel in 20Kg lots is about 50% lower cost.
If one eventually gets to ton quantities then its down to 18% of the present cost.
So all of that is good news....

I've been thinking that I was going to have to manufacturer my own quick disconnects.
Everything I'd found was either too big, to heavy or to expensive.. (often all three)

After a help me beg on Arocket a friend pointed me at some things on E-bay that eventually led me to these...

They are Aluminum, with viton and stainless internals. Off the shelf and not too expensive. The Really cool part is the rocket side is only 49gm!

They are available from multiple places look for FBM3314 and FBM1153. The only way they could possible be better is if they were AN fittings rather than pipe, and availible in multiple sizes. (For all of you that don't do high pressure plumbing, please realize pipe threads are horrible.)

In Pauls  pantheon of pliumbing....
  • Last choice is pipe thread.
  • AN flare fittings are ok to pretty good. Probably not good enough for directly hazardous materials near people. 
  • Swageloc are good, but both pricey and heavy.
  • The Big boys use stainless and all orbital welded connections...
That's it for Today....

Saturday, November 10, 2018

Two chemists walk into a bar, the first one says I'll have H20, the second one says I'll have H2O too... he dies....

Anyone that has followed my rocketry stuff for awhile knows I like H2O2.
(See comments on H2O2 at the very end of this post)
Both  Beal and the British Black Arrow group did some really cool stuff with H2O2.

So I've been thinking about engine cycles....



A:Regen Cat Pack 

 is what I have been running for the past few years. H2O2 comes in cools the engine, goes through a CAT pack and then ignites the fuel injected below the cat pack.
This works reasonably well, it has the following drawbacks...
1)CAT pack limits the H2O2 concentration to about 85%.
2)The CAT pack has a lot of pressure drop.
3)Cat Packs wear out or get contaminated.
4)They are some what expensive (Pure or plated silver screens)

B normal chamber with hypergol (or not)fuel.

I've been given some evidence of an available decent performance hypergol for H2O2.
I've not tested it or fired it personally. (Hypergol means fuel and oxidizer light on contact)
Its basically a traditional regen rocket motor. It needs a traditional injector, so not sure if I'll build a pintile(My fireing) , or a shower head (my fireing)` I've build and fired both with Lox Alcohol before I switched to H2O2.

This allows one to run to 100% H2O2 and to reduce the pressure drop.
The primary drawback is the fuel in small quantities from a chemical supplier is about $425 a liter.
The O:F is 4.9 so  the fuel for a full Class 2 burn is about $1300  For a full Class 3 burn that is 27K, its starting to hurt.... The H2O2 for the same class 3 burn is  $4500 so not totally out of the ballpark..

There has been an experiment that I've wanted to run for a very long time. I've wanted to try and run a wet, no catpack H2O2 engine. I've always wondered how to get it lit.  I think that at some point In testing I'll set up to use the Expensive Hypergol to light the motor, much like TEA/TEB is used in Lox RP engines and see if it continues to run well once the hypergol slug is gone.

C Odd choices....

There is some literature in the world talking about H2O2 gas generators with partial pre-decomposition and thermal decomposition of the full flow. This is the schematic of what I Imagine this might look like....  The H2O2 combines with a small amount of the hypergol to get warm, but not enough to "Burn" all the oxidizer....(This could also be part of the H2O2 flow goes through a cat pack to get hot)  This then enters into a stack of inconel screens, sort of like a cat pack, but not chemically active, its just a place to warm up and cause thermal decomposition...
Before thinking about the hypergol I'd planned to run this test with a silver cat pack and 100% peroxide, the silver cat pack would quickly melt and die, but probably not before getting the inconel screens hot enough to do thermal decomposition.... It seems the screens to do decomposition must get to and maintain at least 600C.

The big drawback to all the thermal decomposition schemes is that hot H2O2 vapor can detonate if it does not decompose.

Why am I posting all this stuff to the blog...

  • One of the primary goals for Unreasonable Rocket , from the very beginning is to excite people to try and do cool rocketry things themselves. It does not take NASA levels of $$.
  • I'm pretty much doing this project by myself in my Garage and at FAR. Last time I did this my Son was helping me, now I'm doing it solo. So using this as a portal to interact with people and maybe inspire people to help with the project is part of the blogging. 
  • Trying to establish a habit of keeping the world up to date, I've set up a Patreon account (I've not turned it on yet) and when I do my first firing in this development cycle and have cool video to share I'm going to turn it on.  (If you think I should activate it now say so...)

    If you want notification of new posts here, I will be announcing them on twitter. I'm @unrocket

*Comments on H2O2 aka hydrogen peroxide.

The hydrogen peroxide that sits in your medicine cabinet and that you put on your cuts is 3 to 5%. Meaning its 5% H2O2 and 95% water, The H2O2 were talking about here is at least 85%.

This high strength peroxide decomposes exo-thermally to steam and hot oxygen.
Any concentration above 72% has enough energy to full vaporize the water content and is thus a hazard as it can make lots of hot gas quickly.

This decomposition needs some thing to induce it, heat, or a catalyst chemical.
  • Thermal decomposition.
  • Metal reusable catalysts (silver, platinum)
  • Consumable Catalysts like the permanganates, etc...
With 85% you can run it through a silver catalyst (CAT Pack) for a very long time.
At 90% long term use will melt /degrade silver. Above 90% Silver does not last very long at all as the decomposing H2O2 melts it away, 98,99 or 100% has a more energy and higher performance as a rocket oxidizer.