Thursday, November 01, 2018

Once more unto the breach....

I posted this to Arocket and got some questions, so I've modified this text to answer some of the questions and add additional details.

The next unreasonable year...

I'm personally at a point where I can take some time off and play with rockets again.

I don't think I can afford to do my full otrag-lite program, but I can do the next step.

So starting in the January time frame I'm going to be working at least 1./2 time on building a 
single tube demonstrator of  my otrag-lite concept.

Some changes from the base design:

Use off the shelf 6061 thin wall 4" al tube for primary tank age rather than the super light carbon tanks I developed. If I get reliable dynamic performance and recovery I might try a carbon tank at the end of the year.

The rocket is going to be 90% H2O2 with hypergolic fuel.
I've agreed to not talk about the fuel in return for being able to use it, so don't ask.

Suffice it that I've seen test data that shows it working in a test environment and RPA modeling of the propellant combination shows  good isp. Overall propellant density is 1.25. Toxcitiy is more benign than gasoline (what I had been using)

Vehicle will be blow down.
For stability reasons the tank-age will be divided in half with pressureant  below the propellant tanks.
Every possible means will be made to make it make it light weight.
IMHO the most important tool in building a high performance rocket is a precision scale.

I'm either going to do externally operated valves or pyro valves still working on that.
Vehicle will be at the class 2 limit with really long burn times, lift off thrust to weight on the order of 1.2, with burn times ~180 second`s. actively stabilized and finless.

The first version of roll control will be cold gas thrusters between the pressurization tank and the propellant tank. most likely a 3d printed Aluminum assembly. If that uses too much gas, then the next solutions tried would be some really tiny fins at the trailing edge of the vehicle and some "Blades" that deflect into the rocket nozzle.

Each area with valves and actuators will have local power and control with the coordination being either a single LIN wire or some form of short range wireless.
I believe a single layer of thin copper foil on top of a capton tape for a lin communication channel is probably lightest and lower drag than 3 or four small antennas. My big question here is if the copper tape will stretch as the rocket pressurizes.

Telemetry will be through a fiberglass patch on the nose cone.

The vehicle should be able to cross the 100 km line.

Recovery will be a balute or reinforceed balloon whose sole purpose is to prevent supersonic reentry. I expect the vehicle to be mostly destroyed on each flight. I Might separate the nose cone with camera and data log on its own very small parachute.

At this point I've secured the long lead items for the project  and I'm cleaning up my shop in preparation.

In the process of developing the design work based on previous efforts and will probably reopen this blog and start showing designs and hardware around the first of the year.

I'll do the initial testing at FAR until I have issues with their altitude limit. 
Then I will probably be looking to launch offshore.

My stretch goal is to bring evidence of flown hardware to Space Access this year.

CAD/CAM  The right tool is probably fusion 360, I tried using it for some projects it about three years ago and it was unusable on a 4K monitor. In the last few days I've updated it and it seems much better. My personal tool of choice is Rhino, as I'm really familiar with it , but I'll probably to use Fusion 360 as much as possible.



Monroe said...

Are you planning any 5-Axis work with fusion 360?

Paul Breed said...

No I have no current need for 5 axis anything....
I think the process will be:
2)3D print in resin on the form 2....
3)Repeat steps 1,2 until happy....
4)3D print in aluminum.
5)Machine the 3d printed parts to clean up sealing surfaces.
Go back to step 1....

Tard Markleson said...

Awesome! So glad Unreasonable Rocket is back!

What's the altitude limit at FAR?

Paul Breed said...

Limit is ~ 50,000 ft.
Can probably be extended to 75K.
Can't got to 100Km.

Ben Brockert said...

Paul, a few thoughts:

* To get a successful flight in not too many attempts you are going to want fins. The dynamics of a small finless rocket through max Q are severe, much worse than anything you see when hovering. A small upset will rapidly put you out of gimbal range. Doing monte carlo sims of the full flight will show you that quickly, if you set that up, but as a first approximation just figuring out how much AoA equals your gimbals around max Q will make it clear. Any quantity of fins will help (note that Long March 2C even has fins) but enough fins to be just stable will also keep the rocket from immediately breaking up if the engine shuts off early.

* Blow down with the ullage under the propellant is an interesting approach, but sounds like it'll make for a lot of complicated bulkheads if you're trying to keep the OML clean. Also any overfilled propellant that falls into the ullage tank will be dead weight.

* We already talked on Twitter about the recovery system, I'm a fan of recovering the payload and crashing the rocket if that's compatible with your program goals. Here you say "prevent supersonic reentry", which is basically impossible for a flight to 100km. At some point it's going to be falling supersonic.

* Regarding space launch sites, Spaceport America is closer to San Diego and makes it possible to stay at a motel at night rather than requiring the whole team to camp. You might be able to get a good deal with them to do the launch, but if you can't there's nothing stopping you from setting up on BLM land outside the spaceport itself and using the same airspace. In the end you're working with the FAA and WSMR in both cases, and I don't know what SpAm would offer you beyond one of Armadillo's concrete pads and gated access.

* On RCS, Gary Hooper showed that it was completely plausible to build a finned rocket with no significant roll.

Jimmy Beal said...

Ben, when you say "Spaceport America is closer to San Diego"...closer than what?

Ben Brockert said...

Closer than Black Rock.

Paul Breed said...

Actually Space Port America and Gerlatch NV are almost exactly the same time distance from home. If one has to pick up things from FAR on the way then Gerlatch is 6 hours closer...

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