Using cold-gas thrusters for stabilization?

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Raketenolli

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I know this is more of a research topic since it might validate the safety code, but since I'm not a US citizen I cannot get access to that forum.

If one wanted to build a scale rocket of a finless original, e.g. Titan, Delta IV, there is no passive stabilization, so active stabilization is required. This could be achieved by
1. Reaction wheels
2. Thrust-vector control on the main motor
3. Attitude control thrusters

Since 1. is just not very exciting and 2. only works as long as the main motor is burning, one is basically left with 3.

My question is now, has anyone ever used a (cold-gas) thruster system for stabilization/attitude control on a Level 2 (or smaller) size rocket?

FYI, I'm TRA Level 1, have a background in aerospace engineering and I'm nowhere near actually building a rocket with such a system -- I just wanted to check out whether it has been done.

Thanks,
Oliver
 
Probably the closest thing is Forrest Mims's experiments with ram air attitude control in the 1970s. He published at least one article in Model Rocketry Magazine. An archive is here: https://www.ninfinger.org/rockets/ModelRocketry/ModelRocketry.html

I'd try and find the issue for you, but my Internet connection is horrifically slow this morning...


Sent from my iPad using Rocketry Forum
 
I don't think #2 is really even possible with hobby rockets. I've been thinking about augmenting a rocket with active roll control using a cold gas thruster. The simple fact of the matter is, though, I don't think any RSO would let a rocket fly that is not already passively stable. On top of that, you would have to carry around pressurized tanks and other heavy equipment. A cool idea, though.
 
I have a friend, Dean Black, who has been sending me information on finless model rockets. He just sent me a paper yesterday. This does not use cold thrusters, but relies on aerodynamics. I have seen a University Space Launch Initiative (I think that is the contest name.) project that used compressed gas for a small amount of forward thrust to reach the 5,000' target altitude. I have never seen cold thrust used for attitude control.

View attachment Facts, Fun and Fallacies about Fin-less Rockets.pdf
 
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I don't think #2 is really even possible with hobby rockets. I've been thinking about augmenting a rocket with active roll control using a cold gas thruster. The simple fact of the matter is, though, I don't think any RSO would let a rocket fly that is not already passively stable. On top of that, you would have to carry around pressurized tanks and other heavy equipment. A cool idea, though.

#2 has been done before. It does well with long burn motors, obviously.
 
You could use clear plastic fins. They take a little bit of work. I have successfully flown clear plastic fin models for the Atlas Mercury (both 1/12 and 1/35 scale), Gemini-Titan (both 1/24 and 1/48 scale), and the Dyna-soar/Titan III (with clear plastic fins and clear tubes).
 
I've seen motor and fin stabilization used successfully. Rocket flew 3 active motors, one didn't light and it still flew perfectly straight. Fins didn't have strong enough servos for flight conditions.

It was flown at FAR, which doesn't fall under NAR/Tripoli codes, but it was pretty damn cool.

As far as cold gas it's possible, but the plumbing and tanks required would be pretty heavy. Roll stabilization via channels in the nozzle would work okay at a research launch, though you'd have to be careful not to over rotate.
 
A cold gas thruster system would be complicated, heavy and very expensive as I believe you need a minimum of (4) high speed valves and nozzle assemblies for pitch and roll control. It has been dempnstrated that In practice, it is easy to use canard fins with miniature servos and an RC flight leveler system to keep your rocket vertical, and you have total control of vertical motion at speeds above ~30 kph for a cost under $200.

Bob
 
I know of a couple hobby/amateur projects which have succeeded with active stabilization. None used cold gas thrusters. My gut tells me cold gas thrusters aren't going to work. I would love to be proven wrong.

Paul Breed used 3 gimballed K motors:
https://rocketdungeon.blogspot.com/2012/11/3xk160-gimbaled-solid-rocket-set-to-fly.html

PSAS with custom electronics and steerable fins:
https://psas.pdx.edu/news/2010-10-17-2/

Alyssa Stenberg used COTS servos and flight controller on an small rocket:

[video=youtube_share;A4M9Uso9EsY]https://youtu.be/A4M9Uso9EsY[/video]

--MCS

.
 
Thanks aerostadt, those things were also new to me but the techniques described seem to rely on motor thrust being available.

I'm obviously looking at the technical challenge as well, not just fixing the problem of an unstable finless rocket. So it really seems like thrusters haven't been employed for stabilization in HPR rockets yet, even though I think it's actually simpler than active fin stabilization or thrust vectoring.

I would guess that with a soda maker CO2 cartridge, a pressure reduction unit, some plumbing and the four valves (pitch and yaw, I'm not looking into roll control), I'd look at less than a 1 kg of material for less than €150, perfect fit for a 4" rocket with an H or I motor.

The closest I found was the attitude control system on NASA's SPHERES zero-gravity experiments https://www.nasa.gov/spheres/ , but the papers focus on the control part and don't really provide any technical details on the thruster system itself -- except for nominal thrust, which is 0.12 N per nozzle. I think an HPR rocket needs more ...

Oliver
 
I don't think #2 is really even possible with hobby rockets. I've been thinking about augmenting a rocket with active roll control using a cold gas thruster. The simple fact of the matter is, though, I don't think any RSO would let a rocket fly that is not already passively stable. On top of that, you would have to carry around pressurized tanks and other heavy equipment. A cool idea, though.

Oh, gimbaled motors have been done. John Pursley (former editor of American Spacemodeling magazine, before it became "Sport Rocketry") has done it. I've seen his work firsthand, and it's something to behold.

Basically he adapted a regular, off-the-shelf model airplane anti-crash autopilot system for use in a rocket, with a sensor ring with four sensors arranged like the cardinal points of the compass... these look out toward the horizon from just under the nosecone of the rocket. These sensors detect the horizon line by detecting light at a wavelength opaque to CO2, therefore the atmosphere above the horizon (sky) appears "black" to the sensor, while the much shorter distances to the horizon and land reaching out to the horizon appears "white" to the sensor. By comparing opposing pairs of sensors outputs, which ideally should both be reading 50% sky, 50% "land" below the horizon, the flight computer can guage the degree of tilt of the model its installed in (plane or rocket). If one sensor is seeing "all white" (looking down toward the ground) and the other is seeing "all black" looking upward into the sky) then the computer knows the vehicle is tilted in that assigned direction (be it pitch or yaw). The other pair of sensors 90 degrees to the first pair work similarly, so the two opposing pairs of sensors detect both pitch and yaw. There is no detection of the roll axis nor correction for it, but it isn't particularly necessary in a finless rocket anyway.

Once the flight computer (anti-crash system) detects the orientation and tilt of the rocket, it generates a corresponding and proportional servo signal to correct that orientation. SO, all one has to do is build a homemade motor mount with a swiveling gimbal (U-joint, basically) with two servos 90 degrees apart from each other-- one to swivel the motor mount back and forth for pitch control, and the other to swing the motor mount side to side for yaw control. The two can work in tandem to swing the motor in both directions at the same time, according to inputs from the stability system. The main thing is to ENSURE that the proper servo is activated by the proper pair of sensors.

Now, the OP is correct in that basically at burnout the stability contribution from the gimbal system is greatly degraded... Even a real rocket that has an engine shut down has no control authority from gimbaling that engine. Thing is, our solid rocket motors DO produce SOME VERY SLIGHT "thrust" from the gases produced from the delay grain (especially in BP motors) and this does contribute SOME control authority during coast... the servos may have to "hard over" (extend to full control throw) to correct the flight path, but from John's experience, the system DOES work, even on a finless rocket. Of course if the rocket has some kind of small, undersize, or SCALE size fins, this helps enormously. John has flown completely finless rockets with this method and had it work beautifully... His Vanguard rocket flight was amazing to behold! He's also used the system in a scale Mercury Redstone with scale-size fins with excellent results, though of course the Redstoned DOES have some smallish fins on it. There's really no reason with proper ballasting that a Gemini launch vehicle could not be similarly flown with such a system. (Ballasted to move the CG ahead of the CP through the use of noseweight).

That said, the rocket needs a certain amount of "natural stability" to make the task easier and for the gimbaled motor to continue to work after motor burnout when its control authority drops precipitously. The Vanguard rocket was an ideal shape for this sort of setup-- the long thin upper stages, with the wider first stage, meant that the CP was further back than on a lot of designs. This setup is NOT well-suited for a "hammerhead" rocket design like say, a finless Ares I, since its design is COMPLETELY THE OPPOSITE, with a large, long, fat upper stage above a long, skinny, much thinner first stage, which will shift the CP forward, requiring an inordinate amount of noseweight to move the CG ahead of the CP or at least to a neutral condition. If the rocket isn't ballasted right, at burnout it will most likely "swap ends" and do a backflip and try to fly backwards through the coast phase...

The important thing is, IT CAN AND HAS BEEN DONE. Electronically controlled roll control has also been done, using a servo to move a small pair of fins in opposing directions to null out any roll rates for a camera rocket. The servos were controlled by a ring of photocells located around the rocket body tube in a half-circle (IIRC) configuration. Each photocell was wired in such a way to detect sunlight falling upon it and convert that into a voltage reading. The electronics were hard-wired in such a way to produce a servo input signal to control the servo and proportionally move the fins depending on which photocell the sunlight was falling directly upon (therefore generating the most voltage) and steer the fins to turn the rocket until the "center" photocell was directly facing the sun-- if it rolled past, the photocells on the other side of it would detect more sunlight, and reverse the servo proportionally to turn the rocket back so the center photocell was facing directly into the sun. The system worked beautifully. It's on the Brittain Fraley website. I would also note here that George Gassaway's "Sun Seeker" rocket used a similar system of a ring of photocells INSIDE the rocket, with sunlight streaming in through a window in the tip of the nosecone (IIRC) to "steer" the rocket so it flew directly toward the sun after liftoff, via servo-controlling the fins. Such a system could also control a gimbaled motor on a finless rocket if one were so inclined to develop it that way.

Later! OL JR :)
 
A cold gas thruster system would be complicated, heavy and very expensive as I believe you need a minimum of (4) high speed valves and nozzle assemblies for pitch and roll control.

You have that right...

I built a cold gas stabilization demo system for the Holloman X-Prize Cup. It was "complicated, heavy and expensive".
It employed an 8 thruster matrix regulated down from 4000 PSI gaseous N2, and also employed a Crossbow IMU.
I'm standing on the right in this clip:
[video=youtube;f-r4FQOCSqQ]https://www.youtube.com/watch?v=f-r4FQOCSqQ[/video]


Here's the same system in development doing a 90 degree roll maneuver:
[video=youtube;SuyFllXpQvg]https://www.youtube.com/watch?v=SuyFllXpQvg[/video]


It's doable, but takes some serious coin, horsepower and modeling to get any credible authority.
 
The pressure reducers I found to date are indeed extremely bulky and heavy, that's true, but a friend hinted towards the paintball scene and check for components there. I'll have to figure out more details on these. I'll still be happy with a system not exceeding 1 kg in mass.

Thanks for the link to the book, that does sound like it covers a lot of what I need to research.

Oliver
 
Shoot! Same here, I can google and see a youtube vid and a one page PDF article, but can no longer access the webpage they dedicated to the project.

I can ask Mathew Kane's father at work next week to ping him about that. Would be good information/data to share when the right person needs it.
 
https://www.clarkson.edu/engineering/aiming_higher.html

[video=youtube;wNyiPxfkR3A]https://www.youtube.com/watch?v=wNyiPxfkR3A[/video]

Nothing with any real "meat" I know your looking for, I will get with his dad at work this week. The report and research was pretty interesting, I had the opportunity to look over it. Hope there is some way to make that effort available to the forum.....
 
Thank you, I have learned that there is PLENTY of info available on actual missile guidance through, get this, PATENTS! They are very descriptive and have lots of diagrams, very good for reverse engineering and modification! :D
 
I know of a couple hobby/amateur projects which have succeeded with active stabilization. None used cold gas thrusters. My gut tells me cold gas thrusters aren't going to work. I would love to be proven wrong.

Paul Breed used 3 gimballed K motors:
https://rocketdungeon.blogspot.com/2012/11/3xk160-gimbaled-solid-rocket-set-to-fly.html

PSAS with custom electronics and steerable fins:
https://psas.pdx.edu/news/2010-10-17-2/

Alyssa Stenberg used COTS servos and flight controller on an small rocket:

[video=youtube_share;A4M9Uso9EsY]https://youtu.be/A4M9Uso9EsY[/video]

--MCS

.

Is Alyssa on Rocketry Forum or available some other way? I have a similar project pending and would love to ask a few questions!
 
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