Rocket Reaction Control system (RCS)

[William Carter]

Hello! I want to build a RCS rocket with 4 mini thrusters on the sides keeping it stable. How would this be done and is it possible? Thanks!

The concept I want to achieve is similar to the video:

 

[watheyak]

The answer is directly related to how much hydrazine you have on hand.

Some? Maybe.
None? No.

 

[Mugs914]

"Hydrazine is not radioactive... And that is the nicest thing I can say about it."

One of my all-time favorite quotes and I can't remember who actually said it.

 

[Neutronium95]

I've seen a few people that have made proof of concept cold gas RCS systems, but I don't think that any of those have flown. It's a really interesting concept, but it would be a very long road to develop a working system, and the software necessary to control it.


Edit: here's a video by Joe Barnard where he talks about his system.

 

[watheyak]

I've seen a few people that have made proof of concept cold gas RCS systems, but I don't think that any of those have flown. It's a really interesting concept, but it would be a very long road to develop a working system, and the software necessary to control it.

The cold gas could be interesting, but I feel like there could be scale issues. But that's just a guess.

 

[Nytrunner]

"Hydrazine is not radioactive... And that is the nicest thing I can say about it."

One of my all-time favorite quotes and I can't remember who actually said it.

A prior HARA president was a lead at Nasa Marshal's propulsion division (now a Tech-Fellow at the center) and specialized in hypergols.

He once told me "The easiest way to tell if someone works with hypergolic propellant is when they wash their hands before they go to the bathroom"

 

[Joe Scuti]

Can you use hydrogen peroxide?

 

[heada]

High concentrated H2O2 has it's own drawbacks. Hard to obtain above 30% unless you order a tanker truck worth, needs a catalyst to decompose but will happily oxidize most catalysts unless you use an expensive one like platinum and last, any contaminate will happily act as the catalyst at the absolute worst time.

If I were to try RCS at the hobby level, I'd go with a high pressurized gas. You can buy CO2 at ~2000psi along with supporting hardware (tanks, fittings, etc) from a paintball store. There are also tanks designed for ~3500psi to ~4000psi compressed air for precharged pneumatic air rifles and the pumps to fill them. You'd need fast acting gas valves (solenoids?) as well as a regulator to step the high pressure down to a level the valves can work at.

 

[mooffle]

Could you do a much simpler setup with 3 or 4 arduino controlled valves and a small tank of compressed air? My only thought is that it would be much more limited to a redirection than a hover.

 

[mooffle]

High concentrated H2O2 has it's own drawbacks. Hard to obtain above 30% unless you order a tanker truck worth, needs a catalyst to decompose but will happily oxidize most catalysts unless you use an expensive one like platinum and last, any contaminate will happily act as the catalyst at the absolute worst time.

If I were to try RCS at the hobby level, I'd go with a high pressurized gas. You can buy CO2 at ~2000psi along with supporting hardware (tanks, fittings, etc) from a paintball store. There are also tanks designed for ~3500psi to ~4000psi compressed air for precharged pneumatic air rifles and the pumps to fill them. You'd need fast acting gas valves (solenoids?) as well as a regulator to step the high pressure down to a level the valves can work at.

You posted before I could refresh, this seems like the only achievable way for a hobbyist to do something like this. At this point though why not just go with steerable forward vanes like so man SAM's have?

 

[heada]

You posted before I could refresh, this seems like the only achievable way for a hobbyist to do something like this. At this point though why not just go with steerable forward vanes like so man SAM's have?

https://www.rocketryforum.com/threads/i-could-use-just-a-little-guidance.122042/

 

[FredA]

RCS has the nice benefit of NOT mixing in an unintentional roll component.

 

[William Carter]

Would thrust vectoring or servo controlled fins be better at guiding/stability?

 

[OverTheTop]

RCS has the nice benefit of NOT mixing in an unintentional roll component.

Only if the rocket is axially balanced properly, otherwise roll will be induced if it is not corrected out.

 

[FredA]

Only if the rocket is axially balanced properly, otherwise roll will be induced if it is not corrected out.

Totally agree -- you need that balance regardless of which control system you attempt - they will all suffer from a lack of balance.

 

[Zeus-cat]

What kind of rocket are you planning on using this with? Most hobby rockets have a motor that burns for 3 seconds or less, so the RCS would mainly be used in the coast phase.

 

[Bruce]

...If I were to try RCS at the hobby level, I'd go with a high pressurized gas. You can buy CO2 at ~2000psi along with supporting hardware (tanks, fittings, etc) from a paintball store. There are also tanks designed for ~3500psi to ~4000psi compressed air for precharged pneumatic air rifles and the pumps to fill them. You'd need fast acting gas valves (solenoids?) as well as a regulator to step the high pressure down to a level the valves can work at...

I wonder if 4,000psi compressed air could be used for the main (lifting) motor on a rocket? Has this been done before? What would be involved? Could it be throttled?

 

[dhbarr]

I wonder if 4,000psi compressed air could be used for the main (lifting) motor on a rocket? Has this been done before? What would be involved? Could it be throttled?

I think you'll find 4k tanks & hardware aren't especially light.

 

[jsdemar]

You may find this useful. Guidance Tutorial.

 

[heada]

I wonder if 4,000psi compressed air could be used for the main (lifting) motor on a rocket? Has this been done before? What would be involved? Could it be throttled?

It'd be very difficult to use that high pressure directly. Most valves aren't designed for it so you have to run the air through a regulator first to restrict the pressure down to a level where the valves can work. With the lower pressure you get less force and so I don't think it'd be enough for main propulsion but a low force RCS could be possible. I don't know of any pneumatic regulators that could be modified in-flight to act as a throttle control. The ones I've seen are manually screwed in or out to set the downstream pressure.

Tank, plumbing, regulator, solenoids, electronics all add up to enough mass that you'd need a normal main propulsion system.

 

[Bruce]

I think you'll find 4k tanks & hardware aren't especially light.

Agreed, weight is always an important issue with rockets and even more so in this case.

But has anyone successfully flown a rocket powered only by compressed air?

 

[Kelly]

But has anyone successfully flown a rocket powered only by compressed air?

Sure, the ever-popular water rockets are powered only by compressed air. (The water is just an ejected mass; all the power to eject it comes from compressed air.)
There are also compressed-air rockets such as stomp rockets, and upscales that use larger compressed air tanks. It's questionable whether these are 'rockets' or just 'projectiles', since all the momentum is applied by an external source on the ground for most of these. Rockets work by ejecting mass, and it's tough to compress air enough to fit a reasonable amount of air mass inside of a rocket (might be enough for guidance purposes, though).

 

[Bruce]

Sure, the ever-popular water rockets are powered only by compressed air. (The water is just an ejected mass; all the power to eject it comes from compressed air.)
There are also compressed-air rockets such as stomp rockets, and upscales that use larger compressed air tanks. It's questionable whether these are 'rockets' or just 'projectiles', since all the momentum is applied by an external source on the ground for most of these. Rockets work by ejecting mass, and it's tough to compress air enough to fit a reasonable amount of air mass inside of a rocket (might be enough for guidance purposes, though).

Agreed, Water Rockets are helped by the mass of the ejected water, so I wouldn't classify them as purely Compressed Air Powered.

And I would classify a Stomp Rocket more as a gun and not a rocket since, as you say the power source stays on the ground.

There are steam powered rockets like the ones that Evel Knieval, Eddie Braun and Mad Mike flew in, but they aren't powered purely by compressed air either.

If you release the air from an inflated toy balloon, it seems to have a sufficient power to weight ratio and that's powered purely by compressed air. Is that the largest pure compressed air powered rocket that has flown?