THRUST VECTORING

[Ayush Chauhan]

Hello guys!

I am a 1st year University Student studying Robotics Engineering but I am also very interested in Space, hence why I am making a reusable rocket. I've had previous experience making a model rocket using solid rocket motors.

Me and 2 other people are working on recreating a SpaceX style rocket.

We have decided to use liquid propulsion system because we get more control over the amount of thrust that comes out.
In terms of what kind of propellent we would use, we are thinking of either using Hypergolic-bipropellant, monopropellant or pressurized cold inert gas.

I would appreciate if anyone could help us with the thrust vectoring aspect of the rocket's propulsion and a bit of advice on the design/components for the rocket's propulsion system.

Thanks.

 

[MarsLander]

Might check out BPS.space.

https://bps.space
https://bps.space/products/thrust-vector-control

 

[rocket_troy]

Well, I've only dabbled with liquids and I haven't done thrust vectoring, but if I was to do it - even as a thought exercise - I would look at separating the combustion chamber from rocket in terms of hard fixed points and transfer the the thrust load from the CC to the vehicle via a spike type rod that sits within a recessed pocket in the vehicle. Propellant fluids would be fed through flexible lines and suitable actuators mounted to the aft of the CC (likely 4).
The theoretical advantage with this approach is it reduces the load requirements on the yaw & pitch actuation. Of course, there's also a need to control roll which can be done with multiple engines or radial thrusters or inertial mass gyroscopic action or whatever.
It's a very very seriously ambitious project that would likely require lots of resources and perhaps 3-4 generations of student turnover to even get to a flyable state I'd imagine.

TP

 

[Ayush Chauhan]

Might check out BPS.space.

https://bps.space
https://bps.space/products/thrust-vector-control

yes I've looked into BPS space, which is where I got my inspiration making a reusable rocket. But I would like to make everything form scratch and not buy anything premade.

 

[Ayush Chauhan]

Well, I've only dabbled with liquids and I haven't done thrust vectoring, but if I was to do it - even as a thought exercise - I would look at separating the combustion chamber from rocket in terms of hard fixed points and transfer the the thrust load from the CC to the vehicle via a spike type rod that sits within a recessed pocket in the vehicle. Propellant fluids would be fed through flexible lines and suitable actuators mounted to the aft of the CC (likely 4).

I would you need 4 actuators mounted? I would say we could do it with just 2 actuators placed horizontally, one controlling x direction and the other controlling the y direction.

The theoretical advantage with this approach is it reduces the load requirements on the yaw & pitch actuation. Of course, there's also a need to control roll which can be done with multiple engines or radial thrusters or inertial mass gyroscopic action or whatever.

Can you please elaborate more on this?

It's a very very seriously ambitious project that would likely require lots of resources and perhaps 3-4 generations of student turnover to even get to a flyable state I'd imagine.

It may sound crazy, but this is a personal project and we have given it 5 years to completely finish making it! Which is exactly the same duration of our course!

 

[rocket_troy]

I would you need 4 actuators mounted? I would say we could do it with just 2 actuators placed horizontally, one controlling x direction and the other controlling the y direction.


Can you please elaborate more on this?


It may sound crazy, but this is a personal project and we have given it 5 years to completely finish making it! Which is exactly the same duration of our course!

Yes, I can't see any reason why you couldn't do it with 2 actuators instead of 4.

What exactly did you want me to elaborate on? The roll control or the comment on the actuation or both?

TP

 

[Alan15578]

Yes, I can't see any reason why you couldn't do it with 2 actuators instead of 4.

What exactly did you want me to elaborate on? The roll control or the comment on the actuation or both?

TP

Yes, but with four actuators you can take out the backlash.

 

[Ayush Chauhan]

Yes, I can't see any reason why you couldn't do it with 2 actuators instead of 4.

What exactly did you want me to elaborate on? The roll control or the comment on the actuation or both?

TP

Can you please elaborate on both? Thanks.

 

[Ayush Chauhan]

Yes, but with four actuators you can take out the backlash.

What do you mean by backlash?

 

[Alan15578]

What do you mean by backlash?

Ask your professor. Backlash is any slop in the control linkage or drive train. Now ask him what "slop" is.

 

[cbrarick]

I think you're biting off more then you can chew. If you've never done liquids, do that first and get good at it. Then work on thrust vectoring. Right now you don't have the knowledge or experience to do both simultaneously. Yes, I know you're in college but that doesn't change the fact you lack experience.

 

[Antares JS]

we are thinking of either using Hypergolic-bipropellant,

Put that out of your mind immediately unless you are prepared and have the facilities and equipment necessary to store, handle, move, load, and burn chemicals whose mere fumes are literally capable of dissolving your lungs.

 

[rocket_troy]

Can you please elaborate on both? Thanks.

Control of roll (without going into the sensory governance) can be achieved a number of ways. Lots depends on your rocket's size and limitations. For small rockets, there's generally only 1 main thrust producing engine, so the use of gimballing multiple small engines opposing each others off-axis thrust isn't a practical option. That still leaves plenty of practical options such as:
Radial Thrusters: generally done with cold gas for this class of rocket and generally controlled using direct acting solenoid valves. Pros: fairly straightforward closed loop control that's available at any speeds. Cons: Heavy, volume hungry & limited gas supply.
Aero control (eg: canards): can be a fair bit of dicking around getting this solution stable both for vehicle stability and over/under shooting with aero conditions always changing. Obviously needs a certain minimum vehicle velocity to work effectively and really should be as close to the vehicle's CG as possible - unless you're using the fins for control. Pros: probably the lightest and minimal volume solution.
Internal Inertial mass: Basically reaction wheels. Probably the easiest solution for control governance but can be heavy as you're basically pushing or pulling against a flywheel to create a countering torque. If space allows for it to be located in the right section of the rocket, the flywheel can also provide gyroscopic stabilising to the other axes.
There are also others which I won't go into like the combination of gyros and fins eg. Rollerons and whatnot.

Regarding the gimballing: on retrospect (for bipropellant CC), you're pretty much stuck with the one option anyway for a vehicle this size. Well, perhaps not: you can still probably manage it with cold gas thrusters or thrust vanes or aero (perhaps not), but just about everyone else who have attempted this for the Lunar Lander Challenge (while back now) used engine gimballing IIRC.

TP

 

[Neutronium95]

@Ayush Chauhan You have chosen an extremely ambitious project to work on. I'm aware of exactly two liquid propelled thrust vectoring rockets that have been built by amateurs that have flown successfully.

If you want to be successful, don't jump straight to build the final rocket as your first project. Tackle some smaller projects to develop the knowledge and skills necessary to achieve your goal. Some example intermediate goals could be:

• Get high power rocketry certs, at least up to level 2, in order to familiarize yourself with general rocketry design and construction.
• Do some basic controls projects, like a balance bot.
• Build a tvc rocket that flies on model rocket motors to develop and evaluate your flight computers and control logic.
• Build and fire an augmented spark igniter.
• Build and static fire your engine design.
• Now add throttling.

This is not a comprehensive list by any means, just a few possible milestones to target before a full up test flight.

For your propellants, you should take a look at the nitrous oxide and alcohol architecture used by Half Cat Rocketry. The propellant choices allow for a significantly simplified feed system, with no need for a separate pressurant gas. And while they aren't entirely benign, the propellants are not as bad to work with as hydrogen peroxide, or any of the hypergolic propellants.

 

[Ayush Chauhan]

I think you're biting off more then you can chew. If you've never done liquids, do that first and get good at it. Then work on thrust vectoring. Right now you don't have the knowledge or experience to do both simultaneously. Yes, I know you're in college but that doesn't change the fact you lack experience.

Yes, I completely agree with you. But we are planning on getting a person from our uni's rocket team to help us who has past experience with liquid engines.

 

[Ayush Chauhan]

Put that out of your mind immediately unless you are prepared and have the facilities and equipment necessary to store, handle, move, load, and burn chemicals whose mere fumes are literally capable of dissolving your lungs.

Yes! That's one of the things on my list to ask our uni's rocket team.

 

[Ayush Chauhan]

Control of roll (without going into the sensory governance) can be achieved a number of ways. Lots depends on your rocket's size and limitations. For small rockets, there's generally only 1 main thrust producing engine, so the use of gimballing multiple small engines opposing each others off-axis thrust isn't a practical option. That still leaves plenty of practical options such as:
Radial Thrusters: generally done with cold gas for this class of rocket and generally controlled using direct acting solenoid valves. Pros: fairly straightforward closed loop control that's available at any speeds. Cons: Heavy, volume hungry & limited gas supply.
Aero control (eg: canards): can be a fair bit of dicking around getting this solution stable both for vehicle stability and over/under shooting with aero conditions always changing. Obviously needs a certain minimum vehicle velocity to work effectively and really should be as close to the vehicle's CG as possible - unless you're using the fins for control. Pros: probably the lightest and minimal volume solution.
Internal Inertial mass: Basically reaction wheels. Probably the easiest solution for control governance but can be heavy as you're basically pushing or pulling against a flywheel to create a countering torque. If space allows for it to be located in the right section of the rocket, the flywheel can also provide gyroscopic stabilising to the other axes.
There are also others which I won't go into like the combination of gyros and fins eg. Rollerons and whatnot.

Regarding the gimballing: on retrospect (for bipropellant CC), you're pretty much stuck with the one option anyway for a vehicle this size. Well, perhaps not: you can still probably manage it with cold gas thrusters or thrust vanes or aero (perhaps not), but just about everyone else who have attempted this for the Lunar Lander Challenge (while back now) used engine gimballing IIRC.

TP

Thanks for the information! I will take this into consideration when planning ahead. and it makes sense

 

[Ayush Chauhan]

@Ayush Chauhan You have chosen an extremely ambitious project to work on. I'm aware of exactly two liquid propelled thrust vectoring rockets that have been built by amateurs that have flown successfully.

If you want to be successful, don't jump straight to build the final rocket as your first project. Tackle some smaller projects to develop the knowledge and skills necessary to achieve your goal. Some example intermediate goals could be:

• Get high power rocketry certs, at least up to level 2, in order to familiarize yourself with general rocketry design and construction.
• Do some basic controls projects, like a balance bot.
• Build a tvc rocket that flies on model rocket motors to develop and evaluate your flight computers and control logic.
• Build and fire an augmented spark igniter.
• Build and static fire your engine design.
• Now add throttling.

This is not a comprehensive list by any means, just a few possible milestones to target before a full up test flight.

For your propellants, you should take a look at the nitrous oxide and alcohol architecture used by Half Cat Rocketry. The propellant choices allow for a significantly simplified feed system, with no need for a separate pressurant gas. And while they aren't entirely benign, the propellants are not as bad to work with as hydrogen peroxide, or any of the hypergolic propellants.

Thank you so much for this information and especially for the milestones. We might just go with those milestones first! (I do need to discuss this with my team). I already have experience with building model rocketry. However, I've not dived into high-power rocketry yet. (But I hope the building and designing part of the rocket should be about the same as low power rocketry, except at high power you also would need to add a GPS tracker, please do add on if I am missing something crucial here).

But speaking of that, I didn't mention our proper goal with the rocket we are trying to achieve at first. (@everyone). I understand that there are a lot of complexities involved, but to abstract our goals, we plan on making a moderate-sized rocket that will fly to about 40-50 meters in the air, hover for about 10 seconds, and then land back, all using thrust vectoring.

• Do some basic controls projects, like a balance bot.

When you mention a balance bot, do you mean something like this?


It balances the ping pong ball on the table.



Thank you so much for the information! We might just decide to go along with these milestones first to get solid foundation of the fundamentals...

 

[NTP2]

Put that out of your mind immediately unless you are prepared and have the facilities and equipment necessary to store, handle, move, load, and burn chemicals whose mere fumes are literally capable of dissolving your lungs.

+1 I was looking into making a small (10cm cubed) mono prop until I saw a video of OH2 dissolving a glove while spinning fire. I got my sanity back quickly after that…

 

[WizardOfBoz]

Trying to understand how 2 motors is superior to 4 with respect to backlash. I mean, Gemini Atlas used two motors for the booster. One could use two (x and y) actuators for all motors. But no spin control. With split (2 sets) or individual (4 sets) of controls you can control spin better but you have a lot more complexity. A lot. I have a PhD in control systems engineering and would counsel breaking the effort into many steps to realize small wins. Five years may be about right.
One other thing: you'll have to control the rocket somehow AFTER the motor burns out. In real life (eg Titan) the second stage, with thrust vectoring gets the craft into space and there's no air to destabilize the craft. I assume that you'll be in the atmosphere so after burnout you ould tumble....

 

[Ayush Chauhan]

+1 I was looking into making a small (10cm cubed) mono prop until I saw a video of OH2 dissolving a glove while spinning fire. I got my sanity back quickly after that…

DAMN

 

[Ayush Chauhan]

One other thing: you'll have to control the rocket somehow AFTER the motor burns out. In real life (eg Titan) the second stage, with thrust vectoring gets the craft into space and there's no air to destabilize the craft. I assume that you'll be in the atmosphere so after burnout you ould tumble....

The plan is to do the launch, hovering, and leading all with the fuel we fill at the start of the launch. So engine efficiency would be a huge factor in our project.

 

[NTP2]

DAMN

I was mistaken it’s a boot…

 

[Ayush Chauhan]

I was mistaken it’s a boot…

Oh wow... that's still crazyy..

 

[WizardOfBoz]

+1 I was looking into making a small (10cm cubed) mono prop until I saw a video of OH2 dissolving a glove while spinning fire. I got my sanity back quickly after that…

Not to be a pedant but I believe you were referring to H2O2. Coz OH2 is also H20...
The video you posted was interesting and useful (pretty eye-opening) to anyone considering peroxide as an oxidizer.