Rocket Steering - Gimbals and Other Methods

tahanson43206 · 2025-03-29 09:02:05

This topic is offered for NewMars members who might wish to add to a collection of links, images and text about how to design a gimbaling system for a rocket.

The leadoff article for this topic is courtesy of NASA (ca 2013) when the Space Launch System was in early development.

https://blogs.nasa.gov/J2X/tag/gimbal-bearing/

The article includes a number of images and diagrams, along with the text.

The J2 had two hydraulic actuators to provide for X and Y changes.

All the thrust of the engine was directed through a single ball bearing that is shown in the article.

(th)

tahanson43206 · 2025-03-29 09:02:50

This post is reserved for an index to posts that may be contributed by NewMars members over time.

(th)

tahanson43206 · 2025-03-31 08:10:38

It seems clear that the rocket engine for the Optical Plane Deep Space Tug must be gimbaled.

I asked Google's Gemini to "think" about the problem, and it came up with a use case I had overlooked. Gemini was unable to find specific numbers for the degree of freedom for gimbaled rocket engines, but we did consider different machines and different scenarios.

Conversation with Gemini
Hi Gemini! Thank you for your assistance with numerous previous questions and inquiries! Today I have a question that may require a bit of digging to answer. I have learned recently that some rocket engines are coupled to their rocket frames using a ball bearing to allow for steering the thrust. I'm wondering if you can find records of how many rockets with steering are using a ball bearing to transfer thrust, and for those cases, how many degrees of freedom are available to maneuver the rocket engine during operation?
It's a very interesting question that delves into the intricacies of rocket engine design. Here's a breakdown of what I've found regarding thrust vector control (TVC) and the use of ball bearings:
Thrust Vector Control (TVC)
TVC is essential for controlling the attitude and trajectory of rockets, especially in space where aerodynamic control surfaces are ineffective.
The primary method for TVC in liquid rockets is "gimbaling" the engine, which involves swiveling the engine or its nozzle.
Gimbaling and Bearing Use
Gimbaling systems often utilize bearings to facilitate this swiveling motion. Ball bearings, or similar bearing assemblies, can indeed be a component within these gimbal systems.
The purpose of these bearings is to allow for smooth and controlled movement of the engine or nozzle while withstanding the immense thrust forces.
It's important to note that while "ball bearings" is accurate, the actual engineering is very complex, and the bearings used in these applications are very specialized.
The Gimbal bearing carries most of the engine thrust load.
Gimbaling typically allows for two axes of rotation: pitch and yaw. This translates to two degrees of freedom for maneuvering the rocket engine.
Degrees of Freedom
Most common gimbal systems provide two degrees of freedom, allowing the rocket to adjust its pitch and yaw.
Roll control is often achieved through other methods, such as:
Separate reaction control system (RCS) thrusters.
In some cases, specialized nozzle designs or exhaust vanes.
Key Considerations
The specific design of the gimbal system, including the type of bearings used, varies depending on the rocket's size, thrust, and mission requirements.
Factors like the extreme temperatures and pressures involved necessitate highly specialized materials and engineering.
It is also worth noting that other methods of TVC exist, such as fluid injection into the exhaust stream.
In summary:
Ball bearings, or similar bearing mechanisms, are used in many rocket engine gimbal systems to enable thrust vector control.
These systems typically provide two degrees of freedom (pitch and yaw) for maneuvering.
Finding exact numbers of how many rockets use this specific bearing type is very difficult, as that information is often proprietary to the companies that produce the rockets.
I hope this information is helpful.
Sources and related content
Thrust vectoring - Wikipedia
en.wikipedia.org
Thin Section Bearings - Use Cases, Benefits and Products
schatzbearing.com
Rocket Physics, the Hard Way: Rocket Engine Engineering - The Mars Society of Canada
www.marssociety.ca
***
Thank you for your opening reply. I note your observation about company proprietary data. However, academic authors are free to discuss the subject of gimbal design and operation. Please look again to see if you can find information about the degree of movement that an author thinks might be needed/acceptable.
You're right to point out that academic and technical papers often provide valuable insights into the design and operational parameters of gimbal systems. While precise, universally applicable figures are elusive, I can offer some context gleaned from these sources:
Factors Influencing Degrees of Movement:
Mission Requirements:
The required degree of movement is heavily dependent on the rocket's mission. For instance, launch vehicles placing satellites into precise orbits demand high accuracy and a certain range of gimbal motion.
Missiles may require rapid and extensive gimbaling for agile maneuvering.
Rocket Dynamics:
The rocket's size, shape, and mass distribution influence the necessary gimbal range.
Aerodynamic forces and control system design also play a role.
Control System Precision:
Modern control systems enable very fine adjustments, even within relatively small gimbal angles. Therefore, high accuracy can be achieved without excessively large movements.
Insights from Technical Papers:
Papers discussing gimbal bearing friction, such as those related to the SLS (Space Launch System), often mention control adjustments in fractions of a degree. This highlights that even minute adjustments are crucial for precise control.
Research on gimbal balance emphasizes the importance of extremely high precision in gimbal systems, particularly for applications like missile seekers. This indicates that the focus is on accuracy rather than vast ranges of motion.
Papers that discuss the control systems of rockets, often show that control of the rocket around the 3 axis of rotation are vital. and that the pitch and yaw control are handled by the gimbled motors, and the roll is handled by other systems.
It is worth noting that the actual degrees of movement are limited by the physical design of the gimbal system, and the connections for fuel and oxidizer to the engine.
General Observations:
While the exact degrees of movement vary, it's safe to say that gimbal systems are designed for precise control within a relatively limited range.
The emphasis is on achieving the necessary accuracy for the specific mission, rather than maximizing the range of motion.
I hope this additional information provides a more comprehensive understanding of the topic.
***
Thank you for this second look, including review of academic sources. Can you find any details about what "limited" means. For example, does "limited" mean a degree or less?
It's challenging to give a single, precise number for the "limited" range of gimbal motion, as it varies significantly. However, I can provide some context that helps to clarify what "limited" means in this context:
Factors Limiting Gimbal Movement:
Physical Constraints:
The design of the rocket and the gimbal system itself imposes physical limits. Fuel and oxidizer lines, actuator ranges, and structural integrity all play a role.
The desire to keep the system as light and compact as possible also drives the design towards minimizing unnecessary movement.
Control System Requirements:
Modern control systems are highly precise, meaning that very small adjustments can have a significant effect on the rocket's trajectory.
Therefore, there's often no need for large gimbal angles. The focus is on accuracy, not extreme movement.
Stability and Control:
Excessive gimbaling can introduce instability, especially during critical phases of flight. Control systems are designed to operate within a range that ensures stability.
Observations From Research:
Research papers, such as those concerning the SLS (Space Launch System), highlight that precise control is achieved with relatively small adjustments. For example, studies on gimbal bearing friction analyze the effects of adjustments in fractions of a degree.
While large angle movements can be achieved, in normal flight operations, the control systems make very small adjustments to keep the rocket on the correct trajectory.
The term "limited" in this context, is much more related to the fact that the movements are small adjustments, for fine tuning of the flight path. So while the system could allow for larger movements, those larger movements are not needed.
In summary:
"Limited" in this context refers to the fact that the needed adjustments are small, and very precise.
While the system may be able to move through a larger range of motion, the control systems are designed to make very small adjustments.
It is more accurate to think of the gimbals as a system for making fine adjustments, rather than a system for making large changes to the flight path.
***
The steerable engines of the SpaceX Falcon 9 and Heavy Lift stages show rapid movement when performing landing maneuvers. The large movements are visible as these vehicles approach landing. The movements are very rapid and quite significant, and I'm sure they are precise as well. The NASA documentation you've found so far seem to be reporting on vehicles that are NOT designed to attempt a landing. I suspect that your earlier observation about company proprietary information would apply here.
You're absolutely right. The SpaceX Falcon 9 and Heavy landing maneuvers demonstrate a very different operational profile than the typical orbital insertion scenario. The visible, rapid, and significant movements you observe are a key part of their controlled descent and landing.
Here's a breakdown of why this is the case and how it relates to the information I previously provided:
Landing Maneuvers vs. Orbital Insertion:
Orbital Insertion:
The emphasis is on precise trajectory control to achieve the desired orbit.
Gimbal adjustments are typically small and gradual, focused on fine-tuning the flight path.
Landing Maneuvers:
The rocket must counteract gravity, wind, and other disturbances to achieve a controlled vertical descent.
Rapid and significant gimbal movements are required to maintain stability and steer the rocket to the landing site.
The control system is actively compensating for dynamic changes in the rocket's position and velocity.
SpaceX specific needs:
SpaceX rockets are designed to be reusable. This requires a very complex control system, and a very robust gimbal system.
The landing maneuver is very dynamic, and requires large, and fast adjustments to the engine angle.
Why the Difference?
The dynamic nature of landing requires a much wider range of gimbal motion and faster response times.
The control system is actively working to maintain stability in a highly unstable environment.
The need for precise landing at a specific location adds another layer of complexity.
Company Proprietary Information:
As you pointed out, SpaceX's landing technology is highly proprietary.
Specific details about the gimbal system's design, range of motion, and control algorithms are not publicly disclosed.
It is very difficult to find detailed specifications of the gimbal systems used in these rockets.
General Observations:
While precise numbers are unavailable, it's clear that the Falcon 9 and Heavy landing maneuvers involve significantly larger and faster gimbal movements than typical orbital insertion scenarios.
The video evidence of the landing maneuvers, shows far larger movements than those discussed in the NASA documentation.
The requirements for a reusable rocket, are much more demanding than those of a single use rocket.
I apologize for the earlier generalized information. Your observation about the landing maneuvers is very accurate, and highlights the difference between those two flight profiles.
***
I am trying to get a sense of how much gimbal movement is needed for a space tug application. I think the application is much closer to the launch requirement than the landing one, when the tug is boosting a payload to escape velocity, for example. In that case, the precise movements you've described seem appropriate. with limited change of the angle. We have another application in mind for the space tug. When vessels return from deep space missions, we would like to connect to them and slow them for insertion into Low Earth Orbit. This application may be somewhere between launch and landing requirements. What do you think?
You've hit on a very interesting and challenging application for a space tug! Let's break down the gimbal movement considerations for your two scenarios:
1. Boosting a Payload to Escape Velocity:
Similar to Launch:
As you correctly observed, this scenario is very similar to a launch phase.
The primary objective is to achieve a precise trajectory and velocity.
Therefore, the gimbal movements would likely be relatively small and gradual, focusing on fine-tuning the flight path.
Emphasis on Accuracy:
Precise orbital mechanics are crucial for escape velocity maneuvers.
The control system would prioritize accuracy over large, rapid movements.
The engine gimbaling would be for small corrections to the trajectory.
2. Decelerating Deep Space Vessels for LEO Insertion:
Between Launch and Landing:
This scenario presents a unique set of challenges that fall between launch and landing requirements.
While not as dynamic as a landing, it requires more active control than a typical launch.
Key Considerations:
Relative Velocity:
Deep space return velocities can be very high, requiring significant deceleration.
The gimbal system must be able to handle the forces and torques involved in this process.
Docking and Alignment:
The space tug must precisely align itself with the incoming vessel.
This requires a combination of translational and rotational maneuvers, which involve gimbaling.
Dynamic Control:
As the tug and vessel decelerate, their combined mass and inertia change, requiring active control adjustments.
The gimbal system must be able to respond to these dynamic changes.
Error Correction:
Minor errors in the incoming vessels trajectory will need to be corrected.
The gimbals will need to be able to make corrections to the vessels trajectory, to ensure a safe insertion into LEO.
Gimbal Movement:
While not as extreme as landing maneuvers, this scenario likely requires a wider range of gimbal motion and faster response times than a typical launch.
The gimbal system must be able to handle both precise fine-tuning and larger, more dynamic adjustments.
The size of the vessel being captured will greatly influence the amount of gimbal movement needed.
In summary:
Boosting payloads to escape velocity requires precise, small gimbal adjustments, similar to a launch.
Decelerating deep space vessels for LEO insertion presents a more dynamic scenario, requiring a wider range of gimbal motion and faster response times.
The second scenario, will require a very robust, and flexible gimbal system.
The precise range of motion will depend on the specific mission parameters, such as the size and velocity of the incoming vessel.
I hope this helps you refine your understanding of the gimbal movement requirements for your space tug applications.
***
Thank you for a helpful discussion. While we have not found specific numbers, we have at least considered the range of applications. Your point about docking is interesting. I would expect thrusters to have the major responsibility in that scenario, but the ability to swing the main engine might be useful. While I'm away, best wishes to you for success as you attempt to help your many other customers.
You're very welcome! I'm glad the discussion was helpful. You're right to point out the role of thrusters in docking. While they are the primary means for fine-tuned translational and rotational maneuvers, the main engine's gimbaling could indeed play a supportive role, especially for larger adjustments or during initial alignment.
Here's why:
Initial Alignment:
The main engine's gimbaling could assist in the initial alignment of the space tug with the incoming vessel, reducing the workload on the smaller thrusters.
This could be particularly useful for larger or more massive vessels, where precise thruster control might be more challenging.
Large Course Corrections:
If the incoming vessel's trajectory requires significant course corrections, the main engine's gimbaling could provide a more efficient means of adjustment than relying solely on thrusters.
This could save propellant and reduce the overall time required for the maneuver.
Stability Control:
During the docking process, the combined mass and inertia of the tug and vessel can create stability challenges.
The main engine's gimbaling could assist in maintaining stability and preventing unwanted rotations.
While thrusters are essential for the fine-grained control needed during docking, the main engine's gimbaling offers a valuable tool for larger adjustments and stability control.
Thank you for your kind wishes! I appreciate it, and I'm always ready to assist when you have more questions.

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tahanson43206 · 2025-03-31 17:04:37

GW Johnson prepared a slide to help us refresh on how gimbaling systems are set up for existing rocket designs.

My impression is that neither of these designs are going to work for the new rocket.

The reason is the nature of the energy delivery process. Most rockets deliver fuel to the combustion chamber where chemical changes occur to liberate energy.

The nuclear rocket (NERVA, for example) supplied energy to the propellant, by heating the propellant as it moves through the reactor.

The Optical Plane Solar rocket is intended to accept solar energy and redirect it to a Hot Bulb heating chamber through which propellant will pass on it's way to the exit port. It would appear that the best place to provide power-take-off force-flow equipment is at the throat of the rocket, just ahead of the expansion bell.

If we are lucky, perhaps Dr. Johnson will create a drawing to show what a gimbal system for such a rocket might look like.

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tahanson43206 · 2025-03-31 17:45:21

And here it is!

The length of the Hot Bulb is currently estimated at 5 meters in length. That number may shrink as we learn more about the optical heating process. The number is conservatively estimated based upon the power specification of 40 megawatts.

kbd512 has proposed a spherical Hot Bulb. Such a configuration would have the advantage of providing a wider range of movement to the thrust vector.

As mentioned previously, this design is in uncharted territory.

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tahanson43206 · 2025-04-01 20:40:59

This is a follow up to Post #4, with reference to Post #5...

The tilting plate method has definite advantages, but for this application, I am concerned about the movement of the head, as shown in Post #5.

If we decide to use the ball bearing and socket system, as shown in Post 4, then the head will move very little, because the ball will be a short distance above the top of the Hot Bulb.

If we design the engine compartment with three or four ribs, then the light can pass between the ribs to illuminate the Hot Bulb, while the ribs carry the thrust up to the ball bearing.

The pistons can remain close to the exhaust port and expansion bell assembly.

A detail that may be of interest to readers is that kbd512 has found a design for a heating chamber ("Hot Bulb") that might allow propellant to be admitted at the bottom of the device so that it travels up the inside of the outer wall to the top, and then descends via a passage to the exit port. The maximum heating is going to be available on that inside of the outside wall, since the photons will be delivered to the outside wall.

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tahanson43206 · 2025-04-07 08:51:10

The Focused Solar Propulsion topic has run into a minor issue .... a traditional gimbal system is not possible.

Because part of the exhaust will be ionized, I decided to ask Google's Gemini to "think" about magnetic steering.

It appears that magnetic steering might be possible, but how effective it would be is a question.

Wernher von Braun used steering vanes in the V2 rockets, but those will erode when subjected to hot exhaust.

Conversation with Gemini
Rocket Engine Magnetic Steering: Hi Gemini! Thank you for your assistance with many previous questions. I am a member of a small team working on a design for a rocket engine. We are updating a design from the 1950's using modern technology. One consequence of our work is the discovery that we cannot gimbal the rocket as would be preferred. The exhaust will be partially ionized. it occurred to me to wonder if a magnet might be able to influence the flow of the exhaust. What do you think?
***
Hey there! It's great to hear from you again, and that's a fascinating challenge you've stumbled upon. Updating a '50s design with today's tech sounds like a blast!
That's a really insightful leap you've made, considering the ionized exhaust. You're absolutely right – a magnetic field can indeed exert a force on moving charged particles, which is exactly what ionized exhaust is. This opens up the exciting possibility of using magnetic fields to steer the rocket's thrust!
Think about it like this: when charged particles move through a magnetic field, they experience a force perpendicular to both their velocity and the magnetic field direction (that's the Lorentz force, $ \vec{F} = q(\vec{v} \times \vec{B}) $). By carefully shaping and directing a magnetic field around the exhaust plume, you could potentially deflect the flow and generate a steering force.
Now, there are definitely some hurdles to consider:
Degree of Ionization: How much of your exhaust is actually ionized? The more ions you have, the stronger the magnetic influence will be. If the ionization level is low, the effect might be minimal.
Strength of the Magnetic Field: Generating a sufficiently strong magnetic field with a manageable weight and power consumption for a rocket engine is a significant engineering challenge. Superconducting magnets might be necessary to achieve the required field strengths without excessive power draw and heat.
Plasma Physics: The behavior of ionized gases (plasma) in magnetic fields can be complex. You'd need to delve into plasma physics to understand how the magnetic field will interact with your specific exhaust composition, temperature, and density. Instabilities and other non-linear effects could come into play.
Efficiency: How efficiently can you deflect the thrust using magnetic fields compared to traditional gimbaling? There will be energy costs associated with generating the magnetic field.
However, the potential benefits are pretty compelling:
No Moving Parts: Magnetic steering would eliminate the need for mechanical gimbaling systems, potentially reducing weight, complexity, and maintenance.
Faster Response Times: Magnetic fields can be adjusted very quickly, potentially leading to faster and more precise thrust vectoring.
Novel Control Possibilities: You might even be able to achieve more complex thrust vectoring profiles than with traditional methods.
There's definitely existing research in areas like magnetohydrodynamic (MHD) propulsion and plasma thrusters that explores similar concepts.
Looking into those fields might give you some valuable insights and point you towards potential solutions or challenges others have encountered.
This is a really cool direction to explore! Keep digging, and I'm here to help if you have more questions along the way. What aspects of this are you thinking about tackling next?
Thank you for your analysis of the situation, and for your identification of pros and cons. We wouldn't be considering this at all if the normal physical steering option were available.
You got it! It sounds like you're really up against a wall with the physical constraints, which makes exploring this magnetic avenue all the more compelling. It's often when you're forced to think outside the box that the most innovative solutions emerge.
Given that physical steering is off the table, focusing on the degree of ionization and the feasibility of generating a strong, controlled magnetic field seems like a logical next step. Understanding those two factors will likely determine whether this concept is a viable path forward for your design.
What kind of data do you have on the expected ionization levels in your exhaust? And have you started looking into different magnet technologies that might be suitable for this application?
Thank you for your follow up question! I'm planning to share your observations with the project team, and if there are follow up requests I'll return to give you a chance to look at them. In the mean time, best wishes for similar success as you attempt to help your many other customers.
Sounds like a solid plan! Sharing these initial thoughts with your team is a smart move. It's always great to get different perspectives on the table.
And hey, thanks for the well wishes! It's genuinely rewarding to explore these kinds of fascinating engineering challenges. Feel free to swing back anytime – I'm always up for diving into the details if your team decides to pursue this magnetic steering idea further. Best of luck with your project!

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tahanson43206 · 2025-04-07 09:35:05

This post is a follow up to the earlier one on magnetic steering...

Electrostatic steering is certainly possible if the exhaust contains ions, but the drawbacks are discouraging.

Here is a transcript of Google's Gemini's reflections on the question:

Conversation with Gemini
Rocket Engine Electrostatic Steering: Hello Again, and thank you for your assistance with many previous questions! I short time ago you and I considered electromagnetic steering for a rocket that is unable to implement mechanical steering. In this session I'd like to invite your consideration of electrostatic heating. Some of the exhaust we are expecting will be ionized, so the ions should be susceptible to electrostatic force. I am thinking of making the expansion bell in four segments, so that each can be given a charge opposite to it's neighbor. In the opening scenario I am proposing four segments. Do you think this idea for steering sounds feasible?
***
Hey there! Always a pleasure to dive into some rocket science with you. Electrostatic steering using those ionized exhaust particles? That's a really interesting angle!
Thinking about your four-segment bell design, where adjacent segments have opposite charges, it definitely opens up the possibility of deflecting those ions. You're right, the electrostatic force would act on them.
However, there are a few things that jump to mind when considering the feasibility:
Degree of Ionization: How much of your exhaust is actually ionized? If it's a small percentage, the electrostatic force might not be strong enough to generate significant thrust vectoring for the entire rocket. You'd need a substantial number of charged particles to make a real difference.
Charge Density and Voltage: To get a meaningful deflection, you'd likely need to apply very high voltages to those bell segments to create a strong enough electric field. This brings up questions about the power requirements and the potential for electrical breakdown or arcing in the
harsh environment of a rocket exhaust.
Ion Mobility and Interaction: How quickly can you change the charges on the segments to achieve responsive steering? Also, the ions in the exhaust stream will be moving at very high velocities. The amount of time they spend within the electric field might be quite short, limiting the extent of their deflection. Plus, consider the interactions between the ions themselves – space charge effects could become significant at higher ion densities.
Material Considerations: The materials used for the bell segments would need to withstand high temperatures and the corrosive nature of rocket exhaust, all while being able to hold a significant electrical charge. That's a tough combination!
Complexity and Weight: Implementing a segmented bell with the necessary high-voltage power supplies and control systems would add complexity and potentially weight to your rocket design, which is always a critical factor.
It's a really clever idea, and the principle of using electrostatic force on charged particles is sound. However, the practical implementation for rocket steering might face some significant engineering hurdles related to the density of ions, the strength of the electric fields you can generate, and the dynamic nature of the exhaust flow.
Have you considered any estimates for the percentage of ionization you expect in your exhaust stream? That would be a key piece of the puzzle!
***
thank you for your analysis of the electrostatic steering option, and for identifying critical risks! At first reading, this option does not sound as attractive as the magnetic steering option. In answer to your follow up question, the amount of ionization could be small, because we may not be able to achieve the desired exhaust temperature. This inquiry and your reply will be supplied to the project team as part of the documentation for review. Best wishes to you for similar success as you attempt to help all your other customers.
***
You got it! It's always best to lay out the potential challenges alongside the exciting possibilities when exploring new tech. Sounds like the magnetic steering option might hold more immediate promise for your project, especially if achieving high exhaust temperatures (and thus higher ionization) is uncertain.
Thanks for including our chat in your documentation – I hope it provides some useful points for your team's review. And the best of luck to you and your project team as you move forward! It's genuinely rewarding to be a part of these early-stage explorations. Feel free to reach out anytime you have more questions or want to brainstorm further. Wishing you all the success!

(th)

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#1 2025-03-29 09:02:05

Rocket Steering - Gimbals and Other Methods

#2 2025-03-29 09:02:50

Re: Rocket Steering - Gimbals and Other Methods

#3 2025-03-31 08:10:38

Re: Rocket Steering - Gimbals and Other Methods

#4 2025-03-31 17:04:37

Re: Rocket Steering - Gimbals and Other Methods

#5 2025-03-31 17:45:21

Re: Rocket Steering - Gimbals and Other Methods

#6 2025-04-01 20:40:59

Re: Rocket Steering - Gimbals and Other Methods

#7 2025-04-07 08:51:10

Re: Rocket Steering - Gimbals and Other Methods

#8 2025-04-07 09:35:05

Re: Rocket Steering - Gimbals and Other Methods

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