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This new topic is offered for NewMars members who might wish to contribute to a collection of links, images and text to illuminate the features of the two kinds of electromagnetic accelerators.
In Post #3 I'll lead off with a conversation with Gemini ... the data collected by Gemini is necessarily limited so I am confident our members will be able to build upon this start to add further insights.
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This post contains a transcript of a conversation with Gemini about rail guns vs coil guns.
Gemini seemed unaware of a version of rail guns that uses magnets oriented at right angles to the track.
Conversation with Gemini
Difference Rail Gun vs Coil Gun - Hi Gemini! Thanks (again) for your help with numerous requests. This one arises from discussion in a small international forum. I'm hoping you might be able to find source material able to help our readers to understand the differences between rail guns and coil guns. the differences are many, starting with the orientation of the magnetic coils, but including the way in which power is delivered to achieve propulsion. There may be other differences as well. I am personally familiar with the mass driver developed by Dr. Gerard O'Neill and his students in the 1980's, but I have been shown that military forces from various nations have pursued both kinds of accelerators for military purposes. This inquiry is oriented toward civilian use of the technology. One application of interest goes back to Dr. O'Neill's work, which was designed to lift material from the Moon for use in building a habitat in space. Another application might be acceleration of a rocket to assist with a flight to LEO.
***
It's a great question, and one that delves into fascinating physics and engineering. You're right to highlight the work of Dr. Gerard O'Neill, whose mass driver concept is a perfect entry point into understanding these technologies for civilian applications.Let's break down the differences between railguns and coilguns, focusing on their mechanisms and implications for non-military uses:
Railgun
How it Works (The Basics):
A railgun uses a principle called the Lorentz force. Imagine two parallel conductive rails. A conductive projectile (often called an armature or sabot) is placed between them, completing an electrical circuit. When a massive current (millions of amperes!) is pulsed through one rail, across the projectile, and back down the other rail, it creates an intense magnetic field perpendicular to the current flow. This interaction between the magnetic field and the current in the projectile generates a force that propels the projectile forward at extremely high velocities.Key Characteristics & Differences:
Propulsion Mechanism: Direct current through rails and armature, creating a Lorentz force.
Physical Contact: The projectile is in direct contact with the rails, acting as a sliding electrical contact. This is a critical difference.
Power Delivery: Requires enormous, instantaneous bursts of power, often from large capacitor banks.
Wear and Tear: Significant wear on the rails due to friction, intense heat from the current, and potential arcing (where material vaporizes into plasma). This limits the lifespan of the rails and requires frequent replacement or advanced materials.
Velocity: Capable of achieving extremely high velocities, often exceeding Mach 6 or 7, due to continuous acceleration along the rails.
Complexity: Conceptually simpler in terms of the underlying physics, but practically challenging due to the extreme forces, heat, and power requirements.
Civilian Applications & Challenges:
Space Launch Assist: Could theoretically be used to accelerate rockets or payloads to assist with reaching orbit (LEO). However, the immense forces, heat, and need for a very long track (potentially kilometers) on Earth make this incredibly challenging and expensive. The atmosphere also presents significant drag at hypersonic velocities.
Lunar/Asteroid Material Launch: As Dr. O'Neill envisioned, on the Moon or an asteroid, where there's no atmosphere and lower gravity, the challenges of drag and structural integrity are reduced. This makes it a more viable option for launching raw materials into space for construction or resource utilization.
Waste Disposal (Theoretical): Could potentially launch waste into space, though the environmental and safety implications are immense.
Coilgun (or Mass Driver, as O'Neill called it)
How it Works (The Basics):
A coilgun (or mass driver) uses a series of electromagnetic coils arranged along a barrel. A projectile, which can be ferromagnetic or have induced eddy currents (if made of a conductive but non-magnetic material like aluminum), is placed within the coils. The coils are sequentially energized in a precisely timed sequence. As one coil pulls the projectile forward, it's switched off, and the next coil ahead is energized, continuing to accelerate the projectile along the barrel through magnetic attraction or repulsion.Key Characteristics & Differences:
Propulsion Mechanism: Sequential activation of electromagnets (coils) to pull a projectile, often leveraging reluctance force or induced currents.
Physical Contact: The projectile generally does not make direct physical contact with the coils or the barrel, instead levitating or being guided by the magnetic fields. This significantly reduces wear and tear.
Power Delivery: Requires precise and rapid switching of current to individual coils. This demands sophisticated electronics and control systems.
Wear and Tear: Much less mechanical wear compared to railguns due to the lack of direct physical contact. This leads to higher reususability and lower maintenance.
Velocity: Can achieve high velocities, but often limited by the switching speed of the coils and the complexity of synchronization. While theoretical limits are high, practical implementations can struggle to match the sheer speed of railguns.
Complexity: Electronically more complex due to the need for precise timing and control of multiple coils and sensors to track projectile position.
Civilian Applications & Advantages:
Space Launch (Mass Drivers): This is where Dr. O'Neill's work is most relevant. His mass driver was essentially a large-scale coilgun designed to launch lunar material. The key advantages for this application are:
Reduced Wear: Essential for a long-lived system operating in a harsh environment.
Versatility: Can potentially launch various types of projectiles, as long as they can be influenced by the magnetic fields.
Modularity: The segmented design allows for easier scalability and maintenance.
Assisted Rocket Launch: Similar to railguns, coilguns could assist in accelerating rockets to LEO, but with the benefit of less wear on the launch infrastructure.
Material Transport on Earth (e.g., within mines or large industrial facilities): For moving heavy loads over long distances efficiently without the need for traditional propulsion systems, especially in controlled environments.
High-Speed Delivery Systems: While still highly theoretical, smaller-scale coilguns could be explored for rapid delivery of packages or specialized materials in certain industrial or logistical settings.
Scientific Research: Coilguns provide a cleaner, more controlled environment for accelerating projectiles for various research purposes compared to explosive methods.
Dr. Gerard O'Neill's Mass Driver
Dr. O'Neill's mass driver was a pioneering concept for civilian space applications, specifically for harvesting lunar resources. It was, in essence, a large-scale, multi-stage coilgun. His work demonstrated the feasibility of using electromagnetic forces to accelerate payloads to escape velocity from the Moon.Key aspects of O'Neill's mass driver:
Lunar Focus: Designed to operate in the vacuum and low gravity of the Moon, mitigating many of the challenges faced by terrestrial electromagnetic launchers.
Superconducting Coils: Utilized superconducting coils for higher efficiency and stronger magnetic fields, though this added to the complexity of cryogenic cooling.
Repetitive Launch: Intended for continuous, high-volume launching of lunar regolith (soil and rock) to space habitats or processing facilities.
Buckets with Superconducting Magnets: The "projectile" was a bucket containing lunar material, often with superconducting magnets embedded to interact with the drive coils.
Summary of Differences:
Feature Railgun Coilgun (Mass Driver)
Magnetic Field Prod. Current directly through rails and armature Sequentially pulsed coils
Projectile Contact Direct contact with rails Generally no direct contact (levitated/guided)
Power Delivery Single, massive, instantaneous pulse Sequentially timed pulses to individual coils
Wear & Tear High (friction, heat, arcing) Low (minimal mechanical stress)
Velocity Potential Extremely high (hypersonic) High, but often limited by switching complexity
Electrical Complexity Conceptually simpler, but power demanding Electronically more complex (timing, control)
Primary Force Lorentz Force Reluctance Force (often) or induced currents
Orientation of Coils N/A (two parallel rails) Coils arranged axially along the projectile's pathExport to Sheets
For civilian applications, especially long-term, high-volume operations like lunar material transport, the coilgun (mass driver) has distinct advantages due to its lower wear and tear and theoretical ability to operate continuously with minimal maintenance. While military applications often prioritize raw power and velocity (where railguns might shine), civilian endeavors lean towards efficiency, durability, and cost-effectiveness over time.It's a fascinating area of research, and the potential for these technologies to revolutionize space travel and other industries remains significant.
***
I was struck by your explanation of the functioning of a rail gun. It would appear that further examination of this design might be helpful. Your explanation described the flow of current from one rail to the other, but if there was an explanation of how the magnetic field creates motive force I confess to have missed it. I have seen pictures that suggest electromagnets might be positioned along the track, with the axis of the winding at right angles to the tracks. If your explanation included those I missed it. If you have a bit more time to invest, please expand a bit on this detail.
You're absolutely right to ask for clarification on how the magnetic field generates motive force in a railgun! It's the core principle, and sometimes explaining the basics can lead to omitting the crucial "why." My apologies if that wasn't clear.
The key to understanding the railgun's propulsion is the Lorentz Force. This fundamental principle of electromagnetism states that a current-carrying conductor (like the projectile in a railgun) experiences a force when placed within a magnetic field. The direction of this force is perpendicular to both the direction of the current and the direction of the magnetic field.
Let's break it down step by step for a railgun:
Current Flow:
You have two parallel conductive rails.
A power source (typically a massive capacitor bank) is connected to one end of these rails.
A conductive projectile (or "armature") is placed between the rails, completing the electrical circuit.
Current flows from the positive terminal of the power source, down one rail, across the projectile, and then back down the other rail to the negative terminal.
Magnetic Field Generation:
Any time an electric current flows through a wire, it generates a magnetic field around that wire. This is a fundamental law of electromagnetism (Ampere's Law).
In a railgun, current flows through both rails and through the projectile.
Consider the magnetic field generated by each rail:
Using the "right-hand rule" (if you point your thumb in the direction of the current, your fingers curl in the direction of the magnetic field), you'll find that the magnetic field lines generated by each rail circulate around that rail.
Crucially, in the space between the two rails, the magnetic fields generated by the currents in each rail add up and are largely directed in a single, perpendicular direction. For example, if the rails are horizontal and the current in one rail goes away from you and the other comes towards you, the magnetic field in between them will be primarily vertical (either up or down, depending on the current direction).
The Lorentz Force on the Projectile:
Now you have two key ingredients for the Lorentz force:
A current flowing through the projectile (from one rail to the other).
A strong magnetic field between the rails (generated by the currents in the rails themselves).
The Lorentz force states that a force will be exerted on the projectile that is perpendicular to both the direction of the current in the projectile and the direction of the magnetic field.
Imagine the current flowing across the projectile horizontally, and the magnetic field between the rails is vertically upwards. Using another version of the right-hand rule (or Fleming's Left-Hand Rule for motors), if your index finger points in the direction of the current and your middle finger points in the direction of the magnetic field, your thumb will point in the direction of the force. This force will be directed along the length of the rails, away from the power source, propelling the projectile forward.
To address your specific observation about electromagnets along the track:
You are spot on with your visual memory, but this detail usually applies to coilguns, not traditional railguns.
In a coilgun, as discussed previously, you do have distinct electromagnets (coils) positioned along the track, with their axes typically aligned with the direction of projectile travel. These coils are sequentially energized to pull the projectile forward. The projectile is often a ferromagnetic material that is attracted by the magnetic field of the energized coil.
In a railgun, there are generally no separate, externally wound electromagnets positioned along the track with their axis at right angles to the tracks. The magnetic field that drives the projectile is self-generated by the immense current flowing through the two parallel rails and the projectile itself. The rails are the "conductors" that create the magnetic field. The force is a direct consequence of the interaction between the current in the armature and the magnetic field created by the currents in the rails.
So, the difference in how the magnetic field is created and how it interacts with the projectile is a fundamental distinction:
Railgun: The rails themselves, carrying high current, are the source of the magnetic field that acts on the current in the projectile. It's a single, integrated electromagnetic system.
Coilgun: Separate, distinct coils are deliberately placed to create timed magnetic fields that interact with the projectile (which may or may not be carrying current itself, but is certainly influenced by the external magnetic fields).
This self-generating nature of the magnetic field in a railgun is what allows for such extreme acceleration, but it also leads to the immense forces trying to push the rails apart and the significant heat generation due to the high currents.
Hopefully, this more detailed explanation clarifies the mechanism of motive force in a railgun and further distinguishes it from a coilgun!
***Thank you for the explanation of the way in which magnetic fields are generated in a rail gun such as the ones you have studied. I would observe that the current path must be from the ends of the rails at the starting point of the acceleration. The current path would become greater as the armature moves away from the starting point. I'm curious about the design of the armature used in a military application, if you have access to any public information. The projectile would appear to have a role in generating a magnetic force of it's own, equal to and opposite to the force generated by the rails. Can you clarify the details of how the armature participates in this interesting phenomenon?
***You've hit upon some excellent points that are crucial to understanding the nuanced physics and engineering challenges of railguns! Let's delve into the armature's role and its magnetic interactions.
The Current Path and Inductance
You are absolutely correct: "the current path must be from the ends of the rails at the starting point of the acceleration. The current path would become greater as the armature moves away from the starting point."This increasing path length is directly related to a fundamental property called inductance. As the armature moves down the rails, the total area of the circuit loop formed by the power source, the rails, and the armature increases. This increase in the loop's area leads to an increase in the inductance of the circuit.
The force in a railgun can be elegantly described in terms of this changing inductance:
F= 21 L′ I2
Where:F is the accelerating force on the armature.
L ′
is the inductance gradient or inductance per unit length of the railgun. This represents how much the inductance of the circuit changes for every unit of length the armature moves.I is the current flowing through the circuit.
This formula shows that the force is proportional to the square of the current and the rate at which the inductance changes as the armature moves. The increasing path length naturally contributes to this changing inductance, and thus, to the accelerating force.
The Armature's Role in Magnetic Field Generation and Interaction
You've also accurately intuited that "The projectile would appear to have a role in generating a magnetic force of its own, equal to and opposite to the force generated by the rails." This is indeed the case, and it's a beautiful demonstration of Newton's third law applied to electromagnetism.Here's how the armature participates:
It's a Conductor (The "Moving Wire"): The armature itself is a crucial part of the electrical circuit. Current flows through the armature, connecting the two rails.
It Generates Its Own Magnetic Field: Just like the rails, the current flowing through the armature creates its own magnetic field around it.
Imagine the current flowing horizontally across the armature. Using the right-hand rule, this current will generate magnetic field lines that circulate around the armature.
The direction of the magnetic field generated by the armature will be opposite to the magnetic field generated by the rails at the location of the rails. This is a key part of the "equal and opposite" force.
Interaction of Fields (The Lorentz Force, Revisited):
The magnetic field generated by the rails (which is generally perpendicular to the plane of the rails and armature) acts upon the current flowing through the armature. This is the primary Lorentz force that pushes the armature forward.
Conversely, the magnetic field generated by the armature's current acts upon the current flowing in the rails. This creates an equal and opposite Lorentz force that tries to push the rails outward and away from each other. This outward force is why railgun rails need to be incredibly strong and well-braced to prevent them from deforming or exploding.
So, the armature isn't just a passive conductor; it's an active participant in the magnetic field generation. The force you feel propelling the armature forward is precisely the result of the interaction between the current in the armature and the magnetic field created by the rails. The reciprocal force is the magnetic field created by the armature acting on the current in the rails.
Armature Design in Military Applications (Unclassified Information)
The design of armatures for military railguns is a highly complex and critical area of research, as it directly impacts performance, efficiency, and most importantly, the longevity of the rails. Rail erosion and damage are major hurdles for practical railgun deployment.Based on unclassified public information, military railgun armatures generally fall into two main categories:
Solid Armatures (or Metallic Armatures):
Description: These are typically solid blocks or segments of highly conductive metals like copper, aluminum, or alloys. They are designed to make direct, sliding electrical contact with the rails.
Advantages: Provide excellent initial electrical contact and can handle very high currents.
Challenges:
Friction and Wear: The immense speed and pressure lead to significant friction, causing erosion of both the armature and the rails. This generates a lot of heat.
Arcing: As the armature accelerates and imperfections in contact arise, micro-arcs can form between the armature and rails. These arcs are extremely hot and cause rapid vaporization and erosion of material from both surfaces, further damaging the rails.
"Welding": If the armature loses sufficient speed or contact, it can "spot weld" itself to the rails due to the intense heat and pressure.
Current Distribution (Skin Effect): At very high frequencies (which effectively occur during the rapid rise of current in a railgun), current tends to flow only on the surface ("skin") of the conductors. This can exacerbate heating and wear at the contact points.
Design Considerations: Military research often focuses on:
Materials: Developing new alloys or composite materials that are more resistant to heat, wear, and arcing.
Shape and Geometry: Optimizing the contact geometry to distribute current and pressure more evenly, minimize arcing, and maintain contact integrity.
Lubrication/Interfaces: Investigating liquid metal interfaces (e.g., gallium alloys) or other specialized coatings to reduce friction and improve contact.
Plasma Armatures:
Description: Instead of a solid conductor, a plasma armature uses a highly ionized gas (plasma) to complete the circuit between the rails. The projectile itself is often non-conductive and is pushed by the expanding plasma.
Advantages:
No Mechanical Contact Wear: Since the plasma doesn't physically rub against the rails like a solid, friction and mechanical wear are significantly reduced.
Self-Healing: Plasma can theoretically "heal" minor discontinuities in contact.
Challenges:
Rail Erosion: While mechanical wear is reduced, the extreme heat of the plasma causes thermal erosion of the rails. The plasma itself can be corrosive.
Plasma Containment: Keeping the plasma confined and stable as it accelerates at extreme speeds is challenging.
Efficiency: Some energy is lost in generating and maintaining the plasma.
"Blowby": Plasma can "blow by" the projectile, reducing efficiency and potentially damaging the gun barrel behind the projectile.
Hybrid Armatures:
Description: These designs attempt to combine the best aspects of both solid and plasma armatures. They might use a solid armature that has plasma contacts at the rail interface, or a solid projectile propelled by a plasma slug behind it.
Goal: To achieve high performance while minimizing the severe wear issues of both pure solid and pure plasma armatures.
Projectile Design (Separate from Armature):
Often, the projectile (the actual munition being fired) is separate from the armature. The armature acts as a "pusher" or "sabot" for the projectile. The projectile itself might be an aerodynamically optimized, kinetic energy penetrator designed for impact without an explosive warhead, relying solely on its immense speed for destructive power. These projectiles will have specific aerodynamic features (fins, shaping) to maintain stability at hypersonic velocities.The challenge for military railguns has always been to achieve sufficient muzzle energy and velocity without destroying the gun barrel in a few shots, which is not practical for combat scenarios. This is where the nuanced design of the armature and the continuous research into advanced materials become paramount.
NewMars members can add value by finding YouTube (or other ) videos that show animation of the forces at work.
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A hypervelocity railgun attached to an automated targeting system might be a good weapon for anti drone defence. Or missile, if it's fast enough/can track the missile. Would be best if the rounds fragment into a cloud after leaving the barrel, like a shotgun. Iron Dome is pretty expensive to run. I know there's Iron Beam, using lasers for this, but perhaps a railgun would be significantly cheaper and so preferable for anti drone defense, keeping the lasers for shooting down fast missiles.
It may be that the primary role of these turn out to be defensive. As someone who is not too fond of war, I like that. I can't see them being vastly more destructive than current shelling is, and kill vs overkill you're still dead. Hmm, maybe it could improve targeting, actually, and reduce collateral damage? Take out the headquarters without so much explosive you take out the school next door too. Explosive rounds could be shot straight into the ground before exploding.
Use what is abundant and build to last
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I remember a while back there was discussion about developing smart shells. These would be something like 30mm cannon shells with the ability to steer their trajectory. Instead of having to fire a hundred rounds to hit something like a drone, the point defence system would fire a single round, which would steer towards the reflected monochromatic light which is used to illuminate the target.
Another option for drones is electrolasers. A laser beam ionises the air creating a trail of ions, which provide a path for electric current. Rather like a bolt of lightening. This would cook the electronics within the drone.
Generally, the problem with railguns is that friction between the projectile and the barrel causes excessive wear. This is especially the case if there is arcing that generates a plasma. But this does depend upon the speed of the shell within the barrel. Tank guns can reach muzzle velocity of 1.7km/s. That isn't far short of the 2.38km/s needed for lunar escape.
Last edited by Calliban (2025-07-22 08:03:42)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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