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# Physics/Orbital Defense Rail Cannon

Question
Hello Mr. Johnson
Might it be possible to use a large rail cannon on the surface of the earth to strike objects in distant orbit or not too much farther away?  Or is the energy needed too great?
Assuming that there is a lot of electricity available but the supply is not unimaginably large like the energy released by the Sun.  The projectile would have to move fast enough that targets could not easily maneuver out of the way.
Also would spinal mounted rail cannons on spacecraft be practical for use in space?  What ranges would engagements likely be fought at?  All of this assuming a much larger and more consistent supply of electricity on the spacecraft than is currently possible.
I'm attempting to write a science fiction story.  I'm not too concerned with precise scientific accuracy and figures I just want the reader to be able to say, "I can see how that might work."  The setting is quite some time in the future of course and it's impossible to say for certain what will be possible.
I suppose the point of my question is to get your opinion on what could and could not be reasonably expected from rail gun technology 100-150 years in the future in this context.  I don't want my science fiction to sound like magic.
Daniel

Hello Daniel,

1. Might it be possible to use a large rail cannon on the surface of the earth to strike objects in distant orbit or not too much farther away?  Or is the energy needed too great?

Yes, this could be done. You don't specify the mass of the projectile or the speed of it, therefore my answer is yes. The mass and speed of the projectile would be selected based on the available energy supply. You said that it would have to move fast enough that targets could not easily maneuver out of the way. But I assume that we have made significant advances in stealth, such that they would not see it coming. The use of a small projectile would be hard to detect. Since I am free to make assumptions, I can justify answering yes to your question.

2. Also would spinal mounted rail cannons on spacecraft be practical for use in space?

In a situation that presents multiple targets, your reaction time in engaging the next target would be slow. I don't believe such a weapon would rule the battlefield. It could be a valuable part of an array of weapons.

3. What ranges would engagements likely be fought at?

I would expect a rail gun to be best at a large distance so that all of the enemy vehicles would be in the same general direction. That would simplify adjusting the aiming from one enemy to another.

Read WHATELEY ISLAND by BRUCE PIERCE. It is science fiction and doesn't try to explain how the technology does what it does. It just describes the results.

I wish you happy writing,
Steve
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Thank you sir.

Physics

Volunteer

#### Steve Johnson

##### Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

##### Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University