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[Image: original source https://www.quora.com/How-many-types-of-bullets-do-we-have]

For example, if a spacecraft does not need a control module, propulsion or means of communication. All it is tasked to do is to take several pictures and transmit them with a light emitter visible to a space-based telescope.

The Rocket fan
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TheMatrix Equation-balance
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  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed. – Rory Alsop Mar 31 '23 at 16:47
  • @TheMatrixEquation-blance. I think there is a good question here about gun launched probes that is not clear in the question as written, can I do an edit to make it less big photo of a bullet and more about the title question? – GremlinWranger Apr 01 '23 at 08:43
  • @GremlinWranger - The questions like space-based gun launcher, lack existing research and development samples. And as such, not accepted well by this community. – TheMatrix Equation-balance Apr 01 '23 at 15:51
  • Also, because of a vacuum, you could have much longer gun barrels in space and much higher exit velocity. – TheMatrix Equation-balance Apr 01 '23 at 16:00
  • GremlinWranger has almost 20,000 reputation. They've demonstrated they understand what the Space SE community accepts/doesn't. – Erin Anne Apr 01 '23 at 19:38
  • It is possible to have a 'steam gun' in space. Instead of gunpowder, a laser would excite molecules of water creating instant steam with very precise force calibration. – TheMatrix Equation-balance Apr 01 '23 at 20:42
  • @TheMatrixEquation-balance there is a fair bit writing around gun launch in space since it is an assumed need for operation from the moon. There are two questions here that I was suggesting splitting out - the first being just how hard can you launch a cubesat type probe and still have it work (many gun systems assume inert payload), which would get answers from the work of HARP and Spinlaunch, the second may already have an answer here and would be what you launch with, noting that speed of sound gives hard limits to gun muzzle velocity involving chemistry. – GremlinWranger Apr 01 '23 at 23:51
  • @TheMatrixEquation-balance Suggested reading would include many of the entries tagged space-gun https://space.stackexchange.com/questions/tagged/space-gun. Even the ones for surface launch in atmosphere are of interest to you since they often include maximum achievable velocities for various systems – GremlinWranger Apr 01 '23 at 23:56
  • @GremlinWranger - I don't think barrel-launching cubesats with traditional solar panels, antennas and complicated mechanics will ever make sense. Even if it is achievable, the price will defeat the purpose. – TheMatrix Equation-balance Apr 02 '23 at 00:35
  • @GremlinWranger - "speed of sound gives hard limits to gun muzzle velocity involving chemistry." - Most of the bullets leave the barrel faster than the speed of sound. Some of the sniper bullets can hit the target before sound reaches it. In vacuum without air resistance, bullet's speed should be limited only by the strength of the barrel, speed of gas explosion (3000 m/s) and the amount of energy (gunpowder) you are willing to spend. – TheMatrix Equation-balance Apr 02 '23 at 00:40
  • @TheMatrixEquation-balance, I think you missed the point of my suggested change, your question was a single paragraph and did not define 'bullet' so you got lots of comments unrelated to your actual Q. The Marco and Polo 3U cubesats successfully operated at Mars, so they make a fixed template for a known viable size to harden for gun launch. If you wanted to know how small you could make a craft that could return an image from an asteroid suggest asking that as a new question, and leave the launch method undefined to avoid things going off track. – GremlinWranger Apr 02 '23 at 01:33
  • @GremlinWranger - One question brings new ideas and new questions. This is how brainstorming is supposed to work. From my point of view, I did get much more information than I originally expected. Thank you! – TheMatrix Equation-balance Apr 02 '23 at 01:41

2 Answers2

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Project HARP is a useful reference for this. The project successfully fired instrumented rounds at 2100 meters per second. This is from a 36 meter barrel so suggests 6000G with enough science hardware surviving to justify the program in the 1960s.

In terms of payload making electronics survive high G is not impossible, though any form of mechanical parts (like fuel valves or antenna) that need to move after firing gets complicated. Probably the biggest issue is power, since solar panels are notably fragile both as a bulk material and the wire to semiconductor bonds if kept light in weight and would presumably need to fold out after firing to get usable area.

This also brings to light another issue with gun fired probes, in that to protect the electronics your chassis needs to by physically substantial, eating deeply into the science payload with structure that post firing is wasted mass (no easy way to stage structural mass out of a gun launch). Also if they are coming from earth this makes your per probe mass cost cost high.

In terms of where you can get, 2100ms is not enough to be useful from LEO but from say lunar L3 it might be able to make various points in the asteroid belt.

The two issues with this is that this leaves you lifting the whole gun system close to earth escape velocity, and when the projectiles get to the asteroid they will not be doing any sort burn to orbit the but instead returning repeatedly to earth's orbit round the sun. Earth will not be there the first time, but if the plan is to fire one of these at every likely mining target in the asteroid belt you will start making owners of earth and lunar orbit infra structure nervous as the odds of impact climb.

And even if the accidental impacts do not upset people, like many high performance space systems this makes a handy weapon if you point it inwards which may either make people nervous, or be how you avoid having your funding cut.

A possibly more sensible place to put this is in the belt itself, since some form of electric gun can probably be built from materials in situ, and used for both thrust and exploration.

This also suggests a possible use case. Taking a photo of the outside of an asteroid is not particularly useful during a high speed fly past, possibly more relevant is to fabricate a projectile of a pure material, fit a basic terminal guidance system and hit the asteroid of interest while watching the spectra of the collision and possibly resulting dust cloud. This would give information about chemical makeup, mass and structural integrity, and 'solves' the communication problem.

GremlinWranger
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“Bullet sized” really has no meaning. Bullets come in 17HMR (1.1 gram) to BMG (47 gram) or even 30mm (833 grams).

If you are planning to spray sub-Kg probes from a space-born Gatling Gun, conservation of momentum will rob the launching spacecraft of equivalent delta-v. How will the spacecraft re-acquire this delta-v?

“Spacecraft does not need communication” and “transmit (images)” is self-contradictory.

If you want to launch multiple small probes, it would be better to

  1. define their mission objective
  2. refine a design which achieves that objective
  3. choose a trajectory
  4. choose a launch mechanism
  5. etc.

I think sub-Kg probes are an interesting idea. The idea needs fleshing out.

Woody
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  • By "Communications" we usually understand the ability to receive messages. In this case, it would only be a precisely timed (to correspond with telescope observation) light emissions. One way message delivery of sorts. – TheMatrix Equation-balance Mar 28 '23 at 01:29
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    @TheMatrixEquation-balance ... Oxford gives "exchange of information" as the definition of communication. Otherwise, its a bit like marriage. – Woody Mar 28 '23 at 01:53
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    How is delivering a message not communication? – Christopher James Huff Mar 28 '23 at 03:12
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    Hey I think some battle ships would like to see your 30mm and raise you 18 inch. – GremlinWranger Mar 28 '23 at 08:44
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    I appreciate the Gatling gun as much as the next red-blooded American but I admit to having no idea how this is supposed to promote space exploration. Are rockets not impressive enough pieces of engineering as they are to capture the public interest? – Cadence Mar 28 '23 at 12:07