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Lets say I want to create a satellite constellation similar to earth's GPS network around the moon or mars with around 24 4U-6U cubesats as shown in this image:

GPS constellation

I was wondering is it possible/practical to launch these small cubesats into their appropriate orbital inclination from an equatorial orbit using some sort of magnetic coil gun or "Gauss cannon".

So as a step by step this would look like this:

  1. Larger ship is in a circular, equatorial orbit of a planet (or moon) and is carrying a bunch of small cubesats and two large magnetic accelerators
  2. The ship points one cannon towards the normal vector and the other at the anti-normal vector
  3. Simultaneously two cubesats are shot out of the cannons (perhaps inside a sabot) and the two shots cancel out the inertia
  4. The larger ship waits the appropriate time and preforms this maneuver again and again until all satellites are launched and positioned

I see several advantages to this system such as:

  • Cubesats can be cheap and don't need a propulsion system
  • A network with many satellites can be set up very quickly
  • The cannon vehicle can be reused

The questions:

  • Is such a system feasible and practical compared to current methods?
  • Could the cannons reach enough speed to set the orbits properly?
  • What would be the accuracy on such a system?
  • Would the satellites encounter extreme heat/magnetic buildup during launch or damage to electronics when fired due to the strong magnetic field? Would encasing them in some sort of sabot prevent this?
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  • $\begingroup$ If the cubesats have no propulsion, you could not insert them from a low circular orbit to a high circular by only using your gauss cannons. See Hohmann transfer orbit If the cubes are accelerated with a short coil gun, the necessary high acceleration will destroy them. Much more structural mass will be needed to avoid that. Small cubesats do not have the electrical power to generate a strong radio signal to be easily received at surface. $\endgroup$
    – Uwe
    Nov 5, 2017 at 17:47
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    $\begingroup$ @Uwe, I'm not talking about sending the cubesats to a higher orbit, their final orbit would have the same orbital altitude just at an orbital inclination of say 45 degrees instead of equatorial. Also, these satellites wouldn't be at Earth GPS altitude but rather a much lower orbit so I think the transmission power could definitely be high enough. $\endgroup$
    – Dragongeek
    Nov 5, 2017 at 17:55
  • $\begingroup$ But changing only the orbital inclination requires much energy and a strong acceleration by the coil gun. Very low orbits would require much more satellites in more orbit planes. To determine the position, you need to receive four or more satellites at the same time. The lower the orbit, the more satellites are needed. $\endgroup$
    – Uwe
    Nov 5, 2017 at 18:11
  • $\begingroup$ @Uwe, I think you're right: It's completely impractical and requires a huge amount of energy. See my answer below. $\endgroup$
    – Dragongeek
    Nov 5, 2017 at 19:34
  • $\begingroup$ Nitpicking time: While "Gauss cannon" tends to be used as a general term for electromagnetic guns (most notably railguns and coilguns), it is technically a specific early design using colliding magnets to propel a projectile. Being rather limited, it hasn't been pursued much. But as almost no-one ever heard of this particular design anyway... $\endgroup$
    – Eth
    Jul 2, 2019 at 8:08

1 Answer 1

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I've run the math! Although it's possible, the instantaneous energy required to do this is just insane. Basically you'd need the power supply of a Nimitz-class Aircraft Carrier to power the thing or a huge bank of capacitors. An orbital inclination change like this for a 5kg satellite would require around 16 megajoules of power or the energy equivalency of around 400ml of kerosene.

Calculations

Note calculation assumes circular orbits

As you can see, the instant power supply capability required is very high and designing a spacecraft which survives an acceleration this extreme would probably become heavier and thus defeat the purpose of the satellites (being light and easy to launch). It's much easier add the extra propulsion systems to position the satellites traditionally.

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    $\begingroup$ Accelerating the cubesat with 336 km/s*s would destroy it anyway. For a tolerable acceleration the necessary tube length will be several hundred to some kilometers long. $\endgroup$
    – Uwe
    Nov 5, 2017 at 19:46
  • $\begingroup$ Why is it orbital height above mars? $\endgroup$
    – Raze
    Nov 5, 2017 at 19:47
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    $\begingroup$ @Raze it just adds the radius of Mars to the number entered. Most descriptions of satellites orbiting mars are given in orbital height above Mars and I find it easier to visualize. $\endgroup$
    – Dragongeek
    Nov 5, 2017 at 19:54
  • $\begingroup$ +1 for a quantitative answer! There's nothing really insane about a bank of capacitors. The challenge of making an operational GPS satellite that could sustain a 34,000 gee acceleration is probably way beyond current capability, you might want address that in your answer. $\endgroup$
    – uhoh
    Nov 6, 2017 at 2:06
  • $\begingroup$ @Uwe I was literally just about to ask that, thanks for the clarification, I figured RUD would be the result of any cubesat fired out of something so ridiculously powerful. 34,332.8571g is pretty absurd even for 0.0077s. Doubt you'd try for a 10 meter railgun anyhow. $\endgroup$
    – Magic Octopus Urn
    Jul 2, 2019 at 13:49

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