# Help me build a space shotgun so I can shoot Venus from Jupiter

If one wants to move an object from orbit around one planet in the solar system and have it collide with another, what information is needed, and how would one go about calculating such a thing?

For example, lets say:

1. I can build stuff around Jupiter, and money and logistics are no object. Whatever piece of physically possible technology I want, I can have there.
2. For experimental purposes, I want to crash Hydrogen filled bubbles of iron at Venus, so that they fall through the atmosphere as meteors.

3. My first thought is to use a huge mass driver to fire the bubbles through space so that most of them crash into Venus,like a giant electromagnetic shotgun firing across the solar system.

Even though I have all these resources, I somehow need the help of StackExchange to learn what exactly I will need to accomplish my goal. So what do I need to do to aim and fire the projectiles?

• How do I calculate a trajectory from one planet to another, taking into account motion of the planets etc? Is there an app for that?
• What is the relationship between precision of aim, mass and speed of the projectile, and vulnerability to deflection by solar wind or gravitational pull of passing objects?

In other words, how do I figure out how fast I need to shoot my projectiles, and what do I need to know/do to aim them so that I have a reasonable chance of hitting my target at that distance, assuming no further adjustments to the trajectory once fired?

• Determining an orbit between two bodies (and the speed of that orbit at the start and end points) is called Lambert's problem. See my answer on physics.se. Feb 4, 2016 at 5:10
• Thanks, I think that is exactly what I was looking for. It looks like there is a Matlab package that does it: mathworks.com/matlabcentral/fileexchange/… Maybe there is something similar for R? Feb 4, 2016 at 8:33

You'd better install some RCS on your projectiles.

The problem is you need quite a bit of energy, accelerating your projectiles to something of order of 20-50km/s depending on alignment. And if your calculation program tells you you need to launch at 25746.32m/s it better not be 25746.28m/s or you'll miss. And keep the angle accurate to about a second (1/3600th of a degree) to keep the direction in check.

Planets are really tiny compared to the vastness of space. Just look at Venus or Mars on the night sky and imagine shooting that with a gun.

Unless you can correct in flight. Very weak engines can go a long way correcting all inaccuracies of the launch system.

Lambert's problem is good for two-body solutions. For case where you need to pass Mars, Earth, Jupiter's moons, and other bodies, you need a numerical solution. An example of a program to provide it is GMAT. You will also need Matlab to perform the actual optimization on top of mission planning.

The gravitational influences of so many moving bodies along the way are too complex to just obtain a neat equation for the trajectory, so instead it's done by simulating flight of the spacecraft and adjusting parameters by a small amount for desired result. (and that of course requires quite a bit of computational power).

• GMAT is free, and Matlab is not required (you can use solvers but not optimizers without Matlab). Feb 4, 2016 at 8:53
• @2012rcampion: Thanks. Edited the answer to include that.
– SF.
Feb 4, 2016 at 8:59
• What is RCS? I can't find it (I doubt it's red sequence cluster survey). Edit: O, did you mean Reaction Control System?
– user10509
Feb 4, 2016 at 12:29
• @JanDoggen: Try this approach instead. One reason why this question belongs on the Space Exploration site, and not Astronomy.SE
– SF.
Feb 4, 2016 at 12:33