Jump Temp – Entering and Exiting Star Systems

If a ship’s pilot wants to leave a solar system, there’s a navigation challenge to plot a course out. A common misconception is that you’d simply point the ship away from the star and start the engines.

In reality it’s not that simple. If you look at the Cassini space craft’s flight path, it actually takes a dive toward Venus before heading into the outer solar system. Looking at any space probe’s flight path thats been launched, we see a spiral flight path. Why is this? Isn’t a straight line the shortest distance between two points?

Theoretically a straight line might be the shortest, but unless you have an unbelievably powerful drive system, it’s wasteful and likely impossible to do.

For another example, if you watch a rocket launch, you ‘ll see the vehicle curve as it flies upward. This was more evident in old space shuttle launches. The roll and the curve of the take off was easier to notice. Why not just fly straight up? For one, if the rocket went straight up it would not enter orbit. It would launch up into the air, possibly making it into space but would then fall back to the earth once it’s fuel ran out. By moving sideways on it’s ascent, when it starts to fall it misses the earth and thereby enters orbit.

If the target is another planet in the star system, it must be moving fast enough to miss falling into the star it is near. This falling toward and missing is how things orbit.

In a similar way, we are orbiting the sun. If a spacecraft were to fly straight away from the sun, it would start to fall back towards the sun as soon as it’s engines were shut off. The further out the space craft traveled, the slower it would fall but it would none the less fall.

Another reason to follow an indirect path is to intersect with planets and other large gravitic bodies that the craft can steal a little momentum from and use it to speed the vehicle up without using its fuel. This gravity assist is crucial for any vessel that has a fuel supply that isn’t infinite. Although it seems strange that Cassini should move away from Saturn so it can get to Saturn faster, flying in an indirect path is the faster and more efficient.

My one player commented how flying out of a system isn’t rocket science (no really, those were his words). I laughed and answered “It absolutely is rocket science. It’s more complicated than it sounds.”

Ships in Jump Temp would never fly directly away from a star, and might occasionally drop toward the star to get a gravity boost from planets. Falling closer to the star in the middle of a system cannot be used for a gravity assist but can be used for an Oberth effect which is a little complicated but if you’re curious, you can check out  on Wikipedia.



5 Replies to “Jump Temp – Entering and Exiting Star Systems”

  1. Apropos of very little (except all this discussion of orbits), I’ve been idly contemplating a slightly-harder-sf hack of Jump Temp, set entirely within the Solar System and eliminating aliens and jump drive. In this schema, spacecraft travel between the various inhabited planets, moons, dwarf planets and KBOs of our system, and the cylinder-colony swarms around many of them; “jump temps” are skilled work-for-passage hirees from the Cylinders who sign on for a given Long Jump (I.e. transit) between planetary orbits, trying to either get somewhere else or earn a permanent paid berth. Probably no rule changes at all.

        1. Let me go and see what I have in the back room. . .

          I have a tiny bit publishing know how and a few tricks I can offer. But if you want text, art or someone to bounce ideas off of let me know.

          1. …huh, this I didn’t expect. Actually, text is the one thing I *would* be good for; frustrated failed writer here. 🙂

Leave a Reply