TransX - The eject function

This function is used when you wish to leave the current minor body. The best time to call it up is before you take off. If you are already in orbit, there are times when it is better to use the Orbit Eject mode instead.


In this tutorial we will be using the default 'Cape Canaverel' scenario that comes with the December 2002 build.

Variable reference

The Eject function has quite a few variables, and it's worth quickly running through them. These instructions all assume you're planning to leave Earth - if you're using TransX on some other planet, just substitute it in Earth's place.

Major view variables

Variables to set up your planned orbit

That's all the variables you need to specify an interplanetary transfer. But there are some other, less important variables as well, which alter your view of proceedings.

View adjusting variables

Minor view variables

None of these variables really make much difference to your interplanetary trajectory, but they can be useful for adjusting the first part of your trajectory - the part that's around the Earth.

Setting up your trip

Most of the planning work actually takes place before you take off. This is because the plan you create affects both your takeoff direction and time.

The first job is to tell the MFD where you are, and where you want to go.

  • Set REF to the big body that both your initial and target bodies orbit around. In this case, that's 'Sun'.

  • Set MIN to the body you're planning to leave. 'Earth'

  • Set TGT to the body you're planning to go to. 'Mars'

After you've made these adjustments, TransX displays the orbits of Earth and Mars (Mars is the outer one of the two). The green line indicates the current position of each planet.



The next stage is to set some prograde velocity. When you set even a little prograde velocity, the targeting system will switch on, and you will start to see some facts and figures about your planned orbit's closest approach to the target. At the moment those facts are that we don't get much closer than 100 million kilometers. We need quite a bit more prograde velocity.

Closest approach is in metres. As is usual in computing circles, K stands for 'kilo-' thousand, M for 'Mega-'a million, G for 'Giga-' a billion, and T for 'Tera-' a trillion. 107G is 107 billion metres, or 107 million kilometres.

Now we've added quite a bit more prograde velocity, and you can see the effect it's had. Our plan now misses Mars by only about 7 million kilometres. Much better, but still not quite there. The main problem is the inclination of our orbit. We haven't changed our orbital inclination at all, and so our hypothetical orbit will be coplanar with Earth's. Mars isn't coplanar with Earth, so we now need to adjust this, and get everything else tuned up.

As you can see, my hypothetical orbit doesn't go miles beyond the orbit of Mars. This helps to keep the velocity at which we will finally encounter Mars down to something reasonable. At the moment, TransX predicts our plan will have us reach Mars at 4.482k per second. And that we will get there when MJD is 52163.80

This is how my major view looked after I'd finished adjusting all the variables. The final figures I went for are:
  • Prograde 2.392k
  • Eject date. 91981.7625
  • Outward velocity 160
  • Ch. plane vel. 1.864k

As you can see, closest approach is now only 450 thousand kilometres. That's definitely good enough. As you'll see, I can't fly accurately enough to make it worthwhile setting the trajectory any more precisely at this stage.

Next: Setting up the minor view

Orbiter Mars - (C) Duncan Sharpe 2003