Before we go.

This is your trusty interplanetary vessel, sitting on the tarmac at Cape Canavarel. It's fairly stylish, but it will feel rather cramped with 5 people inside during 9 months in space. Never mind. (If you prefer you can use any spacecraft with enough oomph to make the trip.).

Your launch date is all set - the plans can be found right here in this scenario. If you'd rather make your own, the launch date I'm using is MJD 51977.62 . If you want to figure out how to set your own launch dates, go here.

You will also need a  recent version of the TransferX MFD. You can't follow through the whole tutorial without it. You need version 1.1 or later.

One thing we need to do right away is set this rather everyday scene in context. We are used to thinking of the ground as stationary. It isn't. The Earth is bowling around the Sun at over 29 kilometers per second. Mars only manages 23. If we're going to Mars, our Deltaglider needs to slow down quite a bit.

On our trip we will escape from Earth, but we'll never escape from gravity. If you weigh 70 kilos, then Earth pulls on you with a force of 687 Newtons - a force your legs have to oppose all the time. But the Sun also pulls on you with a force of 0.4 Newtons. That's about the same force as you need to hold up a calculator. The only reason you don't notice this force is that you, the room you are in, and the whole planet you are on are falling under the influence of this gravitational force. Relative to the Sun, you are weightless already.

The planning stage

Putting it simply, our plan is to fly from one moving planet to another. Both planets move along different curves at different speeds. They are separated by tens of millions of miles of space, and a practical path between the two is typically 100 million miles long. Aiming for Mars over this distance is rather like aiming at a moving tennis ball a mile away from a moving car.

With the TransferX MFD, the first step is to decide on a plan for going to Mars. This should be done before any flying at all takes place, because that plan will influence when we take off, and in which direction.

The first thing we need to do is tell the MFD what we are planning to do.

Start the TransferX MFD by pressing Shift-J (think eJect). Then

  • Press MAJ (sh-M), and type 'Sun' into the input box
  • Press MIN (sh-N), and type 'Earth' into the input box
  • Press TGT (sh-T), and type 'Mars' into the input box

This tells the MFD that we are traveling between Earth and Mars, and that these two bodies orbit the Sun. Once you've done this, you'll see the orbits of Earth and Mars around the Sun appear in Green.

TransferX uses a colour coding scheme for orbits. Thin green lines like these are real planetary orbits. A more solid green line is the current orbit of your spacecraft. Yellow orbits and lines relate to hypothetical or planned orbits. And light grey is used to show the line of intersection between two orbital planes.

At the moment, not much of all this is visible.


Press the 'VAR' button (sh-V). When you do this, a variable will be displayed on the right of the MFD. Pushing the button repeatedly will cycle through various different variables. For the moment, the most important one is 'prograde velocity', which you should select.

You can adjust any variable using the ++ and -- keys (sh = and sh - on the main keyboard). You can also adjust the sensitivity of the MFD to your changes using the ADJ key (sh-J).

If you add a tiny amount of prograde velocity, the TransferX MFD turns on its targeting system. The yellow orbit represents your currently planned orbit. The grey line is the line of intersection between the plane of Mars's orbit, and the plane of your planned orbit. The yellow lines I'll come to.

Cl. App. and Enc.V describe the intersection between your planned orbit and the target planet. At the moment, they're not very meaningful as the two orbits are not even close to each other. Cl. App. is the closest approach distance, and Enc V is the velocity with which you'll encounter the planet. These figures are not going to be anything like accurate until we set up a proper intersection, which is our next task.

The first step is to increase the prograde velocity a bit more. The TransferX MFD breaks the velocity with which you'll leave Earth into three components. Prograde is the velocity along Earth's orbit in the same direction as Earth travels. Adding velocity in this direction is the most effective way to add to your orbital energy. Because of the extra energy, our craft will enter a higher orbit than Earth's, which is what we see here.

The other two directions you can add velocity are outward and to change plane, of which more later.

It's now easier to describe the meaning of the three yellow lines. The one on the left which only goes as far as Earth's orbit represents the point where the MFD currently thinks we're planning to leave Earth orbit. The other two represent the closest approach at the target. At the moment, our closest approach isn't terribly close - 36 million kilometres. Most of that is caused by the fact that we haven't set the point at which we leave Earth orbit correctly yet.

Press 'VAR' until the variable 'Eject Date' comes up. Use the ++ key to change this date from its present value until it's about a day or two into the future. We'll use the time between now and then to get into orbit and properly organised. 

I picked a good day to go to Mars for this scenario. You've probably noticed that the targeting of Mars has improved now that the Min. position has been moved. If you like, you can tweak it to minimise Cl. App. But you won't be able to get much below 6.7 million kilometres just using prograde velocity and the Min position. Our next job is to adjust some other aspects of our velocity when leaving Earth.


Select the Ch. plane velocity variable. This allows you to select how much velocity to use adjusting the orbital plane when leaving Earth. Adjust this in the positive direction until the plane intersection line is aligned with the rest of the intersection lines, as it is on the MFD opposite.

What this means is that the alignment of orbital planes should happen when we reach Mars itself. In practice it will all be part of the orbital insertion burn. Rolling this manoevre up with the orbital insertion burn in this way saves a LOT of fuel. It's the way that NASA flies this trip. Why shouldn't we?

Now is the time to adjust all the variables to get the best possible intersection. To do this, you can use the outward velocity variable as well as the other two. In my setup here, I've got planned closest approach down to 72,000 kilometres. Frankly I won't be able to fly my plan that accurately anyway. Anything under 1,000,000 kilometres is quite OK at this stage - there will be time for course corrections later.

In your setup, you should also be careful of the Encounter velocity. The figure given at this stage is surprisingly close to the speed at which you will actually encounter Mars later. And this speed is not good - the higher it is, the more rocket fuel you will use slowing down when you arrive at Mars. Don't let your projected orbit fly out way beyond Mars, and you should be OK.

This is particularly important for the inner planets. You can encounter giant planets much more sloppily with no real ill effects, but Mars is best encountered as slowly as possible.

The bulk of the setup process is now behind us. We've now decided on our plan for getting from Earth to Mars. Now we need to plan our route from Earth to interplanetary space

More setup, and (finally!) launch