Now we'll make some changes to the bodies in this system.
From the menu bar, choose Edit and then "Modify System". You'll see a dialog box like this appear:
If another body is showing in the top combo box, click on it and choose "Lost Satellite". Then click on 'Edit Body'. You'll see another dialog appear, like this:
In this dialog box you can change any of the information about the body. You can see that because we have assumed that this body is a man-made satellite, its mass is quite low (50kg). In fact, it has been designated as a "lightweight" object - that is, it is so small that Gravitorium doesn't bother working out its miniscule gravitational effects on the Earth and Moon, and is just concerned with how those large bodies influence it. This speeds up the simulation time.
You can choose to make an object "Lightweight" or "Locked" or both. Lightweight objects are accelerated by other bodies but considered to be too small to have a significant influence on major bodies and so can be left out of the calculation when working out how these major bodies will move. A spacecraft, for example, is far too small to influence the Earth in any detectable way.
A Locked body, on the other hand, has a gravitational influence, but is not itself accelerated. There aren't any such bodies in the real universe, but this feature can be useful in playing "what if" science fiction games by allowing you to approximate oddly shaped gravitational structures such as planes or rings.
You can change the object's mass or diameter here, rename it, or click on the hi-color and lo-color boxes to change the display colour for this object. Or you could change its position or velocity. (Note, though, that a more intuitive way to change an object's current velocity is to use the "Apply Delta-V" button on the first dialog box. More on this later).
When you are finished altering, click on "Done". Note that this action does not automatically save the changed system to your hard disk. You'll need to do this manually before you close the program or you will lose your changes.
If you select the 'Apply Delta-V' button on the first dialog box, you will see a simpler and smaller dialog box like this:
This dialog provides a simple way to add or subtract velocity to the object. In particular, you can simulate a spacecraft thruster burn by applying a set acceleration for a certain number of seconds (note, though that for calculational simplicity Gravitorium applies the resulting velocity change immediately, so it can't simulate a small acceleration being applied over a very long time as in an ion drive).
Try applying an acceleration of 50 metres per second per second for about 10 seconds (approximately 5G). Now click on OK and run the simulation again.