the two known planets. The orbits were stable, with the planet closest to 55 Cancri causing the star to make a small orbit of its own. I then ran the same simulation with the third calculated planet, and the system was still stable with the third planet having a slightly elliptical and off center orbit. (You can find more information about the planetary system around 55 Cancri here:  One of the features I found very interesting, is the “Activities”. These consist of 28 pre-programmed simulations that show such things as a rocket launch, gravity assist, and double star systems. Some features are of less obvious use, for example the “Catch that Satellite” and “Two colliding stars.” The help file is adequate, but could use more, maybe something that will tell you why something happened in a simulation. I noticed three problems other than the accuracy. Sometimes when you zoom in to the maximum setting, the program will shut down. When I ran the simulation overnight, I could not operate the zoom with the short-cut keys. Strangely, the Sun, planets, and our moon were pre-programmed into the program to use in your own simulations - yet it neglected to include all of the orbital data for them, which makes the program harder to use (such as setting up a simulation of our solar system). Other than this the program was error free. Aimed at personal users and the educational market, this program is a good deal for the money, especially for schools. It requires only a little knowledge of astronomy and physics/math to run and understand the pre-programmed simulations. Creating your own simulations (such as extrasolar planetary systems) requires more skills, but any dedicated user should be able to figure it out.

• Product:Orbit Xplorer
• Relevant Links: homepage
• Company/Vendor: Tore Ottinson
• Price: $25 shareware, $90 site license
• Category:Physics
• Platforms:Windows 95/98/NT/2000
• Requirements:Windows XP, Vista
• Latest version:2.2.1.0 (January 2009)
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The complete review- There's nothing more fun than playing God, and here's your chance to do it!Orbit Xplorer allows you to design and alter your own solar systems... but it's more than that. ScienceMan can see this program being of considerable usefor examining gravitiational interactions. So how do you use orbit explorer? Well, it's really not that hard, but I wouldn't recommend this program for younger students. They would definitely be intimidated by the parameters screen for configuring your interactions. Originally I was hoping to be able to recommend this simulator junior high courses, but after having played with it for awhile, I think it's more appropriate for high school and college students.Anyway, after choosing how many objects you want in your simulation, simply click on the simlulation tab and watch your perfect simulation take effect;... ooops! Heh, heh. Well, maybe it's not all that easy. It would probably be wise to study the parameters screen first. The settings are fairly straightforward. Choose how many objects you would like in your simulation, and the spreadsheet adjusts accordingly. You can choose to enter parameters for all of your objects from scratch, or you can drag and drop the pre-configured "objects" such as the Earth and the Moon into the spreadsheet and all of the fields will automatically fill.There are a lot of other powerful features included in the parameter screen as you can see. View your sim from different perspectives, changing the scale allows you to zoom in or out, choose to see coordinates, stars, etc. The program includes just about every setting you could want. So now you're ready to build a real WORKING simulation!  

As you can see, you can choose to track the orbit, and create projections as well. Cool! It should also be noted that the program also allows for the display of cool NASA images of the planets as well as a beautiful starry background image. The other excellent feature of this program is the ability to control and measure many aspects of the simulation. You can speed up or slow down the sim, you can call up graphs for position, velocity, acceleration and energy for all of the objects, or view these measures as digital readouts on-screen as the simulation takes place. To top it all off, included sample simulations will have you learning in no time! Interesting problems are addressed in the html format activities; ScienceMan thinks this is a great program, and it is certainly economical. Junior High students would likely become quickly frustrated with having to jump between the parameter and simulation screens, so I wouldn't recommend this program for younger students. But if you're looking for an orbital simulator for your senior high or even your college level class, you will definitely get good use out of Orbit Xplorer! 

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