(click above to download joy.zip, 379 K download, an archive containing the current version of JoyRide.exe. This program is a Visual Basic tool for Windows, that lets you play with designing your own spaceship - or even a fleet!)
The "FUEL" menu: This lets you pick the specific impulse (ISP) (in the rocket equation "c" is the exhaust velocity; the ISP is used here, a value that in English measurment terms = c/32.17) from values for well-known fuels. A table of various fuels and their respective ISPs is also provided:
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A graph is also provided showing the wide range of ISPs and accelerations possible.
There is a table of the major bodies in the Solar System.
A tool for calculating delta-vee's needed to get around the Solar System has been added:
For crewed missions, you can calculate the amount of mass (crew and supplies) required:
These screens all provide data to the main design window:
1) To orbit
First, decide on a weight for your empty ship, the payload you want to get into orbit. Let us say 2000 pounds. Enter 2000 in the Payload window.
Next, put the orbital velocity (your needed speed) of 25000 in the delta vee - assume drag will cost you an extra 5000 feet per second, so change it to 30000.
NOW - are you launching this with gunpowder? Put in the ISP for gunpowder (use the fuel drop down 'black powder').
PRESS 'update' by the GLOW (gross lift off weight), to see how heavy your rocket would be. OVER 3 BILLION POUNDS? Not too practical.
Change this - lets say your rocket can't weigh more than 6000 pounds.
WHAT fuel do you need?
Change GLOW to 6000 and press 'update' by the ISP to find you 'only' need a fuel with an ISP of around 849. The 'propulsion concepts' chart under the fuel window shows that you'll need something like a thermal fission rocket.
2) To the planets
Let us say your rockets have been hauling material to orbit, and you are building a ship to go to Mars. The ship, at Mars, when empty will be 5 tons, or 10000 pounds.
First you need to know how much speed you need. Under 'planner' choose Orbit Calculator. You can enter planetary destinations from the FROM and TO menus. CALCULATE HOHMANN ORBIT calculates the one way trip. Assuming you want to go home, click ROUND TRIP to double the speed requirement. This is in MILES per second, but it updates the main screen in terms of feet per second.
Back on the main screen, choose your fuel, say alchohol/oxygen, from the fuel menu. Then press UPDATE on the GLOW window and you'll see you need a fueled weight of over 622,000 pounds.
If you think your spaceship can't be over 20000 pounds, change the GLOW value to 20000 and press UPDATE on the ISP. This says you'll need and ISP of over 1700. Check the PROPULSION CONCEPTS and you'll see you are going to need Ion engines, laser/solar or thermal fission.