Journey To Mars: Interactive Computer Program

The main program panel on the left displays the positions of the inner planets on any date between January 1, 2000 and September 18, 2019. To help with your planning, you can click near a planet in this panel to get the position of that planet in degrees past the vernal equinox. The panel on the right lets you adjust a number of parameters that affect the display. Below are details about the panel options:
All Sliders: Click at 1. and drag left or right to increase or decrease the value by a significant amount. Click or click and hold at 2. to increase or decrease value by a small amount.
Use the Display Date slider to set the display to any date between January 1, 2000 and September 18, 2019. The yellow number in the upper left is the number of days after January 1, 2000. The Display Speed slider will start the planets moving at one of five different speeds. Move the slider all the way to the left to stop the display. The Show rP checkbox will enable and disable lines from the sun to the perhelion of each orbit. The SC Orbits checkbox will enable and disable display of the orbits of your spacecraft as you plan your journey to Mars.
To start your journey to Mars, set the Departure Date to a date when you want to leave Earth. Next, increase the Departure Orbit until it's aphelion radius (rA) extends up to or past the orbit of Mars. By default, the program assumes you want the space craft to go directly to Mars. If you want it to go past Mars orbit then connect with Mars on its way back in, uncheck the Intersect box.

Manually change the Display Date to some date after your Departure Date. The white dot indicates the position of the space craft on that date. Experiment with different Departure Dates and Departure Orbits and adjust the Display Date to see the results. Continue until you find a Departure Date and Departure Orbit that will get the space craft to Mars.

The Energy Budget in the lower right shows the changes in space craft velocity on the various days of the journey (leaving Earth, getting to Mars, leaving Mars, and getting home). Initially only the departure from Earth is shown. Once you find Departure Date and Departure Orbit settings that will get you to Mars, that point in the journey will be added to the Energy Budget. Watching this area is the easiest way to see if the Departure settings you are trying will work (i.e. if your settings won't get you to Mars, no budget lines will be added dealing with Mars). The total delta is the sum of the absolute value of all of the orbital velocities required. This does not include the energy required to take off from Earth, land on Mars, take off from Mars, and land on Earth. The energy required to do all of that is constant for all possible journeys. To more closely approximate the real energy cost, add 32.6 to the total delta you get for your journey.
Once you get to Mars you will need to find a Return Date and a perihelion radius (rP) for a Return Orbit that will get you back to Earth. Use the same procedure you used to find suitable Departure settings. Remember to try orbits that intersect Earth orbit on the way in and the way out. When you find settings that work, the Energy Budget will be updated to show you all of the velocity changes for the entire journey. Again, watching Energy Budget area as you try different Return values will let you see which values will work.
Bon voyage!