Flight Question Choosing a Departure Date

[DanM]

I'm trying to figure out interplanetary flight, so I'm doing a simple, one way, HTO Mars Flyby in the stock DG. My apopsis will be roughly Mars's Semi-major axis. I calculated that it will take me around 8 months to get to the apopsis, thus, 8 months to Mars. However, I'm having trouble calculating my burn date. Right now I believe that since I'm using the HTO route, I should leave Earth around 8 months before Earth-Mars Conjunction. Am I correct on the burn date?

 

[Tex]

You could add some prograde velocity in TransX till your hypothetical orbit reaches Mars orbit, then advance the date variable forward until you find the next launch window (closest approach). This will give you an exact eject date.

 

[DanM]

I am probably not going to use TransX, I'm taking a more mathematical approach. My question was more if my method of determining ejection date is accurate.

 

[garyw]

This spreadsheet will help. It has the hohmann departure dates for all the major planets for about the next 100 years. It's a useful place to start when checking for launch windows and the forumla may help.

 

[Tex]

I am probably not going to use TransX, I'm taking a more mathematical approach. My question was more if my method of determining ejection date is accurate.

I realize that, but I was simply offering a way you could confirm the eject date while playing Orbiter. :thumbup:

 

[Tommy]

Mars has a very eccentric orbit, so the trip time will vary quite a bit depending on where the Mars Intersect occurs. For best efficiency, try to intercept Mars near its Periapsis.

I do know that the stock "DG-S ready for Launch" scenario starts right at a very good window for a Hohman transfer to Mars.

First let me define two lines, one that starts at the center of the Sun, and passes through the Ejection Point (Ref Sun). The other starts at the center of the Sun, then passes through the Intersect Point. For a Hohman Transfer these two radials will be 180 degrees apart. You want to leave Earth at a point where Earth is six months away from the Intercept Radial, and Mars is 8 months (a better estimation of actual trip time should be used) away from the Intercept Radial. Note that this Intercept Radial will NOT be a conjunction - the Earth will have passed the Intercept Radial before Mars gets there (in fact, it will be (Trip Time) - (6 months) before Mars.