- Dec 2, 2009
- Reaction score
First, I can't reproduce the 1.72km/s delta-v for the eject burn to earth. The best solution I can find around the date 60616.5 is at least double the delta-v, around 3.450km/s.
You should be getting ~3.150 km/s from a ~150 km altitude parking orbit around Mars, which agrees with the trajectory planner's deltaV expenditure. Here is why:
The 1.72 km/s has an asterisk with the explanation: dv from C3 = 0 km²/s². C3 = 0 is equal to the escape velocity, which is √2 times bigger than your parking orbit velocity.
So if you want to calculate the dv for the Trans-Earth Injection burn:
DV _inj = 1.72 + √2*V_po - V_po , where V_po is the velocity of your parking orbit (assuming circular), in km/s.
For an altitude of 150 km above Mars' surface, your V_po is ~3.48 km/s so plugging in this number in we get: 1.72 + √2*3.48 - 3.48 = 3.16 km/s
This agrees with 288 day transfer from Mars to Earth -eject date on 60616.5- with a hyperbolic excess velocity of 4.45 km/s (oV in IMFD's Target Interecept program).
You can calculate the Injection dV from IMFD's oV (outbound Velocity?) with: DV_inj = sqrt(2*V_po² + oV²) - V_po, where DV_inj = injection deltaV, V_po = parking orbit velocity and oV = hyperbolic excess velocity from IMFD.
Plug in the numbers and you get : sqrt(2*3.48² + 4.45²) - 3.48 = 3.155 km/s
The second problem is that I can't find a return trajectory which aligns me for a direct entry for Cape Canaveral. The 'Map Method' (Delta Velocity course program combines with the map) doesn't work in this situation. I think it's because the return trip crosses earth's orbit before the real encounter. It seems to me this messes up the possibility to use the map method. Not sure though.
I am not sure what you mean with "a return trajectory which aligns me for a direct entry for Cape Canaveral". Any arrival at Earth with an equatorial inclination higher than 28.5° should be able to get you lined up with the Cape. If you are aiming for a day-side arrival and want to hit the atmosphere ~45°-60° away from the Cape, already lined up, it should be doable, but will take some refinement during the MCCs on the way back. There are some cases where this isn't possible, so you can try a night-side skip reentry, to get captured and land on your target when you are both on the day-side.