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TGO

Posted 03-29-2016 at 03:32 PM by lzakelj

Quote:
Originally Posted by BrianJ View Post
Thanks Barry.


Hi,
yes, the launch is a challenge, there's not much (if any) dV to spare and the "Briz" 4th stage thrust is comparatively low, so the burns are long and you need them to be as efficient as possible. As far as I know, we don't have any trajectory planning utilities for Orbiter that can handle multiple-burn trajectory plans (possibly TransX can do that? Maybe a TransX expert can enlighten us).
So here's what I do for the Mars Transfer injection using IMFD. From the 175km parking orbit, set up IMFD Course "Target Intercept" and IMFD Orbit Eject as you would for a single burn. Note where IMFD Orbit Eject shows the burn point, you need to keep your periapsis near that point.
Then, I open another IMFD window and plan the first apogee raise burn using IMFD Course "Delta Velocity" for a simple prograde burn to raise the apogee but keep the periapsis where you need it.
N.B. Don't use the "autoburn" function , even in "unshared" mode IMFD will try to use the IMFD Course "Target Intercept" parameters, not the "Delta Velocity" parameters that you want. Just start burning prograde when IMFD "Delta Velocity" says to start.Same for the second apogee raising burn.
For the final escape burn to Mars Transfer trajectory, you still can't leave everything to IMFD Course "Target Intercept" and IMFD Orbit Eject because the burn is so long (and IMFD Orbit Eject uses an instantaneous impulsive burn type calculation). So, note the burn-time-length as planned by IMFD Orbit Eject, and start burning prograde 1/2 burn-time-length before the IMFD Orbit Eject planned burn start time. When you reach the IMFD Orbit Eject burn start time, you can hand over to the IMFD autoburn function and let it finish the burn.
I still had to use 50m/s dV from TGO after separation, to make up shortfall, but I did fluff the first apogee raise burn a bit.
Hope this helps!
Cheers,
Brian

---------- Post added at 12:05 PM ---------- Previous post was at 12:00 PM ----------


Thanks fred :-) Multistage2015 does a good job of getting the Proton to parking orbit. What kind of telemetry info would be interesting for you?

thanks brian you rock :-)
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