Flight Question Using IMFD to Mars - why can't I lower oV

[Genesis27]

Hi there,
I'm following a IMFD playback "Earth to Mars"...trying to learn to fly to Mars using IMFD...and it says to adjust MJD under TEJ to try and lower the oV figure...now I should be getting something like 3400-3500k...but I mine doesn't even move down...it only goes up..at the moment it is 9179 and I can't get it any lower....any ideas why it will not go down ?...I've followed everything so far...Mars as Target, Locked-TOF...but now I'm stuck...help !!!

Hope you can see the attachment

 

[mc_]

It is better to use the "tangential transfer" program to calculate launch window first.

 

[Genesis27]

Hi...thanks for getting back with a reply..how would I do that?...what would I have to do?

 

[STS]

You can´t lift off to mars or another planet or moon or satellite whenever you want. You have to calculate a Launch Window. One idea is watching the target planet´s position and the origin planet´s position in the solar system.

 

[Wishbone]

Search for Trajectory Planner by Piper on the OHM and for Low-Thrust Trajectory Planner by same here. Launch window is very very visible in Traj planner.

 

[dgatsoulis]

Hi there,
I'm following a IMFD playback "Earth to Mars"... I've followed everything so far...Mars as Target, Locked-TOF...but now I'm stuck...help !!!

...No, you haven't "followed everything" so far.

At the begining of the tutorial it says:

Load a default Orbiter scenario "Delta-glider/DG-S Ready for Takeoff"

.
That scenario has a Deltaglider-S on the runway at the Cape, on MJD 51982.68 (March 14th 2001).

That date had been chosen by the tutorial publisher, because that was a [ame="http://en.wikipedia.org/wiki/Launch_window"]Launch window - Wikipedia, the free encyclopedia[/ame] for Mars.

The pic you posted has the scenario set on MJD 55199.730. (January 3rd 2010).
Not the ideal date to launch but still, you should be able to get the oV down to 3810 m/s if you unlock your Time Of Flight (TOF) and push your Time to Intercept (TIn) to MJD 55655.510 (April 4th 2011).

For now, just load the correct scenario and try to follow the instructions. The tutorial you are reading is a great one and you will be able to make Interplanetary flights in no time at all.

Have fun, happy orbiting

 

[jambooger]

First set the adjustment to X10 maybe even X100 then adjust Tin forward and watch Ov and the total. They will begin dopping. Keep adjusting untill the figures begin to rise. Then move the adjustment step down to X1 and fine tune so to achieve the lowest Ov.

Im sure this is not realistic but works well for me

 

[Tommy]

I'm not sure what tutorial you are following, perhaps it's the one from IMFD Full Manual/Playbacks? If so, the process described will work to find an actual launch window no matter what the starting date of the scenario - if you follow that process correctly.

What I did notice is that in your screenshot TEj = 0. That means you plan on leaving "right this instant". The date you are at is NOT a good launch window, and that is why the oV is so high. You need to INCREASE (NOT decrease) the TEj. This is easiest by adjusting the MJD variable underneath the TEj, and if you use 10x adjustments it will increase by one day per click. Please note that you can still decrease the MJD under TEj even when TEj = 0, this will have the effect of shortening the TOF leading to a higher dV and reduce the accuracy of the resulting plan - so make sure TEj is ALWAYS greater than zero.

Keep in mind that you may need to increase the TEj by several months. oV ,may increase, decrease a bit, and increase then decrease again before you get oV down under 4k. Using the net to find a launch window first will help avoid some of that.

Also, while it's not a big deal, I prefer to look for the smallest Total dV, not just the lowest oV.

As for using Tangential Transfer to find a window, it may get you in the ballpark, but the windows for Off-Plane transfers aren't exactly the same as for Tangential Transfers. I'm the one who came up with the process described in IMFD Full Manual/Playbacks - and it does work, every time, if used correctly.

 

[Genesis27]

Thank you so much everyone..I really appreciate your comments, and it's so good to see that there are people on here who are willing to help others like me who are still learning....I shall take onboard (no pun intended)..everything that has been said and see if I can get adjust the IMFD...thank you guys...and happy orbiting...Kind regards, Trevor