TransX TransX to Mars - unexpected escape trajectory

[MetalMania]

I Recently completed my first Earth to Mars flight with TransX, I followed a tutorial (don't recall whose at the moment). I followed the directions and set up my escape and cruise plans, but what surprised me is the initial orbit and Earth escape trajectory. I kind of expected to orient more or less aligned with the ecliptic with a slight plane change direction to match Mars - thinking that most of the planets are generally aligned in this plane. But instead TransX had me launch into a near polar orbit. So, I made my ejection burn as it was set up and went on my way. As I was watching the Earth get more distant with the south pole facing towards me I was thinking "this just doesn't seem right". So I'm picturing my trajectory going "under" the ecliptic plane and on track to intercept Mars from the south into another polar orbit. That seems to be pretty much what happened, I made a few small correction burns along the way and ended up in a near polar orbit of Mars.

Is that normal for TransX to work out a wildly "out of plane" intercept like that? I realize that I'm the one setting the variables, so technically I guess I'm the one setting it up like that, but it was my first time using it and didn't really recognize how it was actually shaping up until I started flying. So I guess my next question would be: if I wanted to make sure it was setting up an "in plane" transfer, what do I need to look for? My main purpose in the flight was to learn how to use TransX, at least in a basic sense. To that end it was a success, but I guess I was just kind of blindly following what it came up with. I'm sure it can be made to set up for a flight profile that one has in mind though.

 

[flytandem]

Congrats on a very successful first TransX trip.

Departing with a very inclined orbit can be normal. It depends both on how much plane change your plan has, plus on the eject orientation used when planning the launch heading. You can also arrive over a pole at Mars for the same reasons.

 

[atuhalpa]

Did you start your flight by reducing your relative inclination to zero before your trans martian injection burn? Also when you set up your flight plan with transX, if you adjust the change plane variable so that the white line (which is the line of nodes where the plane of the two orbits intersect) is approximately halfway between the injection and insertion points, you can make a plane change maneuver using the align plane MFD at that node. If you do this correctly you can insert yourself almost perfectly into Mars' ecliptic plane. There might be a discrepancy between the Rinc (relative inclination) being as low as you can get it and the node for the plane change being halfway between injection and insertion before the burn, but for educational purposes try the halfway there plane change maneuver and see if you like it.

Does this make sense? This may not be the most economical flight plan but it will help you to conceptualize interplanetary maneuvers better.

 

[MetalMania]

I did have a RInc of 0.05 if I remember correctly, but that was relative to the planned trajectory (I think) rather than Mars orbital plane. I rotated the eject orientation as directed in the tutorial to "as close to 90 as possible", which ended up not being very close at all. If I'm understanding you correctly about the placement of the white line, do you mean setting it basically at the mid point of the flight (injection point being the burn to escape from Earth and insertion being the point of Mars intercept)? If that is what you mean, then no - I had it set to overlap the ship and Mars position indicators where they met, which is what I thought you were supposed to do to get a reasonable Cl Approach value. If I'm following what you're suggesting conceptually, if I set the white line in the middle at first I'll probably have a very big Cl Approach value but it will get way closer after making the plane change mid course with the Align MFD? I haven't used IMFD yet but I've read a little bit of documentation for it - this sounds like one of the optional flight profiles you can select (off axis, two plane, or something like that)?

 

[atuhalpa]

I never use eject orientation. I use launch mfd to set up my launch altitude and inclination. Once I am in orbit and reasonably close on my relative inclination I then use transX to set up my burn getting as close as I can using only the prograde velocity variable. Then I set change plane to get the white line at least out of the sphere of influence of the earth. Then I burn my ejection and once I'm on my way I use align plane MFD to change my plane when I get to the node(two plane). I know there are more efficient ways to get to Mars but I am just explaining to you how to slide in to Mars within +/- 1 degree of Mars orbital plane. Once you get your plane aligned then it is really easy to use the outward velocity variable in the maneuver mode to correct your course.

Yes, you are understanding this conceptually. Yes, If you set the change plane variable to get the line to coincide with Mars and your ship's trajectory that means that the node of your ejection/orbital plane and Mars orbital plane will coincide when Mars is at the node, but it also means your orbital plane is completely out of either the Earth's orbital plane or Mars orbital plane(off plane). It really isn't consequential if it is out of the Earth's plane but since it is out of Mars plane it makes course corrections problematic because you must use all three vector variables (outward vel, prograde vel, and change plane vel) to do your course corrections. This is tedious and frustrating. Once you are in plane all you need is one variable, outward velocity and you are there. You might use prograde vel. also but I find that I usually only need outward vel. to nail a destination if my initial ejection burn was close.

 

[MetalMania]

Thanks, that makes sense. So I guess what I could do then is find a launch window with TransX or other appropriate tool, launch into orbit aligned with the ecliptic, use TransX to calculate the eject burn but keep the eject orientation aligned with my current ecliptic orbit (thus meaning I think that I just leave it alone). Then if I set the node to be halfway or wherever along the trajectory, since my ecliptic plane orbit shouldn't be that far inclined from Mars' plane the Alignment burn shouldn't be very big and I'll be in good shape for an in plane approach. I didn't find the correction burns to be too big of a deal the first time, but you're right - I did have to mess around with all the variables a little bit each time and I did make several small corrections. Now I just need to find out how to do a re-entry in the Delta Glider.....