New Release IMFD Full Manual

[thammond]

Thanks for the help guys. I think the light is starting to come on. A stumbeling block I was having was trying to figure out how to get to the correct TEj point (for an orbit eject) A defined in the target intecept program.

But correct me if I'm wrong, the target intercept is more like a rough order of magnitude planning tool to help you get into a parking orbit at about the correct time and inclination to setup an orbit eject program.

Tommy the explanation about the surface launch was very helpful.

 

[Tommy]

But correct me if I'm wrong, the target intercept is more like a rough order of magnitude planning tool to help you get into a parking orbit at about the correct time and inclination to setup an orbit eject program.

You could look at it that way. Target Intercept creates the course, Orbit Eject puts you on that course. The TEj in Orbit eject should be within one orbital period of the TEj in Target Intercept for best results, but there's room for error. The relative position of the source and target bodies rarely change very much in a few hours time, so any error from deviation in eject times is within the reasonable tolerance limit, even less than the error from limited numerical resolution in a digital simulation sometimes.

Of course, Target Intercept does more than provide info to Orbit Eject, it's AB is used for mid-course corrections and plane changes enroute.

 

[markl316]

The reason he didn't wait is because Europa, like most moons, is tidally locked with it's parent planet. The same side of Europa always faces Jupiter.

Well...kinda.
I didn't bother waiting because TIME will tell you when to launch to acheive minimum RInc or EIn. Because I launched from the equator of Europa, thus putting me in a zero inclination orbit, and since Europa is inclined perfectly (not perfectly but perfect enough for our situation) to Jupiter's equator and so is Callisto, no matter when I launched, I would always have an EIn of zero.

 

[Tommy]

Didn't know where you launched from, that was another good reason. That's the thing with moons - if you have good alignment you always will, and if your alignment is bad waiting won't help much any time soon. At best you may get a "better" alignment once per moons orbit, I think.

 

[jedidia]

sorry, I was so hooked up with coding orbiter galaxy lately that I completely forgtoo that I put a question up here...

was the program not giving you a consistant solution

Yes, that's exactly it. Also, I couldn't change the target (was set to ecliptic, couldn't change it to equator. It just stayed at ecliptic). The ref was set to Titan, yes.

Yes, the flashing between several solutions is a problem sometimes. As stated in the do's and dont's, IMFD will not work perfectly 100% of the time. Sometimes that happens to me, it happens to everybody. As you get closer to the planet, it may or may not get better. This will happen maybe 1 in every 20 flights.

Well, not much damage then. I didn't fly since then, so I couldn't say wheather or not the error was reproducable.

jedidia, you said "neither 5.3 or 4.2" worked. I think you probably meant 4.2.1 on that last one, just wanted to be sure.

yeah, it's 4.2.1. It just seemed strange that it wouldn't work in any of them at the same time. Oh well, there's still Orbit MFD, but it can get pretty tough to guess when to start burning when coming in with a velocity that was high enough to get you from earth to Saturn in only one year, with them being in opposition. But, there's still quicksave.

 

[markl316]

Hey jedidia, if you could post a scenario file so I could troubleshoot that would be great.

Mark

 

[jedidia]

Hmmm, I just observed something weird with the Delta-V program.

I' experimenting with Low-thrust high-Isp flights, to see if I could come up with a decent solution of the problem with the current tools. The Delta-V program seems to do a good job, but for one strange occurance:

If I set up a course with the Velocity frame setting and follow the burn vector through the burn, I end up on a course that matches exactly the precalculated course for my inputs under the P30 LVLH program, meaning pretty far of from the course I amied for with the velocity-frame.

If I plot the course with P30 LVLH, And follow the vector, I end up exactly with the course I plotted. So it seems that the burn vector is only valid for P30 settings, making the Velocity-frame effectively useless.

It's not too bad, since one can still plan a very precise course under P30 LVLH, but it's a lot less intuitive to work with than the velocity frame.

Has anyone else encountered this problem, or is it possible to fix this with some configuration options?

Or, for that matter, what does P30 LVLH actually mean, and how do the 3 Delta-V parameters work with it?

 

[Tommy]

I'm not sure what you mean by "P30 LVLH" program. P30 LVLH is a burn mode. It orients the vessel in reference to the global frame, rather than the velocity frame, and is designed to emulate the Apollo burn methods which used the global frame. Check Mark's manual for the section on burn modes to get a better understanding of the difference between thee two modes.

Either way, you should end up on the same course.

 

[jedidia]

Thanks for pointing out that P30 is explained in the manual under burn guidance modes. I see the differences now, and I have a suspicion to where the trouble lies.

As for understanding my problem, open two IMFDs, open the Delta-V program in one, link the other to it and open the map program. Now plan some really long burn (my burn lasted three Ms), and look at the course in the map display. Then switch the guidance mode in the Delta-V program to P30 LVLH, and you will see that the course in the map program changes severly. If you switch it back to Vel.frame and do the burn following the Burn Vector, you will end up with the exact course that was displayed in the map when you switched to P30, NOT the one that was displayed when in vel.frame mode.

As I said, when you plan the course with P30 guidance mode, you will end up with the course you programed. Just that in P30, it's a bit tougher to program, because Vf, Vo and Vp are relative to a global frame, and not necessarily to your actual course...

 

[Tommy]

Just that in P30, it's a bit tougher to program, because Vf, Vo and Vp are relative to a global frame, and not necessarily to your actual course...

Not quite. The ships attitude is oriented to the global frame, but Dv values are calculated in a local vertical frame, based on the ships estimated position at TEj = 0.

There are two main differences between P30 and velocity frame. P30 is reverenced to a body (the reference body selected) and velocity frame is referenced to the velocity vector. Also, in P30 DVp is positive in the orbit anti-normal direction, while in velocity frame it's positive in the orbit normal direction. Note that sometimes IMFD will show a DVi instead of a DVo - it's just the opposite. So, in P30, the DVi vector points directly at the reference body's center, and in velocity frame it is generally towards the body, but always perpendicular to the velocity vector.

Of course, none of this solves your problem. Delta V program uses off-axis burn mode, which doesn't do burn integrations. I suspect the burn is simply too long for Delta V to calculate correctly - especially if you are starting in LEO. If you've used a higher thrust engine to escape Earth, just use the Sun for a reference body and P30 mode should actually be easier than velocity frame.

It might help if I knew what ship you are flying, and what you are trying to do.

 

[jedidia]

It might help if I knew what ship you are flying, and what you are trying to do.

Trying to get from earth to Saturn as a first experiment. I'm using a revamped deepstar, that weights a 1000 tons empty, has 350 kilogramms of propellant and an engine with a Ve of 1e6 m/s and 55kN thrust.

I'm also using IEATmfd for attitude hold and orbit eject.

The procedure is as follows: starting in LEO, I eject in the general direction of saturn using the escape autopilot of IEATmfd (after manually adjusting the periapsis). Then I drift out of the earths SOI, fire up the DV program and set up a burn of about 100ks Delta-V towards saturn, that takes 3Ms to complete.

Of course, none of this solves your problem. Delta V program uses off-axis burn mode, which doesn't do burn integrations.

I think you're wrong about this one. from the manual:

This method (PG) OR Off-Axis Mode is a good choice in many long burn situations.

Plus, as I said, I end up with a perfect trajectory IF I do it in P30 guidance mode (at least TO saturn, arriving there might just get a bit trickier. I haven't reached so far yet...) It just takes a little time to get used to it.

Thanks for pointing out the differences between P30 and Vel.Frame. That should help me getting more familiar with it.

 

[Tommy]

Delta V program uses off-axis burn mode, which doesn't do burn integrations.

The IMFD manual that comes with IMFD states explicitly that off-axis is the only burn mode available in Delta V, and this cannot be changed.

 

[jedidia]

sorry, little misunderstanding here. No, the off-axis mode cannot be changed. However, the manual says that off-axis and prograde guidance modes are the best for long burns, so I think it should do burn integrations?