General Question Orbiter noob - Lunar orbit and Transfer MFD questions

[MetalMania]

Hi All, first post here. Just getting started with Orbiter, I've been following Bruce Irving's "Go Play in Space" as my training manual. I've most recently completed Chapter 4, which is a tutorial for launching the DG into LEO and setting up a lunar transfer, landing at Brighton Beach. I've watched the replay and flown the mission manually a few times - my initial LEO parameters and final base approaches are still kind of sloppy, but I'm making it so I guess that's good progress.

Anyway, I know TransX and IMFD are the tools of choice for interplanetary voyages for many if not most people - but for the moment I'm trying to keep it simple and get my head around the standard Transfer MFD. For Earth - Moon transfers it's simple enough. On 2 of my 3 flights I set up the HTO and accomplished the TLI burn with no problem, however on 1 of them something weird happened. I set up the HTO as usual, but when I started the TLI burn the HTO graphic went off the chart and my DV didn't count down. I had no queues for MECO other than eyeballing the real orbit growing until it crossed the lunar orbit circle, it wasn't a very good transfer to say the least. Anybody have that happen before? Just wondering if it was a bug or if I did something wrong - though I don't think so because it worked fine 2 other times and I don't think I did anything different. I know I didn't accidentally turn off the HTO display, my Dv and Tle, etc were still there, the Dv value just never changed and the graphic representation of the HTO just instantly blew right off the screen as if I had instantly added a ton more Dv to the HTO (which I didn't, all I did was go full throttle on the main engines - and I was using a joystick so wasn't even touching the keyboard or on screen MFD button).

Also, this particular tutorial sets you up for a lunar approach on the leading side of the Moon in it's orbit so you enter into a retrograde orbit. I'm wondering why you would want a retrograde orbit, maybe it doesn't really matter since the Moon's orbit rotation is very slow but I would think on faster rotating planets it would make base approaches very tricky. I also find this approach visually disorienting, you come in "upside down" with the moon on your left in the cockpit view as it would look in a trailing side / prograde direction approach - but it's actually on the right since you're leading it. Actually I'm not sure why you approach it "upside down" in the first place, unless for some reason the prograde autopilot always orients you with the planet to your visual left. Even the Orbit MFD still shows the orbit track passing to the "right" of the Moon, although if you're leading it you would be initially passing to the "left" (this is before the retro burn to enter an elliptical orbit, still displayed as hyperbolic passing by). I know in space positioning is all relative, but it just makes it look like prograde / trailing approaches and orbits and retrograde / leading approaches and orbits are all shown the same way making it difficult to differentiate.

Sorry this is such a long post, when I'm asking questions I like to put them into some context to let people know what I'm doing and what I've tried.

 

[PhantomCruiser]

What you are describing with the transfer MFD has happened to me a few times, but never with a DG, it happened to me with a Vespucci... Recreating the gripe never came easy, but it happened more than once (but less than 10???). Anyway, I made it a habit to not change screens, or mess around with time compression, and quicksave right after I made my transfer.
I haven't had this happen to me in a very long while, my moon missions lately have been with the HLV.
As far as why to approach the moon prograde or retrograde? Smarter minds than me will have to explain that one. I've always assumed that it had to do with conservation of energy/deltaV and being set up for a free return. But I'm just a dumb old wrench turner, not a mathmetatician (but I can use a slide-rule).
Welcome to the forum, BTW, and happy Orbiting.

 

[atuhalpa]

If you install the encounter MFD and enter "earth" as the reference and "moon" as the target it will give you the parameters of your trajectory. If your inclination as read on the encounter MFD is greater than 90 degrees your are coming in retrograde, less than 90 is prograde. TransX will allow you to access the same data but has a steeper learning curve. Does this help?

 

[MetalMania]

Somewhat I suppose, I'll look it up and give it a try. It was just more that if I didn't already know I was approaching on the leading side, the way the presentation appears both visually and on the MFDs (to my inexperienced eyes anyway) I would have thought it was the opposite. Maybe there's some numerical data in the Orbit / Transfer MFDs already that tells you that but I just don't know what to look for yet. Then again maybe not since the Encounter MFD you mentioned sounds like it does that.

As far as plotting for a leading side/retrograde approach, the way I read the text for the tutorial it (to me anyway) seemed to infer that there was some advantage to doing it that way versus a trailing side prograde approach. Maybe there isn't and I just am reading more into it than there really is. Maybe it gives you a better opportunity to make an adjustment if you realize you're off course? In other words, perhaps your chances are better if you're already ahead of the target instead of finding out you're too far behind and won't be able to catch up?

Thanks!

 

[atuhalpa]

You should use standard terminology always. Learning through the forum will be easier if we all speak the standard language. "leading" or "trailing" is gobbledygook. Use "retrograde" or "prograde". Since most every body in the solar system rotates and orbits counterclockwise when looking "down" from ecliptic north, entering the sphere of influence of a body in the same counterclockwise direction is termed "prograde", and entering counterclockwise is "retrograde".

 

[dgatsoulis]

1.There is a similar question in the forum, posted by goretteux. (Newbie question: Left or Right of the Moon?)
For the "Prograde or Retrograde approach to the Moon" part of your post, i think that you'll find the answers there more than satisfactory.
2.Can't help you with the bug you encountered, it has never happened to me, although i think that PhantomCruiser is correct. Not messing with the views or the time compression (no more than 10x) during a burn, should keep you out of harm's way.
3.TransX and IMFD will help you do amazing things in Orbiter once you learn how to use them. (Things like a Grand tour of the Solar System using sling-shots, recreating historical missions (Pioneer, Voyager, Cassini, not to mention the Apollo, etc) or just use your imagination, set up the right date to launch and go wherever you want to go - on minimum fuel!
4.Next MFD you'll want to master is (in my opinion) the Aerobrake MFD.
I think that the first time you'll land spot-on the base you want, is one of the greatest moments you'll get in Orbiter. (But only just ONE of many).

I've been an "Orbinaut" for 4 years now and i think that these "few lines of code" created by Martin and every one else who ever posted even a single add-on in the Hangar or elsewhere, are one of the most educational and entertaining hobbies you'll have.

A word of advice: Check out as many tutorials as you can. There is nothing like watching someone successful at what you are trying to do, and then "set the bar higher" for yourself!

Welcome to the Forum.
Happy Orbiting!

 

[Tommy]

the way I read the text for the tutorial it (to me anyway) seemed to infer that there was some advantage to doing it that way versus a trailing side prograde approach.

The main reason for "leading" the moon is to set up a free return trajectory. I'm not sure that's possible using Transfer, so do whichever you want.

 

[TwoKiwi]

Hi, I'm having the same problem that was stated in the first post. When I try to use the Transfer MFD everything works fine up until the burn. When I burn my projected trajectory flies off the MFD, and I'm forced to eyeball it. I remember using it successfully a while ago, but now I'm trying to use it in Orbiter 2010. Am I doing something wrong, or is it a bug? I can post a video of it happening if you think it will help.

Regards,
TwoKiwi

 

[statickid]

I believe what you guys are describing is this, and this is how i deal with it if i am using transfer:

The hypothetical transfer shows what will happen if your orbit has the selected amount of DV. when you start your burn, it continues calculating what the difference with delta v would be, and thus, blows it into a huge escape route.

I don't know if there is a way to stop if it from doing that, the way i use it, it ALWAYS does this. So my way of dealing with it is to just start my burn and ignore the HTO and stop the burn at delta v= zero. THEN i never had any trouble with my transfer. then you can reset the HTO or turn it off. If its a little off i just make up for it with midcourse corrections :thumbup:

 

[MetalMania]

I don't know, it's weird. Sometimes it happens and sometimes it doesn't. I use it the same way every time so I can't figure out what's causing it. My initial post about it was with 2006 but it just happened to me with 2010 as well. The thing is though, when it's happened to me the Delta V doesn't count down - it's like the HTO values that were on screen are frozen and the HTO ellipse just disappears. It's not even like it goes hyperbolic - the whole orbit ellipse just "blasts off" and leaves the MFD view! So there's no cue left at all when to stop the burn, other than watching the actual orbit grow and trying to visually make the cutoff when the orbit crosses the target orbit. But you really can't tell how close it is to the calculated value. DV is just staying at the value that I set it to when calculating the HTO.

 

[Pyromaniac605]

to the forum! (I win I was the first to use the sign )

I'd recommend using IMFD it isn't that advanced personally I find it easier than TransferMFD.

Darren

 

[Wishbone]

...or LunarTransfer MFD. Engine cutoff is one of the most important moments you can have in Orbiter, so it is advisable to never accelerate time as you're nearing the required dV.

 

[MetalMania]

Yeah, I started this post quite a while ago actually but then hadn't used Orbiter for a while. I've started up again, now with 2010, but I never got so far as to be a pro yet so it's almost like starting from the beginning again. Anyway I had the Transfer MFD issue again and remembered I had opened a thread about it, but couldn't remember if anyone had a resolution so I looked it up and saw that there had been some more posts since the last time I had looked at it (months and months ago).

I had done a couple of Mars flights with TransX a while back, just haven't gotten around to IMFD yet. Transfer MFD to the Moon is just so simple (when you're properly set up for it anyway) when it works like it should I hadn't really felt the need to use another one for it. But the one or two times I've tried to set up a lunar transfer with a more realistic, limited fuel ship than the DG (where I can't afford more than a small burn to fix my Rinc), the advantage of a more flexible tool like TransX or IMFD (and presumably LunarTransferMFD) becomes very clear.

 

[Aeadar]

I noticed this happening myself, in 2006P1, and in 2010, and 2010P1.

In my case it happens because I've saved the scenario a few minutes prior to burn time; so that I can try the burn to see exactly how long it will take to reach the required DV. Then I go back to my 'save point' knowing precisely when to start the burn. That's when I encounter the problem you describe. My solution is to adjust anything on the Transfer HTO (DV, or Eject time) up or down 1 'click' and then back to where I want it just prior to the burn. This seems to 'reset' something, and seems to work whenever I remember to do it.

Also, another advantage of a retrograde lunar orbit is that it puts your shadow ahead of you when landing, although it messes with Align Plane and Orbit Normal vs. Orbit - Normal. For me it helps to visualize the map MFD upside down in those cases.




:hail: