TransX Trouble using TransX

[beaverbenny]

Hello,

So I am trying to work through TexFilms's XR2 Wideawake to Brighton Beach Tutorial but i'm thoroughly stuck at the midcourse burn. I can work through all the tweaking to get adjust my plane and lowest altitude over the moon. I do the burn, switch maneuver mode off. The number change a little bit (i guess because no burn is perfect) but very close. But then when I arrive at the moon, everything is way out. either I hit the moon or Im 1000K above the surface. It seems TransX doesn't at all predict where Im going to be... although im sure its just because Im doing something wrong.

any ideas?

Beaver

 

[blixel]

Hello,

So I am trying to work through TexFilms's XR2 Wideawake to Brighton Beach Tutorial but i'm thoroughly stuck at the midcourse burn. I can work through all the tweaking to get adjust my plane and lowest altitude over the moon. I do the burn, switch maneuver mode off. The number change a little bit (i guess because no burn is perfect) but very close. But then when I arrive at the moon, everything is way out. either I hit the moon or Im 1000K above the surface. It seems TransX doesn't at all predict where Im going to be... although im sure its just because Im doing something wrong.

any ideas?

Are you just doing 1 mid-course correction and then warping time forward all the way to the moon without doing any additional checking? If so, that's your problem.

TransX isn't very accurate. Even a simple Earth → Moon trip may require multiple corrections.

Are you trying to *just get there*? Or are you trying to learn all the ins and outs of using TransX for MCC's?

If it's the former, see if this helps:

If it's the case that you're more interested in learning how to use TransX for MCC's, I have probably at least 100 other videos you could refer to for that.

 

[beaverbenny]

Thanks for the info...

I am trying to learn all the ins and outs of TransX, but Im just beginning. Interested in you 100 or so videos, but want to start big picture and work to details...

Yes, I was just trying one mid course burn and fast forwarding time. Obviously that didnt work so I started doing several burns but the accuracy was so rediculous I thought I was doing something wrong. For example, if I did a currection burn to bring the altitude over the moons surface to say 20 or 50 km, within a few hours of simulation time would be up to 300 or 500 km or it would predict that I'd hit the surface. So I'd do another burn, and another and another and it started to feel like whats the point because the predictions i am using to determine how long to burn and in what direction are so inaccurate to start with...

I was wondering if one of the reasons was because TransX is only considering the earth and the moon and not the sun as the major body for the middle of the journey. So i played around trying to set up TransX that way with an escape from earth, sun as Maj/ earth as Min for the middle and an encounter with the moon 3rd... but couldnt figure out how to set that up.

perhaps another mfd is better for earth moon transfers?

or can TransX become more useful as you get to know it better?

Thanks again...

 

[Castor]

perhaps another mfd is better for earth moon transfers?

If your looking for high energy transfers between the earth and the moon, Lunar Transfer MFD is your best bet. But take your time to learn TransX, it will serve you well later.

 

[ADSWNJ]

I was wondering if one of the reasons was because TransX is only considering the earth and the moon and not the sun as the major body for the middle of the journey.

As far as I recall, TransX is a 2-body calculation - between you and the dominant gravity body influencing you. In a relatively close 3-body environment of you-moon-Earth, the calculation is going to be less precise than say Lunar Transfer MFD which focuses on these 3 bodies.

Generally, you want to course-correct once the target body becomes dominant, and then do it again 50% closer, and so on until your trajectory looks good.

Blixel is the undisputed master of the videos in this area though, so watch these lots of times, take notes and then recreate yourself.

Of course ... if you want to start a new code project to create a TransX NG to rule them all, then you would be a superstar! (Warning: non-trivial task, should you choose to accept it!)

 

[blixel]

Yes, I was just trying one mid course burn and fast forwarding time. Obviously that didnt work so I started doing several burns but the accuracy was so rediculous I thought I was doing something wrong. For example, if I did a currection burn to bring the altitude over the moons surface to say 20 or 50 km, within a few hours of simulation time would be up to 300 or 500 km or it would predict that I'd hit the surface. So I'd do another burn, and another and another and it started to feel like whats the point because the predictions i am using to determine how long to burn and in what direction are so inaccurate to start with...

I use to think that every time things drifted a little, I needed to come out of time warp and do a correction. There are a couple of reasons why that isn't the case. In some flights, the error actually corrects itself as you go forward in time. Sometimes the error will "wobble" in and out. Meaning, it will get worse for a while, then it will "top out", and from there it will actually start getting better. However, that is something you'll only see when going to Venus, Mars, or some other planet. When going from the Earth to Moon, the distance is small enough that you won't experience much, if any "wobble".

So the other reason you don't want to make constant corrections is simply because it isn't necessary. Instead of making a 1/4 m/s MCC, and then warping time forward for 10 or 20 seconds, and then making another 1/4 m/s MCC... instead - warp time forward by a significant amount and then make a slightly larger MCC.

When going from the earth to the moon, I will sometimes make my first MCC as soon as the earth's SOI becomes the weak body. If you have Orbit MFD open, this will be when the earth's gravitational influence (represented by the letter G at the bottom) goes from green to red. This always happens when Earth's G is about 0.49.

At that point, I know I'm still going to have a fair bit of error, so I don't fuss over getting everything exactly correct. But if things are off by quite a bit, I feel like that is a good point to stop and nudge things back in the right direction.

From there, warp time forward until the moon becomes the dominating gravitational source and do another MCC. Then, as ADSWNJ said, keep going forward toward the moon and get 50% closer before doing another MCC. In other words, look at Orbit MFD with the moon referenced. Look at the PeT value. Warp time forward until the PeT is 1/2 of its current value, then do another MCC. The closer you get the moon, the more accurate everything becomes, so the amount of correcting will be less and less. Eventually you'll be so close that it won't make sense to do any more MCC's.

perhaps another mfd is better for earth moon transfers?

or can TransX become more useful as you get to know it better?

Thanks again...

You should learn TransX. There are things you can do with TransX that you simply cannot do with other MFD's. So even if you find that you like another MFD better for going back and forth between the moon, you should still learn TransX.

Having said that, IMFD is a great MFD for the Earth → Moon and Moon → Earth trip. dgatsoulis sat down with me several months back and walked me through the basics of IMFD. I recorded those sessions and put them on my YT channel. Here is part 1.

[ame="http://www.youtube.com/watch?v=btiYvWy-QeM"]Orbiter 2010 - [Part 1] IMFD Training with Dimitris - Earth to Moon - YouTube[/ame]

And here's the entire IMFD playlist:

http://www.youtube.com/playlist?list=PLPu_SHPaJzs7Cp8OBsj41Ka-EIhReBbSJ

 

[beaverbenny]

Thanks for the info!

I watched the earth to moon w/ transx videos from blixel and did some more experimenting (excellent videos). Simply knowing that transx was just inaccurate and not necessarily that I was doing something wrong helped a lot. I can now reliably make the trip and capture on-plane with Brighton beach, landing on the first orbit as per the texfilms video. I've been doing 3-5 MCCs, first at halfway, and in half-again increments. But I will next try the suggestion to do the first one when earth = weak body, second when moon = strong body, and half-again thereafter to see how that works.

Now I am working on the moon => earth trip. After that, I'll play with IMFD.

Of course ... if you want to start a new code project to create a TransX NG to rule them all, then you would be a superstar! (Warning: non-trivial task, should you choose to accept it!)

I only wish I were half as smart as I would need to be to consider such a task. ;p