TransX is burning my toast

[TMac3000]

Okay, so I wanted to do a trip to Saturn. I had never been there before, and heck, I might even get the inclination right and be able to land on Iapetus or something.

So I set up TransX, do my launch, do my mid-course correction 20 mission days later, and then find out that TransX and IMFD are not even close to agreeing on where I will end up! TransX says I will fall well within Saturn SOI, but IMFD says I am going to miss by over 1 A.U. Now, IMFD doesn't lie, and TransX has let me down before, so I can only assume TransX gave me bad data for a planet that is virtually impossible to miss.

Three hours of work down the drain

 

[Andy44]

Well, did you finish the flight or just give up?

TransX requires midcourse-corrections for most transfers, but allows you more flexible planning.

 

[ar81]

Some time ago I suggested that if Orbiter is going to have TransX, it should include the necessary tutorials and documentation.

Tutorials by Flytandem, and good manual with very graphical explanations of what you do and why you do it.

I still use an old IMFD because I never was in need of something else. There is plenty of fuel in Orbiter, and I only fly to watch the landscape.

As for hours of flight... Orbiter helps us to develop patience. Being in a hurry is a good way to go nowhere.

And naturally we usually make mistakes.

 

[Tommy]

I can't explain why TransX and IMFD give you different distances, but suspect it has to do with the type of transfer. Was this an off-plane transfer? Saturn is usually cheaper to get to with a target plane or source plane transfer. In these cases the 1 AU shown by IMFD is well within range if the plane change hasn't been made yet. I'm not familiar enough with Transx tp know how it shows closest approach - it may be assuming you'll make the plane change and showing the CA as if the planes were aligned?

Either way, 1 AU that early in a flight is a minor deviation, and well within acceptable range of a mid-course correction with either IMFD or TransX. It would be very rare if you didn't have at least that large of a variance during your flight - there is always some variance that "comes and gos" a bit during an interplanetary flight.

Also, which IMFD program was showing you that distance? IMFD's Map program is the only one that's truly accurate.

Also, 20 days is rather soon for a MCC on a saturn trip, you may be makiing things worse by doing so - especially if you aren't well clear of the Earth's SOI yet. Closest approach values will change a bit early in a flight, until you are clear of the source planets gravity (note this means being well beyon the SOI, although the source planet is no longer the Primary gravity source, it is still affecting you) TransX and IMFD can both be innacurate and you'll end up making a correction based on bad data when no correction is required. If you actually do need a MCC this soon then there was a problem with the ejection burn.

 

[Cpt CryBaby]

This may not be the problem but it is worth mentioning: Make sure you turn the maneuver mode off between corrections burns when using the TransX MFD. If you leave it on it will continue to compute information based on where you were when you first turned it on.

This is my tutorial for earth to mars with TransX. Sounds like you may be beyond it already but just in case, you can check it out.

http://www.stillmixtup.com/E2M.html

step 44.5 is the one I was writing about above.

 

[TMac3000]

I've been chewing on this little mishap all day, and I realized that I did some things wrong. 20 days is too early for an MCC, and I reset the maneuver parameters one by one instead of just turning maneuver mode off and back on.

I was using the Map program in IMFD (it's the only part of IMFD I ever use), combined with TransX. It showed my predicted solar orbit falling well short of Saturn's orbit, despite that I had carried out the TransX procedures quite meticulously.

Andy44: yeah, I gave up. But I didn't see any alternative, or any way to correct my course But I'll take another swing at it tomorrow

 

[flaugher]

My TransX manual is V3.0. Does anybody know of a newer one? Is anyone working on an update? Duncan? :blackeye:

 

[flytandem]

I've been chewing on this little mishap all day, and I realized that I did some things wrong. 20 days is too early for an MCC, and I reset the maneuver parameters one by one instead of just turning maneuver mode off and back on.

yes, a good habit is to always turn "off" the maneuver immediately after completing the maneuver burn.

 

[kneejo]

if you turn off maneuver mode and change to the last view (of the target you arrive on) you can do small corrections with your RCS linear thrusters to fine-tune your arrival. This is easiest done in prograde direction, with prograde autopilot off. Instead of the projected maneuver you'll see your 'actual' trajectory. On a trip to mars I was able to aim at 200 km above the surface, even getting in the right orbit for the base, when I was weeks away from mars.

On the other hand, when I went to Jupiter, I made a MCC, but ended up behind Jupiter, outside it's SOI. Had to do some major correction burns when I came closer.

I started out with Transfer MFD, cause I wanted to be as hard-core as possible, using the simplest tools available. Then I realized that to fly a 2050 spacecraft with 1980 style fighter-plane MFD's is not realistic either, so I opted for a little more computer control, since that seems very likely in the future.

Without understanding orbital mechanics it's impossible to use any MFD the right way.. you might be able to plan something with an easy interface, but when it comes to correcting your course it comes down to your mind and whatever tools you have to help you plan. Not using the advancements in computer-technology would be plain ignorant. I believe TransX just gives me more versatility to do what I need to do.