General Question TransX or IMFD

[EtherDragon]

IMFD doesn't calculate delta-v over time either - it assumes instantaneous thrust. IMFD works around this limitation by re-integrating the course during the burn - so it's constantly making minor corrections on the direction to get the destination encounter time to be the same.

This limitation in IMFD actually makes it harder to use very low thrust engines - IMFD just gives up mid way through the burn because it thinks the current solution can't be met until next go around.

The end result is that IMFD ends up "wasting" a little bit of Delta-V during ejection burns - but with typical engine thrust/mass ratios in Orbiter the effect is minimal.

 

[jedidia]

IMFD doesn't calculate delta-v over time either - it assumes instantaneous thrust. IMFD works around this limitation by re-integrating the course during the burn - so it's constantly making minor corrections on the direction to get the destination encounter time to be the same.

ahhh... interesting. Still, the trajectories you end up on after days of thrust don't seem too bad so far. I didn't make it to saturn yet, though...

 

[Tommy]

IMFD doesn't calculate delta-v over time either - it assumes instantaneous thrust. IMFD works around this limitation by re-integrating the course during the burn - so it's constantly making minor corrections on the direction to get the destination encounter time to be the same.

It also adjust the start and end of burn differently in modes that support burn integration, however I do agree that it has serious problems if the target velocity can't be achieved in time.

The best way to attempt a low thrust flight with IMFD is to enter orbit quite early, and make a seies of burns at the ejection point to pump the Ap up over several orbits, to where escape velocity is attainable in a short enough burn. As your eccentricity increases, I suspect longer burns will become possible.

 

[jedidia]

The Orbit eject isn't really a problem with the help of IEATmfd, it's the Orbit INSERT that gives me the pain right now...

 

[the.punk]

I use both. It depends on the situation. TransX I use when I want to do a complex flight. Such with slingshots and many parts.
IMFD I use when the trajectorys aren't so complex.
For the beginning I suggest IMFD.
TransX is more complex and you must do more yourself.

---------- Post added at 09:24 AM ---------- Previous post was at 09:21 AM ----------

A con of IMFD is that it leaks with slingshots.

 

[Interceptor]

Thanks, for the great answers guys.

 

[Urwumpe]

Well, you can do slingshots with IMFD, but you can't tweak them as fine as with TransX. TransX is better for planning the slingshots, but it has no serious user interface. In terms of structure, accuracy and time for a navigation solution, IMFD is superior.

And also TransX should fail painfully when the burn time becomes 1/4th of the orbit period. But you can still split a burn, should be basic skill for people flying low-thrust vehicles.

http://www.orbiterwiki.org/wiki/Splitting_an_eject_burn_using_IMFD_and_BTC

 

[the.punk]

Ok. When you are beginning I suggest IMFD, because it is easy to use. You can do all simple interplanetary flights with it.
And then you could learn more about TransX because you can do more complex missions with it.

---------- Post added at 10:01 AM ---------- Previous post was at 09:57 AM ----------

Well, you can do slingshots with IMFD, but you can't tweak them as fine as with TransX. TransX is better for planning the slingshots, but it has no serious user interface. In terms of structure, accuracy and time for a navigation solution, IMFD is superior.

And also TransX should fail painfully when the burn time becomes 1/4th of the orbit period. But you can still split a burn, should be basic skill for people flying low-thrust vehicles.

http://www.orbiterwiki.org/wiki/Splitting_an_eject_burn_using_IMFD_and_BTC

Yes. You're right. You can do slingshots with IMFD. I have done that. But it wasn't very accurate. I made the same slingshot flight with TransX way more better.

For the point with the burn time you're right in that.