Mechjeb Hohmann Transfer with low TWR ships?

[m4rt14n]

Hi, I'm pretty good at launching and piloting without any mods. But I'm starting to try Mechjeb.

I'm trying to travel to minmus from a parked orbit of 100 km. Here's what I have done using mechjeb manuever planner:

1. Add node to match inclination with minmus

2. Add node to hohmann transfer to minmus

3. Execute all nodes

I have a pretty big ship with 1 orange tank with 1 Neva and a command pod/lander science thing. It takes about 10 something minutes to do the Hohmann transfer. However what I'm seeing is that even after the encounter with minmus, Mechjeb keeps firing thrusters to escape Kerbin orbit.... Also it seems that the m/s and timer thing keeps adding after I am far from the node start...

I had to hit abort and fix the path manually.

Is this normal or I'm doing something wrong?

Edited January 27, 2014 by m4rt14n
add more info..

[sarbian]

I have trouble understanding what MJ is doing. But first do you use the release version or the dev version ?

[KhaosCorp]

I have seen this issue before, though its rare.

With some ships (very low TWR) you cant stack nodes at MJ2 will not account for the long burn times. Have you tried doing the nodes seperate in the same ship??

The couple times I have seen this happen it seems as if the length of the burn for first node messes up the calulation MJ did for the second. Not sure how accurate this is, but sure seems like what happens.

Honestly I would recomend fly big low thrust ships like this yourself, as MJ2 will most tiimes not start long burns enough before the node. IMO a 5min burn should be started at around 3min prior to the node..whereas MJ will wait till a min or so. Thats more of a personal preferance thing though tbh....

[Rickenbacker]

I've had this happen when going to Jool with very low TWR. The burn is so long that the projected trajectory misses the encounter, and MJ just keeps burning until it's out of fuel. In those cases it's probably better to set up a manual node, let MJ burn it and then adjust once you're on the way, that seems to work OK.

[m4rt14n]

Yea it seems to be whats happening. Although it misses the intended encounter, it still does encounter but at a different time. I guess its better to do some of the work myself. And to answer the other question, yes it does the same thing with 1 node only.