# STK 11.2: perform a low-thrust optimal transfer

I'm using STK 11.2 to find a minimum-time finite transfer between two coplanar orbits. The first orbit is circular and has a radius 7000km, the second orbit has a semimajor axis = 10000km and eccentricity = 0.1.

For the optimization I use Design Explorer Optimizer (in this version there is no SNOPT or IPOPT). Unfortunately, the solution doesn't converge.

What is wrong in my configuration?

• different question but somewhat related and of interest to future readers: Software for low-thrust trajectory optimization
– uhoh
Sep 23 '20 at 4:17
• First you should move the first propagate out of the TargetSequence. There is nothing to optimize. Second: why to you have a duration as a target? I think you can remove this to. Sep 23 '20 at 10:29
• @CallMeTom The first propagate is in the Target sequence because I want to find the optimal True anomaly to start the maneuver. Duration is a target because I want to minimize it. Sep 23 '20 at 10:46
• @Leeloo: since you have not specified the target AoP and you start on a circular orbit, there is nothing like an optimal true anomaly? (execpt the numerical error produces a pseudo one) Sep 23 '20 at 10:51
• okey ... so to sum up, you have a circular orbit ,one impulsive maneuver and a new SMA.. and this does not converge?? strange... ehh, do you still have the propagate element before the sequence? I said you need to move it out, but does it has an abort criteria? Sep 28 '20 at 11:00

From what I can tell from the parameters in your screenshots, the program has performed a perfectly valid optimisation.

What's more concerning is that the text in you question doesn't match the parameters clearly shown in the screenshots. If there's a configuration page where does values are actually used, why is this not included in the question?

The optimiser has been tasked to achieve these constraints:

• Obtain a semi-major axis between 8000km and 8010km. The value it reached, 7999.57km, is within the tolerances you have specified. The values here are not the 10000km you claim in the question.

• Achieve an eccentricity between 0 and 0.01. The value it reached is 0.00068, safely within. This is not your claimed input of 0.1

Given those two constraints, which has been met, it has minimised the time to a journey under 24 days.

The second concerning thing is the notice about "stop after specified duration". Since the value there is the exact same as what the optimiser output, is it perhaps the case that the provided time is not enough to reach the target orbit? 24 days is not a very long time as far as low-thrust transfers are concerned.

• I dind't catch the second concerning thing. "stop after specified duration" is a control. Oct 2 '20 at 5:15