I am using BatchLSEstimator to refine an initial guess at an orbit and I’m seeing different convergence results with CartesianOrbit vs EquinoctialOrbit. I’m sure that I’m doing something wrong, but can’t spot the error?

I have a very short arc (less than 2s) of az/el/range measurements. I make an initial guess at position/velocity through simple geometry, then refine that with BLS. I just use an analytical Keplerian propagator due to the short time-span. If I initialise with a CartesianOrbit, then the estimator converges in 4 iterations and the residuals are close to zero. If I use an EquinoctialOrbit, then the estimator converges in 36 iterations and the residuals in range are larger than I’d expect.

This is what I mean in numbers (residuals in az - radians, el - radians, range - m) for Cartesian

```
4
[-1.2240578425970483E-5, 7.092818138071388E-5, -0.2394066087435931]
[1.7907838861574987E-5, -5.546324877797604E-5, -0.551989545347169]
[-2.7295146693973038E-5, -1.9620036056877677E-5, 1.1203486216254532]
[-1.7782575352676133E-5, 3.693302303431345E-7, 0.30834507080726326]
[1.5954533016948602E-5, 1.2710312892127984E-5, 0.40259317052550614]
[4.103404743904804E-5, -5.351441522638556E-6, -0.9828750300221145]
[3.476988051254182E-5, -2.0326263433345648E-5, -0.6837378430645913]
[-2.527240480620918E-5, 1.4317318524359468E-5, 0.15829963283613324]
[-3.342359139768547E-5, -6.86127512401491E-5, 0.5306026425678283]
[6.347995177069521E-6, 7.104873892149755E-5, -0.062180155189707875]
```

and for equinoctial

```
36
[-9.26115061883337E-6, 7.553046300529109E-5, 3.252938335062936]
[2.0872866197230167E-5, -5.145506439457881E-5, 2.216291958699003]
[-2.4344761155425942E-5, -1.620611649721937E-5, 3.1640153906773776]
[-1.4847073456447646E-5, 3.1888177171035537E-6, 1.6268466557376087]
[1.887490891183674E-5, 1.493520138723392E-5, 0.9953799655195326]
[4.393905445398971E-5, -3.7213186055429226E-6, -1.11635178537108]
[3.765927525334334E-5, -1.929107235226768E-5, -1.5440260577015579]
[-2.2398866253769967E-5, 1.4757411848032032E-5, -1.4293470934499055]
[-3.0566153465194645E-5, -6.876792126614406E-5, -1.7849487927742302]
[9.189087538885587E-6, 7.029814028652881E-5, -3.106181636918336]
```

I’ve attached the code that I used. The only difference that I can see is that I create either a `CartesianOrbit`

or `EquinoctialOrbit`

from my initial position/velocity guess. I’ve played around with the `positionAngle`

and `positionScale`

options to the `KeplerianPropagatorBuilder`

, but with very little difference in the resulting residuals.

StandaloneTest.java (7.9 KB)