Re: [Orekit Users] Mimic TLEPropagator with Numerical?

Evan,

I tried similar method using the reference you gave. But unfortunately, TLEPropagator is causing some error. Here is the code I used:

odeIntegratorBuilder = DormandPrince853IntegratorBuilder(0.001, 1000.0, 1.e-2)

builder = NumericalPropagatorBuilder(initialOrbitA, odeIntegratorBuilder, PositionAngle.TRUE, 1.e-2)

fitter = JacobianPropagatorConverter(builder, 1.e-6, 5000)

numpropA = fitter.convert(propagator_tleA, 2*T_objA, 251, "central attraction coefficient")

and the error it says is:

JavaError: org.orekit.errors.OrekitException: reset state not allowed

Java stacktrace:

org.orekit.errors.OrekitException: reset state not allowed

at org.orekit.propagation.analytical.tle.TLEPropagator.resetInitialState(TLEPropagator.java:473)

at org.orekit.propagation.conversion.AbstractPropagatorConverter.createSample(AbstractPropagatorConverter.java:265)

at org.orekit.propagation.conversion.AbstractPropagatorConverter.convert(AbstractPropagatorConverter.java:149)

Can you comment on this?

Thank you.

Regards,
Justin

From: Ward, Evan
Sent: Wednesday, March 29, 2017 09:55
To: orekit-users@orekit.org
Subject: Re: [Orekit Users] Mimic TLEPropagator with Numerical?

On Wed, 2017-03-29 at 09:41 -0400, Justin Leblanc wrote:

> Hello Evan,

> Thank you for your time. I never tried PropagatorConverter yet, but I

> cam across it earlier. I would give a try now. But it would be more

> helpful if I have an example or more likely a

> "PropagatorConverterTest" to avoid programming errors also I could

> get a rough idea about timeSpan and nbpoints. Is it possible that you

> can provide me a sample code?

Try taking a look at [1]. It is part of the examples that come with the

library source. This particular example is converting from a

NumericalPropagator to a KeplerianPropagator, but the principle is the

same.

Best Regards,

Evan

[1] https://www.orekit.org/forge/projects/orekit/repository/revisions/m

aster/entry/src/tutorials/java/fr/cs/examples/conversion/PropagatorConv

ersion.java

> Thank you again for your help.

> Regards,

> Justin

> On Tue, Mar 28, 2017 at 4:12 PM, Ward, Evan <Evan.Ward@nrl.navy.mil>

> wrote:

> > Hi Justin,

> >

> > Welcome to Orekit.On Tue, 2017-03-28 at 21:01 +0200, justin4leb@gma

> > il.com wrote:

> > > Hello All,

> > >

> > > I am new in using OREKIT. I was wondering if its possible to

> > mimic

> > > TLEPropagator by incorporating similar force models into a

> > Numerical

> > > propagator. Basically, I am trying to replicate the results of

> > the

> > > "Satellite

> > > Orbital Conjunction Reports Assessing Threatening Encounters in

> > > Space" (SOCRATES) that are given in the celestrak

> > > website :http://celestrak.com/cgi-bin/searchSOCRATES.pl?IDENT=NAM

> > E&NA

> > > ME_TEXT1=&NAME_TEXT2=&ORDER=MINRANGE&MAX=10

> > >

> > > I am able to get exact (very closer : +/-0.1 seconds) closest

> > > approach

> > > results, but not with a Numerical Propagator (with J2

> > perturbations).

> > > I am

> > > aware TLEprop is based on SGP4/SDP4 model but I wonder if it is

> > > possible to

> > > bring that model into Numerical. Because I would like to

> > experiment

> > > by

> > > applying small delta-Vs to the state to increase the closest

> > approach

> > > distance

> > > which cannot be done within a TLEPropagator.

> >

> > Try taking a look at the propagation.conversion package,

> > specifically

> > the PropagatorConverter and PropagatorBuilder. While you won't be

> > able

> > to recover the exact initial condition used to create the TLE

> > (TLE's

> > are a form of lossy compression) it should match to the accuracy of

> > the

> > TLE theory. You'll probably need to experiment with the timeSpan

> > and

> > nbPoints parameters to fit your use case.

> >

> > Best Regards,

> >

> > Evan