Building ODE in python wrapper

Orekit Python Wrapper usage
1

Hi Orekit community,

I’m currently trying to develop a Keplerian propagation using the Runge-Kutta integrator and a hand-made build ODE.
Here is what I developped so far:

def Keplerian_propagation(E0, central_mu, initialDate, finalDate, inertialFrame, nbr_pts, tle_time,pos = True):
    
    '''
    ARGS :
    E0 : Initial Vector [a0,e0,i0,pa0,raan0,M0]
    exposed surface : exterior surface in contact with the thin atmospherical residues
    central_mu : mu of the central body (here the earth)
    initialDate : AbsoluteDate of the initial time
    finalDate : AbsoluteDate of the final time hen the propagation must stop
    inertialFrame : Inertial Frame of reference used in the construction of orbits and propagation
    nbr_pts : Number of points for the propagation
    tle_time : List containing seconds in julian date 
    '''
    
    # Keplerian parameters
    prop_a,prop_e,prop_i,prop_pa,prop_raan,prop_M,prop_orbits = [],[],[],[],[],[],[]
    # Equinoctial parameters :
    prop_Hx, prop_Hy, prop_Ex, prop_Ey = [],[],[],[]
    
    if pos:    
        step = finalDate.durationFrom(initialDate)/nbr_pts
    else:
        step = - initialDate.durationFrom(finalDate)/nbr_pts
    
    a0,e0,i0,pa0,raan0,M0 = E0[0],E0[1],E0[2],E0[3],E0[4],E0[5]
    extrapDate=initialDate
    orbit0 = KeplerianOrbit(float(a0), float(e0) , float(i0), float(pa0), float(raan0), float(M0), PositionAngle.MEAN, inertialFrame, extrapDate, central_mu)
    T_period = float(2*np.pi*np.sqrt(a0**3/central_mu))


    ExpendableOde = ExpandableODE(OrdinaryDifferentialEquation.init(tle_time[0],E0,tle_time[-1]))
    integrator = ClassicalRungeKuttaIntegrator(5*T_period)

    if pos:
        while (extrapDate.compareTo(finalDate) <= 0.0):
        
            Ei = [prop_a[-1],prop_e[-1],prop_i[-1],prop_pa[-1],prop_raan[-1],prop_M[-1]]
            currentTime = extrapDate.durationFrom(initialDate)
            OdeState = ODEState(currentTime,Ei)
            orbit = integrator.integrate(ExpendableOde, OdeState, extrapDate.shiftedBy(step))
            PV = orbit.getPVCoordinates()
            keplerian = KeplerianOrbit(PV,inertialFrame,extrapDate,central_mu)
        
            prop_a.append(keplerian.getA())
            prop_e.append(keplerian.getE())
            prop_i.append(keplerian.getI())
            prop_Hx.append(keplerian.getHx())
            prop_Hy.append(keplerian.getHy())
            prop_Ex.append(keplerian.getEquinoctialEx())
            prop_Ey.append(keplerian.getEquinoctialEy())
            prop_M.append(keplerian.getMeanAnomaly())

            ##### RAAN and PA calculations and normalization from Equinoctial parameters
            to_check_raan = float(np.arctan2(prop_Hy[-1],prop_Hx[-1]))
            moduled_raan = to_check_raan % float(mytwopi)
            prop_raan.append(moduled_raan)
        
            # Now we have raan, we also know that ex = e * cos(raan + pa) so pa = arccos(ex/e) - raan
        
            to_check_pa = float(np.arctan2(prop_Ey[-1],prop_Ex[-1])-prop_raan[-1])
            moduled_pa = to_check_pa % float(mytwopi)
            prop_pa.append(moduled_pa)
            
            prop_M[-1] = prop_M[-1] % float(mytwopi)
            
            prop_orbits.append(KeplerianOrbit(prop_a[-1],prop_e[-1],prop_i[-1],prop_pa[-1],prop_raan[-1],prop_M[-1], PositionAngle.MEAN, inertialFrame, extrapDate, central_mu))

            extrapDate = extrapDate.shiftedBy(float(step))

    
    return prop_a,prop_e,prop_i,prop_pa,prop_raan,prop_M,prop_orbits

And while building the ODE with ExpandableODE i get the following error :
descriptor 'init' for 'OrdinaryDifferentialEquation' objects doesn't apply to a 'float' object. Is there someone who knows how to fix that ?

Thank you in advance
Have a great day
JL

2

Hi @JulienL

OrdinaryDifferentialEquation is a Java interface. You have to implement it in order to initialize the ExpandableODE object. In addition, the method init is a void. So, it returns nothing. Therefore, you can’t use it to create an OrdinaryDifferentialEquation.

The following topic could help you:

Best regards,
Bryan

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