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Presentation given at the AAS/AIAA Astrodynamics Specialists Conference in Hilton Head, SC, on 8/12/12. The classic F and G Taylor series of Keplerian motion are extended to solve the Stark problem and to use the generalized Sundman transformation. Exact recursion formulas for the series coefficients are derived, and the method is implemented to high order via a symbolic manipulator. The results lead to fast and accurate propagation models with efficient discretizations. The new F and G Stark series solutions are compared to the Modern Taylor Series (MTS) and 8th order Runge-Kutta-Fehlberg (RKF8) solutions. In terms of runtime, the F and G approach is shown to compare favorably to the MTS method up to order 18, and both Taylor series methods enjoy approximate order of magnitude speedups compared to RKF8 implementations. Actual runtime is shown to vary with eccentricity, perturbation size, prescribed accuracy, and the Sundman power law. The effects of the generalized Sundman transformation on the accuracy of the propagation are analyzed, and the results are valid for both the Stark and Kepler problems. The Taylor series solutions are shown to be exceptionally efficient when the unity power law from the classic Sundman transformation is applied.
Citation preview
F and G Taylor series solutions to the Stark problem, including general Sundman
transformations
Etienne Pellegrini, Ryan P. Russell, and Vivek Vittaldev
AAS/AIAA Astrodynamics Specialists Conference
Hilton Head, SC, 8/12/13
Examples of Stark trajectories, propagated using F&G Stark series
• Introduction
• The Sundman transformation
• The Stark Problem
• Derivation of the F&G Stark series solutions
• Numerical results – Study of the Sundman transformation – Runtime comparisons
• Conclusions and future work
Summary
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• F&G series: – Taylor series of the f and g Lagrange functions
– Accurate way of propagating the 2-body problem Adapt the method to the Stark problem: 2-body motion
+ inertially constant perturbation
Introduction
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Why the Stark problem? – Good approximation for low-thrust
trajectories and slowly varying perturbations – “Simple” model, close to the 2-body
equations of motion – No TS solutions have been developed in
literature
r
v
r0
v0
• Use of the Sundman transformation – Efficient discretization schemes – Uniformizes the local truncation error (fixed step integrator
possible)
Goal of this work Obtain a fast integration scheme for the propagation of low-
thrust trajectories and/or slowly varying perturbations
Main contributions • Develop recursion formulas for the F&G Stark series &
demonstrate their superior computational efficiency
• Study the effects of the Sundman transformation on Taylor series solutions ; those results are valid for both the Stark
and Kepler problems
Introduction
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Introduced in 1912 by Karl F. Sundman. Used in astrodynamics because it reduces instability, and helps removing collision singularities. [Velez 1974, Nacozy 1976].
• The transformation slows time down as the particle gets
close to a singularity
• Generalized Sundman transformation:
• Modifies the equations of motion:
The Sundman transformation
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
The Sundman transformation
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Effect of the Sundman transformation exponent on the discretization of the orbit
Clustering at apoapse Independent of periapse or
apoapse
Clustering at periapse
• Discovered in 1914 by J. Stark. Has applications in nuclear physics, but also in astrodynamics.
• 2-body motion + inertially constant perturbation
• Equations of Motion:
• Can be used to describe low-thrust trajectories [Rufer 1976, Yam et al. 2010, Lantoine 2011]
The Stark Problem
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Based on classic F&G derivation [Bate, Mueller,White 1971]
• Extra basis vector for out-of-plane motion
• Extra series for keeping track of time
• Have to compute 𝐹 , 𝐺 , 𝐻 , 𝑇
F&G Stark series
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Recursion – Differentiate
– Identify with
– Requires to be able to repeatedly differentiate 𝐹 , 𝐺 , 𝐻 , 𝑇
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Hamiltonian – One of the integrals of motion Change in Hamiltonian
represent the local error
• Benchmarks – 8th order Runge-Kutta-Fehlberg (RKF8)
• Fixed-step numerical integrator
– Modern Taylor Series (MTS) • Similar to F&G Stark series (TS of position and velocity wrt 𝜏) • Coefficients are the same
• Computed using Leibniz’s rule and Automatic Differentiation packages
• Fixed step
Numerical Results
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
RKF8
10-6
10-10
10-14 10-18
Cha
nge
in H
amilt
onia
n
Change in Hamiltonian vs. position on the orbit
Results: Sundman transformation
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Eccentric Anomaly (rad) 0 1 2 3 4 5 6 0 1 2 3 4 5 6
Orbit: ellipse with a = 1 and e = 0.7
RKF8
10-6
10-10
10-14 10-18
Cha
nge
in H
amilt
onia
n
Change in Hamiltonian vs. position on the orbit
Results: Sundman transformation
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Eccentric Anomaly (rad) 0 1 2 3 4 5 6 0 1 2 3 4 5 6
F&G Stark series
10-2
10-6 10-10 10-14
Cha
nge
in H
amilt
onia
n Eccentric Anomaly (rad)
0 1 2 3 4 5 6
Orbit: ellipse with a = 1 and e = 0.7
Results: Sundman transformation
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Maximum change in Hamiltonian (over one revolution) vs. Sundman exponent
𝛼
Max
imum
cha
nge
in H
amilt
onia
n
• Nominal trajectory for timings – 1 revolution, tolerance = 10-12 – a = 1, e = 0.8, p = 0.001*[1,1,1] – 𝑑𝑡 = 𝑐𝑟 𝑑𝜏, 𝛼 = 1 – “Truth” trajectory propagated using F&G Stark order 21, quad
precision, 100 Segments
Timing results: Comparing F&G Stark to MTS and RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Nominal trajectory, top view
0.8
0.4 0 -0.4
-0.8
Y
-2 -1.5 -1 -0.5 0 0.5 X
Nominal trajectory, side view
-0.8 -0.4 0 0.4 0.8 Y
8
4 0
Z
x10-3
• Compute truth using F&G Stark series at high order and quad precision
Results: Comparison algorithm
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Truth
Prescribed accuracy: 𝜖 = 0.001
• For each TS order, increase # of segments until accuracy is met
Results: Comparison algorithm
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G, 5 segments
𝜖 = 10
Truth
Prescribed accuracy: 𝜖 = 0.001
• For each TS order, increase # of segments until accuracy is met
Results: Comparison algorithm
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G, 5 segments
F&G, 10 segments
𝜖 = 10
𝜖 = 3
Truth
Prescribed accuracy: 𝜖 = 0.001
• When specified accuracy is met, time the propagation
Results: Comparison algorithm
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
F&G, 5 segments
F&G, 10 segments
F&G, 50 segments Truth
𝜖 = 10
𝜖 = 3
𝜖 = 0.001
Prescribed accuracy: 𝜖 = 0.001
• For the RK: divide in segments AND in steps per segments until accuracy is met, then time the propagation
Results: Comparison algorithm
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
RKF8 50 segments
4 steps per segments
Truth
𝜖 = 0.001
• Software specifications – Implemented in Fortran – Compiler: gfortran v4.7.0 – F&G Stark coefficient files obtained using Matlab 15.01
• Hardware specifications – Processor: quad-core Intel Xeon W3550 – 3.07GHz clock-speed – 6GB RAM
Results: Setup details
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Speedup of the TS methods compared to the RKF integration when varying eccentricity
8 10 12 14 16 18 20 22 24 Order of the Taylor series
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Speedup of the TS methods compared to the RKF integration when varying the Sundman exponent
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Speedup of the TS methods compared to the RKF integration when varying the tolerance
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Speedup of the TS methods compared to the RKF integration when varying the perturbation magnitude
• Demonstrated unexpected behavior of the TS methods for Sundman exponent of 1 – Classic 3/2 result is confirmed for the RKF8 – Results are valid for both the Stark and Kepler problems
• The F&G Stark series method is up to 50 times faster than a conventional RKF8. – Most efficient for orders between 10 and 15
discretization of about 20 – 40 segments per revolution – For orders above 18, the MTS method is more efficient
• Efficiency is tied to the (perturbed) 2-body problem EOMs – not as good for more complicated dynamics
• Future work – Application to the 1st and 2nd order State Transition Matrices
Conclusions & Future work
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Thank you for your attention! Any questions?
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• C. E. Velez, “Notions of Analytic vs. Numerical Stability as applied to the Numerical Calculation of Orbits,” Celestial Mechanics, Vol. 10, No. 4, 1974, pp. 405–422.
• P. Nacozy, “A Discussion of Time Transformations and Local Truncation Errors,” Celestial Mechanics, vol. 13, No. 4, 1976, pp. 495–501.
• C. H. Yam, D. Izzo, and F. Biscani, “Towards a High Fidelity Direct Transcription Method for Optimisation of Low-Thrust Trajectories,” 4th International Conference on Astrodynamics Tools and Techniques, 2010, pp. 1–7.
• G. Lantoine and R. P. Russell, “Complete closed-form solutions of the Stark problem,” Celestial Mechanics and Dynamical Astronomy, Vol. 109, Feb. 2011, pp. 333–366, 10.1007/s10569-010-9331-1.
• D. Rufer, “Trajectory Optimization by Making Use of the Closed Solution of Constant Thrust- Acceleration Motion,” Celestial Mechanics, Vol. 14, No. 1, 1976, pp. 91–103.
• R. R. Bate, D. D. Mueller, and J. E. White, Fundamentals of Astrodynamics. New-York, NY. Dover Publications, 1971.
References
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Extra slides
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• 6 “revolutions” • a = 1, e = 0.8, p = [0.01,0.01,0.01] • 𝛼 = 1 • Propagated using F&G, order 21
Example trajectory
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Example trajectory, top view Example trajectory, side view
0.8 0.4 0 -0.4 -0.8
-1.6 -1 -0.5 0
Y
X -0.8 -0.4 0 0.4 0.8
0.4
0
-0.4
Z
Y
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
Speedup of the TS methods compared to the RKF integration when varying eccentricity
50
40
30
20
10
0
Spe
edup
ove
r RK
F8
8 10 12 14 16 18 20 22 24 Order of the Taylor series
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
50
40
30
20
10
0
Spe
edup
ove
r RK
F8
8 10 12 14 16 18 20 22 24 Order of the Taylor series
Speedup of the TS methods compared to the RKF integration when varying the Sundman exponent
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
50
40
30
20
10
0
Spe
edup
ove
r RK
F8
8 10 12 14 16 18 20 22 24 Order of the Taylor series
Speedup of the TS methods compared to the RKF integration when varying the tolerance
Results: Speedups vs. RKF8
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
50
40
30
20
10
0
Spe
edup
ove
r RK
F8
8 10 12 14 16 18 20 22 24 Order of the Taylor series
Speedup of the TS methods compared to the RKF integration when varying the perturbation magnitude
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Initial conditions:
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Initial conditions:
• First iteration:
F&G Stark series: recursion equations
Etienne Pellegrini - AAS/AIAA Astrodynamics Specialists Conference - 8/12/13 - Hilton Head, SC
• Initial conditions:
• First iteration:
• Second iteration: