-
Notifications
You must be signed in to change notification settings - Fork 67
/
kepler_orbit_body.hpp
680 lines (636 loc) · 28.4 KB
/
kepler_orbit_body.hpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
#pragma once
#include "physics/kepler_orbit.hpp"
#include <string>
#include "base/optional_serialization.hpp"
#include "geometry/rotation.hpp"
#include "numerics/root_finders.hpp"
#include "quantities/elementary_functions.hpp"
namespace principia {
namespace physics {
namespace internal_kepler_orbit {
using geometry::AngleBetween;
using geometry::Bivector;
using geometry::Commutator;
using geometry::DefinesFrame;
using geometry::Displacement;
using geometry::EulerAngles;
using geometry::InnerProduct;
using geometry::Normalize;
using geometry::OrientedAngleBetween;
using geometry::Rotation;
using geometry::Sign;
using geometry::Vector;
using geometry::Velocity;
using geometry::Wedge;
using numerics::Bisect;
using quantities::Abs;
using quantities::ArcCos;
using quantities::ArcCosh;
using quantities::ArcSin;
using quantities::ArcTan;
using quantities::Cbrt;
using quantities::Cos;
using quantities::Cosh;
using quantities::DebugString;
using quantities::NaN;
using quantities::Pow;
using quantities::Sin;
using quantities::Sinh;
using quantities::SpecificAngularMomentum;
using quantities::SpecificEnergy;
using quantities::Speed;
using quantities::Sqrt;
using quantities::Time;
using quantities::si::Radian;
template<typename Frame>
void KeplerianElements<Frame>::WriteToMessage(
not_null<serialization::KeplerianElements*> const message) const {
Frame::WriteToMessage(message->mutable_frame());
SET_OPTIONAL(message, eccentricity);
WRITE_TO_OPTIONAL(message, asymptotic_true_anomaly);
WRITE_TO_OPTIONAL(message, turning_angle);
WRITE_TO_OPTIONAL(message, semimajor_axis);
WRITE_TO_OPTIONAL(message, specific_energy);
WRITE_TO_OPTIONAL(message, characteristic_energy);
WRITE_TO_OPTIONAL(message, mean_motion);
WRITE_TO_OPTIONAL(message, period);
WRITE_TO_OPTIONAL(message, hyperbolic_mean_motion);
WRITE_TO_OPTIONAL(message, hyperbolic_excess_velocity);
WRITE_TO_OPTIONAL(message, semiminor_axis);
WRITE_TO_OPTIONAL(message, impact_parameter);
WRITE_TO_OPTIONAL(message, semilatus_rectum);
WRITE_TO_OPTIONAL(message, specific_angular_momentum);
WRITE_TO_OPTIONAL(message, periapsis_distance);
WRITE_TO_OPTIONAL(message, apoapsis_distance);
inclination.WriteToMessage(message->mutable_inclination());
longitude_of_ascending_node.WriteToMessage(
message->mutable_longitude_of_ascending_node());
WRITE_TO_OPTIONAL(message, argument_of_periapsis);
WRITE_TO_OPTIONAL(message, longitude_of_periapsis);
WRITE_TO_OPTIONAL(message, true_anomaly);
WRITE_TO_OPTIONAL(message, mean_anomaly);
WRITE_TO_OPTIONAL(message, hyperbolic_mean_anomaly);
}
template<typename Frame>
std::string DebugString(KeplerianElements<Frame> const& elements) {
std::string result = "{";
bool first_entry = true;
auto const append = [&result, &first_entry](std::string const& symbol,
auto const& value) {
result += (first_entry ? "" : ", ") + symbol + " = " +
quantities::DebugString(value);
first_entry = false;
};
auto const append_optional = [&append](std::string const& symbol,
auto const& value) {
if (value) {
append(symbol, *value);
}
};
append_optional("e", elements.eccentricity);
append_optional(u8"ν∞", elements.asymptotic_true_anomaly);
append_optional(u8"δ", elements.turning_angle);
append_optional("a", elements.semimajor_axis);
append_optional(u8"ε", elements.specific_energy);
append_optional(u8"C₃", elements.characteristic_energy);
append_optional("n", elements.mean_motion);
append_optional("T", elements.period);
append_optional("n/i", elements.hyperbolic_mean_motion);
append_optional(u8"v∞", elements.hyperbolic_excess_velocity);
append_optional("b", elements.semiminor_axis);
append_optional("b/i", elements.impact_parameter);
append_optional(u8"ℓ", elements.semilatus_rectum);
append_optional("h", elements.specific_angular_momentum);
append_optional("r_pe", elements.periapsis_distance);
append_optional("r_ap", elements.apoapsis_distance);
append("i", elements.inclination);
append(u8"Ω", elements.longitude_of_ascending_node);
append_optional(u8"ω", elements.argument_of_periapsis);
append_optional(u8"ϖ", elements.longitude_of_periapsis);
append_optional(u8"ν", elements.true_anomaly);
append_optional("M", elements.mean_anomaly);
append_optional("M/i", elements.hyperbolic_mean_anomaly);
result += "}";
return result;
}
template<typename Frame>
std::ostream& operator<<(std::ostream& out,
KeplerianElements<Frame> const& elements) {
return out << DebugString(elements);
}
template<typename Frame>
KeplerOrbit<Frame>::KeplerOrbit(
MassiveBody const& primary,
Body const& secondary,
KeplerianElements<Frame> const& elements_at_epoch,
Instant const& epoch)
: gravitational_parameter_(
primary.gravitational_parameter() +
(secondary.is_massless()
? GravitationalParameter{}
: dynamic_cast<MassiveBody const&>(secondary).
gravitational_parameter())),
elements_at_epoch_(elements_at_epoch),
epoch_(epoch) {
CompleteElements(elements_at_epoch_, gravitational_parameter_);
}
template<typename Frame>
KeplerOrbit<Frame>::KeplerOrbit(
MassiveBody const& primary,
Body const& secondary,
RelativeDegreesOfFreedom<Frame> const& state_vectors,
Instant const& epoch)
: gravitational_parameter_(
primary.gravitational_parameter() +
(secondary.is_massless() ? GravitationalParameter{}
: dynamic_cast<MassiveBody const&>(secondary)
.gravitational_parameter())),
epoch_(epoch) {
GravitationalParameter const& μ = gravitational_parameter_;
Displacement<Frame> const& r = state_vectors.displacement();
Velocity<Frame> const& v = state_vectors.velocity();
Vector<double, Frame> const x({1, 0, 0});
Vector<double, Frame> const z({0, 0, 1});
Bivector<double, Frame> const x_wedge_y({0, 0, 1});
Bivector<SpecificAngularMomentum, Frame> const h = Wedge(r / Radian, v);
// The eccentricity vector has magnitude equal to the eccentricity, and points
// towards the periapsis. This is a vector (the direction of the periapsis
// does not depend on the coordinate system).
Vector<double, Frame> const eccentricity_vector =
v * h / μ * Radian - Normalize(r);
auto const& periapsis = eccentricity_vector;
Vector<SpecificAngularMomentum, Frame> const ascending_node = z * h;
// Maps [-π, π] to [0, 2π].
auto const positive_angle = [](Angle const& α) -> Angle {
return α > 0 * Radian ? α : α + 2 * π * Radian;
};
// Inclination (above the xy plane).
Angle const i = AngleBetween(x_wedge_y, h);
// Argument of periapsis.
Angle const ω = positive_angle(
OrientedAngleBetween(ascending_node, periapsis, x_wedge_y));
// Longitude of ascending node.
// This is equivalent to |OrientedAngleBetween(x, ascending_node, x_wedge_y)|
// since |ascending_node| lies in the xy plane.
Angle const Ω = positive_angle(
ArcTan(ascending_node.coordinates().y, ascending_node.coordinates().x));
Angle const true_anomaly =
positive_angle(OrientedAngleBetween(periapsis, r, x_wedge_y));
SpecificEnergy const ε = InnerProduct(v, v) / 2 - μ / r.Norm();
double const e = eccentricity_vector.Norm();
// We have h, e, and ε. There are three ways of computing each of b, r_pe,
// and r_ap from that (from any two of the elements we have), but only one is
// well-conditioned for all eccentricities.
Length const b = Sqrt(-InnerProduct(h, h) / (2 * ε)) * Radian;
Length const impact_parameter = Sqrt(InnerProduct(h, h) / (2 * ε)) * Radian;
Length const r_pe = InnerProduct(h, h) / ((1 + e) * μ) * Pow<2>(Radian);
Length const r_ap = - μ * (1 + e) / (2 * ε);
elements_at_epoch_.eccentricity = e;
elements_at_epoch_.specific_energy = ε;
elements_at_epoch_.semiminor_axis = b;
elements_at_epoch_.impact_parameter = impact_parameter;
elements_at_epoch_.specific_angular_momentum = h.Norm();
elements_at_epoch_.periapsis_distance = r_pe;
elements_at_epoch_.apoapsis_distance = r_ap;
elements_at_epoch_.inclination = i;
elements_at_epoch_.longitude_of_ascending_node = Ω;
elements_at_epoch_.argument_of_periapsis = ω;
elements_at_epoch_.true_anomaly = true_anomaly;
CompleteConicParametersByCategory(elements_at_epoch_, μ);
CompleteOrientationParameters(elements_at_epoch_);
CompleteAnomalies(elements_at_epoch_);
}
template<typename Frame>
RelativeDegreesOfFreedom<Frame>
KeplerOrbit<Frame>::StateVectors(Instant const& t) const {
GravitationalParameter const& μ = gravitational_parameter_;
double const& e = *elements_at_epoch_.eccentricity;
Angle const& i = elements_at_epoch_.inclination;
Angle const& Ω = elements_at_epoch_.longitude_of_ascending_node;
Angle const& ω = *elements_at_epoch_.argument_of_periapsis;
Length const& ℓ = *elements_at_epoch_.semilatus_rectum;
SpecificEnergy const& ε = *elements_at_epoch_.specific_energy;
KeplerianElements<Frame> elements = elements_at_epoch_;
elements.true_anomaly.reset();
elements.mean_anomaly.reset();
elements.hyperbolic_mean_anomaly.reset();
if (e < 1) {
// Elliptic case.
elements.mean_anomaly = *elements_at_epoch_.mean_anomaly +
*elements_at_epoch_.mean_motion * (t - epoch_);
} else if (e == 1) {
// Parabolic case.
LOG(FATAL) << "not yet implemented";
} else {
// Hyperbolic case.
elements.hyperbolic_mean_anomaly =
*elements_at_epoch_.hyperbolic_mean_anomaly +
*elements_at_epoch_.hyperbolic_mean_motion * (t - epoch_);
}
CompleteAnomalies(elements);
Angle const& ν = *elements.true_anomaly;
struct OrbitPlane;
Rotation<OrbitPlane, Frame> const from_orbit_plane(
Ω, i, ω,
EulerAngles::ZXZ,
DefinesFrame<OrbitPlane>{});
Length const r = ℓ / (1 + e * Cos(ν));
Displacement<Frame> const displacement =
r * from_orbit_plane(Vector<double, OrbitPlane>({Cos(ν), Sin(ν), 0}));
// Flight path angle.
Angle const φ = ArcTan(e * Sin(ν), 1 + e * Cos(ν));
// The norm comes from the vis-viva equation.
Velocity<Frame> const velocity =
Sqrt(2 * (ε + μ / r)) *
from_orbit_plane(Vector<double, OrbitPlane>(
{-Sin(ν - φ), Cos(ν - φ), 0}));
return {displacement, velocity};
}
template<typename Frame>
KeplerianElements<Frame> const& KeplerOrbit<Frame>::elements_at_epoch() const {
return elements_at_epoch_;
}
template<typename Frame>
void KeplerOrbit<Frame>::CompleteConicParametersByCategory(
KeplerianElements<Frame>& elements,
GravitationalParameter const& μ) {
auto& eccentricity = elements.eccentricity;
auto& asymptotic_true_anomaly = elements.asymptotic_true_anomaly;
auto& turning_angle = elements.turning_angle;
auto& semimajor_axis = elements.semimajor_axis;
auto& specific_energy = elements.specific_energy;
auto& characteristic_energy = elements.characteristic_energy;
auto& mean_motion = elements.mean_motion;
auto& period = elements.period;
auto& hyperbolic_mean_motion = elements.hyperbolic_mean_motion;
auto& hyperbolic_excess_velocity = elements.hyperbolic_excess_velocity;
auto& semiminor_axis = elements.semiminor_axis;
auto& impact_parameter = elements.impact_parameter;
auto& semilatus_rectum = elements.semilatus_rectum;
auto& specific_angular_momentum = elements.specific_angular_momentum;
auto& periapsis_distance = elements.periapsis_distance;
auto& apoapsis_distance = elements.apoapsis_distance;
int const eccentricity_specifications = eccentricity.has_value() +
asymptotic_true_anomaly.has_value() +
turning_angle.has_value();
int const semimajor_axis_specifications =
semimajor_axis.has_value() + specific_energy.has_value() +
characteristic_energy.has_value() + mean_motion.has_value() +
period.has_value() + hyperbolic_mean_motion.has_value() +
hyperbolic_excess_velocity.has_value();
int const semiminor_axis_specifications =
semiminor_axis.has_value() + impact_parameter.has_value();
int const semilatus_rectum_specifications =
semilatus_rectum.has_value() + specific_angular_momentum.has_value();
int const periapsis_distance_specifications = periapsis_distance.has_value();
int const apoapsis_distance_specifications = apoapsis_distance.has_value();
CHECK(eccentricity_specifications <= 1 || eccentricity_specifications == 3)
<< eccentricity_specifications;
CHECK(semimajor_axis_specifications <= 1 ||
semimajor_axis_specifications == 7)
<< semimajor_axis_specifications;
CHECK(semiminor_axis_specifications <= 1 ||
semiminor_axis_specifications == 2)
<< semiminor_axis_specifications;
CHECK(semilatus_rectum_specifications <= 1 ||
semilatus_rectum_specifications == 2)
<< semilatus_rectum_specifications;
CHECK_LE(periapsis_distance_specifications, 1);
CHECK_LE(apoapsis_distance_specifications, 1);
bool const must_complete_eccentricity = eccentricity_specifications == 1;
bool const must_complete_semimajor_axis = semimajor_axis_specifications == 1;
bool const must_complete_semiminor_axis = semiminor_axis_specifications == 1;
bool const must_complete_semilatus_rectum =
semilatus_rectum_specifications == 1;
if (must_complete_eccentricity) {
if (eccentricity) {
double const& e = *eccentricity;
turning_angle = 2 * ArcSin(1 / e);
asymptotic_true_anomaly = ArcCos(-1 / e);
} else if (turning_angle) {
Angle const& δ = *turning_angle;
eccentricity = 1 / Sin(δ / 2);
asymptotic_true_anomaly = (δ + π * Radian) / 2;
} else if (asymptotic_true_anomaly) {
Angle const& ν_inf = *asymptotic_true_anomaly;
eccentricity = -1 / Cos(ν_inf);
turning_angle = 2 * ν_inf - π * Radian;
}
}
// TODO(egg): range checks. What do we do with normalizable oddities
// (negative n, T)? What about parabolae? (n = 0, a infinite, and the
// equivalents provide an eccentricity specification...).
if (must_complete_semimajor_axis) {
if (semimajor_axis) {
Length const& a = *semimajor_axis;
specific_energy = -μ / (2 * a);
characteristic_energy = -μ / a;
mean_motion = Sqrt(μ / Pow<3>(a)) * Radian;
period = 2 * π * Sqrt(Pow<3>(a) / μ);
hyperbolic_mean_motion = Sqrt(μ / Pow<3>(-a)) * Radian;
hyperbolic_excess_velocity = Sqrt(-μ / a);
} else if (specific_energy) {
SpecificEnergy const& ε = *specific_energy;
semimajor_axis = -μ / (2 * ε);
characteristic_energy = 2 * ε;
mean_motion = 2 * Sqrt(-2 * Pow<3>(ε) / Pow<2>(μ)) * Radian;
period = π * Sqrt(-Pow<2>(μ) / (2 * Pow<3>(ε)));
hyperbolic_mean_motion = 2 * Sqrt(2 * Pow<3>(ε) / Pow<2>(μ)) * Radian;
hyperbolic_excess_velocity = Sqrt(2 * ε);
} else if (characteristic_energy) {
SpecificEnergy const& c3 = *characteristic_energy;
semimajor_axis = -μ / c3;
specific_energy = c3 / 2;
mean_motion = Sqrt(-Pow<3>(c3) / Pow<2>(μ)) * Radian;
period = 2 * π * Sqrt(-Pow<2>(μ) / Pow<3>(c3));
hyperbolic_mean_motion = Sqrt(Pow<3>(c3) / Pow<2>(μ)) * Radian;
hyperbolic_excess_velocity = Sqrt(c3);
} else if (mean_motion) {
AngularFrequency const& n = *mean_motion;
semimajor_axis = Cbrt(μ / Pow<2>(n / Radian));
specific_energy = -Pow<2>(Cbrt(μ * n / Radian)) / 2;
characteristic_energy = -Pow<2>(Cbrt(μ * n / Radian));
period = 2 * π * Radian / n;
hyperbolic_mean_motion = Sqrt(-Pow<2>(n));
hyperbolic_excess_velocity = Sqrt(-Pow<2>(Cbrt(μ * n / Radian)));
} else if (period) {
Time const& T = *period;
semimajor_axis = Cbrt(μ * Pow<2>(T / (2 * π)));
specific_energy = -Cbrt(Pow<2>(π * μ / T) / 2);
characteristic_energy = -Cbrt(Pow<2>(2 * π * μ / T));
mean_motion = 2 * π * Radian / T;
hyperbolic_mean_motion = 2 * π * Radian * Sqrt(-1 / Pow<2>(T));
hyperbolic_excess_velocity = Cbrt(2 * π * Sqrt(-Pow<2>(μ / T)));
} else if (hyperbolic_mean_motion) {
AngularFrequency const& n_over_i = *hyperbolic_mean_motion;
semimajor_axis = -Cbrt(μ / Pow<2>(n_over_i / Radian));
specific_energy = Pow<2>(Cbrt(μ * n_over_i / Radian)) / 2;
characteristic_energy = Pow<2>(Cbrt(μ * n_over_i / Radian));
period = 2 * π * Radian / Sqrt(-Pow<2>(n_over_i));
mean_motion = Sqrt(-Pow<2>(n_over_i));
hyperbolic_excess_velocity = Sqrt(Pow<2>(Cbrt(μ * n_over_i / Radian)));
} else if (hyperbolic_excess_velocity) {
Speed const& v_inf = *hyperbolic_excess_velocity;
semimajor_axis = -μ / Pow<2>(v_inf);
specific_energy = Pow<2>(v_inf) / 2;
characteristic_energy = Pow<2>(v_inf);
period = 2 * π * Sqrt(-Pow<2>(μ) / Pow<6>(v_inf));
mean_motion = Sqrt(-Pow<6>(v_inf) / Pow<2>(μ)) * Radian;
hyperbolic_mean_motion = Sqrt(Pow<6>(v_inf) / Pow<2>(μ)) * Radian;
}
}
if (must_complete_semiminor_axis) {
if (semiminor_axis) {
impact_parameter = Sqrt(-Pow<2>(*semiminor_axis));
} else if (impact_parameter) {
semiminor_axis = Sqrt(-Pow<2>(*impact_parameter));
}
}
if (must_complete_semilatus_rectum) {
if (semilatus_rectum) {
specific_angular_momentum = Sqrt(μ * *semilatus_rectum) / Radian;
} else if (specific_angular_momentum) {
SpecificAngularMomentum const& h = *specific_angular_momentum;
semilatus_rectum = Pow<2>(h * Radian) / μ;
}
}
}
template<typename Frame>
void KeplerOrbit<Frame>::CompleteConicParameters(
KeplerianElements<Frame>& elements,
GravitationalParameter const& μ) {
auto& eccentricity = elements.eccentricity;
auto& asymptotic_true_anomaly = elements.asymptotic_true_anomaly;
auto& turning_angle = elements.turning_angle;
auto& semimajor_axis = elements.semimajor_axis;
auto& specific_energy = elements.specific_energy;
auto& characteristic_energy = elements.characteristic_energy;
auto& mean_motion = elements.mean_motion;
auto& period = elements.period;
auto& hyperbolic_mean_motion = elements.hyperbolic_mean_motion;
auto& hyperbolic_excess_velocity = elements.hyperbolic_excess_velocity;
auto& semiminor_axis = elements.semiminor_axis;
auto& impact_parameter = elements.impact_parameter;
auto& semilatus_rectum = elements.semilatus_rectum;
auto& specific_angular_momentum = elements.specific_angular_momentum;
auto& periapsis_distance = elements.periapsis_distance;
auto& apoapsis_distance = elements.apoapsis_distance;
CompleteConicParametersByCategory(elements, μ);
CHECK_EQ(eccentricity.has_value() + semimajor_axis.has_value() +
semiminor_axis.has_value() + semilatus_rectum.has_value() +
periapsis_distance.has_value() + apoapsis_distance.has_value(),
2) << elements;
// TODO(egg): some of these formulae are very ill-conditioned near the
// parabolic case, and can be easily rewritten. Investigate.
if (eccentricity && semimajor_axis) {
double const& e = *eccentricity;
Length const& a = *semimajor_axis;
semiminor_axis = a * Sqrt(1 - Pow<2>(e));
impact_parameter = -a * Sqrt(Pow<2>(e) - 1);
semilatus_rectum = a * (1 - Pow<2>(e));
periapsis_distance = a * (1 - e);
apoapsis_distance = a * (1 + e);
} else if (eccentricity && semiminor_axis) {
double const& e = *eccentricity;
Length const& abs_b = e > 1 ? *impact_parameter : *semiminor_axis;
semilatus_rectum = abs_b * Sqrt(Abs(1 - Pow<2>(e)));
semimajor_axis = *semilatus_rectum / (1 - Pow<2>(e));
periapsis_distance = *semimajor_axis * (1 - e);
apoapsis_distance = *semimajor_axis * (1 + e);
} else if (eccentricity && semilatus_rectum) {
double const& e = *eccentricity;
Length const& ℓ = *semilatus_rectum;
semimajor_axis = ℓ / (1 - Pow<2>(e));
semiminor_axis = *semimajor_axis * Sqrt(1 - Pow<2>(e));
impact_parameter = -*semimajor_axis * Sqrt(Pow<2>(e) - 1);
periapsis_distance = ℓ / (1 + e);
apoapsis_distance = ℓ / (1 - e);
} else if (eccentricity && periapsis_distance) {
double const& e = *eccentricity;
Length const& r_pe = *periapsis_distance;
semimajor_axis = r_pe / (1 - e);
semiminor_axis = *semimajor_axis * Sqrt(1 - Pow<2>(e));
impact_parameter = -*semimajor_axis * Sqrt(Pow<2>(e) - 1);
semilatus_rectum = r_pe * (1 + e);
apoapsis_distance = *semimajor_axis * (1 + e);
} else if (eccentricity && apoapsis_distance) {
double const& e = *eccentricity;
Length const& r_ap = *apoapsis_distance;
semimajor_axis = r_ap / (1 + e);
semiminor_axis = *semimajor_axis * Sqrt(1 - Pow<2>(e));
impact_parameter = -*semimajor_axis * Sqrt(Pow<2>(e) - 1);
semilatus_rectum = r_ap * (1 - e);
periapsis_distance = *semimajor_axis * (1 - e);
} else if (semimajor_axis && semiminor_axis) {
Length const& a = *semimajor_axis;
auto const b² = *semiminor_axis != *semiminor_axis
? -Pow<2>(*impact_parameter)
: Pow<2>(*semiminor_axis);
eccentricity = Sqrt(1 - b² / Pow<2>(a));
semilatus_rectum = b² / a;
auto const sgn_a_sqrt_a²_minus_b² = Sign(a) * Sqrt(Pow<2>(a) - b²);
periapsis_distance = a - sgn_a_sqrt_a²_minus_b²;
apoapsis_distance = a + sgn_a_sqrt_a²_minus_b²;
} else if (semimajor_axis && semilatus_rectum) {
Length const& a = *semimajor_axis;
Length const& ℓ = *semilatus_rectum;
eccentricity = Sqrt(1 - ℓ / a);
semiminor_axis = Sqrt(a * ℓ);
impact_parameter = Sqrt(-a * ℓ);
double const& e = *eccentricity;
periapsis_distance = ℓ / (1 + e);
apoapsis_distance = ℓ / (1 - e);
} else if (semimajor_axis && periapsis_distance) {
Length const& a = *semimajor_axis;
Length const& r_pe = *periapsis_distance;
eccentricity = 1 - r_pe / a;
semiminor_axis = Sqrt((2 * a - r_pe) * r_pe);
impact_parameter = Sqrt((r_pe - 2 * a) * r_pe);
semilatus_rectum = r_pe * (2 - r_pe / a);
apoapsis_distance = 2 * a - r_pe;
} else if (semimajor_axis && apoapsis_distance) {
Length const& a = *semimajor_axis;
Length const& r_ap = *apoapsis_distance;
eccentricity = r_ap / a - 1;
semiminor_axis = Sqrt((2 * a - r_ap) * r_ap);
impact_parameter = Sqrt((r_ap - 2 * a) * r_ap);
semilatus_rectum = r_ap * (2 - r_ap / a);
periapsis_distance = 2 * a - r_ap;
} else if (semiminor_axis && semilatus_rectum) {
auto const b² = *semiminor_axis != *semiminor_axis
? -Pow<2>(*impact_parameter)
: Pow<2>(*semiminor_axis);
Length const& ℓ = *semilatus_rectum;
eccentricity = Sqrt(1 - Pow<2>(ℓ) / b²);
semimajor_axis = b² / ℓ;
double const& e = *eccentricity;
periapsis_distance = ℓ / (1 + e);
apoapsis_distance = ℓ / (1 - e);
} else if (semiminor_axis && periapsis_distance) {
auto const b² = *semiminor_axis != *semiminor_axis
? -Pow<2>(*impact_parameter)
: Pow<2>(*semiminor_axis);
Length const& r_pe = *periapsis_distance;
eccentricity = (b² - Pow<2>(r_pe)) / (b² + Pow<2>(r_pe));
semimajor_axis = (b² + Pow<2>(r_pe)) / (2 * r_pe);
semilatus_rectum = 2 * b² * r_pe / (b² + Pow<2>(r_pe));
apoapsis_distance = b² / r_pe;
} else if (semiminor_axis && apoapsis_distance) {
auto const b² = *semiminor_axis != *semiminor_axis
? -Pow<2>(*impact_parameter)
: Pow<2>(*semiminor_axis);
Length const& r_ap = *apoapsis_distance;
eccentricity = (Pow<2>(r_ap) - b²) / (b² + Pow<2>(r_ap));
semimajor_axis = (b² + Pow<2>(r_ap)) / (2 * r_ap);
semilatus_rectum = 2 * b² * r_ap / (b² + Pow<2>(r_ap));
periapsis_distance = b² / r_ap;
} else if (semilatus_rectum && periapsis_distance) {
Length const& ℓ = *semilatus_rectum;
Length const& r_pe = *periapsis_distance;
eccentricity = ℓ / r_pe - 1;
semimajor_axis = Pow<2>(r_pe) / (2 * r_pe - ℓ);
Length const& a = *semimajor_axis;
semiminor_axis = Sqrt(a * ℓ);
impact_parameter = Sqrt(-a * ℓ);
apoapsis_distance = ℓ * r_pe / (2 * r_pe - ℓ);
} else if (semilatus_rectum && apoapsis_distance) {
Length const& ℓ = *semilatus_rectum;
Length const& r_ap = *apoapsis_distance;
eccentricity = 1 - ℓ / r_ap;
semimajor_axis = Pow<2>(r_ap) / (2 * r_ap - ℓ);
Length const& a = *semimajor_axis;
semiminor_axis = Sqrt(a * ℓ);
impact_parameter = Sqrt(-a * ℓ);
periapsis_distance = ℓ * r_ap / (2 * r_ap - ℓ);
} else if (periapsis_distance && periapsis_distance) {
Length const& r_pe = *periapsis_distance;
Length const& r_ap = *apoapsis_distance;
eccentricity = (r_ap - r_pe) / (r_ap + r_pe);
semimajor_axis = (r_ap + r_pe) / 2;
semiminor_axis = Sqrt(r_ap * r_pe);
impact_parameter = Sqrt(-r_ap * r_pe);
semilatus_rectum = (2 * r_ap * r_pe) / (r_ap + r_pe);
}
CompleteConicParametersByCategory(elements, μ);
}
template<typename Frame>
void internal_kepler_orbit::KeplerOrbit<Frame>::CompleteOrientationParameters(
KeplerianElements<Frame>& elements) {
auto& argument_of_periapsis = elements.argument_of_periapsis;
auto& longitude_of_periapsis = elements.longitude_of_periapsis;
auto const& Ω = elements.longitude_of_ascending_node;
CHECK_EQ(
argument_of_periapsis.has_value() + longitude_of_periapsis.has_value(),
1);
if (argument_of_periapsis) {
auto const& ω = *argument_of_periapsis;
longitude_of_periapsis = Ω + ω;
} else if (longitude_of_periapsis) {
auto const& ϖ = *longitude_of_periapsis;
argument_of_periapsis = ϖ - Ω;
}
}
template<typename Frame>
void KeplerOrbit<Frame>::CompleteElements(KeplerianElements<Frame>& elements,
GravitationalParameter const& μ) {
CompleteConicParameters(elements, μ);
CompleteOrientationParameters(elements);
CompleteAnomalies(elements);
}
template<typename Frame>
void KeplerOrbit<Frame>::CompleteAnomalies(KeplerianElements<Frame>& elements) {
auto const& e = *elements.eccentricity;
auto& true_anomaly = elements.true_anomaly;
auto& mean_anomaly = elements.mean_anomaly;
auto& hyperbolic_mean_anomaly = elements.hyperbolic_mean_anomaly;
CHECK_EQ(true_anomaly.has_value() + mean_anomaly.has_value() +
hyperbolic_mean_anomaly.has_value(),
1);
if (true_anomaly) {
auto const& ν = *true_anomaly;
auto const positive_angle = [](Angle const& α) -> Angle {
return α > 0 * Radian ? α : α + 2 * π * Radian;
};
Angle const eccentric_anomaly =
ArcTan(Sqrt(1 - Pow<2>(e)) * Sin(ν), e + Cos(ν));
mean_anomaly =
positive_angle(eccentric_anomaly - e * Sin(eccentric_anomaly) * Radian);
Angle const hyperbolic_eccentric_anomaly =
ArcCosh((e + Cos(ν)) / (1 + e * Cos(ν)));
hyperbolic_mean_anomaly = e * Sinh(hyperbolic_eccentric_anomaly) * Radian -
hyperbolic_eccentric_anomaly;
} else if (mean_anomaly) {
auto const kepler_equation =
[e, mean_anomaly](Angle const& eccentric_anomaly) -> Angle {
return *mean_anomaly -
(eccentric_anomaly - e * Sin(eccentric_anomaly) * Radian);
};
Angle const eccentric_anomaly = e == 0 ? *mean_anomaly
: Bisect(kepler_equation,
*mean_anomaly - e * Radian,
*mean_anomaly + e * Radian);
true_anomaly = 2 * ArcTan(Sqrt(1 + e) * Sin(eccentric_anomaly / 2),
Sqrt(1 - e) * Cos(eccentric_anomaly / 2));
hyperbolic_mean_anomaly = NaN<Angle>();
} else if (hyperbolic_mean_anomaly) {
auto const hyperbolic_kepler_equation =
[e, hyperbolic_mean_anomaly](
Angle const& hyperbolic_eccentric_anomaly) -> Angle {
return *hyperbolic_mean_anomaly -
(e * Sinh(hyperbolic_eccentric_anomaly) * Radian -
hyperbolic_eccentric_anomaly);
};
Angle const hyperbolic_eccentric_anomaly =
Bisect(hyperbolic_kepler_equation,
0 * Radian,
*hyperbolic_mean_anomaly / (e - 1));
true_anomaly =
2 * ArcTan(Sqrt(e + 1) * Sinh(hyperbolic_eccentric_anomaly / 2),
Sqrt(e - 1) * Cosh(hyperbolic_eccentric_anomaly / 2));
mean_anomaly = -NaN<Angle>();
}
}
} // namespace internal_kepler_orbit
} // namespace physics
} // namespace principia