Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Anomalies: An Update Andreas Aste Department of Physics University of Basel Basel, May 15, 2008
Spacecraft Anomalies: An Update 1 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Overview 1
Interplanetary Spaceflight Swing-by Deep Space Network Spacecraft Navigation
2
Prehistory The Pioneer Anomaly
3
Flyby Anomalies in EGAs First Observation Flyby data set
4
Search for Explanations Origin of the Flyby Anomaly Origin of the Pioneer Anomaly
5
Outlook Spacecraft Anomalies: An Update 2 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
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Swing-By Swing-by (or flyby, slingshot, gravity assist): A method in interplanetary spaceflight to alter the path (and the speed) of a spacecraft by the use of a planet or other heavy celestial body. First swing-by-maneuver (1970): Rescue of the Apollo 13 crew. First planned gravity assist (1973): Deceleration of Mariner 10 by Venus in order to reach a stable orbit around Mercury.
Spacecraft Anomalies: An Update 3 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Swing-By Swing-by (or flyby, slingshot, gravity assist): A method in interplanetary spaceflight to alter the path (and the speed) of a spacecraft by the use of a planet or other heavy celestial body. First swing-by-maneuver (1970): Rescue of the Apollo 13 crew. First planned gravity assist (1973): Deceleration of Mariner 10 by Venus in order to reach a stable orbit around Mercury.
Main advantages Higher velocities → distant targets can be reached Saves fuel, time and expense Easy access to orbits far from the ecliptic Can be repeated several times
Trajectories of Pioneer 10 & 11
Spacecraft Anomalies: An Update 3 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Pioneer Trajectories
Spacecraft Anomalies: An Update 4 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Deep Space Network: Spacecraft Navigation
DSN Logo
DSN: International network of communication facilities (large radio antennas) for the support of interplanetary spacecraft missions & radio- und radar astronomy.
3 facilities (distance ∼ 120 degrees) Goldstone DSN Complex, Mojave Desert, California, USA Madrid DSN Complex, Robledo (Madrid), Spain Canberra DSN Complex, Tidbinbilla (Canberra), Australia Goldstone, California
Spacecraft Anomalies: An Update 5 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Deep Space Network
Spacecraft Anomalies: An Update 6 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Navigation Main method for measuring the longitudinal velocity of spacecraft: DOPPLER EFFECT
Basic strategy (Pioneer) DSN reference frequency: Receive frequency: νR = Response signal from Pioneer: νR0 = (240/221)νR DSN receive frequency:
q νE
νE0 =
c−vP c+vP
q
νE
c−vP c+vP
νR
Spacecraft Anomalies: An Update 7 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Navigation Main method for measuring the longitudinal velocity of spacecraft: DOPPLER EFFECT
Basic strategy (Pioneer) DSN reference frequency: Receive frequency: νR = Response signal from Pioneer: νR0 = (240/221)νR
q νE
νE0 =
DSN receive frequency:
→ vP =
bzw. vP =
νE −νE00 c νE +νE00
'
c−vP c+vP
q
νE
c−vP c+vP
νR
19 −∆ν E 221 461 +∆ν E 221
00 1 νE −νE c 2 νE
, mit ∆νE =
νE0 −νE νE
,
without frequency turnaround ratio (hard coded).
Spacecraft Anomalies: An Update 7 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Mysterious Deceleration of the Pioneer Probes John Anderson 1 (Jet propulsion laboratory, Pasadena, Kalifornien): Anomalous deceleration of Pioneer spacecraft since ∼ 1980 towards the sun (or the earth ?). Reliable Doppler telemetry data now available for ∼ 1973-2002 (Pioneer 10), 1974-1990 (Pioneer 11).
1
J. D. Anderson, July 1992 Quarterly Report to NASA Spacecraft Anomalies: An Update 8 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Mysterious Deceleration of the Pioneer Probes John Anderson 1 (Jet propulsion laboratory, Pasadena, Kalifornien): Anomalous deceleration of Pioneer spacecraft since ∼ 1980 towards the sun (or the earth ?). Reliable Doppler telemetry data now available for ∼ 1973-2002 (Pioneer 10), 1974-1990 (Pioneer 11). Pioneer 10: Launch March 2, 1972 / Jupiter flyby Dec 3, 1973 → hyperbolic orbit, radio contact till Feb 2003. Pioneer 11: Launch April 5, 1973 / Jupiter flyby Dec 2, 1974 / Saturn flyby Sept 1, 1979 → hyperbolic orbit, contact till Nov 1995.
1
J. D. Anderson, July 1992 Quarterly Report to NASA Spacecraft Anomalies: An Update 8 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Mysterious Deceleration of the Pioneer Probes John Anderson 1 (Jet propulsion laboratory, Pasadena, Kalifornien): Anomalous deceleration of Pioneer spacecraft since ∼ 1980 towards the sun (or the earth ?). Reliable Doppler telemetry data now available for ∼ 1973-2002 (Pioneer 10), 1974-1990 (Pioneer 11). Pioneer 10: Launch March 2, 1972 / Jupiter flyby Dec 3, 1973 → hyperbolic orbit, radio contact till Feb 2003. Pioneer 11: Launch April 5, 1973 / Jupiter flyby Dec 2, 1974 / Saturn flyby Sept 1, 1979 → hyperbolic orbit, contact till Nov 1995. Pioneer anomaly αPioneer = −(8.74 ± 1.33) · 10−10 m/s 2
1
J. D. Anderson, July 1992 Quarterly Report to NASA Spacecraft Anomalies: An Update 8 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Mysterious Deceleration of the Pioneer Probes John Anderson 1 (Jet propulsion laboratory, Pasadena, Kalifornien): Anomalous deceleration of Pioneer spacecraft since ∼ 1980 towards the sun (or the earth ?). Reliable Doppler telemetry data now available for ∼ 1973-2002 (Pioneer 10), 1974-1990 (Pioneer 11). Pioneer 10: Launch March 2, 1972 / Jupiter flyby Dec 3, 1973 → hyperbolic orbit, radio contact till Feb 2003. Pioneer 11: Launch April 5, 1973 / Jupiter flyby Dec 2, 1974 / Saturn flyby Sept 1, 1979 → hyperbolic orbit, contact till Nov 1995. Pioneer anomaly αPioneer = −(8.74 ± 1.33) · 10−10 m/s 2 Comments Anomalies of Pioneer 10/11 coincide within a range of ∼ 3%. aSun (20 AU) = 1.48 · 10−5 m/s 2 . Remains a mystery... cH0 ' 6.8 · 10−10 m/s 2 , a0 (MOND) ' 1.2 · 10−10 m/s 2 . 1
J. D. Anderson, July 1992 Quarterly Report to NASA Spacecraft Anomalies: An Update 8 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Velocity anomaly
Spacecraft Anomalies: An Update 9 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Pioneer probe design
Weight: 258 kg Energy source: 4 × 40 Watt RGT’s (RGT: Radioisotope thermoelectric generator) Pioneer 10 (final construction stage)
Spacecraft Anomalies: An Update 10 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Pioneer design
Spacecraft Anomalies: An Update 11 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Plutonium 238
Spacecraft Anomalies: An Update 12 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
RTG Radiation Measurement (Cassini-Huygens)
Spacecraft Anomalies: An Update 13 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Soviet RTGs
Spacecraft Anomalies: An Update 14 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist).
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following:
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s Cassini (’99): ∆v = −2.0 mm/s
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s Cassini (’99): ∆v = −2.0 mm/s Rosetta (’05): ∆v = 1.8 mm/s
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s Cassini (’99): ∆v = −2.0 mm/s Rosetta (’05): ∆v = 1.8 mm/s MESSENGER (’05): ∆v = 0.02 mm/s
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s Cassini (’99): ∆v = −2.0 mm/s Rosetta (’05): ∆v = 1.8 mm/s MESSENGER (’05): ∆v = 0.02 mm/s GALILEO (’92): ∆v = −4.6 mm/s (!)
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s Cassini (’99): ∆v = −2.0 mm/s Rosetta (’05): ∆v = 1.8 mm/s MESSENGER (’05): ∆v = 0.02 mm/s GALILEO (’92): ∆v = −4.6 mm/s (!)
The accuracy of the DSN velocity measurement is ∼ 0.01 mm/s.
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby-Anomaly December 1990: J.D. Anderson and other engineers at JPL observe an anomalous velocity increase of space probe GALILEO by ∆v = 3.92 mm/s during an Earth flyby (EGA, earth gravity assist). Further EGAs were investigated in the following: NEAR (’92): ∆v = 13.46 mm/s Cassini (’99): ∆v = −2.0 mm/s Rosetta (’05): ∆v = 1.8 mm/s MESSENGER (’05): ∆v = 0.02 mm/s GALILEO (’92): ∆v = −4.6 mm/s (!)
The accuracy of the DSN velocity measurement is ∼ 0.01 mm/s. Equatorial view of the NEAR flyby
Spacecraft Anomalies: An Update 15 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
The Hyperbolic Trajectory: Only an Approximation Orbit determination of probes is a non-trivial task. Currently, four independent codes are in use: JPL Orbit determination Program (various versions from 1970-2001) Aerospace Corporation Code POEAS (1995-2001) Goddard Space Flight Center: A study in 2003 Orbit determination code from the University of Oslo
Spacecraft Anomalies: An Update 16 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
The Hyperbolic Trajectory: Only an Approximation Orbit determination of probes is a non-trivial task. Currently, four independent codes are in use: JPL Orbit determination Program (various versions from 1970-2001) Aerospace Corporation Code POEAS (1995-2001) Goddard Space Flight Center: A study in 2003 Orbit determination code from the University of Oslo
These programs, e.g., take into account: Parametrized post-Newtonian gravity effects of the Sun/Moon/Planets/large asteroids/ terrestrial and lunar figure (multipole) effects/earth tides/lunar librations Solar radiation, Solar wind pressure, interplanetary dust Spacecraft: Thermal radiation, gas leakage (after correction maneuvers), torques Observation stations: Precession, nutation, sidereal rotation, polar motion, tidal effects, tectonic plate drift, models of DSN antennae. Signal propagation: Dispersion effects due to Solar wind and interplanetary dust.
Spacecraft Anomalies: An Update 16 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
week ending 7 MARCH 2008
PHYSICAL REVIEW LETTERS
PRL 100, 091102 (2008)
Outlook
TABLE I. Earth flyby parameters at closest approach for Galileo, NEAR, Cassini, Rosetta, and MESSENGER (M’GER) spacecraft. The altitude H is referenced to an Earth geoid, the geocentric latitude and longitude are listed for the closest approach location, Vf is the inertial spacecraft velocity at closest approach, V1 is the osculating hyperbolic excess velocity, the deflection angle (DA) is the angle between the incoming and outgoing asymptotic velocity vectors, the angle I is the inclination of the orbital plane on the Earth’s equator, the next four rows represent the right ascension and declination of the incoming (i) and outgoing (o) osculating asymptotic velocity vectors, and MSC is a best estimate of the total mass of the spacecraft during the encounter. The last three rows of the table give the measured change in V1 , the estimated realistic error in V1 , and the prediction of V1 by Eq. (1). The measured V1 for GLL-II is actually —8 mm=s, but it is reduced in magnitude after subtracting out an estimated atmospheric drag of 3:4 mm=s. Parameter Date H (km) (deg) (deg) Vf (km/s) V1 (km/s) DA (deg) I (deg) i (deg) i (deg) o (deg) o (deg) MSC (kg) V1 (mm/s) V1 (mm/s) Equation (1) (mm/s)
³ ³ ) ³ ) ³
GLL-I
GLL-II
NEAR
Cassini
Rosetta
M’GER
12/8/90 960 25.2 296.5 13.740 8.949 47.7 142.9 266.76 12:52 219.97 34:15 2497 3.92 0.3 4.12
12/8/92 303 33:8 354.4 14.080 8.877 51.1 138.7 219.35 34:26 174.35 4:87 2497 4:6 1.0 4:67
1/23/98 539 33.0 47.2 12.739 6.851 66.9 108.0 261.17 20:76 183.49 71:96 730 13.46 0.01 13.28
8/18/99 1175 23:5 231.4 19.026 16.010 19.7 25.4 334.31 12:92 352.54 4:99 4612 2 1 1:07
3/4/05 1956 20.20 246.8 10.517 3.863 99.3 144.9 346.12 2:81 246.51 34:29 2895 1.80 0.03 2.07
8/2/05 2347 46.95 107.5 10.389 4.056 94.7 133.1 292.61 31.44 227.17 31:92 1086 0.02 0.01 0.06
(J. D. Anderson, J. K. Campbell, J. E. Eklund, J. Ellis, J. F. Jordan @ JPL ) Spacecraft Anomalies: An Update 17 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Anderson’s collaborator James Jordan conjectured a connection between the rotation of the earth an the velocity increase. The ansatz is
Spacecraft Anomalies: An Update 18 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Anderson’s collaborator James Jordan conjectured a connection between the rotation of the earth an the velocity increase. The ansatz is Fitting formula ∆v 1 ∆E = = K (cos δi − cos δ0 ), v 2 E K =
2ωE RE = 3.1 · 10−6 . c
Spacecraft Anomalies: An Update 18 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Anderson’s collaborator James Jordan conjectured a connection between the rotation of the earth an the velocity increase. The ansatz is Fitting formula ∆v 1 ∆E = = K (cos δi − cos δ0 ), v 2 E K =
2ωE RE = 3.1 · 10−6 . c
Based on this ansatz, Anderson et al. predicted a velocity increase of 1mm/s for the Rosetta flyby on November 13, 2007.
Spacecraft Anomalies: An Update 18 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Anderson’s collaborator James Jordan conjectured a connection between the rotation of the earth an the velocity increase. The ansatz is Fitting formula ∆v 1 ∆E = = K (cos δi − cos δ0 ), v 2 E K =
2ωE RE = 3.1 · 10−6 . c
Based on this ansatz, Anderson et al. predicted a velocity increase of 1mm/s for the Rosetta flyby on November 13, 2007. Just recently, data analysis revealed that the Rosetta flyby was compatible with an absent anomaly.
Spacecraft Anomalies: An Update 18 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Anderson’s collaborator James Jordan conjectured a connection between the rotation of the earth an the velocity increase. The ansatz is Fitting formula ∆v 1 ∆E = = K (cos δi − cos δ0 ), v 2 E K =
2ωE RE = 3.1 · 10−6 . c
Based on this ansatz, Anderson et al. predicted a velocity increase of 1mm/s for the Rosetta flyby on November 13, 2007. Just recently, data analysis revealed that the Rosetta flyby was compatible with an absent anomaly. Now the JPL engineers await the next Rosetta flyby in 2009...
Spacecraft Anomalies: An Update 18 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
A strange behavior The anomalous acceleration occurring in Earth flybys is of the order of 10−4 m/s 2 - much larger than the Pioneer anomaly. Acceleration phase seems to last only some few minutes. Standard error analysis (atmosphere / ocean tides / solid earth tides / charging of the spacecraft / magnetic moment / earth albedo / solar wind ...) gives no hint to the origin of the anomaly. No consistent explanations from ”new physics” (modifications of relativity etc) yet.
Modeled anomalous acceleration
Spacecraft Anomalies: An Update 19 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Flyby acceleration mismatch
Spacecraft Anomalies: An Update 20 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Search for Explanations: Pioneer Anomaly
Spacecraft Anomalies: An Update 21 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Anomalies: An Update 22 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Anomalies: An Update 23 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Anomalies: An Update 24 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
In 2006, Slava Turyshev (a codiscoverer of the Pioneer anomaly) and Victor Toth (programmer at JPL) started a data recovery program.
Spacecraft Anomalies: An Update 25 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Spacecraft Anomalies: An Update 26 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Preliminary result Turyshev & Toth: The thermal recoil force may explain 28-36 % of the Pioneer anomaly...
Spacecraft Anomalies: An Update 26 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Preliminary result Turyshev & Toth: The thermal recoil force may explain 28-36 % of the Pioneer anomaly...
Turyshev: ”It’s like being on CSI”.
Spacecraft Anomalies: An Update 26 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Outlook
Anomaly mission Spacecraft Anomalies: An Update 27 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
Anomaly mission
Spacecraft Anomalies: An Update 28 / 29
Interplanetary Spaceflight
Prehistory
Flyby Anomalies in EGAs
Search for Explanations
Outlook
John Anderson
Spacecraft Anomalies: An Update 29 / 29
