Flyby anomaly
Encyclopedia
The flyby anomaly is an unexpected energy increase during Earth-flybys
of spacecraft. This anomaly has been observed as shifts in the S-Band
and X-Band
Doppler
and ranging telemetry
. Taken together it causes a significant unaccounted velocity increase of over 13 mm/s during flybys.
are valuable techniques for solar system exploration
. Because the success of these flyby maneuvers depends on the geometry of the trajectory
, the position and velocity of a spacecraft is continually tracked during its encounter with a planet by the Deep Space Network
(DSN).
The flyby anomaly was first noticed during a careful inspection of DSN Doppler data shortly after the Earth-flyby of the Galileo spacecraft
on 8 December 1990. While the Doppler residuals (observed minus computed data) were expected to remain flat, the analysis revealed an unexpected 66 mHz shift, which corresponds to a velocity increase of 3.92 mm/s at perigee
. An investigation of this effect at the Jet Propulsion Laboratory
(JPL), the Goddard Space Flight Center
(GSFC) and the University of Texas has not yielded a satisfactory explanation. No anomaly was detected after the second Earth-flyby of the Galileo spacecraft
in December 1992, because any possible velocity increase was masked by atmospheric drag of the lower altitude of 303 km.
On 23 January 1998 the Near Earth Asteroid Rendezvous (NEAR
) spacecraft experienced an anomalous velocity increase of 13.46 mm/s after its Earth encounter. Cassini–Huygens gained ~0.11 mm/s in August 1999 and Rosetta 1.82 mm/s after its Earth-flyby in March 2005.
An analysis of the MESSENGER
spacecraft (studying Mercury
) did not reveal any significant unexpected velocity increase. This may be that MESSENGER both approached and departed earth symmetrically about the equator (see data and proposed equation below). This may suggest that the anomaly is related to Earth's rotation.
Summary of Earth-flyby spacecraft is provided in table below. The Rosetta data is for its first flyby in 2005; the second flyby produced no significant anomalous increase, and the third a negligible decrease.
Upcoming missions with Earth flybys include Juno
and BepiColombo
.
where ωe is the angular frequency
of the Earth, Re is the Earth radius, and φi and φo are the inbound and outbound equatorial angles of the spacecraft.
In November 2009, ESA's Rosetta spacecraft
was tracked closely during flyby in order to precisely measure its velocity, in an effort to gather further data about the anomaly, but no significant anomaly was found.
. In the case of spacecraft that transit over Earth's rotational or magnetic polar regions, the flyby anomaly is an acceleration rather than a deceleration. It is possible that during an equatorial transit an unmeasured small (relative to Earth) deceleration occurs; this is very similar to the Pioneer spacecraft's deceleration relative to the Sun.
Possible explanations of the flyby anomaly include:
Gravitational slingshot
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
of spacecraft. This anomaly has been observed as shifts in the S-Band
S band
The S band is defined by an IEEE standard for radio waves with frequencies that range from 2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. It is part of the microwave band of the electromagnetic spectrum...
and X-Band
X band
The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...
Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
and ranging telemetry
Telemetry
Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
. Taken together it causes a significant unaccounted velocity increase of over 13 mm/s during flybys.
Observations
Gravitational assistsGravitational slingshot
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
are valuable techniques for solar system exploration
Timeline of solar system exploration
This is a timeline of Solar System exploration ordered by date of spacecraft launch. It includes:*All spacecraft that have left Earth orbit for the purposes of Solar System exploration , including lunar probes....
. Because the success of these flyby maneuvers depends on the geometry of the trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
, the position and velocity of a spacecraft is continually tracked during its encounter with a planet by the Deep Space Network
Deep Space Network
The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
(DSN).
Galileo spacecraft
Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
on 8 December 1990. While the Doppler residuals (observed minus computed data) were expected to remain flat, the analysis revealed an unexpected 66 mHz shift, which corresponds to a velocity increase of 3.92 mm/s at perigee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
. An investigation of this effect at the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
(JPL), the Goddard Space Flight Center
Goddard Space Flight Center
The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
(GSFC) and the University of Texas has not yielded a satisfactory explanation. No anomaly was detected after the second Earth-flyby of the Galileo spacecraft
Galileo spacecraft
Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
in December 1992, because any possible velocity increase was masked by atmospheric drag of the lower altitude of 303 km.
On 23 January 1998 the Near Earth Asteroid Rendezvous (NEAR
Near
- Science, mathematics, technology, biology, and medicine :* Nicking Enzyme Amplification Reaction, a method for in vitro DNA amplification* Near-Earth object, an object in the Solar System whose orbit brings it close to the Earth** Near-Earth asteroid...
) spacecraft experienced an anomalous velocity increase of 13.46 mm/s after its Earth encounter. Cassini–Huygens gained ~0.11 mm/s in August 1999 and Rosetta 1.82 mm/s after its Earth-flyby in March 2005.
An analysis of the MESSENGER
MESSENGER
The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
spacecraft (studying Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
) did not reveal any significant unexpected velocity increase. This may be that MESSENGER both approached and departed earth symmetrically about the equator (see data and proposed equation below). This may suggest that the anomaly is related to Earth's rotation.
Summary of Earth-flyby spacecraft is provided in table below. The Rosetta data is for its first flyby in 2005; the second flyby produced no significant anomalous increase, and the third a negligible decrease.
| Quantity | Galileo I | Galileo II | NEAR NEAR Shoemaker The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a... |
Cassini | Rosetta Rosetta (spacecraft) Rosetta is a robotic spacecraft of the European Space Agency on a mission to study the comet 67P/Churyumov–Gerasimenko. Rosetta consists of two main elements: the Rosetta space probe and the Philae lander. The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by... -I |
Messenger MESSENGER The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury... |
Rosetta Rosetta (spacecraft) Rosetta is a robotic spacecraft of the European Space Agency on a mission to study the comet 67P/Churyumov–Gerasimenko. Rosetta consists of two main elements: the Rosetta space probe and the Philae lander. The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by... -II |
Rosetta Rosetta (spacecraft) Rosetta is a robotic spacecraft of the European Space Agency on a mission to study the comet 67P/Churyumov–Gerasimenko. Rosetta consists of two main elements: the Rosetta space probe and the Philae lander. The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by... -III |
|---|---|---|---|---|---|---|---|---|
| Date | 12/8/1990 | 12/12/1992 | 01/23/1998 | 08/18/1999 | 03/04/2005 | 08/02/2005 | 11/13/2007 | 11/13/2009 |
| Speed at infinity, km/s | 8.949 | 8.877 | 6.851 | 16.01 | 3.863 | 4.056 | ||
| Speed at perigee Perigee Perigee is the point at which an object makes its closest approach to the Earth.. Often the term is used in a broader sense to define the point in an orbit where the orbiting body is closest to the body it orbits. The opposite is the apogee, the farthest or highest point.The Greek prefix "peri"... , km/s |
13.738 | --- | 12.739 | 19.03 | 10.517 | 10.389 | 12.49 | 13.34 |
| Impact parameter Impact parameter The impact parameter b is defined as the perpendicular distance between the path of a projectile and the center of the field U created by an object that the projectile is approaching... , km |
11261 | 12850 | 8973 | 22680.49 | 22319 | |||
| Minimal altitude Altitude Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context... , km |
956 | 303 | 532 | 1172 | 1954 | 2336 | 5322 | 2483 |
| Spacecraft mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:... , kg |
2497.1 | 730.40 | 4612.1 | 2895.2 | 1085.6 | 2895 | 2895 | |
| Trajectory inclination to equator, degrees | 142.9 | 138.9 | 108.8 | 25.4 | 144.9 | 133.1 | ||
| Deflection angle, degrees | 47.46 | 51.1 | 66.92 | 19.66 | 99.396 | 94.7 | ||
| Speed increment at infinity, mm/s | 3.92±0.08 | -4.60± 1.00 | 13.46±0.13 | −2±1 | 1.82±0.05 | 0.02±0.01 | ||
| Speed increment at perigee Perigee Perigee is the point at which an object makes its closest approach to the Earth.. Often the term is used in a broader sense to define the point in an orbit where the orbiting body is closest to the body it orbits. The opposite is the apogee, the farthest or highest point.The Greek prefix "peri"... , mm/s |
2.56±0.05 | 7.21±0.07 | −1.7±0.9 | 0.67±0.02 | 0.008±0.004 | ~0 | −0.004±0.044 | |
| Gained energy, J/kg | 35.1±0.7 | 92.2±0.9 | 7.03±0.19 |
Upcoming missions with Earth flybys include Juno
Juno (spacecraft)
Juno is a NASA New Frontiers mission to the planet Jupiter. Juno was launched from Cape Canaveral Air Force Station on August 5, 2011. The spacecraft is to be placed in a polar orbit to study the planet's composition, gravity field, magnetic field, and polar magnetosphere...
and BepiColombo
BepiColombo
BepiColombo is a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency to the planet Mercury, due to launch in 2014. The mission is still in the planning stages so changes to the current description are likely over the next few years...
.
Proposed equation
An empirical equation for the anomalous flyby velocity change was proposed by J.D. Anderson et al.:where ωe is the angular frequency
Angular frequency
In physics, angular frequency ω is a scalar measure of rotation rate. Angular frequency is the magnitude of the vector quantity angular velocity...
of the Earth, Re is the Earth radius, and φi and φo are the inbound and outbound equatorial angles of the spacecraft.
In November 2009, ESA's Rosetta spacecraft
Rosetta (spacecraft)
Rosetta is a robotic spacecraft of the European Space Agency on a mission to study the comet 67P/Churyumov–Gerasimenko. Rosetta consists of two main elements: the Rosetta space probe and the Philae lander. The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by...
was tracked closely during flyby in order to precisely measure its velocity, in an effort to gather further data about the anomaly, but no significant anomaly was found.
Possible explanations
It is not known whether the flyby anomaly is related to the Pioneer anomalyPioneer anomaly
The Pioneer anomaly or Pioneer effect is the observed deviation from predicted accelerations of the Pioneer 10 and Pioneer 11 spacecraft after they passed about on their trajectories out of the Solar System....
. In the case of spacecraft that transit over Earth's rotational or magnetic polar regions, the flyby anomaly is an acceleration rather than a deceleration. It is possible that during an equatorial transit an unmeasured small (relative to Earth) deceleration occurs; this is very similar to the Pioneer spacecraft's deceleration relative to the Sun.
Possible explanations of the flyby anomaly include:
- Unaccounted Transverse Doppler effect, i.e. the redshift of light source with zero radial and non-zero tangential velocity. However, this cannot explain the similar anomaly in the ranging data, or the possibly related Pioneer anomalyPioneer anomalyThe Pioneer anomaly or Pioneer effect is the observed deviation from predicted accelerations of the Pioneer 10 and Pioneer 11 spacecraft after they passed about on their trajectories out of the Solar System....
. - A dark matterDark matterIn astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
halo around the Earth. - A Modification of Inertia resulting from a Hubble-scale Casimir effectCasimir effectIn quantum field theory, the Casimir effect and the Casimir–Polder force are physical forces arising from a quantized field. The typical example is of two uncharged metallic plates in a vacuum, like capacitors placed a few micrometers apart, without any external electromagnetic field...
(MIHsC). - The impact of General RelativityGeneral relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
, in its weak-field and linearized form yielding gravitoelectric and gravitomagnetic phenomena like frame-draggingFrame-draggingEinstein's general theory of relativity predicts that non-static, stationary mass-energy distributions affect spacetime in a peculiar way giving rise to a phenomenon usually known as frame-dragging...
, has been investigated as well: it turns out to be unable to account for the flyby anomaly. - General Relativity, combined with a rotating universe is proposed to account for the flyby anomaly, the Pioneer anomaly, and the spin-down of the Pioneer craft.
- The anomaly may be due to the rotation of the earth. This rotation induces an azimuthally symmetric gravitational field.
- A plausible hypothesis that accounts for the flyby anomaly is the Sun's continual mass loss through nuclear fusion. Given that the Sun is losing mass at a constant rate of four million metric tons per second, it is well worth considering the effect of this mass loss on the orbital dynamics of bodies in the solar system.
External links
- Claus Lämmerzahl, University of Bremen:The Pioneer Anomaly or Do We Really Understand the Physics With the Solar System? (PDF file; 6.25 MB, 139 pages
- Andreas Aste, University of Basel:Spacecraft Anomalies: An Update(PDF file; 9.8 MB, talk/slides)