Pioneer anomaly

As Pioneer anomaly is a slight deviation of the 1972 and 1973 launched identical NASA probes Pioneer 10 and Pioneer 11 is referred to by their predicted trajectories. When a cause is considered an anisotropic thermal emission of the probes, but can potentially explain much of the observed effect. To date (October 2012) a whole range of explanations has been discussed, from simple effects such as a thrust by gas leaks, to a hitherto unknown physical effect.

A similar phenomenon is unexplained called fly-by- anomaly. Scientists have speculated that both anomalies could have a common ground. But now seems certain that the fly-by anomaly must have another reason.

• 3.1 Other probes
• 3.2 Future Missions

• 4.1 Possible Causes
• 4.2 Anisotropic thermal radiation

General Description

The effect dropped to around 1980, when the spacecraft Pioneer 10 had crossed the orbit of Uranus and about 20 astronomical units was removed from the earth. It was observed that the probe at a constant acceleration of aP unknown origin ( 8.74 ± 1.33 ) · 10-10 m / s ² towards the sun distracted, is thus braked. This corresponds to about one hundred thousandth of the acceleration due to gravity of the solar system and performs over a period of 15 years to a deviation of about 100,000 kilometers ( about 0.0007 astronomical units ) from the calculated position.

At that time, the well-known and taken into account in the calculations of acceleration by the pressure that the solar radiation exerts on the probe, declined to about 4 x 10-10 m / s ². Only because of unexplained acceleration was measured, which went down in the variable radiation pressure before. The deviation of the calculated values ​​were in the measurements of the Doppler effect on the returned radio signals from the probes confirmed ( to the velocity determination) conspicuous and by the measurements of the travel times of the signals ( for distance determination ).

The anomaly, however, was initially not taken seriously and interpreted as random error. It was not until 1994, when the effect did not disappear, he was examined in more detail. The train values ​​systematically analyzed for possible causes back without found a complete explanatory model - this common of the probes Pioneer 10 and Pioneer 11 - who had been away from each other in the almost opposite direction and their data showed the same up to a maximum of three percent difference effect could be.

Detailed Description

Speed ​​measurement of probe

The navigation of the Pioneer probes was performed using the antennas of the Deep Space Network (DSN ), an association of radio telescope facilities of the Jet Propulsion Laboratory (JPL ). The DSN currently consists of large radio telescope facilities in Goldstone / USA, Madrid / Spain and Canberra / Australia. There used to be beyond even facilities in Woomera / Australia and Johannesburg / South Africa These are each complexes of numerous antennas. The antennas were initially mostly diameter of 26 meters, later often 34 or 64 meters, sometimes up to 70 meters. The speed of measurement of the Pioneer probes, which is for the Pioneer anomaly of central importance, took place over the two-way Doppler shift of radio waves. From the ground stations were radio waves of known frequency ( S-band, about 2.11 GHz ) is sent to the satellite (uplink). The satellite receives the signal Doppler-shifted:

Here c is the speed of light, the speed of the probe, the transmitting frequency of the signal at the earth, and the frequency of the received signal from the spacecraft. ( Indices: E = Earth, R = remote ) The probe responds immediately with an 8 -watt transmitter ( antenna diameter: 137 cm) and a transponder with an around the fixed ( and accurate ) factor 240/221 multiplied frequency:

This is necessary as it is in the radio signals to coherent waves and you so avoids distortions by interference of the incident and reflected traveling waves. On the way back the signal ( downlink) is a second time Doppler-shifted identical. The received signal is thus displaced twice the Doppler and by a factor of 240/221.

The relative displacement therefore is given by

In some sources the constant frequency shift is neglected by the electronics by way of illustration, resulting in the simpler form:

Regardless can determine the distance of the probe by the duration of the signal. However, this could only be used at the beginning of the mission to the Pioneer probes.

Since the above- calculated speed is the relative speed of the probe to the earth, but to calculate the barycentric coordinates in the path, is necessary to determine the speed of the antennas on the ground very accurately. Here, we consider:

• Rotation of the earth around the sun and around itself
• Precession
• Nutation
• Sidereal rotation
• Polar motion
• Tidal forces
• Atmospheric conditions
• Plate tectonic movements

In addition, taking into account a multitude of influences on the calculation.

Calculation of the path, and analysis of the data

When calculating the path of the gravitational influence of the sun, the planets, the Moon and the largest asteroids has been taken into account; In addition, the solar radiation pressure, and many other influences on the trajectory of the probes. The maneuvers have unknown strong impact on the size, but they are easy to identify in the measurement data. The theoretical path was with several free parameters - including in addition to the maneuvers and the initial conditions and the size of the anomaly - adapted to the measurements to verify the anomaly and determine.

The calculations have been reviewed by independent persons with five different program packages, thus is a computing or software errors excluded.

Description

The blue shift is constantly increasing. The measured value of the unexplained variation rate of the blue shift is, (5.99 ± 0.01) · 10-9 Hz / s, which corresponds to an acceleration of ( 8.74 ± 1.33 ) · 10-10 m / s ². The acceleration is approximately towards the Sun, the exact direction could not be found - so it could also be that she shows towards Earth, velocity vector or self-rotation axis.

The anomaly appears to be relatively constant, but a slow decrease over time can not be excluded, as far too few data were analyzed. In addition, there are smaller periodic fluctuations, whose origin is also unclear. The acceleration was observed in both Pioneer probes and lies apart by no more than 3%.

Data location

The Pioneer spacecraft were over three decades in contact with the earth. The previous analyzes considered only data from about 11.5 years of Pioneer 10 and Pioneer 11 3.5 years, but he was received up to 27 April 2002 usable data (the last weak signal was received on 23 January 2003 ) by Pioneer 10 and at least until October 1990 usable data from Pioneer 11 so there are about 17.5 years Pioneer 10 and 12.5 years Pioneer 11 data, which have not yet been evaluated; less than a quarter of the data has been used. The data sparked the Pioneer probes have not been digitally recorded before 1987.

A new analysis of all the data is currently in progress. The original idea was the problem that the data were poorly archived; now, however, managed to gather most of the data and restore.

Other probes

The early 1980s, Pioneer 10 was the most distant spacecraft. Therefore, it is not surprising that the observed anomaly was noticed first with her. Due to other, stronger acceleration near the Sun ( as mentioned by the solar wind ), the anomaly is measured only at large distances. Therefore, no deviation can be found at geoorbitalen satellites and lunar probes.

However, it was reported that the same effect also showed the now burned up Jupiter probe Galileo and the European-American Ulysses solar probe, although were less precise and alone not too meaningful for this data. One aspect why the Pioneer probes provide good data, is their simple gyroscopic attitude stabilization (spin stabilization), which is easily predictable and calculable and thus can be easily excluded as a possible source of error. Subsequent long-distance probes such as Galileo or the two Voyager spacecraft were 3-axis stabilized constructed with the result that the velocity of the probe is influenced more by the position control by the control nozzles and can be calculated out less precise.

Future missions

New missions were designed to check and precise determination of the Pioneer anomaly. Thus it has been planned to build a highly symmetric space probe, which is to determine the anomaly at 10-10 to 10-12 cm/s2 and thereby exclude many possible causes or check. Ideally this would be a separate probe; However, it would also be possible to combine them with other space missions.

Alternatively it has been proposed a probe perpendicular to the ecliptic start to test whether the abnormality also occurs.

Explanations

Possible Causes

In the course of time a number of explanations have been contemplated, including:

• Data and calculation errors of any kind
• Effects of the probe itself as Recoil from escaping from the fuel tanks of gas
• Electromagnetic forces due to the electric charge of the probe
• Spatially non-uniform heat radiation, fed by the plutonium energy source or the probe itself
• Non-uniform aging of the surface of the probe, resulting in an uneven heat radiation
• Spatially non-uniform emission of helium ( decay product ) from the plutonium power source

• Gravitational forces of the Kuiper Belt
• Frictional resistance by interstellar matter
• Impacts of micrometeorites
• Inaccurate models of the solar radiation and the solar wind

• Expansion of the universe

• Gravitational effect of dark matter
• Modified Newtonian dynamics ( MOND )
• Frame - dragging

The probe-specific effects are very well studied, however, a declaration by a gas leak or a non- isotropic heat radiation will still not be totally excluded. So writes a group of scientists at the Jet Propulsion Laboratory in its detailed analysis: " Until more is known, we must admit that the most likely cause of the effect is an unknown systematic. ( We ourselves are divided on whether gas leaks 'or' heat ' this, probable cause ' is. ) "

Possible externalities gravitational effects come through an unusual mass distribution in the Kuiper belt or friction caused by interstellar matter in question. The previous measurement data for areas outside the solar system, however, indicate that the density of the interstellar medium and the dust is too low in the Kuiper Belt by several orders of magnitude to account for the effect can. In addition to the effects mentioned above may play a role previously unconsidered predictions of known physics - as a braking effect was found only in 2003 by a spin-rotation coupling. However, this is a factor of 10,000 too small to account for the effect can.

Some scholars see in the anomaly an indication of a "new physics " that is not explained by the established standard theories. One approach is the modified Newtonian dynamics, as this would provide an abnormal acceleration of the probe in the observed order of magnitude.

The magnitude of the acceleration corresponds to within the measurement accuracies of the product of the Hubble constant H0 and the speed of light c of - depending on the measurement method - about ( 7 ± 0.6 ) · 10-10 m / s ². Whether this local cosmological correspondence related to the railway anomaly, is currently also discussed.

Anisotropic thermal radiation

In the Pioneer spacecraft radioisotope batteries generate electrical energy and produce heat 2-5 kW. There are strong indications that the heat is not radiated uniformly in all directions. Instead, it is reflected from the back side of the parabolic antenna. Since the antenna is aligned with the Earth, it directs the heat radiation in the direction of flight and caused a delay. Assuming a heat source of 3 kW and a mass of the probe of 250 kg, is obtained:

Under the assumption that only part of the radiation is focused in the flight direction, the estimation is in the order of the observed effect of 1x10 -9 m / s ².

In April 2011, a team of Portuguese researchers based on new, detailed models for the radiation of heat by means of computer simulations could completely attributed the effect to a non-uniform heat dissipation, especially the reflection of heat radiation at the different components of the probe. Also in April 2011, Bremer researchers presented a method based on the finite element method, with which the measured anomalous acceleration can be completely described as thermal rebound effect. The results of the research group of were confirmed by an analysis of NASA's Jet Propulsion Laboratory in April 2012.

Media

Numerous media reported in the course of time on the Pioneer anomaly. The science magazine New Scientist led in March 2005, the Pioneer anomaly on as one of 13 puzzles of science.

Also the physics journal dealt in its issue of January 2006 with the anomaly. There, a measurement error is also ruled out with high probability.