Voyager 2

Voyager 2 spacecraft is a NASA exploration of the outer solar system as part of the Voyager program. She was launched on 20 August 1977 by the Launch Complex 41 on Cape Canaveral with a Titan IIIE - Centaur rocket. Your identically constructed sister probe Voyager 1 was launched 16 days later on a different trajectory.

The Mission of Voyager 2 is generally considered one of the greatest achievements of NASA and the space, because the probe has exceeded its planned life expectancy far and still regularly sends data back to Earth. She is also the ( after her sister probe) second most distant from the earth, built by people object. The distance from the Sun Voyager 2 was the end of August 2013, some 102.0 astronomical units ( AU), which is about 15.3 billion kilometers.

• 5.1 probe
• 5.2 instruments

Prehistory

The roots of the Voyager program date back to the mid-1960s. There were calculations of trajectories for probes that could be exploited by the late 1970s the favorable positions of the outer planets. In the early 1970s the construction of the Voyager 1 and 2, it was decided. Since they were first planned as an extension of the Mariner series, they were first called " Mariner 11 " and 12. This designation was later dropped due to the large structural differences between the probes. By March 1975, the design phase was completed, and the construction of the probes began.

Mission Objectives

The Voyager probes had no particular research focus, as there were only a few knowledge about the outer planets in the run, which could have been expanded. Therefore, the mission objectives are rather broad:

• Investigation of the atmosphere of Jupiter and Saturn in terms of circulation, structure and composition
• Analysis of the geomorphology, geology and composition of the moons
• More precise determination of the mass, size and shape of all the planets, moons and rings
• Investigation of various magnetic fields with respect to their field structure
• Analysis of the composition and distribution of charged particles and plasma
• Particularly detailed investigations of the moons Io and Titan

The probe and its scientific instruments

Voyager 2 is a multi- meter and 800 -kg spacecraft. It consists essentially of a central annular aluminum cell (diameter about 1.80 m), which is ten square in cross section and is home to much of the electronics, a satellite dish (diameter about 3.6 m) and a 2.5 m boom, which carries the bulk of the scientific instruments. The energy generated by three radionuclide. Voyager 2 and Voyager 1 are identical.

Functioning of the mission

Starting and flight

Voyager 2 was launched from Launch Complex 41 of the Cape Canaveral AFS with a Titan IIIE - Centaur rocket on 20 August 1977. 16 days later started her sister probe Voyager 1, at a slightly different trajectory. As Voyager 1 had a slightly higher starting speed (15,0 km / s compared to 14.5 km / s ), Voyager 2 was passed on December 15 at a distance of 1.75 AU from its sister probe.

Flight time to Jupiter was about 20 months.

Technical Problems

A few months after the start it was found that the sensor platform of Voyager 2 was not extended. After many attempts it succeeded yet. In the analysis of the fault, the fact played a role that you had not communicated 207 days long after starting with the probe. The reason for this was again an overload of the ground team, because at the same time the Galileo project was prepared, so many resources were withdrawn from the Voyager program. The CCS of the probe had interpreted the lack of signals as faulty function of the primary transmitter and switched on 2 April 1978 to the standby transmitter. In this, however, a member for the automatic adjustment of the transmit and receive frequency was broken. The relative velocity between Earth and spacecraft fluctuated, depending on where the Earth in its orbit around the sun happened to be, resulting in a Doppler effect. Since the defective part is no longer compensated for the frequency shifts, the wireless connection broke off very often. So you sent on April 6, a command that activated the primary transmitter again. This was but failed now complete and so you had to take the defective part standby transmitter back into service. It solved the problem of the Doppler effect by precomputed him and the transmission frequency stopped manually. Since Voyagers receiver had a bandwidth of only 96 Hz, the slightest deviation in the frequency generation could lead to a disconnection. Already a warming of the probe of 0.25 K could cause a critical difference, which is why the temperature control higher priority has been given.

On February 23, 1978, it was found during a test of the scanning platform that a gear stuck and correct alignment prevented. During the next three months we came to the conclusion that a soft foreign bodies, probably was a piece of insulation film between the gears. By repeatedly activating the electric motors that could eventually crushed, and the scan platform made ​​operational again.

Jupiter

As Voyager 2 on April 25, 1979 arrived in the Jupiter system, she broke her sister probe Voyager 1 in the exploration of the planet almost seamlessly from. The trajectory of Voyager 2 was chosen so that they could examine some moons of that side which Voyager 1 had remained hidden. The newly discovered rings and the night side of Jupiter should be examined more closely. Have explored the moons Amalthea, Io, Europa, Callisto and Ganymede, all before the Jupiter passage. It also measurements by means of the PPS instrument could be carried out, which was unusual at Voyager 1. During the two-day primary phase in the vicinity of the moons of Jupiter and when the probe was consistently supported by the 64- m antennas of the Deep Space Network, which limits the maximum data rate of 115 kbit / s could be achieved. As Voyager 2 on August 5, left the Jupiter system, they had sent 13,350 images back to Earth and passes the planet at a distance of 643,000 km. By fly- by maneuver the probe was accelerated to 16 km / s and was now on course to Saturn.

Detail of Jupiter

Jupiter's rings in false color

A volcanic eruption on Io

The moon Callisto

The Valhalla crater on Callisto ( center right)

The moon Ganymede

Close-up of Europe

Saturn

The exploration of Saturn showed the very high wind speeds of Saturn, especially near the equator, where Voyager 2 could measure speeds of up to 500 meters per second. This blow mainly in an easterly direction, slow down with increasing latitude and from 35 ° north / south direction to rotate the West. Voyager 2 could also detect a very strong symmetry of the wind conditions between the northern and southern part of Saturn's what some scientists evaluated as an indication of currents through the planetary interior.

The probe could also study the upper atmosphere of the planet through the RSS instrument as a result of their flight path. At the surface, a minimum temperature of 82 K ( -191 ° C) at a pressure of 70 mbar was measured. In the largest possible measurable depth there was a temperature of 143 K ( -130 ° C ) at a pressure of 1200 millibars. It also aurora -like phenomena north of 65 ° latitude have been discovered and in the UV region in the mid-latitudes. The latter occurs only in sunlight and are still puzzling, because the charged particles of the sun at least occur on Earth only in the polar regions and not in middle latitudes.

Saturn S- rings in false color

The moon Hyperion

The moon Janus

A low resolution image of Prometheus

The icy moon Enceladus

The moon Titan

The moon Iapetus

Extension of the mission

In the spring of 1981, the first correction maneuvers have been performed to bring Voyager 2 at Uranus. This was not originally intended, since the probe would already have been on the road eight years on arrival, or twice the predicted or projected service life. Internal studies assumed that only a 65 percent chance existed that would reach Voyager 2 Uranus functional. Due to the very limited computing capacities of the probe extensive work on the ground was necessary, which cost about 30 million U.S. dollars per year. Despite these circumstances, NASA approved a continuation of the mission, especially because, besides the two Voyager probes Viking 1 only gave a more active planetary probe at that time.

It was necessary to revise the software massively. A project scientists expressed this way: " The probe, which reached Uranus, is not the same, which has left the earth." Essentially, there were three major issues: the extremely low data rate due to the large distance (four times lower than that of Saturn), the reduced energy output of the radionuclide of only 400 watts ( 420 watts were necessary for the full operation ) and low light intensity, the longer exposure times required, and thus increased the risk of blurred images.

The problem of data transmission is decreased from two sides: First, the data volume was reduced, on the other, the reception has been improved. The latter was achieved by the additional use of other receiving antennas. Normally, the telemetry over a 64- m antenna of the DSN was settled, which / s allowed for a data rate from 7.2 to 9.6 kb. But this was not enough to cope with the large amount of scientific data in the Uranus passage. Therefore an additional 34 m and 64 m were added antenna connected so that a data rate of 21.6 kbit / s could be achieved.

On the other hand, it was possible to reduce the data volume significantly. Thus, replacing the Golay error correcting code by the advanced method of Reed-Solomon, which stressed significantly less bandwidth for similar performance. This measure alone, the usable data rate could be increased by 70%. However, this approach had the disadvantage that the hardware for the Reed - Solomon coding was not duplicated, as was the case with the Golay code, and thus the reliability was no longer given. In the very large image files that most stressed bandwidth with distance, now lossy compression was applied. An elaborate methods such as Huffman coding, however, was not feasible due to the very limited computing and storage resources for this purpose. However, you could make use of the fact that the area outside the planet edge in the four corners of the image contained virtually no relevant information. Instead of 8 bits to send per pixel, only 3 bits have now been shipped, which describes the brightness difference to the previous point. However, we had to reduce the reliability for this measure, by waiving the reserve FDS computer as this has now been used for the performance of the compression algorithms. In sum, the transfer of an image from the Uranus system now took only 15 % longer (104 seconds) than at Saturn, although the bandwidth was reduced by three quarters.

The problem of reduced power supply was met with a firm timetable stipulated when each instrument was allowed to be active. This plan was created with the help of simulations, in which was determined when each instrument brought the greatest benefit. More complicated is designed to deal with the long exposure times that were necessary due to the low light intensity. The biggest problem here was the magnetic tape, which started off the live storage of the image data with the start of exposure and the probe offset a small jerk, which s clearly led streaking at an exposure time of up to 1.44. This effect would be compensated with the targeted use of thrusters. However, these only 5 milliseconds could be operated, which was a problem because the built-in nozzle had to work according to the specification for 10 ms in order to function properly. After they had tried the 5 - ms cycle of several identical models on the earth, and finally at Voyager 1, but showed that you could use with Voyager 2, the method easily.

Six days before the flyby, there were other problems in image transmission. In the compressed images suddenly bright and dark lines appeared. For troubleshooting was invited down a complete memory dump from the FDS. Here it was found that a memory cell, a 1 instead of the correct 0 included. Since the memory cell responding to any commands to the modified software to correct the error. Four days before the flyby, the image system worked properly again.

Uranus

On November 4, 1985 Voyager 2 began their observations of Uranus.

False-color image of Uranus ' rings

The heavily rutted moon Miranda

Uranus in false color

Detail from Miranda's surface

The moon Umbriel

The also strongly deformed moon Ariel

Preparation of the Neptune reconnaissance

After leaving the Uranus system quickly turned the question of the exact trajectory, Voyager 2 should take in the upcoming passage of Neptune. Since, according to Neptune no other goal more should be served, could be chosen from many possible paths. Each route had concerning monitoring their own advantages and disadvantages, so the teams tried to push each best path for her portfolio. The atmospheres department demanded a close as possible flyby, the planet scientists wanted to introduce Voyager 2 as close as possible to the only achievable moon Triton and the Department of particles and radiation measurement preferred a more distant flyby. At the end, they agreed on a compromise, which also included the now newly discovered rings of Neptune. The route should introduce the probe up to 4800 km of Neptune and saw a passage from Triton at a distance of 38,500 km ago. The route was released in the summer of 1986 and on 14 February 1987, the thrusters were activated for one and a half hours, which brought the final probe on its course to Neptune. Since the Neptune system was poorly understood, it also stored a set of instructions for an emergency course, if unforeseen hazards should threaten the probe seriously.

In the transmission of scientific data, the same problem arose as the Uranus - passage, the distance was increased still further. In order to once again significantly lower reception level, due to the large distance and the weaker power of the probe ( 370 W, 30 W less than with Uranus), counteract, the reception facilities have been improved on the earth. These included the following measures:

• Poorer noise receiver to the DSN antennas ( 55 % reception level )
• Magnification of 64 m to 70 m in diameter antennas
• Interconnecting the antennas in Canberra ( partially also an additional 64- m antenna in Usuda )
• And connecting the antennas of Goldstone with those of the Very Large Array

These measures data rates from 19 to 22 kbit / s were achieved. In addition, they improved the evaluation of the S-band experiment, since the reception level fell later below a critical level, so that one could see into the atmosphere of Neptune deeper.

In the observations, the mission team had to work with even greater restrictions than Uranus. By 30 W lower energy level even less instruments could be operated in parallel. To comply with this measure software current power consumption and switched instruments from when the limits are exceeded. Due to the large distance also increased the signal propagation times, so that the probe had to work increasingly autonomous. We therefore created based on the web data which have been obtained in a timely manner, to enable accurate calculations possible, multiple instruction sets for the respective phases of flight and sent them to the probe.

This was possible mainly through further waiver of redundant computer systems so that there is sufficient disk space and processing capacity was available for new functions. Judging by their age and the officially projected lifetime Voyager 2 was in a remarkably good condition. In addition to the early primary transmitter failed some memory blocks were only defective in the two FDS computers and the PPS instrument some filters had failed.

Neptune

On 6 June 1989, the active Neptune phase of the probe began 80 days before the flyby. The intensive observation of the Neptune system began then two months later, on August 6, 20 days before the flyby. This then took place on August 26 at a distance of 4828 km. The observation period ended on 2 October 1989, after more than 9000 images were transferred.

Already on March 18, still a good three months before the active phase, intense, narrow-band radio signals from Neptune could be captured and so his inner rotation speed can be determined. During the primary phase could be found by very long exposures, the rings of Neptune, whose existence could only guess before. For measurements of the magnetic field, it turned out to be much weaker than that of the Uranus.

When flying through the Neptune system Voyager could find nine new moons 2 equals. As these moons were not yet known, one could not change much of the monitoring program. Only Proteus was discovered early enough to be observed in more detail can. The previously known Triton, however, could be examined very closely and was a key point of the scientific mission. First, Voyager 2 was able to determine its exact size. In the literature, then took a diameter of 3800-5000 km of which, however, turned out to be wrong: The measurements gave a diameter of 2760 km. Triton's surface showed little impact craters and had a rather corrugated profile with no great height anomalies on. As a predominant colors appeared brown and white. The latter is a result of volcanic activity on the moon. Geysers hurl large amount of liquid nitrogen in the air, which as a white nitrogen snow descends then freezes at -210 ° C and on the surface. The atmosphere Tritons was investigated with the RSS instrument, there was only one pressure 10-14 μBar at ground level.

The moon Triton

Neptune's "Great Dark Spot "

The ring system of Neptune

The moon Proteus

A mosaic Tritons

Interstellar Mission

Since the passage of Neptune during the Voyager 2 as its sister probe Voyager 1 is on the way to the outer regions of the solar system and beyond. The aim of the " Voyager Interstellar Mission " (VIM ) is the study of the edge regions of the solar system and the surrounding interstellar space. Here, Voyager 2 is moving at a speed of 3.3 astronomical units per year on a track 48 ° ( south ) to the ecliptic. In August 2007, the spacecraft crossed three years after Voyager 1 the termination shock and entered the " Heliosheath " said outer region of the heliosphere one in which to mix the solar wind and interstellar medium.

Old (left) and new (right) idea of ​​the solar magnetic field

Position and course of Voyager 1 (red) and Voyager 2 15 February 2009 from three different perspectives

The heliosphere of the sun, the heliopause and interstellar space to Alpha Centauri - size ratios

Current status

Probe

• Distance traveled (as ): 22.581 billion km = 150.94 AE

• Remaining fuel: 26.25 kg
• Performance of the radionuclide: 262.4 watts ( about 44 % power loss )
• Data rate real time: 0,016 kbit / s ( 34 m antennas of DSN)
• Maximum data rate: 1.4 kbit / s ( with 70 - m antennas of the DSN, Booth 1999)

Instruments

Booth: 2008

Voyager Golden Record

In " Golden Voyager Record" is a data record which is made of copper and is plated with gold ( protection against corrosion). On her image and audio information about humanity are stored. On the front there is among other things a kind of instructions and a map showing the position of the sun relative to 14 pulsars.

Distance Chart

Popular Cultural Reception

Voyager 2 and its sister probe Voyager 1 attracted particularly during their early mission phase much attention, even in the general public. This is mainly due to the extraordinary mission profile ( particularly with regard to the distances ) and the very high quality for that time color photographs diverse motives. The idea of sending a " message to Space" by the Voyager Golden Record - plate attracted great attention.