Long Distance Call from 18 Billion Kilometres

Voyager Keeps On Keeping On

Introduction by Robert Brand

It seems that nearly 35 years ago was only yesterday. I clearly remember the excitement of the launch of Voyager II and then soon after Voyager I. I was even at Parkes for the Voyager II encounters with Uranus and Neptune. I was on the tail end of the Giotto project when Voyager was  flying past Uranus and then I was visiting again when it encountered Neptune. That was some 23 odd years ago for that last encounter.

OTC of course had action to take with critical coverage of the various encounters and I also took part in those. Mostly is was “Don’t Touch”.

Closest approach to Uranus occurred on January 24, 1986 by Voyager 2.

Closest approach to Neptune occurred on August 25, 1989 by Voyager 2.

I have been watching closely over the years as it progressed to its current point on the edge of our solar system. The data rates have fallen as the distance has increased. Data rates are now around 1.2kb per second. It would not be able to send back happy snaps quickly if it had anything to snap! Parkes and Tidbinbilla regularly talk with the craft

The Radioisotope Thermoelectric Generators (RTGs) that provided approximately 470 w of 30 volt DC power at launch are slowing dropping in power and are expected to expire around 2025. Implications for the craft are at the bottom of this post.

Signs Changing Fast for Voyager at Solar System Edge

August 03, 2012     JPL, NASA

Two of three key signs of changes expected to occur at the boundary of interstellar space have changed faster than at any other time in the last seven years, according to new data from NASA’s Voyager 1 spacecraft.

For the last seven years, Voyager 1 has been exploring the outer layer of the bubble of charged particles the sun blows around itself. In one day, on July 28, data from Voyager 1’s cosmic ray instrument showed the level of high-energy cosmic rays originating from outside our solar system jumped by five percent. During the last half of that same day, the level of lower-energy particles originating from inside our solar system dropped by half. However, in three days, the levels had recovered to near their previous levels.

Voyager 2 to Switch to Backup Thruster Set This artist’s concept shows NASA’s two Voyager spacecraft exploring a turbulent region of space known as the heliosheath, the outer shell of the bubble of charged particles around our sun. Image credit: NASA/JPL-Caltech

A third key sign is the direction of the magnetic field, and scientists are eagerly analyzing the data to see whether that has, indeed, changed direction. Scientists expect that all three of these signs will have changed when Voyager 1 has crossed into interstellar space. A preliminary analysis of the latest magnetic field data is expected to be available in the next month.

“These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space,” said Edward Stone, the Voyager project scientist based at the California Institute of Technology, Pasadena, Calif. “We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space.”

The levels of high-energy cosmic ray particles have been increasing for years, but more slowly than they are now. The last jump — of five percent — took one week in May. The levels of lower-energy particles from inside our solar system have been slowly decreasing for the last two years. Scientists expect that the lower-energy particles will drop close to zero when Voyager 1 finally crosses into interstellar space.

“The increase and the decrease are sharper than we’ve seen before, but that’s also what we said about the May data,” Stone said. “The data are changing in ways that we didn’t expect, but Voyager has always surprised us with new discoveries.”

Voyager 1, which launched on Sept. 5, 1977, is 11 billion miles (18 billion kilometers) from the sun. Voyager 2, which launched on Aug. 20, 1977, is close behind, at 9.3 billion miles (15 billion kilometers) from the sun.

“Our two veteran Voyager spacecraft are hale and healthy as they near the 35th anniversary of their launch,” said Suzanne Dodd, Voyager project manager based at NASA’s Jet Propulsion Laboratory, Pasadena. “We know they will cross into interstellar space. It’s just a question of when.”

The Voyager spacecraft were built by JPL, which continues to operate both. JPL is a division of the California Institute of Technology. The Voyager missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate in Washington.

For more information about the Voyager spacecraft, visit: http://www.nasa.gov/voyager .

Power Systems

Spacecraft electrical power is supplied by Radioisotope Thermoelectric Generators (RTGs) that provided approximately 470 w of 30 volt DC power at launch. Due to the natural radioactive decay of the Plutonium fuel source, the electrical energy provided by the RTGs is continually declining. At the beginning of 2008, the power generated by Voyager 1 had dropped to ~ 285 w and to~ 287 w for Voyager 2. Both of these power levels represent better performance than the pre-launch predictions, which included a conservative degradation model for the bi-metallic thermocouples used to convert thermal energy into electrical energy. As the electrical power becomes less and less, power loads on the spacecraft must be turned off in order to avoid having demand exceed supply. As loads are turned off spacecraft capabilities are eliminated. The following table identifies the year when specific capabilities have or will end as a result of the available electrical power limitations.

VOYAGER 1
VOYAGER 2
Power Off Plasma (PLS) Subsystem.

2007-032

PLS Heater

2007-130

Power Off Planetary Radio Astronomy Experiment (PRA)

2008-015

2008-052
Terminate scan platform and Ultra Violet (UV) observations
~EOY 2010
1998-316
Termination of Data Tape Recorder (DTR) operations
~2015*
2007-248**
Termination of gyro operations
~2016
~2015
Initiate instrument power shutdown
~2020***
~2020***
Can no longer power any single instrument
No earlier than 2025
No earlier than 2025

* Limited by ability to capture 1.4 kbps data using a 70m/34m antenna array
In order to maximize the duration of the fields and particles data acquisition capability,

** Voyager 2 DTR operations was no longer needed due to a failure on the high waveform receiver on the Plasma Wave Subsystem (PWS) on June 30th, 2002.

Termination of gyro operations ends the capability to calibrate the magnetometer instrument with magnetometer roll maneuvers (MAGROLs). These maneuvers are performed 6 times a year, on each spacecraft, and consist of a spacecraft attitude maneuver of 10 successive 360 degree turns about the roll axis. Data from a MAGROL allow the spacecraft magnetic field to be determined and subtracted from the magnetometer science data. This is important since the spacecraft magnetic field is larger than the solar magnetic field being measured. The termination of gyro operations also means an end to the attitude maneuvers used to check the combined calibration of the Sun Sensor and the High Gain Antenna pointing direction for maintaining communications with the ground.

*** Science Instruments power shutdown order has not been determined.

The following experiments are expected to be operating by 2020:

Voyager 1: Low-Energy Charged Particles, Cosmic Ray Subsystem, Magnetometer and Plasma Wave Subsystem.

Voyager 2: Low-Energy Charged Particles, Cosmic Ray Subsystem, Magnetometer, Plasma Wave Subsystem and Plasma Subsystem.

The above Courtesy of NASA

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