Excellent Long-term Partnership between Voyager and the Deep Space Network
By: Dr. Peter T. Poon, Telecommunications and Mission Systems Manager
By: Dr. Peter T. Poon, Telecommunications and Mission Systems Manager
NASA’s Deep Space Network (DSN) has been in partnership with Voyager 1 and Voyager 2 since 1977, providing daily communications support to the two very distant spacecraft. The excellent partnership continues as the Voyager twin spacecraft explore the regions of our universe near the area where the solar wind meets the interstellar winds – areas never before explored by human-made objects.
Voyager 1 reached a historic milestone in 2004 when it crossed the termination shock where the solar wind slows abruptly from a speed that ranges from 700,000 to 1.5 million mph. Another important milestone was reached on August 15, 2006 when Voyager 1 became 100 AU (Astronomical Unit) from the Sun! One AU is the average distance from Earth to the Sun, 150 million km, or 93 million miles.
In 2007, Voyager 2 crossed the termination shock multiple times at about 84 AU in the southern Solar System, analogous to surfing across an ocean wave that moved in and out. Since Voyager 1 crossed the termination shock at about 94 AU in the northern part of the Solar System, the crossings of the twin Voyager spacecraft showed the asymmetry of the heliosphere, which may be due to an interstellar magnetic field pushing inwards more in the south than the north as described by Voyager Project Scientist and former JPL Director Dr. Ed Stone who leads the team of Principal Investigators. The excellent Project team effort is led by Project Manager Ed Massey, and many have contributed significantly to the outstanding project, as described by a sample of team members’ quotes.
As of September 1, 2008, at the speed of light, it took about 14 hours and 52 minutes for a signal from Voyager 1, which was about 107 AU away from the Sun, to reach one of the giant antennas of the DSN, and about 11 hours and 58 minutes for Voyager 2, which was nearly 87 AU away from the Sun.
The above to the right, which depicts the termination shock, heliosphere, heliosheath, heliopause and bow shock, shows Voyager 1 having crossed the termination shock and Voyager 2 before crossing the termination shock. The source of the diagram and information is the Voyager Project. The solar wind is a stream of electrically charged ions ejected from the Sun’s atmosphere, which sweeps past all the planets at supersonic speeds. It creates a bubble around the Sun, called the heliosphere, which extends far beyond the orbits of the planets. Inside the heliosphere is a boundary called the termination shock where the speed of the supersonic solar wind is suddenly reduced. The outer boundary of the heliosphere, where the expanding solar wind is balanced by the inward pressure of interstellar matter is called the heliopause. The heliosheath is the region between the termination shock and the heliopause. A bow shock forms as the Sun progresses through the ionized interstellar gas.
Because of the enormous distances and the resultant weak signals from the spacecraft, the large antennas and the very sensitive receivers of the DSN are required to provide the necessary communications capabilities. The DSN is the world’s largest and most sensitive spacecraft communications network. It consists of three deep space communications complexes located approximately 120 degrees of longitude apart around the world: at Goldstone, California; near Madrid, Spain; and near Canberra, Australia. This placement permits continuous communication with a spacecraft.
Each deep space communications complex provides capabilities required to perform telemetry data processing, including signal reception and amplification, signal demodulation and decoding, and data extraction. It also provides a capability to send commands generated by the project to the Voyager spacecraft. All DSN complexes are linked to JPL via a world-wide communications network.
The Deep Space Network, the premier network for deep space communications, allows the Voyager spacecraft to continue to send new and unique data from the far reaches of space. Voyager 1 is the farthest spacecraft from the Sun, even beyond the recently discovered Sedna, and Voyager 2 is the second farthest operating spacecraft. As these distances continue to increase, the DSN has implemented new techniques, such as arraying of antenna and combining of weak signals, that will allow continuing excellent support of the Voyager spacecraft.
The thrilling discoveries during Voyager’s many years of exploration, including the grand tour of the outer planets, would not have been possible without the sustained exemplary support of the Deep Space Network. The excellent Voyager-DSN partnership continues during the Voyager Interstellar Mission as Voyager 1 and 2 explore the transition region between the heliosphere and interstellar space and are poised to become humanity’s first interstellar probes.
The spacecraft are continuing to return data about interplanetary space and some of our stellar neighbors near the edges of the Milky Way.
As the Voyagers cruise gracefully in the solar wind, their fields, particles and waves instruments are studying the space around them. In May 1993, scientists concluded that the plasma wave experiment was picking up radio emissions that originate at the heliopause — the outer edge of our solar system.
The heliopause is the outermost boundary of the solar wind, where the interstellar medium restricts the outward flow of the solar wind and confines it within a magnetic bubble called the heliosphere. The solar wind is made up of electrically charged atomic particles, composed primarily of ionized hydrogen, that stream outward from the Sun.
Exactly where the heliopause is has been one of the great unanswered questions in space physics. By studying the radio emissions, scientists now theorize the heliopause exists some 90 to 120 astronomical units (AU) from the Sun. (One AU is equal to 150 million kilometers (93 million miles), or the distance from the Earth to the Sun.
The Voyagers have also become space-based ultraviolet observatories and their unique location in the universe gives astronomers the best vantage point they have ever had for looking at celestial objects that emit ultraviolet radiation.
The Ultraviolet Spectrometer (UVS) is the only experiment on the scan platform that is still functioning. The scan platform is parked at a fixed position and is not being articulated. The Infrared Spectrometer and Radiometer (IRIS) heater was turned off to save power on Voyager 1 on December 7, 2011. On January 21, 2014 the Scan Platform Supplemental Heater was also turned off to conserve power. The IRIS heater and the Scan Platform Heater were used to keep UVS warm. The UVS temperature has dropped to below the measurement limits of the sensor; however, UVS is still operating. The scientist expect to continue to receive data from the UVS until 2016, at which time the instrument will be turned off to save power.
Yet there are several other fields and particle instruments that can continue to send back data as long as the spacecraft stay alive. They include: the cosmic ray subsystem, the low-energy charge particle instrument, the magnetometer, the plasma subsystem, the plasma wave subsystem and the planetary radio astronomy instrument. Barring any catastrophic events, JPL should be able to retrieve this information for at least the next 20 and perhaps even the next 30 years.