NASA’s most iconic and two of the well known space probes Voyager 1 and Voyager 2 were launched in 1977, one month apart from each other from the Cape Canaveral facility in Florida. The two probes were originally designed to study the outer solar system with flybys of Jupiter, Saturn, Uranus and Neptune. While an encounter with Pluto could also have been arranged, however a more promising flyby of Titan took precedence.
Both the Voyager probes are currently exploring the outermost limits of the sun’s magnetic field and the realms of interstellar space. Had both the Voyager probes ended their missions right after completing their initial mission, it still would be one of the biggest achievement in the history of mankind.
Even after doubling their intended journey already, the Voyagers continue to transmit critical scientific data back to earth, which has led to the discovery of various unknown aspects of our solar system and beyond. It is also helping researchers to answer complex questions about the evolution of planets in the solar system. Below are few of the most interesting facts and statistics about Voyager probes that one should know.
15. Voyagers Were Originally a Part of the Mariner Program
The two Voyager probes were initially conceived under the Grand Tour Program, in which a total of four robotic probes would visit all the five outer planets in our solar system (Pluto was considered a planet back then). The program was cancelled after the estimated cost of the entire mission exceed $1 billion.
The idea of a Jupiter-Saturn flyby was however revived in a downscale mode under the Mariner program. Mariner was a 10 mission program, which performed the first planetary flyby of the inner planets in the mid 1960s. Instead of four, only two probes were sanctioned to conduct a flyby of four outer planets and Saturn’s moon Titan. The program was later renamed the Voyager, couple of months before the launch in 1977.
14. The Voyager 2 was Launched Before Voyager 1
To take the full advantage of the rare planetary alignment, the two probes were launched using two different trajectories. The Voyager 2 was the first to launch on August 20th 1977. It visited Jupiter, then Saturn and the timing of its launch allowed the probe to visit Uranus and Neptune.
Voyager 1 was launched about two weeks after the Voyager 2 from Cape Canaveral launch site. The probe took a more direct route and reached Jupiter three months before her sister probe. It encounter Saturn a year later in 1980 and then went on to explore the interstellar space. A Titan flyby was an important component of Voyager 1 trajectory.
13. The Golden Record
Both probes carry a specially carved gold-plated audio and video disc. The disc contains sounds and images of selected objects and creatures on earth to portray the diversity of life here, for intelligent lifeforms out there in space. The records carry images of Earth, the sounds of other animals, a wide collection of music, along with other scientific information.
It also carries verbal greetings in 55 different languages. All the contents of the golden record were selected by the famous astronomer Carl Sagan, along with others like Frank Drake, Timothy Ferris and Ann Druyan.
12. Voyager 1 Took the Farthest Ever Image of Our Solar System
The Pale Blue Dot (the blueish dot about halfway down the brown band in far right) is the Earth from 6 billion kilometers.
On Feb 14, 1990, after the Voyager 1 passed the orbits of Pluto, it took one last picture of the Earth and solar system. At that time the probe was 6 billion kilometers away from the Sun or at a distance of 40.5 AU (Pluto is 39.5 AU). It took the first ever “family portrait” of the Sun along with the planets.
In this image, Earth appears nothing more than a tiny dot in the space, occupying less space than a pixel. The idea of taking an image of the earth of this magnitude was initially suggested by the Carl Sagan back in 1980.
11. How Big Are The Voyager probes?
Without antennas and outer structures, the core body of the probes is not more than 4 meters on each side. Both carry various identical structures of different heights. At the time of launch, the Voyager weight was around 815 kilograms, including fuel. In comparison, it is much lighter than even a compact car.
According to an estimation, the current weight of the Voyager 1 and Voyager 2 is 733 kg and 735 kg respectively. The difference in weight is due to the fuel remaining in both the probes, which are used to power the thrusters.
10. Where are the They Now?
Position of the Voyager Probes in Logarithmic scale
The Voyagers are surely the farthest man made objects in the space, but where are they exactly? According to NASA, the data retrieved from Voyager 1 at the end of 2012 indicated that the probe had already left the solar system. By June 2012, the probe started detecting changes in its environment and reported a significant increase in radiation from the interstellar space, which are normally deflected by the heliosphere.
The probe is now more than 21 billion kilometers away from the earth in the interstellar medium, travelling at an estimated velocity (relative to the Sun) of 16.9995 kps. The Voyager 2 on the other hand is about 17.5 billion km away from the Earth and is currently travelling through the heliosheath.
9. Where they are heading?
Image of Sirius taken from the Hubble Space Telescope
Unless they collide with any interstellar object and come to an abrupt end, both the Voyagers are bound to wander the Milky Way for eternity. Though the Voyager 1 is not headed towards any particular star, in about 40,000 years, it will make a close pass by of the star Gliese 445, located 17.1 light years away from the earth in the constellation of Camelopardalis.
Her twin sister, the Voyager 2 is expected to reach the interstellar space sometime between 2019 to 2020. Based on its current trajectory and velocity, it is expected to pass by the star Ross 248 in 40,000 years. If left undisturbed, it should come within 4.3 light years distance to Sirius, the brightest star in the night sky in about 296,000 years.
8. How They Communicate With Earth?
Canberra Deep Space Communication Complex Image Courtesy: Ryan Wick
The communication apparatus of the two probes was designed to withstand harsh conditions and were intended to be used beyond the limits of the solar system. They normally transmit data with the help of a high-gain antenna, which are then received by NASA’s Deep Space Network satellites here on Earth.
In situations where any of the space probes are unable to send data in near real time, an on-board DTR or digital tape recorder can store the 64 kilobytes of data and send it back to earth based receivers some other time.
7. Computers Used on Voyager Spacecrafts
There are basically three types of computers on-board both the Voyager spacecrafts. With two of each type.
Computer Command System (CCS): It’s a 18 bit, interrupt type processor with a non-volatile memory. CCS basically has two broad functions; receive instructions from the earth based controllers and administer the spacecraft and look out of any malfunctions. It controls various important functions in the probe, including cameras, fault detection, sequencing routines and antenna pointing routines.
Flight Data System (FDS): Flight Data System is a 16 bit word machine with modular memories. It carries an imaging parameter table, which controls all the visible light operation of the on-board camera.
Attitude and Articulation Control System (AACS): The Attitude and Articulation Control System guide the orientation of the probe and controls the direction of high gain antenna.
6. And How Fast Are Their Computers?
The computers aboard in Voyager probes have 69.3 kilobytes of memory in total, each. That’s enough for an average JPEG image file. At their maximum, its machines are capable of performing 81,000 instructions/second. An old smartphone is probably 7,500 times faster. Moreover, both the probes send data back to earth at the rate of 160 bits per seconds, that’s way slower than even a dial up connection.
5. How Much longer can the Voyagers Continue to Function?
A diagram of RTG fuel container
To power their electric instruments, both the Voyagers are equipped with three radioisotope thermoelectric generators or RTGs, with each having 24 pressed plutonium-238 oxide spheres. Due to the fact that the total power output of these generators declines over time, power management has now become an important component of the mission.
The mission controllers have opted to disable various on-board instruments on both the probes which are less likely to provide any important information in order to save energy. However, engineers believe that they have to start shutting Voyager 2 instruments one by one from 2020 to extend its life. Both the probes are expected to relay information until its power dries out in 2025.
4. What Are their Most Important Discoveries?
Vulcanic Explosion on jupiter’s moon Io
The Voyagers began their journey of scientific exploration shortly after reaching Jupiter. At that time, it was only the second mission to study the gas giant. Here, both Voyagers made close studies about its moon and magnetic field, the probes were the first to detect Jovian planetary rings. Volcanic eruption on the surface of Io, one of Jupiter’s moons, was also captured by Voyager 1.
Then, during their flyby of Saturn, they discovered the high concentration of hydrogen in its upper atmosphere and its fluctuating temperatures in different pressure zones. One of the main interest of the Voyager 1 was a flyby of Titan, which was known to have an atmosphere.
Further exploration of Saturn’s moon Titan resulted in future missions like Galileo mission and the Cassini mission to Saturn as well as the discovery of three new satellites at Saturn using Earth-based instruments.
3. Voyager 2 Discoveries During its Uranus and Neptune Flyby
A high resolution image of Neptune’s bright cloud streaks
To this day, Voyager 2 remains the only probe to visit the two ice giants at very far end of the solar system. Voyager studied about Uranus’ complex atmosphere, found several new moons and its ring system. For the first time, we were able to discover the significant magnetic field of the planet.
Even though, Neptune has been studied for years with the help of more advanced telescopes, data from Voyager 2 is still considered the best in Neptune’s case. Voyager 2’s flyby of this big icy planet revealed its dynamic atmosphere and furious winds, which were nine times stronger than anything on the Earth.
One of its mysterious discoveries on Neptune was the Great Dark Spot. However, the spot disappeared during the Hubble’s observations in 1994.
2. A Group of Amateur Radio Astronomers Tracked Voyager 1 in 2006
Back in 2006, a group of amateur radio astronomers from the AMSAT Germany tracked down Voyager 1 after receiving radio signals from the probe. It was an unprecedented feat and currently remain that way. The data was later cross-checked and verified by the researchers at the Deep Space Network station at Madrid, Spain.
In 2014, NASA announced that the distant probe had entered a region of space called heliosheath and was at 94 AU.
1. Have they actually exited the solar system?
An artist impression of the Oort cloud
The answer is no. Sometimes its mentioned that the Voyager probes along with Pioneers 10 and 11 have already left the solar system but it is technically not true. Right now there are five man-made satellites that have crossed all the known planets in our solar system, the latest being the New Horizons but none of them have actually exited the solar system.
To depart our solar system in a true sense, one need to cross the Oort cloud. The Oort cloud is basically giant spherical shell orbiting the Sun, which is comprised of billions of small and large icy bodies. Researchers believe that the actual limits of the solar system is extended to the outer edge of the Oort cloud, which stretches from 0.8 – 3.2 light years.
From their current positions, Voyagers will take about 300 years to reach the Oort cloud and another 30,000 years to cross it.