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44 years and more than 20 billion kilometers in space: The source that feeds two Voyager spacecraft

Category: English  |   20 Август 2021    

44 years and more than 20 billion kilometers in space: The source that feeds two Voyager spacecraft

Voyager-2 is an active space probe launched by NASA on August 20, 1977 as part of the Voyager program for exploring the distant planets of the Solar System. This is the first and only terrestrial spacecraft that reached Uranus (in January 1986) and Neptune (in August 1989). And today it is exactly 44 years since Voyager 2 was launched into space. His achievements are more than grandiose, and even scientists consider his progress impressive. However, energy is needed for its functioning, and NASA scientists thought about this long before the launch of the probe. The method of powering the space probe has been used for more than two dozen space probes for many years.


Radioisotope thermoelectric generator


The more common name is RITEG. This is an innovative method of providing energy to space probes for long-term travel. RITEG is a kind of battery, but it works a little differently compared to conventional batteries. It is better to say that this is a nuclear battery. It functions due to the decay of radioactive material with the release of heat, which is then converted into energy using a thermocouple.


The thermocouple produces a voltage that depends on the temperature. In fact, the difference between temperatures is converted into voltage. When two different metals are connected, and there is a temperature difference between them, a magnetic field is created, which is then converted into a current. How is this difference created?


The main component of all this is a container with radioactive material, called fuel. When the radioactive material decays, it releases heat, which heats one side of the thermocouple — one of the metals. On the other hand, the cold temperature occurs due to the temperature of the environment and deep space, which, as you already know, is very cold. This is an easy way of explaining to imagine the device. However, in reality, these things are much more strictly controlled.



Fig. 1 - The RITEG model


How long will they last?


But, as they say, nothing lasts forever. Each of the radioactive materials has a half-life. The half-life is not the only characteristic that you need to keep in mind when choosing a material: the ability to produce high-energy radiation, the tendency to release heat from radiation decay, a large ratio of thermal power to mass are also among the most important things. The initial list of 1,300 considered radioactive isotopes was reduced to 47 with suitable characteristics. So, what is the half-life?


In fact, it tells us how long it takes for atoms to undergo radioactive decay. This helps specialists choose a material with a longer half-life. Thus, the number of suitable materials is reduced from 47 to 3, the most commonly used: plutonium-238, curium-244 and strontium-90.


How does Voyager 2 work?


Voyager 2 is working with plutonium-238. In total, 3 RTGS, which it is equipped with, were able to provide a space probe with a power of 470 watts at launch. The power is gradually halved every 87.7 years. Why 87.7? This is the half-life of plutonium-238. Now it all comes down to how NASA manages the resources that the spacecraft has at its disposal. And they are incredibly good at doing this so far, saving a lot of energy by shutting down systems that are not needed (permanently) or broken with no chance of improvement. The PPS (Photopolarimetric System) was the first Voyager-2 instrument that was disabled due to a malfunction in 1991, which saved 1.2 watts.


Over time, in order to save energy, other devices were turned off, but it is still expected that by 2025 or a little later, Voyager 2 will no longer be able to power any device. However, it should be noted that he worked longer than most scientists expected, and his results are excellent. Even after Voyager 2 no longer sends signals to Earth, it will continue its journey through space until it possibly reaches another star, if it does not collide with something along the way.


The history of the Voyager 2 space probe


Voyager 2 was launched on August 20, 1977, which is 16 days earlier than Voyager 1.


The Voyager 2 mission initially included studying only Jupiter and Saturn, as well as their moons. The flight path also provided for the possibility of passing by Uranus and Neptune, which was successfully implemented.


The device is identical to Voyager 1. Due to gravitational maneuvers near Jupiter, Saturn and Uranus, Voyager-2 was able to shorten the flight time to Neptune by 18 years (compared to the flight from Earth along the Homan trajectory).


  • On July 9, 1979, the maximum approach to Jupiter (71.4 thousand km). Voyager 2 came close to Europa and Ganymede, the Galilean moons not previously explored by Voyager 1. The transmitted images allowed us to put forward a hypothesis about the existence of a liquid ocean under the surface of Europa. A survey of the largest satellite in the Solar System — Ganymede-showed that it is covered with a crust of "dirty" ice, and its surface is much older than the surface of Europa. After examining the satellites, the device flew past Jupiter.



Fig. 2 - A snapshot of the surface of Europe


  • On August 25, 1981, the maximum approach to Saturn (101 thousand km). The trajectory of the probe passed near the Saturn moons Tethys and Enceladus, the device transmitted detailed photos of the surface of the satellites.



Fig. 3 - Photo of Enceladus


  • On January 24, 1986, the maximum approach to Uranus (81.5 thousand km). The device transmitted thousands of images of Uranus, its moons and rings to Earth. Thanks to these photos, scientists have discovered two new rings and examined nine already known ones. In addition, 11 new Uranus satellites were discovered. The images of one of the moons — Miranda-surprised the researchers. It is assumed that the small satellites cool down quickly after their formation, and are a monotonous desert dotted with craters. However, it turned out that on the surface of Miranda there are valleys and mountain ranges, among which rocky cliffs were noticeable. This suggests that the history of the moon is rich in tectonic and thermal phenomena. Voyager 2 also showed that the temperature at both poles of Uranus was the same, although only one was illuminated by the Sun. The researchers concluded that there is a mechanism of heat transfer from one part of the planet to another. On average, the temperature of Uranium is 59 K, or −214 °C.


  • On August 24, 1989, the device flew 48 thousand km from the surface of Neptune. Unique images of Neptune and its large satellite Triton were obtained. Active geysers were discovered on Triton, which was very unexpected for a satellite remote from the Sun and cold. 4 new satellites were discovered.




Fig. 4 - Photo of a Newt



Fig. 5 - Photo of Neptune


  • On August 30, 2007, the spacecraft reached the boundary of the shock wave and entered the heliopause region.


  • On January 24, 2011, NASA celebrated the 25th anniversary of the Voyager 2 encounter with Uranus. At that time, the spacecraft was about 14 billion km from the Sun, and Voyager 1, sent to study Jupiter and Saturn, flew more than 17 billion km away from the Sun.


  • On November 4, 2011, a command was sent to switch to a spare set of orientation system engines. After 10 days, a confirmation of the switch was received. This will allow the device to work for at least another 10 years.


  • On December 10, 2018, NASA confirmed that Voyager 2 overcame the heliopause and entered interstellar space. The probe remains within the Solar System, the gravitational boundary of which is located beyond the outer edge of the Oort Cloud, a collection of small objects under the gravitational influence of the Sun.


  • On November 2, 2019, NASA announced that it was ready to publish data obtained by the spacecraft in the interstellar medium. On November 4, 2019, five articles were published in the journal Nature Astronomy, each of which describes the results from one of the five Voyager-2 instruments — a magnetic field detector, two particle recorders in different energy ranges and two instruments for studying plasma — a gas consisting of charged particles.


Performance and the expected future fate of the device


By 2012, electric power had fallen by about 45 %. Nevertheless, it is expected that the minimum electricity supply required for research will be maintained until approximately 2025.


  • In about 300 years, the probe will reach the inner edge of the Oort Cloud and it will probably take another 30,000 years to leave it.


  • In 40,000 years, Voyager 2 will pass at a distance of 1.7 light-years from the star Ross 248.


  • In about 296 thousand years, Voyager 2 will disperse from Sirius at a distance of 4.3 light-years.


A gold plate is fixed on board the device, on which the coordinates of the Solar System are indicated for potential aliens and a number of terrestrial sounds and images are recorded.


Sources: New-Science.ru, Wikipedia

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