69 KB of memory and tape storage to conquer space

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When the Voyager probes were launched into space in 1977, they incorporated the latest computer systems. However, like the computers that made it possible for us to set foot on the Moon for the first time, in these times they are exceedingly less capable than the mobile phones we use every day. Still, after almost 45 years exploring the cosmos, these spacecraft are still working.

They have become the first objects created on Earth to enter interstellar space and, if it weren’t for the fact that their radioisotope thermoelectric generators, those in charge of providing energy to operate, are losing power every year and NASA has decided to gradually start to turn off its instruments would continue to function, possibly, for many more decades.

A ship designed for a long duration mission

Although the original plan for Voyager called for its missions to last about four years, the design of the Voyagers turned out to be so good, and the hardware so durable, that They have been exploring space for almost 45 years, which could undoubtedly be described as an engineering achievement at the time. Let’s see what are the computer systems that have allowed these ships to achieve such a feat.

Voyager 1 and 2 probes share the same internal configuration of their computer systems, that is, they are identical. As explained by NASAeach of them has three computers: Computer Command System (CCS), Attitude and Articulation Control System (AACS), and Flight Data System (FDS).

Voyager

Voyager probe at NASA laboratories

Computer Command System. It is one of the neuralgic points of the ship. It is directly connected to the power supply and is responsible for controlling the main functions of the probe. It maintains the adequate temperature for the correct functioning of the components in the extreme temperatures of the space.

It is also responsible for managing navigation, controlling all the instruments that must be turned on and off, and the total configuration of communications. It also includes an autonomous fault detection system, which triggers automatic procedures that can respond to problems, including activating backup components to keep the probe working.

Space is not as empty as we thought: Voyager 1 detects stable plasma emissions beyond the Solar System

As we can see, there are many mission critical functions. All this with an ability to run 11,000 instructions per second and with 69 KB of memory, about 100 thousand times less memory than what we have in a current smartphone. “Voyager computers have less memory than the key fob that opens your car door,” says Linda Spilker, a JPL scientist who worked on the Voyager missions, in an interview with Scientific American.

Articulation and Attitude Control System. This system is identical to the CCS and is responsible for keeping the antenna pointing towards the Earth, thus preventing communications from being interrupted. In addition, when the CCS receives an order to change trajectory, the AACS is in charge of executing it, something that happened one of many times about five years ago when NASA activated the probe’s thrusters after 37 years of inactivity, a task that surprisingly it was completed successfully.

Flight Data System. If we previously mentioned that the AACS and the CSS are identical systems but with different functions, the FDS is literally another world. NASA needed a computer that was fast enough to handle the data, so it made a big bet on using CMOS circuitry.

Voyager Flight Control

Flight Data System

It was a type of circuit that was low-power, fast and tolerant to a wide range of voltages, making it the ideal choice for this space mission. However, remember that we are talking about the seventies, CMOS was completely new, so JPL decided to adopt them with some skepticism, and assuming the risks.

The FDS, which can run 80,000 instructions per second, is in charge of managing the 11 instruments (there are currently fewer in operation), the scientific images and the engineering data. The latter have to do with the state of the probe and allow NASA teams to know if there is a problem, and even take preventive actions to avoid damage to the equipment.

It should be noted that these computers work in a language assembler. Incredibly, back then there weren’t dozens of programmers focused on this task. According to NASA itselfthe software team consisted of one person between 1974 and 1977, with a maximum of four people working full time in 1975.

recording magnetic tape

8 track magnetic tape

An interesting fact is that during their journey through space, the probes constantly send information to Earth. This is because they have a very small storage system, although there are times when the communication link is interrupted. In these cases, Voyagers can store data “locally”. And what support do you use? Some tapes eight-track magnetic tapes that overwrite themselves over and over again.

And, as a curiosity, it should be noted that there are not only two Voyager probes. There are three! Engineers built a third unit, which is a Development Test Model (DTM). The craft was displayed at the National Air and Space Museum for nearly a decade.. However, in 1987 the spacecraft returned to JPL to assist in the development and construction of the Magellan probe.

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In Xataka | Space is not as empty as we thought: Voyager 1 detects stable plasma emissions beyond the Solar System

When the Voyager probes were launched into space in 1977, they incorporated the latest computer systems. However, like the computers…

When the Voyager probes were launched into space in 1977, they incorporated the latest computer systems. However, like the computers…

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