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Probing Voyager spacecraft longevity

Posted: 04 Mar 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Voyager? Jet Propulsion Laboratory? reliability? redundancy? electronics parts?

The term "elderly integrated circuits" does not roll easily off the tongue. Yet there are, far from earth, integrated circuits that in semiconductor terms are very elderly indeedand that are still functioning.

They are, of course, components on-board the two spacecraft launched in 1977 and known as Voyager 1 and Voyager 2. As of December 7, 2012, Voyager 1 was 11.5 billion miles (18.51x109km) from earth, and Voyager 2 was 9.4 billion miles (15.13x109km) from earth. Later this year both will complete their thirty-sixth year of flight. Together, because their paths have been far from straight, they have travelled over 30 billion miles (48.28 x109km).

Light traveling from the sun currently takes over 14 hours to reach Voyager 2, and over 17 hours to reach Voyager 1. Seventeen hours is not a light-year, certainly, but it is a respectable portion of a light-day.

Voyager Assembly

Figure 1: A Voyager during assembly. Courtesy: NASA/JPL-Caltech.

The original mission was for both spacecraft to visit Saturn and Jupiter and to send back data that would help greatly in our understanding of the solar system and its evolution. The original mission was completed as planned in four years. The subsequent 32 years of reporting have been a gigantic bonus.

To find out what made such durability and reliability possible, I asked the folks at the Jet Propulsion Laboratory (JPL) two questions:

  • How did engineers in the 1970s manage to obtain integrated circuits and other components what would last this long?
  • How did they ensure that the systems they assembled would also last so long?

Chris Jones

Jones attributes Voyagers' reliability to nine "first principles" in systems engineering.

A small part of the answer seemed obvious: silicon semiconductor line-widths were much larger in the days when components for the Voyagers were being manufacturedprobably from 10?m or larger down to about 3?m. Gigantic by today's standards, but virtually immune to short circuits or other malfunctions caused by electromotive forces (EMF).

To learn the details, I talked with Chris Jones, Assistant Director for Flight Projects and Mission Success at JPL. Jones started at JPL as a systems engineer back in 1969. He agreed that ICs made in the 1970s had the potential for long life. Systems going into the Voyagers used ICs packaged in ceramic, glass and metal, but not plastic, even though plastic packages were available then.

Most of the components were manufactured in the few years before the launch in 1977, he noted. But four of the six computers installed on the Voyagers were residual designs from the Viking programme, dating back to 1969.

The extraordinary longevity of the electronics and systems depends primarily on the list of "first principles" that JPL engineers carefully worked out to give these two spacecraft the best chance for fulfilling their missions. Chris Jones outlined the nine principles:

1. Select quality parts suppliers.
This is the most important principle. Every manufacturer claims to make great components, but you have to know enough to avoid buying a given part from a manufacturer who doesn't make the best.

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