Voyager 2 was launched on August 20, 1977. Sixteen days later, Voyager 1 was launched on September 5, 1977.

Why was the first spacecraft numbered #2 and the second spacecraft numbered #1?


Clarification: One would expect that the first spacecraft to be manufactured would be the first ready for launch. Since that didn't happen, there is more to the story, and that is what this question is about.

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    That still doesn't explain why #2 was launched first. – Dr Sheldon Nov 12 at 11:12
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    Voyager 1 was started later but used a faster trajectory. From wikipedia "On November 7, 2012, Voyager 2 reached 100 AU from the sun, making it the third human-made object to reach 100 AU. Voyager 1 was 122 AU from the Sun" , "In 2013 Voyager 1 was escaping the solar system at a speed of about 3.6 AU per year, while Voyager 2 was only escaping at 3.3 AU per year.[41] (Each year Voyager 1 increases its lead over Voyager 2) ". – Uwe Nov 12 at 12:11
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    There is a very good documentary on the Voyager spacecraft called "The Farthest" available on Netflix. I watched it a few nights ago and the numbering was explained there as well. – James Nov 12 at 16:57
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    While I don't know for sure, I would think that something like the Voyagers would be built in parallel, rather than one after the other. – jamesqf Nov 12 at 17:57
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    On MER we numbered the builds, but used letters for the launches. So MER-1 was built before MER-2. MER-A would both launch and arrive first, and MER-B would launch and arrive second. We weren't sure which hardware would launch first, and in fact due to how system testing on the two units was laid out, MER-2 became MER-A (Spirit), and MER-1 became MER-B (Opportunity). – Mark Adler Nov 12 at 21:18
up vote 67 down vote accepted

Voyager 1 was the first to reach Jupiter and the first to reach Saturn, as it was launched on a "shorter and faster trajectory" (Wikipedia, NASA). So the numbering was chosen to reflect the order of the main part of the mission, not the launches.

I have not found any sources explicitly stating that as the reason, but the arrivals at Jupiter and Saturn received much more publicity than the launches, and at the time it certainly seemed natural that the first Voyager mission to reach Jupiter would be Voyager 1.

In Exploring Space by William E. Burrows, there is the following footnote:

Three weeks before the scheduled launch, the spacecraft that was originally to be Voyager 2 developed mechanical problems. As a result, a "spare" that actually carried the designation Voyager 3 became Voyager 2. Once repaired, the original Voyager 2 was made Voyager 1. The original voyager 1 was shipped back to JPL.

This at least shows that the naming had nothing to do when when each piece of hardware became available, since they renamed the hardware when they had to swap it out.

A reference to a NASA memo or even contemporaneous media coverage specifically supporting this reason would be a better answer, but this is what I have.

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