Planetary Pioneer

Tom Krimigis, exploring the solar system since 1965.

Dr. Tom Krimigis with a flight spare of the Low-Energy Charged Particle detector currently flying on the Voyager 1 and Voyager 2 spacecraft. (Johns Hopkins University Applied Physics Laboratory)

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What is it like still working on the Voyager program today, nearly four decades after the two spacecraft launched?

Voyager for me is the mission of my life, my pride and joy. It was the first really complicated instrument that I designed when I came to APL.

Which instrument was that?

The low-energy charged particle instrument: LECP. Unfortunately we were not smart enough to make pronounceable acronyms in those days. [The building of this instrument] illustrates the issues of whether you want to risk things or not. In the early days of the space program you didn’t want to put mechanically moveable devices in space, simply because nobody knew how to lubricate them and it could get stuck—that would be a big problem. My colleagues and I really wanted to make measurements by viewing every direction in the sky. But Voyager spacecraft was always pointed at Earth to download the data. So we had to put a little stepper motor to rotate our instrument. The engineers here at APL were telling me, “Oh you’re crazy, this thing is going to get stuck after a couple of months, and then you won’t be able to do anything with it.”

We tested this stepper motor for about 500,000 steps, because the initial mission was to explore Jupiter and Saturn and that would have taken just four years. We all now know that the spacecraft is alive and well after 37 years in space, and the little stepper motor has gone past 6.5 million steps without failure. But more importantly, we were able to measure the speed of the solar wind after the plasma instrument from MIT that was intended to make that measurement failed soon after Saturn. This measurement was absolutely crucial in determining how far the solar atmosphere extended into the galaxy.

Then, after August 25, [2012, when Voyager 1 crossed the heliopause], the thinking was that things are going to be absolutely calm. Nothing was expected to be moving. There’s no solar wind, no disturbances from the magnetic field. But what we find is that this is absolutely not true. Last year we got hit by a tsunami that originated on the sun and 14 months later hit Voyager, even though we were outside the magnetic envelope of the sun. The stepper device enabled us to determine that radiation (cosmic rays) were not equally intense from all parts of the sky—as they were expected to be—the tsunami scrambled the whole distribution. So the nearby galaxy is not the quiet calm sea that we all expected, it’s one that has all kinds of fluctuations. I get up every morning and look at last night’s data from Voyager!

You are one of the few people who has worked on missions to every planet and Pluto, so what have been some of the more surprising moments?

I have to say that seeing the volcanoes on Io, the moon of Jupiter, on Voyager 1 was the most amazing thing that I’ve personally run into—and so [it was with] all of my other colleagues, because nobody ever knew that there were extraterrestrial volcanoes anywhere. That stands out as a high moment in the level of excitement that we feel when we work with these instruments and make these measurements. In my case I should have had the foresight to see that, because before we ever got to Jupiter we began to see ions of sulfur and oxygen—very far away from Jupiter. We knew that that was very strange, you’re not supposed to see these elements, they’re not that abundant. We stepped into the magnetosphere of Jupiter and we kept seeing lots of this stuff but it never occurred to us that they were coming from a volcano. That was a most surprising moment!

Then the second surprise was getting out of the solar system and into the galaxy. And the way it happened—that was absolutely thrilling.

Within planetary science, what is the next big question? Where should we be sending a probe?


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