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.

Dr. Stamatios M. (Tom) Krimigis has his fingerprint on many of the unmanned space missions that have left this planet, from the Mariner spacecraft that did the first flyby of Mars in 1965 to the Cassini spacecraft that is still sending back data from Saturn today. He designed a particle detector that continues to operate on both Voyager 1 and 2 as they travel out beyond our solar system. To honor his long career at the Johns Hopkins University Applied Physics Laboratory, he was awarded with the 2015 National Air and Space Trophy for lifetime achievement. Dr. Krimigis spoke with departments editor Heather Goss in January.

Air & Space: One of your biggest accomplishments is getting NASA to start its Discovery Program—a series of innovative, low-cost spacecraft missions—in 1992. You got a lot of pushback when you began promoting this idea. What made you think it was the right path for NASA?

Krimigis: It was the right path for the NASA planetary program, which is an important distinction. The Explorer program had been in existence since the beginning of NASA. It was mostly solar and space physics and some astronomy, but it had been a program that had a certain amount of money every year for missions costing—most of them—less than $100 million apiece.

However, no one had thought of applying that concept to the planetary program. The closest that the planetary program had come to a low-cost concept in the 1980s was the Planetary Observer program, and that started out as an effort to spend like $300 million for a Mars mission. By 1989 it was already pushing $500 million, and everyone was guessing that it would end up costing more like $1 billion. At the time I happened to be a member of NASA’s Planetary Science Subcommittee to study the new missions, and I said, “We’re looking at the wrong paradigm. Why don’t we adopt the Explorer concept as a potential low-cost planetary missions program?” Jeff Briggs was then the director of planetary exploration at NASA, and after I described the concept and how it could be used, he came up to me and said, “Would you like to send us an unsolicited proposal so you can study it from the Applied Physics Laboratory?” That eventually gave rise to the Discovery program.

We came up with a concept that would be less than $150 million per mission [through the first month of operations], and when that report became public most people sort of laughed and said, “oh yeah?” Up until that time every planetary mission was costing several hundred million or more. Of course it’s not just enough to suggest an idea; the proof is in the pudding. If you’re really going to push a new concept then you have to demonstrate that it works. We competed at that time with JPL and were selected to do the NEAR mission, which was the first Discovery mission. We had estimated that it would cost about $112 million, which was substantially less than the $150 million guideline, and by the time we finished it had cost us about that amount, so we ended up turning money back to NASA, which had never happened before. I have a picture of me giving a check to Dan Goldin and Senator [Barbara] Mikulski after we launched NEAR in 1996.

Now, more than two decades after the Discovery Program started, cubesats are the big trend, and there’s talk about using them for planetary missions. Do you think that’s a real option, or is that concept overhyped a little bit?

I think it is overhyped for a very simple reason: You need a certain amount of power to send data back from a planet, and that means you’ve got to have fairly large solar panels, which are of course heavy and somewhat expensive. On the other hand, there are concepts [involving cubesats] that people could use, and I think they’re being circulated as we speak, about getting more science out. For example, you’ve probably heard about the Europa Clipper mission, and in fact it was [proposed] in the NASA budget for the first time this year. The intent is to go and orbit Europa, the satellite of Jupiter, and that’s going to be a fairly big and expensive spacecraft, but what can one do with cubesats? Well you can have a number of small cubesats that you can shoot off from the main spacecraft that would collect data at different places around Europa simultaneously and transfer the data to the main spacecraft, which would then send it to Earth. That kind of scheme would work in the sense that it really enhances the science, and for not very much more cost, because you cannot just send a cubesat to Jupiter on its own. There isn’t enough power and mass and everything else to really do a decent job on the science.

You worked on the Mariner program in the early 1960s, including Mariner 4, the first spacecraft to fly by Mars. What it was like to be a part of these early missions?

Needless to say, for a graduate student it was an exhilarating experience because at that time things were moving very quickly. Professor [James] Van Allen, my thesis advisor [at the University of Iowa], called me into his office and said, “How about being the co-investigator on Mariner, the first mission to Mars, and building an instrument that could discriminate between electrons and protons?” I said, “I’m not sure I know how to do that.” He said, “You’ll learn.” That was his way of teaching you—he’d throw you overboard and see if you could swim.

The launch was a year and a half away. I finally got that detector working about a month before we launched. It was an agonizing experience but it was a lot of fun. At the time we knew about the Van Allen belts of Earth, but nobody knew if any other planet had radiation belts. Our main objective was to see if there were Van Allen belts at Mars.

Of course, we flew fairly close to Mars but we didn’t find any radiation belts. That was a big disappointment. But we discovered other things on the way, things like the fact that the sun was emitting fast electrons, which nobody knew before that time. That’s how I learned firsthand how to do things fairly quickly in building space hardware; but we also built some Earth satellites at Iowa—the first university-built spacecraft were actually built at the University of Iowa. So when I came to APL and found that they were already building spacecraft with a very short timetable, it was easy for me to fit into the culture—I already had it. That’s what led to eventually saying, “Hey, why can’t planetary missions be done like this?,” which led to the Discovery program.

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?

Being a principal investigator on Cassini and knowing about all of the discoveries there, I have to say that investigation of [Saturn’s moon] Titan in detail is really an intriguing possibility. The discovery by Cassini of these lakes and rivers of methane at minus 182 degrees centigrade is just astounding. In addition, there is an inference that there is an underground ocean of liquid water under the crust of Titan. To go and land there, and watch the weather, and float in the lakes and see lightning and other things as they operate in the primitive atmosphere of mostly nitrogen and methane and acetylene—it would be a terrific exploratory mission. And it is possible with today’s technology. I think that’s one big objective.

The other part at Saturn is, of course, the Enceladus geysers that are coming from the south pole, which have all these organic materials with no real understanding of where that organic material is coming from. I think of these two questions just because I’m so intimately involved in the Cassini mission.

But I have to say that now that we know what we know from Voyager, I think the country is missing a big opportunity to really further explore where our solar system is headed into the galaxy. We have been studying for years—by “we” I mean the whole scientific community—what’s called an interstellar probe that would go much faster than Voyager and get into the galaxy and provide data for the next 30-40 years, but unfortunately, the funding isn’t there to do such pioneering missions anymore.

Do you think New Horizons will provide some of that data?

Not really, New Horizons of course will do this exploratory mission of Pluto, and after that we’re going to try to head it to a Kuiper belt object, but it is not as fast as Voyager, simply because in addition to going by Pluto we will also do this KBO flyby. So New Horizons will not have either the communications capability or the speed, even if it lives as long as Voyager. We’re going to have to come up with a brand new mission with new technology and ways to speed it up a lot, maybe by getting the gravitational assist from the sun itself to really move it out at a speed at least three to four times that of Voyager. And I don’t see that happening, unfortunately.

My dream for years had been to do a solar probe, and finally we are doing that here at this laboratory. It’s called Solar Probe Plus. It will get within six million kilometers of the sun after we launch in 2018. So we’re making progress—we have a mission to a star!

Get the latest stories in your inbox every weekday.