Q&A with New Horizons Principal Investigator Alan Stern

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Profile | Alan Stern
Principal Investigator for NASA’s New Horizons mission


Approaching 15 Minutes of Fame

For Alan Stern, the wait is almost over. On July 14, NASA’s New Horizons spacecraft, after a journey spanning nearly a decade, will fly past Pluto at 50,000 kilometers per hour, becoming the first spacecraft to make a close approach to this distant world that, for three-quarters of a century, was classified as the ninth planet. Images and other data returned so far by the spacecraft have offered tantalizing hints of what to expect when the spacecraft makes its closest approach.

NASA got a brief scare July 4 when a computer glitch caused a momentary loss of communications and sent the probe into safe mode. But the problem was quickly resolved and New Horizons resumed normal operations and data collection July 7.

For Stern, the flyby will be the culmination of an effort that started long before the spacecraft’s January 2006 launch or even NASA’s November 2001 approval of the mission. He was among a small group of planetary scientists that started campaigning for a Pluto mission back in the late 1980s, supporting earlier mission concepts that never got off the ground, like Pluto Fast Flyby and Pluto-Kuiper Express. Those years of advocacy, planning and spacecraft development work are now on the verge of coming to fruition.

After the Pluto flyby, and pending approval by NASA, New Horizons will move into the Kuiper belt of small planetary bodies. To date, two such objects have been identified as candidates for a possible flyby.

Stern spoke with SpaceNews senior staff writer Jeff Foust June 29, just hours after astronomers using assets including NASA’s Stratospheric Observatory For Infrared Astronomy observed Pluto pass in front of a star as a tune-up for the New Horizons flyby.


What was the importance of the SOFIA and other observations?

I heard from multiple sources that SOFIA detected an atmosphere. That was important from my standpoint because we have such a big stake in atmospheric science on the flyby. There wasn’t much risk that the atmosphere would collapse between last year and this year, but the actual confirmation of it being there today is good news.

How does that affect your planning for the flyby?

That doesn’t really go into our planning because all the plans were written and the spacecraft sequences have been tested. But it bodes well for very good results coming out of that.

What are you doing now to prepare for the flyby?

It’s a layered and very complex operation. We have new data coming to the ground every day. Today we got new images, ultraviolet spectroscopy, infrared mapping spectroscopy, and fields and particles data. So that’s one thread. Another thread is that we are doing mission planning. We just signed off on the last review in which we looked over the simulator results for the command load that we’ll execute at closest approach. So we’re doing mission planning as we’re analyzing data.

At the same time, the optical navigation activities continue for hitting the aim point. And we’re still conducing hazard searches. We haven’t yet found anything that is of concern, but every time we get closer, we win in two different ways. We win in light sensitivity, and we win our ability to see in close as our field of view expands.

We’re also talking with the media. There’s so much interest in this mission, honestly, it’s way beyond the normal space press. A lot of people on the science team and mission operations team are spending some effort on that. We’re also working Kuiper Belt Object (KBO) planning because we have to execute the targeting maneuver in the fall, so there are some elements of KBO targets, KBO selection, and Hubble data helping us refine the orbits of the targets.

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Artist’s conception of New Horizon’s spacecraft on its Pluto flyby. Credit: NASA

What’s the risk of any hazards, like moons or rings, to the spacecraft as it flies past Pluto?

We’re now able to see much better than Hubble. We can look for objects that are more than an order of magnitude fainter, so a factor of several times smaller and several times less massive than anything you can see from Earth, even with Hubble. But the watch, the seven weeks of suspense, actually ends on Friday [July 3]. And then we will continue to be vigilant.

We had established an estimated probability of loss of mission due to a debris strike at about 1 in 10,000 before we got started. We have now pushed that down considerably from there by being able to search for fainter satellites, and faint rings, and things like that. We could fly through the system and look back — and we’ve planned this — and we could well then see tenuous rings, like at Uranus. But if they’re that faint, then you can fly right through them. There’s no hazard. We’re looking at being in pretty good shape, but we’re not quite done. [On July 1, NASA announced that the hazard search had ended, finding nothing that would require New Horizons to change course.]

What is the health of the spacecraft?

The spacecraft is operating flawlessly. It’s running on all of its prime systems: we are not using any of its backups. Fuel is good. So far the trajectory burns we’ve planned or already executed add up to about 20 percent of the amount we budgeted for targeting. That’s really good news. That leaves us a little bit more fuel in our pocket for the Kuiper Belt. All the instruments are operating and returning good data. Of the seven instruments, six of them are already returning useful data of the Pluto system or the Pluto plasma environment. One of them, the radio science experiment, doesn’t kick in until we’re much closer.

What happens on the day of the flyby itself?

We’re sending data down now: not just imagery but other data, such as from the spectrometers. And each day up until the encounter, there will be new images with better and better resolution each day. On the 12th and 13th [of July] there will be some really juicy data coming to the ground for composition and geology of both Pluto and Charon, and the smaller moons as well.

On encounter day, the spacecraft doesn’t send any data home. It spends the whole day collecting data. The spacecraft is doing over 300 observations that day. Then, on the 15th, the day after the flyby, it starts downloading. Every day for about a week we get a major data drop with different kinds of data: imagery, spectra, particles and fields, atmospheric occultation, etc. There will be plenty to see.

How are the data going to be released?

Our arrival date, the 14th, will be the 50th anniversary, to the very day, of the first spacecraft arrival at Mars, Mariner 4. In those days, Mariner 4 sent 22 megabits to the ground. It took them several months to ship it to the ground, at 8.33 bits per second. That included 21 images and other data sets.

July 3 photo of Pluto taken form New Horizons. Credit:NASA/JHUAPL/SWRI
July 3 photo of Pluto taken form New Horizons. Credit:NASA/JHUAPL/SWRI

We’re sending back several thousand times that amount of data. We put every single high-resolution image, and there are multiple images per day taken for any purpose, on a website where anyone can download them. People are having a ball with some of those images.

We will have a major press conference at the Applied Physics Laboratory on the 15th, the day after the flyby, and then NASA will hold a big press conference on the 17th, and again on the 23rd. We’re also being followed around by four different TV networks doing documentaries about New Horizons: Discovery Channel, PBS Nova, National Geographic and NHK. Those will all air the week of the flyby.

You’re also a part of the European Space Agency’s Rosetta comet mission. Are there any lessons, scientific or technical, from that mission that you can apply to New Horizons?

It’s pretty complicated. The Europeans run their missions differently. I just run one instrument team on that. But that instrument, which is an Alice ultraviolet spectrometer, has its sibling on New Horizons. The very first Alice we built is on Rosetta. The second one is on New Horizons, the third one is on Lunar Reconnaissance Orbiter, and the fourth one is on Juno. So we do learn lessons from the different Alices.

Scientifically, I expect we’ll have a lot to say. Rosetta is studying a small Kuiper Belt object that came into the inner solar system from the Kuiper Belt. And New Horizons is going all the way to the Kuiper Belt to study the largest thing in the Kuiper Belt. So they are intellectually related in terms of what we’re trying to do, to understand the Kuiper Belt and the accretion processes that led to larger planets. All these things fit together into a bigger puzzle of solar system science.

NewHorizonsB_NASA02.jpg
Credit: NASA

What happens after the flyby?

I would not be surprised, if it turns out to be as interesting as some of us think, that there’s going to be serious discussion of a return mission that’s much more in depth. For those of us on New Horizons, this is the beginning. Now we’re going to have data. Now we’re going to have years of getting the data to the ground and analyzing it and building models to try and understand this place. And it’s not just one place, it’s six places with all the satellites. And then we’ve got a KBO flyby to go propose. If we get it, we’ve got to plan that flyby, navigate it, execute it, and then get that data. Then there’s an interstellar mission like Voyager. We have [radioisotope thermo-electric] power on the spacecraft that lasts into the 2030s. New Horizons, I think, has a bright future. We could even get a second KBO flyby. For most of us, we’re just dying to get our hands on the data.

What is the status of the proposed KBO flyby?

The Hubble time we got last year located two feasible targets. They’re both arrivals in 2019, one in January and one in March. We have been repeatedly observing with Hubble in order to refine their orbits with the objective of getting the targeting burn resolution to be very good. They both continue to look good to us.

We will go to NASA Headquarters in August and make a recommendation to choose between the two targets. We can only go to one or the other, since they’re in different directions. We have to do targeting maneuvers in the fall because if you wait, the fuel cost goes up and we very quickly eliminate our ability to do the mission. We need to do the burns in 2015.

Then, next year, when NASA conducts its senior review, we’ll write a proposal for the funding. Our current mission runs through 2017, but to fly to a KBO requires funding for that part of the mission. NASA will make a call on that at some point late next year.

Do you plan to spend some time getting back into commercial projects like Golden Spike and suborbital research after the flyby?

Yes. Probably a number of people I know are going to be after me because they all gave me grace for the last six months to take a break and do New Horizons. On Rosetta, I had my deputy principal investigator, Joel Parker, take over May 1 with the instructions that unless something really goes “red alarm,” I don’t want to hear about Rosetta. I’m not even going to read the weekly reports. I’ll come back Aug. 1.

Have you been surprised by the public interest in the Pluto flyby?

It’s much greater than anything I can think of in recent memory. I went downtown and briefed [NASA Administrator] Charlie Bolden and [NASA Associate Administrator for Science] John Grunsfeld on this, and they both felt like this was going to be the story of the year, maybe the story of the decade. It’s an extreme event. There’s nothing like it. There’s been nothing like it since Voyager, and when you couple it with that there’s nothing like it planned to happen again, it gets a lot of people’s attention. A friend of mine told me, “I’m being bombarded by magazines. Your mission’s on the cover of every one of them.”

The band Styx, also the name of Pluto's fifth moon, recently visited Stern at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Credit: NASA, Joel Kowsky
The band Styx, also the name of Pluto’s fifth moon, recently visited Stern at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Credit: NASA, Joel Kowsky

Your typical mission doesn’t have four documentaries being made about it in real time. It doesn’t show up so ubiquitously. We have three hundred press that are registered to be at the flyby from every continent except Antarctica. This is a qualitatively different response from other missions that just arrived at their targets, at Mars or Ceres. Something about Pluto makes it more interesting. I want to channel that into general interest about space exploration and [Science, Technology, Engineering and Mathematics] careers. It’s heartwarming for those of us who have worked on this, in some cases for 25 years and in almost every case for 15 years as a project, to see it come to fruition and that people really are interested.

At a minimum, we’re going to get our Andy Warhol 15 minutes of fame on New Horizons, that’s for sure. It’s probably mostly related to what we see on Pluto. It’s clearly not a boring iceball, and neither is its big satellite, Charon. We’ll see what they have to attract.

How does it feel to be so close to finally being there?

It’s simultaneously thrilling and surreal. When something’s in your future for that long, and you work on it every day, it’s a little strange to be two weeks out, but at the same time, we get new data every day, and it’s just thrilling. We’re seeing a lot we couldn’t see from the Hubble or ground-based telescopes. Across the board, it’s just exciting, scientifically, to see all of this come to fruition.