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New Horizons: The Beauty of Hibernation

I’ve always had a great interest in Iceland, stemming from my studies of Old Norse in graduate school, when we homed in on the sagas and immersed ourselves in a language that has changed surprisingly little for a thousand years. There’s much modern vocabulary, of course, but the Icelandic of 1000 AD is much closer to the modern variant than Shakespeare’s English is to our own. Syntactically and morphologically, Icelandic is a survivor, and a fascinating one.

New Horizons’ journey to Kuiper Belt Object MU69 occasions this reverie because the mission team has named the object Ultima Thule, following an online campaign seeking input from the public that produced 34,000 suggestions. The word ‘thule’ seems to derive from Greek, makes it into Latin, and appears in classical documents in association with the most distant northern areas then known. In the medieval era, Ultima Thule is occasionally mentioned in reference to Iceland, and sometimes to Greenland, and may have been applied even to the Shetlands, the Orkneys and, probably, the nearby Faroes. Northern and on the edge, that’s Ultima Thule.

The new Ultima Thule is a natural coinage, as New Horizons’ principal investigator Alan Stern (SwRI) has noted:

“MU69 is humanity’s next Ultima Thule. Our spacecraft is heading beyond the limits of the known worlds, to what will be this mission’s next achievement. Since this will be the farthest exploration of any object in space in history, I like to call our flyby target Ultima, for short, symbolizing this ultimate exploration by NASA and our team.”

Hence the beauty of space exploration. On Earth we eventually reach our Ultima Thule, whichever place we want to assign the name, whereas in space there’s always the next one. And indeed, New Horizons may get the chance to go after another Kuiper Belt Object after MU69. Future explorations will always find more distant targets in the cosmos.

Image: Artist’s impression of NASA’s New Horizons spacecraft encountering 2014 MU69, a Kuiper Belt object that orbits 1.6 billion kilometers beyond Pluto, on Jan. 1, 2019. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Steve Gribben.

Now 6 billion kilometers from Earth, New Horizons has exited hibernation as of 0212 EDT (0612 UTC) on June 5, with all systems in normal operation. We’re now in the process of uploading commands to the computers aboard the spacecraft to begin preparations for the Ultima Thule flyby, including science retrieval and subsystem and science instrument checkouts. Things are heating up — we’re not that far from August, when New Horizons will begin making observations of its target, imagery that will provide information about any needed trajectory adjustments.

But back to that hibernation, which this time around lasted 165 days. New Horizons is now fully ‘awake’ and will remain so until late 2020, when all data from the Ultima Thule encounter should have been sent back to Earth. Hibernation itself was an ingenious innovation that would maximize efficiency by reducing the cost of mission control staffing. After all, a sleeping bird requires only a skeleton crew to maintain basic communications during this period.

The sheer ingenuity of the New Horizons design comes across here. No other NASA mission has attempted hibernation, but the experience of missions like Voyager demonstrated how useful it could be. Voyager required about 450 people to run flight operations, according to David Grinspoon and Alan Stern in Chasing New Horizons. Contrast that with a New Horizons flight staff of fewer than 50 people.

The numbers are striking when you look at how the project team changed after launch as well. In the four years before New Horizons’ 2006 departure, more than 2500 people were involved in building, testing and launching the spacecraft. They included those working on the Radioisotope Thermoelectric Generator (RTG) that converts radioactive decay into electricity, the ground systems necessary to monitor the mission, and of course the rocket that would launch it.

Within a month after launch, all that had changed. “The big city that was New Horizons was reduced to a small town,” write Grinspoon and Stern. As the book memorably states:

During the long years of flight to Pluto, only a skeleton crew of flight controllers and planners, a handful of engineering ‘systems leads,’ the two dozen members of the science team, their instrument engineering staffs, and a small management gaggle was needed. Alan [Stern] recalls, “Just weeks after launch nearly everyone went their own way, and the project was reduced to a little crowd of about fifty belly buttons. All of a sudden I looked around and it hit me: there are just a few of us — a tiny team — and we’re the entire crew that’s going to fly this thing for a decade and 3 billion miles and plan the flyby of a new planet.”

Image: Flight controllers Graeme Keleher and Anisha Hosadurga, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, monitor New Horizons shortly after confirming the NASA spacecraft had exited hibernation on June 5, 2018. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Mike Buckley.

When New Horizons reached Pluto, 9.5 years had passed since launch, but because of hibernation, most of the craft’s primary systems only had 3.5 years of operational time clocked against them, which means the spacecraft was, for all intents and purposes, years younger than it would otherwise have been. Early hibernation periods tested out the concept not long after launch, easing into a process that soon increased hibernation periods to months at a time.

As New Horizons left its last hibernation period before the Pluto/Charon flyby, Alan Stern chose a ‘wake-up song’ for the occasion, a tradition dating back to Gemini 6 when flight controllers played ‘Hello Dolly’ to wake up astronauts Wally Schirra and Thomas Stafford. Stern chose ‘Faith of the Heart,’ a theme from the TV series Star Trek: Enterprise, with its lyric “It’s been a long road, getting from there to here.” Little did the team know at the time that the ‘heart’ of the title would be echoed by a famous feature on the surface of Pluto itself.

If you haven’t read Chasing New Horizons (Picador, 2018), I can’t recommend it strongly enough. This is the best inside account of a space mission I’ve yet read. Tomorrow I want to dig a little deeper into the book and talk about the New Horizons mission in context as we now begin the exciting process of preparing the craft for yet another encounter.


Comments on this entry are closed.

  • ljk June 11, 2018, 11:29
  • Ioannis Kokkinidis June 11, 2018, 14:21

    In the 4th century Pytheas of Massalia was sent out by his home city state to find out where are the Tin Islands where tin, which was important for the economy of Massilia came from. He crossed the Pillars of Hercules, known today as the straight of Glbraltar, into seas that were not well known to my ancestors and reached the British Islands, a land that even when Julius Caesar invaded it three centuries later where mysterious and mostly unknown. He circumnavigated the British islands, and then sailed northwest from them and after 6 days sailing he came upon an island, twice the size of Britain that he called Thule. Eventually he sailed further north and reached the ice caps, becoming the first person, or at least the first Mediterranean person, to do so. Now if he had sailed northeast he would have reached a land twice the size of Britain, Scandinavia. If he did sail northwest, he could have reached Iceland which at the time was uninhabited. The problem is that his work or works did not survive, most likely destroyed during the sacking of Constantinople by the Crusaders of the 4th Crusade. What has survived are quotations in other authors who are often second hand. Now Thule entered the mind as a far away and exotic land detached from the rest of the world, the term Ultimate Thule apparently comes from Aeneas while there is also another lost novel from the Princepatum, in Greek, by Diogenes Laertius “On the wonders beyond Thule” which is also known for being the oldest known novel to include space travel. It is Diogenes Laertius that Lucian satirizes in his True Story, among with many others. Let’s see what the naming scheme of Ultimate Thule will be.

    • Paul Gilster June 11, 2018, 14:50

      Excellent, Ioannis, and thanks for that reminder about Diogenes Laertius !

  • Martinache June 11, 2018, 15:11

    I have just finished “Chasing New Horizons”. I confirm this is excellent reading, I definitely recommend it! By the way, two details curiously reminded me of “2001, a Space Odyssey”: The hibernation of the New Horizons spacecraft (versus hibernation of three astronauts in “2001”) and the name of the New Horizons operations manager: Alice Bowman (versus Dave Bowman in “2001”). I suppose Arthur C. Clarke would have liked it!

  • Biologist June 11, 2018, 15:40

    Long-time reader, love this web site and admire the effort and dedication!

    A (perhaps naive) question regarding this:
    “the Radioisotope Thermoelectric Generator (RTG) that converts radioactive decay into electricity”

    Does it actually save energy to not use the RTG, given that the radioactive decay occurs no matter what? Or is the goal of the hibernation rather to spare wear and tear on other spacecraft components?

    • Paul Gilster June 11, 2018, 15:52

      The major motivation seems to have been to reduce the size of the support team and still perform all the critical mission functions. But saving wear and tear on the components is also an advantage, to be sure. As to the RTG, I may have to ask about that, and will see what I can find out.

      • Biologist June 11, 2018, 16:11

        Ah of course. Thank you!

      • Ron S. June 11, 2018, 16:38

        This article is a good general intro to the RTG. I have not read the book itself.

      • Patient Observer June 11, 2018, 20:22

        Radioactive decay and the resultant heat can not be regulated. Presumably, electricity produced by the thermocouples (or whatever) would be dissipated through resisters or perhaps the circuit would simply be broken. As mentioned, the advantages of hibernation are mostly economical in terms of reduced labor and possibly less wear and tear on those instruments that can suffer wear and tear from operation.

        • J. Jason Wentworth June 12, 2018, 1:14

          Some RTGs, including some made-for-space-use ones, are equipped with a control rod (like those used in fission reactors). The RTG control rod is only used to fine-tune the unit’s heat output, and it can’t be re-set in flight, and:

          Even solar-powered spacecraft have the same problem of “What do we do with excess power?” ESA’s Giotto Halley’s Comet probe has an “excess power dumper.” This is a bank of resistors that dissipated excess electricity around perihelion of Giotto’s solar orbit (or if the spacecraft was using less than the full output of the solar cells at any time), while maintaining the load on the solar array within its design tolerances.

    • Biologist June 12, 2018, 13:38

      Thanks for all these insights!

  • Robin Datta June 11, 2018, 18:06

    This is what Wikipedia has to say: https://en.m.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

    Of course radioisotopes will continue to do their own thing, regardless of hibernation or otherwise: radioactive decay cannot be shut down (AFAIK). They are chosen carefully: decaying too fast, lots of energy with too short a lifetime; decaying too slow, a long lifetime, but not enough energy.

    • J. Jason Wentworth June 12, 2018, 1:23

      With a good battery system, long-life space probes could use low-output, long-life (slow-decay radioisotope) RTG(s). If the spacecraft was designed to spend much of its time in hibernation (only using its instruments and radios at encounters [and when it might “check in” at intervals], the RTG(s) could trickle-charge the batteries, which–perhaps along with the RTG(s)–would power the probe’s systems during the electricity usage-intensive encounters. Interstellar probes might also utilize such an arrangement.

    • Michael Fidler June 12, 2018, 1:54

      This is where Kilopower could be useful:

      “Nuclear reaction control is provided by a single rod of boron carbide which is a neutron absorber that is initially inserted, so that pre-launch radiation is negligible. Once the reactor reaches its destination, the neutron absorbing poison rod is removed to allow the nuclear chain reaction to start.[7] Once the reaction is initiated, it can not be stopped completely, although the depth of insertion provides a mechanism to adjust the heat output from the reactor core to the load demand.”


    • J. Jason Wentworth June 12, 2018, 10:05

      I’ve liked that informative Wikipedia RTG article ever since I came across it a few years ago–thank you for posting its link here! (There’s an automated weather station outside of town here in Fairbanks that had operated for decades, powered by an RTG–until people found out the RTG was there a few years ago; because “nuclear power is bad,” a diesel generator now powers the station…*SIGH*). Also:

      Another, related type of device is the atomic battery (see: http://en.wikipedia.org/wiki/Atomic_battery ), which doesn’t convert the heat of decay into electricity. There are three main types–direct charging generators, betavoltaic units, and alphavoltaic units (and also a fourth experimental type, the optoelectric nuclear battery, see: http://en.wikipedia.org/wiki/Optoelectric_nuclear_battery ). All of these devices use either the charged particles (beta particles [high-speed electrons] or alpha particles [helium nuclei]) emitted by radioisotopes, or–in the case of the optoelectric nuclear battery–use light produced by a radioisotope-excited medium, which is photovoltaically converted into electricity. These devices could also, if desired, be used in concert with rechargeable (chemical [polymer, etc.]) batteries for power-intensive encounters, and:

      These devices, as research on ones that power heart pacemakers has already shown (I hope I never need a pacemaker, but if I ever do, I want a nuclear-powered one, because they’re good for a lifetime), can be very small. They can also be made very thin, which would be a boon to Dr. Mason Peck’s “spacecraft-on-a-chip” Sprite space probes, which could be sent to the stars (probe-to-probe “in a probe stream” radio or laser communication, and perhaps direct laser communication, could transfer their data and pictures back to Earth).

  • Curious June 11, 2018, 23:39

    If NASA can implement a small fission systems like KiloPower it would have the advantage over RTG that it can be turned on and off. Thus if we can master long lived machinery, we could imagine a probe that is sent on say a 100+ year journey and then wakes up with its full power capability for a decade of exploration at whatever distant place we sent it to.

    • J. Jason Wentworth June 12, 2018, 10:40

      NASA’s Kilopower reactor (see: http://en.wikipedia.org/wiki/Kilopower [plus additional links in this article]) recently passed all of its milestone tests. It will be made in four versions, producing from 1 kilowatt to 40 kilowatts of power. While powering a Mars encampment is–at least as far as I’ve seen–the most frequently-illustrated and referred-to application of the Kilopower reactors, they would also be useful on the Moon (for electricity *and* heat [perhaps also using the heat directly] during the lunar nights, as well as augmenting solar arrays’ power for electricity-intensive operations during the lunar days). In addition, the Kilopower reactors could be used, with suitable modifications (quite possibly not very extensive ones), to power NEP–Nuclear Electric Propulsion–ion drive, Hall Effect thruster drive, and electrothermal drive (arcjet http://en.wikipedia.org/wiki/Arcjet_rocket and resistojet http://en.wikipedia.org/wiki/Resistojet_rocket [this article mentions a NASA study for using biowaste for resistojet propulsion, with cubic zirconia heating elements: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19870004992.pdf , like Spacecoach: https://www.centauri-dreams.org/?s=Spacecoach ]) spacecraft, and:

      NEP would enable probes and manned spaceships to travel anywhere in the solar system (with centrifugal artificial gravity and suitable radiation shielding and crew diets). It would also facilitate high-total impulse inter-orbital (and not just around the Earth) space tugs, which would be very helpful for building up and maintaining a human space presence and infrastructure. This time around, we simply cannot allow space nuclear reactor power to be derailed. Without it, we’re gravely handicapping and needlessly self-limiting ourselves (like a hang glider pilot trying to fly with one arm tied behind his or her back) with regard to where we can go–and what we can do–in space.

  • J. Jason Wentworth June 12, 2018, 9:29

    There is also a D-type asteroid (number 279) in the outer main belt, orbiting close to Jupiter, that is named Thule (see: https://en.wikipedia.org/wiki/279_Thule ); fortunately, it won’t be confused with Ultima Thule, and:

    I don’t know how it is pronounced in Icelandic (I’m more familiar with traditional names of Icelandic horses, such as Elska, Dropi, Tulle, Lilja, etc.), but I learned–from the Danes at Thule Air Force Base in Greenland, by way of a late friend of mine who worked there as a civilian contractor–to pronounce Thule as “TEW-lee” (the asteroid 279 Thule article says it’s “THEW-lee”). The original Greek pronunciation is, of course, the authentic one, just as Io is pronounced “EE-oh,” not “EYE-oh” as is common in English. Also:

    In 1979, some people, seeing the Galilean moons’ names listed on Voyager pictures (especially in sans-serif fonts), thought that Io was named “10” (“Ten”), and wondered why. :-) Actually, before all of Jupiter’s non-Galilean moons were given official names (the smaller satellites’ names were used unofficially for decades), they *were* numbered (usually, but not always, with Roman numerals; Jupiter V, Amalthea, is the most famous), a system which stemmed from Galileo’s rivalry with Simon Marius, who had proposed names for the four large moons. The actual Jupiter X (Jupiter 10) is Lysithea, one of the prograde-orbiting irregular satellites.

  • ljk August 5, 2018, 13:25