Hubble Looks at Voyager’s Future

by Paul Gilster on January 11, 2017

Nothing built by humans has ever gotten as far from our planet as Voyager 1, which is now almost 21 billion kilometers from Earth. We’ve talked about the future of both Voyagers before in these pages — Voyager 1 passes within about 1.6 light years of the star Gliese 445 in some 40,000 years, its closest approach to a neighboring star. Voyager 2, which is now almost 17 billion kilometers out, closes to within 1.7 light years of Ross 248 in the same 40,000 years.

My case for doing what Carl Sagan once discussed, giving each Voyager a final kick with its remaining hydrazine, so that those closing distances could be reduced, can be found in Voyager to a Star. It would be a symbolic and philosophical act rather than a scientific one, as both Voyagers are losing their ability to transmit data and will be silent in about a decade. And nothing can reduce those huge timeframes, which means that any such symbolic statement would be made to the future, a way of saying we are learning to be a starfaring species.


Image: In this artist’s conception, NASA’s Voyager 1 spacecraft has a bird’s-eye view of the solar system. The circles represent the orbits of the major outer planets: Jupiter, Saturn, Uranus, and Neptune. Launched in 1977, Voyager 1 visited the planets Jupiter and Saturn. The spacecraft is now 21 billion kilometers from Earth, making it the farthest and fastest-moving human-made object ever built. In fact, Voyager 1 is now zooming through interstellar space, the region between the stars that is filled with gas, dust, and material recycled from dying stars. Credit: NASA, ESA, and J. Zachary and S. Redfield (Wesleyan University); Artist’s Illustration Credit: NASA, ESA, and G. Bacon (STScI).

Meanwhile, we still have two viable spacecraft in the outer reaches of our Solar System, taking data on interstellar material, magnetic fields and cosmic ray hits and giving us a sense of what the local interstellar medium (LISM) is like. That’s crucial information, of course, for one day we hope to have not just a few but many spacecraft operating on the edge of interstellar space, and going beyond our system will require us to know the nature of the medium through which they move. On that score, the best book I know is Bruce Draine’s Physics of the Interstellar and Intergalactic Medium (Princeton, 2010). I enjoyed talking to Draine (Princeton University) at the latest Breakthrough Starshot sessions.

As you can imagine, learning more about the interstellar medium is a prerequisite if you’re thinking of pushing something up to 20 percent of lightspeed, as Breakthrough Starshot is, so the topic was a lively one at those meetings. At the recent American Astronomical Society meetings in Texas, we learned that astronomers have been using Hubble data to supplement what Voyager has been giving us, charting the hydrogen clouds and other elements of the LISM. Seth Redfield (Wesleyan University), who leads the study, offers this comment:

“This is a great opportunity to compare data from in situ measurements of the space environment by the Voyager spacecraft and telescopic measurements by Hubble. The Voyagers are sampling tiny regions as they plow through space at roughly 38,000 miles per hour [61,000 kph). But we have no idea if these small areas are typical or rare. The Hubble observations give us a broader view because the telescope is looking along a longer and wider path. So Hubble gives context to what each Voyager is passing through.”


Image: In this illustration, NASA’s Hubble Space Telescope is looking along the paths of NASA’s Voyager 1 and 2 spacecraft as they journey through the solar system and into interstellar space. Hubble is gazing at two sight lines (the twin cone-shaped features) along each spacecraft’s path. The telescope’s goal is to help astronomers map interstellar structure along each spacecraft’s star-bound route. Each sight line stretches several light-years to nearby stars. Credit: NASA, ESA, and Z. Levy (STScI).

The Hubble work makes it clear that in two thousand years or so, Voyager 2 will move out of the interstellar cloud that surrounds the Solar System before moving into another cloud, in which it will remain for as much as 90,000 years. The astronomers find slight variations in the abundances of the chemical elements in these clouds, which could chart a history involving different paths to formation. We do know that as the solar wind pushes against the interstellar medium, the heliosphere can be compressed, only to expand again when the Sun moves through lower-density matter. For more, see this Hubblesite news release.

We still haven’t built the next generation LISM explorer, one crafted from the outset as an interstellar data gatherer. As much as the Voyagers continue to give us, we have to remember that they were designed as planetary probes, their survival to this point being an amazing and unexpected gift, but one that has to be adapted to the medium through which the spacecraft move. A spacecraft fine-tuned for exploration beyond the heliopause is a goal that continues to see its share of study (more on this soon), but when it will fly remains an open question.


{ 18 comments… read them below or add one }

Thomas Goodey January 11, 2017 at 12:37

But surely burning off the remaining hydrazine in this essentially meaningless manner would mean that the Voyagers could no longer maintain attitude, so they couldn’t send any more signals back to Earth? That would be a serious loss.

In any case, of course these craft won’t simply be left to coast along through interstellar space, i.e. completely lost to humanity. When we have the capability, which may be quite soon, I have no doubt that they’ll both be brought back for display in the Smithsonian.


Paul Gilster January 11, 2017 at 21:14

What I suggest in the article is that the burn occur toward the end of the spacecrafts’ useful life, when we’ve received about all the data we can from them.


Thomas Goodey January 12, 2017 at 4:44

But how do you know that nothing new will turn up? Even near the end of the spacecrafts’ useful life, something in their environment might change that could be interesting. I think it would be wasteful and destructive to sacrifice our furthest reporting outposts in space, just for some kind of psychological demonstration which (a) would not be noticed by more than 0.01% of the human population of Earth, and (b) would be basically meaningless anyway. The Voyager probes should not be treated like party fireworks!


George King January 12, 2017 at 14:43

Is this really an either-or prospect?

At some point in 2025, if I understand things correctly, there won’t be enough power generated by the RTG to power even a single scientific instrument and we’ll then be left, for a relatively brief time, with only a tracking signal.

Does the final functional deadline at which the burn has to be done — as a matter perhaps of the remaining onboard power needed to set up and conduct the burn — substantially predate the point at which all recoverable science will have ceased?

The Voyagers no doubt will encounter many interesting and wondrous things in their journeys across the aeons.

But, after some point, they will bear only silent witness to the wonders before them.


Thomas Goodey January 12, 2017 at 17:47

Well, I don’t know the exact timetable of how the Voyagers will lose their various capabilities. But I maintain that we should continue to operate each of them to continue receiving scientific data, right up to the time point at which doing so becomes impossible (apparently the cause will be, either because there isn’t enough remaining electrical power, or because there isn’t enough remaining hydrazine for attitude maintenance). When we absolutely cannot receive any more scientific data, then we may do any mad stunt, if we can; it won’t be important.


Paul Gilster January 12, 2017 at 21:05

The Voyagers’ electrical power and thruster fuel will be exhausted in no more than a decade, and perhaps earlier. Here’s a snip from my essay:

“Somewhere around 2018 Voyager 1 will shut down its data tape recorder, just as Voyager 2 shuts down its gyros. As instruments go quiet, all power will be shunted to interstellar wind measurements and communications with the distant Earth. As we reach 2020, the few instruments still able to operate by sharing power will be unable to be supported. We’ll be left with only a tracking signal that can last perhaps as late as 2025.”

As I say in my essay, I hope we can keep them sending data as long as possible. Once we’re at the end, a final command could trigger the trajectory-changing burn. I’ve never argued for doing anything that would shut down their data return early.


Thomas Goodey January 13, 2017 at 3:00

This argument of yours assumes that it will be the electrical power that runs out first, still leaving some thruster fuel remaining. If that actually happens, then, after the sending back of data has completely failed, there is no harm in burning off the hydrazine – provided that the probe is still listening for commands, which presumes some residual electrical power. I suppose it’s a bit of a balancing act.


Paul Gilster January 13, 2017 at 9:45

A balancing act indeed, but I think it can be done.


Alex Tolley January 12, 2017 at 0:12

We’ve talked about research over generations in te past. Out of interest, are there any readers of this blog who were born after the Voyagers were launched and are therefore getting information from a probe launched in the previous generation? How do you feel about this?


Infinite123Lifer January 13, 2017 at 0:11

Hi Alex, I am not sure if I understand your question completely, namely if your asking about what that generation thinks about what to do in the probes final moments or in general how we feel about the missions in our hearts, so I will answer both if that is ok.

I actually do not fall in the category you are referring to, I was born 6 days before the launching of Voyager 2. August 14th 1977 I came into this world, and when I first learned of the Voyager launches probably in 4th or 5th grade the fact that they were launched in 1977 caught my eye, naturally I was more than a little curious. Since then, and to this day thanks to all those who have come before us and the amazing individuals who accomplish these feats of a species I oftentimes have thought how special it was to have been born as somewhat of a precursor, for my Life at least :) to the launch of these explorers. Perhaps I hear you thinking, whats so special about that happenstance, you might question this almost astrological thinking, and rightfully so, coincidence or not though, it happened that way and in my mind the Universe could not have planned it better. Since only I live my Life, things are always relative to me in my mind. When I was very young I would see whales being killed, species wiped out, hatred, bombs, war, racism … and oftentimes I would lose touch, overwhelmed with grief, distraught to the point of thinking things were hopeless … honestly the destruction of the whales almost drove me mad and to death, I could not tolerate mankind no more … and then these stories about Voyager and Hubble would work their way into my life, rejuvenating my entire being, giving me cause, purpose and hope. I did not feel so alone. I felt there were others who dared to dream, who dared to defy the impossible for the sake of wonder. When it comes to Voyager 1 and 2 just being born the same year it feels to me (and I carry this with me) special. I cannot reiterate enough times how important projects like these are. They save lives by allowing the dreamers dreams to come alive, the light bulbs in our minds eye to shine brighter, the passing of time rooted in conversation about such feats, to actually happen! In a world that can be dark and cold fraught with carelessness and destruction, Voyager is immune, the feelings I have for that immunity are encouraging to me.

You know it is funny, I was reading this article the other day and thinking while I was reading Paul’s excellent writing (consequently I find myself rereading these essays several times, for it takes the man not a sentence to send my mind racing about with imaginative ideas and just cool cool stuff, so that I am thinking multiple wonders while still reading and I have to go back, Paul is literally a muse for me and I try to honor that by not posting here, lol, as I am somewhat chaotic, misinformed and consequently not qualified on the subject matter …) I was thinking how or when will we finally catch up to these creations of ours, picturing the capture of one of the Voyagers in my mind and the attitudes of those involved and then I forgot what I had read and moved onto the comments where the first comment by Mr Goodey suggested exactly that, bringing them back. It is that feeling when you get chills, like your connected to the Universe around us, in part for our part, even if it is just thought, what a precious gift, all … of it … that is. Of course I had not thought about the Smithsonian, I was moreso in my mind focusing on the sentiment of the possible reality.

The Voyager craft are beyond special to me, Hubble, Cassini, Kepler and many many others are as well, they peeled back humanity’s cap so to speak, smashed the limits of possible and granted generations to come wonder and reality, the reality of what IS out there. I wish I could have done the same for others as was done for me.

As for what to do with the probes, I would leave that in the hands of their creators. I remember the article Paul wrote about the final moments and what to do with these craft … I wept at the beauty in the actions he suggested and the reasoning behind it, honestly, I cried. It is a thoughtful approach to a silent but golden end, even if we did not learn one very last piece of data … I think it shows our heart and not our greed for the information and if people can have a heart and soul behind the dedication to space than we are surely to learn more information. Sometimes, just sometimes you have to make your stand or your statement, and with those acts sometimes comes sacrifice. I do not think the sacrifice outranks the sentiment in this particular case, even if one of the Voyagers were to fly right by a Planet 9. Some of us, some of us need the sentiment every now and again. Thank you for your time.

The people that make things like this happen are a gift to the rest of us. May your voyages forever be special and your atoms forever reused.



Paul Gilster January 13, 2017 at 9:46

Chad, thank you for your thoughts and especially for those kind words! Much appreciated.


ajay January 13, 2017 at 6:35

are there any readers of this blog who were born after the Voyagers were launched

Not quite – I shared the planet with the Voyagers for a little under two months. I am afraid that my memories of the period are somewhat indistinct.


Wojciech J January 14, 2017 at 5:34

I was born couple of years after Voyagers were launched.
When I was a kid, the main aspect of the mission seemed to be delivering a symbolic message to the stars of humanity’s existence. Only when I grew up later, did I learn about the scientific profile of these probes.
As I grew up in Eastern block, Voyagers were covered quite often by popular science programs in television and newspapers, and there was no prejudice or resentment despite them being made by USA, showing that space program went above conflicts on Earth.
But as I said above, the main point they always spoke about was that they carry a message from our civilization to the stars.


Thomas Goodey January 14, 2017 at 16:01

But realistically speaking, that whole idea of “the Voyagers are carrying a message to the stars” was an appeal to the minds of the stupidest sector of the public – and therefore naturally wildly excited the writers for television and the newspapers. Nobody with any sense has ever had a realistic expectation that, after many tens of thousands of years, one of the Voyagers would be found by another civilization. The atomic batteries would by then be utterly completely flat, so the craft couldn’t emit the slightest radio signal, and thus it would just be one more small miscellaneous bit of junk drifting around in space.


Michael Spencer January 12, 2017 at 7:21

I guess I thought this work– examining the future of these future machines– would have been performed some years ago.


Thomas Goodey January 12, 2017 at 10:31

What do you mean, examining their future? Of course people have always been thinking what would be the best thing to do with them before they stop operating.


Michael Spencer January 13, 2017 at 7:30

I meant- why hadn’t Hubble looked at the path before?


Michael January 13, 2017 at 13:57

I see this image as that of a child, the two voyagers are their hands feeling into the darkness and Hubble’s views as their eyes.

We have not even started to see into the vastness, it inspires wonder and trepidation.


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