Voyager 1 Nearing Interstellar Space

by Paul Gilster on June 18, 2012

It should come as no surprise to anyone who follows Centauri Dreams that I am a great admirer of Ed Stone, the former director of the Jet Propulsion Laboratory (from 1991 to 2001) and more than any single scientist, the public face of many of our missions to the outer Solar System. Stone’s work on space projects began as far back as 1961 with the cosmic ray experiments he designed for the Discoverer satellites, but it was as project scientist for the Voyager missions that he became a familiar figure to audiences worldwide. His tenure at JPL saw missions like Mars Pathfinder, the Sojourner rover, Deep Space 1 and the launches of Cassini and Stardust.

That, of course, is only a partial list, but it gives you the drift. This morning I’m thinking about Stone again because of a quote he provided for a recent JPL news release. Here again he’s talking about the Voyagers, which are pushing up against the edge of the system:

“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be. The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the solar system’s frontier.”

Image: Dr. Stone (center) and members of the Voyager mission discuss the spacecraft’s closest approach to Jupiter, March 1979. Credit: NASA/JPL.

As seems to be a habit of the Voyagers, they are again approaching an exciting encounter. In the other room I still have the VCR tapes I made of Voyager II’s 1989 Neptune flyby — amazing to think it’s been so many years! — and I recall remarking to my wife that night that these doughty machines still had some life in them, and that, who knows, they might keep giving us information for another decade or so. If I had done my homework back then, I would have realized that we might get both spacecraft through to 2020 or so, when the power output of their radioisotope thermoelectric generators will decline too steeply for operations to continue.

A morning check shows that Voyager 1 is 16 hours, 39 minutes and 2 seconds light travel time from us, while its sister ship is 13 hours, 35 minutes and 13 seconds of light travel time away. Impressive for journeys that began in 1977 and a real tribute to our ability to build systems that can last. The Voyagers’ interstellar mission is all about studying not only the Kuiper Belt but the heliosphere and the elusive boundary between the region of the Sun’s influence and true interstellar space. That included the famous ‘Pale Blue Dot’ image showing a group portrait of the Solar System, including the faint Earth, as seen from outside. And while it is true that New Horizons left Earth faster than either Voyager, our Pluto/Charon probe is now moving at 15 kilometers per second, while Voyager 1 maintains a brisk 17.26 kilometers per second.

An indication that interstellar space looms near is that Voyager 1, in the period from early 2009 to early 2012, has measured a 25 percent increase in galactic cosmic rays, with an even more rapid increase in the spring of 2012. The science team will now be watching for a change in the intensity of energetic particles generated inside the heliosphere, a kind of ‘bubble’ of charged particles inflated by our star’s solar wind. A sharp dropoff will be another flag for leaving the system, as will a major change in the direction of magnetic field lines around the spacecraft.

As for Ed Stone, he’s on record as saying that the biggest surprise of the Voyager missions was the discovery of Io’s volcanoes, but he notes that as the missions unfolded, they continually surprised us. Doubtless even our best estimates of the passage into interstellar space will come up short of the reality as we learn more about the boundary through which all future interstellar craft will have to pass. Says Stone:

“When the Voyagers launched in 1977, the space age was all of 20 years old. Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”

For that matter, who knew how long we’d be able to work with these spacecraft even if they did approach the margins of the Solar System? The numbers are daunting but our deep-space tracking antennas are up to the job: The signal that the Voyager probes return to Earth is 10-16 watts, which works out to one part in 10 quadrillion. The Voyager Interstellar Mission team notes that a digital watch operates at a power level 20 billion times greater than this, and yet we’re still hoping for another decade or so of data. If power were not a problem (and low hydrazine levels), we might be talking about another century or more of contact with the spacecraft unless they lost their lock on the distant Sun.

And after the Voyagers reach interstellar space? The next boundary will be the region where the Sun’s gravity is no longer dominant, a distance about halfway to the nearest star (although neither spacecraft is pointed at Proxima Centauri). It should take the long-silent Voyagers about 37,000 years to reach that threshold.

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David H June 18, 2012 at 9:57

I met Professor Stone at the IUGG congress in Birmingham in 1999. Paul, I’m with you, it was a complete thrill to meet the man at last. He had given a union address on the subject of ‘Mars and the search for life elsewhere’.

Watching over the years as the Voyagers made their discoveries was (is) a fantastic experience. Some recollections that might or might not be accurate are that the mission controllers on at least one occasion had to reprogram the on-board computer of at least one spacecraft to avoid an address that corresponded to a memory bit that had been knocked out, probably by a gamma ray and that over the years, data compression algorithms improved, allowing more data to be returned so far from Earth than originally expected. I agree that the discovery of Io’s volcanism was fabulous!

Let’s hope that the spacecraft keep a lock on the Sun for years to come!

Tony Bittan June 18, 2012 at 11:02

What was the book you were reading before “Deep Space Propulsion??” I looked into it earlier and came back and now it’s gone, and I can’t recall what it was!

Paul Gilster June 18, 2012 at 13:04

Tony, it was Johnson and McDevitt (eds.), Going Interstellar:

http://www.amazon.com/Going-Interstellar-Les-Johnson/dp/1451637780/ref=sr_1_1?s=books&ie=UTF8&qid=1340039025&sr=1-1&keywords=going+interstellar

I’ll be having some further thoughts about it tomorrow.

Interstellar Bill June 18, 2012 at 18:19

Eventually the Voyagers will be visited by astronauts, who will recharge its radioactive batteries and leave a co-orbiting beacon to mark its location for space traffic control. Later, Kuiper-Belt settlers will consider it a must-visit for spacesuited family poses, until preservationists start rationing visits.

James Jason Wentworth June 18, 2012 at 21:50

I wonder if Ed Stone and Charles Hall (the director of the Pioneer program at the NASA Ames Research Center) ever had a friendly wager over which team’s spacecraft (JPL’s Voyager 1 or 2, or Ames’ Pioneer 10 or 11) would reach interstellar space *in working order* to report back on the conditions there?

Mark June 18, 2012 at 22:47

I’m afraid the Voyagers will not be flying in 37,000 years. There is nothing outside the solar system. I predict that the final signal heard from Voyager will be a glassy “TING” as it smacks into the celestial sphere containing the fixed stars at 39,000 MPH, utterly destroying the probe (and incidentally not harming that most perfect celestial sphere in the least) and then the wreckage will simply fall to the bottom of the Universe where all our other space probes will eventually end up.

And some day, mark my words, we will be held to account to clean up the mess down there and we will rue the day we ever launched space probes willy nilly into space without a means to bring them back.

Tony Bittan June 19, 2012 at 3:43

Many thanks!

Michael Spencer June 19, 2012 at 7:17

I wonder how New Horizons is equipped for later service? How much fuel, instruments, and power…and what kind of life is expected after Pluto. One does hear of an extended mission, but not much else.

But it’s beyond an extended solar system mission that interests most of us here. Given the speed of this little traveler, I wonder how long it will take to pass (in terms of distance from the sun) the intrepid Voyagers?

ljk June 19, 2012 at 9:27

Don’t forget Pioneer 10 and 11!

http://www.orionsarm.com/eg-article/47c1b07834a5f

And the Voyagers may have even more bizarre encounters, should the Singularity happen:

http://www.orionsarm.com/eg-article/49f9b4b02ce26

Or they might be found by highly intelligent spacefaring dolphins:

http://www.ricksternbach.com/voyfound.jpg

And everybody knows what happened to Voyager 6 after it fell into that black hole and emerged on the other side of the galaxy:

http://en.memory-alpha.org/wiki/V'Ger

However, New Horizons was a major disappointment, as the CDs it carried were rendered useless by cosmic radiation ages ago, and the rest of the items were reminiscent of trinkets from some small town’s time capsule. It was as if the people who put them together did so at the last minute and without bothering to ask for any outside assistance on the matter.

In essence, the artifacts aboard the probe were quite hard to interpret without common references present – a violation of the now mandatory interstellar law that all vessels traveling beyond the legal borders of their planetary systems must carry comprehensible information indicating their purpose and the nature of their creators and home worlds, otherwise risking automatic destruction and a heavy fine imposed upon their builders and/or their surviving descendants, if any.

http://www.collectspace.com/news/news-102808a.html

Interestingly, the space probe did possess the remains of a human being prominent to the reason for its primary mission, but as the sample was small and completely carbonized, little could be done in terms of recreating the person for further examination and eventually bioengineering an entire servile race from the remains to be sold to the highest bidder.

And as for humanity’s first deliberate interstellar probe, Nomad, launched in August of 2002, no one has heard from it since that encounter with a meteorite….

http://en.memory-alpha.org/wiki/Nomad

ljk June 19, 2012 at 9:36

James Jason Wentworth said on June 18, 2012 at 21:50:

“I wonder if Ed Stone and Charles Hall (the director of the Pioneer program at the NASA Ames Research Center) ever had a friendly wager over which team’s spacecraft (JPL’s Voyager 1 or 2, or Ames’ Pioneer 10 or 11) would reach interstellar space *in working order* to report back on the conditions there?”

LJK replies:

Pioneer 10 and 11 were not expected to last but a few years beyond their primary missions to Jupiter and Saturn, so there probably was no wager. The Voyager probes, on the other hand, were expected to last a long time, between 2020 and 2025 are the usual dates.

http://voyager.jpl.nasa.gov/mission/interstellar.html

http://www.area52online.com/sections/columns/marks_column/data/mission/vim.htm

Pioneer 11 was last heard from in November of 1995 and Pioneer 10 kept signalling until February of 2003. They come from a family of long-lived deep space probes: Several of the earlier members in solar orbit, launched in the mid to late 1960s, were being heard from as late as 2000. I bet if someone tried again they could detect at least Pioneer 6.

http://en.wikipedia.org/wiki/Pioneer_6,_7,_8,_and_9

ljk June 19, 2012 at 11:11

And the entertaining (if often terrible when it came to science and physics) SF series Space: 1999 had its own Voyager One with a propulsion system called the Quellor Drive which creates very deadly “fast neutrons” (and do not ask what happened with Voyager Two):

http://www.space1999.net/catacombs/main/models/w2mvoyager1.html

Star Trek Voyager dealt with something similar regarding a probe ironically named Friendship 1:

http://en.memory-alpha.org/wiki/Friendship_One_(episode)

Michael June 19, 2012 at 14:14

Years, actually decades, ago I was involved in fabricating the RTG’s used by Voyager.

To this day I still get a kick out of the fact that a million years after humanity ceases to exist something I helped make will still exist.

James Jason Wentworth June 20, 2012 at 20:52

LJK wrote:

“Pioneer 10 and 11 were not expected to last but a few years beyond their primary missions to Jupiter and Saturn, so there probably was no wager. The Voyager probes, on the other hand, were expected to last a long time, between 2020 and 2025 are the usual dates.”

I’m not so sure about that. I think the longevity of the solar-orbiting Pioneer 6 – 9 probes and the Pioneer Venus Orbiter (which spent its life in a more hostile radiation environment than what Pioneer 10 and 11 experienced before and after their Jupiter encounters) gave the Pioneer program personnel cause to believe that Pioneers 10 and 11 (particularly Pioneer 10) might remain functional for many years after their Jupiter flybys.

Also, being spin-stabilized rather than using active 3-axis stabilization, there was “less to break” in the Pioneer probes (the Voyagers could have lost guidance due to Jovian radiation damage to their electronics). Pioneer 11 did get the “less good” RTG set, so its earlier demise (earlier than Pioneer 10) was not a surprise. In the 1970s, there were discussions (mentioned in Robert M. Powers’ 1979 book “Planetary Encounters”) about listening to the Pioneers–perhaps to one onboard instrument at a time–for decades after their Jupiter encounters by using the Arecibo dish (only for brief periods each day, of course, since it is a fixed dish). Perhaps this will be done with the Voyagers and New Horizons after they recede beyond the effective range of the Deep Space Network stations.

James Jason Wentworth June 20, 2012 at 21:08

Michael wrote:

“Years, actually decades, ago I was involved in fabricating the RTG’s used by Voyager.

To this day I still get a kick out of the fact that a million years after humanity ceases to exist something I helped make will still exist.”

Only a *million* years? What a pessimist! :-) Seriously, though, did you and/or any of your co-workers write your own interstellar message(s) on areas of the RTGs that would not be visible after they were assembled (or did you at least consider doing it)? I would have found it hard to resist such a rare opportunity to send a message that maybe, just maybe, might puzzle or delight alien scientists eons hence…

ljk June 21, 2012 at 9:39

James Jason Wentworth said on June 20, 2012 at 20:52:

LJK wrote:

“Pioneer 10 and 11 were not expected to last but a few years beyond their primary missions to Jupiter and Saturn, so there probably was no wager. The Voyager probes, on the other hand, were expected to last a long time, between 2020 and 2025 are the usual dates.”

“I’m not so sure about that. I think the longevity of the solar-orbiting Pioneer 6 – 9 probes and the Pioneer Venus Orbiter (which spent its life in a more hostile radiation environment than what Pioneer 10 and 11 experienced before and after their Jupiter encounters) gave the Pioneer program personnel cause to believe that Pioneers 10 and 11 (particularly Pioneer 10) might remain functional for many years after their Jupiter flybys.”

LJK replies:

James, you need to note that when Pioneer 10 and 11 were sent to the Outer Sol System in the early 1970s, the Space Age was not even twenty years old. Most satellites did not last more than a few years in the harsh environment of space, and those that were still operating out there like Pioneer 6-9 weren’t even a decade old.

Here is the quote from Chapter 6 of the 1977 edition of the NASA Publication Pioneer Odyssey (SP-349) on just how long the Pioneer team members thought their robotic emmisaries would last way out there in deep space:

http://history.nasa.gov/SP-349/sp349.htm

“The question is: will the spacecraft be able to return information from so far away? The survival of Pioneer to the vast distances beyond Jupiter is very important in checking on the changes to the solar wind in the outer Solar System. And, if all goes well, both Pioneers should do this, though Pioneer 11 may not survive its encounter with Saturn, particularly if it passes through the inner ring plane. Even as the RTG power supply output begins to fall due to an expected decreased output from the power-converting thermopiles, experiments can be cycled shut off and then later brought on again – to conserve power and store this power in the battery for short periods of data transmission to the limits of communications distance-possibly to 20 times Earth’s distance from the Sun, i.e., some two billion miles.”

So the answer is, they thought the RTGs might keep the Pioneers functioning out to roughly the orbit of Neptune, which at the time was way beyond anything any satellite had ever accomplished in terms of distance and endurance.

Thankfully for science, the two literally pioneering probes lasted way beyond their warranties, which was no doubt encouraging to the Voyager team who could then declare that their space vessels would keep operating for decades, as they have.

Spacecraft engineers and scientists tend to play it conservative anyway. Remember how they kept saying the Mars Exploration Rovers (MER) Spirit and Opportunity were guaranteed to last only 90 days on the Red Planet. Even MER Principal Investigator Steve Squyres said he did honestly not think they would make it beyond 120 to 150 days in the harsh Martian environment at best. To everyone’s surprise, Spirit kept transmitting until 2010 and Opportunity is still roving and returning data from Mars after traveling over 21 miles across the planet’s surface since 2004. And these robots were solar powered to boot!

As for your question to Michael on whether he and others put messages or mementos on the Voyagers (not including the attached Voyager Interstellar Records, of course), I too would be curious to know if they did. I know it has happened in the past with deep space probes.

I recall a National Geographic Magazine article on the early Pioneer probes sent towards the Moon in the late 1950s which had one photograph showing a rocket technician signing his name and a good luck message on the launch shroud of the Pioneer 2 probe. Other writings from other workers were also visible. Of course those particular messages never got very far as they would be deployed along with the shroud as soon as it opened to release Pioneer 2 into space.

But I know others have put items aboard space probes, both officially and otherwise. An American flag was snuck onto the Mariner 1 and 2 Venus probes and a similar flag was rolled up into the support structure of Surveyor 1, which made the first true soft landing on the Moon in 1966. And since they would had almost no weight, I bet there are signatures on most of those probes, but I would love to know the details as well.

Archaeologists have learned a lot from graffiti from ancient societies, such as at Pompeii, and I am sure future explorers will appreciate the personal notes on the ancient vessels they find in deep space.

James Jason Wentworth June 22, 2012 at 2:01

I have “Pioneer Odyssey” and other smaller NASA publications on the missions. In the early 1990s I talked with Dr. Lawrence Lasher at the Pioneer program office at NASA Ames, and he said that the unexpected tenacity of Pioneers 6 – 9 and the Pioneer Venus Orbiter, in addition to DSN station receiver sensitivity improvements (as well as enlarged dishes at the DSN stations) would make it possible to receive data from Pioneer 10 and 11 for longer than they had thought back in the early 1970s.

If memory serves, Mariner 4 (and presumably Mariner 3 as well) has a national origin seal (with the words “United States of America”) on one of its outer skin panels. Who knows–maybe it was added partly because of the American flag that was sneaked aboard Mariner 2 (“Better an official national identifier than a surreptitiously-added item that might float loose and jam or short out a critical spacecraft system!”)?

I chuckled at that Pioneer 1 photograph, too–if they wanted to sign something, they should have signed the spacecraft or (it that was “off-limits”) the final (third) stage of the Thor-Able launch vehicle! At least it had a chance of reaching either the Moon or solar orbit (the stated goal of Pioneers “0″ through 3 was simply “to place an instrument payload ‘in the vicinity of the Moon’”), as they couldn’t confidently predict either a lunar flyby, insertion into lunar orbit, or a lunar impact. The Juno II-launched Pioneer 3 and 4 probes had no chance of orbiting the Moon because they had no onboard propulsion systems–they would either escape from Earth after a lunar flyby (as Pioneer 4 did), make a Luna III-type “figure-eight” orbit around both the Earth and Moon, or impact on the Moon, although this last possibility would have been unlikely.

ljk June 22, 2012 at 14:36

James Jason Wentworth said on June 22, 2012 at 2:01:

“If memory serves, Mariner 4 (and presumably Mariner 3 as well) has a national origin seal (with the words “United States of America”) on one of its outer skin panels. Who knows–maybe it was added partly because of the American flag that was sneaked aboard Mariner 2 (“Better an official national identifier than a surreptitiously-added item that might float loose and jam or short out a critical spacecraft system!”)?”

LJK replies:

That very information is found in the 1985 NASA Publication Far Travelers: The Exploring Machines (SP-480) by Oran W. Nicks, which is online here:

http://history.nasa.gov/SP-480/sp480.htm

As NASA’s Director of Lunar and Planetary Programs at the time, Nicks at first did not approve of the small American flags being snuck aboard Mariner 1 and 2 for fear of them somehow interfering with the Venus mission as well as potentially seeming unseemly (he did not like the fact that the Soviet probe Luna 2 spread a ball of metal pendants of the Soviet state seal all over its impact site on the Moon in 1959).

http://www.mentallandscape.com/V_Pennants.htm

By the time of Mariner 3 and 4, when a team member wanted to have an engraved Seal of the United States on the hexagonal bus exterior of the Mars probes, Nicks was still cautious but more open to the idea, and by the time that Pioneer 10 and 11 were carrying identical golden plaques into the galaxy, he was actually pleased enough to mention them in said book.

Here is the quote about the Seal of the USA on the Mariner Mars probes from Far Travelers:

“We did not always agree on everything, but my respect for Jack’s abilities made it possible for me to compromise without distress. One such compromise sticks in my mind, when we disagreed on a “judgment call.” It seems relatively unimportant now, but I was concerned at the time. Our disagreement arose over Jack’s plan to have one of the shiny aluminum covers on a Mariner Mars spacecraft compartment embossed with the seal of the United States. He had a cover made up with the seal so we could see what we were talking about, but since it was fastened by only a few screws, the final decision on whether to use it could be made at the last minute. His view was understandable; we were competing with the Russians in the race to the planets, and Americans could be proud that our “trademark” would be exhibited for current and future generations to see. My concern was that we might be accused of exhibitionism, something distasteful to me, for I was deadly serious about doing the mission for other reasons. The Russians had bragged about landing a pendant on the Moon, and I wanted no part in that disgusting game.

“Since the shiny aluminum surface was important for proper thermal control, I questioned whether the embossing, however light, might negatively influence the thermal properties. Jack agreed that tests would be made with the panel in place. Since my greatest concern was that critics would misinterpret this symbol as a lack of seriousness on our part, I further insisted on a low-profile, no-publicity approach for the addition. The panel with the seal was installed, the tests were made, and even after the successful flight there was very little publicity about the seal, and none at all negative.”

ljk June 22, 2012 at 14:39

I found an actual photograph of the Seal of the USA on the Mariner 4 Mars probe on this Web page:

http://www.pianeta-marte.it/satelliti_artificiali/USA/english%20_mariner_4.htm

James Jason Wentworth June 23, 2012 at 1:59

Thank you for posting those links! They also make possible what might be called “psychological archaeology,” being testaments to human attitudes at those times. I was surprised at their attitude toward national identification markings on the probes; I find nothing jingoistic about either the Mariner 3 & 4 seals or the Luna 2 pendants. If Lunokhod 1 or 2 had been used to write “Marx Rocks!” (or the equivalent in Russian) in the lunar soil, or if “USA #1!” had been engraved on our probes, that would have been “over the line.” :-)

ljk June 24, 2012 at 10:11

James, keep in mind that the early negative attitude I posted about was from a single person, Oran W. Nicks, the man in charge of those early lunar and planetary exploration days for NASA. As you know, almost every American deep space mission from 1958 until 1964 had failed in one form or another, while the Soviets kept having very public triumps (and hiding their multiple failures, something NASA was unable to do).

While I ultimately do not agree with Nick’s initial negative attitude towards momentos aboard space probes, I can understand his concern. A number of probes were lost because of small errors, the most infamous being Mariner 1, which happened to be the mission Nicks was first assigned to. If you read The Far Travelers, you will see how much the loss of that probe affected him, as it is the focus of the first chapter in his book.

As I also said, eventually Nicks warmed to the idea of momentos aboard these probes and understood why team members would place flags and other relevant items aboard those exploring machines. He even mentions the Pioneer Plaques at one point with a very different attitude than those symbols of the USA on Mariners 1 through 4.

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