Saturday, September 15, 2007

Voyager's Grand Tour

Launched from Cape Canaveral (Credits: JPL/ NASA) on September 5, 1977, spacecraft Voyager 1 has reached ...

Jupiter on March 5, 1979, transmitting splendid photos of the cloudy giant (Credits: JPL/NASA), and

Saturn on November 12, 1980 (Credits: JPL/ NASA), before leaving the plane of the Solar System. Its sibling Voyager 2, launched a few days earlier on August 22, 1979, visited Jupiter and Saturn and went on to ...

Uranus (Credits: JPL/ NASA) - arriving there on January 24, 1986, just days before the Challenger catastrophe - and beyond to ...

Neptune (Credits: JPL/ NASA). Following the encounter with the other blue planet on August 25, 1989, it is now heading towards somewhere in the constellation Telescope. Even after the ...

... long journey (Credits: JPL/BEACON project) of now 30 years ...

... both spacecraft (Credits: JPL/NASA) are still intact, exploring the outher reaches of the heliosphere, and transmitting data to Earth.

Voyager 1 has now reached a distance more than 100 times further away from the Sun than Earth, while Voyager 2 has covered more than 80 times this distance (Credits: Heavens Above).

If ever someone should pick up one of the probes, the curious alien might listen to sounds from a distant planet, encoded in a strange way in a funny golden disk (Credits: JPL/NASA).
Travelling to the stars is not difficult, if we believe what we see in science fiction movies. Push some button, and a miracle occurs: The starship will rush away at warp speed, or take a shortcut through hyperspace - bringing us in no time to whatever destination we would like to in our interstellar neighbourhood. In the real world, unfortunately, things are not that easy.

Last week, we were reminded of the space probe that is currently the most advanced human-made object heading for the stars: Voyager 1, a satellite that has started its journey 30 years ago, on September 5, 1977, is now 104 times further away from the Sun than the Earth, and aiming towards some point in the constellation of Ophiuchus. Voyager 1 is leaving the Solar System at a speed of 17 km per second, and in about 40,000 years, it will come "close" - within 1.7 lightyears - of a red dwarf star currently in the constellation Ursa Minor called AC+79 3888.

Of course, the main purpose of Voyager was not to reach some obscure star in an incalculable future, but to explore the outer planets of the Solar System. In the 1960s, scientists and engineers at the NASA recognised that they could seize the opportunity of a quite unique constellation of Jupiter, Saturn, Uranus and Neptune, and send a space probe on a Grand Tour visiting all these planets in one journey. Thus, the Voyager program came into being. Voyager 1 paid a visit to Jupiter, transmitting splendid pictures of its stormy cloud cover, and detailed views of its moons, and to Saturn, catching the first close-up views of its ring, before taking the bearing of its current course. Voyager 1's sibling Voyager 2, launched two weeks earlier, took a more leisurely itinerary, and following its visits to Jupiter and Saturn,it became the first space probe to reach Uranus and Neptune. I vividly remember being fascinated by the photos of Uranus and its moons - transmitted just days before the Challenger catastrophe - and stunned by the white cirrus clouds on top of the blue gas cover of Neptune.

The Voyagers' science mission was not completed with the exploration to the outer planets: Voyager 1 has, over the last years, transmitted data that help to understand the outer rim of the heliosphere - the region around the Sun dominated by the solar wind, the stream of particles constantly blown into space by the Sun. The zone where the diluting solar wind is finally stopped by the interstellar gas is called the termination shock. Voyager 1 is supposed to have passed the termination shock in December 2004, and Voyager 2 will explore this frontier soon, in a slightly different direction.

For energy supply to keep alive their instruments and transmit data to Earth, the Voyagers can't count on solar panels. The Sun is reduced to a mere bright spot in the sky for Voyager 1: At a distance of 100 Astronomical Units, thus, a hundred times further away than Earth, the Sun's shine is 10,000 times fainter than it is for us, and plain daylight has dimmed to roughly 45 times the light of the Full Moon. Technically speaking, the Sun's apparent magnitude has dropped by 10 from -26.7 to a mere -16.7, as compared to -12.6 for the Full Moon, where a difference of 5 on this logarithmic scale corresponds to a factor 100. Hence, energy is supplied by a so-called Radioisotope thermoelectric generator: Heat produced by the decay of radioactive nuclei is converted into electric energy using the Seebeck effect. The Voyagers have been equipped with plutonium 238. The device yields a maximal electric power of 160 Watt, and, given a half-life of 88 year for the isotope, is sufficient to keep running the electronics of the probes until the 2020s.

Communication with the Voyagers is maintained by radio telescopes of the Canberra Deep Space Communication Complex (CDSCC) at Tidbinbilla near Canberra, Australia - once a month with Voyager 1, and on a daily basis with Voyager 2. The CDSCC is part of NASA's Deep Space Network, which maintains contact on a regular basis with a multitude of space probes exploring our Solar System - you can check out the schedule on this website. Communication with Voyager 1 requires patience: a radio signal takes 14.4 hours for the one-way trip between the spacecraft and the Tidbinbilla antenna!

The Sidney Morning Herald had a very interesting article a few days ago (thank you, Kerstin) about the Tidbinbilla space tracking station, and the problems facing the engineers there to maintain communication with a spacecraft from the early years of the electronic age. Tidbinbilla's spokesman Glen Nagle is cited stating "The Voyager technology is so outmoded, we have had to maintain heritage equipment to talk to them." John Murray, an engineer who has been working at the telescope for 40 years and now explains to younger technicians how to maintain the hardware, finds it funny that the equipment and machines that are older than them.

When the Voyagers will finally get out of reach in 15 years or so, they will be far out, but most probably, they will not even have left the outskirts of the Solar System. Dwarf planet Eris is currently at a distance of 100 AU, only a bit closer to the Sun than Voyager 1, and although Eris is now next to its aphelion, there may be many other, similar transneptunian objects further out.

The golden disks with recordings of sounds from Earth onboard the Voyagers will have to travel for thousands and thousands of years before they might come into the realm of other stars, and maybe into the reach of some intelligent aliens. Timothy Ferris, in his thoughtful NYT essay The Mix Tape of the Gods, reminds us that "358,000 years will elapse before Voyager 2 approaches the bright star Sirius", and that "Out there, our concepts of velocity become provincial."

Indeed, the speed of spacecraft would have to increase by a factor of 1000 at least before one could reasonably start thinking about interstellar travel. Blueprints for such spaceships might even exist already - as, for example, for the Project Daedalus - and they might even be scientifically sound. However, if I think about the problems to maintain such a small-scale endeavour that is the International Space Station, or to ignite nuclear fusion on Earth - problems that should be overcome before a fusion-driven 50,000 ton spaceship could be assembled in orbit - such proposals appear as the daydreams of enthusiastic engineers, easily bursting at the confrontation with reality.

This is a last, humbling lesson the Voyagers can teach us: to remind us of the incomprehensible vastness of Space, and how difficult it will be to reach the stars.


  1. The $30 million Google Challenge calls for private venture to land a working moon rover. Current physics demands a $billion effort. There is no clever way out of Earth's gravitational well.

    The energy required to low Earth orbit a lump of coal is its heat of combustion. We need better science before better engineering. (120 tons of useless Space Scuttle leave only 25 tons net payload at launch.)

    If we want to plunder the universe we must first knock the mud off our shoes. All discovery is insubordination. Question authority and birth the future.

  2. Dear Stefan, These Voyager 2 snapshots (you can call them 'the human element') give another layer of meaning to your Voyager 1 and 2 story too. Thanks for writing this post.

  3. Hi Uncle Al,

    There is no clever way out of Earth's gravitational well.

    This seems to be the main problem... but I am not sure if

    We need better science before better engineering.

    unless somehow there may be a hidden twist to manipulate gravity... but this is more fiction than science?

    My impression is that the different proposals for interstellar spaceflight may not be forbidden by any laws of science, but just prohibitive because they require enormous amounts of energy and money to kick them off in the first place, and rely on extremely complex technology which would have to work without fault and on its own for a very long time.

    At least to advance to the outer Solar System and towards the Oort cloud, the Solar Sails seem to be quite a clever idea - but true, some radical new ideas would probably be helpful.

    Best, stefan

  4. Dear Amara,

    thanks for the link to these photos - wow, that's indeed interesting... documenting a truely historical moment!

    Have a nice Sunday,


  5. "or to ignite nuclear fusion on Earth - problems that should be overcome before a fusion-driven 50,000 ton spaceship could be assembled in orbit - such proposals appear as the daydreams of enthusiastic engineers, easily bursting at the confrontation with reality."

    I know what you mean Stefan,
    sometimes we feel like science fiction is only just round the corner, but the reality is that manned spaceflight inside our solar system (to the moon and mars) are still trmendous feats to be achieved.

    Travelling any further is definitely beyond us for a good while, and it can and will only be achieved in progressive stages.

    I don't see any quantum leaps or wormholes opening up any time soon.

    But hey a trip to Australia from Britain must have been a daunting thought in its day, even with stops along the coast of Africa, India and Malaysia on the way.

    I think the people most suited for space travel are still the Navy, after all if you can handle six months in a nuclear submarine or aircraft carrier - you should be able to handle a trip to mars.

    But it is hard to believe that since Man landed on the Moon, the best google can offer is £30 million for pics from the Moon. Surely the Japs will be collecting that as soon as they pass GO

  6. Ah, I remember working at Parkes Radio telescope (aka The Dish) in 1989. Some NASA people were there laying cables for the Neptune encounter, which ended up being played live in a square in Sydney.

  7. General Relativity is internally self-consistent and mathematically valid. Humans are stuck on Earth therein. Either falsify weak founding postulates (isotropic vacuum, Equivalence Principle) or finesse a theory superset containing loopholes (string theory? Nah).

    I'm doing my part. If you visit Hell around 2050, look for the fellow perpetually recrystallizing benzil to large unflawed prisms. Nasty.

  8. Dear Stefan,

    Eris not a Kuiper Belt object, it is a transneptunian object (TNO) in the region known as the scattered disk. The Kuiper Belt has an edge, at about 50 AU, that puzzled planetary scientists for some time. A natural explanation to that 'edge' was found by Levison and Morbidelli via their and their colleagues "Nice Model" (2005) that implements a concept called dynamical friction in the later stages of our solar system formation, while the gas giants are migrating inward and outward, scattering and dragging other bodies with them. Neptune is particularly important for the shape and location of today's Kuiper Belt, according to their model. See the following 2003 Nature paper, which built up the work to the 2005 Nice model:

    Forming the Kuiper Belt by the Outward Transport of Objects During Neptune’s Migration by Levison and Morbidelli

  9. P.S. The Voyager 2 encounter of Uranus will be forever linked in the Voyager 2 scientists' minds to the Challenger accident. I was at JPL during that encounter, and with a group of planetary scientists when we had just finished our daily morning scientific briefing on the previous day's Voyager results. The TV monitor of the Challenger launch was in the science briefing room. Then we saw the explosion on the monitor. The silence was deafening. Some tears. Numbness for the rest of the day by everyone at the lab. A terrible day.

  10. Thinking in terms of Lagrangian effects, the very idea that positioning satelittes in certain positions, allowed us to think about travel in space. Sailing sure.

    Now thinking in such geometrics is itself interesting, and how this can be done with measure.

    Tragedies in any job can indeed be crushing.

  11. Dear Stefan:

    Thanks for this great post! In the absence of anything intelligent to add

    Voyage, voyage
    Plus loin que la nuit et le jour
    Dans l'espace inouï de l'amour
    Voyage, voyage
    Sur l'eau sacrée d'un fleuve indien
    Et jamais ne revient

    ~ Desireless - Voyage Voyage



    PS: ah, and isn't French such a beautiful language to sing in?

  12. Dear Amara,

    Eris not a Kuiper Belt object, it is a transneptunian object (TNO) in the region known as the scattered disk.

    ... thank you very much for that information and the explanations about the Kuiper belt's edge. I have changed that statement to there may be many other, similar transneptunian objects further out.

    Let me just ask a question, since I do not quite understand this classification: Is the Kuiper belt a spatial region of objects with certain orbital parameters, or is it a class of objects with specific characteristics, say icy, rocky, with a certain density, or something like that? I mean, there are asteroids on orbits far within the asteroid belt, which are classified as asteroids nevertheless, and the perihel of Eris is less than 40 AU, so it fits within the Kuiper belt. Does one know if these Scattered disk objects are geologically similar or different to the Kuiper belt objects?

    The Voyager 2 encounter of Uranus will be forever linked in the Voyager 2 scientists' minds to the Challenger accident. I was at JPL during that encounter, ...

    Oh, I see that you are listed as a co-author of that paper "Photometry from Voyager 2: Initial Results from the Uranian Atmosphere, Satellites, and Rings" in the Science issue of July 4, 1986 on the Uranus encounter (DOI: 10.1126/science.233.4759.65) - that makes me appreaciate even more that you like the post :-)

    In these days in January 1986, I was in the middle of the written exams for the Abitur... I believe French was the day following the Challenger disaster.

    Best regards, Stefan

  13. Dear Bee,

    fascinating, that's another voyage back to the 1980s! Thank you so much :-)... I had never understood the lyrics, but it really sounds good! And I don't remember if I had ever seen this video, and that Bettina Rheims was involved in music videos is also a surprise :-)

    Cheers, Stefan

  14. Hi Kea,

    Some NASA people were there laying cables for the Neptune encounter, which ended up being played live in a square in Sydney.

    Public Viewing for the Neptune Encounter? That's really cool!

    I cannot remember anything similar from (Western) Germany... But in that August 1989, everyone here was more concerned about what was going on in the East, with more and more people from the GDR escaping to the BRD embassies in Hungary and Czechia.

    Best regards, Stefan

  15. Hi quasar,

    Sometimes we feel like science fiction is only just round the corner, but the reality is that manned spaceflight inside our solar system (to the moon and mars) are still trmendous feats to be achieved.

    That's exactly what I wanted to say... I mean, science fiction movies usually give a totally wrong impression of the distances in Space, and the time and energy it will take to bridge them.

    ... after all if you can handle six months in a nuclear submarine or aircraft carrier - you should be able to handle a trip to mars.

    Ah, that comparison to a submarine sounds good!

    BTW, these photos from the egyptian temple with the airplanes and spaceships - I have to say they look quite photoshopped to me ;-)...

    Best regards, Stefan

  16. Dear Stefan,

    It's a fine distinction, and the generic term KBO has been used for so long that I think it will stick as description in casual conversation. Probably the only people who such a distinction might matter are those who are working on that region of the solar system. Since you asked, though: Reading in Wikipedia:

    "According to the Minor Planet Center, which officially catalogues all trans-Neptunian objects, a KBO, strictly speaking, is any object that orbits exclusively within the defined Kuiper belt region regardless of origin or composition. Objects found outside the belt are classed as scattered objects.[58] However, in some scientific circles the term "Kuiper belt object" has become synonymous with any icy planetoid native to the outer solar system believed to have been part of that initial class, even if its orbit during the bulk of solar system history has been beyond the Kuiper belt (e.g. in the scattered disk region)."

    That Voyager Uranus Photopolarimeter (PPS) dataset became an odd kind of hobby because my supervisors ran out of funding for me to work on that project around 1988. I didn't want to stop, though, because it was too fun. That was my scientific programmer career years and you see, funding issues haven't changed.

    The funny thing is that I kept meticulous notes on every aspect of the Voyager 2 Saturn and Uranus rings stellar occultation PPS datasets; all of the star calibrations for example, and then moved those boxes of notebooks (10) and my corresponding 9 track data tapes from home to home (and country to country) for years. Sometime around 1994, the PDS Rings Node archiving manager told me that I had the only copies of some of those star calibration datasets and he collected them and converted from VAX VMS format to something more archivable. Which was a lucky thing because termites attacked that box the in the following year. My notebooks survived more-or-less (some holes here and there). In 2002, in my next career as a postdoc in Heidelberg, I used my tattered but still readable 15-20 year-old notebooks to review the final PDS Saturn and Uranus PPS Rings datasets for NASA.

    So you see, archivable contributions to science can come from the strangest places.

  17. lol Stefan,
    the helicopter definitely looks very 'modern' - but I meant that even ancient man has studied the stars and dreamt of travelling to the stars - after all Pharaoh was meant to BE (become) or reside in his very own home Star after death.

    I was trying to follow on from your thread about space & distance. Seems we may be able to send manned spacecraft to the moon and mars, but anything beyond our solar system or to other galaxies would have to be a one way journey - in a 'lifetime' - of course there can always be next generations bred along the way.

    Like the explorers on earth who ventured out looking for new lands never knowing if they'd come back.
    After all there is still much debate even today when or whether vikings first colonised Greenland, and where native americans came from, whether tribes walked from Alaska to Siberia or Siberia to Alaska.

  18. Dear Amara,

    than you for the explanations, and sharing your story about the Saturn and Uranus ring data!

    The wikipedia entries on the Kuiper belt, the scattered disk and the TNOs are really very informative - I've only now looked into them in more detail.

    Best regards, Stefan

    Hi Quasar,

    with regards to interstellar manned flight - I've been thinking also about the similarities to the exploration of Earth - there are for sure similarities, but I would say also a big difference. The problem may not be that you cannot come back. With interstellar flight you know quite sure before you even have started that you will have to travel very very long, very far, without a chance to stop in between, and even then you cannot be sure where you will arrive. And you have to rely on your technology all the time... It's maybe similar to start crossing the Ocean on a small ship - but even then you could gather rainwater or fish to refresh you supplies.

    Best regards, Stefan

  19. I hope everyone has seen the movie THE DISH about Parkes during the Apollo missions.

    Insterstellar travel would be possuble if we had more efficient matter/energy conversion. Even nuclear fusion converts only 0.7%, working on that.

  20. Hi Stefan,
    there in lies the cruc of the matter, you cannot go into space on a small boat - it would have to be a Noah's Ark.

    Self sustaining in every sense of the word - not just energy, but able to grow(?) food, and able to produce oxygen & water.

    Of course as Louise points out, once you've got the above, then you want (or need) more 'power' and maybe more speed - but you are still talking of moving tens or hundreds of thousands of tonnes, rather than any small satellite.

  21. The ultimate goal cannot be commercial (or private) - the ultimate goal will be exploration funded by governments - as to who gets to pick the crew, and who'd be the lucky ones - only time will tell.

    But it is in the nature of man to explore, and space is the final frontier. I still can't believe that man spaceflight to the Moon dies a death, once other countries start aiming for Mars and the Moon it will again become a 'race' to see who or which inter-governmental or trans-continental collaboration can get there first.

    I guess competition can add an edge to any race or search.
    First Fusion Reactor could be Online by 2016
    Fusion in the fast lane
    US Fusion Science
    Chirac led signing of international fusion test reactor

  22. The Gravity Landscape and Lagrange Points

    Or just thinking differently. Sure we start off dreamily, but the hard facts is always the science. It always progressed though.

    Given new theories and ways in which currents situations exist, how are such things given further insight "unless you give new propulsion systems used for exploration?"

    A black hole is an object so massive that even light cannot escape from it. This requires the idea of a gravitational mass for a photon, which then allows the calculation of an escape energy for an object of that mass. When the escape energy is equal to the photon energy, the implication is that the object is a "black hole". See here also

  23. Hi Louise,

    I hope everyone has seen the movie THE DISH about Parkes during the Apollo missions.

    I've heard about that movie, but not actually seen it... Maybe I should try to ge the DVD ...

    Best, stefan



Comment moderation on this blog is turned on.
Submitted comments will only appear after manual approval, which can take up to 24 hours.
Comments posted as "Unknown" go straight to junk. You may have to click on the orange-white blogger icon next to your name to change to a different account.