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On Artifacts Future and Past

How are you affected by the cave paintings at Lascaux? The paleolithic art in this region of southwestern France dates back perhaps 18,000 years, depicting large animal figures, human forms and abstract symbols. Some believe the paintings even contain astronomical pointers — star charts — but theories on how to interpret them abound, and whatever spin we put on them, we’re confronted by the mystery of evocative imagery reaching out over centuries. Lascaux and other such sites take us beyond civilization and into the realm of deep time, a place where our parochial concerns are dwarfed by this reminder of humanity’s aggregated experience.

Early cave art reaches almost twice as far back as the 10,000 year clock proposed by Danny Hillis and the Long Now Foundation hopes to take us forward. Yet the experience of the two is in some ways similar. Building a clock designed to tell time by the year and century places our short lives in perspective and demands we take a view that encompasses our remote descendants. Long-term thinking, forward or back, is about identifying the forces shaping the human experience and asking what we can do today to influence an outcome we will never live to see.

In some ways, artifacts like the Voyager Golden Record are cousins of the cave paintings, for they collect various statements about who we are and project them into the realm of deep time. It’s equally hard to imagine what far future audience the cave painters might have had in mind, if any, and what audience the Golden Records might one day achieve. But for chance we might never have learned about Lascaux, the paintings of which were discovered by a French teenager in 1940. And what chance is there that some extraterrestrial civilization may one day recover an intact Voyager, long silent but bearing the testimony of the record that identifies its makers?


Image: One of the cave paintings of Lascaux, a chance discovery that brought the early human experience to vivid life. Credit: Wikimedia Commons.

I’m thinking about Lascaux this morning because a scene from the cave art is one of the images chosen by writer and artist Trevor Paglen for a multimedia project called The Last Pictures, an archive of 100 black and white photographic images launched into geosynchronous orbit aboard a communications satellite in November. Paglen had been contemplating the fact that most satellites in low Earth orbits eventually return to Earth, forced down by the inexorable processes of orbital decay. But communications satellites, almost 36,000 kilometers above the equator, are up there for good. “These satellites are the longest-lasting things that humans have ever made,” Paglen told The Atlantic’s Austin Considine in a recent interview. “Very few, if any, traces of human civilization [will remain] on the surface of the earth. But a ring of dead satellites and spaceships will remain in orbit, essentially, forever.”

So Paglen set about choosing photographs that would record the human experience, working with artists, scientists, philosophers and anthropologists to decide how to encapsulate it. Drawing on the expertise of a team at MIT and weighing the physical constraints for an archive he saw as lasting several billion years, the chosen images were etched into a silicon wafer that was bolted along with its protective shell onto the EchoStar XVI, a satellite operated by Dish Network. The satellite is expected to carry programming for 15 years, the archive to survive for billions more.

Have a look at Considine’s piece, which reproduces several of the images, including art from Lascaux as well as cherry blossoms against a clear sky, a waterspout in the Florida Keys and a group of orphan refugees from Greece and Armenia wading into the sea for the first time. How you cull 100 images out of the vast possibilities in archives around the world is a story in itself, and it’s clear that Paglen had no didactic agenda in their selection. No captions accompany the satellite-born text (although they are available in an accompanying book available through Paglen’s site). Like the cave paintings, Paglen’s images are evocative without shedding obvious meaning, capable of deep layers of interpretation and conveying a sense of shared experience.

Considine’s interview is itself moody and interesting. Here’s a bit more of it:

Sagan’s records implicitly assumed we would be around for an alien follow-up call. It tried — ambitiously, if somewhat arrogantly — to make a good first impression. “The Last Pictures” assumes it is impossible to say anything universal or lasting about humanity, and that we’ll be long gone by the time its pictures are discovered, if they’re found at all.

“This is not a project that’s supposed to explain to aliens what humans are all about and be the definitive record of human civilization,” Paglen said. It is, he added, “a collection of images that explained to somebody in the future what happened to all of the people who built the dead spaceships in orbit around the earth. And how they killed themselves.” (Or perhaps were killed?)

As art, this is work that proceeds without any certainty of a future audience, and makes its statement by that very ambiguity. If our species works its way through the thousand traps of technological growth and survives, the Paglen photographs become a time capsule of the sort we tend to stick in the cornerstone of buildings, and we can imagine humans of the future looking upon the ancient satellite as no more than a curiosity. If we don’t survive, we can imagine the same faint chance the Voyagers have of being detected and studied by some other intelligence, a thought that adds an almost unbearable poignancy to some of these images.

I wouldn’t want to try to convey the experience of an entire species through any series of images, and with a number as small as 100, the choice seems hopelessly arbitrary. But what gives the work a certain fascination is that we live in an era when we can create something that could outlive its makers not just by millennia but by eons. There will be more such things as we continue to push out into the Solar System, with space probes that continue their journeys long after they have fallen silent, and all will bear witness to the civilization that put them in motion. That in itself is evocative of the deep mystery we all face as we confront our existence, a mystery the cave painters surely felt as they captured hunters, bison and aurochs on walls of ancient stone.


Comments on this entry are closed.

  • Thomas Mazanec January 7, 2013, 13:01

    Will the aliens be able to date the Clarke Orbit satellites by how much the Earth’s rotation has slowed down?

  • Gregory Benford January 7, 2013, 14:17

    In my book DEEP TIME I detail a lot about this. Most interesting for a portrait of humanity that Jon Lomberg principally designed, see http://www.jonlomberg.com/articles/a_portrait_of_humanity.html

    Gregory Benford

  • Mark January 7, 2013, 14:26

    Rather than an archive that would last billions of years in orbit, I’d like to see some sort of international agreement among spacefaring nations that satellites carry sufficient resources to de-orbit themselves after their useful life is over. Long before these archives reach an audience a billion years hence, someone or something is going to have to go up there and clean up the mess orbiting the planet.

  • coacervate January 7, 2013, 15:04

    Bulls! Bulls!

    Thought provoking, thanks! as usual.

    I’ve adopted the habit of turning casual conversations towards this topic. About half of the people in my circle believe this century will see catastrophe, that the fabric of human civilization is unravelling. Some combination of climate, pollution, war, tectonics and of course death from the sky will push us over the edge.

    Be of good fettle me hearties. There’s 7 billion of us. Twill take a mighty smite indeed to extinctify the lot of us. If we go, it will be by way of the Krell I’ll wager!

  • Alex Tolley January 7, 2013, 16:21

    The idea that these dead satellites will still be in orbit after humans have either disappeared or lost the ability to use space is just depressing. Like Mark, I would hope that we learn how to dispose of space junk and keep the orbital resource useful. Why geosynch satellites make better time capsule locations than those on the earth (or even the moon?) is not clear to me at all.

  • Peter Chapin January 7, 2013, 19:14

    I tend to agree that the long term future of satellites in orbit is for them to be disposed of by our descendants. I also wonder if the long term future of the Voyager Golden Records is to end up in the Smithsonian. If we ever do acquire advanced propulsion systems the temptation will be great to go out there and get them ourselves. Unless… they are declared to be some kind of “Terrian Historic Treasure” and left alone by an act of the world government!

  • Col January 7, 2013, 20:59

    My thoughts on this echo Mark & Alex Tolley. Rather than billions of years, I suspect this archive will soon be forgotten, eventually to vanish unremarked down the maw of a geostationary “garbage truck” within a couple of thousand, as our descendants clean up our mess in preparation for construction of an enduring geostationary infrastructure. On the other hand, an archive like this housed on the moon in a black obsidian monolith with 1:4:9 proportions would be superb!

  • Eniac January 8, 2013, 0:04

    Why geosynch satellites make better time capsule locations than those on the earth (or even the moon?) is not clear to me at all.

    Not to get subducted and melted into magma is one reason Earth is not such a great choice. A particular advantage of GEO is that these satellites are easily found, even in the unlikely event they are completely forgotten.

    Unless… they are declared to be some kind of “Terrian Historic Treasure” and left alone by an act of the world government!

    Good luck with that. Even if Earthlings, Martians, and Ooort dwellers are all subdued in the iron grip of the World Government, the Alpha Centaurians will get them!

  • Stan January 8, 2013, 1:39

    The idea that a civilization that has developed so far beyond us would find the pictures very interesting speaks only of our sense of importance to ourselves.

  • Eric January 8, 2013, 2:05

    As an archaeologist, I think this is a fun discussion. What survives to be discovered and interpreted in the future greatly depends on specifics. Geo-synchronous satellites seem like a good bet, since little would disturb them, they seem to be mainly made of nonperishable materials, and better yet, they’d be relatively easy to discover for anyone capable of actually retreaving them.

    Although records, messages, and other mementos on space probes are poignant, they are less likely to see any notice, simply because the are so few probes compared with more mundane space artifacts (commercial satellites).

    Don’t forget, archaeologists usually find and study ancient trash, and try to understand garbage in context with other garbage and debris. For some ancient societies that did not build elaborate big architecture or monuments or even clear cemeteries, their trash is their only trace.

  • ethanol January 8, 2013, 2:10

    Alex Trolley: On earth, geology / meddling kids destroys things relatively quickly. In orbits higher than geosynchronous, the faster relative rotation of the earth pumps energy into the orbit by tidal forces, pushing the satellite outwards (like the moon). Lower draws it inward (like Phobos). Geosynchronous is stable. Until the earth’s rotation slows down, when it is effectively in a sub-geosynchronous orbit. I wonder if they have taken this into account?

  • jkittle January 8, 2013, 9:27

    I like the idea of a deep space human time capsule, purpose build and made with several replicates. the purpose would be to document our world and our times and civilization to future generations. Launched out of earth orbit to some orbital space with meaning, and set up to emit a signal once every year or so for tracking. Designed with a minimum lifetime of 1,000 years. Could be done with today’s technology. Pretty sure you could raise a few million bucks around the concept.

  • Michael Spencer January 8, 2013, 9:58

    My heart is stilled viewing those images, Paul.

  • A. A. Jackson January 8, 2013, 11:14

    On our Earth orbit satellite population as an archaeological artifact:
    (1) We have to consider the population before the International Mitigation by way of the UN was signed , I don’t know maybe 15 years ago.
    All space faring nations , even China*, (except a couple of rouges) have signed on to provide some method of limiting the lifetime of satellites and booster stages to some finite lifetime, less than 100 years.
    So those will be gone.
    (2) Almost all Low Earth Orbit satellites will be gone quickly.
    (3) High Earth Orbit satellites have lifetimes of about 1000 years or so, even GPS satellites don’t last.
    (4) GEO satellites can last a long time , dead ones are put into storage orbits.
    But those can’t last forever, I don’t know what the upper limit is. I know the higher the inclination the shorter the time before they re-enter and solar radiation pressure works on their eccentricity.
    Consider this, if the Moon were moved to polar orbit about the Earth , due to Solar perturbations it would hit the Earth in lest that 5 years!
    Even Lagrange point satellites are not stable forever , the Solar perturbations make their orbit unstable , even Jupiter does some work there.
    One also has to factor in Solar Radiation Pressure , tho it’s a longer time process.
    This ignores catastrophic cascading of satellite collisions which would pulverize the whole LEO population and the GEO too.
    If our civilization vanishes , in even a 100,000 years years there may be no Earth – Lunar space satellite population.

    There is an active program for debris removal , if that materializes , then even more thinning.

    *Hopefully the Chinese don’t whack one of their own satellites again.

  • ljk January 8, 2013, 11:37

    ethanol said on January 8, 2013 at 2:10:

    “Alex Trolley: On earth, geology / meddling kids destroys things relatively quickly.”

    Not just little vandalizing brats: Ignorant and apathetic adults have done more than their fair share of destroying large swaths of human history – the Library of Alexandria being just among the most famous example of our cultural lobotomies.

    In addition, any good archaeologist will tell you how much has been lost to black market grave robbers who destroy the history around the valuable objects they steal to sell illegally to the highest bidder. It is practically an industry in itself.

    Reading the comments here, most of which seem to disparage what is essentially an art project that did no harm and cost them nothing, I am surprised this is the same forum that supports and promotes humanity’s efforts to literally reach for the stars. With pessimism like this, along with our destructive tendencies, I am not surprised that we are so far back from where we should be in this endeavor.

    If ETI are similar to us as certain scientists are saying, this may be yet another factor to add to the Fermi Paradox.

  • NS January 8, 2013, 14:28

    “The idea that a civilization that has developed so far beyond us would find the pictures very interesting speaks only of our sense of importance to ourselves.”

    We still find cave paintings interesting after tens of thousands of years. Of course the painters weren’t painting for us, but for themselves. Probably their ideas of what they were doing were drastically different from ours.

    It’s not possible to guess what will be of interest to the future. Our legacy will be what was of interest to ourselves, some small part of which MAY speak to the millenniums to come.

  • johnq January 8, 2013, 14:43

    >If we go, it will be by way of the Krell I’ll wager!

    The “Forbidden Planet” way is one possibility, to be sure. And there are many others, some of them variants of a Krell-type Singularity. All we know (quoting physicist X regarding the Fermi Question/Paradox), is that the chain breaks somewhere, perhaps several wheres (with varying degrees of probability). In the past or still in the future, who can know or guess?

    I find myself from time to time contemplating pictures of the magnificent Andromeda Galaxy, and wondering why we don’t see anything resembling, you know, interstellar travel/civilization stuff? There or anywhere. Maybe our instruments are too weak, or it’s too soon (are we the first ones in the Local Group?), or they achieve star-hops in Andromeda in ways utterly different from anything we can imagine. Or did they go inward and are playing system-wide social network games for all dreary eternity?

    Whatever the reason, Andromeda looks vacant, “pristine” in a word. And maybe when we get there we will liven up the joint, but mostly I get worried.

  • JoeP January 8, 2013, 15:46

    I was just thinking…can an Earth based high powered pulse laser be used to de-orbit space junk? Might make the cleanup easier.

  • NS January 8, 2013, 16:05

    “Andromeda looks vacant…”

    I think it was Kardashev who said we might be taking as natural features things that are actually astro-engineering (i.e. the anthill next to the freeway scenario). Arguably the distinction between “natural” and “artificial” is a bit dicey anyway — if intelligence/consciousness/whatever are products of nature, aren’t their results products of nature too, or at least of nature once removed?

  • Rob Henry January 8, 2013, 19:13

    A A Jackson wrote “Consider this, if the Moon were moved to polar orbit about the Earth , due to Solar perturbations it would hit the Earth in lest that 5 years!”.

    And that is so counterintuitive that I would like a reference and wish to check the calculations myself even if it is peer reviewed.

  • Rob Henry January 8, 2013, 21:11

    OK Jackson, I think I have adequate calculations to at least disprove you assertion now, here goes…

    The minimum possible delta V budget required to change the moon’s trajectory to hit the Earth is always the Hohmann transfer orbit. Here that is so close to cancelling the Moons orbital velocity of 1023m/s, that I will just call that budget 1000m/s (round figures are nice).

    Now the absolute magnitude (let’s pretend that its direction is always perfect for our cause) of the amount of further acceleration that the moon receives from the sun, and that the Earth does not (the solar tide) is 2GM * (its further distance from the sun than the earth) / (distance from the Sun cubed)

    So how do we get the maximum effect of (its further distance from the sun than the earth)?
    In an orbit aligned to the solar equator this is the area under the sine curve times the orbital diameter. Normally this would add to zero but here we use the average of its absolute value, so it is r/PI, where r is the diameter of the moon’s orbit. Adjusting for the fact that this is a polar orbit, we get r/PI^2.

    Now, plugging that distance into the equation we find an average acceleration of 3*10^-6 m/s, so it would take over 10 years just to access the minimum necessary delta V budget from your “Solar perturbations”

  • Col January 9, 2013, 5:51

    ljk – “Reading the comments here, most of which seem to disparage what is essentially an art project that did no harm and cost them nothing, I am surprised this is the same forum that supports and promotes humanity’s efforts to literally reach for the stars. With pessimism like this, along with our destructive tendencies, I am not surprised that we are so far back from where we should be in this endeavor. ”

    Hi ljk, I think you are misinterpreting the intent of the comments (mine included). I don’t see anyone quibbling with the artistic value of the project, indeed the images I have seen are all beautiful & evocative of how “we” would like to have ourselves remembered. (Where “we” appears to me to be a somewhat white anglo-saxon male specific perspective, but perhaps thats just my own biases showing).

    Rather, I think the comments somewhat to be expected from the kind of people who would be drawn to this blog, as while applauding the art they tend to focus on the engineering practicality of actually getting the image archive to last for a billion+ years. Given the bent of people on here to speculate about “deep future”, it is unsurprising that the choice of geostationary orbit might attract criticism, given that it is highly unlikely to be a survivable environment for the stated period.

    Hence my own suggestion that a tastefully appointed 1:4:9 monolith on the moon might serve the purpose better. It would be kind of neat if the species establishing Clarke style monoliths turned out to be us!

  • ljk January 9, 2013, 11:40

    A Billion Years In The Future, This Disc Containing 100 Images Will Tell Our Story

    Think you could tell the story of the human race in only 100 pictures?

    That’s the challenge that MIT resident artist Trevor Paglen tackled when he conceived The Last Pictures five years ago. The goal of the project is to record a montage of human life and achievements onto a medium that can last until intelligent life in the distant future discovers it, even if it takes a billion years for them to find it.

    The aim isn’t simply to create a visual history of humanity necessarily, but a collection that synergistically offers more depth and narrative about human civilization. As Paglen describes it: “The Last Pictures isn’t really an archive so much as a kind of silent film or visual poem.”

    Full article here:


    To quote:

    According to Paglen, the majority of the images are from the the last century or so, or “the historical moment that geostationary spacecraft come from.” But the images aren’t necessarily limited to that time period. The collection includes more historical pictures such as cave paintings and trains, but there was “no effort to make something comprehensively historical.”

    After all, it would be difficult to properly reflect achievements across all human endeavors evenhandedly in 100 snapshots.

    As he stated in an email:

    The collection is meant to function in a much more hesitant, impressionistic manner. All the images were selected for various historical or conceptual reasons, but the final collection works very much like a montage. Moreover, there wasn’t really any effort to describe the “current state of technology” either – there are only 100 images, and they’re black and white (for technical and aesthetic reasons).

    I wanted the Artifact to feel anachronistic at the outset, something that has the feel of a relic in the first instance. There are formal relationships, motivic relationships, and thematic relationships that span the collection. Some themes have to do with the anthropogenic transformation of the earth’s surface and biosphere, histories of vision and knowledge, pictures about pictures, fragments of the state, and so on.

    The Last Pictures is in no way meant to be a grand representation of what-humanity-is-all-about. It’s much more limited in scope, having to do with an uncertain relationship to “progress,” technology, the environment, and the future itself.

  • ljk January 9, 2013, 11:45

    Artist’s project to blast gold-plated artifact disc into orbit

    ‘The Last Pictures’ disc, which could circle the Earth for billions of years, contains just 100 black and white photos

    By Lucas Mearian

    October 3, 2012 06:00 AM ET 11 Comments.

    Computerworld – The problem: You want to send images into space and you want them to last 5 billion years. The solution: A gold-plated disc.

    That’s the idea behind The Last Pictures project, which is scheduled to blast off in the next few months.

    The project involves attaching a silicon disc encased in gold to the outside of a communications satellite. The disc will include just 100 etched photos, which are meant to be a cultural artifact for aliens to find if mankind is no longer here when they come knocking.

    The disc, designed by researchers at MIT and Carleton College, is filled with images chosen by artist Trevor Paglen and a team he put together, who are working with the nonprofit arts organization Creative Time and the media and satellite company EchoStar.

    Full article here:


    To quote:

    Once the images were etched, one question remained for everyone involved in the project. What impression might aliens get from the artifact?

    “I think one part of me thinks it will mean nothing at all to them. That part of me understands the way we see images now is very culturally specific,” Paglen said. “But I also worked with scientists at MIT and those guys thought these images would be found by robots, and those robots would understand what they meant.”

  • ljk January 9, 2013, 14:47


    Data Saved In Quartz Glass Might Last 300 Million Years

    By Timothy Hornyak

    Most cultural institutions and research laboratories still rely on magnetic tape to archive their collections. Hitachi recently announced that it has developed a medium that can outlast not only this old-school format but also CDs, DVDs, hard drives and MP3s.

    The electronics giant partnered with Kyoto University’s Kiyotaka Miura to develop “semiperpetual” slivers of quartz glass that Hitachi says can preserve information for hundreds of millions of years with virtually no degradation.

    The prototype is made of a square of quartz two centimeters wide and two millimeters thick. It houses four layers of dots that are created with a femtosecond laser, which produces extremely short pulses of light. The dots represent information in binary form, a standard that should be comprehensible even in the distant future and can be read with a basic optical microscope. Because the layers are embedded, surface erosion would not affect them.

    The medium has a storage density slightly better than that of a CD. Additional layers could be added, which would increase the density. But the medium is more remarkable for its durability. It is waterproof and resistant to chemicals and weathering, and it was undamaged when exposed to 1,000-degree heat for two hours in a test. The results of that experiment led Hitachi to conclude that the quartz data could last hundreds of eons.

    “If both readers and writers can be produced at a reasonable price, this has the potential to greatly change archival storage systems,” says Ethan Miller, director for the Center for Research in Intelligent Storage at the University of California, Santa Cruz. The medium could be ideal for safekeeping a civilization’s most vital information, museum holdings or sacred texts. The question is whether the world as we know it would even last that long. “Pangaea broke up less than several hundred million years ago,” Miller adds. “Many quartz-based rocks from that time are now sand on our beaches—how would this quartz medium fare any differently?”

    This article was originally published with the title Super Long-Term Storage.

  • James Jason Wentworth January 10, 2013, 9:49

    Being the Philistine that I am with regard to much art, my reaction to this and other similar projects (even the Pioneer 10 & 11 plaques and the Voyager 1 & 2 records) is a shrug and “That’s nice.” I am far more interested in getting on with the task of making humanity more than a single-planet people, with a corresponding multi-world economy. If humanity succeeds in doing these things, it is more likely that any visiting alien archaeologists won’t have to dig through the remains of human civilization to learn about its builders, but will be able to interview them.

  • A. A. Jackson January 12, 2013, 15:09

    @Rob Henry

    Yes I know the thing about the Moon hitting the Earth sounded kinda crazy to me too.
    The calculation is in:

    Essays on the Motion of Celestial Bodies by V.V. Beletsky (Aug 15, 2001) Birkhauser Verlag
    Page 95 .
    I checked with a celestial mechanics friend of mine and he says it’s true.
    He did a computer simulation of it:


    Beletsky gives an analytic proof I don’t have the energy to copy down.
    Beletsky is a grand master Russian celestial mechanics guy and the book mentioned above is amusingly eclectic.
    I have a copy, but the book is expensive , I finally broke down and bough a used copy , still at a steep price.
    Many large university libraries have it.
    Dr. Doug Hamilton , see web page above, told me that the great celestial mechanics researcher Y. Kozai discovered this long ago but he never publicized the result.

  • Rob Henry January 13, 2013, 16:38

    A A Jackson, thanks for the reference. If true, this must have been found many times by various researchers and discarded as an obvious error, with only the Russians brave enough to publish.

    In that simulation the semi-major axis is constant (to within my ability to measure it) as it changes from a circular to a rectilinear orbit, as opposed to a Hohmann transfer where it would be halved. This takes more energy, but the perturbations are significantly larger. Even so, it looks to me as if this process must be at least 50% efficient at summing the effect of each tidal push compared to the perfect delta V budget, and possibly closer to 100%. I am wondering why we often can’t make intelligently directed low thrust transfers this efficient compared to high thrust ones.

    And one afterthought. I am thus wondering if that constant semi-major axis in that simulation is due to the assumption of a constant lunar period – which would be very reasonable given a less extreme outcome. Could this all be an artifact of that!

  • Rob Henry January 13, 2013, 16:50

    Another afterthought Jackson. If this effect is not the result of some solar/lunar orbital resonance, it should be true for Uranus where tides are only 7000 times less. Wouldn’t the eccentricities of its regular satellites be pumped right up, and tidal heating become extreme?

  • A. A. Jackson January 14, 2013, 9:01

    Rob Henry, it was discovered by the Japanese expert in celestial mechanics Yoshihide Kozai


    For Uranus:
    The intermediate inclinations 60° < i < 140° are devoid of known moons due to the Kozai instability. In this instability region, solar perturbations at apoapse cause the moons to acquire large eccentricities that lead to collisions with inner satellites or ejection. The lifetime of moons in the instability region is from 10 million to a billion years.

    It is a resonance mechanism:


  • ljk January 16, 2013, 16:07

    I am including this link because it has images from The Last Pictures that have not been duplicated numerous times over – and there does not seem to be a database yet of all the photographs from this art project:


    This one also has not typically shown images plus a discussion of the lecture event about The Last Pictures in Bryant Park in NYC last September:


    I sincerely hope a publically available recording of that event is available somewhere.

  • Paul January 20, 2013, 19:42

    “The minimum possible delta V budget required to change the moon’s trajectory to hit the Earth is always the Hohmann transfer orbit.”

    This is actually not true. Ignoring the sun, boosting to the moon to extreme distances, then doing a small delta-V to put it back on an earth-intersecting orbit, would require less delta-v than a Hohmann orbit.

    (In general, the minimum delta-V trajectory between two coplanar circular orbits is this two part trajectory, not the Hohmann trajectory, when the ratio of the radii of the orbit exceeds a certain value.)

  • Thomas Hackney January 21, 2013, 3:56

    J.J. Wentworth is right on with his last comment about the more important business of “getting on with the task of making humanity more than a single-planet people.” Heck, the country has been pussyfooting for more than half a century. Heck, we could have sent a 150 pound payload to the moon in 1954(!), according to Werner von Braun, but the Whitehouse and Pentagon shot the little-known project (“Project Moon”) down because it didn’t want to embarass the Navy IGY project, or some such deal. This was when they were building the first Navaho Launch complex. The idea was to take the three-barrel version of the Navaho rocket engine, put a Redstone on top, replacing the warhead section, and put two sold stages on. Von Braun, Asa Gibbs, Don Burris and Marty Caiidin worked out the entire booster, ran it through a computer, designed and built it. They had 28,900 miles an hour in the bank. But when the papers were presented they were clamped “secret” by the Secretary of the Air Force (Donald Quarles) and never released.

  • ljk January 22, 2013, 15:10

    Thomas, it was actually called Project Orbiter. See here:


    To quote:

    “1954 June 25 – . LV Family: Redstone. Launch Vehicle: Jupiter C.
    Project Orbiter begun. – . Nation: USA. Related Persons: von Braun. Spacecraft: Explorer A.

    “In a meeting, Dr. Wernher von Braun, Frederick C. Durant III, Alexander Satin, David Young, Dr. Fred L. Whipple, Dr. S. Fred Singer, and Commander George W. Hoover agreed that a Redstone rocket with a Loki cluster as the second stage could launch a satellite into a 200-mile orbit without major new developments. This became a joint Army-Navy study project after meeting at Redstone Arsenal on August 3. Project Orbiter was a later outgrowth of this proposal and resulted in the launching of Explorer I on January 31, 1958.”

    And here:


  • Rob Henry January 22, 2013, 15:40

    Paul, when I did orbital dynamics long ago the lecturer said that Hohmann transfer had been proved in theory as the minimum energy path between to circular orbits. He was notably reliable so I trust this.

    Here the two orbits are Lunar and 1700km. If what you are saying is correct, then the energy saving must be less than the extra energy with which the moon impacts the Earth in that revised scheme. Offhand, I can’t see how that is sufficient to lower the efficiency of the summation of perturbations to just a few percent – and since a good deal of their effect should cancel on opposites sides of the orbit, the efficiency of the summation of these perturbations still looks like a huge mystery to me.

  • Rob Henry January 24, 2013, 21:55

    I finally got around to running the figures with the Earth and Moon point masses surrounded by light spheres of there apparent diameters (which I assume was what A A Jackson’s referenced simulation did) then simplified further by making the moon have negligible mass compared to the Earth (that second simplification was me being lazy) and found that the velocity difference from a moon falling from 405,000 km or 810,000km (= a rectilinear orbit with the same semi major axis) was just 49 m/s. Thus Paul’s correction could only save a maximum of around 5%. This might be important if you are planning a mission on a tight delta V budget, but insignificant in this context.

  • Rob Henry January 24, 2013, 22:25

    Doh! I have done something very wrong in my previous calculations. Paul is more correct than that! I suspect that it is this…Hohmann is probably proved as the minimum energy transfer between two circular orbits, not minimum delta V budget.

    Note that in a Hohmann transfer to the edge of LEO from a distant body, we would cancel nearly all its orbital velocity, but to send it to infinity would take (2^0.5 – 1) of this ie 59% less.