The fact that Earth once had a spacefaring civilization on it will be obvious, and remain obvious indefinitely for multiple reasons, one of which is the quantity and composition of objects in geostationary orbit. Even if all satellites are thoroughly smashed to bits by micrometeors, they’ll eventually make a chart like fig 3-3 in this paper. Spectroscopy on orbital debris would also pretty easily reveal it to be artificial.
List price for a Falcon 9 launch is $62M, so putting an object in orbit with the desired message fits in the specified budget, with some left over for the payload. A shiny meter-sized object in orbit is quite easy to spot with ground-based telescopes and radars, so the challenge would be (1) making a satellite which can survive micrometeor impacts for 500M years, and (2) making it obvious that they should go retrieve that satellite rather than some random dead comsat.
There is a graveyard orbit above the geostationary orbit, where old satellites are moved.
There was already an attempt to put messages on a very long and stable orbit.
Also, “Arch Mission” send a crystal with data with Falcon Heavy to Mars. Below is the section from my published article on the topic which was removed to make the article shorter:
6.4. Satellites
A heavy satellite on relatively high Earth orbit could exist a very long time. The main risks for a satellite are micrometeorite erosion, temperature changes, and gravitational perturbations. A specially designed satellite with a message could be a lead ball in an orbit above geosynchronous orbit. Its orbit should be orientated in a way that tidal forces will make it rise, the same way as the Moon’s orbit is constantly rising. With an equatorial orbit, the number of light-dark cycles would be far higher than on the moon. However, a polar orbit could avoid light dark cycles if the orbit remained stable.
The benefits are that many satellites already exist and some information carriers could be added to new satellites. Satellites are easily observable even with naked eye, and their artificial origin would be rather obvious based on their chemical composition. One planned data storage satellite is Asgardia (Harris, 2017). The Russian company Kriorus is planning to send frozen brains into orbit (Kriorus, 2017). Students are planning a space time capsule (Liszewski, 2017).
In 1976, the satellite LAGEOS was sent on an orbit 6000 km above Earth with a plaque with a message to the future designed by Carl Sagan. It is estimated that it will fall into Earth in 8.4 mln years (Popular Science, 1976).
In 2012, an artist created a silicon disk with 100 images and put it on geostationary satellite Echostar 16, which will be later moved to a graveyard orbit, where it is expected to remain for billions years (Campbell-Dollaghan, 2012).
This was my thought exactly. Construct a robust satellite with the following properties.
Let a “physical computer” be defined as a processor powered by classical mechanics, e.g., through pulleys rather than transistors, so that it is robust to gamma rays, solar flares and EMP attacks, etc.
On the outside of the satellite, construct an onion layer of low-energy light-matter interacting material, such as alternating a coat of crystal silicon / CMOS with thin protective layers of steel, nanocarbon, or other hard material. When the device is constructed, ensure there are linings of Boolean physical input and output channels connecting the surface to the interior (like the proteins coating a membrane in a cell, except that the membrane will be solid rather than liquid), for example, through a jackhammer or moving rod mechanism. This will be activated through a buildup of the material on the outside of the artifact, effectively giving a time counter with arbitrary length time steps depending on how we set up the outer layer. Any possible erosion of the outside of the satellite (from space debris or collisions) will simply expose new layers of the “charging onion”.
In the inside of the satellite, place a 3D printer constructed as a physical computer, together with a large supply of source material. For example, it might print in a metal or hard polymer, possibly with a supply of “boxes” in which to place the printed output. These will be the micro-comets launched as periodic payloads according to the timing device constructed on the surface. The 3D printer will fire according to an “input” event defined by the physical Boolean input, and may potentially be replicated multiple times within the hull in isolated compartments with separate sources of material, to increase reliability and provide failover in case of local failures of the surface layer.
The output of the 3D printer payload will be a replica of the micro-comet containing the message payload, funneled and ejected into an output chute where gravity will take over and handle the rest (this may potentially require a bit of momentum and direction aiming to kick off correctly, but some use of magnets here is probably sufficient). Alternatively, simply pre-construct the micro-comets and hope they stay intact, to be emitted in regular intervals like a gumball machine that fires once a century.
Finally, we compute a minimal set of orbits and trajectories over the continents and land areas likely to be most populated and ensure there is a micro-comet ejected regularly, e.g., say every 25-50 years. It is now easy to complete the argument by fiddling with the parameters and making some “Drake equation”-like assumptions about success rates to say any civilization with X% coverage of the landmass intersecting with the orbits of the comets will have > 25% likelihood of discovering a micro-comet payload.
The only real problem with this approach is guaranteeing your satellites are not removed in the future in the event future ancestors of our civilization disagree with this method. I don’t see a solution to this other than through solving the value reflection problem, building a defense mechanism into the satellites that is certain to fail—as you start getting close to the basic AI drive of self-preservation and will anyway be outsmarted by any future iteration of our civilization—or making the satellites small or undetectable enough that finding and removing them is economically more pain than it is worth.
I have been thinking about satellites and I come to two main objections:
1) Instability. The fact that we do not observe other natural satellites except Moon implies that all other orbits in this system maybe unstable—not sure, but why we can’t see even a smallest boulder?
2) Cost. The rate of natural erosion in around 1 mm in 1 mln years, or 1 meter in 1 billion years, not counting for larger collisions. This implies that the size of the satellite should be at least a 4 meters in diameter, and assuming that it is made from lead, it will weight 350 tons. Putting a ton on GEO costs now at least 10 mln USD, so only launch will cost 3.5 billions dollar, and as launch is typically only a fraction of cost of the payload, the whole project will cost more than 10 billion USD. For such price there many more useful things could be done. For example, opportunistic payloads on planned landers at Moon cold craters will cost only a fraction of this cost.
I also sceptical for any long-term working machinery before full blown molecular manufacturing, which could be used as eternal nest of ants for the messaging.
Where did you get your numbers? Falcon Heavy brings up 26 tons to GEO for 90 million (by the price on the website without additional deals).
Also given the time-spans that are involved it would make sense to wait for BFR to bring down the prices. It also would be a good payload for a maiden mission.
I used earlier prices for Falcon, not prices of the larger ones. The longer we could wait, the cheaper would be such mission, but the chance that some existential catastrope will happen before it is growing.
The fact that Earth once had a spacefaring civilization on it will be obvious, and remain obvious indefinitely for multiple reasons, one of which is the quantity and composition of objects in geostationary orbit. Even if all satellites are thoroughly smashed to bits by micrometeors, they’ll eventually make a chart like fig 3-3 in this paper. Spectroscopy on orbital debris would also pretty easily reveal it to be artificial.
List price for a Falcon 9 launch is $62M, so putting an object in orbit with the desired message fits in the specified budget, with some left over for the payload. A shiny meter-sized object in orbit is quite easy to spot with ground-based telescopes and radars, so the challenge would be (1) making a satellite which can survive micrometeor impacts for 500M years, and (2) making it obvious that they should go retrieve that satellite rather than some random dead comsat.
There is a graveyard orbit above the geostationary orbit, where old satellites are moved.
There was already an attempt to put messages on a very long and stable orbit.
Also, “Arch Mission” send a crystal with data with Falcon Heavy to Mars. Below is the section from my published article on the topic which was removed to make the article shorter:
6.4. Satellites
A heavy satellite on relatively high Earth orbit could exist a very long time. The main risks for a satellite are micrometeorite erosion, temperature changes, and gravitational perturbations. A specially designed satellite with a message could be a lead ball in an orbit above geosynchronous orbit. Its orbit should be orientated in a way that tidal forces will make it rise, the same way as the Moon’s orbit is constantly rising. With an equatorial orbit, the number of light-dark cycles would be far higher than on the moon. However, a polar orbit could avoid light dark cycles if the orbit remained stable.
The benefits are that many satellites already exist and some information carriers could be added to new satellites. Satellites are easily observable even with naked eye, and their artificial origin would be rather obvious based on their chemical composition. One planned data storage satellite is Asgardia (Harris, 2017). The Russian company Kriorus is planning to send frozen brains into orbit (Kriorus, 2017). Students are planning a space time capsule (Liszewski, 2017).
In 1976, the satellite LAGEOS was sent on an orbit 6000 km above Earth with a plaque with a message to the future designed by Carl Sagan. It is estimated that it will fall into Earth in 8.4 mln years (Popular Science, 1976).
In 2012, an artist created a silicon disk with 100 images and put it on geostationary satellite Echostar 16, which will be later moved to a graveyard orbit, where it is expected to remain for billions years (Campbell-Dollaghan, 2012).
This was my thought exactly. Construct a robust satellite with the following properties.
Let a “physical computer” be defined as a processor powered by classical mechanics, e.g., through pulleys rather than transistors, so that it is robust to gamma rays, solar flares and EMP attacks, etc.
On the outside of the satellite, construct an onion layer of low-energy light-matter interacting material, such as alternating a coat of crystal silicon / CMOS with thin protective layers of steel, nanocarbon, or other hard material. When the device is constructed, ensure there are linings of Boolean physical input and output channels connecting the surface to the interior (like the proteins coating a membrane in a cell, except that the membrane will be solid rather than liquid), for example, through a jackhammer or moving rod mechanism. This will be activated through a buildup of the material on the outside of the artifact, effectively giving a time counter with arbitrary length time steps depending on how we set up the outer layer. Any possible erosion of the outside of the satellite (from space debris or collisions) will simply expose new layers of the “charging onion”.
In the inside of the satellite, place a 3D printer constructed as a physical computer, together with a large supply of source material. For example, it might print in a metal or hard polymer, possibly with a supply of “boxes” in which to place the printed output. These will be the micro-comets launched as periodic payloads according to the timing device constructed on the surface. The 3D printer will fire according to an “input” event defined by the physical Boolean input, and may potentially be replicated multiple times within the hull in isolated compartments with separate sources of material, to increase reliability and provide failover in case of local failures of the surface layer.
The output of the 3D printer payload will be a replica of the micro-comet containing the message payload, funneled and ejected into an output chute where gravity will take over and handle the rest (this may potentially require a bit of momentum and direction aiming to kick off correctly, but some use of magnets here is probably sufficient). Alternatively, simply pre-construct the micro-comets and hope they stay intact, to be emitted in regular intervals like a gumball machine that fires once a century.
Finally, we compute a minimal set of orbits and trajectories over the continents and land areas likely to be most populated and ensure there is a micro-comet ejected regularly, e.g., say every 25-50 years. It is now easy to complete the argument by fiddling with the parameters and making some “Drake equation”-like assumptions about success rates to say any civilization with X% coverage of the landmass intersecting with the orbits of the comets will have > 25% likelihood of discovering a micro-comet payload.
The only real problem with this approach is guaranteeing your satellites are not removed in the future in the event future ancestors of our civilization disagree with this method. I don’t see a solution to this other than through solving the value reflection problem, building a defense mechanism into the satellites that is certain to fail—as you start getting close to the basic AI drive of self-preservation and will anyway be outsmarted by any future iteration of our civilization—or making the satellites small or undetectable enough that finding and removing them is economically more pain than it is worth.
I have been thinking about satellites and I come to two main objections:
1) Instability. The fact that we do not observe other natural satellites except Moon implies that all other orbits in this system maybe unstable—not sure, but why we can’t see even a smallest boulder?
2) Cost. The rate of natural erosion in around 1 mm in 1 mln years, or 1 meter in 1 billion years, not counting for larger collisions. This implies that the size of the satellite should be at least a 4 meters in diameter, and assuming that it is made from lead, it will weight 350 tons. Putting a ton on GEO costs now at least 10 mln USD, so only launch will cost 3.5 billions dollar, and as launch is typically only a fraction of cost of the payload, the whole project will cost more than 10 billion USD. For such price there many more useful things could be done. For example, opportunistic payloads on planned landers at Moon cold craters will cost only a fraction of this cost.
I also sceptical for any long-term working machinery before full blown molecular manufacturing, which could be used as eternal nest of ants for the messaging.
Where did you get your numbers? Falcon Heavy brings up 26 tons to GEO for 90 million (by the price on the website without additional deals).
Also given the time-spans that are involved it would make sense to wait for BFR to bring down the prices. It also would be a good payload for a maiden mission.
I used earlier prices for Falcon, not prices of the larger ones. The longer we could wait, the cheaper would be such mission, but the chance that some existential catastrope will happen before it is growing.