Laser Geodynamics Satellites (LAGEOS) is a couple of (artificial… of course) satellites orbiting around our Earth. Their original aim was to provide an orbiting laser ranging benchmark for Earth geodynamical studies. It was back in the 1976 when LAGEOS-1 was launched by NASA followed in 1992 by LAGEOS-2 (NASA and ASI…). Two launches without too much claim and advertising for one of the most long-lasting missions ever conceived.
Both satellites are actually two balls (looking like golf balls) made of high-density passive laser reflectors. More in detail, they are brass spheres covered with aluminium of 60 cm diameter and 400-410 kg mass. Spread over they surfaces there are 426 reflectors made of glass and germanium. Measurements can be made by transmitting from Earth ground stations pulsed lasers toward the satellites that reflect the pulses and measuring the travel times. In addition the shape, attitude-independent measurements and the orbit allows for using the satellites also for determine the geoid shape, the tectonic plate movements, and the distortion predicted by the general relativity caused by a rotating mass.
In the end the two satellites are completely passive, without any attitude control means and without any electronic on board. In order to provide a stable reference for geodynamical studies (which means an extremely high accuracy in determining the positions of points on the Earth), the golf balls have been placed in very stable medium altitude orbits at about 5900 km altitude.
As a consequence of the orbital altitude, shape and mass of the satellites, LAGEOS-1 (LAGEOS-2 has very similar features…) is doomed to reentry on Earth in … 8.400.000 years! At some point in more than 8 millions years some of our descendant (…or any other species enough intelligent to survive to us) will see a ball coming from the past.
A real time capsule.
The plaque includes the numbers 1 to 10 in binary. In the upper right is the earth with an arrow pointing to the right, indicating the future. It shows a #1 indicating 1 revolution, equaling 1 year. It then shows 268435456 (in binary; 228) years in the past, indicated by a left arrow and the arrangement of the Earth’s continents at that time. The present is indicated with a 0 and both forward and backward arrows. Then the estimated arrangement of the continents in 8.4 million years with a right facing arrow and 8388608 in binary (223). LAGEOS itself is shown at launch on the 0 year, and falling to the Earth in the 8.4 million year diagram.
I’ll never see the satellites with my own eyes (well… I guess), and I can imagine the astonishment of anyone seeing that plate in millions of years (it si much more than a fossil we can discover nowadays!) .
My hope, as per today, is that the satellites will be still checked (even form time to time) for the millenniums to come, to avoid that far from eyes the satellites will be forget while they can still be considered as alive.