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Do you ever miss the 70s?  That time will never return (although stagflation and oil crunches might make an unexpected comeback from the weird devil’s brew of bad economic and geopolitical policies which we are experimenting with) however there is a more positive reminder of the age of disco in the very heavens themselves.  At present, there are three disco balls in orbit around Earth.  The first and most significant is actually a 70s artifact: LAGEOS (Laser Geodynamics Satellite) was launched from Vandenberg Air Force Base on May 4th 1976.  The 408 kilogram (900 pound) satellite has no electronic components ore even moving parts: it is a brass sphere studded with 426 jewel-like retroreflectors. 422 of these retroreflectors are made from fused silica glass (to reflect visible light), however the remaining 4 are germanium, for infrared experiments.


Orbiting the entire planet every 225.70 minutes, LAGEOSl is a pretty stupendous piece of space art in its own right, however it was designed for a serious scientific purpose.  Lageos provides an orbiting laser ranging benchmark.  To quote

Over the past 40 years, NASA has used LAGEOS to measure the movement of Earth’s tectonic plates, detect irregularities in the rotation of the planet, weigh the Earth and track small shifts in its center of mass via tiny changes in the satellite’s orbit and distance from Earth.

Measurements made using LAGEOS have also been used to confirm Einstein’s general theory of relativity, since measurements made on this scale demonstrate a measurable “frame dragging effect” (which you are going to have to figure out with some help from your favorite physicist).  The satellite also illustrates the Yarkovsky effect, which explains how an object is heated by photons on one side will later emit that heat in a way which slows the object.  This latter effect will eventually cause LAGEOS’ orbit to deteriorate and bring it tumbling to Earth.  Scientists estimate this will happen 8.4 million years from now, so there is still time to contemplate this sphere.  Also there is a small time capsule on board to capture certain scientific truths and human ephemera for the long ages.


LAGEOS was so useful and proved to be such a success that NASA launched an identical sister craft in 1992 (how did I miss all of these interesting events?).  This still leaves one disco ball satellite unaccounted for.  The final craft is “The Humanity Star” which serves no purpose other than being art.   Launched on January 21st of this year (2018), the humanity star is a regular polygonal solid with 65 triangular sides.  It is made of carbon fiber embedded with enormously reflective panels and is meant to be seen twinkling in the night sky to make humankind collectively reflect on our shared home, the Earth.  The Humanity Star orbits much lower than the LAGEOS satellites.  They are  5,900 kilometres (3,700 miles) from Earth’s surface, whereas the humanity star is only 283.4 kilometers (176.1 miles) away from the planet at its perigree.  It whips around the Earth every 90 minutes on a circumpolar orbit (which means it is visible from everywhere at some point.  You could look up where it is online and go out and find it with fieldglasses.  The object glimmers and shimmers in unusual ways, sometimes appearing as bright as Sirius (the brightest star save for the sun), but usually twinkling like barely visible stars.  The Humanity Star won’t last long—it is scheduled to fall into Earth’s gravity well and burn up in fall of this year, so check it out before it is gone.  The craft was controversial: some serious aerospace mavens objected to launching an object into orbit to serve no purpose other than art, yet, as an artist I am happy to know it is out there.  Maybe go look at it and let me know if it inspires you.


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