Space Station SPHERES run circles around ordinary satellites

NASA astronaut Thomas Marshburn tests the SPHERES-Vertigo investigation hardware, which resembles eye goggles, as it flies aboard the International Space Station. 

Credit: NASA

These are, in fact, the droids that NASA and its research partners are looking for.

Inspired by a floating droid battling Luke Skywalker in the film Star Wars, the free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) have been flying aboard the International Space Station since Expedition 8 in 2003.

Although there have been numerous SPHERES investigations held on the orbiting laboratory, four current and upcoming SPHERES projects are of particular significance to robotics engineers, rocket launch companies, NASA exploration and anyone who uses communications systems on Earth.

The SPHERES-Vertigo, Department of Defense (DOD) SPHERES-Rings, SPHERES-Slosh and SPHERES-Inspire II investigations all use the existing SPHERES space station facility of these self-contained satellites.

Powered not by an astronaut's use of the Force, but by AA batteries, the satellites act as free-flying platforms that can accommodate various mounting features and mechanisms in order to test and examine the physical or mechanical properties of materials in microgravity.

Each satellite is an 18-sided polyhedron and is roughly the size of a soccer ball.

NASA's Ames Research Center in Moffett Field, Calif., operates and maintains the SPHERES research facility aboard the space station, which is funded by the Human Exploration and Operations Mission Directorate at NASA Headquarters in Washington.

SPHERES provide a unique low risk, low-cost, long-term microgravity research facility that supports quick-reaction testing of technologies that can be repeated numerous times.

Alvar Saenz Otero, Ph.D., associate director and SPHERES lead scientist at the Massachusetts Institute of Technology (MIT) Space Systems Laboratory describes the reusability of SPHERES for multiple microgravity investigations by saying, "if anything goes wrong, reset and try again!"

Operating intermittently since February 2013, the SPHERES Visual Estimation and Relative Tracking for Inspection of Generic Objects (SPHERES-Vertigo) investigation uses what looks like eye goggles and other new hardware and software on multiple satellites during testing.

The purpose of the study is to build 3-D models of a target using mapping algorithms and computer vision-based navigation.

These additions to the satellites help researchers create 3-D maps of a previously unknown object for navigation by flying the SPHERES in a path around that object while taking photos.

Brent Tweddle, a postdoctoral associate with the MIT Space Systems Laboratory, said the SPHERES-Vertigo project differs from previous SPHERES experiments by "adding a pair of stereo cameras, which see, perceive and understand their world visually and can communicate with satellites using Vertigo goggles."

The goggles act "like their own little intelligence block that sticks on the front end of the SPHERES and allows them to see the rest of the world that they want to navigate through," explained Tweddle.

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Satellite quantum-communication circles

Communications protected by quantum encryption systems offer unconditional security – if you know which way is up.

A new quantum protocol is the first that promises to work independently of orientation, which will prove vital if quantum communications are ever to be sent via satellites.

Many quantum encryption protocols work by measuring the "up" or "down" spins on pairs of entangled photons shared between a sender, conventionally called Alice, and a receiver called Bob.


The two members of an entangled pair of photons always have an opposite spin from one another. If an eavesdropper were to intercept one, the very act of reading it would affect the entangled pair in a detectable way.

The distance record for quantum encrypted communications between two sites on Earth is 144 kilometres. If quantum encryption is to go global the data must be sent via satellite links, and here the conventional method hits a snag: a spinning satellite's sense of up and down changes over time, making it harder to interpret a photon's spin and establish a key.

Clockwise corkscrew
A team at the University of Bristol in the UK has invented a protocol independent of orientation that exploits the fact that photons can have an entangled circular polarisation as well as entangled spin.

Circularly polarised light can be imagined to corkscrew either clockwise or anticlockwise along its axis of travel. The two forms are readily identified regardless of the receiver's orientation.

Some modern 3D-movie projector systems already polarise light in this way to differentiate the two images used to form the 3D illusion. Doing so ensures that a cinemagoer wearing polarised glasses sees the 3D effect even if they tilt their head.

A 3D system that uses horizontally and vertically polarised light to differentiate the two images only works if the viewer's glasses are orientated in the same up-and-down direction as the theatre projector – in other words, only if the glasses and the projector share the same physical frame of reference.