Down to Earth: From Space to Selfies

What happens when the science and technology of space comes Down to Earth? Dr Stuart Higgins explores how the space race spawned the selfie…

Stuart - Welcome to Down to Earth from the Naked Scientists.The mini-series that explores the spinoffs from space technology that are being used in life on Earth. I’m Dr Stuart Higgins…

This episode, we’re talking about how the need to make better cameras for spacecraft gave us camera phones and selfies.

In the 1990s at the Jet Propulsion Laboratory in California, physicist and engineer Eric Fossum and his team were working on the problem of digital cameras for satellites. For years, satellites had been beaming back some of the most spectacular images of our universe, but the current technology was proving problematic.

At the time, early digital cameras used charge-coupled devices, other wise known as CCDs. In a CCD, each pixel is effectively a tiny square of  the material silicon. A voltage of light to the silicon pushes out charges leaving a charge free region at the surface. If a photon of light strikes this area, it generates an electrical charge. By varying the voltage between adjacent regions, this packet of charge is passed along the row of pixels until eventually it’s read by a circuit that converts the charges into a digital signal, which is used to make the digital image.

Whilst this technology is great for its high sensitivity, it was causing space scientists problems. The sensors used a lot of power and were sensitive to radiation that could cause ‘noise’ in the images. The scientists wanted a way to reduce the required power supply and radiation shielding to make the spacecraft lighter and, therefore, easier to get into space.

So Eric and his team set about developing a new technology called Active Pixel Sensors. Rather than passing the chargers from each pixel along a line, every pixel in an active pixel sensor has a tiny circuit that’s built into the back of it, which converts the light directly into a digital signal. These digital signals could be read out in parallel more quickly than in a CCD, and the overall circuit needs less power to operate.

The sensors could also be manufactured using the same production lines as silicon microprocessors enabling cheap production. Cheap, low power image sensors were initially used in webcams, but it was the advent of the camera phone that really allowed them to take off. The technology was spun out into a company led by engineer and entrepreneur Sabrina Khomeini, one of the team from the Jet Propulsion Laboratory.

It’s been licensed to major image sensor manufacturers in advance to the point where a smartphone in our pockets can now produce broadcast quality video and images. The ability to readily take photos has revolutionised the modern world, perhaps epitomised by the Oxford Dictionary’s 2013 word of the year - ‘selfie’.

So that’s how developing better cameras to put on satellites for space exploration led to the low cost, low power image sensors that are used in many of our modern devices.