The New Horizons probe is only capable of transmitting data back at two kilobits per second

Data transfer from Pluto probe to take over a year

Slow downlink times mean the data captured by the Pluto probe New Horizons will take roughly a year and a half to make it back to Earth.

The spacecraft, which has now passed the dwarf planet, is able to stream data back to mission controllers at an average of only two kilobits per second, compared to the 48Mbit/s achieved by a 4G wireless network. Spacecraft communications are typically measured in bits rather than bytes, which are equivalent to eight bits.

This isn’t due to an oversight by Nasa’s engineers, however, but simply due to the fact that radio signals sent over such vast distances – Pluto is currently just under three billion miles from Earth – not only take a long time to travel but are also very weak, resulting in slow downlink times.

The transfer rate would be even slower if it weren’t for the fact that the data has been compressed and is being picked up by Nasa's Deep Space Network (DSN), which has facilities in three strategic sites around the world.

These sites are spread across the globe to allow signals from space to be monitored around the clock – with one site at Goldstone, in California's Mojave desert, another in Canberra, Australia, and the third in Madrid, Spain.

The network features some of the American space agency's largest antennas, with each DSN site boasting a huge 70-metre wide dish antenna capable of tracking a spacecraft billions of miles from Earth. The spacecraft's dish by comparison is only 2.1m in diameter.

But the long wait should be well worth it, as the data will give scientists the first close-up images of the surface of Pluto captured by New Horizons' telescopic camera, the Long Range Reconnaissance Imager (Lorri).

One Lorri photo, even compressed, amounts to 2.5 megabits of data so at 2kbit/s it will take nearly 21 minutes to return a single Lorri image to Earth.

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