Space

Deep-space lasers smash data speed records over interplanetary distances

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An artist's impression of Psyche, orbiting near the asteroid of the same name
NASA
An artist's impression of Psyche, orbiting near the asteroid of the same name
NASA
A diagram illustrating the distance record achieved in the new laser communication test, between Earth and the spacecraft Psyche
NASA/JPL-Caltech

NASA’s Psyche spacecraft, farther away than the Sun, has sent data through a laser over a record-breaking distance, and done so even faster than expected.

Radio frequencies remain the most reliable medium for deep space communication, connecting Earth with Mars rovers, planetary orbiters, and all the way out to interstellar space with the Voyager probes. But it can be slow to beam huge amounts of data across the solar system – for example, it took New Horizons 15 months to send the 50 GB of data from its close encounter with Pluto back to Earth.

Using light could drastically speed up that process, at least in some cases. Data can be encoded more densely into light waves than radio waves, allowing larger packets to be sent in a shorter time. So far, high speed tests have beamed data in lasers between satellites and the ground, and even from lunar orbit to Earth, but things get trickier over longer distances.

Now, NASA has broken the distance record for data transmission via lasers. On April 8, the Psyche spacecraft, currently en route to the asteroid belt, beamed data back to Earth from over 140 million miles (225 million km) away. That’s about one and a half times the distance to the Sun, and 14 times farther than the first test of the equipment back in November.

A diagram illustrating the distance record achieved in the new laser communication test, between Earth and the spacecraft Psyche
NASA/JPL-Caltech

The goal was to prove that the spacecraft could transmit at up to 1 Megabit per second (Mbps), but that was far surpassed, with the test clocking speeds of up to 25 Mbps. The Deep Space Optical Communications (DSOC) instrument onboard Psyche sent a copy of engineering data to Palomar Observatory in California, while simultaneously sending the same data to NASA’s Deep Space Network via radio.

For context, Netflix recommends 25 Mbps to stream the service in 4K.

“We downlinked about 10 minutes of duplicated spacecraft data during a pass on April 8,” said Meera Srinivasan, operations lead on the project. “Until then, we’d been sending test and diagnostic data in our downlinks from Psyche. This represents a significant milestone for the project by showing how optical communications can interface with a spacecraft’s radio frequency comms system.”

Other recent experiments include sending data from ground stations to Psyche and back – a round trip of 280 million miles (450 million km) – in a single night, and using multiple receivers in different regions to pick up the signal at the same time, which could be important if weather conditions in one area interrupt the connection.

The team says this tech demo is a key step towards faster communication of high resolution images and data that will be needed when humans eventually set foot on Mars.

Source: NASA

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4 comments
veryken
Need explanation of how it relates to sunlight that takes about 8 minutes to travel from the Sun to the Earth. This much was taught in high school and should be common knowledge. How does 25 Mbps relate to that for laser communications, which is essentially light speed. Then "single night" for a round trip to a distance that's about 1.5x the Sun's distance. What? How? Why?
TheDaleks
@ veryken Light is a much higher frequency than radio waves, and it is frequency that limits the data transmission speed. To transmit data, the shape of the electromagnetic wave can be modified to represent the data, and this can then be undone when the signal is received. The frequency of light waves is around 400-750 trillion Hertz (Hz), meaning we can do this around 400-750 trillion times per second. With typical radio we might be able to do this "only" 100 million times per second. We would receive the signals at the same time, but light can carry more information per second than radio.
Gregg Eshelman
What's needed is a Deep Space LASER Network or DSLN. Put a probe around every planet, every moon, every large asteroid. Put some into different inclinations of Solar orbit. Every probe should have several LASER receivers and transmitters. Put multi-spectrum cameras on all of them, including full/natural color. Put various other instruments on them too.

Then all their observations can be sent back to Earth at top speed via LASER "bucket brigade" along more than one path to ensure it all arrives. The data could be split up and sent in several parallel streams to arrive even faster by increasing the bandwidth.

Another possibility having all those instruments all over the Solar System is synthetic aperture instruments for observing distant things with a "lens" that's effectively the diameter of the Solar System. Coordinating where they all aim would be the tricky bit.
Maverick
@veryken - with the current equipment, the current data transmission rate is 25 Mbps, and over time, we expect transmission rates to improve into 100 Mbps - 1 Gbps ranges.

The transmission *time* will still be limited by the maximum speed of the laser and presuming no interference or relay delays, the transmission time is the speed of light, i.e. 186,000 miles / sec. At their closest approach, Earth and Mars are about 34 million miles apart, which means a minimum data transmission time of 182 seconds, regardless of transmission size. Clearly not fast enough to have an audio or video Facetime call, but definitely fast enough for timely transmission of mission data and other important updates from any future colony back to Earth.

Maybe some future technology will allow us to use quantum entanglement for near-realtime communication.