by Charlie Danaher, Danaher Cryogenics
Bridging Interplanetary Distances
Having a conversation between someone on Earth and Mars is not as science fiction as it used to be. That is thanks to scientists at NASA’s Jet Propulsion Laboratory (JPL) in Southern California and their successful demonstration of the Deep Space Optical Communications (DSOC) project. Danaher Cryogenics is honored that one of our cryostats could play a modest role in this historic achievement.
Scientists have long been struggling to develop a system that could transmit high data rates to and from a spacecraft at distances beyond the lunar orbit. It has also long been known that a laser-based system could theoretically exceed transmission rates possible with radio telecommunications and enable data rates needed for things like high-resolution images, large science datasets, and high-definition video streaming, which is of particular importance for human missions to Mars.
Optical communication has been used between Earth and the moon, about 250,000 miles away. However, if we want to be able to adequately communicate with astronauts on Mars, we would have to increase that distance by three orders of magnitude further.
From Theory to Flight
In order to test this technology, NASA decided to fly an optical communication terminal on board the Psyche spacecraft to emulate links from Earth-Mars distances on its way to the asteroid belt. The Psyche spacecraft was launched from the Kennedy Space Center on October 11, 2023. Soon thereafter, on December 11, 2023, the mission met a major milestone by streaming an ultrahigh-definition video more than 19 million miles away (approximately 80 times the distance between Earth and Mars) at a rate of 267 megabits per second.
About a year later, on December 3, 2024, the project set another optical communications record by downlinking Psyche data from 307 million miles away.
seen the 1 K detector array, attached to the Chase GL4’s
cold stage. Credit: NASA
How It All Works
The 3-kilowatt laser beam starts at JPL’s Table Mountain Facility near Wrightwood, California, and travels as far as over 300 million miles – farther than the average distance between Earth and Mars – to the DSOC receiver that is mounted on the Psyche spacecraft. This laser beam helps Psyche properly aim its own communication laser back toward Earth. After being properly aligned, Psyche then sends a return signal back down to Earth, arriving at Caltech’s Palomar Observatory in San Diego County.
This returning laser beam conveys information by sending a sequence of bursts of photons. You can kinda think of it like Morse code. Due to the vast distance traveled, by the time the return laser beam reaches Earth it has scattered over an area about the width of the U.S. and is consequently very faint. This is where Palomar’s 200-inch Hale Telescope comes in handy. Those few photons are captured, gathered, and directed to a cryogenically cooled, high-efficiency detector array. That detector array has an active area of about 0.3 mm across, or roughly 300 million times smaller than the area of the capturing telescope.
Deep inside the Hale Telescope dome resides a Model 106 cryostat. And deep inside that cryostat – inside multiple layers of radiation shielding – resides a Chase Research Cryogenics GL4 Sorption Cooler. This subsystem maintains the detector array at 1 K, well below its critical temperature of 3 K.
This extremely cold cryogenic environ-ment is important for a couple of reasons. Primarily, so that the photon detector is superconducting. Secondarily, it is important to shield the detector from any ambient photons like those emitted by surfaces inside the cryostat. It is at this detector array that those photons, after traveling for millions of miles, are converted to electrical signals. The information contained in these photons can be used for navigation, health updates of astronauts, and, of course, the science.
Between November 2023 and September 2025, the DSOC mission successfully downlinked 13.5 terabits from deep space, with speeds as high as 267 megabits per second, which is comparable to household broadband. As NASA states, “A new era of space communication has begun. And it all starts with a beam of light.”
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