NASA’s Cold Atom Lab (CAL) is the first facility inside the International Space Station to produce clouds of “ultracold” atoms that can reach −459ºF, a fraction of a degree above absolute zero. Nothing in nature is known to hit the temperatures achieved in laboratories like CAL, which means the orbiting facility is regularly the coldest known spot in the universe.
CAL was transported to the space station in May 2018 and is now capable of producing ultracold atoms on a daily basis. Five scientific teams are scheduled to carry out experiments using CAL throughout 2019, with three experiments already under way.
But why are scientists cooling atoms to such an extreme low?
Specifics vary, but ultracold atoms can be more than 200,000 times slower than room temperature atoms, opening up new ways to study atoms and to use them for investigating other physical phenomena. Such conditions support CAL’s primary science objective: seeking to conduct fundamental physics research while trying to understand the workings of nature at the most fundamental levels.
“With CAL we’re starting to get a really thorough understanding of how the atoms behave in microgravity, how to manipulate them, how the system is different than the ones we use on Earth,” says Rob Thompson, a cold atom physicist at NASA’s Jet Propulsion Laboratory and CAL’s mission scientist. “This is all knowledge that is going to build a foundation for what I hope is a long future of cold atom science in space.”
Laboratories on Earth can produce ultracold atoms, but on the ground, gravity pulls on the chilled atom clouds and they fall quickly, giving scientists only fractions of a second for observation. Magnetic fields can also be used to “trap” the atoms and hold them still, but that restricts natural movement. In microgravity, however, the cold atom clouds float for much longer, giving scientists an extended view of associated behavior.
According to NASA, the process to create cold atom clouds begins with lasers that lower the temperature by slowing atoms down. Radio waves then cut away the warmest members of the group, further lowering the average temperature before the atoms are released from a magnetic trap and allowed to expand.
This process results in a drop in pressure that, in turn, naturally causes another drop in the cloud’s temperature (the same phenomenon that causes a can of compressed air to feel cold after use). In space, the cloud has longer to expand and thus reaches even lower temperatures than what can be achieved on Earth, essentially down to about one ten billionth of a degree above absolute zero, perhaps even lower.
Ultracold atom facilities on Earth typically occupy an entire room and the hardware is often left exposed so that scientists can adjust the apparatus if necessary. Building a cold atom laboratory for space posed several design challenges. First, there was the matter of size as CAL flew to the station in two pieces, both a metal box a little larger than a minifridge and a second one about the size of a carry-on suitcase. Second, CAL was designed to be operated remotely from Earth, so it was built as a fully enclosed facility.
CAL also features a number of technologies that have never been flown in space before and thus have to be sealed so tightly that almost no stray atoms can leak in. The lab needed to be able to withstand the shaking of launch and extreme forces experienced during the flight to the space station. It took the teams several years to develop unique hardware that could meet the precise needs for cooling atoms in space.
“Several parts of the system required redesigning, and some parts broke in ways we’d never seen before,” says Robert Shotwell, CAL project manager and chief engineer for JPL’s astronomy, physics and space technology directorate. “The facility had to be completely torn apart and reassembled three times.”