The Deep Space Atomic Clock (DSAC) was a miniaturized, ultra-precise mercury-ion

atomic clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...

for precise

radio navigation Radio navigation or radionavigation is the application of radio waves to geolocalization, determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of Radiodetermination-satellite servi ...

in deep space. DSAC was designed to be orders of magnitude more stable than existing navigation clocks, with a drift of no more than 1

nanosecond A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit (e ...

in 10 days. It is expected that a DSAC would incur no more than 1

microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, ...

of error in 10 years of operations. Data from DSAC is expected to improve the precision of deep space navigation, and enable more efficient use of tracking networks. The project was managed by NASA's

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...

and it was deployed as part of the U.S. Air Force's Space Test Program 2 (STP-2) mission aboard a

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rocket on 25 June 2019. The Deep Space Atomic Clock was activated on 23 August 2019. Following a mission extension in June 2020, DSAC was deactivated on 18 September 2021 after two years in operation.

Overview

Current ground-based atomic clocks are fundamental to deep space navigation; however, they are too large to be flown in space. This results in tracking data being collected and processed here on Earth (a two-way link) for most deep space navigation applications. The Deep Space Atomic Clock (DSAC) is a miniaturized and stable mercury ion atomic clock that is as stable as a ground clock. The technology could enable autonomous radio navigation for spacecraft's time-critical events such as orbit insertion or landing, promising new savings on mission operations costs. It is expected to improve the precision of deep space navigation, enable more efficient use of tracking networks, and yield a significant reduction in ground support operations. Its applications in deep space include: * Simultaneously track two spacecraft on a downlink with the

Deep Space Network The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA' ...

(DSN). * Improve tracking data precision by an order of magnitude using the DSN's Ka-band downlink tracking capability. * Mitigate Ka-band's weather sensitivity (as compared to two-way

X-band The X band is the designation for a band of frequency, frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is set at approximately 7.0� ...

) by being able to switch from a weather-impacted receiving antenna to one in a different location with no tracking outages. * Track longer by using a ground antenna's entire spacecraft viewing period. At Jupiter, this yields a 10–15% increase in tracking; at Saturn, it grows to 15–25%, with the percentage increasing the farther a spacecraft travels. * Make new discoveries as a Ka-band — capable radio science instrument with a 10 times improvement in data precision for both

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

and occultation science and deliver more data because of one-way tracking's operational flexibility. * Explore deep space as a key element of a real-time autonomous navigation system that tracks one-way radio signals on the uplink and, coupled with optical navigation, provides for robust absolute and relative navigation. * Fundamental to human explorers requiring real-time navigation data.

Principle and development

Over 20 years, engineers at NASA's

have been steadily improving and miniaturizing the mercury-ion trap atomic clock. The DSAC technology uses the property of mercury ions' hyperfine transition frequency at 40.50

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

to effectively "steer" the frequency output of a

quartz oscillator A crystal oscillator is an electronic oscillator circuit that uses a piezoelectric crystal as a frequency-selective element. The oscillator frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable clock ...

to a near-constant value. DSAC does this by confining the mercury ions with electric fields in a trap and protecting them by applying magnetic fields and shielding. Its development includes a test flight in

low Earth orbit A low Earth orbit (LEO) is an geocentric orbit, orbit around Earth with a orbital period, period of 128 minutes or less (making at least 11.25 orbits per day) and an orbital eccentricity, eccentricity less than 0.25. Most of the artificial object ...

, while using GPS signals to demonstrate precision orbit determination and confirm its performance in

. The Deep Space Atomic Clock-2, an improved version of the DSAC, will fly on the

VERITAS In Roman mythology, Veritas (), meaning Truth, is the Goddess of Truth, a daughter of Saturn (mythology), Saturn (called Cronus by the Greeks, the Titan (mythology), Titan of Time, perhaps first by Plutarch) and the mother of Virtus (deity), Vi ...

mission to Venus in 2028.

Deployment

The flight unit is being hosted — along with four other payloads — on the Orbital Test Bed satellite, provided by General Atomics Electromagnetic Systems, using the Swift satellite bus.OTB: The Mission
. Surrey Satellite Technology. Accessed on 10 December 2018. It was deployed as a secondary spacecraft during the U.S. Air Force's Space Test Program 2 (STP-2) mission aboard a

rocket on 25 June 2019.

References

External links

DSAC: Description and Nominal Mission Operations
{{DEFAULTSORT:Deep Space Atomic Clock Atomic clocks Electronic test equipment Astronautics Gravimetry Spacecraft launched in 2019 SpaceX commercial payloads