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 betwe ...

for precise

radio navigation Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination. The basic principles a ...

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 10 seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...

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 equal to 1000 ...

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 and NASA field center in the City of La Cañada Flintridge, California, La Cañada Flintridge, California ...

and it was deployed as part of the

U.S. Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sign ...

Space Test Program 2 Falcon Heavy is a partially reusable heavy-lift launch vehicle that is produced by SpaceX, an American aerospace manufacturer. The rocket consists of two strap-on boosters made from Falcon 9 first stages, a center core also made from a Falcon ...

(STP-2) mission aboard a

SpaceX Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal o ...

Falcon Heavy Falcon Heavy is a partially reusable heavy-lift launch vehicle that is produced by SpaceX, an American aerospace manufacturer. The rocket consists of two strap-on boosters made from Falcon 9 first stages, a center core also made from a Falc ...

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 network of American spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA's interplanetary ...

(DSN). * Improve tracking data precision by an order of magnitude using the DSN's

Ka-band The Ka band (pronounced as either "kay-ay band" or "ka band") is a portion of the microwave part of the electromagnetic spectrum defined as frequencies in the range 26.5–40 gigahertz (GHz), i.e. wavelengths from slightly over one centime ...

downlink tracking capability. * Mitigate

's weather sensitivity (as compared to two-way

X-band The X band is the designation for a band of 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 rather indefinitely set at approxi ...

) 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 () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

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 In atomic physics, hyperfine structure is defined by small shifts in otherwise degenerate energy levels and the resulting splittings in those energy levels of atoms, molecules, and ions, due to electromagnetic multipole interaction between the ...

frequency at 40.50

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

to effectively "steer" the frequency output of a quartz oscillator 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 orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never m ...

, while using

GPS signal GPS signals are broadcast by Global Positioning System satellites to enable satellite navigation. Receivers on or near the Earth's surface can determine location, time, and velocity using this information. The GPS satellite constellation is ope ...

s 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 Veritas is the name given to the Roman virtue of truthfulness, which was considered one of the main virtues any good Roman should possess. The Greek goddess of truth is Aletheia (Ancient Greek: ). The German philosopher Martin Heidegger argues ...

mission to Venus in 2028.

Deployment

The flight unit is being hosted — along with other four 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

(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