Deep Space Atomic Clocks - Spacecraft Autonomy

The technological demonstration marks a major milestone in the development of robotic explorer navigation and the functioning of GPS satellites.

To figure out where they are and where they're heading, spacecraft that go beyond our Moon communicate with base stations on Earth. 

NASA's Deep Space Atomic Clock is trying to give far-flung astronauts greater navigational autonomy. 

The expedition announces success in its effort to enhance the capacity of space-based atomic clocks to measure time reliably over extended periods of time in a new article published today in the journal Nature.

  • This characteristic, known as stability, has an effect on the functioning of GPS satellites that help people navigate on Earth, thus this research may help next-generation GPS spacecraft become more autonomous.
  • Engineers transmit signals from the spacecraft to Earth and back to determine the course of a faraway spacecraft. 
  • On the ground, they employ refrigerator-sized atomic clocks to record the timing of those signals, which is crucial for accurately calculating the spacecraft's location. 
  • However, for robots on Mars or at farther locations, waiting for the signals to complete the journey may take tens of minutes or even hours.
  • Those spacecraft could compute their own location and orientation if they carried atomic clocks, but the clocks would have to be very reliable. 

To assist us get to our destinations on Earth, GPS satellites contain atomic clocks, which must be updated many times a day to maintain the required degree of stability. 

  • More reliable space-based clocks would be required for far space missions.
  • The Deep Space Atomic Clock has been running onboard General Atomic's Orbital Test Bed spacecraft since June 2019, and is managed by NASA's Jet Propulsion Laboratory in Southern California. 
  • According to the latest research, the mission team established a new record for long-term atomic clock stability in space, surpassing the stability of existing space-based atomic clocks, including those on GPS satellites, by more than ten times.

Each Nanosecond Is Mission Critical

All atomic clocks have some level of instability, resulting in a difference between the clock's time and the real time. 

  • If not rectified, the offset, although little at first, quickly grows, and in spacecraft navigation, even a minor offset may have significant consequences.

One of the primary objectives of the Deep Space Atomic Clock mission was to track the clock's stability over time. 

  • After more than 20 days of operation, the team reports a level of stability that results in a time variation of fewer than four nanoseconds, according to the new study.
  • According to Eric Burt, an atomic clock physicist for the project at JPL and co-author of the new study, “an error of one nanosecond in time equates to a distance uncertainty of approximately one foot.” 
  • “To maintain this degree of stability, certain GPS clocks must be refreshed multiple times a day, which implies GPS is heavily reliant on ground connection. 
  • The Deep Space Atomic Clock can extend this out to a week or more, providing an application like GPS a lot more autonomy.”

The new paper's stability and subsequent time delay are approximately five times better than the team's last report from the spring of 2020. 

  • This is an improvement in the team's measurement of the clock's stability, not in the clock itself. 
  • Longer operational durations and almost a year's worth of extra data allowed them to increase their measurement accuracy.

The Deep Space Atomic Clock mission will end in August, but NASA announced that work on the technology will continue: 

  • The Deep Space Atomic Clock-2, a better version of the cutting-edge timekeeper, will fly to Venus on the VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) mission. 
  • The new space clock, like its predecessor, is a technology demonstration, which means its aim is to improve in-space capabilities by creating sensors, hardware, software, and other technologies that don't exist now. 
  • The ultra-precise clock signal produced by this technology, developed by JPL and supported by NASA's Space Technology Mission Directorate (STMD), may aid autonomous spacecraft navigation and improve radio scientific observations on future missions.

“NASA's choice of Deep Space Atomic Clock-2 for VERITAS testifies to this technology's promise,” said Todd Ely, principle investigator and project manager for the Deep Space Atomic Clock at JPL. 

“On VERITAS, we want to put this next-generation space clock to the test and show how it may be used for deep space navigation and science.”

General Atomics Electromagnetic Systems of Englewood, Colorado supplied the spacecraft for the Deep Space Atomic Clock. 

It is supported by NASA's Human Exploration and Operations Mission Directorate's Space Communications and Navigation (SCaN) program and STMD's Technology Demonstration Missions program at NASA's Marshall Space Flight Center in Huntsville, Alabama. 

The project is overseen by JPL.

~ Jai Krishna Ponnappan

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