Technologists in Sync: Deep Space Atomic Clocks

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How Can Atomic Clocks Help Humans Arrive On Mars On Time?

Autonomous Navigation - Overcoming Technological Limitations

NASA navigators are assisting in the development of a future in which spacecraft may safely and independently travel to destinations such as the Moon and Mars.

Today, navigators guide a spacecraft by calculating its position from Earth and transmitting the data to space in a two-way relay system that may take minutes to hours to give instructions.

This mode of navigation ensures that our spacecraft remain connected to the earth, waiting for instructions from our planet, no matter how far a mission goes across the solar system.

This constraint will obstruct any future crewed voyage to another planet.

How can astronauts travel to destinations distant from Earth if they don't have direct control over their path?

And how will they be able to land properly on another planet if there is a communication delay that slows down their ability to alter their trajectory into the atmosphere?

The Deep Space Atomic Clock, a toaster-sized clock developed by NASA, seeks to provide answers to these concerns.

It's the first GPS-like device that's tiny enough to go on a spaceship and steady enough to operate.

The technological demonstrated allows the spaceship to determine its location without relying on data from Earth.

The clock will be sent into Earth's orbit for a year in late June on a SpaceX Falcon Heavy rocket, where it will be tested to see whether it can assist spacecraft in locating themselves in space.

If the Deep Orbit Atomic Clock's first year in space goes well, it may open the way for one-way navigation in the future, when humans can be led over the Moon's surface by a GPS-like system or safely fly their own missions to Mars and beyond.

Navigators on Earth guide every spaceship traveling to the furthest reaches of the universe.

By allowing onboard autonomous navigation, or self-driving spaceship, the Deep Space Atomic Clock will alter that.

Deep Space Navigation

Atomic clocks in space are not a novel concept.

Every GPS gadget and smartphone uses atomic clocks on satellites circling Earth to calculate its position.

Satellites transmit signals from space, and the receiver triangulates your location by calculating the time it takes for the signals to reach your GPS.

At the moment, spacecraft beyond Earth's orbit do not have a GPS to help them navigate across space.

GPS satellites' atomic clocks aren't precise enough to transmit instructions to spacecraft, where even a fraction of a second may mean missing a planet by kilometers.

Instead, navigators transmit a signal to the spaceship, which bounces it back to Earth, using massive antennas on Earth.

Ground-based clocks keep track of how long it takes the signal to complete this two-way trip.

The length of time informs them how far away and how quickly the spaceship is traveling.

Only then will navigators be able to give the spacecraft instructions, instructing it where to travel.

"It's the same idea as an echo," Seubert said. "If I scream in front of a mountain, the longer it takes for the echo to return to me, the farther away the mountain is."

Two-way navigation implies that a mission must wait for a signal containing instructions to traverse the enormous distances between planets, no matter how far into space it travels.

It's a procedure made famous by Curiosity's arrival on Mars, when the world waited 14 minutes for the rover to transmit the word that it had landed safely with mission headquarters.

A one-way communication between Earth and Mars may take anything from 4 to 20 minutes to get between the planets, depending on where they are in their orbits.

It's a sluggish, arduous method of navigating deep space, one that clogs up NASA's Deep Space Network's massive antennae like a busy phone line.

A spaceship traveling at tens of thousands of kilometers per hour may be at a completely different location by the time it "knows" where it is during this interaction.

Atomic Clocks To Compute Precise Locations In Space

This two-way system may be replaced with an atomic clock small enough to go on a mission but precise enough to provide correct instructions.

A signal would be sent from Earth to a spaceship in the future.

The Deep Space Atomic Clock aboard, like its Earthly counterparts, would measure the time it took for that signal to reach it.

After that, the spacecraft could compute its own location and course, effectively directing itself.

Having a clock aboard would allow onboard radio navigation, which, when coupled with optical navigation, would provide astronauts with a more precise and safe method to navigate themselves.

This one-way navigation technique may be used on Mars and beyond.

By sending a single signal into space, DSN antennas would be able to connect with many missions at the same time.

The new technique has the potential to enhance GPS accuracy on Earth.

Additionally, several spacecraft equipped with Deep Space Atomic Clocks might circle Mars, forming a GPS-like network that would guide robots and people on the surface.

The Deep Space Atomic Clock will be able to assist in navigation not just on Earth, but also on distant planets. Consider what would happen if we had GPS on other planets.

Burt and JPL clock scientists Robert Tjoelker and John Prestage developed a mercury ion clock that, like refrigerator-size atomic clocks on Earth, retains its stability in space.

The Deep Space Atomic Clock was shown to be 50 times more accurate than GPS clocks in lab testing. Every ten million years, there is a one-second mistake.

The clock's ability to stay steady in orbit will be determined by its demonstration in space.

A Deep Space Atomic Clock may launch on a mission as early as the 2030s if it succeeds.

The first step toward self-driving spaceship capable of transporting people to distant planets.

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

It is supported by NASA's Space Technology Mission Directorate's Technology Demonstration Missions program and NASA's Human Exploration and Operations Mission Directorate's Space Communications and Navigations program. The project is overseen by JPL.

~ Jai Krishna Ponnappan

Courtesy - NASA.gov

You may also want to read more about Space Missions and Systems here.

Atomic Clocks

The Critical Need For High Fidelity Atomic Clocks

The Deep Space Atomic Clock, developed by NASA, may be the most stable atomic clock ever sent into space. But what exactly does it imply, and how do clocks relate to space navigation?

The planned launch date for a technological demonstration that may change the way humans explore space is June 24, 2019.

The Deep Space Atomic Clock, developed by NASA's Jet Propulsion Laboratory in Pasadena, California, is a significant improvement over satellite-based atomic clocks that, for example, allow GPS on your phone.

In the end, this new technology may allow spaceships to go to faraway places such as Mars on their own. But, first and foremost, what is an atomic clock?

What makes the Deep Space Atomic Clock unique is how it is utilized in space navigation.

What is the purpose of using clocks to travel in space?

Navigators transmit a signal to a spacecraft to calculate its distance from Earth, which the spacecraft subsequently returns to Earth.

Because the signal travels at a given speed, the time it takes to complete the two-way trip indicates the spacecraft's distance from Earth (the speed of light).

While it may seem difficult, most of us utilize this idea on a daily basis. It's possible that the food shop is a 30-minute walk from your home.

You can calculate the distance to the shop if you know you can walk a mile in 20 minutes.

Navigators can determine a spacecraft's trajectory: where it is and where it is going, by transmitting various signals and collecting several measurements over time.

Quartz crystal oscillators are utilized in almost all contemporary clocks, from wristwatches to satellites.

When voltage is given to quartz crystals, they vibrate at a specific frequency, which is used in these devices.

The crystal's vibrations work like a grandfather clock's pendulum, keeping track of how much time has passed.

Navigators require clocks with precise time resolution - clocks that can measure billionths of a second - to determine the spacecraft's location to within a meter.

Clocks that are very steady are also required by navigators.

"Stability" relates to how consistently a clock counts a unit of time; for example, the length of a second must be constant across days and weeks (to better than a billionth of a second).

What are the connections between atoms and clocks?

Quartz crystal clocks aren't particularly steady by space navigation standards.

Even the best-performing quartz oscillators may be off by a millisecond after just one hour (one billionth of a second).

They may be wrong by a whole millisecond (one thousandth of a second), or 185 miles, after six weeks (300 kilometers).

This would have a significant effect on determining the location of a rapidly moving spacecraft.

To attain better stability, atomic clocks combine a quartz crystal oscillator with an ensemble of atoms.

After four days, NASA's Deep Space Atomic Clock will be off by less than a nanosecond, and after ten years, it will be off by less than a microsecond (one millionth of a second).

This is the equivalent of being one second off every ten million years.

Atoms are made up of a nucleus (protons and neutrons) that is surrounded by electrons.

On the periodic table, each element represents an atom with a specific number of protons in its nucleus.
Although the number of electrons swarming about the nucleus may vary, they must all occupy distinct energy levels, or orbits.
An electron may ascend to a higher orbit around the nucleus after receiving a shock of energy in the form of microwaves.

To accomplish this leap, the electron must receive precisely the correct amount of energy - which means the microwaves must have a very particular frequency.

The energy needed to get electrons to shift orbits varies per element, but it is constant for all atoms of a particular element throughout the universe.

For example, the frequency required to alter the energy levels of electrons in a carbon atom is the same for all carbon atoms in the universe.

Mercury atoms are used in the Deep Space Atomic Clock; a different frequency is required to cause those electrons to shift levels, and that frequency will be constant for all mercury atoms.

"It's really the essential element for atomic clocks because the energy difference between these orbits is such a precise and stable number," said Eric Burt, an atomic clock scientist at JPL.

"It's because of this that atomic clocks can outperform mechanical clocks."

The ability to detect this constant frequency in a specific atom provides science with a universal, uniform time measurement.

The number of waves that travel through a given location in space in a given unit of time is referred to as "frequency."

It is therefore feasible to estimate time by counting waves.

In reality, the frequency required to have electrons jump between two particular energy levels in a cesium atom determines the official measurement of a second.

The frequency of the quartz oscillator is converted into a frequency that is applied to a group of atoms in an atomic clock.

Many electrons in the atoms will shift energy levels if the calculated frequency is accurate.

There will be much fewer electrons jumping if the frequency is wrong.

This will establish whether and how much the quartz oscillator is off-frequency.

The quartz oscillator may then be steered back to the proper frequency using a "correction" defined by the atoms.

The Deep Space Atomic Clock calculates and applies this kind of adjustment to the quartz oscillator every few seconds.

What makes the Deep Space Atomic Clock special?

Onboard the GPS satellites that circle the Earth, atomic clocks are employed, although even these need to be updated twice a day to counteract the clocks' inherent drift.

Those updates are provided by more reliable atomic clocks on the ground, which are enormous (typically the size of a refrigerator) and not built to withstand the physical rigors of space travel.

NASA's Deep Space Atomic Clock is designed to be the most stable atomic clock ever flown in space, up to 50 times more reliable than the atomic clocks on GPS satellites.

Mercury ions are used to produce this stability.

Ions are atoms that are not electrically neutral but have a net electric charge.

Atoms are confined in a vacuum chamber in any atomic clock, and in certain of those clocks, atoms interact with the vacuum chamber walls.

Changes in the environment, such as temperature, will induce comparable changes in the atoms, resulting in frequency inaccuracies.

Because the mercury ions have an electric charge, they may be confined in an electromagnetic "trap" to avoid this interaction, enabling the Deep Space Atomic Clock to reach a new degree of accuracy.

Such accuracy makes autonomous navigation feasible with little communication to and from Earth for missions traveling to distant destinations like Mars or other planets, which is a significant advance over how spacecraft are presently guided.

General Atomics Electromagnetic Systems of Englewood, Colorado supplied the spacecraft for the Deep Space Atomic Clock. It is supported by NASA's Space Technology Mission Directorate's Technology Demonstration Missions program and NASA's Human Exploration and Operations Mission Directorate's Space Communications and Navigations program. The project is overseen by JPL.

~ Jai Krishna Ponnappan

Courtesy - NASA.gov

You may also want to read more about Space Missions and Systems here.

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.