NASA's Deep Space Atomic Clock is flying on the Orbital Test Bed satellite, which launched
on the SpaceX Falcon Heavy rocket with around two dozen other satellites.
The Deep Space Atomic Clock will change the way we navigate spacecraft and even how we
send astronauts to Mars and beyond. The Deep Space Atomic Clock will help spacecraft navigate
autonomously through deep space. No larger than a toaster oven, the instrument will be
tested in Earth orbit for one year, with the goal of being ready for future missions to
other worlds.
The Deep Space Atomic Clock is a serious upgrade to the satellite-based atomic clocks that,
for example, enable the GPS on your phone.
Ultimately, this new technology could make spacecraft navigation to distant locations
like Mars more autonomous. But what is an atomic clock? How are they used in space navigation,
and what makes the Deep Space Atomic Clock different?
Watch this video for the answers.
First let us see about Why do we use clocks to navigate in space.
To determine a spacecraft's distance from Earth, navigators send a signal to the spacecraft,
which then returns it to Earth. The time the signal requires to make that two-way journey
reveals the spacecraft's distance from Earth, because the signal travels at a known speed
i-e the speed of light.
While it may sound complicated, most of us use this concept every day. The grocery store
might be a 30-minute walk from your house. If you know you can walk about a mile in 20
minutes, then you can calculate the distance to the store.
By sending multiple signals and taking many measurements over time, navigators can calculate
a spacecraft's trajectory: where it is and where it's headed.
Most modern clocks, from wristwatches to those used on satellites, keep time using a quartz
crystal oscillator. These devices take advantage of the fact that quartz crystals vibrate at
a precise frequency when voltage is applied to them. The vibrations of the crystal act
like the pendulum of a old, grandfather clock, ticking off how much time has passed.
To know the spacecraft's position within a meter, navigators need clocks with precision
time resolution - clocks that can measure billionths of a second.
By space navigation standards, quartz crystal clocks aren't very stable. After only an hour,
even the best-performing quartz oscillators can be off by a nanosecond (one billionth
of a second). After six weeks, they may be off by a full millisecond (one thousandth
of a second), or a distance error of 300 kilometers. That would have a huge impact on measuring
the position of a fast-moving spacecraft.
Atomic clocks combine a quartz crystal oscillator with an ensemble of atoms to achieve greater
stability. NASA's Deep Space Atomic Clock will be off by less than a nanosecond after
four days and less than a microsecond (one millionth of a second) after 10 years. This
is equivalent to being off by only one second every 10 million years.
Atomic clocks are used onboard GPS satellites that orbit the Earth, but even they must be
sent updates two times per day to correct the clocks' natural drift. Those updates come
from more stable atomic clocks on the ground that are large (often the size of a refrigerator)
and not designed to survive the physical demands of going to space.
Up to 50 times more stable than the atomic clocks on GPS satellites, NASA's Deep Space
Atomic Clock is intended to be the most stable atomic clock ever flown in space. It achieves
this stability by using mercury ions.
For missions going to distant destinations like Mars or other planets, such precision
makes autonomous navigation possible with minimal communication to and from Earth - a
huge improvement in how spacecraft are currently navigated.