Humanity has used clocks since we became aware of the concept of time. And as technology has improved, so have our timing methods. Today, many people rely on digital clocks to track times and tell us when to wake up (even though physical alarm clocks are coming back into fashion). But these clocks are too rudimentary for the rigors of space. Or should we say inaccurate?
Every time NASA launches something into space or even orbit, they are equipped with an atomic clock. Even GPS satellites use atomic clocks instead of traditional timekeeping methods because the latter are inherently flawed. No two clock mechanisms are exactly the same; tiny, almost imperceptible imperfections disrupt the precision with which they measure time. Some clocks are simply faster than others due to uncontrollable side effects from how they are made, which is not well suited to space travel. The slightest error in timing may be all that prevents a satellite from maintaining its orbit and returning to Earth as a fiery artificial comet.
Even in an ideal world where all clocks synchronize time with each other, most are still not accurate enough to meet NASA standards. Digital clocks track time because their internal quartz crystals oscillate at a specific frequency: 32,768 times per second. Each time the internal crystal reaches its 32,768th vibration, it counts as one second for the clock. In theory, at least. In reality, quartz clocks slow down over time. After an hour, they deviate by a nanosecond. After six weeks, this difference reaches at least one millisecond. This cumulative error explains why perfect timing is extremely complicated. And why NASA relies on atomic clocks.
What’s wrong with atoms and atomic clocks?
Atoms are the building blocks of reality. The Earth is made up of atoms. You are made of atoms. Hell, nuclear explosions are made of atoms. Well, the atoms of nuclear elements split and release megatons of energy, but same difference. So what makes atoms perfect little timekeepers? They are 100% natural.
Unlike manufactured parts, all atoms of a given element are identical and do not wear out or slow down over time. However, atoms are not the smallest particles in the universe; Each atom consists of a nucleus composed of protons and neutrons, as well as a variable number of electrons that orbit the nucleus. When atoms receive energy of a specific frequency, their electrons change orbits. Scientists can measure this exact frequency to get an accurate measurement of time. Well, almost accurate.
Certainly, the science behind this timing process is far from reliable. Atomic clocks transfer this frequency of energy using quartz crystal oscillators which, as we have already established, are inaccurate at the best of times. Usually the oscillation frequency of quartz is correct, causing most of the electrons to jump their orbits, but sometimes this is not the case, and only a few change orbits. Atomic clocks can calculate the changes needed to get the crystal oscillator back on track. This self-correction makes atomic clocks much more accurate than other artificial clocks.
In space, no one hears you asking for an update
All GPS satellites use atomic clocks for their synchronization, and these satellites remain in contact with Earth. Not only because many people still use handheld GPS devices that rely on these satellites, but also to receive timing updates. It turns out that even though GPS atomic clocks are accurate, they still require corrections from larger, more stable ground-based clocks that cannot survive in space. But NASA is designing special atomic clocks that can operate far from Earth.
The deep space atomic clock (DSAC) is a relatively new form of atomic clock. First launched in 2019, this space chronometer miniaturizes the technology used in the aforementioned terrestrial atomic clocks while also reducing energy demand. The secret ingredient to DSAC and its capabilities is mercury, specifically mercury ions. Normally, atoms are housed in vacuum chambers and any environmental changes can cause frequency errors. While most atomic clocks use neutral atoms, mercury ions carry a charge, meaning they can remain in an “electromagnetic trap” that is not vulnerable to the ravages of space.
Ultimately, DSAC could be 50 times more precise than the atomic clocks on GPS satellites. It is still subject to some natural errors, but the DSAC drift only totals less than a nanosecond every four days. This represents a cumulative error of one second after 10 million years. It’s not perfect, but it’s not like anyone will live long enough to notice. There’s a good chance that when we finally get to Mars, our rockets will use DSAC timing technology.
