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SpaceX plans to take off its Falcon Heavy rocket – the world's most powerful operational launch system – for the third time on June 24th.
When the rocket reaches 230 meters high from Cape Canaveral, Florida, it will carry 25 small spacecraft in its nose, including a revolutionary clock designed to be the most accurate ever used in space.
NASA has created this multi-million dollar watch, called the Deep Space Atomic Clock (DSAC), which tracks time in the space with unparalleled accuracy without being too heavy or too big nor to consume too much energy.
The DSAC, which is the size of a four-slice toaster, is designed to keep the exact time to one-ten millionth of a second in a year.
However, obsessive timing is not the primary goal of DSAC. The ultimate goal of the project is to help robots and crewed vessels to navigate autonomously into the solar system without instructions from the Earth. It is something space vehicles can not do today, but this capability would open the door to more flexible missions and could make some scientific instruments more powerful.
Todd Ely, navigator and director of the DSAC experiment, believes that this type of clock will also be crucial for future explorers of the human space. Without an on-board atomic clock such as the DSAC, astronauts en route to Mars could wait up to 15 minutes for the Earth's timing signals to reach their spacecraft (because the light takes a very long time to travel the ground to go to distant spaces). At that time, it may be too late.
"If we go to Mars, the crew members will want to know where they are and they will have to know it – potentially in real time – they have to make trajectory adjustments at the last minute," Ely said. said Business Insider.
How does the atomic clock work in deep space
Modern clocks are magnified tuning forks. Many wristwatches, for example, keep time by passing a small electric current through a quartz crystal. The quartz reacts by vibrating at a precise frequency, then this buzz is decomposed into units that cause the advancement of seconds, minutes and hours.
But all clocks have a drift – a measurement of inaccuracy – due to impurities in materials, temperature variations, magnetic disturbances and other factors.
This drift does not represent much for wristwatches, maybe 20 microseconds (or 0.002% of a second) a day. This is not a problem for those of us who are trying to get to a meeting at the hour. In the space, however, "the stability and accuracy of the clock become extremely important," said Ely.
For example, NASA and other agencies monitor the position and speed of a spacecraft by sending a radio signal and indicating the time it took for the machine to return it. Since the light travels at 670 616.629 mph, a 10-minute round trip time would mean that a spacecraft is about 111.8 million miles from the Earth. (A similar principle also allows GPS satellites to tell us where we are on the surface of the Earth.)
But it also means that the daily drift of a 20 microsecond clock can introduce an error of nearly 4 miles – which corresponds to the distance traveled by the light in this ephemeral period of time. And that could mean missing a critical window for a maneuver in space, or even crashing into the surface of a planet instead of landing it gently.
At present, agencies like NASA are using ground-based atomic clocks to tackle this problem.
Instead of using materials like quartz to generate a frequency similar to that of a tuning fork, atomic clocks use vapors or plasmas from a carefully chosen periodic element. In the case of DSAC, this element is mercury.
Atoms are ionized to remove one or more external electrons, which allows them to be trapped and cooled in a small space. A laser is then projected onto the ionized atoms, the remaining electrons absorb some of this light, rise in energy and descend quickly. When the excited electrons release the energy that they have temporarily absorbed, they reemit it as light of a different and highly predictable frequency. It is this signal – the glow of excited electrons – that can be used to keep the time with extreme accuracy.
Ionized atoms may collide with the walls of their container, which may nevertheless cause drift. Atomic clocks therefore use a number of tricks to confine them, including the "cooling" of lasers and electric fields.
The atomic clocks found in GPS satellites use the rubidium element, while the more accurate atomic clocks use cesium, which unrolls about 2,300 times less daily movements compared to a wristwatch. But DSAC mercury ions, Ely said, constitute a "particularly unadorned tuning fork".
Mercury ions do not require as much power or space, said Ely, adding that they should help DSAC to surpass the reliability of any atomic clock currently available on GPS satellites or other spacecraft.
"If we can reproduce what we saw in the field during our tests, once DSAC is in the space, it should be the most stable atomic clock in the space," did he declare. "We actually talked to the Air Force about its potential use in future GPS or other satellites [Department of Defense]type applications ".
How the atomic clock in deep space could change the space flight
Finally, Ely and his collaborators want to reduce DSAC into a smaller, more efficient (but equally stable) atomic clock for future deep space missions.
This could change the game, because at the moment, NASA's spacecraft have to wait for mission control instructions. This is because there is no GPS for distant spaces: all the best atomic clocks are located on Earth, which gives the browsers located there (like Ely) the best information for programming maneuvers. Earth engineers therefore download instructions several hours before a maneuver, which means they run the risk of not taking into account unforeseen conditions or problems during the final moments of a Mars landing.
Having a DSAC-type device on a spacecraft may render unnecessary the fact that the vehicle is waiting for help from the Earth. Instead, a spacecraft could "listen" to an hourly broadcast from an atomic clock on Earth, and then compare it to its local time (similar to GPS). This would allow the spacecraft to estimate its own location and speed at that time.
Such information may allow a spacecraft to calculate and automatically execute a change of course if there is an attractive target for exploration or imminent danger – things the Earth does not know about. would not know for crucial minutes because of the limited speed of light.
"You have a very powerful set of data to calculate your trajectory very accurately, very robustly and in real time for autonomous navigation," said Ely.
For the moment, however, the initial objective is to show that DSAC can maintain its synchronization error below 2 nanoseconds per day. Ely said his team was no more than about 0.3 nanoseconds (0.00000003% second) per day; In other words, it would take more than 9.1 million years for the stopwatch to light up by one second.
"A good measure for us is to try to stay in this area" do not drift beyond a few inches during part of the day "and its stability level is at the nanosecond or better in a day, "said Ely" We have seen this kind of performance on the ground and hope to be able to do the same thing in the space. "
The DSAC could also help future scientific instruments to map the bowels of the ice moons that hide oceans of water, such as Europa or Ganymede, with currently impossible precision. Indeed, the ability to better record subtle changes in speed transforms a spacecraft into a gravity sensor, which can in turn reveal the presence of hidden structures of the planet.
Similarly, accurate timing can help turn cameras into ultra-precise, radar-type navigation sensors because the light they record – and when – can be used as telemetry data. This gives robots and astronauts more tools to reach their destination in space.
Perhaps more important for crewed missions, the DSAC can give spacecraft multiple options for navigation.
"Say you have a broken camera system – well, you're not dying – you can start relying on radio data," said Ely. "You have not lost the ability to navigate."
Of course, this is not yet a reality: DSAC must first work in space, then the concept must be reduced to a version of the size of a palm that consumes maybe 40% less energy .
"What we learned by developing our prototype unit is that we know how to significantly reduce the size of the next version," said Ely.
SpaceX plans to launch DSAC between 23:30 ET on 24 June and 3:30 ET on 25 June. The deployment of 25 satellites, one of which DSAC is hitchhiking, will take several hours. The company plans to stream a webcast of the launch via YouTube live over the web.
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