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The first one is going to OTB, which is the Orbital Test Bed (quite cool!) rather than off-track betting.

Question: Once the technology matures, where would one deploy deep space atomic clocks? What is the long-term plan for deploying this technology?

fyi The von Kármán Lecture Series: 2016 Deep Space Atomic Clock is linked in How far from earth have atomic clocks (or ultra-stable oscillators) been placed and monitored?

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  • $\begingroup$ This question is different from Where will Deep Space Atomic Clock orbit “after” Earth? which I've just found in Astronomy SE $\endgroup$ – uhoh Jun 6 at 0:18
  • $\begingroup$ A deep space atomic clock should be far away from Earth, much farther than navigation satellites in MEO or GEO. But would a single DSAC be useful or should there at least three or four for deep space position measurement? $\endgroup$ – Uwe Jun 6 at 14:32
  • $\begingroup$ @Uwe that's why I said "clocks" (plural) $\endgroup$ – uhoh Jun 6 at 15:29
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Where would one deploy deep space atomic clocks?

In practically any vehicle that goes beyond Earth orbit.


The press releases imply that these Deep Space Atomic Clocks will form the basis of a solar-system wide equivalent of GPS. While that might be the eventual outcome, that is not the immediate advantage. The immediate advantage is that this technology will effectively increase the capacity of NASA's Deep Space Network by a significant amount.

Currently the DSN determines the range and range rate to a spacecraft using two DSN antennae. One broadcasts a signal to the spacecraft, the other receives a signal from the spacecraft. In between, the spacecraft receives the signal sent by the outgoing DSN antenna and sends it right back to the receiving DSN antenna. This two-way ranging provides the extremely precise range and range rate measurements that are needed to estimate where the spacecraft is/was. The spacecraft's state can be determined only after collecting a number of such measurements. The downside: This takes two DSN antennae.

There is a one-way ranging alternative that only requires one DSN antenna. If the time tag on a signal from a spacecraft can be trusted, the difference between the time tag on when a message from the spacecraft was sent and the time tag on when the message was received on Earth yields the range to the satellite. That however requires an extremely stable spacecraft clock, much more stable than the best crystal oscillators can provide. The Deep Space Atomic Clocks should be more than accurate / stable enough to enable this one-way ranging.

In the future, spacecraft that communicate with one another might be able to bypass the need for communicating with the Earth. But that's science fiction future, at least for now. The realistic future is that this technology will make the DSN much more efficient.

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  • $\begingroup$ Excellent answer, thanks! In addition to the roughly factor of two savings in scheduled time slots, it probably also removes some scheduling complexity; a single receive session might be easier to schedule than a correlated transmit/receive pair of sessions that meet the constraints of the particular delay and position on the celestial sphere. $\endgroup$ – uhoh Jun 7 at 0:55
  • $\begingroup$ But what about the receiption of these Deep Space Atomic Clocks signals, should it be done by the DSN antennas on Earth only, or also by other deep spacecrafts to determine their position? $\endgroup$ – Uwe Jun 7 at 14:15
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    $\begingroup$ @Uwe - To what end? Most interplanetary spacecraft do not navigate their position/velocity state with respect to the solar system. And why? GPS satellites broadcast time, position, and velocity. This proposed technology does not do that. It sends time only. And how? GPS relies on the satellite and receiver being somewhat close to one another, a few tens of thousands of kilometers. A solar system-wide GPS-like system would require tens of thousands of satellites. $\endgroup$ – David Hammen Jun 8 at 21:03

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