Recent advances by groups at MIL Lincoln Labs and the Jet Propulsion Laboratory have demonstrated that it is possible to detect single photons emitted by lasers from very large distances. The current record holder is the LADEE Laser Communication system, which was able to operate from lunar distances. The technique uses cryo-cooled nanotubes. The current performance is of order 2 bits per photon. That system uses a 10cm optics on the spacecraft, and a 1-meter telescope on the ground. As the StarChip cruised out, it would rely on communications from earth to update its clock and its estimation of the stars’ ephemeris (orbital position at specific times).
The ground system and the StarChip transmitter will implement forward error correction, matched filtering, and other contemporary approaches to increasing the gain of this transmission through signal processing, beyond the direct detection of single photons that has already been demonstrated in existing systems. The Starshot light beamer would be used in reverse, as a receiving array to receive the laser communications from the nanocraft. Using it as a phased array telescope would offer a sufficient collecting area to receive the signal.
Apr 12, 2016 23:16
Derek Motloch
Posted on: Breakthrough Initiatives
How do we submit ideas that may help the project? I have ideas on how we could speed up communication, increase redundancy if there is a failure, etc.
Apr 12, 2016 23:19
Derek Motloch
Posted on: Breakthrough Initiatives
The basic idea would be to have the crafts form a mesh network with all the crafts near by and communicate together as well as in coordination back to Earth. This would increase bit rate and offer other advantages.
Apr 13, 2016 00:45
Carl Monson
Posted on: Breakthrough Initiatives
I invision a chain of communication relay probes launched in succession after the initial volley of detector probes. These single purpose probes would have to be launched frequently enough over the 20 year mission to have overlapping of their range for redundancy.
Using a relay chain would reduce the power requirement per probe (reducing weight), reduce the needed focus and aiming precision, and reduce signal dispersion that would be otherwise unavoidable over 4 light years.
Quantity could be the solution if advances in single stage laser communication prove insufficient for the distance and signal to noise, or prove too bulky to fit within the probe parameters.
Apr 13, 2016 04:29
Duk Tape
Posted on: Breakthrough Initiatives
This should not be attempted until quantum entanglement communication equipment and methods are developed.Then when the probe arrives the quantum radio sends the information instantaneously to a lab here. I'd rather see your resources and intellect pushing that technology closer. Its far more useful for our deep space needs and human space travel now than miniaturizing probes circa old tech.
Apr 13, 2016 06:23
Ryan Whitchurch
Posted on: Breakthrough Initiatives
Quantum entanglement sounds like an interesting and elegant solution. From what I've read, there are a number of serious issues to solve, such as decoherence. And, doesn't there still need to be a signal sent from the point of origin (Earth) to the distant sensor timed to coincide with the moment of desired measurement of the sensor state? Or am I misunderstanding the concept?
http://phys.org/news/2014-07-scientists-quantum-entanglement-amplified.html
Apr 13, 2016 13:29
Karen Pease
Posted on: Breakthrough Initiatives
@Duk Tape, etc:
That is not how quantum entanglement works. It's a common popular misconception (repeated frequently in sci-fi) that quantum entanglement allows for the instantaneous transmission of information at faster than the speed of light. It's quite true that the state collapse is instantaneous, but it *does not transfer information*. You can't choose what value it collapses to, and nor can you tell if the other side collapsed it or whether you're the one who collapsed it. The speed of light as a limitation to the rate of transfer of information is still very much a hard limit in our existing physics models. Quantum physics does not provide a workaround to it.
Apr 14, 2016 04:49
Test Test
Posted on: Breakthrough Initiatives
Hello,
It's worth noting that, while diffraction limited optics are required for beaming, the same is not true for receiving. Simple 'light buckets' equipped with photomultipliers are sufficient, if the source is a rapid pulse. Arrays of 12-28 meter class telescopes of this design already exist, and many more are planned for the near future.
Take a look at http://adsabs.harvard.edu/abs/2016ApJ...818L..33A , and refs therein.
Apr 17, 2016 06:22
john.hayden1@gmail.com
Posted on: Breakthrough Initiatives
To what degree is the signal reception problem made worse by the fact the spacecraft will be transmitting (faintly) from so close in angular separation to a very bright star? How will 1-2 photons be detectable - what kind of SNR is required? ....
Put another way: the star's output at the laser frequency needs to be extremely constant for the message output to be detectable. Communication techniques can aid extracting the signal from higher magnitude noise, but some study should be made to identify the limiting characteristics of the communication channel.
Also: would space-based receivers (deployed 25yrs after launch) provide advantages? Very large antenna areas might be achievable 45yrs from now, using lightsail-like fabrics.
