Communication | Receiving images with light beamer array

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 18, 2016 21:04 Ryan Whitchurch Posted on: Breakthrough Initiatives

The research paper by Philip Lubin calculates (page 25-28) example data transmission rates and (page 28-30) discusses background interference at the proposed transmission wavelength. It's pretty interesting and provides some answers or at least signposts to some of these questions.

Refer to the "Research" section of this website or go to:

Jun 04, 2016 12:52 Posted on: Centauri Dreams

Since we will not be getting images back from the target system for many years we have more time to build up our deep space network and build larger receiver/transmitters.

Jul 25, 2016 02:34 Breakthrough Initiatives Posted on: Breakthrough Initiatives

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."

The challenges involved in forming and using an array of nanosats.
They will be initially spaced at least 40 Gm apart; with one beamer launching satellites continuously.
Due to the limitation in aiming, the nanosats will be randomly spread over 1-2AU at alphaC (150-300Gm).
Differences in initial final velocity of 10-6=1ppm will result in additional spreading of about 40Gm(#ppm dif velocity) at alphaC.
In order to communicate the nanosats will have to face each other. Assuming 100Gm inter-satellite distance: diffraction limited spot at second satellite =2104 m; received photon flux =21011 photons/sec, pointing required 0.2 arcsec.
Acquiring a random attitude nanosat is difficult, however given enough poer we could keep all nanosats pointed along the Sun-alphaC axis to within a fraction of an arcsec.

LISA mission technology development is an example of spacecraft with 1W lasers at 5 Gm distance (30 cm telescopes).

Prof. Sasha Buchman, Breakthrough Initiatives

Jul 25, 2016 02:36 Breakthrough Initiatives Posted on: Breakthrough Initiatives

Apr 17, 2016 06:22 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."

Ideally the transmission should happen with alphaC at the back while pointing to the Sun. This might not work out as the 2 AU flyby takes only 5,000 sec (2,500 sec/AU). One alternative would be to transmit 3 days later from 100AU past alphaC. This would both reduce the alphaC interference and increase the Sun to alphaC light ratio by 104.

– Prof. Sasha Buchman, Breakthrough Initiatives

Aug 31, 2016 09:57 Posted on: Centauri Dreams

Using the array may not be ideal to receive signals, the system would be great at launching many receivers into orbit awaiting information return.

Dec 06, 2016 18:32 Breakthrough Initiatives Posted on: Breakthrough Initiatives

"Aug 31, 2016 09:57 Posted on: Centauri Dreams

Using the array may not be ideal to receive signals, the system would be great at launching many receivers into orbit awaiting information return."

Thanks for your ideas. At this time it is assumed that a space based system adds costs and complications that outweigh the disadvantages of an atmosphere. If this assumption turns out to be false we must consider a space based approach.

- Avi Loeb, Breakthrough Starshot

Mar 12, 2017 10:30 Posted on: Centauri Dreams

If we have these small sails we can launch many into space to form a large receiver and transmitter without having to accommodate the main laser system to act as both transmitter and receiver which could negativity alter its overall costs.

Mar 21, 2017 19:03 Breakthrough Initiatives Posted on: Breakthrough Initiatives

Mar 12, 2017 10:30 Posted on: Centauri Dreams

Thanks for your input. This is indeed a good idea. The problem is launch cost and operations cost of operating on orbit. Currently we estimate the costs will be dramatically higher to operate in space than on the ground. Also the ground based facility will be idle for much of the day so it will be available to perform dual duty.

- Pete Klupar, Breakthrough Starshot

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