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.

Dec 31, 2019 04:21 Randy Sookoo Posted on: Breakthrough Initiatives

Attached is a VERY high level idea (brainstorm) along the same lines as Prof. Sasha Buchman. I think we should explore all options without putting money as a constraint at this point. Some ideas although expensive at the initial thought could be customized to be made economical. Just my two cents.,

So, since the distance is HUGE (~4 light years), therefore it's a bit impractical to use only ground stations for receiving data. There needs to be a communication nanosat network built in parallel with the nanocraft deployment to Alpha Centauri. Time is not on our side with this project since it will take a generation to get any data back should this concept of light sails work.

So, a nanosat communication network could be deployed in clusters in increments, thereby eliminating single points of failures. The nanocrafts could use the nansat network similar to how airplanes use cell towers/LEO satellites for providing wi-fi to passengers. The nanosat network could potentially use TCP/IP routing protocols to get the data back to the geo-sat network orbiting earth and, then back to ground SATCOM facilities. There would need to be custom tuning of the TCP/IP to limit re-transmissions due to propagation delays. Custom routing protocols may need to be developed.

There are challenges with this design since communications based nano crafts will have to be positioned along the path to Alpha Centauri. My diagram has them at every 5 years but, that's just for illustration. I don't know what is the max distance for laser transmission using optoelectronics is but, that would be the limiting factor as to the distance between the nanosat clusters. Ofcourse, this will all need to be tested in a small scale to determine if it will work.

Again, this is all VERY high level and, wanted to share my thoughts. Any and all comments welcomed!

-Randy Sookoo, Computer Network Engineer

Dec 31, 2019 04:22 Randy Sookoo Posted on: Breakthrough Initiatives

Attached is a VERY high level idea (brainstorm) along the same lines as Prof. Sasha Buchman. I think we should explore all options without putting money as a constraint at this point. Some ideas although expensive at the initial thought could be customized to be made economical. Just my two cents.,

So, since the distance is HUGE (~4 light years), therefore it's a bit impractical to use only ground stations for receiving data. There needs to be a communication nanosat network built in parallel with the nanocraft deployment to Alpha Centauri. Time is not on our side with this project since it will take a generation to get any data back should this concept of light sails work.

So, a nanosat communication network could be deployed in clusters in increments, thereby eliminating single points of failures. The nanocrafts could use the nansat network similar to how airplanes use cell towers/LEO satellites for providing wi-fi to passengers. The nanosat network could potentially use TCP/IP routing protocols to get the data back to the geo-sat network orbiting earth and, then back to ground SATCOM facilities. There would need to be custom tuning of the TCP/IP to limit re-transmissions due to propagation delays. Custom routing protocols may need to be developed.

There are challenges with this design since communications based nano crafts will have to be positioned along the path to Alpha Centauri. My diagram has them at every 5 years but, that's just for illustration. I don't know what is the max distance for laser transmission using optoelectronics is but, that would be the limiting factor as to the distance between the nanosat clusters. Ofcourse, this will all need to be tested in a small scale to determine if it will work.

Again, this is all VERY high level and, wanted to share my thoughts. Any and all comments welcomed!

Just a note, the website isn't allowing me to upload my .jpg drawing.,

-Randy Sookoo, Computer Network Engineer

Apr 08, 2020 12:34 Kamil Kartal Posted on: Breakthrough Initiatives

Language of Mars and Proxima B (and of vessel)

https://www.facebook.com/notes/kamil-kartal/language-of-mars-and-proxima-b-and-of-vessel/2704783146248258/

May 21, 2020 15:27 Breakthrough Initiatives Posted on: Breakthrough Initiatives

All “outside the box” thinking along these lines is strongly encouraged! There may be innovative system concepts that should be further pursued. In considering your idea, however, there are a few issues you need to take into account. Probes have no means of stopping or slowing, so they are always moving away from earth at 10-20% of c. At 20% of c the propagation distance between probes is 1.5 AU per hour inter-launch interval, with a one-way signal propagation delay of 12 minutes. Due to energy limitations, only one probe can be launched at a time, and as a practical matter the inter-launch interval is probably more on the order of a day or week. So not only are inter-probe propagation delays large, but the propagation distances are on the order of the outer planets to earth. If you want a nanosat network in the vicinity of the target star at all times, it will have to be regularly re-launched (at an estimated energy cost for each individual node launch on the order of $5M USD). When a node is near the target star it may be able to derive photovoltaic energy, but only for a few hours at most. Due to the large signal propagation delays, any sort of retransmission protocol is likely to be impractical, especially at the target star to earth distances (where the one-way signal propagation delay is 4 years). Thus it is likely we will have to rely on forward error-correction coding (with a low but non-zero level of residual errors) exclusively. The transmission links among your nodes will accumulate the data from multiple probes, and require correspondingly higher data rate as a result.

Direct-to-ground transmission involves a long signal propagation distance, true, but this can be compensated by using a large collector on earth, something that could never be reproduced on a low-mass probe. Our calculations tend to suggest that direct-to-ground transmission can obtain considerably higher data rates as a result, but of course this comes at the expense of a large and expensive terrestrial collection array (fortunately a one-off). We are putting together a draft paper with this calculation right now.

David G Messerschmitt
Member, Starshot Advisory Committee
Roger Strauch Emeritus Professor, Dept. of EECS, University of California at Berkeley

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