As several posts on this blog have already let on, I am very excited about Breakthrough Starshot. (the collaboration between Steven Hawking and Yuri Milner into funding research into developing really small spacecraft, that by use of solar sails, would be launched towards Alpha Centauri)
One of the questions that has been needling away in the back of my mind has been communication back to Earth. (this question is also a focus for some of the Breakthrough Starshot team's research) The problem is relatively straightforward, under this mission strategy to get probes to another solar system, you need to make really really low mass probes. Less mass means less energy necessary to get to really high speeds. Totally reasonable, the trade off is, the smaller you make the probe, the less space it has for things like, power generation and communication equipment. The less energy you have to communicate, the harder it is to be heard. Imagine trying to look for a lightning bug while looking at a massive spot light (this is not my analogy, I took it from a National Geographic story that I semi-recall on the search for exoplanets (alas I don't remember it enough to provide a source right now)). The lightning bug in this story is our probe, the spot light, Alpha Centauri's stars. Searching for this lightsource aka, the probes data transmission might just be too crazy, even for our future generation's technology.
Let us not rely on the amount of signal a single gram of space probe can generate. There is a beautiful alternative, and it is part of the probe's design, the solar sail. The solar sail for even an incredibly small probe, would need to be huge, according to wikipedia, a solar sail 800 m by 800 m would produce just over 5 Newtons of force (imagine the amount of effort it takes to pick up a can of soda. Now imagine you need enough material that when spread out the sail would cover 128 football fields. That's a lot of area, potentially that is a lot of room for a potentially useful communications tool. One potential means of using all of that area for a good secondary use, would be to create a material, that for some frequencies of light, it is incredibly reflective, preferably to the color of light that the lasers used to push the probe towards Alpha Centauri would use. That part is easy, make a substance that is really reflective of one color, the challenge would be this, in addition to reflecting that one frequency of light, it would need the ability to change the frequency of light coming through one side to another on the other side. Imagine for instance this special material when you shine blue light at it, on the other side yellow light would shine through. Scientists are already doing work along those lines with materials called quantum dots. If future researchers are very clever we could make special quantum dots that change one type of photon into another, but only if that quantum dot has been told to. So now when we shine our blue light at this special material, normally blue light shines through, but when we specially alter that material (think apply a certain voltage, a chemical agent, what have you) now that light is yellow. (I'm using actual colors for "ease" of communication).
2059 The first Breakthrough Starshot probe begins to fly through Alpha Centauri system, the incredibly small command module begins recording the data that scientists have waited over 25 years for, on its journey through this new solar system. As the probe gets closer to Alpha Centuari A, systems unused since leaving the inner solar system over 20 years ago begin to activate. On board controllers initiate a test sequence, confirming that the signalling quantum dots embedded in the solar sail can still convert the star's UV light down to one of A's emissions gaps. After confirming that the system works, the probe begins to rapidly flicker, alternating between allowing light through unchanged, and emitting downshifted light that astronomers can detect trillions of miles away.
2063 Scientists confirm what had been suspected for years, clear indicators of potential microbial life changing the atmosphere of one of the moons of the Centauri system.
The core concept here doesn't necessarily require that the solar sails only manipulate one small band of the electro magnetic spectrum. I honestly don't know what the limits would might be. It could be that the system can alter several energy frequencies, but only be altered one time. (this still leaves the potential for some simple yes/no messages being sent back) for example Yes probe 1125 is working correctly and No it hasn't detected some type of organic molecule we associate with life.
Anyways I hope you enjoyed, feed back and questions are always welcome.
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