71–80 of 274 posts
Moreover, to keep the beam tightly focused on one probe at a time would require an adaptive optics system that compensated for atmospheric turbulence — something astronomers know how to do over a span of 10 meters, the size of a big telescope mirror now, but not over a mile. Would it be easier just to put the lasers on the moon?
Or just in orbit. Way easier, no need to overcome moon's gravity.
So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes? And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (I…
Earlier quoted context omitted.
I love these napkin calculations. The relativistic effect shifts the frequency by 22.47% for 0.2c. Given a 445nm laser (the powerful blue ones), that's 545nm when redshifted (green). It's a bit of a jump, but that wavelength is still smack in the "solar atmospheric absorbtion spectrum window" -- you won't lose much of the energy in the atmosphere. Reading this page diagonally [ http://www.edmundoptics.com/resources/a…
Umm... 0.5% of 100GW is 500MW, or about the power of a nuclear reactor. The spaceship won't survive a millisecond. We need way better than 99.5%.
I am a self-proclaimed 'newbie' when it comes to understanding energy, astronomy, and physics in general, but I have a few questions and any answers or opinions would be appreciated: 1.) Why in the world does the 'Light / Laser Beamer' need to be physically located on earth? Why not in space? 2.) Is building 'check-points' for both data and power atop the planets not a possibility? (Solar, chemical, etc).
Earlier quoted context omitted.
I love these napkin calculations. The relativistic effect shifts the frequency by 22.47% for 0.2c. Given a 445nm laser (the powerful blue ones), that's 545nm when redshifted (green). It's a bit of a jump, but that wavelength is still smack in the "solar atmospheric absorbtion spectrum window" -- you won't lose much of the energy in the atmosphere. Reading this page diagonally [ http://www.edmundoptics.com/resources/a…
Umm... 0.5% of 100GW is 500MW, or about the power of a nuclear reactor. The spaceship won't survive a millisecond. We need way better than 99.5%.
"Use a material with better than 99.999% reflectivity. Usually, highly reflective surfaces are dielectric mirrors, which are composed of ‘sandwiches’ of material, with each layer reflecting back a modest fraction of the total. Each layer needs to be at least a quarter of a wavelength thick. The weight can be reduced by using a monolayer with high reflectivity at the correct wavelength. Based on recent research, this could be achieved by a ‘hole-pocked’ layer, highly reflective for very specific angles where reflectivity caustics arise. (These caustics occur for wavelengths of light that are actually longer than the sheet thickness.)"
http://breakthroughinitiatives.org/index.php?controller=Foru...
The project estimates are completely off. Building a 1gigawatt power plant costs 10billion. Let alone building 100 of them. Also making the laser array. Also you can't have reflection without absorption. Also we don't have solar sails that fit the bill. This project is barely physically and economically plausible. Its not a question of scaling, or engineering. The physics just don't work. We have a way to get a space…
Second, we have mirrors that can reflect up to 99.999% of a single wavelength of light(such as that emitted by a laser)[0]. There is a detailed analysis of the concept in [0] and the Breakthrough Foundation has a detailed list of challenges associated with this project at [1].
Getting the laser out of the atmosphere is probably one of the biggest challenges with this.
[0] http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-R... [1] http://breakthroughinitiatives.org/Challenges/3
So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?
That is a good question. The Voyager spacecraft send out detectable signals with a ~20 Watt signal. This is larger than the ~3 W signal that a smartphone sends, but by less than an order of magnitude. Voyager is at ~130 AU. Alpha Centauri is at ~275,000 AU. With the 1/r^2 decrease in signal, that means the signal from earth will be smaller by a factor of ~3 x 10^6. Now, supposing we have ~1000 of these smartphone pro…
https://en.wikipedia.org/wiki/Interstellar_medium#Radiowave_...
Not to mention there is also additional cosmic radiation outside the heliosphere. Something the size of a chip is going to be extremely vulnerable. Slower rad-hard electronics are going to be the order of the day, but even with thousands of these things, it's going to take a toll.
So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?
Thinking out loud: You need an ingenious design that allows the laser sail to double as a directional antenna. And you pick a frequency which is not radiated by many other objects in space so it's easier to pick up the dim signal. And then you build a ginormous radio telescope bigger than any ever built before. Luckily you have a decade or two to build the telescope after the probes are launched.
Depending on what maneuvering profile these things will have, it might be desirable to have a "semi-phased" design that can be steered to a limited degree without physically moving the spacecraft.
And, it also goes without saying that this antenna probably needs to be flexible or at least articulated in order to deploy.
NASA has previously done some really interesting antenna designs with genetic algorithms. You just need to figure out what the goodness function here should be.
https://ti.arc.nasa.gov/m/pub-archive/1244h/1244%20(Hornby)....
I wonder what plans they have for communicating with a probe light-years away. Consider New Horizons. It has a power budget and antenna gain way beyond something that can be crammed into a few grams. Yet, the bit rate is so low it's still sending back data it gathered in 2015 from an encounter mere light-hours away. Even if the laser propulsion aspect of this works out, I think communicating with something that far a…
http://www.icarusinterstellar.org/vint-cerf-qa-on-interstell...