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The Sun as a Gravitational Lens
JRehling
post Mar 24 2017, 06:16 PM
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I titled this topic thusly to avoid the connotation of "solar" as it is often used, speaking of the Sun's radiation as an asset.

This mission concept, which is almost shockingly radical, is on firm scientific grounds, but would deliver a tremendous capability at the cost of some considerable engineering resources.

The concept is: At a distance of >550 AU, the Sun could be used as a gravitational lens to magnify a given target located on the other side of the Sun. The magnification that could be achieved is in principle (here's a word you don't encounter often in the engineering realm) infinite. A recent study by Landis delves into the issues far better than I can here:

https://arxiv.org/abs/1604.06351

In a nutshell, a potential mission would fly a telescope out to >550 AU (four times Voyager 1's current distance) and would look back towards the Sun, which would be hidden behind an occulting screen, so that a target antipodal to the Sun would be magnified far beyond what any existing telescope can achieve. The image of, say, an exoplanet located tens of light years away would actually be too large (~10 km at the focal plane) for a telescope to collect the whole image at once. It would, in effect, see one "pixel" at a time, and to image an entire exoplanet, it would have to scan back and forth across the image, either actively or passively, either scanning one strip across the exoplanet or making some effort to gather a 2D image.

Because of the orbital dynamics, the craft would be essentially an interstellar craft rather than sun-orbiting as we normally think of it. It could not effectively observe multiple different targets because it would have to travel considerable distances to aim at a new target, although observing multiple planets in the same exoplanet system seems to be achievable. If we wanted to observe five different exoplanet systems, we would have to launch five different copies of this mission.

The Trappist-1 system introduces a case where a mission like this might have a respectable ROI. One telescope launched to Trappist-1's focal location from the Sun would perhaps be able to scan several or all of the planets in the system, either in 1D or 2D mode, perhaps repeatedly – the details depend upon the resources for propulsion to make the scanning work. The focal distance for Trappist-1, however, would be significantly farther than 550 AU. Landis' paper suggests that something more like 2500 AU would be required. That is very far, but not nearly as far as the stars are. It seems like the most painful requirement would be to get a telescope with a good amount of propulsive capability out to that distance before the mission planners die of old age.

The requirements are fantastic, but it seems like a good possibility that this would be cheaper than the seeming alternatives.

I'm not sure that I've ever read about a mission concept so radically different than anything I'd read before. It seems feasible – just hard.
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nprev
post Mar 29 2017, 12:58 AM
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ADMIN NOTE: It's all been fun, but please review rule 1.9 re sci-fi engineering...let's keep our collective feet on the ground, so to speak. wink.gif


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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