Megapixel Exoplanet Imaging in Weeks not Years via Gravitational Lens Missions

Slava G. Turyshev and his team are on their phase III NASA NIAC project to develop a solar gravitational lens telescope. At optical or near-optical wavelengths, the amplification of light is on the order of 200 billion times and with equally impressive angular resolution. If we can reach this region beginning at 550 AU from the Sun, we can perform direct imaging of exoplanets. An imaging mission is challenging but feasible, using technologies that are either already available or in active development. Under realistic conditions, megapixel imaging of Earth-like exoplanets in our galactic neighborhood requires only weeks or months of integration time, not years as previously thought.

The team has been investigating sending one meter telescopes out about twenty times further than Pluto to use the gravity of the sun bending light. The sun is 865000 miles across which is 109 times wider than the earth. The gravity lets you leverage the sun as a giant light collector.

A mission that begins its imaging campaign at 650 AU would thus benefit from the increasing SNR as it progresses to larger heliocentric distances. This would allow such a mission to gradually improve its resolution, while keeping integration times sufficiently short to study temporally varying effects, such a diurnal rotation.

There are other challenges. In this study, they modeled the solar gravitational field as a monopole field, not yet accounting for deviations in the form of the field’s quadrupole and higher moments. They also have not yet accounted for the aforementioned temporal effects, including planetary motion, rotation, and varying illumination. This work is on-going for multipolar contributions and for properly capturing the dynamics, along with work on establishing a technically feasible mission design and architecture. Results will be published elsewhere when available.

Pixel spacing is an issue because of the size of the image we are trying to recover. The image of an exoplanet the size of the Earth at 1.3 parsecs (the distance of Proxima Centauri from the Earth), when projected onto an image plane at 1200 AU from the Sun, is almost 60 kilometers wide. We are trying to create a megapixel image, and individual image pixels are not adjacent. In this case, they are 60 meters apart. This actually reduces the integration time of the data to produce the image.

Integration time is reduced when pixels are not adjacent, at a rate proportional to the inverse square of the pixel spacing. Total cumulative integration time of less than 2 months is sufficient to obtain a high quality, megapixel scale deconvolved image of that planet. Furthermore, even for a planet at 30 pc from the Earth, good quality deconvolution at intermediate resolutions is possible using integration times that are comfortably consistent with a realistic space mission.

Imaging an Earth-like planet at the distance of 30 parsec (pc) with a diffraction-limited telescope, would need an impractical 90,000 meter telescope aperture. Interferometers with a large 90,000 meter baseline would require integration times of hundreds of thousands to millions of years to reach a reasonable signal-to-noise ratio.

Arxiv – Resolved imaging of exoplanets with the solar gravitational lens. The new phase 3 in progress report.

The final report for the phase 2 project.

Hat Tip to Centari Dreams.

Previous SGL Mission Analysis

:Previous work suggests a gravitational lens mission could start in 8 and arrive 15 years after launch.

Extreme metamaterial ceramic solar sails survive a close pass of our sun to reach speeds of 60-70AU per year which is over 0.1% of light speed. Theis propel low mass spacecraft using a dive to extreme proximity to the sun (just 2-5 solar radii). This velocity is 20 times more than Voyager 1. The technology enables reaching Jupiter in 5 months, Neptune in 10, surpassing Voyager 1 in 2.5 years and getting to the solar gravity lens location in just 8.5 years.

Metal sails that can survive a 5 solar radii pass of the sun would be able to go at 40AU per year. These systems could reach the solar gravity lens (600 AU) in about 15 years. Two-meter telescopes at the gravitational lens would be able to image megapixel resolution images of exoplanets.

Artur Davoyan works with Turyshev. Turyshev has the NIAC study on gravitational lens missions. Turyshev has proposed launching telescopes to the solar gravitational lens starting in 2028. If the materials that are can handle more heat and do not absorb as much heat can be used for solar sails, then they could reach the lens in 2037-2043.

Roccor LLC has a grant to develop 1000 to 10,000 square meter solar sails. They are developing composite trussed trac (T-Trac) boom systems. The original Trac will be flight validated on the upcoming near earth asteroid scout mission. T-TRAC has a triangular cross-section. Roccor holds an exclusive license for the Flexible Unfurlable and Refurlable Lightweight (FURL) solar sail developed and tested by the Air Force Research Laboratory.

SOURCES- Arxiv, Centauri Dreams
Written by Brian Wang,

15 thoughts on “Megapixel Exoplanet Imaging in Weeks not Years via Gravitational Lens Missions”

  1. Dealing with the light pollution from earth, including the sunlight reflected from earth, will be the practice needed to deal with blocking sunlight so the solar gravitational lens telescope is usable.

  2. Sure, this might be a possible precursor to a solarscope, but it's likely that light pollution on Earth might make this untenable here. Venus, perhaps? Not quite as cheap, but the atmosphere might be easier to work with.

  3. The minimum focal length is where the Einstein ring gets out from behind the corona. The maximum is where the Einstein ring drops below the noise floor in brightness. So the maximum depends on the target.

  4. The big issue is that the degree of magnification is such that a single telescope is only good for one pixel at a time. the delta V requirement comes from having to maneuver around between the pixels, and then synch up with the target's subjective motion all over again for each pixel, possibly a million times.

    The paper cited was a best case analysis assuming no proper motion or rotation of the target, by the way.

    This calls for a moderate acceleration, very high delta V thruster, maybe nuclear electric. Solar sail is a no go, the Sun is just another star that far out, and chemical propulsion isn't in the cards either. It's nuclear or nothing.

  5. Gravitational lenses are sort of odd. The farther a photon passes the Sun, the less it is bent by gravity. So the light comes to a focus from all sides at a greater distance. The *minimum* focal distance is 550 AU, but the Sun creates a "focal line" that extends far beyond that.

  6. This is really interesting. Tech is progressing exponentially. I am pretty confident that before 2030, we will figure out tech needed to build spaceships/transport systems which will be able to achieve 1-10% of the speed of light and we can have those expoplanet pics around 2030 or earlier.

  7. Wouldn't a solar sail-powered telescope moving quickly enough to reach its destination in 15 years be moving too quickly to be useful? It's only going to be in the 550 AU sweet spot for a few days (moving at 10 AU a week!), then it's going to sail (pun intended) right on past.

  8. That’s why the first mission needs to be opposite the Sun from the galactic core. Lots of things will zip by.

    The next foci mission—opposite the Sun from Andromeda…also target rich. I would say save Barnard star for last…but it too is a lens. So have one orbit the Sun counter to the motion of Barnards Star—and now you have two focal lines for ultra deep swaths.

  9. Would it be worth the additional complexity of a gravity assist at from Jupiter using this sort of sail?

  10. Not convinced that such targets can be so easily tracked with the observer able to maintain exact reciprocal viewing point. the dV is huge.

  11. Since the image pixels are so large, rather than a conventional 2D CCD, what you want is a long structure with single-pixel detectors spaced out along it (fairly simple to fabricate on silicon). Then either rotate the structure, move sideways, or wait for the planet's own motion to build up an image.

    Not mentioned in the text above, although it may be addressed in the study, is planets are in orbit around their parent star. So they don't hold still for long image integration times. Using large single-pixel silicon will reduce integration time.

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