In What might the first deep space telescope using the Sun or Jupiter as a gravitational lens be like? I speculated that the detector for a gravitational lens telescope would be a big array of conventional telescopes and included the first image below, though for the space application the telescopes would be hundreds or thousands of kilometers apart.

I just saw the Launch Pad Astronomy video 4 Future Space Telescopes NASA wants to build and the screen shot shows a cluster of space telescopes known as "pearls".

Every few years Earth would launch another cluster, basically these are disposable focal plane arrays though calling it a focal plane proper is a bit of a stretch.

Where is this concept coming from? Who's work is this?

Question: Where is this "clusters of pearls" design for a solar gravitational lensing telescope discussed in detail? Who's developing this?

I'm not asking about the space artist, it's the optical and mission designers I'm after.

In the video I've seen a reference to Slava Turyshev and Victor Toth but I'm not sure that's the right avenue to pursue here.

screen shot from the Launch Pad Astronomy video "4 Future Space Telescopes NASA wants to build"

Stanford plenoptic camera array used to research light fields


Stanford plenoptic camera array used to research light fields


1 Answer 1


The expression "clusters of pearls" was coined by some of our team members as we were working on developing a plausible conceptual framework for a Solar Gravitational Lens mission.

The key issues that need to be addressed are this:

  1. A successful SGL mission requires multiple "mission-capable" spacecraft: spacecraft that host a telescope with (at least) a 1-meter aperture and of course the required hardware for power, propulsion and communication. Why multiple spacecraft? The telescope is used as a single-pixel detector in an image plane that spans many kilometers. It basically observes the (faint) Einstein ring of the target as it appears around the Sun and measures its brightness. As it moves laterally in the image plane, the brightness changes. These brightness measurements form the pixels in the image plane. However, navigating in that image plane with the requisite meter-scale precision is not possible. What is possible is navigating, e.g., with respect to a reference spacecraft that uses no propulsion and thus follows an inertial trajectory. Once we know our motion with respect to that local inertial frame, we know how our position changes relative to the image.

  2. There is also the problem of light contamination since the faint ring is observed against the much brighter corona. Differenced measurements using multiple spacecraft would help with removing this bright background, leaving only the unavoidable stochastic shot noise.

  3. The only reasonably mature propulsion technology that can get us there in reasonable time (650 AU in less than 30 years) is solar sailing with a close perihelion. But sailcraft are small, much too small to carry a sizable telescope. So there is a need for multiple small sailcraft that might self-assemble into a "mission-capable" spacecraft after the acceleration phase, during cruise.

  4. The possibility was raised that perhaps a string of such groups of spacecraft could also act as communications relays, since sending a signal back from 650 AU is not easy. I am a bit skeptical about this, both in terms of reliability and also practicality; sure, relays are nice, but one big telescope on Earth or in LEO catching that signal from 650 AU might be more efficient not to mention substantially cheaper and more reliable. Still, it's a concept worth thinking about.

So we have lots of tiny sailcraft, self-assembling into several "mission capable" craft, with the option of having multiple "waves" of such craft being sent at some intervals and working as signal relays before arrival.

But no, nothing like that plenoptic setup. That would require hundreds of "mission capable" spacecraft at 650 AU even for a very low resolution image, and I don't think that's realistic. Would be nice though, as it would resolve many of the toughest problems if we could take an instantaneous snapshot of the entire multi-square-kilometer image plane instead of scanning it at one pixel (or a few pixels) at a time.

None of this is being developed just yet; what might happen in the foreseeable future is a "TDM", or technology demonstration mission, which would show that close perihelion sailcraft, "Sundivers", can indeed survive perihelion and achieve very high egress velocities. Such spacecraft can have multiple uses (e.g., solar polar missions, low-cost planetar flybys) demonstrating their viability before an SGL mission. See https://arxiv.org/abs/2303.14917 for some details.


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