Comment by superkuh | Hacker News Reader

Comment by superkuh | Hacker News Reader

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It's not a new idea and there already have been dozens of papers, and entire books (http://erewhon.superkuh.com/library/Space/Spacecraft/Deep%20...), published about using the solar gravitational focus as a lens and sending a spacecraft there. In fact NASA was already funding early mission studies like the Heliopause Electrostatic Rapid Transit System (HERTS) a decade ago.

And not only is it good for planetary sciences, it's good for cosmology too since it enables looking at the truly small scale structure of the cosmic microwave background. A mission to the gravitational focal line opposite some star should be one of the highest priorities.

http://erewhon.superkuh.com/library/Space/Spacecraft/Diffrac...

http://erewhon.superkuh.com/library/Space/Spacecraft/Direct%...

http://erewhon.superkuh.com/library/Space/Spacecraft/Image%2...

http://erewhon.superkuh.com/library/Space/Spacecraft/Mission...

http://erewhon.superkuh.com/library/Space/Spacecraft/Photome...

http://erewhon.superkuh.com/library/Space/Spacecraft/Resolve...

I'm an engineer (current job is designing and building small spacecraft), so forgive me for raining on physicists' dreams, but a huge reason such a telescope is not currently practical is the enormous amount of propellant required to get you there and then station keep to stay focused on a target. The latter is usually glossed over in this concept but it alone blows mission cost out of the water. Would make James Webb look like a cute little project.

If you don't have an active propulsion system for station keeping then you cannot pick targets. Who wants that? Nobody.

This concept is 50 years off at minimum.

That's why the NASA study (HERTS) suggested using an electrostatic solar sail. It's only consumables are the noble gas and/or metal plating of the hollow cathode electron emitters used to keep the craft positively charged.

Actual station keeping +- a few meters once out on the gravitational focal line opposite the target system (which itself is moving) would require some cold gas thrusters that would limit the duration of the mission. But the forces and accelerations required are very small when you're 600 AU out from the sun and even the photon pressure isn't throwing things off anymore.

Yes, getting out there with enough mass for station keeping would be hard and it'd require new methods. Either electrostatic solar sails, or a more traditional H-reversal oberth burn close to the sun.

Claudio Maccone's proposal, to put a radio telescope at the solar focal point for SETI or communications purposes, is included as a chapter titled "Radio Links enabled by Gravitational lenses of the Sun and Stars" in the book Communications with Extraterrestrial Intelligence edited by Douglas Vakoch [1].

[1]. https://www.seti.org/book/communications-extraterrestrial-in...

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