Ion engines could take us to the solar gravitational lens in less than 13 years

Thank you, from someone who never ever ever wants to watch a video to get a few paragraphs of content.

- "ideal power plant that can output 1 kW per kg of weight"

I wished I remember where I read about this engineering problem, because it's an entertaining one. The main constraint on your [kW/kg] past a certain point is heat dissipation—the mass of the radiators rejecting waste heat into the vacuum of space. Thermal radiation scales like [temperature^4] (a very fast-growing function), so that parameter's obvious—you have to scale your exhaust temperature as high as you can engineer. That's how you shrink the radiator size. And you still need to run a heat engine—you need a significant temperature gradient, on top of the already-high exhaust temperature, to get useful work out of it. That's the temperature output of your primary heat source. So, the high-level design solution is: you have an array of infrared radiators glowing red, and a nuclear fission reactor glowing orange. That's the way to get a high power/mass ratio in space.

Also, everything's built around pipes of molten metals of different species (optimized heat transport), and the heat engine is like a steam turbine that spins on boiling molten potassium metal. (I think?) They're really exciting-looking machines. I wish someone would build one!

1 kW/kg is an ideal power plant. Does the paper define a minimally-viable one?

If we beef up the chemical stage, e.g. by launching on Starship and re-fuelling in LEO, can we make do with 100 or even 10 kW/kg?

(Also, to put 550 AU in perspective, Voyager 1 is 165 AU out [1]. At 38,000 mph Voyager 1 [2] travels about 3.6 AU/year [a]. Going straight out, it would reach the Solar gravitational lens in 2131 [b].

[1] https://science.nasa.gov/mission/voyager/where-are-voyager-1...

[2] https://en.m.wikipedia.org/wiki/Astronomical_unit

[a] (38026.77 x 24 x 365) / (9.2956 x 10^7)

[b] 2024 + (550 - 165) / a

NASA has designs for thermoacoustic power plants that are much denser than this, but I note that they seem to be conveniently ignoring the weight of the fuel tanks in those calculations. If the generator were for instance 2% of the weight of the system, that means it has to be 50x as powerful as the goal.

With this unrealistic ion thruster method they estimate 13 years, whilst the realistic solar sail Turyshev method, which is actually planned, needs 17 years. Just the payload is much less.

This is pure science fiction, with no real practical benefit.

I've been aware of gravitational lensing before but this is the first time I've heard of it being used to resolve exoplanets.

This is super exciting and needs to be made a higher priority than it is considering our only other way around this is to build gigantic telescopes far beyond our current capabilities.

Unless you have two beams, it would have to AC. You'd have to keep the series capacitance low enough that a significant amount of power is conducted (which might kill it). Remember that free space impedance is 377ohms sqrt(mu0/eps0) so non-photonic power likes to become Lambertian radiation.

I don’t think it leaves behind a trail of ionized gas. The positive and negative ions get recombined.

While you could get a _platform_ there in those months, “what’s the point of it”? You would like to get a _payload_ there able to do science as well, so a USB Stick sizes spacecraft may not be suitable (for now) for it.

I can however imagine a proper ion-thrusted satellite with enough Antenna gain to communicate from 550AU back with real science.

“Before this decade is out… “

When Kennedy committed us to go to the moon, the first American hadn’t even orbited the Earth.

Previous generations just used to get shit done.

Simply slap together some antimatter and matter my friend, and all your problems are solved.

So fine, use 1960s general atomics tech and do a pulse nuclear drive.

We'll have the technology in 10 years.

Just like 20 years ago.

I came here to say this. But also, for those who don't know. this is referring to "Project Hail Mary" by Andy Weir, author of "The Martian".

(Caution, many spoilers in the Wikipedia article) https://en.wikipedia.org/wiki/Project_Hail_Mary

Do you honestly think this wouldn’t be taken into account? I’m sure even without reading the article this is exactly the sort of thing that will be accounted for in any serious proposal.

It’s not as if our species doesn’t have millennia of experience with sailing ships to compare to when evaluating how to manage navigating to a specific point using either a powered or sailing vessel, or decades of experience maneuvering spacecraft at high velocities with high precision using both thrusters and gravitational slingshots within the solar system.

I think that's only a challenge at all because of how mass and power limited such a craft would be. The obvious solution is to use lasers.

It might even be possible to use a modulated retroreflector on the craft-- e.g. we fire a high power low divergence beam at the craft and it reflect it back. By modulating the reflection in can send back data with practically no power usage.

The angles accepted by the reflector could be fairly hard and so the difficult pointing problem would only exist on our end.

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Nuclear explosions release mostly heat and radiation. Are you turning your pusher plate into high energy plasma with the explosion and using that to propel your spacecraft? My gut feeling is that your total ISP for this is disappointing compared to the amount of mass you add for the huge store of nuclear bombs.

This famously appears in the plot of the Three Body Problem scifi series by Liu Cixin!