Rainbow spacecraft and how humanity might end

19.32, Thursday 6 Aug 2020

I’m a proud member of the British Interplanetary Society so I go to lectures at the HQ in Vauxhall from time to time, and every month I get the latest edition of their academic journey, JBIS, through the letterbox.

You should be a member. As a taster, I’ve put the table of contents of the latest JBIS on my Instagram, and I’ll type it out here too:

General Interstellar Issue

Protocols for Encounter with Extraterrestrials: lessfroms from the Covid-19 Pandemic

Water and Air Consumption Aboard Interstellar Arcs

Habitability of M Dwarfs: a problem for the traditions SETI?

On a Spectral Pattern of the Von Neumann Probes

Reworking the SETI Paradox: METI’s Place on the Continuum of Astrobiological Signaling

Dynamic Vacuum Model and Casimir Cavity Experiments

Good stuff!

It’s a bit of an oddball institution. JBIS is always delivered late, and it all feels a bit fuddy-duddy and old white guy, then suddenly there’s a remark in a lecture about asteroid mining being commercially viable in 2046 and somebody in the audience from BAE or Lockheed or similar stands up and says, actually we’re using 2044 in our planning.

And they also did the first ever engineering study of an interstellar mission, back in 1973-78, and that became the foundation for everyone else’s work since. The list of space projects BIS has influenced is staggering.

It’s the conversations over lunch.

At an event a few years back, I bypassed the sandwiches and honed in on some particularly intense looking chocolate cake, and accidentally got talking to a guy who it turned out specialised in existential risks to humanity. So I asked him to tell me his favourite way that humanity could end. In the event, he gave me two.

First, we could get hit by an exotic particle, called a strangelet I think (it was a long time ago, I only half remember). It would be a quirk of physics and the effect would be that the Earth would get converted into a cloud of more strangelets in about a millionth of a second. So that would be that and we would never know.

Second, he said, there’s a type of apocalypse called something like the economic zombies scenario and it was problematic for him because he felt we were on that track, and it was inevitable.

The short version is this, as far as I can recall:

The history of humans and technology is that we outsource human functions in the name of economic efficiency. Don’t dig by hand, get a spade. Don’t do mental arithmetic, get a calculator. Etc.

So the logic of that is hard to escape. Imagine two communities. One chooses to adopt technology, the other doesn’t – perhaps because they have anticipated this outcome and are trying to avoid it. In the long term, the community that outsources and adopts the technology will out-compete the one that doesn’t.

On and on it goes. Until eventually we can see that the final impediment to efficiency is consciousness itself. So we end up outsourcing our individual planning and decision making, taking the human out the loop. Brain implants or some such.

At each stage of this, the next step is logical and inevitable. We’re on the road.

What this guy said is that if you then visited this future Earth, aliens visiting in a spaceship, say, what you would see is a planet of billions of humans, a hive of activity, doing exactly what we do now but with verve and incredible efficiency – and dead behind the eyes.

Economic zombies. The end.


JBIS. Sometimes the academic papers have an unexpected poetry.

There’s a paper from 2018 that has stuck in my head ever since.

As background, there’s a way to propel probes called a solar sail – essentially a giant, reflective sail, unfurled when the probe is sufficiently far from anything else. As sunlight hits it, the probe accelerates… just a touch. In space, there’s no friction to slow you down. So the probe gets faster and faster… It’s slow to get going but incredibly efficient because the probe doesn’t have to carry its own fuel.

So! This paper says that, instead of reflecting the light, it can be diffracted – photons split into component colours as they pass through the sail instead of being reflected. And that provides momentum, which is neat and the point of it. The paper is called Flying on a Rainbow - A Solar-Driven Diffractive Sailcraft.

Abstract: Radiation pressure afforded by natural broadband sunlight upon a transmissive diffractive sail is theoretically and numerically investigated. A grating period of one micrometer is found to convert 83% of the solar black body spectrum into sailcraft momentum. Non-optimized orbit-raising trajectories for diffractive and reflective sails are compared. Potential advantages of diffractive sails are also described.

The advantages: photons both propel the craft but can also, after they pass through, charge photovoltaic cells. So light does double duty. Second, the sail can also alter direction opto-electronically (rather than having to physically shift the whole thing, which is hard because solar sails are vast).

But but but. The image of it all.

A populated, far future solar system - the planets and the asteroids teeming with life in its infinite variety - but each only a tiny dot in the vast and deep dark gulf of space.

Between these outposts, we can imagine hairline necklaces around the sun, barely curving transfer orbits – optimal arcs from one oasis to the next, set by celestial mechanics and gravitational potential.

And along these invisible paths, discernible only through the eyes of mathematics, against the black desert of space: continuous trains of spacecraft, their movement barely visible at this distance, fragile metal habitats and cargo ships each at the centre of their own football-field silk-thin sail, tacking on sunshine, and that, when you look through it, diffracts the sun and the stars behind into dazzling rainbow shards.

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