Wednesday, April 13, 2016

Going interstellar

I'm interested in the Internet blogosphere reaction to Yuri Milner's $100 million investment into the new starwisp.

Incidentally, Milner is quoted at having £3 billion in his bank account, so his proposed investment is 3.3% of his wealth. It's not however coming out in one lump sum - I hear talk of a 10 or 20 year programme of research.

Let's be optimistic and say a decade. Then Milner is spending 0.33% of his wealth per year on this project. Given his likely return on assets invested, this is a rounding error in his global interest rate.

Luboš Motl focuses, as expected, on the physics of the thing. He writes,
"We want to accelerate a few grams to c/5. The kinetic energy may still be "barely" computed by the non-relativistic formula and it is E = mc2/50. If m were 5 grams, we get 9 trillion joules."
Now, one kiloton of TNT (a small nuke) is equivalent to 4 trillion joules, so when this interstellar probe hits the atmosphere of a planet around Alpha Centauri, it's going to look to the alien inhabitants like someone detonated a 2 kt nuke in their atmosphere. Did anyone mention we're going to send a swarm of these things?

This kind of first strike is a bit extreme, even for me ... .

Steve Sailer is reminded of the famous Larry Niven and Jerry Pournelle book, "The Mote in God's Eye", and sees a parallel with immigration policy:
"A half-dozen centuries in the future, humanity has stumbled into a fortuitous discovery of a faster than light interstellar travel technology and spreads out across the habitable planets of the galaxy, never encountering any other intelligent life.

"Then a slower-than-light spacecraft driven by a light sail arrives from an unexplored solar system.

"Our Space Navy goes to visit the planet that sent it and discovers a civilization that seems as advanced as ours, except they don’t have our faster-than-light travel technology, so they are stuck in their solar system, except for sending out the occasional expensive probe. We can visit them, but they can’t visit us.

"Their extremely gracious ambassadors greet our ambassadors in a most affable manner.

"The book then turns into an ecological detective story as a few suspicious Earthlings try to unravel the complex story of the Moties’ nature before diplomacy gets too far advanced to put the brakes on proposals such as sharing the FTL drive with the aliens in the name of interstellar harmony and goodwill. We wouldn’t want to be seen as speciesist, now would we?"
Centauri Dreams wonders about the project itself, the timescales and whether it would work. No-one seems to have seen the engineering plans for the interstellar device, but with accelerations estimated in the region of 20,000-60,000g you can forget anything with a framed structure. The ultrathin sail will be the entire device, embedding sensors, communications and control.
"Writing for The Atlantic, Ross Andersen describes the sail this way in Inside a Billionaire’s New Interstellar Mission:

"Picture a thin disc about the size of a round picnic tabletop. It would have miniaturized electronics onboard, including a power source, cameras, photon thrusters for navigation, and a laser for communication. Some of this kit would be bundled into the disc’s center, and some would be distributed through the rest of the sail. But it would all be a single unit: If you saw it streaking by, it would look like a flat, round sheet of reflective material.

"We’ve also got a problem in that concept, because Jim Benford has pointed out that a flat sail is not a good ‘beam-rider’ — we’ll likely have to look at the kind of curved sail designs both Jim and brother Gregory Benford have studied in lab work at the Jet Propulsion Laboratory. But get a sail under that beam successfully and it reaches Pluto the day after launch, as Andersen notes. Another 20 years and it’s streaking through the Alpha Centauri system."
It's easy to poke holes in the mission concept as we currently understand it:
  • The device can't be slowed so dwell-time on target is under a second
  • For similar sums we could image exoplanets with near-Earth space telescopes
  • Future progress might obsolete the probes before they even arrived.
Better to let the study programme think creatively about what you could actually do better with a relativistic flyby.


Most optimistic timeline:

2016: R&D project starts
2026: Infrastructure build project starts (10 years)
2036: Launch (and 20 year coast to Alpha Centauri)
2060: Results received back here on Earth.

We get the results in 44 years, when I will be 109 years old. Hmm.

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