back to article Lightsail space tech gets tailwind from Caltech breakthrough

Centuries after Western explorers used sail power to discover a world hitherto unknown to them – although well known to people who already lived there – science fiction writers and engineers have wondered if space exploration might be similarly powered by lightsails. The idea of using light from a nearby star or remote laser …

  1. User McUser
    Joke

    As used in hospitals...

    In their experiment, the researchers used a 50 nanometer thick microscopic silicon nitride membrane suspended on special strings.

    They must be using Simpson's brand Individual Imperial Stringettes - "Just the right length!™"

    1. JimmyPage
      Happy

      Re: As used in hospitals...

      Pest control ?

    2. Fr. Ted Crilly Silver badge

      Re: As used in hospitals...

      'Away with floods! Away with the dull, workaday tidal waves!'

  2. Eclectic Man Silver badge

    Control

    An actual interstellar light sail would have to survive many years, possibly hundreds of years in transit, and potential damage to the sail that might render it asymmetrical and therefore difficult to control the trajectory under laser propulsion from Earth or near Earth.

    I know that we have very sensitive telescopes now, but detecting a signal from a probe sent even to Proxima Centauri, a mere 4.22 light years away is, I suspect, well beyond our current capabilities. So lots of research to do before we hoist the main (solar) sail. I just hope they manage to get something launched in my lifetime.

    1. Throatwarbler Mangrove Silver badge
      Joke

      Re: Control

      To borrow from the commentard above, just connect a very long nanoscale string to the probe and relay information back along it.

    2. LybsterRoy Silver badge

      Re: Control

      Its not the years in transit that are the problem. Can you imaging an Earth where we can keep a laser running and pointing in the right direction for more than a couple of years. Plus you couldn't site it on Earth because "think of the global warming" and I'm a bit unsure any country would like a tool such as that hanging over their metaphorical and actual heads.

      1. Fr. Ted Crilly Silver badge

        Re: Control

        I dunno either, could go and ask the Moties I suppose.

    3. DJO Silver badge

      Re: Control

      The trick is not to send one but dozens on a staggered launch schedule so the trailing ones act as repeaters for the forward ones, that way they don't need to carry a powerful transmitter, it just needs to be powerful enough to get to the sail 3 or 4 down the line (that allows for casualties en-route). Also it means you can have some sails with scientific instruments with weedy transmitters and some just as repeaters.

      The sails can't stop, they may be able to slow down a tiny bit from the target star but the first one, being the fastest one will only have a day or so to do any useful science but it can tell the following sails what to look at while they zip through the target system.

      There are other problems, the main one is the lasers. Ground based won't work because the atmosphere is too attenuating and we're on a spinning orbiting object so pointing a beam at something possibly a light year or two away would be tricky. So a space based laser is the only option and I'm sure the governments of the world will be perfectly happy to let someone set up a sodding great multi-gigawatt precision targetting space laser. (What could possibly go wrong with that?)

      If it was to happen it wouldn't take hundreds of years, it should be possible to get the things up to 10% of the speed of light, maybe more, so a 50 year travel time should be manageable.

  3. GBE

    How many femtoNewtons in a femtoWales?

    The research team recorded a radiation pressure force of 70 fN (femtonewton or 10 [to the −15 newtons]) from a laser with the power of 110 Watts per centimeter squared, [...]

    What's the official Register unit of force?

    1. Bebu sa Ware
      Windows

      Re: How many femtoNewtons in a femtoWales?

      The research team recorded a radiation pressure force of 70 fN (femtonewton or 10 [to the −15 newtons]) from a laser with the power of 110 Watts per centimeter squared, [...]

      «What's the official Register unit of force?»

      The Norris [No] apparently 1.0 cNo = 1N (or for the heathen or the faredge rabble~0.225 lbs force)

      So 70 fN = 70x10-15 N = 70x10-17 No ie 700.0 aNo (attoNorris)

      The Caltech press release states the "sail" was a 40 μm square so 1.6 nm2 or 0.077 nWales† thus the pressure would be 700.0 aNo/0.077 nWales or 9.1 μNo/Wales.

      (I imagine the locals would apply more pressure to their native soil after a successful Dragons try against All Blacks at Cardiff Arms.)

      The units of 100W per sq cm apart from being in themselves a daft choice is a power density - power [Watts] per area [square metres] W/m2 but el Reg irresponsibly doesn't have a unit for energy let alone power but Norris.linguine and Norris.linguine.sec-1 should respectively serve or badgers.Csheep2 and Norris.Csheep etc.

      Conversion of seconds into nanoTruss or microScaramucci all too ephemeral especially the second for y.t. and doesn't correspond meaningfully with linguine.Csheep-1

      FWIW I think the "special strings" were special (silicon nitride) springs not some putative entity in a theory of everything (or of anything [at all]).

      † The official abbreviation W is easily confused with Watts, Wa might be preferable or Cy for Cymru

      1. GBE

        Re: How many femtoNewtons in a femtoWales?

        «What's the official Register unit of force?»

        The Norris [No] apparently 1.0 cNo = 1N (or for the heathen or the faredge rabble~0.225 lbs force)

        Brilliant! Somehow I completely missed the fact that there's an offical Reg units conversion page.

  4. fpx
    Boffin

    So the the lightsail, you can send a spacecraft to some other star system in a few hundred years? Great! And then what? After having accelerated to relativistic speed, the spacecraft will arrive at relativistic speed, with no means of slowing down. So it has a few minutes to observe, and then it's off into a much bigger void beyond.

    1. -maniax-

      Don't forget that the first probes to visit the outer planets* did "high" speed fly-bys lasting only a few minutes effectively but were still able to provide enough data to keep the boffins busy ever since.

      And it's not just the data gathered during the fly-by that matters, the approach also provides oodles of data as does the ongoing journey afterwards , NASA?\JPL? are still receiving transmissions from at least one of the Voyagers if not both all be it very limited in nature now due to power constraints

      There's no reason the first interstellar probes can't do the same for whichever systems they get aimed at although I'll admit that given the timescales involved it would be nice to get more than a few blurry snapshots & fuzzy data readings from any such probes rather than have to wait for further probes to be sent after we've proved we can do it

      *Voyagers 1 & 2 for those who have been hiding under a big rock at the bottom of a very deep cave for the last half century

    2. DJO Silver badge

      If it takes "hundreds of years" it'll be barely relativistic. Say it takes 100 years assuming it accelerates more in the first part of the mission and mainly coasts after the laser range is too great it may peak at 6% of the speed of light so to cover the inner solar system (1AU in and 1AU out) will take about 5 hours so plenty of time to make lots of observations.

      If faster, say a 50 year trip and a maximum speed of 12% of the speed of light (which is roughly the target) it'd have over 2 hours in the inner system and a day or more on the approach and departure.

      Not long but long enough and anyway they are not going to launch a single sail, there will be several.

  5. Baximelter

    Avi Loeb proposed this idea a few years ago in his book "Extraterrestrial" about the Oumuamua visitor.

  6. Hurn

    F=ma

    "We wanted to know if we could determine the force being exerted on a membrane just by measuring its movements. It turns out we can."

    Let's see:

    We know the mass of the membrane (or can calculate using density x volume). Check.

    We can measure the movement (linear distance) and determine acceleration (by measuring at discrete time intervals, thanks to a clock). Check.

    It appears there should have been little doubt, unless the question was posed for funding / grant approval purposes.

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