Silicon and silica oxide nanomaterials would be best for laser pushed sail

California Institute of Technology researchers have worked out that super thin structures made of silicon and silica oxide convert waves of infrared light into a momentum that would accelerate a probe to speeds of around 60,000 kilometres (37,000 miles) per second [20% of light speed].

Optimized thin film structures could be promising candidates for a laser-driven light sail, providing the means of efficient propulsion as well as radiative cooling. For the optimal mass case (sail mass = payload mass). Researchers introduced the concept of reflectivity adjusted area density (RAAD) as one relevant figure of merit that seeks to minimize the constraints on the power and the size of the laser array. In addition, they demonstrated that structures which combine materials with high mid-infrared extinction coefficients (such as SiO2) and high near-infrared refractive index (such as Si) can be tailored to maintain a desired steady-state temperature for a range of near-infrared absorption coefficient values. The structures and materials analyzed in this study are intended to highlight the versatility of multilayer thin film structures to achieve a desired multiband optical response for a very low mass. In addition to materials analyzed here, other potential candidates could include IR-active materials such as silicon nitride, silicon carbide, or doped silicon, to name a few.

Light sails propelled by radiation pressure from high-power lasers have the potential to achieve relativistic spaceflight. In order to propel a spacecraft to relativistic speeds, an ultrathin, gram-sized light sail will need to be stably accelerated by lasers with ∼MW/cm2 intensities operating in the near-infrared spectral range. Such a laser-driven sail requires multiband electromagnetic functionality: it must simultaneously exhibit very low absorptivity in the (Doppler-broadened) laser beam spectrum in the near-infrared and high emissivity in the mid-infrared for efficient radiative cooling. These engineering challenges present an opportunity for nanophotonic design. Here, we show that designed thin-film heterostructures could become multifunctional building-block elements of the light sail, due to their ability to achieve substantial reflectivity while maintaining low absorption in the near-infrared, significant emissivity in the mid-infrared, and a very low mass. For a light sail carrying a payload, they propose a relevant figure of merit—the reflectivity adjusted area density—that can capture the trade-off between sail mass and reflectivity, independent of other quantities such as the incident beam power, phased array size, or the payload mass. They present designs for effective thermal management via radiative cooling and compare propulsion efficiencies for several candidate materials, using a general approach that could apply to a broad range of high-power laser propulsion problems.

Nanoletters -Nanophotonic Heterostructures for Efficient Propulsion and Radiative Cooling of Relativistic Light Sails

Thin-film structures with Si and SiO2 layers that minimize the reflectivity-adjusted area density W2 through constrained optimization, for different values of αSi. Here, P0/mp = 100 GW g−1 and the maximum allowed temperature is set at Ts = 1000 K. Structure parameters are given. Higher refractive index of silicon combined with radiative cooling properties of silica enables more efficient propulsion relative to silica-only structures. For large absorption (e.g., α = 10−2 per centimeter), thicker layers of silica are needed to ensure equilibrium sail temperature does not surpass Ts; as a result, there is a penalty in W. Red arrow denotes the incident laser light.

17 thoughts on “Silicon and silica oxide nanomaterials would be best for laser pushed sail”

  1. There is a practical limit to how long it would take to reach the peak speed. Basically once your probe reaches the outer limits of our own solar system you won’t be able to focus a useful amount of power onto the sail. So there won’t be any more acceleration after that. With that in mind you can do some rough order-of-magnitude calculations. In terms of a trip to another star, that means that just about all the trip will be at the peak velocity. The acceleration component will be negligible in terms of the total trip time. Previous studies have been more explicit that they think the best choice is payload mass = sail mass. That is, sail mass of 5 grams, plus a payload of 5 grams for a total launch mass of 10 grams. How you can make a 5 gram probe that can possibly send any information back from lightyears away is left as an exercise for the reader.

    Reply
  2. There is a practical limit to how long it would take to reach the peak speed. Basically once your probe reaches the outer limits of our own solar system you won’t be able to focus a useful amount of power onto the sail. So there won’t be any more acceleration after that.With that in mind you can do some rough order-of-magnitude calculations.In terms of a trip to another star that means that just about all the trip will be at the peak velocity. The acceleration component will be negligible in terms of the total trip time.Previous studies have been more explicit that they think the best choice is payload mass = sail mass. That is sail mass of 5 grams plus a payload of 5 grams for a total launch mass of 10 grams.How you can make a 5 gram probe that can possibly send any information back from lightyears away is left as an exercise for the reader.

    Reply
  3. There is a practical limit to how long it would take to reach the peak speed. Basically once your probe reaches the outer limits of our own solar system you won’t be able to focus a useful amount of power onto the sail. So there won’t be any more acceleration after that. With that in mind you can do some rough order-of-magnitude calculations. In terms of a trip to another star, that means that just about all the trip will be at the peak velocity. The acceleration component will be negligible in terms of the total trip time. Previous studies have been more explicit that they think the best choice is payload mass = sail mass. That is, sail mass of 5 grams, plus a payload of 5 grams for a total launch mass of 10 grams. How you can make a 5 gram probe that can possibly send any information back from lightyears away is left as an exercise for the reader.

    Reply
  4. There is a practical limit to how long it would take to reach the peak speed. Basically once your probe reaches the outer limits of our own solar system you won’t be able to focus a useful amount of power onto the sail. So there won’t be any more acceleration after that.With that in mind you can do some rough order-of-magnitude calculations.In terms of a trip to another star that means that just about all the trip will be at the peak velocity. The acceleration component will be negligible in terms of the total trip time.Previous studies have been more explicit that they think the best choice is payload mass = sail mass. That is sail mass of 5 grams plus a payload of 5 grams for a total launch mass of 10 grams.How you can make a 5 gram probe that can possibly send any information back from lightyears away is left as an exercise for the reader.

    Reply
  5. There is a practical limit to how long it would take to reach the peak speed. Basically once your probe reaches the outer limits of our own solar system you won’t be able to focus a useful amount of power onto the sail. So there won’t be any more acceleration after that.

    With that in mind you can do some rough order-of-magnitude calculations.

    In terms of a trip to another star, that means that just about all the trip will be at the peak velocity. The acceleration component will be negligible in terms of the total trip time.

    Previous studies have been more explicit that they think the best choice is payload mass = sail mass. That is, sail mass of 5 grams, plus a payload of 5 grams for a total launch mass of 10 grams.

    How you can make a 5 gram probe that can possibly send any information back from lightyears away is left as an exercise for the reader.

    Reply
  6. For now, this is just an exercise on how to maximise the specific pressure of the sail material. How long it takes to accelerate will depend on this figure, the sail area, and how much power will be shone on the sail, which will be subject to mostly economic constraints once this project is brought to tech-readiness.

    Reply
  7. For now this is just an exercise on how to maximise the specific pressure of the sail material. How long it takes to accelerate will depend on this figure the sail area and how much power will be shone on the sail which will be subject to mostly economic constraints once this project is brought to tech-readiness.

    Reply
  8. I didn’t see anything in here about how long it would take to reach such speeds, and what kind of payload you could put on it (when they say optimal case is payload mass = sail mass, does the payload include the sail?). But even if you only get to 5% of light speed by the time you get to Alpha Centauri, at least that’s something that could happen in my lifetime. It sounds like the materials aren’t too exotic, it can be feasible.

    Reply
  9. I didn’t see anything in here about how long it would take to reach such speeds and what kind of payload you could put on it (when they say optimal case is payload mass = sail mass does the payload include the sail?). But even if you only get to 5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of light speed by the time you get to Alpha Centauri at least that’s something that could happen in my lifetime. It sounds like the materials aren’t too exotic it can be feasible.

    Reply
  10. This would be very cool to send probes and see some exoplanets up close. Of course, the probe would whiz on past, but it could still send back better pictures than we can get from here.

    Reply
  11. This would be very cool to send probes and see some exoplanets up close. Of course the probe would whiz on past but it could still send back better pictures than we can get from here.

    Reply
  12. With the new reusable rockets we have the means to both put a huge array of lasers in space to push such sails and protect from missiles attack.

    Reply
  13. With the new reusable rockets we have the means to both put a huge array of lasers in space to push such sails and protect from missiles attack.

    Reply
  14. For now, this is just an exercise on how to maximise the specific pressure of the sail material. How long it takes to accelerate will depend on this figure, the sail area, and how much power will be shone on the sail, which will be subject to mostly economic constraints once this project is brought to tech-readiness.

    Reply
  15. I didn’t see anything in here about how long it would take to reach such speeds, and what kind of payload you could put on it (when they say optimal case is payload mass = sail mass, does the payload include the sail?).
    But even if you only get to 5% of light speed by the time you get to Alpha Centauri, at least that’s something that could happen in my lifetime. It sounds like the materials aren’t too exotic, it can be feasible.

    Reply
  16. This would be very cool to send probes and see some exoplanets up close. Of course, the probe would whiz on past, but it could still send back better pictures than we can get from here.

    Reply

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