Powering Communication for an Interstellar Probe

There was a November 2019, NASA Workshop on Interstellar Propulsion. It was part of the 2019 Interstellar Symposium. The workshop focused on physics-based propulsion technologies that have the potential to meet the goal of launching an interstellar probe within the next century and achieving .1c transit velocity: Beamed Energy Propulsion, Fusion, and Antimatter.

The state-of-the-art of each was examined, and competing approaches to advancing the Technology Readiness Level (TRL) were presented and assessed for synthesis into a report that will serve as the blueprint for possible future interstellar propulsion technology development.

Geoffrey Landis looked at providing power for communication for an interstellar probe that weighs a couple of grams. He looks at using a system to generate power from a system that has been accelerated to 10-20% of the speed of light. The probe would interact with the interstellar plasma and with magnetic fields of the target solar system.

19 thoughts on “Powering Communication for an Interstellar Probe”

  1. First thing to do is lower the speed requirement. Cathedrals took hundreds of years to build. We can wait. The second thing is to lower the mass. The probe should be a biological system, a spore. When it reaches where it is going it will plant itself and grow what it needs to get back to us like solar panels and antenna.

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  2. Which only increases the odds of failure to the 100th power, of course. Unless it’s set up to allow the signal to skip several relays if one or two fail…

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  3. How does the signal booster relay probe get the power needed to relay the signal?
    It faces exactly the same power restrictions as the original probe. Albeit needing to broadcast back half the distance distance.

    But your original probe has this big power generator achieved by interacting the speed of the probe with the magnetic field of the target star. Meanwhile your relay probes are in interstellar space. They have no magnetic fields to interact with, no sunlight to get solar power from. They need batteries (probably nuclear) which the analysis above shows can’t meet the bill with current tech.

    It may be feasible with hundreds of relay probes in a long line. Each one only needs send the signal 1/100 times as far, so needing 1/10 000 times the energy.

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  4. You can’t relay the message back through multiple probes. Because the probes only generate decent amounts of power when they are decelerating through the magnetic field of the target star.
    In interstellar space they’ve got no big power source.

    And I agree, their number of 300 kJ needed for the message back home is what needs a lot more explanation and sourcing.

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  5. I have to say, I think they’re being absurdly optimistic about the power budget to transmit data across several light years, unless the plan is to send a long line of these probes, and have the signal hop from one to the next. And even then they’re being optimistic.

    Sure, as a theoretical matter, using the whole width of the probe as the aperture, in an otherwise dark universe, you could probably pull it off. But, of course, the universe isn’t dark.

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  6. I believe they’re actually doing some research into integrating laser cooling into the propulsion. In theory it ought to be possible, but would require that the laser shift frequency in a manner that tracks the speed of the sail very, very closely. Well, alternatively you could incorporate something into the sail with a tunable, very narrow absorption window.

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  7. Please stop wasting money on science-fiction. Interstellar space is a harsh environment, and we don’t have the technology to make a trip like that. All of this is academic. We should be focusing our resources on LEO infrastructure and interplanetary Business opportunities. These are the things that will get us off of this planet.

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  8. So, it turns out that as a “sort-of-smart physics goat”, I like to “flesh out” the numbers. And these don’t quite foot.  

    It is abjectly not likely that a high-reflectance extremely-low absorption ‘near magic’ metamaterial film sail can be conjured at less than 25 g/m². The diameter is 4 m. The area therefore is 12.8 m². The mass of the sail, less the frame, tethers, controller, all that, 314 g. The frame, tethers, electrical conductors … 80 g. 

    At an acceleration of 15,000 G (147,100 m/s²), the whole lot (0.396 kg) is 58,350 N. At a film-reflectivity of 90%, and absorption of 0.25% of (10% = 100% – 90%) through-radiation, … a film delivering about 6×10⁻⁹ N/W, then it takes 9,700,000,000,000 W of impinging radiation to achieve 15 kG. (kilo-G’s).  

    The sail will absorb 2.4 billion W, over 12.6 m² or 193 MW/m².  As a blackbody (best case) radiator, using T⁴ = P/σ, we get T = 7,600 °K. Rather warm. Warmer in fact than surface of Sol, our friendly giant. 

    Now that, of course, isn’t going to fly.  
    Ahem, sorry. 

    At most, the film realistically cannot exceed 500°K, or so, … so working backward, 500⁴ = P/(σ = 5.67×10⁻⁸) … → (3,500 W/m² … ÷ 0.25%) ÷ 90% = 1.575 MW/m² of actual reception energy. 

    Giving about 0.12 N, which at 0.396 kG is 0.300 m/s² (0.031 G) of real acceleration. If ΔV = at, is 20% of ‘c’ = 299,792,458 m/s then it would take 6.34 years, and 40,000 AU to achieve 20% c.

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

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  9. Added bonus: the more power you extract from your kinetic energy, the more you slow down, and the longer you get to observe the target.

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  10. Wishful-thinking based propulsion technologies, common in interstellar mission studies.

    Pixie-dust based propulsion technologies, common in sci/fi.

    Alas, they tend to not be very effective.

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