[AR] Re: Fast radio bursts as light sail propulsors
- From: Nels Anderson <nels.anderson@xxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 15 Mar 2017 12:36:45 +0000
On the off chance we have a few minutes before the Beserkers arrive, it
might be interesting to discuss the paper itself.
On 03/10/2017 04:01 PM, (Redacted sender monsieurboo for DMARC) wrote:
My conclusion is that the authors' equations may well demonstrate that
this */can /*be done, but they offer nothing more than handwaving
about /*how */it could be done. Lacking any details of the
engineering, I'll have to leave it in the category of "then magic
happens" for now.
I'd say the authors' engineering proposition is essentially a
30,000-km-diameter solar powersat, except that it's on a massive planet
rather than in space. Presumably most of the planet is covered with
solar receivers, microwave transmitters, antennas and radiators. If you
built a phased array all over the planet, you could minimize side lobes,
shape the beam nicely and point it in any direction you wanted without
regard to the planet's rotation. I imagine the planet's atmosphere
might be modified to prevent weather from interfering with the outgoing
microwave beams, solar collection or radiation of heat.
Aside from the gargantuan scale, it doesn't seem particularly
impossible. What does boggle the human mind, however, is the
environmental impact statement. I guess our extraterrestrial friends
are not big on those (Berserkers probably wouldn't be!).
I'm wondering, though, whether the authors aren't making too much of the
30,000-km size scale that pops out of multiple arguments (all figures
are good to an order of magnitude only):
1. At 1 AU from a sun-like star, a 30,000-km-diameter solar collector
gathers about 1e25 erg/s of power;
2. 1e25 erg/s beamed at 1 GHz through a diffraction-limited
30,000-km-diameter aperture produces the typical observed flux of 1 Jy
(1e-23 erg/s/cm2) at the typical inferred distance of 1 Gpc; and
3. A 30,000-km-diameter radiator can eliminate 1e25 erg/s of waste heat
at 100 degC.
My feeling is that there are enough variables here that three
order-of-magnitude numbers coinciding is not terribly significant.
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