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This answer to "Next Generation Arecibo Telescope (NGAT)... would combine a 314-metre-wide platform with a swarm of 9-metre dishes on top" What would that look like? links to an interesting 2021 presentation on the subject (viewable here and here) which among many other justifications emphasizes the dearth of high power astronomical planetary radar1 transmitting capability now that the Arecibo dish is no longer with us. What's now left is primarily a relatively small amount of transmitting time and power from The Greenbank Telescope, though there are future plans to expand on that.

See also

What caught my attention was the upgrade in power from something like 2 MW to 10 MW (pulsed). Over a 300 m aperture. That's a power density of about 140 watt per square meter impinging on a satellite in LEO that is unlucky enough to pass through the beam's 300 meter footprint. (LEO is still in the near field; beam really doesn't start expanding appreciably until GEO at ~40,000 km)

For a sensitive receiving antenna on a satellite in low Earth orbit, especially for some electronic communications surveillance or satellite constellations that recieve directly from handheld devices (or fancy wristwatches) that's a huge amount of power, even though it might be at a somewhat different frequency.

As much as astronomers complain about light and radio (in the form of radar, especially 24/7 day/night mapping of earth at high resolution using say 10 kW SAR) from small antennas with large divergence which can potentially burn out a radio telescope's front end receiver2, what about a potential 10 MW highly collimated beam from a large diameter radiator pointing right back at them?

Question: Do high power radar astronomers3 try to avoid beaming power at (at least some) artificial satellites as they pass overhead?


1maping of solar system body surfaces, precision tracking and imaging of asteroids - particularly those that might hit us in the future

2 How do radio astronomers avoid having their receivers burned out by ground-imaging radar from satellites?

3that's high power radar, not (necessarily) high power astronomers :-)

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  • $\begingroup$ related space.stackexchange.com/questions/8661/… Mind also, that solar intensity is ~1400W/m^2. So 140W is only 0.1 of that... but possibly at sensitive frequency $\endgroup$ Aug 19, 2023 at 6:38
  • $\begingroup$ @planetmaker non sequitur - a completely irrelevant red herring considering how radio receivers work. $\endgroup$
    – uhoh
    Aug 19, 2023 at 7:36

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Yes, If the satellite is at zenith do have protocols and codes to address this like Arecibo dishes.

140 W is a lot less, as compared to the solar constant and even normal lasers, which is not considering the decay in intensity to LEO (which would be near 110 W/m2), though satellites have shields adapted for the spread of signals, homogeneous/non-isotropic signals where as these send signals that are much more focused and monochromatic.

It could have 50-50 chances of penetrating the shield and causing damage to sensitive electronics, because the shielding, aluminum is a natural Faraday's cage, it shields it from radiation (the mesh in the microwave). But few areas where it is not shielded, the radiation would penetrate harming the equipment and payload.

However the major reason of caution is not this, if it sensitive to the particular band, transmitted by the telescope, it will consider it as an uplink and cause disturbance in it's signal and the noise to signal ratio would be uneven, leading to wrong data, and perhaps abnormal behavior.

That's why few uplink stations transmit at an protected frequency so that other things capable of transmitting don't overlap and coincide with the frequency.

One more issue, would be if the downward facing antenna, detects it. Because it would amplify the signal many times, which would lead to overheating. Actually via the conversation of Etendue, the intensity of the signal amplified could never by greater than the source, so technically the heating caused by the light rays, would be similar to the heat required to produce those light, though the uplink has safety precautions, the satellite may or may not have the heat dissipation equipment therefore there is a high chance of it getting overheated and damaged.

I would like to give one example (as specified in this paper), which the other way around when a Starlink satellite had electromagnetic leakage from it's equipment , it interfered with radio telescopes (not radar) so similarly signals from Earth can be easily heard till the LEO at least there is a pretty decent chance that this occurs, considering the amount of satellites in the sky.

Thanks!

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  • $\begingroup$ @asdfex Sure. Sorry for the inconvenience $\endgroup$
    – Arjun
    Aug 19, 2023 at 10:09
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    $\begingroup$ I mention SAR and communications satellites in my question, which have downward-pointing antennas connected to sensitive amplifiers. These could find themselves staring directly into the 140 W/m^2 beam with front-end amplifiers sensitive enough to pick up nanowattt signals. That's not something that shielding addresses. $\endgroup$
    – uhoh
    Aug 19, 2023 at 10:30
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    $\begingroup$ Please use the correct capitalization for units. Capitalization may not matter for British or US units, but it matters in the Metric system & its scientific offshoot, SI Units. $\endgroup$
    – Fred
    Aug 21, 2023 at 5:54
  • $\begingroup$ @Fred Thanks, Noted. $\endgroup$
    – Arjun
    Aug 22, 2023 at 10:41
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    $\begingroup$ @Uhoh Thanks for telling me that, I am updating my answer $\endgroup$
    – Arjun
    Aug 22, 2023 at 10:49

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