4 ms·

I'd bet someone could pretty easily build an alarm that goes off every time one of these things is looking at you. That radar blast has got to be massive. This

by px43 6y ago

I'd bet someone could pretty easily build an alarm that goes off every time one of these things is looking at you. That radar blast has got to be massive. This definitely couldn't be a 24/7 thing from those satellites. I wonder how much radar time one of those things has before it needs to recharge/refuel.

leoedin 6y ago
Power usage isn't necessarily huge. I worked on a SAR satellite a few years ago with a total RF power of <1kW. It's pulsed as well - you send an RF "chirp" at a sub-1kHz pulse frequency. Depending on imaging mode the average power draw is probably in the 500W-1kW range. That had a much larger resolution (6m rather than 50cm), but the resolution is a function of frequency and antenna design as much as power. The SAR concept essentially creates an image by sending out a known RF chirp and then, for each pixel of the image, correlating the response with the expected signal from that pixel. That correlation means that even if the received signal is below the noise floor you can create an image.
- px43 6y ago
  Great info, much appreciated. Still seems like kind of a lot of something that's supposed to live in space for years at a time. Presumably solar panels recharge a battery when it can, but continuous operations seem out of the question without some pretty large panels. Maybe I'm underestimating modern solar panels or something.
  - madlag 6y ago
    Efficiency of solar panels on satellites is about 40%. That means ~ 700W/m2 if correctly oriented. That's quite a lot of power, even if you stay 50% of the time in night while orbiting Earth. So no need for huge panels usually. (Updated : more like 40%, not 50%)
asdfadsfgfdda 6y ago
Or just track the orbits, these are all published by NOARD. Most satellites do not change orbits often. Even easier, Capella-1 is in a sun synchronous orbit, so it will always pass overhead at the same local time, at noon or midnight. https://www.n2yo.com/satellite/?s=43791 https://www.n2yo.com/satellite/?s=43791

by px43 6y ago

leoedin 6y ago

Power usage isn't necessarily huge. I worked on a SAR satellite a few years ago with a total RF power of <1kW. It's pulsed as well - you send an RF "chirp" at a sub-1kHz pulse frequency. Depending on imaging mode the average power draw is probably in the 500W-1kW range. That had a much larger resolution (6m rather than 50cm), but the resolution is a function of frequency and antenna design as much as power. The SAR concept essentially creates an image by sending out a known RF chirp and then, for each pixel of the image, correlating the response with the expected signal from that pixel. That correlation means that even if the received signal is below the noise floor you can create an image.

px43 6y ago
Great info, much appreciated. Still seems like kind of a lot of something that's supposed to live in space for years at a time. Presumably solar panels recharge a battery when it can, but continuous operations seem out of the question without some pretty large panels. Maybe I'm underestimating modern solar panels or something.
- madlag 6y ago
  Efficiency of solar panels on satellites is about 40%. That means ~ 700W/m2 if correctly oriented. That's quite a lot of power, even if you stay 50% of the time in night while orbiting Earth. So no need for huge panels usually. (Updated : more like 40%, not 50%)

asdfadsfgfdda 6y ago

Or just track the orbits, these are all published by NOARD. Most satellites do not change orbits often. Even easier, Capella-1 is in a sun synchronous orbit, so it will always pass overhead at the same local time, at noon or midnight. https://www.n2yo.com/satellite/?s=43791 https://www.n2yo.com/satellite/?s=43791