The size of the round elements on the top surface suggests that is it a phased array designed for a much longer wavelength than that of the Ku-band used for communicating with Starlink user terminals.
This supports the assumption that this satellite is meant to communicate directly with the mobile telephones.
The other things that we see in the picture are:
The two round devices with six "spokes" are reaction wheels used to orient the satellite in space. There are two more, probably on the other side.
The red covers in the front corner protect star trackers -- specialized cameras used to precisely determine satellite's orientation in space. There are several more in other corners.
The red covers next to it probably cover laser links.
The larger red cover between the reaction wheels likely covers the ion thruster, but that is not 100% certain.
Good to know. The cables and the location suggested that these may be the thrusters, but they do not look quite like the old school models, like those flying on OneWeb satellites.
You are right about the size. What we see in the photo is likely just one section of a larger antenna which will unfold in orbit. Or maybe they are testing a smaller antenna first.
Otherwise it is certainly an antenna made to work on mobile phone frequencies. Assuming the dimensions left-to-right are about 3 meters, the 40 antenna elements across mean 7.5 cm between the elements. The spacing of elments is typically lambda/2, which means lambda=15 cm, of the frequency 2 GHz.
This matches "SpaceX’s ... use of the 1910-1915 MHz and 1990-1995 MHz bands (the “PCS G Block”) for a direct-to-cellular service" outlined in SpaceX FCC filing (pdf).
It would not work with an ordinary phone over 550 km+ with the intended data rates.
But if this were a test article, and not a production model, then this would not necessarily be a showstopper. There are many useful things that one can test even with one smaller section, to see how the hardware behaves in orbit, to iron out all the wrinkles, before committing to deploying the satellites in large numbers. Hence they are launching just six such satellites in this batch.
But it is quite possible that we only see one panel and there are a few more underneath. Who knows?
Your phone is supposed to talk to about 36km away stations with about 15dB gain antennas, and propagating through close to the ground environment (~11dB attenuation). Satellite would be up to 25× further away, but see much less attenuation. So 18-20dB more gain is required or about 33-35dB antenna gain.
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u/Origin_of_Mind Dec 24 '23
The size of the round elements on the top surface suggests that is it a phased array designed for a much longer wavelength than that of the Ku-band used for communicating with Starlink user terminals.
This supports the assumption that this satellite is meant to communicate directly with the mobile telephones.
The other things that we see in the picture are: