Re: [Starlink] Starship's 4th flight test was magnificent

[David Lang <david@lang.hm>]

Ulrich Speidel wrote:

> The opposite case occurs (in principle) when transmitting from the 
> ground (or a re-entering spacecraft) to a non-GSO sat above you, with a 
> geostationary sat lurking behind your satellite in the distance. In this 
> case, the bit of signal beam (think light beam as in car headlights) 
> that shines past the non-GSO sat - you could jam that satellite's 
> receiver and spoil someone's Superbowl (or worse, Superbowl ads!). This 
> is somewhat less critical than the opposite direction, though, mainly 
> because you're trying to hit a target that's maybe 1000 km away whereas 
> the part of the geostationary orbit that cops the beam leftovers is 
> 40,000 km or so away. This means that your signal (which suffers 
> spherical spreading) is around 40^2=1600 times lower at the 
> geostationary sat than at your intended receiver. That's about 33 dB in 
> difference, which helps, but then again, the geostationary satellite 
> user's uplink suffers the same spread - and may not be aiming at 
> producing the same signal level at the satellite antenna as you are 
> aiming for on your non-GSO satellite. So there is also a risk here of 
> some interference. But in most cases, transmitting up is OK and power is 
> more of a matter of what you can afford down on the ground (OK, it's 
> more complex than that, but that's for another post).

As I understand it, Starlink does not have ground stations transmit towards the 
geostationary satellites, they only target the starlinks when they are not in 
line to avoid exactly this problem)

> Conventionally, if you had to communicate your re-entry video or audio 
> feed to a ground station, you had to communicate *through* that cone's 
> wall. Similarly, if you wanted to go "up", you had to go to a TDRSS 
> satellite, of which there were only a small number in orbit - and the 
> one visible to you would have been on the other side of the plasma cone 
> wall with high probability. With Starlink, you have potentially a few 
> dozen satellites within field of view, and the chances of having one 
> within view out the back of the cone are relatively good (but not 
> guaranteed). The other day, they got lucky that the star(link)s lined up ;-)

As I underand it, it's not just luck, the Starship is so much larger than 
anything else that the plasma does not just wrap around the craft and close up 
behind it, the sheer size of the craft gives the plasma a chance to cool a bit 
(and you can see that in the videos)

Also, if it was 'luck' then they were lucky on both Starship reentry flights 
(and since the ship was tumbling during flight 3, that would be saying a lot)

David Lang