JF Mezei wrote on Sat, 8 Jun 2019
13:52:24 -0400:

On 2019-06-08 05:05, Fred J. McCall wrote:

Do the ****ing math. Given 50 satellites per orbital plan at around
400 km altitude

One orbinal plane at 340km, 50 satellites. Each travels at roughly
27,000kmh covering circumference of roughly 42,000.

Do the math. That is one satellite in that one orbital plane passing
avery 1.9 minutes.


Uh, so? You must have a hell of a time merging with traffic, since
I'm pretty sure there is a lot less than 1.9 minutes between cars in
the traffic stream.


Now, the 340km altitude will be covered by 7500 satellites, at 50 per
orbital plane, this means 150 orbital planes, or roughly one orbital
plane every 2.5°, or about 300km apart. So if you target re-entry to
pass between 2 satellites in one orbital plane, odds are there will be
satellite in the orbital plane 300km away.


So what?


Remember that in order to provide reliable service, there needs to
always be at least one low orbit satellite over any one spot in served
areas.


No. There needs to be at least one low orbit satellite with LINE OF
SIGHT. This is not the same thing as 'over'.


So if BFS is targeting a landing at the Wall Street heliport in
Manhattan, odds are that there will be a satellite over Manhattan at any
point in time.


No. There will be a satellite with LINE OF SIGHT to Manhattan. Not
the same thing as 'over'.


The problem is that when you land on a target, your de-orbit time needs
to be very precise to hit that target landing zone.


This is really only true for a pure ballistic reentry. Nothing that
reenters under control is pure ballistic.


But if that time
doesn't coincide with a 2 minute gap between satellites, what do you do?
wait for an orbit where the de-orbit time does match a gap between 2
satellites?


Think about it. A satellite will move roughly 7.5 km in ONE SECOND. So
any given satellite is 'in the way' for something like 400
milliseconds, even if you adopt a preposterous 'safety window' of
missing by at least a kilometer.


If youa re targetting "somewhere" in the Pacific ocean, then you have
much more leaway in when you de-orbit and thus can more easily find a
gap through which you can pass.


No. Space is mostly empty regardless of where you want to come down.
Think about it. If you for some reason need to fly directly through
the orbital plane of a group of satellites (already a bad assumption,
as you could simply avoid that) your path to ground will be blocked
for 0.4 seconds every 114 seconds even if you use a huge safety margin
like 1 km. That's like you're blocked for 0.35% of the time. In
other words, your flight path is clear more than 99.6% of the time. If
you DON'T need to fly straight through one of those orbital planes,
your flight path is clear 100% of the time.


Now, add not only Starlink but also Oneweb. Does the math still resuilt
in the "no brainer" you assume?


Yes. And I didn't 'assume' anything. I understood the issue, which
puts me far, far ahead of you.

If you
can't hit a 1600 kilometer 'slot' to reenter, you probably have no
business putting things in orbit.

How did you come up with 1600km?
Circumference at 340km altitude is ~42000km. You have 50 satellites,
that means 840km between satellites. It takes 1.9 minutes for a
satellite at ~27,000kmh to travel 840km.


I apologize. My number is a bit less than twice too large as I
accidentally took a figure for Earth diameter as radius. My error
should have been obvious to you, SINCE I GAVE THE BLOODY NUMBERS I
USED (which you apparently 'cleverly' removed).


Repeat this for the 1 or 2 orbital planes to the west, knowing that
satellites in orbital plane are strategically phased to cover the gaps
between 2 satelites in the orbital plane next to it (to ensure customers
have continued connectivity).


No. You still only have to fly through, at most, ONE orbital plane,
which means you are blocked AT MOST for 400 milliseconds out of each
114 seconds.

Even taking your preposterously large upper number of 100 km for a
'near miss' (the actual 'warning threshold' is about an order of
magnitude smaller than that)

So they are happy with 10km distance from another satellite during
er-entry? Is re-entry considered with same standards for distance
between objects in stable orbits with constant speeds and altitude?


Actually they're 'happy' with much closer passes than that. That 10
km is the 'alert threshold' for DEBRIS. It's that big because debris
aren't under active control and because it's merely a "you might want
to start paying attention to this" alert.

yourself and eliminate a lot of stupid questions on your part.

If you know everything, yet unwilling to explain without insults, whyt
do you even come here?


If you know nothing, yet unwilling to do any work at all to inform
yourself, why do you even come here?

This isn't your personal teaching hospital, bucko. The rest of us
don't exist to answer your stupid questions only to have you then
argue about the answer because reality just isn't what you wanted. You
need to do one of two things. You either need to actually inform
yourself and then argue or else ask questions and say 'thank you' when
someone exerts the effort to answer you. Note that your typical
combination of ask questions and then argue with the answer is right
out.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn