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Posted by J. J. Lodder on February 15, 2009, 6:39 am



> + nospam@de-ster.demon.nl (J. J. Lodder):
>
> > If you think that real time tracking to about one meter
> > and a fraction of a millisecond is possible
> > you should tell others howto,
>
> That was exactly my thought on the subject too. But then I wondered:
> Aren't the GPS satellites tracked to the meter or less? Don't they have
> to be, for GPS to work? On the other hand, they are much farther out,
> and so move a lot more slowly, and they are of course equipped with all
> sorts of stuff (radios, super accurat clocks and computers) that should
> let them help with their own tracking. Pinpointing a defunct satellite
> zipping along in low earth orbit by radar is probably quite a bit
> harder.

Sure, for a sat equiped with a nanosecond clock and a transponder,
no problem.

Jan

Posted by Uwe Hercksen on February 18, 2009, 4:35 am




Harald Hanche-Olsen schrieb:

> That was exactly my thought on the subject too. But then I wondered:
> Aren't the GPS satellites tracked to the meter or less? Don't they have
> to be, for GPS to work?

Hello,

Only the GPS staellites are tracked with this precision. This is
possible because these satellites are equipped with precise atomic
clocks and their orbits will pass the special ground stations for
tracking two times a day. Also the ground stations have precise and
synchronized atomic clocks. Only with the atomic clocks the distance
between several ground stations and a satellite may be measured with the
necessary precision.

A dead russian satellite could not be tracked with this precision.

Bye


Posted by Wayne R. on February 18, 2009, 7:28 am


On Wed, 18 Feb 2009 10:35:13 +0100, Uwe Hercksen

>Harald Hanche-Olsen schrieb:
>> That was exactly my thought on the subject too. But then I wondered:
>> Aren't the GPS satellites tracked to the meter or less? Don't they have
>> to be, for GPS to work?
>Hello,
>Only the GPS staellites are tracked with this precision. This is
>possible because these satellites are equipped with precise atomic
>clocks and their orbits will pass the special ground stations for
>tracking two times a day. Also the ground stations have precise and
>synchronized atomic clocks. Only with the atomic clocks the distance
>between several ground stations and a satellite may be measured with the
>necessary precision.
>A dead russian satellite could not be tracked with this precision.

Can't radar provide sufficient precision & accuracy to define orbital
ephemera adequate to calculate collision probability? (I think so but
defer to anyone with direct radar knowledge.)

Whether it's actually done or not is a wholly separate thing, of
course.

Posted by Richard Owlett on February 18, 2009, 8:36 am


Wayne R. wrote:

> On Wed, 18 Feb 2009 10:35:13 +0100, Uwe Hercksen
>
>
>>Harald Hanche-Olsen schrieb:
>>>That was exactly my thought on the subject too. But then I wondered:
>>>Aren't the GPS satellites tracked to the meter or less? Don't they have
>>>to be, for GPS to work?
>>Hello,
>>Only the GPS staellites are tracked with this precision. This is
>>possible because these satellites are equipped with precise atomic
>>clocks and their orbits will pass the special ground stations for
>>tracking two times a day. Also the ground stations have precise and
>>synchronized atomic clocks. Only with the atomic clocks the distance
>>between several ground stations and a satellite may be measured with the
>>necessary precision.
>>A dead russian satellite could not be tracked with this precision.
>
>
> Can't radar provide sufficient precision & accuracy to define orbital
> ephemera adequate to calculate collision probability? (I think so but
> defer to anyone with direct radar knowledge.)
>
> Whether it's actually done or not is a wholly separate thing, of
> course.

But that assumes "speed of light" *exactly* the same in all media -
vacuum of space, ionosphere with varying ion density/depth, and
troposphere with varying amounts of water vapor. It aint ;)


Posted by Wayne R. on February 18, 2009, 12:27 pm


On Wed, 18 Feb 2009 07:36:41 -0600, Richard Owlett

>But that assumes "speed of light" *exactly* the same in all media -
>vacuum of space, ionosphere with varying ion density/depth, and
>troposphere with varying amounts of water vapor. It aint ;)

Okay, I'm convinced and give up - there's no way to get usable
accuracy using anything on Earth to track stuff in space. (It's NBD to
track stuff on Earth using stuff in space, though, right?)

Why is the space junk "tracked" then? Just to keep count?

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