[amsat-bb] Re: Malaysian airliner puzzle

[Tom Busch]

Now I get it...

The satellite "pings" the plane, which responds with "I am here."  By
measuring the round trip time between the transmit and receive signals, the
satellite can determine the aircraft's distance, and thus the angle to it.

Article here:  http://theaviationist.com/2014/03/16/satcom-acars-explained/

Tom WB8WOR

On Mon, Mar 17, 2014 at 1:28 PM, Chandler Heath <convergx at gmail.com> wrote:

> I read that the "handshakes" were still occurring when they lost contact
> with the aircraft. In an article posted here from the Inmarsat web site
> Inmarsat mentioned that they and their partner Sita are working with
> officials to use handshakes to triangulate the position.
>
> On the topic of Steering, the satellites have the capability to "steer"
> spot beams to address capacity needs, but to "steer" for one subscriber
> would make things worse for the others.
>
> Here is a link on the Sita service OnAir. I don't know how accurate it is,
> but here it is for anyone that may want to learn more.
>
> http://en.m.wikipedia.org/wiki/OnAir_(telecommunications)
>
> Sent from my iPhone
>
> > On Mar 17, 2014, at 11:11 AM, Tom Busch <tom at bloomington.com> wrote:
> >
> > Looks like I'm wrong.  The "Steering" info wasn't from CNN.  It's from
> this
> > Huffington Post article:
> >
> http://www.huffingtonpost.com/2014/03/16/malaysia-airlines-takeover_n_4972889.html
> .
> > I still would like to know how the satellite knows.
> >
> > It also says that these "pings" occur every hour, so I suppose it could
> > have kept flying for an hour after the last contact.
> > Tom  WB8WOR
> >
> >> On Mon, Mar 17, 2014 at 11:28 AM, Tom Busch <tom at bloomington.com>
> wrote:
> >>
> >> The news has been reporting that they are using the angle of the last
> >> known ping from the ACARS system to the satellite.  This is where the
> >> 40-degree arc around the satellite comes from.
> >>
> >> What I don't understand is how INMARSAT knows what that angle is.  CNN
> >> says that the satellite steers its antenna to the location where it
> expects
> >> the next ping, but that doesn't make sense.
> >>
> >> I have been looking for the algorithm, but I can't find it.  Signal
> >> strength? Some sort of electronic steering?  Trade secret?  I don't
> know.
> >>
> >> Tom WB8WOR
> >>
> >>
> >>> On Sun, Mar 16, 2014 at 10:57 PM, R.T.Liddy <k8bl at ameritech.net>
> wrote:
> >>>
> >>> Tony,
> >>>
> >>> They would use the time differential between receipt
> >>> to measure the distance versus the location of the
> >>> satellites. The more satellites, then the more accurate
> >>> the triangulation.
> >>>
> >>> 73,   Bob K8BL
> >>>
> >>>
> >>> ________________________________
> >>> From: Anthony Japha <tjjapha at earthlink.net>
> >>> To: amsat-bb <amsat-bb at amsat.org>
> >>> Sent: Sunday, March 16, 2014 4:49 PM
> >>> Subject: [amsat-bb] Malaysian airliner puzzle
> >>>
> >>>
> >>> Thanks Rick,
> >>> How do those sats determine distance to the source?
> >>> Tony, N2UN
> >>>
> >>> ---
> >>> This email is free from viruses and malware because avast! Antivirus
> >>> protection is active.
> >>> http://www.avast.com
> >>> _______________________________________________
> >>> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the
> author.
> >>> Not an AMSAT-NA member? Join now to support the amateur satellite
> program!
> >>> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
> >>> _______________________________________________
> >>> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the
> author.
> >>> Not an AMSAT-NA member? Join now to support the amateur satellite
> program!
> >>> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT-NA member? Join now to support the amateur satellite
> program!
> > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>