[Smwg] PIF question -- off earth aperture coordinates

[Barkley, Erik J (3970)]

Anthony, yes, agreed.  Nonetheless, this is what seems to be in use for Mars relay coordination. In our case, we are basically making sure that the PIF can address what current agency practice is.  Longer term we can certainly have a more involved discussion but the fact that this is in place and apparently working tends to make think that it's at least not egregiously "wrong" :)

Best regards,
-Erik

From: SMWG <smwg-bounces at mailman.ccsds.org> On Behalf Of Anthony Crowson
Sent: Tuesday, October 9, 2018 02:25
To: Barkley, Erik J (3970) <Erik.J.Barkley at jpl.nasa.gov>; Colin.Haddow at esa.int
Cc: CCSDS Service Mgmt WG <smwg at mailman.ccsds.org>
Subject: Re: [Smwg] PIF question -- off earth aperture coordinates

There is over 25,000 m elevation difference on Mars so yes, it may well be important there.
Altitude above sea level or some other datum requires a reference geoid. Center of the planet would seem naively at least not to, though perhaps even that is less simple than one might hope.

From: Barkley, Erik J (3970) <Erik.J.Barkley at jpl.nasa.gov<mailto:Erik.J.Barkley at jpl.nasa.gov>>
Sent: 06 October 2018 03:28
To: Colin.Haddow at esa.int<mailto:Colin.Haddow at esa.int>; Anthony Crowson <anthony.crowson at telespazio-vega.de<mailto:anthony.crowson at telespazio-vega.de>>
Cc: Bui, Tung (397G) <Tung.Bui at jpl.nasa.gov<mailto:Tung.Bui at jpl.nasa.gov>>; CCSDS Service Mgmt WG <smwg at mailman.ccsds.org<mailto:smwg at mailman.ccsds.org>>
Subject: PIF question -- off earth aperture coordinates

Colin, Anthony,


As you may recall, the PIF has an accommodation for specifying the coordinates for apertures on celestial bodies other than earth.  You may also recall that we (NASA/JPL) are supporting one of the prototypes for the PIF exchange. In working through this, we have found out that indeed the Mars relative Lat/Long coordinates are used for determining the communication geometry for the overflight orbiters.  But the PIF appears to be a tad bit deficient in that it only specifies Lat/Long whereas the current local implementation used in coordinating all of this also supplies altitude as part of the coordinate information. Given that Mars definitely has variations in local terrain altitude, I think this is in fact important to include in the PIF. In fact in poking around with the internal services I made a query that returned location information indicating over 3,300 m in elevation -- I suspect that if we are to be accurate etc. this has some bearing on the communication geometry in terms of properly reporting range and/or light time. However, somewhat interesting to me is that the altitude is from the center of the planet.  It seems a bit odd but it also makes sense in that there really is no definition of "sea level" for Mars.  So my suggestion is to add an altitude parameter as indicated below.  Perhaps we can further discuss this at the Berlin meetings.

Best regards,
-Erik


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