PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2007-07-27 NOTE = " E-mail and other messages concerning MGS Radio Science on or about 1997/257." END_OBJECT = TEXT END From flemoine@olympus.gsfc.nasa.GOV Tue Sep 23 16:30:28 1997 Received: from olympus.gsfc.nasa.gov (olympus.gsfc.nasa.GOV [128.183.201.97]) by magellan.Stanford.EDU (8.8.5/8.8.3) with ESMTP id QAA09319 for ; Tue, 23 Sep 1997 16:30:28 -0700 (PDT) Message-Id: <199709232330.QAA09319@magellan.Stanford.EDU> Received: by olympus.gsfc.nasa.gov; Tue, 23 Sep 1997 23:30:35 GMT From: Frank Lemoine Subject: J2000 to MME To: rsimpson@magellan.stanford.edu, trish@rodan.jpl.nasa.gov Date: Tue, 23 Sep 97 23:30:34 GMT Cc: flemoine@olympus.gsfc.nasa.GOV Mailer: Elm [revision: 70.85] Content-Length: 2035 Status: O Trish and Dick: Peggy Jester mentioned today she had heard from Owen Short that there was recently a change implemented in the c-kernels. They now refer to MME (mars mean equator, rather than j2000), and that this change occurred shortly after orbit insertion. Have you heard anything about this? Is this change documented in an email messge, or memo? What would be the implications of the change? when peggy first mentioned this "change", I thought it would be internal to the c-kernels, and irrelevant if we used SPICE to dump the quaternions. Now, I'm not so sure. When I compare the quaternions on sept 13 and 14 at midnight I get (note the discontinuity, as one switches to a new CK file). the c-kernel is loaded the clock kernel is = /geod8/MGS/kernels/6310218A.SCK the s/c clock kernel is loaded the leap second kernel is = /geod8/MGS/kernels/naif0006.tls the leap second kernel is loaded utc time tag q0 q1 q2 q3 --------------------------------------------------------------------------- 1997 SEP 13 23:59:51.9985 .487651759 -.764746299 -.228377192 -.353839961 1997 SEP 13 23:59:55.9985 .489247262 -.763724921 -.227643733 -.354315809 1997 SEP 14 00:00:03.9985 .040066396 -.762847177 -.447878174 -.464611676 1997 SEP 14 00:00:07.9985 .041677038 -.762763245 -.446899431 -.465549305 Likewise if one derives the pointing, one gets: ra-x dec-x ra-y dec-y ra-z dec-z 1997 SEP 13 23:59:51.9985 47.0998 18.5697 -89.4271 65.1590 -37.4081 -15.9016 1997 SEP 13 23:59:55.9985 47.1003 18.5693 -89.8602 65.3148 -37.4899 -15.6758 1997 SEP 14 00:00:03.9985 76.9449 42.2963 -42.6712 28.5097 25.4890 -34.4065 1997 SEP 14 00:00:07.9985 76.9445 42.2956 -42.8818 28.6649 25.2502 -34.2672 what do you make of this? Frank ------------------------------------------------------------------------- -------------------------------------------------------------------------- From rsimpson Tue Sep 23 19:00:47 1997 Received: (from rsimpson@localhost) by magellan.Stanford.EDU (8.8.5/8.8.3) id TAA09471; Tue, 23 Sep 1997 19:00:45 -0700 (PDT) Date: Tue, 23 Sep 1997 19:00:45 -0700 (PDT) From: Dick Simpson 723-3525 Message-Id: <199709240200.TAA09471@magellan.Stanford.EDU> To: flemoine@olympus.gsfc.nasa.GOV, rsimpson@magellan.stanford.edu, trish@rodan.jpl.nasa.gov Subject: Re: J2000 to MME Content-Length: 525 There is little to no documentation on C-kernels. My assumption has been that they were being generated in a way that was consistent with use during Mars Observer. I've heard nothing about a change in reference. I can see why Mars mean equator might be useful for some applications, especially once the spacecraft were in Mars orbit. But I would think the J2000 reference might be more universal. Let's hope that Trish can find out what happened. Your discontinuity at the 13/14 Sept boundary is pretty dramatic.