[LEAPSECS] LEAPSECS Digest, Vol 51, Issue 23

Finkleman, Dave dfinkleman at agi.com
Mon Feb 7 14:37:38 EST 2011

This discussion exposes the fact that we don't all have to work in the
same reference frame or time system - as long as we understand what we
are using and make it clear to users. Orbit data transfer standards
developed by CCSDS and others require sufficient metadata that users can
reproduce your results with the same outcome and transform your data
into the time system and reference frame they wish to use. Metadata
also includes characteristics of the geopotential model. There is no
point in propagating to high order and degree initial information that
was created at low order or degree, for example. Unfortunately, some
operators don't know what is inside the black box. We accommodate this
by requiring the fields but not the real content. If geopotential info
fields are filled with default characters, we know that this idiot
doesn't even know what he did and discount his input. Lying is another
story. However, there are institutional sanctions for providing false
information. Like, you get cut off from everyone else's data.

These lessons came hard. For example, lack of gravitational metadata
led to low perigee events in Superbird 6, a Comsat. The launch provider
included lunar gravitation and the on-orbit operator did not. The
handover state provided by the launch agency did not lead to the desired
final orbit for the operator.

With regard to what is significant and what is not. If someone raised
the issue, then it must be significant to him. If the others don't care
or it doesn't matter to them, it won't matter if they have the
additional information or greater precision. I've said this before, "We
don't create standards for people who don't need them. We create
standards for those who do need them." The "don't cares" usually don't
get a vote. GRACE mission data is available in near real time for those
who worry about Earth tides and millimeters of ocean height! (The units
are cm/sec^2, which are now called Gals -- for Galileo.)

Dave Finkleman
Senior Scientist
Center for Space Standards and Innovation
Analytical Graphics, Inc.
7150 Campus Drive
Colorado Springs, CO 80920

Phone: 719-510-8282 or 719-321-4780
Fax: 719-573-9079

Discover CSSI data downloads, technical webinars, publications, and
outreach events at www.CenterForSpace.com.

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