Subject: An (Inter)Planetary Checkout Monitor
From: Daniel Adamo <[email-masked]>
To: ATIG <[email-masked]>
Date: Tue, 01 May 2018 09:36:00 -0700

ATIG Members-

Those of you with history in trajectory operations at Mission
Control-Houston (MCC-H) will be familiar with the MSK 2300 Checkout Monitor
display.  Since its inception in the 1960s, MCC-H has always had a Checkout
Monitor with which to display a state vector's Cartesian position/velocity
components and associated orbit elements/parameters at a specified time.
Notably, all states displayed in Checkout Monitor have been geocentric
except during the brief period from approximately 1968 to 1972 when MCC-H
supported Apollo Program lunar landings.

As documented in recent ATIG uploads, my Swift software development exploits
with JPL's planetary ephemerides accessed through the Cspice library have
led to the need for a Planetary Checkout Monitor (PCM) to display state
vectors/elements/parameters from those ephemerides.  An example snapshot of
this display's current incarnation is attached.

Interactive widgets at the top of a PCM govern the state vector obtained
from JPL ephemerides when the "Fetch State" button is clicked.  The fetch
epoch may be specified as a UTC date and time or as a dynamic barycentric
time (TDB) expressed as a Julian date (JD).  Inputs to either fetch epoch
option are immediately reflected in the other such that they're always
synchronized.  Above the fetch epoch widgets are 3 pop-up menus, each with
selectable items for the Solar System barycenter, the Sun, eight planets,
Pluto, and the Moon.

The "Target Ephem." menu selects the ephemeris whose state vectors are
displayed relative to the ephemeris selected by the "Observer Ephem." menu.
Thus, a position vector in a state displayed by PCM will have the Target
object's center at its "head" and the Observer object's center at its
"tail".  In the specific case of the attached PCM, lunar geocentric states
are being displayed.  Near the bottom of PCM output, there are exceptions to
the Observer-centered theme in order to display Observer nadir position
parameters on the Target.

The "Source Ephem." pop-up menu's input governs PCM processing leading to
its final two lines of output.  The selected Source object can be regarded
as being the source of illumination or other radiation.  In the attached
example, Moon-Earth-Sun elongation near 147 deg indicates the Moon has a
gibbous phase as observed from Earth and illuminated by the Sun.  The
"Waxing" phase trend (as opposed to "Waning") indicates full Moon phase is
upcoming.  The final line's Source latitude with respect to the Target's
Observer-centered orbit is equivalent to the Sun's beta angle in MCC-H
jargon as applied to a low-Earth orbit.

Operationally, all PCM output is mono-spaced text, any segment of which can
be copied-and-pasted as desired.  You are invited to send comments or
questions about this output.  Should any of you wish to share lunar
geocentric test results at

Ephemeris Fetch UTC = 2017y 246d Sun (09-03) 11:58:50.816
Ephemeris Fetch TDB JD = 2458000.00000000d,

I'd be interested to see your results.

-Dan