STO Observing Tables
18-Dec-2011 DRAFT
Methodology
Based upon the minutes of the science telecons, latest information on the instrument, and constraints
imposed by elevation limits and battery charging from the solar panels, I have generated a set of
observing schedules for distinct phases of the flight. In this document, I introduce the phases of flight
along with the associated tables for the first three.
Phase 1
The first phase of the flight is characterized by a set of engineering and initial science goals, and limited
by a lower elevation limit of 45 degrees. On the engineering side, we will be tuning the receivers and
determining our pointing offsets. At the same time, the first science goal is to get spectra of any kind
out of our receivers to prove that they work. To find the pointing sources (NGC 3576 and G322.164) we
will start with a spiral map of 5’x5’ squares starting at the expected bright center spot previously
observed with AST/RO in CI and spiraling outwards from there. Once the CI peak is found with the
spiral, we will recenter the coordinate system and move to phase 2. As you’ll see in Fig. 1 (Dec 25 with a
45 degree lower limit), the pointing sources are not always available so we will also begin small maps on
the nominal bright CII spot in G328 and the 330 and 342 b-strips.
Fig 1: STO visibility over McMurdo on Dec 25 with a 45 degree lower limit. Green indicates positive solar
panel charging of the batteries (45 degree solar angle +-20), while red is discharging, and yellow is just
beyond the positive charging cutoff and so may be neutral (but in any case for the 342 b-strip the Sun
moves to a better position day by day after Dec 25).
Phase 2
We begin phase 2 with our pointing understood and the receivers fully tuned. Around this time we will
be able to bring the lower elevation limit down to 40 degrees as the LHe slowly boils off in the dewar.
This 5 degree elevation change makes a big difference for our visibility, as seen in Fig 2, and we are in a
good position for charging the solar panels. We probably will still be looking for a good CII spectrum,
and thus the map on G328 is still small (5’x5’) alternating OTF scans in the l and b-directions to
crosshatch the region, and is supplemented by the 330 and 342 bstrips to fill out the 24 hour period.
Pointing checks on G322.164 and NGC 3576 are still undertaken periodically to confirm our pointing
knowledge at CI and to determine if there is a bright CII spot in our pointing sources.
Fig 2: Comparing to Fig. 1, with a lower elevation limit of 40 degrees, the visibility changes dramatically
and with the date change to Jan 1, the 342 b-strip is now fully in the green. The G322 pointing source is
starting to drift out of the positive charging angle and hence is now yellow.
Phase 3
With a CII spectrum on one or more sources in hand, phase 3 should follow quickly on the heels of phase
2. Phase 3 is characterized by larger maps (0.5 deg x 0.5 deg) to place the CII in context and should yield
a map of CII around whatever peaks we have found. Eta Car now appears in the observing table, but it is
difficult to schedule since it discharges the solar panels and conflicts with the 342 b-strip. We may need
to take some test observations there and decide whether it is worth the battery charge that will be
required.
Phase 4
Phase 4 begins when the LHe runs out. With no LHe, the constraint on elevation may be removed if we
have chosen not to place a hard-limit strap on the dewar (yet to be determined). If there is no elevation
limit, the visibility constraints are as shown in Fig. 3. Note that as the Sun continues to move, we will be
focusing more of our efforts around the 342 b-strip since locations at lower l along the Galactic plane
will not be achievable for more than a few hours at a time as the battery discharges. I have not yet
prepared an observing table for Phase 4, but will do so once we decide upon the trade-offs for the warm
mission.
Fig 3: 15 days later the Sun has moved substantially, but with a lower limit of 0 degrees, the 342 b-strip
is available 24 hours a day with positive charge.