Spitzer Documentation & Tools
Spitzer Telescope Handbook
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Appendix D.                  List of Figures


Figure 2.1: Spitzer Project organization during development phase 1996 - 2003. This diagram portrays functional responsibilities rather than reporting paths.

Figure 2.2: Spitzer Project organization during operations phase, 2003-2020. This diagram portrays functional responsibilities rather than reporting paths.

Figure 2.3: The outer shell forms the boundary of the CTA, which incorporates the telescope, the cryostat, the helium tank, and the three instruments.  Principal Investigator-led teams provided the instruments, while Ball Aerospace provided the remainder of the CTA.  Lockheed-Martin provided the solar panel and the spacecraft bus.  The observatory is approximately 4.5m tall and 2.1m in diameter; the mass at launch was 861kg.  The dust cover atop the CTA was jettisoned 5 days after launch.  (Image courtesy of Ball Aerospace).

Figure 2.4: The warm launch architecture of Spitzer as it was flown [right] is compared with an earlier cold launch concept similar to the predecessor IRAS and ISO missions.  The warm launch concept achieves the same mission lifetime and primary mirror size as the cold launch approach, but at a fraction of the cost.  Some of the reduction in cost and mass was achieved by streamlining Spitzer’s measurement capabilities, but the warm launch concept retains the core functionality required for the execution of Spitzer’s most important programs.

Figure 2.5: The phases of the Spitzer Mission from launch to decommissioning. In this diagram Spitzer is shown at the pitch angle needed to communicate with Earth. As the mission progressed, this angle increased. In this document the phrase ‘the warm mission’ collectively refers to the Warm and Beyond Missions.

Figure 2.6: Program types for science observations in the Spitzer mission. The cryogenic mission ran from August 2003 to May 2009, and the warm mission ran from July 2009 to Jan 2020. Legacy and GTO programs were cryogenic mission only, Exploration Science, Frontier Legacy and Snapshot programs were warm mission only. The dip in hours of observations during 2009 is due to IWIC. DDT time increased in 2014 for the Frontier Fields, and at the end of mission (see section 3.1)

Figure 3.1: Science instrument apertures projected onto the sky.  Because of the optical inversion in this projection, the section of sky closest to the projected Sun is on the MIPS side of the focal plane, e.g. to the right in this view.  Because the spacecraft did not rotate about the line of sight, this vector is fixed relative to the focal plane on the sky.  The IRAC sub-array fields are shown by the small boxes in the lower corners of both IRAC arrays.  (The 8.0 and 5.8 µm sub-arrays are on the right and the 4.5 and 3.6 µm sub-arrays are on the left.)  Note that for figure clarity, the widths of the IRS slits as shown are rendered substantially larger than their actual scale. The PCRS, or Pointing Control Reference Sensor, is a small visible wavelength array used initially to monitor the boresight alignment of the telescope and the spacecraft star sensors and, subsequently, to position targets on spectroscopy slits and photometry arrays.

Figure 3.2: Basic external view of Spitzer. The observatory coordinate system XYZ (shown in Figure 3.4) is an orthogonal right-hand body-fixed frame of reference.  The X-axis passes through the geometric center of the top surface of the spacecraft, is parallel to the CTA optical axis (which passes through the primary and secondary mirror vertices), and is positive looking out of the telescope.  The Z-axis intersects the line forming the apex of the two surfaces of the solar panel.   The Y-axis completes the right hand orthogonal frame.  The X-axis origin is defined such that the on-axis point between the CTA support truss and the spacecraft bus mounting surface is located at X = +200 cm, in order to maintain positive X values throughout the observatory.  The Sun always lies within 2ş of the XZ plane (i.e., the roll angle is constrained to ±2ş).

Figure 3.3: Cryogenic Telescope Assembly.

Figure 3.4: Observatory Coordinate System.

Figure 3.5: Spitzer’s solar orbit projected onto the ecliptic plane and viewed from ecliptic North.  In the rotating frame, the Earth is at the origin and the Earth-Sun line is defined as the X-axis. “Loops” and “kinks” in the trajectory occur at approximately 1-year intervals when Spitzer is at perihelion.  Spitzer’s orbit is also slightly inclined with respect to the ecliptic.

Figure 3.6: The main geometric observing constraints form an area called the Operational Pointing Zone (OPZ).

Figure 3.7: OPZ boundaries for 24 Nov 03 (0h UTC), with dots representing the actual locations of the telescope boresight for the subsequent 24 hours.

Figure 3.8: Variation of length of visibility period as a function of ecliptic latitude for all of the targets in the April 2003 ROC.  (This figure is provided as indicative of the general concepts, despite the fact that the ROC has changed substantially since April 2003.)

Figure 3.9: Total days of visibility per year in equatorial, ecliptic and galactic projections.

Figure 3.10: Example of time evolution of visibility zones over a year; see text.

Figure 3.11: Spitzer Telescope Assembly.

Figure 3.12: The deviations in the flight primary mirror surface.  The RMS error was measured at cryogenic temperatures to be 0.067 microns rms over the entire clear aperture, meeting the specification of 0.075 microns rms.

Figure 3.13: Theoretical PST for 24 microns off-axis as a function of azimuth.

Figure 3.14: Theoretical PST as function of wavelength for fixed azimuth on-axis.

Figure 3.15: Schematic view of Spitzer focal plane from above, looking down the boresight.  The solar panel is on the IRS side of the spacecraft.  This figure shows the region of the focal surface where the pick-off mirrors for each instrument are located.  This is in contrast to where the apertures project onto the sky.  See Figure 3.1 for comparison.

Figure 4.1: The life cycle of a Spitzer observation.  The detailed definition of observations will occur at the time of each annual proposal solicitation.

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