We seek to measure Pluto's albedo below 2100Å, to better constrain surface composition. COS observations will provide a substantial improvement in the S/N of Pluto spectra from <1800Å to 2100Å. Accumulation of past HST/FOS spectra yields extremely low S/N below 2000Å (S/N of only 1-3 in 100Å bins; Krasnopolsky 2001). We expect to achieve S/N=5 at 1950Å with 10Å binning. In addition to spectrally broad albedo measurements, these observations could reveal line or molecular band emission, such as C I 1931Å or CO 1993Å.

COS NUV spectra of Pluto from 1700 to 2100Å using G230L at 3000Å central wavelength, for a total of 5 orbits. Only one grating position (central wavelength) is required to cover the specified wavelength band. Observations will be divided into two visits: 2 orbits at one central meridional longitude, and 3 orbits at another; in this way, the spectra can be coadded for the greatest signal-to-noise, and compared to look for longitude-specific differences in absorption spectrum. The chosen longitudes (90 and 270 degrees) correspond to greatest angular separation of Charon from Pluto, reaching 0.85"; the position angle (CCW from north) of Charon from Pluto is about 150 and 330 degrees for these cases. ORIENT is specified in order to minimize spectral confusion, by aligning Charon in the cross-dispersion direction. ORIENT calculation: U3 axis is at 135 degrees from COS +Y (spatial) direction, and at 135+180 = 315 degrees from -Y With Pluto viewed at CML = 90, Charon is near position angle 153 degrees; Pluto-Charon vector can extend along either +Y or -Y. So we have ORIENT near 135+153 = 288 degrees or near 315 + 153 = 468 ==> 108 degrees. With Pluto viewed at CML = 270, Charon is near position angle 333 degrees (180 degrees from above). Same calculation as above -- 135 + 333 ==> 108 degrees orient, 315 + 333 ==> 288 degrees. We've specified the desired CML +/- 15 degrees, which provides ~12 hr obs windows; ORIENT window of +/- 5 degrees keeps 4+ months available. SOLAR SYSTEM 12 false 0.0 0.0 false false false false false false SUPPORTED SOLAR SYSTEM about 1 magnitude dimmer in mid-UV relative to visible, based on albedo measurements -- 0.2 - 0.25 in mid UV, instead of 0.5 - 0.66 in visible (used mV = 15 solar-type spectrum for ETC) Specified window -- CML of 90+/-10 degrees -- puts Charon near largest separation from Pluto, and at position angle near 150 degrees. F(2400)=1E-16 PLANET PLANET PLUTO STD=PLUTO CML OF PLUTO FROM EARTH BETWEEN 80 100 EARTH SOLAR SYSTEM Specified window -- CML of 270+/-10 degrees -- puts Charon near largest separation from Pluto, and at position angle near 330 degrees. F(2400)=1E-16 PLANET PLANET PLUTO STD=PLUTO CML OF PLUTO FROM EARTH BETWEEN 260 280 EARTH COS/NUV Spectroscopic No No G230L Using ephemeris for target 12042-01-PLUTO-90LONG ephemeris data for target 12042-01-PLUTO-90LONG does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 10.182 to 12.060. ephemeris interval: 10.031 to 12.032 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12042 :visit-id "01" :proposal-version -1 :trans-version "20091209" :date "24-Feb-2010 09:37:15.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "32" :si-bright-earth-limb-angle 20.0 :data-volume 252304 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12042 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12042 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 116 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12042 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 0 :internal-dur-at-end 116 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12042 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 0 :internal-dur-at-end 428 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 3 0 COS ETC: COS.A204186 for estimation of acquisition time. Assumed solar-type Kurucz spectrum with effective m_V=15.0, normal airglow. S/N = 40 in 23.5s ETC: COS.A204190 gives buffer-time of 2/3 * 26913s Using ephemeris for target 12042-02-PLUTO-270LONG ephemeris data for target 12042-02-PLUTO-270LONG does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 10.182 to 12.060. ephemeris interval: 10.031 to 12.032 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1282988168000 100.0 (Tic-Visit :proposal-id 12042 :visit-id "02" :proposal-version -1 :trans-version "20091209" :date "24-Feb-2010 09:37:17.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "32" :si-bright-earth-limb-angle 20.0 :data-volume 261040 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12042 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12042 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 116 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12042 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 0 :internal-dur-at-end 428 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 2 0