Herschel Observers' Manual

List of Figures

1.1. Roll-out of the launcher for the Herschel-Planck mission on 13 May 2009 with the dark, threatening storm clouds visible behind.

1.2. Launch of the Herschel-Planck mission on an Ariane 5-ECA at 13:12:02UT on 14 May 2009. The Herschel-Planck mission logo is clearly visible at the top of the fairing. The fine weather and clear blue sky contrasts sharply with the conditions for roll-out (Figure 1.1), or those prevalent only a few hours before launch as the VIPs were taken to the launch viewing area in heavy rain during an intense storm.

1.3. Herschel flies free! The moment of separation of Herschel from the Sylda, which is still attached to the upper stage and covering Planck. This image was taken with the backward-facing camera on Herschel: called the VMC. The coastline and cloudscape below Herschel are clearly visible.

1.4. A sequence of images taken by British amateur astronomer Richard Miles using the 2-m Fawkes South Telescope in Australia, of Herschel (right), Planck (left, incorrectly labelled as Herschel) and the Sylda between the two, 26 hours after launch, at approximately half the distance to the Moon. These were the first observations of the Herschel-Planck constellation to be reported. The movement of the three relative to the stars in the three minutes between the first and last image is quite obvious.

1.5. The telemetry received at MOC showing the oscillation in gyro response measured by the current to the gyros as the heavy cryocover swung open and oscillated, causing the entire satellite to wobble slightly until it had reached a stable open position. The large oscillation seen in this gyro signal (marked by the mauve coloured vertical lines on the monitor screen), showing the gyros activating to stabilise the satellite orientation, was the first evidence that the cryocover opening had been carried out successfully. Five or six oscillations occurred before the spacecraft stabilised completely again.

1.6. A comparison of images of M51 at 160 microns for ISO, Spitzer and the Herschel sneak preview image, showing the improved resolution and sensitivity from Herschel's larger mirror. No comparable image exists from IRAS, which had a long wavelength cut-off of 100 microns, so the IRAS 100 micron image is shown for comparison. The comparison of images also reflects the vast improvements in detector technology over the years.

1.7. The Sneak Preview images of M51 in the three PACS bands, taken blind after cryocover opening on June 14/15th 2009.

1.8. The SPIRE First Light images of M74 (NGC 628) in 250, 350 and 500 microns, obtained on 2009 June 24. Messier 74 is a face-on Sa galaxy in Pisces, at approximately 32 million light years distance with a visual diameter of approximately 10 arcminutes.

1.9. The SPIRE First Light image of M74 (NGC 628) combined as an RGB image (B=250 microns, V=350 microns, R=500 microns), obtained on 2009 June 24, compared with a Palomar Sky Survey RGB image on the same scale (blue layer = B, green layer = R, red layer = I) to show the comparison between the SPIRE first light image (right) and the Palomar Observatory Sky Survey image (left). This comparison shows where the star forming regions of the galaxy, bright to Herschel, are situated.

1.10. The HIFI First Light spectra of DR21, obtained on 2009 June 22, superimposed on a Spitzer image of DR21 and its surrounding region. In the inset we see an enlargement of DR21, which is part of a large star-forming complex in Cygnus, with the positions where the three HIFI spectra represented were taken, superimposed on the image.

1.11. The browse product for the first successfully processed scheduled science observation made by Herschel. This is OBSID 1342183651 of the QSO SDSSJ1602+4228, made for AOTVAL_kmeisenh_2, a 2799 second exposure starting at 15:52:46UT on September 11th 2009 in Point Source Photometry mode showing an apparent faint detection at 160 microns (right hand image) where we see the weak pattern of negative and positive images from the chop/nod cycle that must be combined to give the final image and photometry. The left hand image was taken at 70 microns.

1.12. The browse product for the first scheduled science images taken of a Solar System Object (SSO) made by Herschel. These are OBSIDs 1342183654 (top, 100 microns left, 160 microns right) and 134218365 (bottom, 70 microns left and 160 microns right) of Pluto, made for AOTVAL_thmuelle_2, starting at 17:01:46UT and 17:30:17UT on September 11th 2009 in Point Source Photometry mode. We see the pattern of negative and positive images from the chop/nod cycle on the individual photometer matrices, which must be combined to give the final image and photometry.

1.13. The browse product for the first SDP observation made by Herschel. This is OBSID 1342183677 of the QSO RXCJ0658.5-5556, made for SDP_eegami_3, a 6631 second exposure starting at 02:51:12UT on September 12th 2009 in SPIRE large map mode. This is an RGB image with the SPIRE 500 micron channel as the red layer, 350 microns as green and 250 microns as blue.

1.14. The browse product for the first SPIRE spectroscopy observation made by Herschel. This is OBSID 1342187893 of the AGN Mark 231, made for SDP_pvanderw_3, a 7141 second exposure starting at 07:17:14UT on December 9th 2009.

1.15. The browse product for one of the first HIFI science observations made by Herschel on the first day of the HIFI PSP programme (actually the 4th HIFI observation of PSP). This is OBSID 1342191484 of Sgr B2, made for KPGT_ebergin_1, a 61 second exposure starting at 06:29:20UT on March 1st 2010.

1.16. M31's once and future stars. A combined Herschel and XMM-Newton (x-ray) image of M31 showing dusty star-forming regions (Herschel) and the point-sources that represent highly evolved stars (XMM-Newton). The Herschel data were taken at 250 microns with SPIRE between 17 and 21 December 2010. In the XMM-Newton RGB image, red sources are those that have soft x-ray spectra, dominated by low-energy x-ray emission; these are normally low-mass x-ray binaries, while the blue sources are sources with hard x-ray spectra, dominated by high-energy emission, which are high-mass compact binaries with a neutron star, or black hole secondary. This image contains what is effectively a snapshot of the star formation history of M31 and its two satellite galaxies, M32 (superimposed on the spiral arm below the nucleus of M31) and M110 (very faintly visible in the Herschel image to the top right). Whereas M110 is essentially a dying galaxy, with only a tiny residual of star formation and no massive stars at all, M31 is very much alive and boiling with star formation activity in the dark rifts between its spiral arms.

1.17. Galaxies spread like grains of sand on a beach. Every source in this GOODS-N field, which is about the size of the Full Moon, is a distant galaxy. The insert to the left shows the indivdual frames in each of the SPIRE bands while the main image combines them as an RGB. The colour of the galaxy gives an indication of its red shift and, hence, distance: the reddest galaxies are the most distant and may be as much as 12 000 million light years away; blue objects are relatively nearby and may be as close as 6000 million light years. In the inset to the lower left we see, to the same scale, the very best sub-millimetre image of this field that had ever been obtained from the ground at this time. This inset image is the result of 20 nights of exposure from Mauna Kea with the James Clerk Maxwell Telescope + SCUBA, in exceptional observing conditions; this image is to the same scale as the Herschel image - the full SCUBA field is 2.5 arcminutes diameter - and shows exactly 5 sources compared to Herschel's 15000 sources in the full 4x4 degree field of this region, detected in just 16 hours of exposure.

1.18. Cryostat temperatures from April 28th to May 4th 2013. The graph is initially stable at 1.7K before starting to rise around 12:30UT on April 29th, marking the evaporation of the last drop of helium. The solid black line marks the point at which an internal temperature of 2.0K was reached, marking the formal criterion for declaring End of helium. The plot shows the slow rise of the cryostat temperature after End of Helium (EoH) was declared. Temperature curves are shown for the T111 (red curve), T106 (navy blue curve) and T107 (green curve) sensors, which were in different positions inside the cryostat. As each sensor went out of limits it shoots vertically off the scale. Approximately five days after boil-off the temperature reached 20K and the T106 and T107 sensors went out of limits simultaneously (Graphic courtesy: MOC).

1.19. The final science observation executed before End of Helium. There is a strong detection of the OH line at 1107.9GHz (270.6 microns) in the HIFI Band 4b spectrum of the star OH 32.8-0.3. The two panels show the horizontal (left) and vertical (right) polarisation component of the spectrum.

1.20. Herschel departing Lagrange, observed from Earth 17h before the main burn started. This image was taken on May 12th 2013, by British amateur astronomer Peter Birtwhistle, from Great Shefford Observatory (Minor Planet Center site code J93), approximately 90km west of London, using a 40cm reflector. The image is the sum of 60 individual exposures of 20s each, stacked on the motion of Herschel. The field of view is 6.6 arcminutes wide by 8.2 arcminutes high.

1.21. Screen in the Main Control Room at MOC showing (left hand plot) the rapid drop in pressure in the reaction chamber of the thrusters as the fuel was exhausted. This drop in pressure indicated that the fuel was close to exhaustion, allowing the final commands to cut the burn, stabilise the spacecraft and to passify to be carried out in a controlled manner.

1.22. Martin Kessler, Head of ESA's Science Operations Department, sends the final command to Herschel at 12:25 GMT (14:25 CEST), 17th June 2013, from the Main Control Room at ESOC, Darmstadt.

1.23. The screen in the Main Control Room at MOC showing the output from the frequency analyser. This would normally show a strong signal at the frequency of the Herschel transponder. The flat line shows that the signal from the Herschel transponder had dropped to zero after switch-off. The point at which the transponder signal dropped to zero marked the end of the Herschel mission.

1.24. Telemetry on one of the consols in the Main Control Room at MOC showing the flatlining of the telemetry after transponder switch-off.

1.25. The last ground-based image of Herschel taken to date after passivation. This image was obtained on 2013 September 24 by British amateur astronomer Richard Miles, with the 2.0-m Fawkes South Telescope at Siding Spring. The total exposure is 85 minutes in very good seeing, made of 34 individual 150s exposures, tracked on the predicted motion of Herschel. Even in such a deep exposure, taken in good conditions, Herschel is right at the limit of the capabilities of this telescope.

1.26. The light curve of Herschel from all observations reported to the Minor Planet Center (MPC) from launch until September 2013. During the initial stages after launch the different members of the Herschel-Planck constellation were reported as Planck, HP01 (Sylda), HP02 (Herschel), HP03 (Upper stage), HP04 (unidentified co-orbiter), etc. The brightness of Herschel was strongly dependent on its orientation and was, in a single night of observation, observed to vary by more than 5 magnitudes (greater than a factor of 100 in brightness) according to what reflecting surfaces were presented to Earth as the telescope slewed around the sky. The rapid fade as Herschel moved away from Lagrange in summer 2013 is obvious in this plot.

2.1. The Herschel spacecraft had a modular design. On the left, we see the "warm" side and on the right, we see the "cold" side of the spacecraft, the middle image details the major components.

2.2. The Herschel telescope flight model seen in the clean room at ESTEC, prior to transport to Kourou.

2.3. The Herschel cryostat.

2.4. The Herschel service module.

2.5. Herschel s/c axes (from [RD1])

2.6. Left:The position of the Lagrange points for the Sun-Earth/Moon system. L2 lies 1.5 million kilometres from Earth. Right: An example of a Lissajous orbit around L2. The orbit x and y-axis are as shown in the plot on the left, the z-axis is normal to paper.

2.7. A representation of Herschel's orbit around L2 from top, side and front perspectives (i.e. seen along the z, y and x axes). The Earth is located at (0,0,0) in each plot. The red tracks are the projection on the three orthogonal planes of the 3D orbit from launch through to the end of June 2013, showing its position (blue dot) on May 8th 2013, nine days after End of Helium, already moving away from L2 as a result of the initial escape manoeuvre, which can be identified as a kink in the track, particularly in the perspective from above (top left), above the Earth's orbital plane. The horizontal and vertical axis scales are different, thus the orbit's shape is severely distorted in this view, although details of the individual loops around L2 are better visible than in an equal axis plot. A plot with the two axes on an identical scale to remove this distorion is shown in Figure 2.8. Plot generated by Jon Brumfitt based in the orbit file generated by the Flight Dynamics Team at MOC.

2.8. Herschel's orbit from launch to the end of June 2013, as for Figure 2.7 plotted with equal axis scales to give a more faithful representation of the orbit shape, at the cost of some loss of fine detail. The rapidity of the satellite's drift away from L2 after the disposal burn is manifest in this image. Plot generated by Jon Brumfitt based in the orbit file generated by the Flight Dynamics Team at MOC.

2.9. Top: The sky visibility across the sky as a fraction of the total hours through the Herschel mission, represented as a colour scale (shown at right) where black represents 30% visibility and white represents permanent sky visibility. Bottom: sky visibility for two sample dates. Shadowed areas represent inaccessible sky areas.

2.10. A schematic diagram of the Herschel/Planck avionics.

3.1. The Herschel Focal Plane showing the field of view of the telescope and the positions of the different instrument apertures within it. The purpose of the telescope SIAM (Spacecraft Instrument Alignment Matrix) was to provide exact offsets to each of the apertures from the reference position used in pointing so that the target is accurately centred in the aperture of interest.

3.2. The black body spectrum of the far infrared dust peak of a star-forming galaxy of 10 solar masses showing the effect of redshift on the spectrum. At z=5 the peak moves to the long-wavelength end of Herschel coverage with SPIRE. The result of this is that the colour of a galaxy in a SPIRE RGB image gives a good estimate of its redshift and thus distance, with strongly red galaxies in SPIRE image being the most distant.

3.3. A PACS 70 micron image of the debris disk around Fomalhaut. The debris disk is well resolved. This is one of the few cases where Herschel also detects a hot star as, at 16 light years distance, Fomalhaut is close enough to be strongly detected at short wavelengths.

3.4. An RGB image of Betelgeuse and its environment constructed from PACS images at 70, 100 and 160 microns. North is to the top left and east to the bottom left in this view. A series of arcs can be see to the left (northeast) of the star; these are shells of material shed by the star in its supergiant phase. An intriguing feature of this image is the vertical bar to the left, which it is hypothesised may be the edge of an interstellar cloud that is being illuminated by the star; if so, the outer shell will collide with it in approximately 5000 years.

3.5. An example of use of the SPIRE PACS Parallel Mode. This is a Galactic Plane image from L=316 degrees, just north of Alpha Centauri, taken by the Hi-GAL project, as part of their 360 degree survey around the Galactic Plane. The use of bands from 70-500 microns in a single observation allows the different warm and cool dust emission to be identified, sampling a wide range of temperature and of physical conditions. The ability of Parallel Mode to cover large areas of sky rapidly was vital to the success of the Hi-GAL mapping.

3.6. A PACS composite spectrum of Neptune from 57 to 190 microns (upper pane) and the corresponding line identifications (lower pane). The spectrum is dominated by water emissions at short wavelengths, with methane, carbon moxide and deuterated hydrogen important above 90 microns. From Lellouch et al.: 2010, A&A, 518, L152

3.7. A full spectrum scan of Orion KL taken with HIFI for KPGT_ebergin_1. This spectrum shows the extraordinary number of spectral lines visible in this source. A total of 75 000 lines have been detected in the spectrum, only 20 000 of which have been identified so far, of which 5000 are from methanol. The gap in the spectral coverage between bands 5b and 6a is clear in this view with its linear frequency scale.

3.8. The sky distribution of AOR centres for the 11650 accepted Key Programme AORs. Although there is a concentration both in the Galactic Plane and at the Galactic Poles, the overall distribution is remarkably homogeneous.

3.9. Proposal Handling System load at closure of the OT2 Call. Shortly before closure the system was receiving and processing a proposal submission every 15 seconds.

3.10. Comparison of the Proposal Handling System load at closure of the OT1 and OT2 Calls. The pattern is almost identical, demonstrating that the Herschel community are creatures of habit!

3.11. Comparison of the fraction of time requested for each of the Herschel instruments (counting SPIRE PACS Parallel Mode as a separate instrument) as a function of the three major Calls for Proposals during the mission. The overall level of demand for the instruments changes very little from Call to Call although it is noticeable that demand for Parallel Mode decreased sharply after the Key Programme Call as it became evident that, for many programmes, it was more efficient to use SPIRE only. In flight knowledge of the instrument performance showed that Parallel Mode had only very limited applications for cosmological programmes due to the far shallower depth reached by the PACS component of the data.

3.12. Comparison of the fraction of time requested for each of the Herschel sub-instruments as a function of the three major Calls for Proposals during the mission. The relative demand for the different sub-instruments was remarkably stable between the closure of the initial Call in 2007 and the final Call in 2011.

4.1. Temperatures of the primary mirror (M1), cryostat vacumm vessel (CVV) and sun-shield measured from OD40 to OD660. The monotonic increase of temperature from up to OD300 was well correlated to the seasonal temperature variation model.

4.2. The brightness of the night sky, excluding the contribution of the extragalactic background (from [RD5], adapted from Leinert et al. 1998, A&A, 127, 1). The spectral ranges covered by the PACS and SPIRE instruments of the Herschel Space Observatory are indicated. Atmospheric contributors, affecting ground-based observation in the optical and NIR, have been also displayed. In the absence of confusion, the far infrared sky is darkest around 350 microns where zodiacal light, CMB and cirrus are all close to their minimum values.

4.3. SREM calibrated count rates in three counters (TC1, TC2 and TC3), re-binned in intervals of five minutes. from the 30th of October 2009 (OD 170) to 27th March of 2011 (OD 683). The slight decline of the count rates can be explained by an increased solar activity and the subsequent increase of shielding to Galactic cosmic rays. Several events are visible, the most conspicuous, a small proton flare, detected in OD-663 (7-8 March 2011).

4.4. The smoothed sunspot number since 1995, covering Solar Cycle 23 and 24, along with the end-of-helium version of the predicted curve, which had undergone radical revision since the pre-launch previsions of a possibly extremely high maximum for Solar Cycle 24. In fact, the prediction for maximum has been revised downwards every year since 2009 and the current maximum is on course to be the lowest since 1906 (Solar Cycle 14) with its peak of 64.

4.5. The sequence of x-ray (top) and high-energy proton (bottom) activity. From top to bottom we have the soft x-rays (1-8 Angstroms), hard x-rays (0.5-4 Angstroms), low energy protoms (>10MeV), medium energy protons (>50MeV) and high energy protons (>100MeV). Evidence suggests that Herschel was only sensitive to very high energy protons.

4.6. SREM calibrated count rates for the 2012 January 23 and January 28 solar proton storms. The arrival of the shock wave from the Coronal Mass Ejection can be seen as a sharp peak in the proton flux approximately 36 hours after the initiation of the January 23 event; this peak is most clearly seen in the data at the lowest energies. For some of the Solar Proton Events observed during the Herschel mission, due to the rapid decay of the event at higher energies, there may be little or no signal at energies above 50MeV when the shock wave finally arrives.

4.7. SREM calibrated count rates from the archive of calibrated SREM data http://proteus.space.noa.gr/~srem/herschel/ for the entire mission. There was a higher level of background cosmic ray flux at the start of the mission, corresponding to solar minimum. From early 2010 the cosmic ray flux dropped continuously to the end of mission. There are three very small gaps in the plotted data due to the fact that on three ODs early in the mission, on-board anomalies led to corrupted SREM data. Plot prepared by Ingmar Sandberg on behalf of the SREM Team.

4.8. The daily rate of bit flips in Herschel mass memory through the mission, averaged over 3 month intervals, along with the best least squares fit to the data. Plot prepared at HSC from information supplied by MOC.

4.9. As in Figure 4.8, supressing the data from the first six months of the mission when the rate of Mass Memory bit flips was highest (this conforms to a statistical rule of thumb that "if a trend in a graph disappears when you cover about 10% of the data with your thumb, then the trend is, most likely, not real"; the rate of bit flips is seen to be constant, within the errors -- the best least squares fit, in red, shows no significant trend in rate -- and the dispersion is consistent with a Poissonian distribution of errors in a constant signal. Plot prepared at HSC from information supplied by MOC.

4.10. An example of source confusion. This SPIRE image of the Lockman Hole (the red layer is 500 microns, green is 350 microns, blue is 250 microns) the surface density of galaxies is so great that the entire image is filled. The background is not dark sky, but instead it is composed of fainter and more distant galaxies on which the brighter galaxies are superimposed. See Figure 3.2 for an explanation of the significance of the colours of the different sources.

4.11. An example of source confusion compounded by cirrus emission. In this section of the ATLAS survey a region of cirrus emission can be seen near the top of the image, adding to to the confusion caused by the high density of sources.

4.12. Cumulative (left) and differential (right) 24 μm number counts from [RD10]. The differential counts have been normalised to an Euclidean slope, dN/dSν ∼ Sν^-2.5. The curves show predictions from different recent models, including that from Lagache et al. 2003.

4.13. Comparison of straylight optical models produced by M. Ferlet (priv. comm.) and observational results. In the top row, a Herschel observation has been planned with Jupiter in position 'I', while in the bottom row the Moon has been placed in position 'F'. In both cases, there is a very good agreement between the model prediction and the straylight results.

5.1. Herschel Space Observatory Ground Segment during flight operations. For post-Operations, the MOC branch is no longer used, nor is HOTAC. Otherwise the interactions remain essentially identical in post-Operations to the Operations model, although with modified aims and priorities.

6.1. The final state of Herschel sky coverage. All 37 000 successful Herschel science observations are represented with their correct sizes. It is immediately obvious that, although the AOR centres are remarkably homogenously distributed around the sky (see Figure 3.8), in terms of actual sky area covered, the sky coverage is quite variable, with certain areas such as the Galactic Plane and Galactic Poles particularly well covered.

6.2. Beating the confusion limit for Solar System Objects. This SPIRE image of Makemake uses the technique of subtracting the background using the shift in position between two epochs and subtracting one frame from the other. The trans-Neptunian Object (TNO) Makemake has an estimated flux of 15mJy at 250 microns, with a confusion noise sigma of 6mJy. A weak, but clear detection is obtained in this image with 15 repetitions (NB: the confusion noise is effectively reached in 2 repetitions). This is thought to be the faintest target to be detected with SPIRE.

6.3. Position angle variation for sources on the ecliptic and at the ecliptic pole, in the zone of permanent sky visibility. For sources at intermediate ecliptic latitude the annual range of variation of PA will be between these two extremes. These plots were made originally for a Herschel launch in 2007, but the range and timescale of variation remains unaltered for the actual launch date.

6.4. An illustrative example of position angle variation for a target close to the permanent visibility zone on the sky (high ecliptic latitude). The position angle variation for PACS for an object at an ecliptic latitude of 59.5 degrees, close to the point of permanent visibility. The horizontal position is PA=000 degrees. The plotted positions of the PACS imaging detectors are for a hypothetical case with 2008 March 31st (start of visibility window) PA=127.4 degrees, 2008 June 15th (mid-window) PA=054.6 degrees, 2008 September 10th (end of visibility window) PA=333.7 degrees. The situation is effectively identical for other dates.

6.5. An illustrative example of a case where orientation constraints were essential. The Galactic Plane mapping programme -- HiGal -- required interlocking tiles around the full 360 degrees of the galactic Plane. This was achieved by setting an orientation contraint so that the 2x2 degree tiles would align horizontally. When the orientation constarint was relaxed slightly to ease scheduling problems, a tile would appear rotated; this was the case for the fourth tile in this strip of the Milky Way from Galactic Longitude 319 to 310 degrees from Centaurus to Crux.

6.6. An illustrative example of a case where a fixed time observation was essential. Asteroid 2005 YU55 crossed the PACS field of view so fast that it could only be observed by scanning along the path of the asteroid in the sky, at a fixed time when the asteroid was predicted to pass through the field of view. The asteroid was captured once on each scan leg, giving an image on the frame for each scan that were then combined to produce the final image. This is the 70 micron map in sky coordinates.

6.7. The path of (134340) Pluto between 2011 and the end of the mission superimposed on an IRAS image (red channel is 100 microns, green channel is 60 microns, blue channel is 25 microns). In 2011 it was embedded still deep in the clouds of the Galactic Centre region, making it essential to observe it as late as possible before the End of Helium, as it climbed southwards out of the Galactic Plane.

6.8. PA variation for a typical solar system object: Neptune's satellite Triton. Note how the PA variations over the course of a full observing window amount to less than 2 degrees. This made it effectively impossible to accomodate map orientation or chopper angle avoidance constraints. Although this example was calculated originally for a Herschel launch in 2007, the amplitude and timescale of variation remains the same for the actual launch date.

6.9. The background variation for Triton at 80 microns. The background is dominated at this wavelength by the Zodiacal Light contribution. As the elongation changes over the course of the observing window the background effectively doubles with time. At longer wavelength the ISM component will also change as the target moves across areas of different background. For objects relatively close to the Sun the ISM component may vary enormously in a comparatively short space of time. Although this example was calculated originally for a Herschel launch in 2007, the amplitude and timescale of variation remains the same for the actual launch date.

6.10. The variation of the elongation of Io from the centre of Jupiter with time. The area in grey is the region when Io is either superimposed on the disk of Jupiter (in transit) or behind the disk of Jupiter (occulted). HSpot does not warn the user if the visibility of a planetary satellite is limited in this way. Even when not confused with the disk of the planet, a satellite of Jupiter may not have been visible due to parasitic light from the planet, or to the danger of the planet impinging on the detector. All observations of the satellites of Jupiter and Saturn had to be made with extreme care to ensure that the planet did not enter the field of view.

6.11. The variation in the offset of Io from the centre of Jupiter through an entire visibility window. The grey ellipse represents the approximate mean size of the disk of Jupiter. Note that the entire area of this plot is smaller than the field of view of either PACS or SPIRE. If requesting observations of a planetary satellite the observer needed to check the visibility of the satellite using the JPL Horizons program at the url: http://ssd.jpl.nasa.gov/horizons.cgi.

7.1. The default Mission Planning Cycle that was the basis for scheduling in routine phase. Especially towards the end of the mission the Mission Planning cycle was a strong function of the sky distribution of targets as the remaining visibility and the need to complete scheduling before the end of helium was driving the Mission Planning Schedule.