Monday May 18th 2009. Day 4.


Things continue to be relatively quiet in terms of problems. Today Mission Control has concluded the initial Low Earth Orbit Operations (LEOPS) phase of the mission and has switched to the commissioning of the spacecraft and its instruments. In layman’s terms, the satellite is alive and well and there is nothing to stop us going into a detailed checkout, including observations. However, initial observations are only checking that everything is alive, that data transmission occurs correctly, that the detectors function, etc. (there are literally hundreds of checks to be performed, as would be expected with such an incredibly complicated system) The cover will remain on the cryostat until we are certain that there is no contamination and that it is safe to remove it, which will be in about a month. In other words, all that the instruments can see, even when they are switched-on, is the telescope cover. This though is useful because it means that we should have a nice, dark, even field to look at and check the performance of the detectors.


Today we have also had our first surprise. During the Commissioning Phase planning is described as “fluid”, which means that it could change at any time if issues arise or extra checks or needed, or others are delayed. After some discussion, it was decided that instead of switching-on the first instrument on Friday, it should be advanced to tomorrow. This was being discussed during they morning leading to two of our colleagues here waiting nervously to hear whether or not they should head off to the airport rapidly. In the end the call came and by mid-afternoon they were scurrying off to Mission Control. The big moment will come shortly after lunch tomorrow. The instrument that is being switched-on is SPIRE, the long wavelength camera-spectrograph and is our least delicate instrument. The cargo bay of a rocket is not a particularly friendly place for delicate instruments and there is always a danger, despite all the testing, that something might break during launch. If SPIRE switches-on with no problems it will be a big fillip for the team. This means that the first observations with SPIRE will be advanced 3 days to Friday, so our Mission Planners have to work fast to re-plan the observations to take into account the change in plans.


Herschel is retreating and dimming rapidly. At 00UT tonight Herschel will be 564 000km from Earth in the constellation of Serpens and receding at 0.87km/s. Signals take 1.9s to reach the satellite. We are now getting on for 1.5 Lunar Distances away and still moving away quite quickly, although the Earth’s gravitational field is slowing it progressively. Many telescopic observations of the receding objects have been made. The Minor Planet Center is tracking six objects in total, although it is not at all obvious which is which. It seems that Planck is now firmly identified but, looking at the light curve for the four brightest objects below, it is obvious that many times people are not observing the object that they think that they are observing. Herschel is either HP02 or HP03 in the light curve below, but what do we make of the apparent 3 magnitude outburst on May 17th??? It is obvious that people are, at times, confusing objects in their reports: only for the objects labelled “Plank” and “HP01” are the magnitudes really consistent.




I can’t resist adding this image from Gustavo Muler in Lanzarote. Amazing!



Amateur astronomers continue to get amazing sequences of images. You can check out some of the best ones in the unofficial Herschel Image of the Day archive, here:


Frequent updates are provided during the day on the Herschel Twitter (ESAHerschel) here: