Wednesday May 20th 2009. Day 6.


Another good day of solid progress with several big highlights for us. It’s hard to explain how it feels to be doing for real the things that we have pretended to do with simulated data for so long. Tonight real data is coming down from a real instrument on a real satellite that really is in space. It’s a huge moment. During the day the Mission Planners, who have asked to be known on the Herschel Twitter as “The Mission Planning Gang” have sent their first real file of observations to be transmitted to the satellite. They have planned the observations and generated the file that goes to Mission Control, with the full sequence of what has to be done and when and Mission Control generate all the tens of thousands of instructions that have to be transmitted to the satellite to execute these observations. These instructions will be transmitted tomorrow and stored in Herschel’s on-board memory to be executed autonomously on Friday. So, over these next few days, we exercise the whole chain of observing: receiving the observing requests and software code from the instrument teams, checking it, preparing the observations, passing them to Mission Control, generating the commands for the satellite, transmitting them, storing them on board, executing them later, receiving the telemetry, processing it, propagating it to the Instrument Control Centres, reducing the observations and putting data in the Herschel Science Archive. That ALL there is to it!


Over a year of tests, trials and simulations, the whole sequence has been tested time and again and more often than not some pesky problem has appeared meaning that it didn’t quite work. Well, now, after so much practice, it is becoming quite routine. It is not the same as doing this day after day for months on end, but we are genuinely amazed at how well things are working right now. Undoubtedly new problems will surface, but they should be small ones (please!)


On Friday, Herschel will fly solo for the first time.


We also had another big step in preparing the instruments. Today SPIRE continued their check-out activities. Yesterday it was the SPIRE photometer that was checked-out, today it was the spectrometer. A vital part of this was to move the latch pin that held the spectrometer firmly in place through the stress and vibration of launch. A vital part of the check-out process was to open this pin and free the spectrometer. This was done successfully to the delight of the SPIRE as it meant commanding a physical mechanism on board to move, always a worry the first time. It’s fair to say that the SPIRE team are jubilant.


It is still early days, but the signs are good. Things are working well so far.


We have finally resolved the mystery of what object is which in the Herschel field of view. The very brightest object of all is, logically enough, the Ariane Upper Stage; this was the Minor Planet Center’s HP03. Two of the objects are very interesting. The one dubbed “HP02” is Herschel, as many suspected. It’s light curve is very curious:



There is a 3 magnitude brightening on the afternoon and evening of May 17th. What could have caused our brightness to increase by a factor of about 20? We are moving very much straight away from the Earth with the solar panels facing us. Probably it was a slight manoeuvre that allowed a much more reflective surface to appear. Planck, the Ariane upper stage and the Sylda all show nice, well-behaved light curves.


Even more curious is object HP05. This object was found to have separated from the Ariane upper stage just after launch. This object shows some curious non-gravitation motion as if it is very light and subject to radiation pressure, or out-gassing. A very light object might be a piece of insulation that has come off, or a sheet of the ice that forms around the cold cryogenic tank. The light curve of HP05 is curious.



The curve is the fit to the light curve expected if it is just reflecting sunlight. It is not; it seems that HP05 is fading, It is the only one of the objects (apart from Herschel) that does not fit a nice curve of reflected sunlight. This makes me even more convinced that it is a piece of ice that was shaken off the upper stage and that is evaporating progressively.


Tomorrow’s image of the day is a real Herschel curiosity.


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