Sunday May 31st 2009. Day 17.


It was too good to last. Quite frankly it looks like we are overstaffed at weekends and I have a feeling that the number of people on duty will be sharply reduced in the future. However, Mission Planners and Data Processors are definitely needed and had a busy morning. By 3pm today we had planned and sent the remaining days of observations and were, for the first time in the mission so far, a couple of days ahead of the game. I suggested to the Mission Planner that if we did not hear that there was a problem soon that he should go home, but he agreed to hang on for a while. At 4pm my ‘phone rang…


It was the Flight Dynamics expert from Mission Control. “Houston, we’ve had a problem”. The next four hours were intensely interesting.


Herschel has reaction wheels on board to control the pointing. These are essentially large flywheels that, by being spun up to different speeds, balance the spacecraft like a gyroscope, pointing in the desired direction. Over the course of time, momentum starts to build up in the wheels that has to be bled off. Similarly, we can get into a situation where a wheel can be slowed far too much by a manoeuvre. If the reaction wheels are forced beyond their limits the spacecraft will place itself into safe mode and at least a day of observations will be lost. Flight Dynamics cares for the reaction wheels like they are their own babies and quite right too. The long and the short of it was that we had a serious violation. Unfortunately, we have no way to predict when this may happen, so we had little or no chance of avoiding it.


This was what we were on duty for. There was a problem and we got on with solving it as rapidly and as efficiently as possible. And, to be honest, it was fun and very satisfying to solve a problem like this. By the end of the afternoon everything was resolved, but I am betting that tomorrow morning’s briefing will be a bit livelier than usual.


Back to Robocop in the evening. It is in the typical Paul Verhoven style: lots of dramatic music, loads of corpses and enough violence to satisfy the most bloodthirsty. Entertaining, but not exactly a classic.


I am trying to finish an article on photometry of the objects in the Herschel constellation for The Astronomer magazine, but it is proving to be slow going. Still, it’s been a good weekend: we earned our pay.


Unofficial Herschel image of the day archive:


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


You can follow Herschel testing and observations in real time on the Twitter.