Tuesday February 24th 2009. Launch -51 days.

Today, two examples of what happens in a launch: first when everything goes right and then when it goes horribly wrong. Recently MOC – the Mission Operations Centre – Mission Control at Darmstadt, in Germany, has been holding its own simulations of the launch and control of Herschel and Plank. Part of the simulation has been to rehearse the countdown and launch and then, of course, rehearse operating Herschel and Plank as they make the long cruise to Lagrange. While this was being done, a Webcam was recording the sound in the Control Room. This is what you should hear, if you are one of the privileged few who can be there during the countdown:

 

http://www.esa.int/SPECIALS/Operations/SEMY1CWX3RF_1.html

 

Click on the icon at the top right of the video panel to get sound. If any of the controllers at Mission Control says “No Go!” the appropriate panel on the launch status will change from green to red indicating a problem with one or other of the satellites and the launch will be aborted.

 

Then, from NASA’s Orbiting Carbon Observatory (OCO), we have an example of how things can go horribly wrong:

 

http://news.bbc.co.uk/1/hi/sci/tech/7907602.stm

 

The launch, made last night, on board a Taurus XL rocket, appears absolutely nominal (there’s our favourite buzzword!) Then we flash to the control room and discover that it is not. It seems that the fairing that protects the satellite at the top of the rocket as it blasts through the denser parts of the atmosphere, failed to separate properly. This has left OCO apparently trapped inside the upper stage, unable to separate from the rocket, even though it was successfully placed in orbit.  [Update: early reports were misleading. Actually the upper stage fell into the sea off Antarctica because it was too heavy to get into orbit with the fairing still attached]

 

At lunch today, before we heard of the OCO failure, we were discussing just how tricky the Herschel-Plank launch is and discussing the satellite separation sequence. Multiple things have to happen correctly in sequence. First, the fairing should open, exposing Herschel and Plank and the Scylda support platform that separates them (this will be visible in images from an on-board camera). Then, with the upper stage’s path correctly aimed at Lagrange, Herschel has to separate. We then slightly change the orientation and free the Scylda support that held the weight of Herschel; unless this is successful, Plank cannot separate. Finally, with Plank free and exposed, the orientation is changed, once again and Plank is separated. This separation manoeuvre is very delicate because all three parts have to be released in separate directions so that they do not collide, without changing their orbit so much that they do not arrive correctly at Lagrange. This part has been done time and time again but, as OCO has shown, it can still go wrong if one of the many components involved fails to work properly. That’s why, even if everything seems okay, no one will be breathing until about 15 or 20 minutes after launch when we get the confirmation of correct separation of the two satellites. However simple the manoeuvre may appear to be; however many times it has been carried out successfully, there is always a danger in space that something unexpected may go wrong.

 

Once we are al Lagrange we have another delicate manoeuvre and, this time, one that ESA has never previously attempted and that is to put the two satellites in orbit about the L2 Lagrange point. Herschel has no retro rocket, only manoeuvring thrusters, so our velocity has to be exactly right to be captured. Plank, in contrast, goes to Lagrange much faster and will enter a smaller, tighter orbit and must be slowed to be put into orbit: if that rocket fails to fire, Plank will only be able to wave goodbye to Lagrange as it sails past. Initially, this would not be a disaster because either Herschel or Plank would still get great data even in a free solar orbit. The problem is that they would rapidly drift out of communications range. This would NOT make us happy.

 

Today, I was able to make a small presentation to the Boss and our System Engineer. A few weeks ago I saw a news item about the incredible success of the reproduction of a British Government wartime propaganda poster. Described as perhaps the most effective propaganda poster ever produced, its message, aimed to avoid panic in the population in the case of a Nazi invasion of the British Isles was “Keep calm and carry on” (or, as a colleague put it, have a cup of tea and just keep working normally). This seemed such a suitable message for Herschel that I ordered three copies, which now adorn the walls of my office and the offices of the Boss and System Engineer respectively. You can see an image of the poster here:

 

http://www.barterbooks.co.uk/catalog/product_info.php?cPath=430&products_id=32036

 

We will try to remember this message over the next few weeks.