SOFIA's heart is really sensitive, which is why the doors to it are usually only opened when she is on 'Cloud 9'. At altitudes in excess of 12 kilometres, the air is very clean and there is no danger that the mirror inside SOFIA will become dirty. Any maintenance on the mirror – a thorough cleaning or its installation or removal – brings with it a high risk of damage.
At the heart of the joint NASA and DLR airborne observatory, SOFIA, is a 2.7-metre, 800-kilogram primary mirror made of fragile glass – a custom-made reflector for which there is no replacement. This is why it is only ever handled with 'velvet gloves' and treated like the princess from the fairy tale 'The Princess and the Pea'. Should the mirror break, it would be the end of SOFIA.
Yet the telescope doors have been opened on the ground? read more