Here's a nice labelled version of the image: http://www.mpe.mpg.de/7464825/erass1_annotated-1592554887.png
11 posts • joined 13 Jan 2017
You can switch instruments in an X-ray telescope, like in Chandra. There's a cost associated with doing that, however. The fewer moving parts you have in space, the better, because of reliability. It's also a lot cheaper to have a more simple mission. However, switching instruments can be beneficial. You can move the instrument module (like Chandra), or move the mirrors, like the future Athena mission is planning.
For a mission, it may also be cheaper or easier to build multiple telescopes, rather than one big telescope. The choice of number or size of mirrors also affects its performance at different energies, so there is optimisation for the type of science you want to do.
I could tell you there are three telescopes because there are three main instruments - EPIC-pn and two EPIC-MOS (EPIC=European Photon Imaging Camera). pn and MOS are two different types of detector. These detectors give imaging capability with lower resolution simultaneous spectra.
In fact, it's a bit more complex than that. Half the light from the two EPIC-MOS cameras is split using a reflection grating and passed to the RGS instruments (RGS=Reflection Grating Spectrometer). The RGS give high resolution spectra of bright X-ray sources. There's also the UK contribution, which is an ultra-violet telescope, the optical monitor (OM), which also observes what XMM looks at. Unfortunately that UV telescope has never been used much because it has a few issues.
Sounds like the sub-ether radio in Hitchiker's Guide, where you had to sit infuriatingly slowly not to change channels: http://www.technovelgy.com/ct/content.asp?Bnum=1329
A loud clatter of gunk music flooded through the Heart of Gold cabin as Zaphod searched the sub-etha radio wave bands for news of himself. The machine was rather difficult to operate. For years radios had been operated by means of pressing buttons and turning dials; then as the technology became more sophisticated the controls were made touch-sensitive--you merely had to brush the panels with your fingers; now all you had to do was wave your hand in the general direction of the components and hope. It saved a lot of muscular expenditure, of course, but meant that you had to sit infuriatingly still if you wanted to keep listening to the same program.
Zaphod waved a hand and the channel switched again
No - don't use wstring unless you have to, as it's mostly broken. You'd either need 32 bit characters for the whole of unicode (on linux), wasting enormous amounts of space, or encode things into 16 bit characters (on windows). For example: https://stackoverflow.com/questions/11107608/whats-wrong-with-c-wchar-t-and-wstrings-what-are-some-alternatives-to-wide
Instead, the best approach is to use std::string, and encode everything as UTF-8.
I'm actually involved with this project (on the science rather than hardware side). It's actually quite hard to keep cool in space due to the lack of air and convection. One side of the telescope will always be heated by the sun and the detector electronics produce heat. One of the big efforts of design for eROSITA was the heat pipe system which cools the cameras passively (search for a PhD thesis if you're interested). There are radiators on the side of the telescope away from the sun to radiate the heat into space. The CCD cameras are kept cool to prevent degradation by high energy particles.
You're lucky - it usually takes 2 to 3 days here for a transfer here in Germany. This is for a country who prefers using bank transfers to using credit and debit cards online. I've experienced that for an internal bank transfer too. It's not only the UK who has terrible banks.
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