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Posted by: paranoid123 Feb 29 2008, 04:31 PM

I am wondering.

When space based telescopes like IR telescopes, ones used for astrometry, or planet hunting end their mission lifespan or use up mission critical expendables likes coolant, can they be converted to be used as regular optical telescopes? Telescopes like Spitzer and Kepler still have mirrors and regular CCD cameras right?

Posted by: nprev Feb 29 2008, 04:47 PM

I kind of doubt that they have "regular" (i.e., visible-light-sensitive) CCDs, at least with respect to IR instruments. Not sure about UV devices, but I think that they're a lot more tolerant of higher temps. IR detectors use all sorts of exotic materials that generally have to be kept at cryogenic temperatures to function.

Think the problem is that the detectors for non-visible band instruments are mounted permanently in the scope's focal plane, so there's no way to get them out of the way, nor any sensors onboard that could interpret visible light. Might be cool for a future scope to have a rotable focal plane that could present another set of sensors for use once the primary mission's exhausted, but of course the other limiting factors such as attitude control consumables, gyro/inertia wheel longevity, etc. must be considered before deciding to invest in such a potential extended mission before launch...to say nothing of the anticipated returns of such an effort.

Posted by: dvandorn Feb 29 2008, 05:05 PM

Designs can be quite dissimilar. Chandra, for example, has "mirrors" that resemble concentric tubes which funnel X-rays to the detector. Nothing like a focusing mirror set or a CCD array in that baby.

-the other Doug

Posted by: NGC3314 Feb 29 2008, 05:44 PM

Something of the sort happened when WIRE's cryogens were lost before beginning its prime IR mission - a few clever folks realized that there was interesting work in asteroseismology and exoplanet transits to be done with the CCD on its star-tracker, originally intended for attitude determination. Being in such a stable environment lets you start out at precision levels which are very difficult to get from the ground and imprpve matters from there. For this to be an option, you need something to happen which ends the primary mission but leaves attitude control, power, and telemetry. The "Warm Spitzer" mission almost qualifies, continuing use of the two shortest-wavelength camera modes once cryogens are depleted (coming up this year, alas). ISO continued work a bit after cryogen depletion, doing a near-IR spectral atlas of bright stars. As best I can recall, IRAS and maybe ISO were used to train ground controllers on live but otherwise useless spacecraft for a while after end of mission.

Posted by: siravan Feb 29 2008, 09:09 PM

AKARI (Astro-F), JAXA's IR telescope has this capability. During its primary mission, it surveys the sky in IR 2-180 um until its liquid helium reserve runs out, then it works as a near IR telescope using "mechanical cooling":

http://www.ir.isas.jaxa.jp/AKARI/Outreach/unyou_e.html

Posted by: Del Palmer Feb 29 2008, 11:23 PM

On the contrary, Chandra has several CCDs, and they are also sensitive to visible light (optical blocking filters are used to allow only X-ray photons to pass).

Posted by: dvandorn Mar 1 2008, 04:00 AM

Really? Interesting -- you didn't get that impression from the detailed documentary that ran on NASA-TV six times a day for two months... they referred more to "X-ray detectors," IIRC.

Good to know -- thanks, Del!

-the other Doug

Posted by: siravan Mar 1 2008, 05:05 PM

Based on ACIS website (Chandra's Imagings Spectrometer), it is very sensitive to visible light as well as X-ray, hence the dark mask in front of the CCD:

http://acis.mit.edu/acis/eb-paper/detector.html


However, Chandra also has an aspect camera, which works in visible light and is used for fine pointing. In fact, it has been successful in doing science independently:

http://adsabs.harvard.edu/abs/2007AAS...211.6003N