FIRP : Far-Infrared Photometer

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What's the FIRP !?

We describe the design and calibration of the Far-Infrared Photometer (FIRP: Lange et al. 1994, Hirao et al. 1996; see IRSA IRTS Bibliography Listing), one of four focal plane instruments on the Infrared Telescope in Space (IRTS). The FIRP will provide absolute photometry in four bands centered at 150, 250, 400, and 700 microns with spectral resolution wavelength/wavelength spread is approximately 3 and spatial resolution delta theta = 0.5 degrees. High sensitivity is achieved by using bolometric detectors operated at 300 mK in an AC bridge circuit. The closed-cycle He-3 refrigerator can be recycled in orbit. A 2 K shutter provides a zero reference for each field of view. More than 10% of the sky will be surveyed during the 3 week mission lifetime with a sensitivity of less than 10-13 W per sq cm per sr per 0.5 degree pixel.

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Specifications

Size	Irregular shape : 16 x 15 x 11 cm3 (overall)
Weight	2185 g
Electrical Power Dissipation	Cold part : 2-3 mW (typical), 17 mW (peak), Warm part : 2 W
Cryogenic Parameters
Tcoldplate	<1.8 K
Thousing	1.92 K
Ttelescope	1.91 K
Tstill	293 mK
Tphot	319 mK
Tpump	2.1 K
3He lifetime	10 days
3He cycle time	15 hrs
Cooling power of still	12 J
Heat load (on still)	14.6 microW
Entrance aperture	4 mm diameter (0.5 deg on sky) Winston Concentrator with flare entrance aperture
Detectors	Composite bolometers in AC bridge with dark reference detectors
Shutter frequency	1/8 Hz(4 sec open / 4 sec closed - 8 sec / FOV)
Cold amplifiers	Model J-1, Infrared Laboratories
Data rete	Standard : 6 kb/s, Reduced : 3 kb/s

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