Status
NIRAD consists of three systems: (1) CO2 detector, (2) power and data acquisition, and (3) gas-handling. All three systems have flown previously. The CO2 detector was first flown in 1999 as part of CORE+ instrument during RISO and ACCENT and again in 2004 during PUMA-A. There have been no changes to the detector, other than inspection and routine maintenance. The power and data acquisition system were new for PUMA-A, and are flown here without change, other than to software. The gas-handling system is the same as that flown in May 2004, except that it is now packaged into a single box that contains the detector and power/data system.
The detector is packaged in a vacuum housing to facilitate management of temperature and pressure. At power-up the housing is pumped down to ~300 hPa by one stage of a diaphragm pump and held at this pressure throughout the flight. Thus, at pressure altitudes < 300 hPa the pressure within the housing is above ambient. By design, if the pressure differential is significantly greater than about 5 psi, the O-ring seals leak. A redundant additional mechanical safety relief valve (set for ~15 psi or less) is placed on the housing.
Two 1.2 L epoxy-coated, fiber-wrapped aluminum bottles (DOT rated and certified) are filled to ~1600 psi before flight with zero air doped with CO2. These ‘standards’ are sampled repeatedly during flight to provide an accurate standard for reference to the NOAA/CMDL CO2 scale. Two-stage regulators provide a service pressure of ~25-30 psig throughout flight. The bottles and regulators are backed with safety relief valves.
The diaphragm pump is current-limited for a ‘soft start’ (that is, there is no electrical surge on startup, allowing for use of compact, highly efficient Vicor VI-100 DC/DC converters.
