WASS


The Wisconsin All-Sky Survey (WASS) sounding rocket program was a project to map the diffuse X-ray background at multiple bands between 0.1 and 6 keV using a proportional counter detector flown on a series of rocket flights between late 1972 and early 1980. All but two flights were launched from White Sands Missile Range in New Mexico (Flights 13.103 and 13.102 in November 1973 were launched from Woomera in South Australia). Two similar versions of the instrument were flown, refered to as payloads III and IV. Payload III flew on just two of the earlier flights (see table below) and possessed a smaller cross sectional area, but otherwise very similar to the payload IV version. The flight 25.045 had a malfunctioning attitude control system. Scan paths for the rocket flights used in the survey, shown in galactic coordinates. The path for flight 25.045 is shown as a dashed line.

Date Target (l,b) Flight No Peak Altitude
(km)
Payload
8 Dec 1972 168.2, -9.5 13.083 184.0 III
1 Nov 1973 227.9,-56.4 13.103 174.0 IV
12 Nov 1973 226.8,-66.6 13.102 178.0 III
20 Jul 1974 64.2,+12.8 13.084 196.0 IV
8 Nov 1975 131.8,-29.2 13.049 179.0 IV
15 Jan 1977 183.5,+15.3 13.122 196.0 IV
25 May 1977 54.0,+41.6 26.061 192.0 IV
6 May 1978 52.2,+63.7 13.137 200.0 IV
15 Mar 1979 193.7,+50.7 25.045 216.0 IV
21 Jan 1980 192.1,+41.4 25.051 216.0 IV

The instrument on all the sky survey flights was a gas proportional counter with three-sided anticoincidence, filled with a 90% argon/10% methane mix at ∼1 atm pressure at 20° C (780 torr for the White Sands launches, 860 torr for the Woomera launches). It was equipped with honeycomb collimators that gave a 6.5° field of view. The data were collected while scanning a fan-shaped pattern, with the field motion typically proceeeding at a rate of 5°.5 s-1. An inertial attitude control system provided an absolute accuracy of pointing during the flight of about 2° while a pair of 35 mm cameras provided post-flight aspect calibration to roughly 0°.2 accuracy. Each individual flight scanned roughly one eighth of the sky.

Both payloads IV and III had similar designs, but the payload III version had smaller dimensions. Specifically, payload IV used a carbon-filter counter with with 830 cm2 net open area, and a boron-filter counter with 475 cm2 open area. Payload III, used on two of the early flights, contained smaller counters with 460 cm2 net area for the carbon filter and 260 cm2 for the boron filter. Other specifications of anticoincidence layers and front and back layer materials were otherwise the same.
Data were collected in 7 different spectral bands. The pulse-height limits defines each of the bands, while the energies define where the net response falls to 20% of maximum for the band

 
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      Band Name          Pulse Height          20% Reposnse 
                          Limit (keV)           Points (keV)
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       B                 0.06-0.35              0.13-0.188
       C                 0.06-0.45              0.16-0.284
       M1                0.50-0.65              0.44-0.93
       M2                0.65-0.85              0.60-1.1   
       I                 0.85-1.2               0.77-1.5
       J                 1.20-2.0               1.10-2.2
       2-6 keV           2.00-6.0               1.80-6.3
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