Document Source: Dr. Carol G. Maclennan and Dr. Tom Armstrong, May 23, 1995

5.2.1 Introduction

The LAN (HISCALE) instrument on the Ulysses spacecraft has now completed five years of successful interplanetary data-gathering, including the several-week-long encounter with the Jovian magnetosphere (February 1992) and the traversal of the south and north poles of the Sun. This report is an in-depth look at the five inflight calibrations to date (November 1995) in order to verify the continuing health of the instrument as the spacecraft continues on course for its second solar orbit. Inflight calibrations are performed by closing the covers which are provided for three of the five telescopes. All covers have radioactive sources rigidly affixed to the inside. Upon spacecraft command, the covers are closed by thermally-driven bi-metallic springs attached to each cover. The telescopes will then count the source emissions. Another command removes the power from the heaters and causes the covers to open slowly and completely. Information about the alpha-particle-emitting sources attached to the covers is given in Table 5.10. αα

Table 5.10 LAN Calibration Sources

Figure 5.5 is a photograph of the instrument showing the LEFS60 detector on the left, with the LEMS120 cover. The LEMS120 telescope is behind the LEFS60. On the right can be seen the LEMS30 telescope; its cover is seen edge-on to its right. The telescope seen to the furthest right is the WART (CA) with its cover below and slightly to its left. Figure 5.6 shows the relative configuration of the detector telescopes. Covers are provided for the LEMS and the WART (CA60) telescopes.

Figure 5.5 The HISCALE instrument

Figure 5.6 Configuration of LAN detector telescopes

 A detailed drawing of the cover for the LEMS120 telescope is shown in Figure 5.7. The Am source is located in the center of the cover. The sources on the covers of the other telescopes are similarly located, the two calibration sources for the WART being packaged together in the center of the cover. As noted, five inflight calibrations have been performed to date. Table 5.11 (information courtesy of S.E. Hawkins, III) gives the times of the close and open cover commands. Two commands (A and B) are required for each operation, and this set of commands operates all three of the covers.

Figure 5.7 LEMS120 cover (outside)

Table 5.11 LAN calibration history

This report is organized as follows. Section 5.2.2 describes plots from several LAN standard data analysis programs showing typical signatures of the calibrations. Section 5.2.3 describes some IDL analysis of the PHA matrix during the calibrations. Section 5.2.4 shows the response of the MFSA (32-channel) spectra to the calibration sources. Section 5.2.5 contains an analysis of the time taken to open and close the covers. Section 5.2.6 discusses the detection of alpha particles from the WART source over the poles of the Sun.

Next: 5.2.2 Typical Signatures