The Current Status of Solid-state Slit Camera aboard MAXI
Hiroshi Tomida,1 Hiroshi Tsunemi,2 Satoshi Nakahira,3 and MAXI/SSC team1

Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency,
3-1-1 Yoshinodai, Chuo, Sagamihara, kanagawa, 252-5210 Japan
2Department of Earth and Space Science, Osaka University,
1-1 Machikaneyama, Toyonaka, Osaka 560-0043 Japan
3
Human Spaceflight Technology Directorate, Japan Aerospace Exploration Agency,
2-1-1 Sengen, Tsukuba, Ibaraki, 305-805 Japan
E-mail(HT): tomida.hiroshi@jaxa.jp
Abstract

We present the current status of the performance of the Solid-state Slit Camera (X-ray CCD camera ofthe MAXI mission). The charge transfer efficiency (CTE) of the CCDs have been degrading, and the energy
resolution has been also degrading. On the other hand, the cooling capability of the MAXI/SSC has beenstable since the beginning of the in-orbit operation. The radiator temperature and camera temperatureshows no significant change without those coming from the Sun-orbit plane angle, and the cooling powerof the Peltier devices has been unchanged. Then, the CCD temperatures have been stable.
Key words: MAXI: SSC — X-ray Camera: CCD

1. CCD performanceFig.1 represents the spectrum of Cu-kα line obtainedwith SSC-H/CCDID-0, that are those applied for withthe correction of CTE (charge transfer efficiency) andtemperature-gain dependency. Fig.2 represents the longterm trend of the pulse height of Cu-kα line and the line
width of all CCDs. We can see gradual broadening of theline width and the shift of the Cu-line center. The causesof the width broadening are degradation of the chargetransfer efficiency, and inaccurate gain-corrections. The
performance degradation is more serious for the CCDs
whose position is close to the camera slit. The intensityof charged particles is higher at the position closer tothe slit, which likely causes the deference of the degradation level. The energy resolution of SSC-Z/CCDID-0
is very bad, which is due to the insufficient cooling powerof the Peltier cooler. Then, we should not use the dataof SSC-Z/CCDID-0. In the MAXI operation, the dataof SSC-Z/CCDID=0 have not been down-linked. Between Mar 2013 and Apr 2014, SSC-Z was not operated
due to the on-board-computer trouble. After the nonoperation period, SSC-Z has functioned completely. The
performance of the SSC-H and Z had been gradually degraded. For the detailed spectrum analysis of SSC, weshould be careful when you use the data obtained after2014.

Fig. 1. Cu-Kα line profiles of SSC-H/CCDID-0. 6 spectra are extracted from single-pixel event data in 6 different periods, thatare shown above each panel.

Fig. 3. Temperature trend of the radiator panels (left) and SSC
camera body (right). Each dot represents the one-day averaged
temperature. MAXI has two radiator panels.

Fig. 2. Trend of characteristics of Cu-kα line. The center and width of
the Gaussians are plotted. Each dot (spectrum) is extracted fromthe 3-months integrated data. In each panel, data of 16 CCDs
are plotted.

2. Cooling Capability
CCD chips of SSC are cooled with Peltier coolers in theCCD devices, and the heat from the Peltier coolers aretransported to radiator panels on the surface of MAXI
payload via the loop heat pipe. Fig.3 (left) shows thelong term trends of the radiator temperature, and Fig.3(right) shows that of SSC camera body. The orbital
plane of the International Space Station precess every 70days, then the temperatures show the periodic change according to the precession. However no inclination can beseen. There is no degradation for the cooling capabilityof the radiator and loop heat pipe system in the 7-years
MAXI in-orbit operation. The temperature change ofthe camera body around 2014 corresponds to the periodthat SSC-Z was not operated due to the computer trouble. During this period, the heat generation from SSC
was small compared with that in other period. Fig.4shows the temperature difference of CCD chips and camera body, which represents the colling power of Peltier
devices. Peltier Current is 1.0 A and 0.82 A for SSC-Hand SSC-Z, respectively. No significant degradation canbe seen. A small change around 2014 in SSC-H is due tothe temperature increase pf camera temperature when
SSC-Z was not operated.

Fig. 4. Cooling power of 32 Peltier devices. The vertical axis
shows the temperature difference between CCD ship and camerabody. The left upper, right upper, left bottom, and right bottom panel are the data of SSC-H/CCDID0-7, SSC-H/CCD8-F,SSC-Z/CCD0-7, and SSC-Z/CCD8-F, respectively.