[P-CG11_28AM1] Instrumentation for space science

[PCG11-01] Problems of DC Probe Measurement onBoard Mini/Microsatellite

*Koichiro OYAMA¹ (1.Plasma and Space Science Center, National Cheng Kung Universoty,Taiwan)

Keywords:microsatellite, Dc Langmuir probe, surface area, contamination

DC Langmuir probe is one of the key instruments to study ionosphere by satellite. It needs a counter electrode whose conductive surface are is at least 1000 times larger than that of surface area of the electrode. This requirement is usually fulfilled for large satellites which have been launched so far for ionosphere study. Now we are jumping into an era to use tiny satellites. Then we will encounter serious problems for DC Langmuir probe measurements. Conductive surface area of the satellite becomes much less than 1000 times, or even equal to the surface area of electrode. As a result, measurement of electron density becomes unreliable, because potential of the electrode with respect to the satellite (counter electrode) cannot reach ambient plasma potential where electron density is calculated. For the worst case, DC Langmuir probe is in double probe region, where the maximum current is controlled by ion current. An electronics needs to measure low current. although to measure the low current is not impossible with low frequency response. Another more serious problem is contamination of electrode as well satellite surface. To avoid the effect of contamination, probe bias of DC Langmuir probe need to be swept with about 10 Hz. These two factors make it possible to use DC Langmuir probe, because to measure low current with high frequency is not possible. We review problems which raises for the ionosphere measurement by small satellite, and propose one solution to avoid these problems to accomplish accurate measurements. The data which have been used here are the contribution of three students, G. S. Jiang, W. H. Chen, and Y. W. Hsu, Plasma and Space Science Center, National Cheng Kung University,Taiwan.