## 3 Results
### Ground Tests
Then, the voltage was biased from \(-10\) V to \(10\) V across the resistor. During this test, no plasma environment conditions were applied. Figure 10b,c shows the results from the calibration of the DLP instrument while Table 5 includes the calibration results for the four channels in the DLP system. Results from the ground tests in the LEO plasma chamber show that the Ten-Koh DLP is provided with an electron temperature of \(1.38\) eV and a plasma density of \(1.91\times 10^{12}\) m\({}^{-3}\). As a reference, the LEO plasma chamber produces plasma densities in the range of \(10^{11}-10^{12}\) m\({}^{-3}\), meaning that the DLP results were plausible. \begin{table}
\begin{tabular}{l l l l} \hline \hline \multirow{2}{*}{**Channel**} & **Measured** & **Relative Error from** & **Relative Error from** \\  & **Resistor** & **1 [G\(\Omega\)]** & **Resistor** \\  & **Value [G\(\Omega\)]** & **Nominal Value in \%** & **Resistance in \%** \\ \hline
1 (CHA1) & \(1.0010\times 10^{9}\) & 0.1 & 0.82 \\
2 (CHB1) & \(1.0180\times 10^{9}\) & 1.8 & 2.53 \\
3 (CHA2) & \(1.048\times 10^{9}\) & 4.8 & 5.5 \\
4 (CHB2) & \(9.944\times 10^{8}\) & 0.56 & 0.15 \\ SMU2400 & \(9.929\times 10^{8}\) & 0.71 & — \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Calibration results for all four channels of the Ten-Koh DLP instrument. Figure 10: Ground tests results for: (**a**) DLP I–V curve results for different number of samples (DAC step size) and the results comparison to an ideal DLP I–V curve on the left; (**b**) DLP measuring circuit comparison with the SMU for the same plasma conditions inside the LEO plasma chamber; and (**c**) DLP sensitivity and linearity relative calibration by using a 1 G\(\Omega\) resistor and the SMU2400 instrument. The DLP system has a linear response as expected inside its operating range. The current saturation in channel CHA2 is due to its higher gain compared with the other channels. During the ground test of the DLP system, the EM satellite structure and the DLP electrodes mounted on it, as well as the plasma source were kept static inside the plasma chamber. The face of the satellite structure where the electrodes were mounted was positioned toward the direction of the plasma source (0 deg) inside the chamber and data were acquired. Then, after removal of the plasma and vacuum, the satellite structure was rotated by 180 degrees, i.e., the electrodes were facing away from the plasma source. Another set of measurements was acquired in this configuration. Only these two tests were conducted in order not to occupy the plasma chamber for longer than absolutely necessary, due to the high demand for the facility. However, the two tested orientations, with the DLP electrodes facing towards and away from the plasma flow, captured the two extreme thicknesses of the sheath in which the experiment would operate. This was associated with a reduction in the magnitude of the measured current in an order of 10\({}^{-1}\) A. Under flight conditions, the lack of attitude control invariably affects the results as the alignment of the DLP electrodes with respect to plasma flow varies continuously. In this regard, attitude knowledge is critical to provide the location of each DLP sweep and to understand how quickly the attitude is changing. The sampling rate also plays an important role because sweeps with higher resolutions require more time for the data acquisition and, therefore, the attitude will change more during the sweep. Because the attitude and attitude rates were uncertain, the experiment was designed to be configurable by software via an up-link command. The parameters that can be set by software are:  
* Resolution: The number of samples for each I-V sweep can be a set of up to 16 bits voltage increments. Three exemplar cases are presented in Table 4--different resolutions can be implemented depending on the satellite rotation conditions. * Biasing voltage range: The biasing voltage range can be selected from \(-\)10 to +10 V (default), or be any other combination in that range.