## 4 Experiments and Results
### Part B--Hot Gas Propulsion  
In order to test the functionality of the test equipment and the principle, a test at 80 \({}^{\circ}\)C was carried out, the temperature being within the operation limits of the valve and of the entire test equipment. After this test, a comparison between the impulses at cold gas and at hot gas was made. The illustration of the impulse of the cold gas (from Figure 11) in parallel with the impulse from the hot gas are represented in Figure 12. The tests at low temperature are displayed in blue and the one at high temperature, 80 \({}^{\circ}\)C, in red. It can be noticed that the force value for the hot gas is somewhat bigger than the force value obtained for the cold gas, in total, as a significant increase in total impulse is recorded. The impulse increase is in absolute values from 7.87 to 8.02 Ns, with an increase of 2%. This difference is percentage wise so small because at small values of opening time, there is a strong influence coming from the valve recoil. Therefore, at 0.05-0.1 s, a force of small intensity can be noticed which acts in opposition to the movement, but which destroys the force distribution. This influence is present utilizing the detail from Figure 13, corresponding to the first impulse from the cold gas from Figure 11.  
The recoil effect is represented in Figures 13 and 14b. The recoil effect reduces the thrust force on average by 0.3 N, irrespective of the valve opening time. This is due to the direction of the valve movement, in opposition to the direction of the thrust force. In Figures 13 and 14b, the force would have been represented by a spike in the line, in the opposite direction from the spike which is represented in both figures. Therefore, the developed force of the discharged hot gas would have been higher by 0.3 N.  
If the case with a valve opening of 0.3 s is analyzed, the valve influence is less pronounced, therefore, there is an increase of 2.4% for the same temperature interval. As an evolution, it was observed in Figure 14a that in this case, there is also a difference between the force and the impulse for the cold gas in comparison with the hot gas. The influence of the valve recoil on the force/impulse can be seen in Figure 14b. The fact that the gas warming inside the tank was carried out with respect to the state Equation must be noticed. Therefore, in Figure 15, the pressure variation with temperature increase six presented. This variation is displayed in Figure 13 for this case, together with the relevant detail in the warming  
Figure 12: Comparison between the impulse for cold gas (\(T_{0}\) = 26 \({}^{\circ}\)C) and hot gas (\(T_{f}\) = 80 \({}^{\circ}\)C) for the valve opening time of 0.1 s at a 10 s interval. interval. The warming interval is 26-80 \({}^{\circ}\)C. The decrease in pressure after 80 \({}^{\circ}\)C corresponds to the valve opening in order to produce the impulses. The following fact must not be neglected: in the moment of a N\({}_{2}\) quantity discharge from the service tank, the temperature drops suddenly (around 3 \({}^{\circ}\)C) because of the mass ejection outside the system. The fluid temperature in the system tends to increase because of the tank thermal inertia, the nitrogen warming being more pronounced as more quantity of fluid from the tank is reduced with each valve opening. Furthermore, as the quantity reduces with each discharge in the atmosphere, the temperature inside the tank does not decrease as much as at in case of the first discharge. This can be noticed in the 75-85 \({}^{\circ}\)C temperature interval in Figure 15, where at 80 \({}^{\circ}\)C the valve opens. Because the correction maneuvers on the orbit require (usually) equal impulses, the comparison of the cold gas impulses with the impulses after the service tank heat-up from 22 \({}^{\circ}\)C to 60 \({}^{\circ}\)C-100 \({}^{\circ}\)C-125 \({}^{\circ}\)C was carried out.