## 5 Conclusions  
The conclusion of the tests and the subsequent data extrapolations is that the specific impulse of the hot gas propulsion system increases by 173.24% over the obtained specific impulse at 25 \({}^{\circ}\)C where no heating of the tank was carried out. The temperature of 450 \({}^{\circ}\)C is the temperature which the propellant tank reaches in space, when its heating is carried out by the mirror. Therefore, the operational life of an LEO satellite increases 2.73 times. The maximum thrust force is 8 N when the valve opening time is 0.4 s.  
The maximum thrust force which the hot gas propulsion system achieves is 9.21 N, at 27 bar, achieved after heating up the buffer tank to 125 \({}^{\circ}\)C and opening the valve for 0.3 s.  
The limitations of this study are measurement related. The discharged gas speed at the nozzle was neither measured or determined. Therefore, the specific impulse could not be calculated and as a result, the total impulse (which is correlated with the autonomy of the hot gas propulsion system) was not determined from the specific impulse. By determining the total impulse from the specific impulse, less result errors would have occurred and the calculation procedure would have been more straightforward.  
Therefore, for future experiments, a lightweight propellant tank will be developed with a 0.7 L volume and fitted with six valves and nozzles  
In the future, it is of interest to test the new concept for a wider range of temperatures, up to 450 \({}^{\circ}\)C, which is the mirror temperature threshold. It is intended to carry out the tests in vacuum and temperature conditions similarly to the values from the cosmic space for LEO.  
Important aspects which will arise when deploying the LEO satellite onto the orbit are control related. The linear parabolic mirror destined for space will comprise two symmetrical parts which will be folded until the first correction maneuver. When they unfold, they will create the complete mirror. The mirror will be silver plated and the valve-nozzle assemblies will be fitted in a manner to cover all ranges of necessary correction movements, which means a 360\({}^{\circ}\) action. Problems that will arise are control-related: The correction maneuver can alter the position of the satellite in space, therefore, all corrections will be limited to a valve opening time of maximum 0.3 s. Therefore, no gas will be wasted. The mirror destined for testing has a mass of 2105 g. The mirror destined for the space application will have a mass of 1100 g and will be made out of 2 mm-thick CFRP. Furthermore, the service tank/buffer tank will have a mass of 460 g. Including all the valves, piping and sensors, the total mass of the system destined for space will be of 3150 g, therefore 1150 g heavier than a comparable cold gas propulsion system, in terms of tank capacity, quantity of propellant carried onboard and developed thrust.  
Conceptualization, C.S. and G.C.; methodology, H.S.; software, A.R. and A.T.; validation, A.T.; writing--original draft preparation, H.S., C.S., G.C., A.T., T.T., A.R.; writing--review and editing, H.S., G.C.; supervision V.S.; project administration, V.S. All authors have read and agreed to the published version of the manuscript. This work was carried out within STAR, \"STRAUSS\" Project, Grant no. 130/2017, Project supported by the Romanian Minister of Research and Innovation. The authors declare no conflict of interest.