## 2 System Analysis and Design Methodology
### MIMPS-G ConOps  
Micro e-Pump feed system is considered unconventional for in-space propulsion, especially for small-sized spacecraft. The electric pump feed system (see Figures 6, 11 and 11) is primarily responsible for the delivery of propellant from very low storage pressure to high-pressure requirements of the thrust chamber at a given propellant mass flow rate (\(\dot{m}\)). Moreover, it is required to circulate streams of propellant over a heat source for vaporization and to use the vapor (non-catalytically decomposed) of the liquid propellant to keep the storage tank at the required minimal pressure levels for proper pump operation--typically describes an autogenous pressurization system. The heating of the propellant streams will take place through radiative heat transfer from the decomposition chamber. A preliminary clearance value was set between the thruster chamber wall and the spiral tubing intended for propellant stream heating; the reason behind this was, first, to avoid unneeded power consumption due to heat loss to the propellant stream tubes during the pre-heating phase of the thruster's catalyst, and secondly, to eliminate any risk of transient heat loss on introducing propellant streams during the operation phase. Accurate sizing of the spiral tubing is pending verification, considering heat transfer estimation and propellant vaporization characteristics. The design of this part is expected to undergo several iterations and modifications in the prototyping and testing phases. One of the advantages of this concept is that no separation within the tank is required-no need to separate the feed-back vapor unlike the case of feeding back catalytically decomposed gaseous propellant-thus avoiding actuating and separation mechanisms as in case of piston expelled tanks, or material compatibility problems with green propellants as in the case of using bellows or elastic diaphragms.  
An optional vapor auxiliary propulsion for reaction control and attitude control requirements can be integrated. This optional subsystem incorporates a small catalytic bed and lighter weight thrusters compared to the primary monopropellant thruster and shall present a \"multimode\" propulsion system when incorporated--multimode propulsion is capable of utilizing the same propellant tank for different types of propulsion at the same time [6; 40; 41]. The catalytic bed shall increase the temperature of the vapor, thus increasing performance, moreover, ensures homogenous exhaust. This concept is complemented and reinforced by the research work of [PERSON] and [PERSON] (2019) on the H\({}_{2}\)O\({}_{2}\) vapor propulsion system [42]. Of course, HAN and ADN-based propellants differ completely from H\({}_{2}\)O\({}_{2}\), but the analogy intended here is in using the propellant vapor over the relevant catalytic bed to increase its temperature and ensure homogeneity, thus increasing the propulsion performance. The vapor auxiliary system modeling will not be incorporated in the design stage presented in this article.  
A micro three-way flow control valve is required to control the flow from the micro e-Pump outlet to the thruster and the propellant streams heating cycle. It should be observed that technological advancements in, and availability of, controlled microvalves are inevitable for such feed and pressurization system to succeed on this small-size scale. One final advantage to mention, but not the last, for this feed system is the ability to precisely control the propellant mass flow rate (\(\dot{m}\)) and pressure (\(p_{c}\)) to the thruster chamber, thus controlling and maintaining a constant thrust level over almost the whole mission life-time. This unconventional concept may also be applicable for feed and pressurization systems of liquid bipppellant propulsion of small-satellites and spacecraft.