PDF Publication Title:
Text from PDF Page: 007
as an increasingly significant fraction of propellant produced each day is lost to boiloff. If the electrolysis rate is such that a given propellant goal can be reached, Eq. (3) provides the required time t: ln(1−𝐿𝑀) 𝑡=− 𝑅 (4) 𝐿 The total propellant that must be electrolyzed to reach this goal is Rt>M. In the process, a certain amount of propellant ML=Rt-M is lost. The propellant that is needed at the end of electrolysis M depends on the payload mass M0 plus the solar panel mass S and the V of the maneuver to be performed: ∆𝑉 𝑒 𝑀=(𝑀 +𝑆)(𝑒𝑉 −1) (5) Using Eq. (5) in Eq. (4) provides the electrolysis time and hence the total propellant which must be launched and then electrolyzed, as a function of the V of the maneuver, the specific impulse or exhaust velocity of the engine, and the mass of the payload and its solar array. To mitigate the issue of propellant boiloff, burns can be performed in smaller pulses instead of a single impulsive burn. For example, raising an orbit apoapsis could be done with less propellant boiloff, and no loss in maneuver efficiency, by electrolyzing continuously, but pulsing at each periapsis instead of waiting to collect all propellant needed. Maximum propellant efficiency is achieved during continuous operation, when propellant is consumed as fast as it is produced. However, this may introduce its own inefficiency in the form of increased V, and hence propellant, requirements for lower thrust maneuvers compared to impulsive ones. This part of the trade is beyond the scope of this paper, and will be examined in future work. This section examines the sizing of a solar panel array as a function of maximum required V in a single maneuver, for a 58 t payload—the approximate combined mass of the habitat, engines, and Orion crew vehicle together for all architectures examined in this study. A larger, heavier solar panel array contributes to payload mass and requires a greater amount of propellant for the maneuver, while a smaller, lighter solar panel array increases the electrolysis time and allows more propellant to be lost in the process. Figures 3 shows propellant required for maneuvers of 1, 2, 3, and 4 km/s at Earth with 0.1% boiloff per day and a specific impulse of 450 s, as a function of the solar panel mass from 1 to 10 t. The need to store propellant for future maneuvers is not considered here, because all of the architectures described in this paper refuel before Mars orbit injection and/or trans-Earth injection for the return trip. The optimal solar array mass for each V is shown in Table II-5. During the course of the mission, solar solar panels degrade, reducing power production. Also, at Mars, solar irradiance is 44% that at Earth.35 Figure 4 shows the same for solar panels at Mars, that have degraded to 90% effectiveness and are receiving 44% of the irradiance they had at Earth, for a net reduction to 39.6% power. Electrolyis takes longer, and more propellant is lost to boiloff in the process. However, for trans-Earth injection, the payload mass is significantly reduced—by approximately 11 to 47 t. So, less baseline propellant is needed. The optimal solar array mass for each V is shown in Table II-5 for Earth, and Table II-6 for Mars. While some propellant is lost to boiloff during electrolysis even with optimum solar panel mass, the results compare favorably to that lost if it were stored cryogenically throughout the mission, even with extremely efficient storage for the latter. For example, for a 47 t payload at Mars, with 0.1% boiloff per day and 3.03 t of solar panels, 21.523 t of propellant must be electrolyzed over 123 days, with a loss of 5.94% for a final total of 20.245 t for a 1.5 km/s maneuver. For a cryogenic propulsion module that travels with the crew and is stored for 713 days before being used for trans-Earth injection, 76% of the stored propellant is lost. If this cryogenic storage is more efficient than the intermediate storage for the electrolysis propulsion system, with 0.01% boiloff per day, 13.3% of the propellant is still lost before TEI, so that more propellant is needed even with much more efficient cryogenic storage. In practice, increasing the solar array mass from the optimum allows the thruster to ready for maneuvers faster at the cost of slightly increasing the total propellant required. Also, the optimal array masses for Mars and Earth are different because of the different payload mass, power production, and maneuvers required. A nearly optimal array for one planet could be one slightly above the optimal value for the greatest expected maneuver, such as 3.1 t for Mars, and 5.1 t for Earth. Tables II-7 and II-8 show the performance off a 3.1 t solar array at both, while Tables II-9 and II- 10 show the performance of a 5.1 t solar array at both. The 5.1 t array performs well, requiring at most 3.5% more water for electrolysis than optimal. In exchange, the time to electrolyze in preparation for maneuvers is significantly cut, by 10.3% to 63.7% depending on the maneuver. The selection must consider the options of departing from different initial trajectories, such as LEO, HEO, and the Earth-Moon Lagrange point 2 (LL2) in the next subsection. The results of this section—the different trajectory options available, maneuver time and launch vehicle mass constraints—lead to a solar array mass of 5.1 t (170 kW) as the baseline for the architectures discussed in Section III. 7 American Institute of Aeronautics and Astronautics 0 Downloaded by NASA LANGLEY RESEARCH CENTRE on January 30, 2018 | http://arc.aiaa.org | DOI: 10.2514/6.2018-1537PDF Image | Water Electrolysis for Propulsion of a Crewed Mars
PDF Search Title:
Water Electrolysis for Propulsion of a Crewed MarsOriginal File Name Searched:
water-electrolysis-propulsion.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Power up your energy storage game with Salgenx Salt Water Battery. With its advanced technology, the flow battery provides reliable, scalable, and sustainable energy storage for utility-scale projects. Upgrade to a Salgenx flow battery today and take control of your energy future.
CONTACT TEL: 608-238-6001 Email: greg@salgenx.com (Standard Web Page)