Figure 1(b) The proposed process layout of the water atomization process.

Debris collection method

The DHEM space broom proposed by V.R.Sanal Kumar et al. [19] is chosen as a profitable method for the collection of space debris to the ISS. The feedback controlled variable sweeping speed DHEM space broom will be capable of capturing all the space debris nearing to the ISS including the non-functional objects having an average size between 1 cm and 10 cm, which are moving with different velocities and directions and polluting the space environment and creating risk to live satellites and space vehicles. Note that the debris capturing net made ofGraphene material, and the bidirectional plasma thruster [29], could be other options for space debris collection for the operational protection redundancy. The technology of the net proposed by ESA [30] in this regard could be used for capturing the debris after decelerating it using plasma thrusters.

Debris sorting method

A mechatronic control device, with cameras and/or lasers, is proposed for separating the irregular-shaped debris into discrete materials, viz., magnesium, aluminum, etc. [31]. The device could achieve to sort out 2000-3000 particles per second, with a minimum power consumption (~1 kW) [32, 33].

Debris melting method

The amount of electrical energy required for the electrical channel induction furnace for melting the collected debris in ISS is estimated onboard using an algorithm with traditional thermodynamics’ equations. The evolved gases from the molten debris are collected in separate canisters for the profitable design of the space thrusters for numerous applications onboard and off board, which comprises the desirable orbital tweaks of the ISS. The entire system will be in a capsule facilitated with an artificial gravity generator to create a gravity induced free-falls of fluids. As stated earlier, an artificial gravity could be created using an artificial gravitational field using frame-dragging or gravitomagnetism [25] or by invoking a centripetal force.

The powder fuel production

A well- designed tundish is equipped in the ISS for storing the liquid paste in the molten state (see Fig.1(b)).And for converting the molten material into small granules, a high velocity water jet is facilitated in the atomization process in thespace lab with multiple nozzles. The small granules could be placed in the alloy powder box after sorting out, and the water will be recycled through the dewatering system and filters. The collected granules are dried and the sizes of the granules are regulated according to onboard applications. A loss of 3-5 % is anticipated during the sieving of powders. The required water for the atomization administration is acquired from the proposed recycling, alkaline fuel cell, and electrolysis methods. The proposed electrolysis method is the alkaline water electrolyzer, which could operate at a low temperature (80o C – 200o C) with an efficiency of 70-80 %. The proposed system is capable to prevent powder oxidation and thermal self-ignition [34]. Note that until recently (2019) water atomization process was not used to creating aluminum and aluminum alloy powders primarily due to the anticipated detonation risk due to the secretion of hydrogen as a result of powder interaction with water. Furthermore, water atomization process was not, recommended due to the apprehension of powder oxidation and the deterioration of powder properties. Admittedly, these problems have been resolved at the Institute for Problems of Materials Science (Kiev, Ukraine). These are succinctly reported by Oleg D. Neikov et.al. [34].
In our system, the heat energy obtained from the electrolysis process is used for drying the powders. The desired powders are separated with an objective for creating feigned soil in the ISS for cultivating pharmaceutical flora. Furthermore, the other selected metal powders are mixed with oxidizers and binders for making solid propellants for chemical propulsion. The powders, essentially aluminum, obtained with the desirable properties of solid propellants could be used for micro-thrusters for nanosatellites or devising other propulsion systems in the space lab. The silicon powder segregated from the debris powder could be used for making artificial soil in the ISS for vegetation as it plays important roles in mineral nutrition of plants. Note that silicon fertilizers today are very common in many crop production systems worldwide as it shows the significant amount of evidence in improving crop productivity [35]. The comprehensive process layout highlighting the water atomization process is shown in Figure 1(b). As mentioned earlier, the water atomization process and the other systems will be placed in a capsule where the artificial gravity environment persists. In this study, we are suggesting a water-cooling method for cooling down the system. The steam evolved during the process will be collected in a different water vapour storage canister. The steam will be regulated in the gaseous phase and will be used for the selective thrust-vectoring of the space station / ISS. Alternatively, steam evolved during the process can also be recycled and used as water resources for the atomization process. The temperature inside the capsule is maintained using the ATCS (Active Thermal Control System) which is currently used in the ISS to regulate the temperature [36]. However, a further experimental study on water atomization and the cooling system in a microgravity environment is required for its qualification.