## 3 Results
### Identify Sources of Uncertainty and Generate Alternatives in Satellite Megacontellation Scenarios  
From interviews with industrial practitioners, it emerged that one of the biggest sources of uncertainty in megaconstellation businesses is the type of propellant that will be most convenient to use in the future. While the existing electric propulsion market is mostly based on xenon (Xe) propellant, the development of megaconstellation projects requires to evaluate alternatives propellants that are either cheaper or compatible with the higher volumes required. Xenon is an expensive substance and is not produced in high quantity. Furthermore, the need for xenon in other industrial sectors is likely to increase its price in the future. For example, the automotive industry's increased use of xenon for headlights has resulted in a higher demand for xenon. There is a need to investigate the benefits and constraints that could be obtained from cheaper alternative propellants such as krypton (Kr) obtained from non-traditional supply sources [50]. After applying'real options' principles [24], the following alternatives were identified in order to accommodate changes in the use of propellant. The alternatives are visualized in Figure 4 together with their performances (Power, Thrust, Isp) and reliability levels. This input data is shown in a qualitative fashion to protect company sensitive information. However, the data is within \"assumable\" ranges than can be extrapolated from literature (e.g., [51; 52; 53]) and publicly available material ([40; 41; 42; 43]). Also, the values for performances, masses, reliability and costs can be estimated using already published models (e.g., [47; 48; 49]). Figure 3: Proposed method to trade flexibility and qualification ability against functional performances and unit costs. The authors believe that the lack of disclosure of this input data (while undermining the complete transparency of the results) is still relevant to fulfill the purpose of the case study. As stated in the introduction, the purpose of this case study is to demonstrate the methodology in an industrially relevant set-up, rather than a detailed comparison between alternative propellant systems. The novelty of the methodology (compared to previous studies) is the ability to include variations in market behavior, beyond variations of 'traditional' attributes such as masses and performances. Therefore, this paper has focused more on providing the input data regarding the variation of the market parameters, which are introduced in the next sections (e.g., Table 1). The alternatives are summarized as follows. Option 1 is labelled as _Single development, Xe optimized design_: in this option, the possible use of alternative propellants is disregarded, and the manufacturers follow the cost-efficient strategy of developing and optimizing only an existing design compatible with xenon. This strategy exploits the current know-how of the company and ensures to provide an EP in a cost-efficient manner with good power and reliability levels. Option 2 is labelled as _Double development, Xe and Kr optimized_: in this option, the possibility to use both xenon and krypton is enabled by the parallel development, test and qualification of two separated systems. While this strategy ensures the flexibility of offering customers both a xenon and a \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & **Market 1** & **Market 2** & **Market 3** \\ \hline Final Orbit (km) & 1500 & 1200 & 800 \\ Constellation Size (Number of Satellites) & 300 & 900 & 4000 \\ Min Constellation Size (Number of Satellites) & 100 & 300 & 500 \\ Number of Satellites per Launch & 20 & 40 & 60 \\ Cost Xenon (k\(\epsilon\)/kg) & 3 & 3 & 3 \\ Cost Krypton (k\(\epsilon\)/kg) & 0.5 & 0.5 & 0.5 \\ Satellite Mass without EP (kg) & 800 & 600 & 400 \\ Launch Cost per Kilo (k\(\epsilon\)/kg) & 4 & 3 & 1.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Input data for the market scenarios considered in the present study.