# From the Martian Surface to Its Low Orbit in a Reusable Single-Stage Vehicle--[PERSON]
## 3 Results
### Design Analysis
#### 3.5.2 Reliability  
The goal is to use Charon to transport humans on Mars for as long as possible--ideally for 75 launches over 20 years. This high number of launches from the same vehicle considerably increases the risk of LOM, LOC, and LOV. This means that the vehicle shall be designed to be as reliable as possible, explaining the need for redundancy in all critical subsystems, and the abort system capable of detaching the crew capsule from the rest of the vehicle, would the need arise.  
Because of this, the SL-LOC probability is required to be below 0.5%. Over 75 launches, this combines to a LOC probability of 31.3%. While this is high, it is deemed acceptable, as the first missions on Mars, requiring such intense use of a single vehicle, are accepted to be  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Flight Phase** & **Delta-V [m/s]** & **MGA** & **MGA Delta-V [m/s]** \\ \hline Vertical flight & 92 & 25\% & 114 \\ Gravity turn & 4533 & 5\% & 4759 \\ Hohmann transfer & 46 & 5\% & 48 \\ Inclination change & 289 & 5\% & 304 \\ Re-entry insertion & 261 & 25\% & 274 \\ Landing burn & 338 & 25\% & 423 \\ Flight Reserves (5\%) & 278 & 0 & 278 \\
**Total** & **5837** & **6\%** & **6200** \\ \hline \hline \end{tabular}
\end{table}
Table 4: Delta-V budget.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Subsystem** & **Mass [kg]** & **MGA Mass [kg]** \\ \hline Life support & 456 & 548 \\ Abort & 4259 & 5111 \\ Power & 1047 & 1256 \\ Communication & 31 & 37 \\ GNC & 1933 & 2320 \\ Aerothermal & 2399 & 2879 \\ Structure & 15,517 & 18,621 \\ Propulsion & 2621 & 3146 \\ Payload & 1200 & 1200 \\
**Dry mass** & **28,263** & **33,918** \\ Propellant mass & 137,886 & 164,807 \\
**Wet mass** & **166,149** & **198,725** \\ \hline \hline \end{tabular}
\end{table}
Table 3: Mass budget.  
of high risk. The SL-LOV and SL-LOM probabilities have been agreed to be of 2.5% and 5.5%, respectively.  
In comparison, the Space Shuttle had a loss of crew probability of 1 in 100 [54], and these vehicles were used for a maximum of 39 flights. The non-crewed reusable Falcon 9 Block 5 also has a landing failure rate of 5 in 59, or 8.5%, with a maximum of 9 flights for a single vehicle [55].  
To assess whether or not Charon fits these requirements, a fault tree analysis has been carried out. To build it, all different subsystem and part failures that would lead to either SL-LOC, SL-LOV, or SL-LOM have been listed. Then, taking into account the failure probability for a single component, the total number of components, and the number of redundant components, the combined failure probability is computed. Different components failure were also assessed. Individually, these would not lead to any failure, but combined, they would. For instance, a fire in the capsule would lead to LOM, as the fire would need to be suppressed, the crew put back in their pressurised suits, and [PERSON] would get back to the base. An oxygen leak from the life support in itself would not lead to any loss, as the tank could be emptied, and the two other tanks in the capsule would still be usable. However, if a fire were to start combined with an oxygen leak, this scenario would lead to LOC.  
This work of listing all components and scenario lead to 34 possible failures leading to LOM, 23 to LOV, and 38 to LOC. For the sensitivity analysis of the final LOM, LOV and LOC probabilities, the individual event probabilities were assumed to be normally distributed. The standard deviation was chosen to be 30% of the mean value. The calculation of the final probabilities was run 10,000 times, varying all parameters simultaneously according to their respective normal distributions. The computed LOM, LOV, and LOC probabilities are presented in Table 5, along with their sensitivity analysis.