# Space Habitat Data Centers--For Future Computing
## 6 Feasibility and Performance Evaluation
### Performance Evaluation and Benefits--Computing-Resource-Related QoS
In addition, accessing the SHDC instead of HAP computing platforms reduces computing resource access latency by 24.5% on average. The results in Figures 7 and 8 show the forwarding latency when the HAP computing platform and terrestrial computing platforms are accessed through HAP forwarding links respectively. Results in Figures 7 and 8 shows that the forwarding latency increases with forwarding HAPs. Analysis of results in Figures 7 and 8 shows that increasing the number of forwarding HAPs from 1 to 3, 1 to 2, and 2 to 3 increases the forwarding latency by [96.1%, 61.3%, 90%] and [44.7%, 35.6%, 14.2%] on average respectively. The use of the SHDC instead of HAP and terrestrial data centres via forwarding reduces the computing platform access latency. Extensive simulations show that the compute resource access latency is reduced by up to 98.5% on average. \begin{table}
\begin{tabular}{c c c} \hline \hline
**S/N** & **Parameter** & **Value** \\ \hline
21 & Number of Space Habitat Data Centers & 3 \\ \hline
22 & Space Habitat Data Center Altitude–[1, 2, 3] & [921.1, 252.5, 383.7] km \\ \hline
23 & Number of High Altitude Platforms & 4 \\ \hline
24 & High Altitude Platform Altitude (Mesosphere)–[1, 2, 3, 4] & [25.4, 74.1, 67.5, 71.9] km \\ \hline
25 & Size of Data Transmitted by High Altitude Platforms–[1, 2, 3, 4] & [1.4, 0.997, 0.45, 1.96] Mbps \\ \hline
26 & Inter–High Altitude Platform Link Speed & [1.92, 0.69, 0.08] Mbps \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._  
Figure 6: Simulation results for the compute resource access latency for existing and proposed cases. The evaluation also investigates how the use of SHDCs enhances space segment accessible computing resources. The simulation uses test SHDCs hosting a limited number of servers and five LEO space vehicles. Two space vehicles are utilised for executing algorithms and processing data related to space astronomy. Three LEO SHDCs (each with three servers) are considered. The utilised values are in Table 4. The investigation of accessible computing resources for the existing scheme is done considering two cases. In the first case, the existing orbital edge computing [19] is considered. Figure 8: Forwarding latency when accessing terrestrial computing platforms by forwarding through HAPs. Figure 7: Simulation results for the forwarding latency in the case of accessing high-altitude platforms (HAPs). The second case is one in which the computing resources on space vehicles are accessed in addition to that of existing orbital edge computing. The accessible computing resources are also investigated as an important QoS metric. The launch and use of SHDCs increases the amount of computational resources available for satellite data processing. This is because the SHDCs can host a significant number of servers in comparison to existing space edge computing platforms found in [PERSON] et al. (2019). The accessible computing resources are investigated using the performance evaluation parameters presented in Table 4.  
The result of the accessible computing resources is shown in Figures 9 and 10. The simulation also investigates how the use of up to two SHDCs enhances accessible computing resources. The result in this case is shown in Figure 10. Analysis shows that using one SHDC and two SHDCs instead of existing scheme without and with space vehicles increases accessible computing resources by \([65.3\%,46.7\%]\) and \([77\%,64.7\%]\) on average, respectively. In addition, increasing the number of SHDCs from one to two improves accessible computing resources by \(33.8\%\) on average. \begin{table}
\begin{tabular}{c l l} \hline \hline
**S/N** & **Parameter** & **Value** \\ \hline
1 & Number of Satellites & 10 \\ \hline
2 & Number of Epochs & 15 \\ \hline
3 & Number of Space Vehicles and Space Habitat Data Centres & \(5,3\) \\ \hline  
ompute Resource Utilisation on Space Vehicles-[3; 4; 5] & [63.8\%, 37.2\%, 28.8\%] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation parameters for investigating accessible computing resources.