# Satellite-Aided Consensus Protocol for Scalable Blockchains
## 7 Conclusions and Future Research  
Utilizing satellite systems for advanced public blockchains is a promising approach, due to ubiquitous connectivity and wide coverage. Hence, this study proposed a novel satellite-aided consensus protocol for efficient space-terrestrial blockchains. Unlike existing works [19; 20], we used satellites as neither full blockchain nodes nor relays. In our study, we do not rely on costly consensus protocols such as PoW but designed a proper working principle according to the space-terrestrial networks' characteristics. We analyzed the system performance regarding throughput and security. In terms of security, we took both adversarial miners and satellites into consideration. In the throughput analysis, we investigated the maximum throughput under the capacity limits and further modeled the  
Figure 5: Comparison of the proposed protocol and PoW regarding throughput and safety. Figure 6: The impact of network delay on the throughput of the proposed protocol. case with propagation delays by a Markov chain. Compared with the traditional PoW, the proposed consensus protocol exhibits higher scalability. Remark that satellite-aided blockchains also open several interesting future directions. * Access control. As pointed out in Section 4, a larger fraction of adversarial satellites \(\beta_{s}\) will increase the confirmation error probability, which means an adversary can make the blockchain more vulnerable by hacking satellites. Therefore, access control is vital to the space-terrestrial blockchains [43]. On the one hand, our protocol does not require (or allow) terrestrial networks to upload data to satellites, which reduces the risks as another advantage. On the other hand, context-aware access control [44] should be considered as a potential approach to safeguard satellites further. * Multiple satellite coordination. A constellation of satellites can multicast oracles for more extensive coverage, which can benefit space-terrestrial blockchains. Our protocol can easily expand from a single satellite setting to a constellation of participation satellites. However, it might compromise the blockchain security since more vulnerabilities are exposed in a constellation. More works need to be done for a practical space-terrestrial blockchain with multiple satellites. * Information propagation model. In Section 5.2, we assess the impact of propagation delay by only considering \(i_{\Delta}\), the fraction of informed nodes after one round. However, in the real world, network delays could be long-tailed or even unbounded [29]. A more general information propagation model is needed to characterize the terrestrial network and evaluate the throughput more accurately in future works. Conceptualization, X.L., Z.D. and X.G. ; methodology, X.L., Z.D. and X.G. ; software, Z.G. and Y.L. ; validation, X.L., Z.G., and Y.L. ; formal analysis, X.L., Z.G. and Z.D. ; investigation, X.L., Z.G., and L.Y. ; resources, X.L., J.W., Z.D. and X.G. ; data curation, Z.G. and Y.L. ; writing--original draft preparation, X.L. ; writing--review and editing, X.L., Z.G., [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]; visualization, [PERSON] and [PERSON]; supervision, [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]; project administration, [PERSON], [PERSON] and [PERSON]; funding acquisition, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This work is supported in part by the National Key R&D Program of China under Grant 2018 YFB1801103. The work of [PERSON] is supported in part by the National Natural Science Foundation of China under Grant 61901111; the Natural Science Foundation of Jiangsu Province under Grant BK20190331; and the Research Fund of the National Mobile Communications Research Laboratory, Southeast University, under Grant 2019B02. The work of [PERSON] is supported in part by the National Natural Science Foundation of China under Grant 61801114.