# Secure and Transparent Space Exploration Data Management Using a Hybrid Blockchain Model
## 1 Introduction  
The rapid advancement of space exploration has led to increased international collaboration among space agencies, research institutions, and private enterprises. Countries such as the United States, Russia, China, and member states of the European Space Agency frequently conduct joint missions, technology exchanges, and collaborative research projects. However, managing and securing space-related data across multiple organizations. Involving multiple organizations presents serious challenges in terms of integrity, transparency, and confidentiality. Traditional space data management systems rely heavily on centralized infrastructures, which are prone to single points of failure, unauthorized access, and data tampering risks pose risks such as data tampering, unauthorized access, and single points of failure. As data sensitivity grows--covering astronaut activity records, spacecraft diagnostics, and extraterrestrial observations--trust in data handling mechanisms becomes a mission-critical requirement.  
Blockchain technology [1] provides a decentralized alternative, enabling transparent and tamper-resistant record-keeping provides a decentralized approach to data management, ensuring integrity and transparency. Moreover, such technologies have shown promise in enhancing cybersecurity [2] and securing inter-agency data transactions. Yet, public blockchains are often unsuitable for sensitive data due to their transparency andperformance limitations. However, a fully public blockchain system is not suitable for storing confidential or mission-critical data due to privacy concerns and high computational costs. In contrast, private blockchains [3] offer controlled access but lack global verifiability, transparency, and inter-organizational verification mechanisms. This leads to a trade-off between privacy and transparency, which is especially pronounced in multinational space missions.  
To overcome this, we propose a hybrid blockchain architecture [4] that integrates the benefits of both public and private blockchains. Recent studies have demonstrated the applicability of hybrid blockchain models for secure and privacy-preserving applications across various domains, such as vehicular networks [5] and decentralized file storage systems utilizing Soulbound tokens [6]. These works highlight the increasing relevance and versatility of hybrid blockchain architectures in addressing both transparency and confidentiality challenges. In this model, non-sensitive data--such as mission logs--are stored on a public blockchain [7], enabling universal access and verification. Sensitive data are retained within a private blockchain, protected via cryptographic access control mechanisms. Data integrity is guaranteed using zero-knowledge proofs [8], allowing verifiers to confirm authenticity without exposing private content. Among various ZKP techniques, zk-SNARKs are particularly suitable due to their succinct proof size and efficient on-chain verification [9].  
To ensure interoperability and near-real-time consistency across chains, the system employs the Cross-Chain Interoperability Protocol [10], which supports event-driven communication between smart contracts deployed on separate blockchains. This method avoids reliance on centralized oracles [11] and ensures secure synchronization. Smart contracts [12] enforce access control policies through a role-based access control model, allowing only authorized roles to retrieve sensitive data.  
This paper presents a practical implementation of the proposed architecture using Ethereum and Hyperledger Fabric. The model was validated through a case study involving extravehicular activity data from NASA and Roscosmos. The system demonstrated high integrity verification, strong access control, and feasible synchronization performance. As international collaboration in space exploration intensifies, this approach provides a foundational framework for trustworthy, decentralized, and auditable data management in cross-agency missions.