https://www.coindesk.com/bitcoin-nodes-need/
It's well known that bitcoin is designed as a decentralized peer-to-peer (P2P) network. However, what's often lost in translation is the sheer amount of machinery that is needed to maintain this global infrastructure.
For example, in order to validate and relay transactions, bitcoin requires more than a network of miners processing transactions, it must broadcast messages across a network using 'nodes'. This is the first step in the transaction process that results in a block confirmation.
To function to its full potential, the bitcoin network must not only provide an avenue for transactions, but also remain secure. By using a number of randomly selected nodes, the network can reduce the problem of double spending – when a user attempts to spend the same digital token twice.
However, bitcoin doesn't just need nodes, it requires lots of fully functioning nodes – nodes that have the bitcoin core client on a machine instance with the complete block chain. The more nodes there are, the more secure the network is.
This is one of the reasons there is a plan to put bitcoin nodes in space, and that the plan has important implications for bitcoin.
The problem is, the number of nodes on the network is dropping, and core developers believe it may continue to do so.