A network test system seeks to improve visibility into the real-time operation of a network system or subsystem of a spacecraft through the use of a port from each relevant network to a spacecraft test interface. The network test system includes a packet switch operatively coupled downstream from a SERDES receiver and operatively coupled upstream from a SERDES transmitter. The packet switch in conjunction with the signal replicator in the SERDES receiver taps off a data stream of the network activity so that the port allows an observation device to passively observe the network activity. The system is adapted to increase real-time observation of network activity without disturbing the network.