Challenges and opportunities of wireless sensor networks (WSNs) in space applications are presented. The investigation of internet protocols, ad hoc routing and commercial-off-the-shelf (COTS) wireless communication protocols for efficient and reliable network design is addressed. In order to facilitate the analysis, several application scenarios of space-based WSNs are given, including autonomous formation flying, very-small-satellite cluster/swarm, fractionated spacecraft, onboard sensor network and surface vehicles for planetary exploration. Criteria that contain network scale, link range, degree of dynamics, data rate, power consumption, time intensive requirement, and degree of cooperation are proposed in order to classify applications and choose the most potentially applicable technologies. Different levels of challenges to implement each application are also compared.