<p>Current methods for initial orbit determination (IOD) of newly detected space objects, such as the admissible region (AR) and its derivatives, generally yield high initial uncertainty. This makes it difficult and time-consuming to establish custody of new objects. Previous work has mitigated this issue for objects generated by breakup and deployment events using random finite set (RFS) spawning transition densities. However, these spawning models are defined in Cartesian state space and therefore require precise knowledge of when the new object separated from its parent. This paper presents a new IOD method based on the theory of ARs that leverages the parent object’s estimated (probability density function probability density function (PDF) to provide a unique combination of benefits compared to prior techniques for RFS-based spawning and AR-based IOD: an orbit estimate is created from a single measurement of a new object, no time knowledge is required, the resulting PDF is relatively small (depending on the assumed maximum change in velocity), and the method is able to adapt to changes in the rate at which new objects appear over time. The new method is shown to provide significantly lower initial uncertainty and enable faster acquisition of custody than an AR birth model in simulated breakup and deployment scenarios.</p>