AbstractAlthough there is no doubt about the feasibility of personal communications via small satellites in low earth orbit, there is considerable uncertainty about the size of the market, whether the specific applications will be business or personal in context, about the market relationship between voice services and data services, and the implications for system design of any information that might be developed on these questions.This paper will develop the concept that the key to understanding low orbit small satellite communications systems is the message delivery time requirement of markets and that the data services market has a widely varying range of acceptable data delivery times. We estimate the distribution of data delivery time versus population of users on a global basis.A second concept to be developed in this paper is that low orbit satellites are in some respects matched to global data delivery applications because of the daylight time zones and natural delays they impose.Using the estimated market size versus message delivery time, we show that there is a significant design implication for the space segment in terms of the number of satellites, the orbit period, and the use of crosslinks. It will be further shown that the difference in complexity of data and voice services with respect to cost argues for the rapid emergence and success of data services.Finally, we will show that a preferred terminal architecture may be an accessory orappliquefor a personal computer, rather than a small dedicated satellite terminal, based on the extant population of personal computers. A review of the planned terminal architectures of emerging systems reveals that using a personal computer as the basis for a terminal has not yet received wide interest. In particular, the new laptop smaller computers may be the natural catalyst for personal satellite data services in facilitating the terminal.