In this paper, the feasibility of single-stage-suborbital (SSSO), single-stage-to-orbit (SSTO), and two-stage-to-orbit (TSTO) rocket-powered spacecraft is investigated using optimal control theory. Ascent trajectories are optimized for different combinations of spacecraft structural factor and engine specific impulse, the optimization criterion being the maximum payload weight. Normalized payload weights are computed and used to assess feasibility.

The results show that SSSO feasibility does not necessarily imply SSTO feasibility: while SSSO feasibility is guaranteed for all the parameter combinations considered, SSTO feasibility is guaranteed for only certain parameter combinations, which might be beyond the present state of the art. On the other hand, not only TSTO feasibility is guaranteed for all the parameter combinations considered, but a TSTO spacecraft is considerably superior to a SSTO spacecraft in terms of payload weight.

Three areas of potential improvements are discussed: (i) use of lighter materials (lower structural factor) has a significant effect on payload weight and feasibility; (ii) use of engines with higher ratio of thrust to propellant weight flow (higher specific impulse) has also a significant effect on payload weight and feasibility; (iii) on the other hand, aerodynamic improvements via drag reduction have a relatively minor effect on payload weight and feasibility.

In light of (i) to (iii), with reference to the specific...