SSTO vs TSTO design considerations—an assessment of the overall performance, design considerations, technologies, costs, and sensitivities of SSTO and TSTO designs using modern technologies

Abstract

It is generally believed by those skilled in launch system design that Single‐Stage‐To‐Orbit (SSTO) designs are more technically challenging, more performance sensitive, and yield larger lift‐off weights than do Two‐Stage‐To‐Orbit designs (TSTO’s) offering similar payload delivery capability. Without additional insight into the other considerations which drive the development, recurring costs, operability, and reliability of a launch fleet, an analyst may easily conclude that the higher performing, less sensitive TSTO designs, thus yield a better solution to achieving low cost payload delivery. This limited insight could justify an argument to eliminate the X‐33 SSTO technology/demonstration development effort, and thus proceed directly to less risky TSTO designs. Insight into real world design considerations of launch vehicles makes the choice of SSTO vs TSTO much less clear. The presentation addresses a more comprehensive evaluation of the general class of SSTO and TSTO concepts. These include pure SSTO’s, augmented SSTO’s, Siamese Twin, and Pure TSTO designs. The assessment considers vehicle performance and scaling relationships which characterize real vehicle designs. The assessment also addresses technology requirements, operations and supportability, cost implications, and sensitivities. Results of the assessment indicate that the trade space between various SSTO and TSTO design approaches is complex and not yet fully understood. The results of the X‐33 technology demonstrators, as well as additional parametric analysis is required to better define the relative performance and costs of the various design approaches. The results also indicate that with modern technologies and today’s better understanding of vehicle design considerations, the perception that SSTO’s are dramatically heavier and more sensitive than TSTO designs is more of a myth, than reality.