fewer hardware parts and hence less parts need to be developed, manufactured, assembled and operated. What are then the drawbacks. The suggested SSTO concepts such as Delta clipper and Beta 2 are designs that presses the SoA in materials, propulsion and operations. This can be seen by using the most basic of rocket formula for calculating the added velocity given by a stage. This is the “Tsiolkovsky “ equation. In this case it is used to calculate the total velocity during the ascent to orbit. [] The AV is normally for Ariane about 9350 m/s for a Earth to LEO launch. However for a SSTO a “minimum” total AV of 8250m/s [Koelle, 1992] has been suggested. The lower Av suggested is possible due to the use of an extreme low orbit 70 x 200 km. g is the gravity constant 9.81 Isp is the average specific impulse during the entire launch. Current design on high thrust and high performing cryogenic engines for Earth to orbit (SSME, Vulcain, LE-7) use fixed area ratio nozzles. The current European Vulcain engine has an area ratio of 45 and has a ground level Isp of 335 s and a vacuum Isp 430 s. SSME has 365s and 450s respectively [Heald, 1991]. The average of these engines are some 410-420s. If instead a nozzle design had a variable area ratio or was otherwise adaptable, then this mean Isp could be increased to 425s to 435 s In (Mig / Mbo) is the natural logarithm of the ratio between the rockets mass at ignition versus the mass at burnout. This can be restated using the structural factor II :Mstructure / Mpropellant or the propellant fraction 1 / II. Today's large cryogenic rocket stages typically have a structural factor of 0.1 i.e. 10% of the stage mass is the structure and the engines.. Numbers for Ariane 5, H-II first stages are 0.097 and 0.13. The STS external tank (which is only the tank) but 5-10 more propellants has a II of 0.04. New material could replace today's materials then the II would change from 0.1 to 0.09,0.07 or even 0.05 Results Assuming a vehicle with about 400 ton total mass and running the formula with today's values of AV 9350 m/s an Ispav= 410 s and a 11=0.1, would result in negative payload (14 tons) if allowing for additional masses in the order of 18 tons If that same vehicles would be build in near term with the use of deployable nozzles having - Ispav 425 - and state of the art commercial materials -11=0.09- and by using the lower AV of 8250 this would result in a payload 8 tons, a 2% payload fraction However it is most probable that the SSTO system would be reusable. Hence the recovery system and increased life of components engine would lead to a heavier system. By assuming that a 50% higher structural factor would account for this the resulting vehicle would again produce a negative payload.(-9 ton) However by using near term technology for adaptable nozzles which would result in an increased Ispav of 435 and a structural factor of 0.08 and assuming that the 18 ton factor can be decreased to 10 tons, then the delivered payload is again 7-8 tons. The conclusion is that a successful SSTO vehicle seems feasible, if done by taking a stepped approach starting by demonstrating the available technology with an expendable vehicle. The vehicle can then later be updated which new technologies to achieve reusability Space Transportation Systems for the 21st century—Spaceplanes Trends Towards Next Generation Space Transportation Systems Constructions of usable and low-cost space transportation systems are under development, for use as Earth to Orbit vehicle. During the initial stages of spaceflight there is a significant amount of air present. If new engines using air-breathing technology can accelerate these systems up to more than Mach 18 using atmospheric oxygen, these can achieve orbit using a single stage, like an airplane. The United States, former U.S.S.R, China, Japan and France, the Space developed countries, are all
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