The X-33 program was initiated to develop a testbed to demonstrate the industrial capability for an operational sustained use launch vehicle (Venture Star). Within the NASA Future X Trailblazer program there was an Upgraded X-33 that was to focus on materials and other upgrades. In the authors' view the most significant gains could have been realized by upgrades to the propulsion cycle and the questioning the SSTO concept of operation. The propulsion cycles examined are all rocket based cycles. Specifically, these are: turbopump rocket, topping cycle rocket, expander cycle rocket, air augmented rocket, ram rocket, LACE rocket and a deeply cooled air cycle rocket. The vehicle size, volume, and structural weight remained constant. The system weights vary with the propulsion system cycle. An increase in specific impulse reduced the mass ratio to achieve a given velocity thus reducing the propellant weight required. That reduction could be converted into increased payload weight or an increased velocity for the same propeilant weight.. This analysis was extended to Venture Star for selected engine cycles. The results show that the X-33 test bed could have been a valuable frequent flight test bed for achieving a higher flight rates. The published maximum speed is about 15,000 ft/sec. With upgraded propulsion systems enabled velocity increments approaching orbital speeds. Vehicle layout and data from http:// www.venturestar.com.
展开▼
