Another solution of improvement is using the Energia main engine. In this case, the Saturn 5's payload will roughly increase from 119 tons to 145 tons. In terms of cost this solution seems to be better. __________ Table 8.9 Engine performance- comparison between F-l and RD-170________ Additional Boosters for the First Stage Another method of improvement is adding solid/liquid boosters for the first stage. Candidates are the Solid Rocket Boosters (SRB) of the US Shuttle and the liquid booster of the Energia. It is more efficient to use the Energia boosters, because of the higher performance of this boosters. They use liquid propellant and therefore they have a higher specific impulse. In this case structure changes would be required to attach the boosters on the first stage. In our point of view the future use of the updated Saturn 5 seems to be an interesting possibility. Analyzing the first ideas given above it looks feasible, but needs some more detailed studies. Big Dumb Booster - Pressure Fed with Large High Thrust Engines. This system has been considered in the early 1960's as a method of placing large payloads into orbit. The vehicle uses tankage made in shipyards rather than in the very precise environment of a typical aerospace clean room. The reason shipyards are used is because the size of the tankage is extremely large and very thick. This is in contrast to the thin-walled tankage designs that are typical of flight systems like the Space Shuttle or Ariane. Thick tank walls are required because the tank pressure is high: (50 to 100 Bar). 8.5.4 Bulk The bulk cargo would only be concerned with cost and resiliency. Depending on strategy a HLLV, mass driver / RAM accelerator or laser propulsion could be used. Having a transport thats launches only bulk i.e. metal, water, glass would mean on orbit production of metal structures, LH2 / LOX and solar panel covers. This would be economic if launch cost was low enough. Also it would prepare for materials delivered from a future lunar base. RAM Accelerator The ram accelerator is a chemically driven mass driver. Tests of speed up to 3 km/s and masses up to 20 grams have been demonstrated. The basic idea is to fill tube with premixed gases of hydrocarbons/hydrogen and oxygen. By having separators within the tube, difference in mixtures and hence also the Mach number can be obtained. By firing a free flying ram like projectile into the tube a combustion is obtained by the shock wave behind the projectile. This combustion can presently accelerates the projectile with over 30.000g. The whole system is robust and inherently scalable. It is today envisaged that a 4 km tube on the side of a mountain could accelerate 2 ton projectiles with 500 gs to 10 km/s. In the projectile a rocket engine for orbit injection would be included. The resulting payload fraction to LEO could be as high as 40%. The orbital cost for this bulk transporter is significantly -at least two orders of magnitude- lower then current launch costs. 8.6 Technology Assumptions The characteristics of a space transportation system is directly related to the state of the available technologies. The purpose of this section is to define, for each of the basic technologies, the forecast level of performance from years 2002 to 2042. The following sections will mainly consist in an
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