D
dwightlooi
Guest
It is well known that solid boosters have inferior performance to liquid boosters, and nothing can be further apart than a Hydrogen Booster and a Solid Booster. Is that really true? Well, if you measure performance in terms of payload mass as a fraction of lift off mass, it is definitely true. But is that important?<br /><br />To illustrate the point let us consider two boosters -- the all hydrogen Delta IV (medium 4,0) and a hypothetical Affordable Solid Launch Vehicle (ASLV). Both are 2-stage vehicles. <b>The Delta IV lifts off at 260 tons and puts 8.6 tons into LEO. </b>That is a payload fraction of 3.3%. <b>The ASLV takes off at 1185 tons and it puts 9 tons into LEO.</b> That is a pathetic payload fraction of 0.76%. This is really bad even for all-solid boosters -- for reference, the Taurus 4-stage all solid LV gets a payload fraction of 1.87%. But we are trying to build a simple vehicle whose only purpose is to meet or exceed the Delta IV's payload capacity – let efficiency be damned -- so we are going to make it an inefficient 2-stage design. So, yes, the Delta IV is 4.34 times more efficient. <b>But guess what? The two rockets ARE the same size! </b>You see... Solid boosters are about 1150 kg per cubic meter, whereas hydrogen boosters are around 280 kg per cubic meter. So in the end, you have two boosters which are practically the same size; same diameter and height. <b>And, they have comparable payload capacity. So one has to ask... does mass efficiency matter? Should it be the leading factor to consider when designing a launch vehicle?</b><br /><br />Surely the solid booster is simpler. Instead of two sets of engines with turbopumps, combustors and complex plumbing, you have nothing. No moving parts. Instead of huge tanks full of highly cryogenic liquids, and the need for insulation and ground support facilities to deal with them, you have nothing. No liquids, no fueling apparatus, no insulation, no fear of low temperature cracking, no need to fuel or defuel th