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Rockwell also investigated a number of vertically launched heavy-lift RLV concepts. The
parallel-burn VTVL multistage concept illustrated here would have consisted of a core stage +
six flyback boosters. All engines would ignite at liftoff so the orbiter's engines are
automatically checked out as well. Rockwell regarded this as a safer procedure than series-burn
configurations (e.g. see Boeing's VTHL TSTO) which do not use the orbiter engines before 2nd stage separation. Propellant would crossfed from the booster tanks during ascent, so the upper stage separates with its tanks full. The boosters would also have carried airbreathing engines for thrust augmentation during launch as well as fold-out wings for horizontal landing. Other benefits included a high payload-to-GLOW ratio, plus reduced development and operations costs due to extensive use of small modular boosters. Each booster would weigh 113,972kg at separation -- booster pairs are jettisoned at propellant depletion -- and the ascent propellant load was 551,144kg The VTVL core stage would have a mass of 252,265kg at touchdown and a gross liftoff weight (including a 272,155kg payload) of 2010,321kg. The total gross liftoff weight is 6000t.
Another Rockwell solar power satellite (SPS) transportation concept from 1980. This VTHL TSTO would "only" have had a LEO payload capability of 120 tonnes. Rockwell's cost analysis indicated such vehicles would be more versatile in their potential applications and much easier & cheaper to develop. The transportation cost would be $0.9B (=33%) higher than if a 300-400t RLV were used, but the overall SPS cost would still be lower since the smaller RLV costs $5B less to develop.
”Advanced Launch Vehicle Systems and Technologies” – Bell, AAS 1977/vol.36/p.117; SPACEFLIGHT 1978/p.135
”Transportation for Solar Power Satellites” – Shelton, SPACEFLIGHT 1982/January/p.2