Shuttle-Derived Heavy Lift Launch Vehicle

Based on the Shuttle-C concept which has been the subject of various studies since the 1980s, the HLV was a Shuttle-Derived Launch Vehicle (SDLV) that proposed to replace the winged Orbiter from the Space Shuttle stack with a side-mounted payload carrier.

The Exploration Systems Architecture Study (ESAS) in 2005 also investigated a Shuttle-C option for Project Constellation, again only in an uncrewed version.

All these concepts intended the side-mounted carrier to be an autonomous spacecraft which would detach from the External Tank after main engine cut-off, similarly to the Space Shuttle.

A 7.5 meters (25 ft) diameter payload carrier with a separable fairing weighing 51,000 pounds (23,000 kg) would take up the space usually occupied by the rest of the orbiter.

The basic vehicle would not have an upper stage, requiring the payload to perform orbit circularization and possibly trans-lunar injection burns.

Virtually no change to the existing Space Shuttle infrastructure, from the Vehicle Assembly Building to the External Tank barge to the launch pads, was to be required.

[citation needed] Alternatively, the United Launch Alliance (ULA) proposed that their Dual Thrust Axis Lander (DTAL) could fit in a side mount payload shroud.

[5] The HLV's 4-segment SRBs were to deliver a specific impulse (Isp) of 267 sec and a thrust of 5,900,000 pounds-force (26 MN) and burn for about 155 seconds.

The SSME main engines were to be flown at 104.5% and deliver a specific impulse (Isp) of 452 sec and 1,500,000 pounds-force (6.7 MN) (vacuum) and burn for about 500 seconds (depending on the mission profile).