The Earth-to-Orbit Segment (ETOS) was the working name for a launch vehicle proposed by Andrews Space in 2004, as part of their architecture study for the Constellation/Vision for Space Exploration program. It was to be a new heavy-lift crew and cargo vehicle, capable of supporting (with distributed lift and on-orbit tugs, and coupled with their Crew Exploration Vehicle and Lunar Surface Access Module concepts) crewed lunar missions.

To the maxiumum extent possible, ETOS made use of existing components. The core stage would be a modified Atlas V Common Core Booster (built by Lockheed Martin, prior to the formation of United Launch Alliance), while the two side boosters would be modified Zenit first stages (taking advantage of design accomodations already present in Zenit's design for dual use as the Energia booster). The fairing would be a standard Atlas V 500-series fairing. Only the upper stage would be newly developed, with 6.5 meter diameter tanks and a new RS-XX (placeholder for then-unknown designation) engine.

Note that the upper stage is only barely modeled here, due to lack of available reference material. ETOS never progressed beyond the initial study phase, and no real design work was done for the new upper stage other than basic dimensions and performance targets.

Recommended for use with my Atlas V model: https://www.cgtrader.com/3d-models/space/spaceship/atlas-v

All materials and textures are packed into the .blend file. Unapplied modifiers and instancing have been used to reduce file size and enable easy editing.