Composition of the list table 1 Removed the info on Falcon X Heavy and Falcon XX since those are just proposed concepts that haven t yet reached nowhere near the project stage 2 Removed the info stating that Saturn INT 21 had one launch It has never flown the booster used for Skylab was an actual Saturn V with the 3rd stage modified into Skylab itself The entry for Saturn INT 21 should probably be deleted altogether but unlike two heavy Falcons it was under development coming much closer to becoming an operational vehicle so I m not sure 3 Added clarification to Space Shuttle entry that it is regarded here as an integrated launch system and not a standalone heavy booster also removed the note stating Like Soviet Energia Buran system despite of integrated design of rocket and orbiter US Space Shuttle may be comparatively considered as launcher for such superheavy payload as manned spaceplane But it should be noted that the orbiter could not hold more tha 25 000 kg Such reasoning is not entirely justified It can be considered as such only with serious reservations since Shuttle s Orbiter acts de facto as a returnable third stage which can not be replaced with anything else and has to be brought back to Earth whereas other boosters can hypothetically or practically like Saturn V Skylab case have the load they put in LEO modified And certainly the Shuttle system can not be part of this comparative list based on similarity with Energia Buran the note says like Soviet Energia Buran system since Enegia booster could be adapted to carry basically any appropriately configured and balanced payload piggybacked on its side not just the orbiter