(a) References in this column apply to entire row unless specifically replaced
(b) All monetary values in un-inflated dollars based on reference publication date except as noted
(c) CY2008 estimate from description in 1993 reference system
(d) Requires first stage to ~5 km/s
(e) Subject to very rapid increase via bootstrapping
(f) Requires Boeing proposed DF-9 vehicle first stage to ~4 km/s
(g) Based on Gen-1 reference design, 2010 version
(h) Jules Verne's novel, From the Earth to the Moon. Newton's cannonball in the 1728 book A Treatise of the System of the World was considered a thought experiment.[13]