Apollo Applications Program “asteroid mission”
“NASA Halley Mission”
[further Shuttle-era cancellations]
Piazzi
Vesta
CRAF (Comet Rendezvous Asteroid Flyby)
Clementine (…technically)
Clementine II
NEAP/NEAF (Near-Earth Asteroid Prospector/Flyby)
CONTOUR (Comet Nucleus Tour- yes, I know the case doesn’t work out)
SOCCER (initial concept of Hayabusa…)
“MUSES-CN” rover (cut NASA rover for Hayabusa)
Champollion (initial concept of Rosetta…)
WIRE (Wide-field InfraRed Explorer- arguably…)
PKE (Pluto-Kuiper Express- New Horizons competitor…)
Calathus
Marco Polo
Plymouth Rock
ARM (Asteroid Redirect Mission, multiple parts)
Arkyd 100, etc…
Sentinel
CAESAR (Comet Astrobiology Exploration Sample Return)
Caroline and/or Castalia
PROCYON (Proximate Object Close flyby with Optical Navigation)
AIM (Asteroid Impact Mission- initial Hera concept…)
NEA Scout
Aster (so far…)
Janus (so far…)
…ad quasi-astra…