Spacecraft That Never Flew: Cancelled, Unconfirmed and Unlaunched Designs

Blue Gemini was a United States Air Force project first proposed in August 1962 for a series of seven flights of off the shelf Gemini spacecraft. It was meant to give the Air Force crewed spaceflight experience before the planned Manned Orbital Development System, and it is recorded as cancelled.

General Electric proposed MOOSE in the early 1960s as an emergency bail-out kit for a single astronaut. It packed a small deorbit rocket, a heat-shielded plastic bag filled rigid with foam, and a parachute into a suitcase-sized container of about 200 pounds, but neither NASA nor the Air Force showed interest and it was shelved by the end of the decade.

McDonnell Douglas proposed Big Gemini to NASA in August 1969 as an enlarged, higher-capacity Gemini intended to be an all-purpose way to reach orbit. The missions it was pitched for ended up flying on Apollo or the Space Shuttle instead, and it is recorded as cancelled.

Blackstar is the reported name of a secret United States orbital spaceplane whose existence has never been officially confirmed. Aviation Week and Space Technology described it in March 2006 as a program running since at least the early 1990s, so this stop is a claim about a craft rather than a documented vehicle.

The Crew Exploration Vehicle was the name NASA gave to the crew spacecraft its Vision for Space Exploration called for. NASA ran a design competition among contractors, and the winning design became the Orion spacecraft, so this entry marks the requirement and the contest rather than a single built vehicle.

The Mars Telecommunications Orbiter was a planned NASA Mars orbiter meant to provide improved communications relay for landers, rovers and other spacecraft working on the Martian surface. It was cancelled before it flew.

The Advanced Cryogenic Evolved Stage, or ACES, was a liquid oxygen and liquid hydrogen upper stage proposed by United Launch Alliance for eventual use on its Vulcan rocket. It was aimed at longer on-orbit life for upper stages and studied as an in-space propellant depot, but it never won full development funding.

Boeing submitted its Human Landing System concept to NASA on 5 November 2019 under the Artemis NextSTEP H solicitation, presenting it as the quickest and simplest way to land astronauts on the Moon by 2024. NASA did not select it for funding when it announced its Artemis lander awards on 30 April 2020.

KEO was a proposed space time capsule meant to carry messages from people today to humanity fifty thousand years in the future, when it would reenter the atmosphere. Delays including the September 11 attacks and the restructuring of the European Space Agency followed, and in July 2025 the organizers announced the project would close without launching the satellite.