ESA's Proposed missions: Spacecraft that won't see the light of day.
In the six decades humanity has explored space, we've done some pretty cool things. We've landed rovers on Mars, sent probes to the outer planets, and touched the Sun. But for every mission that get's selected, many more are scrapped, likely never to see the light of day. This article will delve into many (but not all) proposed missions that were never selected, as well as proposals that are still ongoing. Some proposals have limited information available, so this list is incomplete. This list only includes serious proposals. The Uranus Orbiter and Probe (UOP) isn't included in this list because I made a dedicated article on it.
Eddington
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| Artist's concept of Eddington observatory. Credit: ESA/Medialab |
Eddington was an observatory designed to notice tiny variations in starlight, and would be able to find Earth-sized planets around other stars. Canada's MOST telescope and ESA's CoRot observatory were planned as precursors to the Eddington mission.
Eddington was planned to use its four telescopes to observe possible planetary systems around 500,000 stars. Eddington would compliment NASA's Kepler telescope if it was launched. Unfortunately, due to budget overruns, the mission was canceled in 2003.
Darwin
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| Artist's Illustration of one of Darwin's telescopes. ESA/Medialab |
Darwin would have been a constellation of interferometer observatories that would survey 1000 nearby stars for rocky planets. The observatories would also be able to analyze exo-Earth atmospheres. The constellation would contain three or four observatories, capable of peering into the infrared spectrum.
The seperate telescopes would observe the same star at once, and cancel out the star's light to get data on the possible planets that orbit around it. The observatories would also combine the planet's light together, amplifing it, and making it easier to analyze.
The observatories would launch on two Soyuz launches, and orbit around the Sun-Earth Lagrangian point 2. This is the same region the James Webb Space Telescope is located. The study concluded in 2007, an the observatories were canceled due to their complexity.
Lunar Lander
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| Mockup of ESA's Lunar Lander. Credit: German Aerospace Center (DLR) CC BY 2.0 |
ESA's Lunar Lander was supposed to be Europe's first Lunar surface mission. It would have also been the first spacecraft to land in the Moon's south polar region. The mission was lead by the German Aerospace Center (German acronym DLR), with Astrium as the prime contractor. The lander wasn't funded, and shelved in November 2012 at ESA's Ministerial Council. While Germany was willing to fund just under half the mission, they couldn't find anyone to fund the second half.
Don Quijote
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| Hidalgo impacts an asteroid with Sancho in the forground. Credit: ESA/AOES Medialab |
The Don Quijote mission was an asteroid impactor proposal. The mission would consist of an orbiter (Sancho) and an impactor (Hidalgo). The mission takes its name from the fictional Spanish knight Don Quixote, with the orbiter named after his squire, and the impactor was named after a minor Spanish title.
The main spacecraft would use a modified SMART-1 satellite bus, while the impactor would be based off of the LISA Pathfinder spacecraft. While the mission wasn't carried out, a similar project was undertaken with NASA's DART spacecraft, which impacted Dimorphos, a moonlet of Didymos, on September 26, 2022.
MarcoPolo
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| Artist's concept of MarcoPolo. Credit: ESA |
MarcoPolo was a proposed sample return mission that's had many iterations from 2005 to 2015. The mission was initially studied by ESA with the Japenese Aerospace eXploration Agency (JAXA). As the proposal evolved, many different targets were considered. MarcoPolo was rejected two times, in favour of Solar Orbiter and the Euclid telescope. The mission was later modified into the MarcoPolo-R and MarcoPolo-2D proposals.
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| Early Marco Polo lander concept. Credit: ESA |
These later mission concepts would target 2008 EV5, or Ryugu. Ryugu was later visited by JAXA's Hayabusa 2 mission, with samples returned in 2020. While the mission was proposed 4 times in total, all have been rejected.
STE-QUEST
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| Illustration of exoplanet systems. Credit: ESA/C. Carreau |
The Space-Time Explorer and QUantum Equivalence Principle Space Test (STE-QUEST) was a proposed mission that would use Rubidium atomic clocks to test Einstein's Equivalence Principle to a high precision.
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| Preliminary design for STE-QUEST. Credit: ESA |
The spacecraft would be launched on a highly elliptical orbit in 2024, and have a mission duration of five years. The mission concept was proposed in 2010, and selected for further study in 2011. In 2014, STE-QUEST lost to the PLATO exoplanet observatory.
The mission likely would have faced many delays and issues even if it was selected, expecially since Europe no longer launches their payloads on Soyuz rockets after the Russia/Ukraine war.
EChO
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| Concept design for EChO. Credit: ESA |
The Exoplanet Characterisation Observatory (EChO) was a dedicated exoplanet studying mission. It was proposed along with MarcoPolo, STE-QUEST, and LOFT. All were rejected in favour of the upcoming PLATO telescope.
LOFT
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| Concept of LOFT. Credit: LOFT team/IAPS/INAF Rome/Thales Alenia Space Italia/ESA/NASA |
The Large Observatory For X-Ray Timing (LOFT) is an X-Ray telescope proposal. The mission would be devoted to observing X-Rays from black holes an neutron stars. LOFT wasn't selected, in favour of the PLATO mission. However, LOFT has been resubmitted, and has a second shot for a possible (but unlikely) launch in 2025.
MUSE
The Mission to Uranus for Science and Exploration (MUSE) is similar to the recent Decadal Survey recommondation. However, this was initially a European proposal. The orbiter would spend two years orbiting Uranus farther away, and then would spend several more years in the inner system to analyze Uranus's moons.
Like the UOP concept, MUSE would possess an atmospheric probe to analyze Uranus's atmosphere like the one sent aboard the Galileo spacecraft. The concept wasn't selected, but later was considered for a NASA New Frontiers mission. This version of the mission would launch aboard an Atlas V rocket. Again, the proposal wasn't selected.
ODINUS
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| ODINUS logo. Credit: SkywalkerPL |
Origins Dynamics and Interiors of the Neptunian and Uranian Systems (ODINUS) was a proposal to visit the Ice Giants of the solar system. The mission would launch two probes: Freyr to Uranus, and Freyja to Neptune.
The spacecraft's proposed names come from the twin dieties of the Norse pantheon. On their way to their destinations, the spacecraft would perform fundemental physics science to test MOND theory, and measure the interplanetary solar wind.
Once in orbit around their targets, the spacecraft would use ion propulsion to lower their orbits, and get better views and data on the inner satellites of Uranus and Neptune. Due to lack of radioisotope reactor availability, and the cost and complexity of the mision, the ODINUS proposal was never selected.
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