Trident (spacecraft)


Mission typeReconnaissance, flyby of outer planets
Mission duration13 years (planned)
Start of mission
Launch dateProposed: 25 October 2025
(with a backup in October 2026) [1]
Flyby of Earth (gravity assist)
Closest approach28 October 2026 [2]
Flyby of Venus (gravity assist)
Closest approach25 March 2027 [2]
Flyby of Earth (gravity assist)
Closest approach7 February 2028 [2]
Flyby of Earth (gravity assist)
Closest approach7 February 2031 [2]
Flyby of Jupiter, Io (gravity assist)
Closest approach28 June 2032 [2]
Distance1.24 RJ or 88,650 km (55,080 mi)
Flyby of Neptune, Triton
Closest approach28 June 2038 [2]
← Psyche

Trident is a space mission concept to the outer planets proposed in 2019 to NASA's Discovery Program.[3][4] The concept includes flybys of Jupiter and Neptune with a focus on Neptune's largest moon Triton.

In 2020, Trident was selected along with three other Discovery proposals for further study, with two expected to be selected to fly as Discovery 15 and 16.[5] Up to two will be selected by summer 2021 to become a full-fledged mission and will launch later in the decade. The proposed launch date in October 2025 (with a backup in October 2026) would take advantage of a once-in-13-years window, when Earth is properly aligned with Jupiter. The spacecraft would use the gravitational pull of Jupiter as a slingshot straight to Triton for an extended 13-day encounter in 2038.[1]


Triton is the largest moon of Neptune. In 1989, Voyager 2 flew past the moon at a distance of 40,000 km (25,000 mi),[6] and discovered several cryovolcanoes on its surface. Triton is geologically active, its surface is young and has relatively few impact craters. It has a very thin atmosphere. Voyager 2 was only able to observe approximately 40% of Triton's surface.

The Trident concept was proposed in March 2019 to NASA's Discovery Program. The mission concept is supported by NASA's Ocean Worlds Exploration Program and it is intended to help answer some of the questions generated by Voyager 2's flyby in 1989.[7]


Trident takes advantage of an efficient gravity assist alignment of Jupiter and Neptune (that occurs once every 13 years) to capitalize on a narrow observational window that enables assessment of changes in Triton's plume activity and surface characteristics since the previous encounter of Neptune-Triton by Voyager 2 in 1989.[3][8]

With the advances of high-resolution imaging and a unique orbital configuration of Triton in 2038, Trident would be able to obtain a near-complete map of the Neptune's moon during its sole flyby. Trident would pass through Triton's thin atmosphere, within 500 km (310 mi) of the surface, sampling its ionosphere with a plasma spectrometer and perform magnetic induction measurements to assess the potential existence of an internal ocean.[3] The principal investigator is Louise Prockter, director of the Lunar and Planetary Institute in Houston, Texas.[8]

The launch vehicle proposed for Trident is the Atlas V 401, if it is not replaced with the Vulcan.[2]

Neptune Moon Triton - Proposed Trident Mission (16 June 2020)


Instrument[2] Functionality
Infrared spectrometer 2-100 km, near-global compositional mapping at 1-5 μm wavelength.
Narrow angle camera Anti-Neptune regional mapping and limb imaging (≤ 200 m).
Wide-angle camera Sub-Neptune and haze imaging and change detection (≤ 2,500 m).
Triaxial magnetometer Ocean detection.
Radio science Atmospheric occultations for neutral and electron profiles; gravimetry observations
Plasma spectrometer Atmospheric charged particles. Energetic inputs to ionosphere.

Objects that Trident would visit

See also

  • Argo, a 2009 Triton flyby mission concept
  • New Horizons probe, performed a Pluto flyby in 2015
  • New Horizons 2, a mission proposed in 2002 which might have included a Triton flyby
  • Triton Hopper, a lander concept to Triton


  1. ^ a b "Proposed NASA Mission Would Visit Neptune's Curious Moon Triton". NASA. 16 June 2020. Retrieved 2 July 2020. This article incorporates text from this source, which is in the public domain.
  2. ^ a b c d e f g h "Implementation of Trident: A Discovery-Class Mission To Triton" (PDF). Universities Space Research Assotiation. 23 March 2019. Retrieved 26 March 2019.
  3. ^ a b c NASA proposes mission to Neptune moon Triton. Paul Scott Anderson, EarthSky 28 March 2019.
  4. ^ "Exploring Triton With Trident: A Discovery-Class Mission" (PDF). Universities Space Research Assotiation. 23 March 2019. Retrieved 26 March 2019.
  5. ^ "NASA Selects Four Possible Missions to Study the Secrets of the Solar System". NASA. 13 February 2020. This article incorporates text from this source, which is in the public domain.
  6. ^ Gray, D (1989). "Voyager 2 Neptune navigation results". Astrodynamics Conference: 108. doi:10.2514/6.1990-2876.
  7. ^ Hendrix, Amanda R. (2019). "The NASA Roadmap to Ocean Worlds". Astrobiology. 19 (1): 1–27. doi:10.1089/ast.2018.1955. PMC 6338575. PMID 30346215.
  8. ^ a b Neptune's Moon Triton Is Destination of Proposed NASA Mission. David W. Brown, The New York Times. 19 March 2019.