OCEANUS (Origins and Composition of the Exoplanet Analog Uranus System) is a mission concept conceived in 2016 and presented in 2017 as a potential future contestant as a New Frontiers program mission to the planet Uranus.[2][1] The concept was developed by the Astronautical engineering students of Purdue University during the 2017 NASA/JPL Planetary Science Summer School. OCEANUS is an orbiter, which would enable a detailed study of the structure of the planet's magnetosphere and interior structure that would not be possible with a flyby mission.[2]
Because of the required technology development and planetary orbital dynamics, the concept suggests a launch in August 2030 on an Atlas V 511 rocket and entering Uranus' orbit in 2041.[1]
Ice giant sized planets are the most common type of planet according to Kepler data. The little data available on Uranus, an ice giant planet, come from ground-based observations and the single flyby of the Voyager 2 spacecraft, so its exact composition and structure are essentially unknown, as are its internal heat flux, and the causes of its unique magnetic fields and extreme axial tilt or obliquity,[1] making it a compelling target for exploration according to the Planetary Science Decadal Survey.[2][3] The primary science objectives of OCEANUS are to study Uranus' interior structure, magnetosphere, and the Uranian atmosphere.[1]
The required mission budget is estimated at $1.2 billion.[1] The mission concept has not been formally proposed to NASA's New Frontiers program for assessment and funding. The mission is named after Oceanus, the Greek god of the ocean; he was son of the Greek god Uranus.[4]
Since Uranus is extremely distant from the Sun (20AU), and relying in solar power is not possible past Jupiter, the orbiter is proposed to be powered by three multi-mission radioisotope thermoelectric generators (MMRTG),[2][1] a type of radioisotope thermoelectric generator. There is enough plutonium available to NASA to fuel only three more MMRTG like the one used by the Curiosity rover.[5][6] One is already committed to the Mars 2020 rover.[5] The other two have not been assigned to any specific mission or program, [6] and could be available by late 2021.[5] A second possible option for powering the spacecraft other than a plutonium powered RTG would be a small nuclear reactor powered by uranium, such as the Kilopower system in development as of 2019.
The trajectory to Uranus would require a Jupiter gravity assist, but such alignments are calculated to be rare in the 2020s and 2030s, so the launch windows will be scant and narrow.[2] To overcome this problem two Venus gravity assists (in November 2032 and August 2034) and one Earth gravity assist (October 2034) are planned along with the use of solar-electric propulsion within 1.5 AU.[1] The science phase would take place from a highly elliptical orbit and perform a minimum of 14 orbits.[1] If launching in 2030, reaching Uranus would occur 11 years later, in 2041,[1] and it would use two bipropellant engines for orbital insertion.[1]
Alternatively, the SLS rocket could be used for a shorter cruise time,[7] but it would result in a faster approach velocity, making orbit insertion more challenging, especially since the density of Uranus' atmosphere is unknown to plan for safe aerobraking.[6]
The 12.5 kg scientific payload would include instruments for a detailed study of the magnetic fields and to determine Uranus' global gravity field: [2][1]
GAIA (Gravity and Atmospheric Instrument Antenna) – it would utilize the on-board communications antenna, transmitting in both X band and Ka band frequencies for radio science that would allow maping Uranus' global gravity field.
UnoCam (Uranus' Juno Cam) – is a visible light, color camera to detect navigation hazards in Uranus' ring system and to provide context and panoramic images.
URSULA (Understanding Real Structure of the Uranian Laboratory of Atmosphere) – an atmospheric probe that would be jettisoned into the atmosphere of Uranus just before orbit insertion. It would descend under a parachute and measure the noble gas abundances, isotopic ratios, temperature, pressure, vertical wind profiles, cloud composition and density,[2] via a mass spectrometer, atmospheric structure instrument, nephelometer and ultra-stable oscillator. The total mass of the probe's instruments is about 127 kg.[1]
^ abcdefghijklmnopBramson, A. M; Elder, C. M; Blum, L. W; Chilton, H. T; Chopra, A; Chu, C; Das, A; Delgado, A; Fulton, J; Jozwiak, L; Khayat, A; Landis, M. E; Molaro, J. L; Slipski, M; Valencia, S; Watkins, J; Young, C. L; Budney, C. J; Mitchell, K. L (2017). "OCEANUS: A Uranus Orbiter Concept Study from the 2016 NASA/JPL Planetary Science Summer School". 48th Lunar and Planetary Science Conference. 48 (1964): 1583. Bibcode:2017LPI....48.1583B.
^ abcdefgElder, C. M; Bramson, A. M; Blum, L. W; Chilton, H. T; Chopra, A; Chu, C; Das, A; Davis, A; Delgado, A; Fulton, J; Jozwiak, L; Khayat, A; Landis, M. E; Molaro, J. L; Slipski, M; Valencia, S; Watkins, J; Young, C. L; Budney, C. J; Mitchell, K. L (2017). "New Frontiers-Class Missions to the Ice Giants". Planetary Science Vision 2050 Workshop. 1989: 8147. Bibcode:2017LPICo1989.8147E.