NASA-ESA-Uranus Pathfinder
NASA-ESA-Uranus Pathfinder
Uranus Pathfinder was a mission concept for the Uranian system evaluated in the 2010s by the European Space Agency.[1] In 2011, scientists from the Mullard Space Science Laboratory in the United Kingdom proposed the joint NASA–ESA Uranus Pathfinder mission to Uranus. It would have been a medium-class (M-class) mission to be launched in 2022, and was submitted to the ESA in December 2010 with the signatures of 120 scientists from around the globe. ESA caps the cost of M-class missions at €470 million.[2][3][4] Uranus Pathfinder was proposed in support of ESA's Cosmic Vision 2015–2025.[5] The mission study including several possible combinations of launch dates, trajectories, and flybys (gravity assists), including flybys of Earth, Venus, and of the planet Saturn.[6] Indeed, the study noted the velocity change requirements are only marginally higher than for typical missions to Saturn of this period.[7]
In the baseline concept, UP is an ESA–NASA bilateral mission and it would launch on an Atlas V 551 in January 2025 on an Venus–Earth–Earth interplanetary transfer to Uranus, reaching Uranus orbit in November 2037 after a cruise phase lasting 12.8 years.
It would orbit Uranus in a highly eccentric 45-day polar science orbit, with close periapsis distances to Uranus to make high fidelity measurements of Uranus's gravitational and magnetic fields.
The scientific payload has a strong heritage in Europe and beyond and includes: narrow angle camera, visible/near-IR imaging spectrometer, thermal IR bolometer, radio science, magnetometer, radio and plasma wave detector, and plasma detector.
The mission would use the Earth communication stations at New Norcia (X band), and Cebreros (X and Ka bands) during its long cruise to the Uranian system.[8]
Possible flyby/gravity assist combinations studied:[9]
VVE (Venus–Venus–Earth)
VEE
EVVE
VEES (Venus–Earth–Earth–Saturn)
VVEES
For power, the proposal suggests using a European radioisotope thermoelectric generator based on americium-241, with NASA's MMRTG and ASRG mentioned as possible backup options, which would provide more power.[10]
The Uranus Orbiter and Probe is an orbiter mission concept to study Uranus and its moons.[1] The orbiter would also deploy an atmospheric probe to characterize Uranus's atmosphere. The concept is being developed as a potential large strategic science mission for NASA. The science phase would last 4.5 years and include multiple flybys of each of the major moons.
The mission concept was selected as the highest priority Flagship-class mission by the 2023–2032 Planetary Science Decadal Survey, ahead of the Enceladus Orbilander.[3][4] A Neptune orbiter mission concept, Neptune Odyssey, that would address many of the same scientific goals regarding ice giants was also considered, but for logistical and cost reasons a mission to Uranus was favored.
The original proposal targeted a launch in 2031 using a Falcon Heavy expendable launch vehicle with a gravity assist at Jupiter, allowing arrival at Uranus in 2044. In 2023, however, NASA announced that due to a shortfall in plutonium production a mid to late 2030s launch would be more likely.[2]
Voyager 2 is the only space probe to have visited the Uranus system, completing a flyby on January 24, 1986. The 2011-2022 Planetary Science Decadal Survey recommended a Flagship-class orbiter mission to an ice giant with priority behind what would become the Mars 2020 rover and the Europa Clipper.[5][6][7] Ice giants are now appreciated as a common type of exoplanet, precipitating the need for further study of ice giants in the Solar System.[8] The ice giants Uranus and Neptune were seen as unique yet equally compelling scientific targets, but a Uranus orbiter and atmospheric probe was given preference for logistical and cost reasons.[5][7] A Uranus orbiter would logically follow Flagship-class orbiter missions undertaken at Jupiter and Saturn (Galileo and Cassini, respectively).
In 2017, prior to the 2023–2032 survey, a committee narrowed twenty mission concepts to three scenarios for Uranus and a fourth for Neptune.[8][9][10][11] A mission to Neptune is viewed by some to be of greater scientific merit[12] because Triton, likely a captured Kuiper belt object and ocean world, is a more compelling astrobiology target than the moons of Uranus (though Ariel and Miranda in particular are possible ocean worlds).[13] There was also a study that considered a New Frontiers-level Uranus orbiter mission concept if a Flagship-class mission to Neptune were favored.[14] Nevertheless, again due to cost and logistical considerations including launch vehicle availability and available launch windows, the 2023–2032 Planetary Science Decadal Survey recommended the Uranus Orbiter and Probe instead of an analogous proposal for Neptune, Neptune Odyssey.[3][4]
The orbiter paired with an atmospheric probe will address a variety of scientific questions across all aspects of the Uranus system:[3]
How does atmospheric circulation function, from interior to thermosphere, in an ice giant?
What is the 3D atmospheric structure of the weather layer?
When, where, and how did Uranus form, how did it evolve both thermally and spatially, including migration, and how did it acquire its retrograde obliquity?
What is Uranus' bulk composition and its depth dependence?
Does Uranus have discrete layers or a dilute core, and can this be tied to its formation and tilt?
What is the true rotation rate of Uranus, does it rotate uniformly, and how deep are the winds?
What dynamo process produces Uranus' complex magnetic field?
What are the plasma sources & dynamics of Uranus' magnetosphere and how does it interact with the solar wind, Uranus' upper atmosphere, and satellite surfaces?
What are the internal structures and rock-to-ice ratios of the large Uranian moons and which moons possess substantial internal heat sources or possible oceans?
How do the compositions and properties of the Uranian moons constrain their formation and evolution?
What geological history and processes do the surfaces record and how can they inform outer solar system impactor populations? What evidence of exogenic interactions do the surfaces display?
What are the compositions, origins and history of the Uranian rings and inner small moons, and what processes sculpted them into their current configuration?
The atmospheric probe element of this mission would study the vertical distribution of cloud-forming molecules, thermal stratification, and wind speed as a function of depth. The 2010 mission design envisioned a probe of 127 kg (280 lb), less than half that of the Galileo atmospheric probe.[7] A later design study suggested results could be significantly enhanced by adding a second probe which could be as small as 30 kg (66 lb) in mass and about 0.5 m (20 in) in diameter.[15]
MUSE (Mission to Uranus for Science and Exploration[3]) is a European proposal for a dedicated mission to the planet Uranus to study its atmosphere, interior, moons, rings, and magnetosphere.[2][4] It is proposed to be launched with an Ariane 6 in 2026, travel for 16.5 years to reach Uranus in 2044, and would operate until 2050.[4]
The European Space Operations Centre would monitor and control the mission, as well as generate and provide the raw data sets. In 2012, the cost was estimated at €1.8 billion.[2] The mission addresses the themes of the ESA Cosmic Vision 2015–2025.[2] This was designed as an L-Class[clarification needed] flagship level mission; however, it is constrained by the need for RTGs.[5] MUSE was also analyzed in the US as an Enhanced New Frontiers class mission in 2014.[3]
The orbiter science phase would consist on the Uranus Science Orbit (USO) phase of approximately 2 years in a highly elliptic polar orbit to provide best gravimetry data, during which 36 Uranus orbits are performed.[4]
Subsequently, the orbiter will continue to the Moon Tour (MT) phase, which would last three years. During this phase, the periapsis would be raised, facilitating nine flybys of each of Uranus' five major moons: Miranda, Ariel, Umbriel, Titania, and Oberon.[2][4]
Because of the long distance from the Sun (20 AU on average), the orbiter would not be able to use solar panels, requiring instead four Advanced Stirling Radioisotope Generators (ASRGs) to be developed by ESA.[2][4] The propulsion system for the Earth-Uranus transfer would be chemical: Monomethylhydrazine and Mixed Oxides of Nitrogen (MMH/MON) propellant combination is used.[4]
Understanding why Uranus emits such a small amount of heat can only be done in the context of thermodynamic modeling of the atmosphere (density, pressure, and temperature). Therefore, the atmosphere needs to be characterized from both a composition and a thermodynamic point of view.[2] The chemical information to retrieve is the elemental concentrations, especially of disequilibrium species, isotopic ratios and noble gases, in combination with information regarding the distribution of aerosol particles with depth.
Twenty days before entry, the atmospheric probe would separate from the spacecraft and enter the outer atmosphere of Uranus at an altitude of 700 km at 21.8 km/s. It would descend by free fall and perform atmospheric measurements for about 90 minutes down to a maximum of 100 bars (1,500 psi) pressure.[2][4]
In 2014, a paper was released considering MUSE under the constraints of an enhanced New Frontiers mission. This included a cost cap of US$1.5 billion, and one of the big differences was the use of an Atlas V 551 rocket.[3]
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 (20 AU), 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]
UMAG (Uranus Magnetometer) – is a magnetometer to study the magnetosphere and constrain models for dynamo generation.
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]
In 2009, a team of planetary scientists from NASA's Jet Propulsion Laboratory advanced possible designs for a solar-powered Uranus orbiter. The most favorable launch window for such a probe would have been in August 2018, with arrival at Uranus in September 2030. The science package would have included magnetometers, particle detectors and, possibly, an imaging camera.[9]
A mission to Uranus is one of several proposed uses under consideration for the unmanned variant of NASA's heavy-lift Space Launch System (SLS) currently in development. The SLS would reportedly be capable of launching up to 1.7 metric tons to Uranus.[12]
In 2013, it was proposed to use an electric sail (E-Sail) to send an atmospheric entry probe to Uranus.[13]
In 2015, NASA announced it had begun a feasibility study into the possibility of orbital missions to Uranus and Neptune, within a budget of $2 billion in 2015 dollars. According to NASA's planetary science director Jim Green, who initiated the study, such missions would launch in the late 2020s at the earliest, and would be contingent upon their endorsement by the planetary science community, as well as NASA's ability to provide nuclear power sources for the spacecraft.[14] Conceptual designs for such a mission are currently being analyzed.[15]