Europa Multiple Flyby Mission

History

Europa has been identified as one of the locations in the Solar System that could possibly harbor microbial extraterrestrial life. Immediately following the Galileo spacecraft's discoveries, JPL conducted preliminary mission studies that envisioned a capable spacecraft such as the Jupiter Icy Moons Orbiter (a $16B mission concept), the Jupiter Europa Orbiter (a $4.3B concept), an orbiter ($2B concept), and a multi-flyby spacecraft: Europa Clipper.

The proposed Europa Clipper is still in its planning phase, but the approximate cost is estimated at $2 billion. The mission is a joint project between the Johns Hopkins University's Applied Physics Laboratory (APL), and the Jet Propulsion Laboratory (JPL).

In March 2013, $75 million USD were authorized to expand on the formulation of mission activities, mature the proposed science goals, and fund preliminary instrument development, as suggested in 2011 by the Planetary Science Decadal Survey. In May 2014, a House bill substantially increased the Europa Multiple Flyby Mission funding budget for the 2014 fiscal year from $15 million to $100 million to be applied to pre-formulation work.

Following the 2014 election cycle, bipartisan support was pledged to continue funding for the Europa Multiple Flyby Mission project. The executive branch has also granted $30 million for preliminary studies.

In April 2015, NASA offered to the European Space Agency to submit concepts for an additional probe to fly together with the Europa Clipper spacecraft. It could be a simple probe, an impactor or a lander. An internal assessment at ESA is underway to see if there is interest and funds available, opening a collaboration scheme similar to the very successful Cassini-Huygens approach.

In May 2015, NASA chose nine instruments that would fly on board the orbiter. They will cost about $110 million over the next three years. In June 2015, NASA announced its approval of the mission concept, allowing the orbiter to move to its formulation stage, and in January 2016 it approved a lander as well.

In February 2017 the mission moved from Phase A to Phase B. Phase B is the preliminary design phase of the mission.

Objectives

The goals of Europa Clipper are to explore Europa, investigate its habitability and aid in the selection of a landing site for its lander. Specifically, the objectives are to study:

Ice shell and ocean: Confirm the existence, and characterize the nature, of water within or beneath the ice, and processes of surface-ice-ocean exchange.

Composition: Distribution and chemistry of key compounds and the links to ocean composition.

Geology: Characteristics and formation of surface features, including sites of recent or current activity.

The Europa Clipper would not orbit Europa, but instead orbit Jupiter and conduct 45 flybys of Europa at altitudes from 25 to 2,700 km (16 to 1,700 mi) each during its mission. Each flyby would cover a different sector of Europa in order to achieve a medium-quality global topographic survey, including ice thickness. The Europa Clipper could conceivably flyby at low altitude through the plumes of water vapor erupting from the moon's icy crust, thus sampling its subsurface ocean without having to land on the surface and drill though the ice.

Strategy

Because Europa lies well within the harsh radiation fields surrounding Jupiter, even a radiation-hardened spacecraft in near orbit would be functional for just a few months. Another key limiting factor on science for a Europa orbiter is not the time the instruments can make observations. Rather, it is the time available to return data to Earth. Most instruments can gather data far faster than the communications system can transmit it to Earth because there are a limited number of antennas available to receive the scientific data.

Studies by scientists from the Jet Propulsion Laboratory show that by performing several flybys with many months to return data, the Europa Clipper concept would enable a $2B mission to conduct the most crucial measurements of the cancelled $4.3B Jupiter Europa Orbiter concept. Between each of the flybys, the spacecraft would have seven to ten days to transmit data stored during each brief encounter. That would let the spacecraft have up to a year of time to transmit its data compared to just 30 days for an orbiter. The result would be almost three times as much data returned to Earth, while reducing exposure to radiation.

The Europa Clipper would inherit tested technology of the Galileo and Juno Jupiter orbiters with regards to radiation protection. Shielding will be provided by 150 kilograms of titanium. To maximize its effectiveness, the electronics will be nested in the core of the spacecraft for additional radiation protection.

Power

Both radioisotope thermoelectric generator and photovoltaic power sources were assessed to power the orbiter. In September 2013 it was decided that solar panels are the least expensive option to power the spacecraft. Early analysis suggest that each panel will have a surface area of 18 m² (190 sq ft) and produce 150 watts continuously when pointed towards the Sun while orbiting Jupiter. While in Europa's shadow, batteries will enable the spacecraft to continue gathering data. However, ionizing radiation can damage solar cells. The Europa Clipper's orbit will pass through Jupiter's intense magnetosphere, which is expected to gradually degrade the solar cells as the mission progresses.

The alternative to solar panels was a Multi-Mission Radioisotope Thermoelectric Generator, fueled with plutonium-238. The power source has already been demonstrated in the Mars Science Laboratory mission. Five units are currently available, with one reserved for the Mars 2020 rover mission and another as backup. On October 3, 2014, it was announced that solar panels were chosen to power Europa Clipper. The mission's designers determined that, despite the fact that solar power is only 4% as intense at Jupiter as it is in Earth's orbit, solar was both cheaper than plutonium and practical to use on the spacecraft. Despite the increased weight of solar panels compared to plutonium-powered generators, the vehicle's mass had been projected to still be within acceptable launch limits.

Scientific payload

The spacecraft payload and trajectory are subject to change as the mission design matures. While the Europa Clipper spacecraft is well equipped for Europa studies, which include plume detection and characterization, it is limited in its ability to fully analyze Europa water plumes.

The nine science instruments for the orbiter, announced in May 2015, have an estimated total mass of 82 kg (181 lb) and are listed below:

E-THEMIS

The Europa Thermal Emission Imaging System (E-THEMIS) will provide high spatial resolution, multi-spectral imaging of Europa in the medium- and long-wave infrared bands to help detect active sites, such as potential vents erupting plumes of water into space. This instrument is derived from the Thermal Emission Imaging System (THEMIS) on 2001 Mars Odyssey orbiter, also developed by Philip Christensen. Principal investigator: Philip Christensen, Arizona State University

MISE

The Mapping Imaging Spectrometer for Europa (MISE) instrument will image in the short-wave infrared band to probe the surface composition of Europa, identifying and mapping the distributions of organics, salts, acid hydrates, water ice phases, and other materials to determine the habitability of Europa's ocean. From these measurements, scientists expect to be able to relate the moon's surface composition to the habitability of its ocean. MISE is built in collaboration with the Johns Hopkins University Applied Physics Laboratory (APL). Principal investigator: Diana Blaney, Jet Propulsion Laboratory

EIS

The Europa Imaging System (EIS) is a visible-spectrum wide and narrow angle camera instrument that will map most of Europa at 50 m (160 ft) resolution, and will provide images of selected surface areas at up to 0.5 m resolution. Principal investigator: Elizabeth Turtle, Applied Physics Laboratory

UVS

The Ultraviolet Spectrograph/Europa (UVS) instrument will be able to detect small plumes and will provide valuable data about the composition and dynamics of the moon's exosphere. Principle Investigator Kurt Retherford was part of a group that discovered plumes erupting from Europa while using the Hubble Space Telescope in the UV spectrum. Principal investigator: Kurt Retherford, Southwest Research Institute

REASON

The Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) is a dual-frequency ice penetrating radar instrument that is designed to characterize and sound Europa's ice crust from the near-surface to the ocean, revealing the hidden structure of Europa's ice shell and potential water pockets within. This instrument will be built by JPL. Principal investigator: Donald Blankenship, University of Texas

ICEMAG

The Interior Characterization of Europa using Magnetometry (ICEMAG) is a magnetometer that will measure the magnetic field near Europa and in conjunction with the PIMS instrument will probe the location, depth, thickness and salinity of Europa's subsurface ocean using multi-frequency electromagnetic sounding. Principal investigator: Carol Raymond, Jet Propulsion Laboratory

PIMS

The Plasma Instrument for Magnetic Sounding (PIMS) measures the plasma surrounding Europa to characterise the magnetic fields generated by plasma currents. These plasma currents mask the magnetic induction response of Europa's subsurface ocean. In conjunction with the ICEMAG instrument, it is key to determining Europa's ice shell thickness, ocean depth, and salinity. PIMS will also probe the mechanisms responsible for weathering and releasing material from Europa's surface into the atmosphere and ionosphere and understanding how Europa influences its local space environment and Jupiter's magnetosphere. Principal investigator: Joseph Westlake, Applied Physics Laboratory

MASPEX

The MAss SPectrometer for Planetary EXploration/Europa (MASPEX) will determine the composition of the surface and subsurface ocean by measuring Europa's extremely tenuous atmosphere and any surface materials ejected into space. Jack Waite, who led development of MASPEX, was also Science Team Lead of the Ion and Neutral Mass Spectrometer (INMS) on Cassini spacecraft. The INMS was developed as a facility instrument at NASA Goddard Space Flight Center under the direction of Dr. Hasso Niemann. Principal investigator: Jack Waite, Southwest Research Institute

SUDA

The SUrface Dust Mass Analyzer (SUDA) mass spectrometer instrument will measure the composition of small solid particles ejected from Europa, providing the opportunity to directly sample the surface and potential plumes on low-altitude flybys. The instrument is capable of identifying traces of organic and inorganic materials in the ice of ejecta. Principal investigator: Sascha Kempf, University of Colorado Boulder

Additional probes

Nanosatellites

Since the Europa Clipper mission may not be able to easily modify its orbital trajectory or altitude to fly through the episodic water plumes, scientists and engineers working on the mission have investigated deploying from the spacecraft several miniaturized satellites of the CubeSat format, possibly driven by ion thrusters, to fly through the plumes and assess the habitability of Europa's internal ocean. Some early proposals include Mini-MAGGIE, DARCSIDE, and Sylph. The Europa Clipper would relay signals from the nanosatellites back to Earth. With propulsion, some nanosatellites could also be capable of entering orbit around Europa.

Biosignature Explorer for Europa

NASA is also assessing the release of an additional 250 kg (550 lb) probe called Biosignature Explorer for Europa (BEE), that would be equipped with a basic bi-propellant engine and cold gas thrusters to be more agile and responsive to the episodic activity on Europa and sample and analyze the water plumes for biosignatures and life evidence before they are destroyed by radiation. The BEE plume probe would be equipped with a proven mass spectrometer combined with gas chromatograph separation. It would also carry a UV plume targeting camera as well as visible and IR cameras to image the active region with better resolution than the Clipper mother ship instruments. The BEE probe would fly through at 2-10 km altitude, then make a quick exit and perform its analysis far from the radiation belts.

Lander

An early Europa Clipper concept calls for a small lander about 1 meter in diameter, perhaps about 230 kg (510 lb) with a maximum of 30 kg (66 lb) for instruments. Suggested instruments are a mass spectrometer and a Raman spectrometer to determine the chemistry of the surface. The lander would be delivered to Europa by the main spacecraft and possibly require the sky crane system for a high precision, soft landing near an active crevasse. The lander would operate about 10 days on the surface using battery power.

The Europa Clipper would take about three years to image 95% of the surface of Europa at about 50 meters per pixel. With this data, scientists could then find a suitable landing site. By one estimate, including a lander could add as much as $1 billion to the mission's cost.

The NASA Europa Lander would be a separately launched spacecraft building on the EMFM mission. Previously, NASA had evaluated a lander attached to EMFM, but the strong congressional support lead to a full separate mission for the lander by 2016.

Launch options

A baseline profile for the mission involved launch aboard an Atlas V 551. By using a Venus-Earth-Earth gravity assist trajectory the transit time to Jupiter would be about 6 years. The baseline design of Europa Clipper includes a launched with NASA's Space Launch System (SLS) heavy lift launch vehicle that could arrive at Jupiter on a direct trajectory in less than 3 years.