sabato 3 maggio 2014

Following the decadal survey: NASA focus on Europa mission

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In what is a significant step forward in planning for a mission to Jupiter’s moon Europa, NASA has released a Request for Information to the science and engineering communities for ideas regarding a mission to the Jovian moon to help address fundamental questions about the moon and the search for life beyond Earth.

The Decadal Survey: Mars, Europa, and Uranus –

Stemming from recommendations of the 2013-2022 Visions and Voyages for Planetary Science report, also known as the Decadal Survey, published on 7 March 2011, NASA has taken the next step toward the realization of a mission to Europa – a destination that received prominent billing in the Decadal Survey.

The mission to Jupiter’s moon received second priority behind a new Mars rover mission and ahead of a mission to Uranus and its moons, all of which were classified as part of NASA’s Flagship Mission series.

Following the initial release of the Decadal Survey recommendations, NASA immediately took steps to begin studying a mission to Europa.

In late 2011, NASA commissioned a Europa lander concept study along with concept missions for a Europa flyby mission and a Europa orbiter mission.

For the flyby mission, NASA’s Jet Propulsion Laboratory and Applied Physics Laboratory received a presentation dubbing the mission Europa Clipper.

The mission would orbit Jupiter itself, not Europa, but would be inserted into a Jovian orbit that would allow for a minimum of 45 low-altitude flybys of Europa over the course of the mission. 

The proposal calls for the Europa Clipper spacecraft to carry ice penetrating radar, a shortwave infrared spectrometer, a topographical imager, and an ion and neutral mass spectrometer to study the habitability aspects of Europa and help select sites for a future Europa lander mission.

The Europa Orbiter mission would instead help characterize the subterranean ocean of Europa and also help reveal the moon’s interior structures.

Under this proposed mission, the Europa Orbiter would carry a mapping camera, a laser altimeter, a radio subsystem suite of instruments, a magnetometer, and a Langmuir probe to determine the electron temperature, electron density, and the electric potential of plasma around Europa.

The third and final of the Europa mission concept studies is the Europa Lander, which would help determine the moon’s habitability and characterize its astrobiological potential by confirming the presence and determining the characteristics of water within and below Europa’s icy outer crust.

Pointedly, all three of these concept missions are long-term orbital missions in the Jovian system – meaning NASA’s commitment to a mission at Europa would be a long-term, in-situ exploration mission, not a flyby mission.

In the United States fiscal year 2014 budget, Congress authorized $80 million in funding for the Europa mission concept studies, and NASA’s fiscal year 2015 budget request asks for an additional $15 million for continuation of the concept studies.

The Request for Information:

The specifics of the Request for Information (RFI), released 28 April 2014, ask for concepts for a Europa mission costing less than $1 billion (U.S.), a figure that excludes the launch vehicle.

Specifically, the RFI lists the five major scientific objectives of the proposed Europa mission.

These objectives include characterization of the extent of Europa’s ocean and its relation to the deeper interior of the moon as well as characterization of the ice shell and any subsurface water, including their heterogeneity, and the nature of the surface-ice-ocean exchange.

Furthermore, the mission will need to determine global surface compositions and chemistry, especially as related to habitability; help scientists understand the formation of surface features, including sites of recent or current activity; identify and characterize candidate sites for future detailed exploration; and understand Europa’s space environment and interaction with Jupiter’s magnetosphere.

Z81“This is an opportunity to hear from those creative teams that have ideas on how we can achieve the most science at minimum cost,” said John Grunsfeld, Associate Administrator for NASA’s Science Mission Directorate.

“Europa is one of the most interesting sites in our solar system in the search for life beyond Earth. The drive to explore Europa has stimulated not only scientific interest but also the ingenuity of engineers and scientists with innovative concepts.”

Interest in Europa has steadily increased in previous years as scientific findings have pointed to the existence of a liquid water ocean under the moon’s icy crust – an ocean containing more water than all of Earth’s oceans combined.

Furthering those findings, the Hubble Space Telescope, in December 2013, observed water vapor above Europa’s frigid south polar region, providing the first strong evidence of water plumes erupting off the moon’s surface.

While the RFI is not a request for proposal or formal procurement, and is therefore not a solicitation or commitment by the United States government, it does signify a subtle growth in NASA’s focus toward the outer solar system.

For Europa, the mission concept studies, if they come to fruition, would make the moon only the second moon in the outer pantheon of the solar system to receive a dedicated mission.

Saturn’s moon Titan was the first outer solar system moon to receive a dedicated mission when the Huygens lander, piggybacking with the Cassini spacecraft, landed on the surface of Titan on January 15, 2005.

The historical lack of, but importance of, exploration of the outer solar system:

This week’s step forward for the Europa mission represents a slowly growing focus for NASA toward exploration of the outer solar system – a region of the solar system that is seemingly routinely forgotten in terms of robotic exploration mission funding and execution.

Part of the reasoning behind this lack of focus on the outer solar system has, without a doubt, been a necessary focus for NASA on the development of near-Earth space transportation technologies, the establishment of permanent human habitation in space via the International Space Station, and a focus on robotic precursor missions to Mars ahead of the first human mission to the red planet.

But also factoring into the equation is the sheer amount of time and energy it takes to get a spacecraft to those regions.

To place a probe into orbit of one of the outer planets, it is not simply a matter of aiming the spacecraft directly at the point where the planet will be at the time of spacecraft arrival.

Mission planners and engineers must take into account the relative velocity and trajectory at which a probe must approach one of the outer giants to be captured by the planet’s gravity and pulled into a stable orbit.

This becomes a very tricky balance when selecting missions for the outer reaches of the solar system: either you have to sacrifice in-situ exploration at the target to get the probe there as quickly as possible (New Horizons to Pluto) or you have to sacrifice science time for a multi-year and sometimes hazardous trek through the solar system for gravity assist maneuvers in order to get the probe to one of the outer planets at a low enough velocity and on the correct low-angle-of-encounter trajectory to be captured by that planet’s gravitational field (Galileo, Cassini, and Juno).

Thus, exploration of the outer solar system has been confined primarily to flyby missions performed principally by the Pioneer 10 and 11 probes and the two Voyagers.

To date, only the Galileo (ended in 2003) and Cassini (still active) missions have been long-term, in-situ exploration missions at Jupiter and Saturn, respectively. 

Uranus and Neptune have received no in-situ exploration missions, and have only been flown-by once, by Voyager 2 in 1986 (Uranus) and 1989 (Neptune).

Beyond that, the Juno mission to Jupiter and the New Horizons mission to Pluto are the only two new, but-not-yet-arrived-at-their-destination missions of NASA’s (and humanity’s) in the outer solar system. 

New Horizons is itself a high-velocity fly-by only mission of Pluto while Juno will be only the third long-term in-situ explorer mission of the outer solar system when it arrives at Jupiter in August 2016.

Thus, the NASA Europa mission, if realized, will become only the fourth or fifth such long-term, in-situ mission (depending on the launch date of the European Space Agency’s Jupiter Icy Moon Explorer mission – currently set to launch in 2022) of the outer solar system.

Thus, with two of the world’s principal space agencies setting their sites on long-term missions to the Jovian system’s moons, and a yet-to-be-addressed proposal for a Uranian exploration mission, the prominence of robotic exploration of the outer solar system is slowly rising – exploration that could have a profound influence on our knowledge of the development of life on worlds other than Earth.
(Images via NASA)


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