Keep the shuttle flying: Fwd: Uranus, Neptune in NASA’s sights for new robotic mission

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From: "Gary Johnson" <gjohnson144@comcast.net>
Date: August 26, 2015 at 12:15:56 PM CDT
To: "Gary Johnson" <gjohnson144@comcast.net>
Subject: FW: Uranus, Neptune in NASA's sights for new robotic mission

Uranus, Neptune in NASA's sights for new robotic mission
August 25, 2015 by Stephen Clark
NASA's Voyager 2 mission captured this image of Uranus during its January 1986 flyby, the only encounter with the distant ice giant. Credit: NASA
NASA has asked scientists to assess how to design and fly robotic space probes to Uranus and Neptune, the last of the solar system's classical planets yet to be orbited, likely ensuring the huge icy worlds are near the top of the space agency's to-do list in the coming decades.
Led the Jet Propulsion Laboratory, the study will look at ideas for orbiters that could be dispatched Uranus and Neptune in the late 2020s or early 2030s and study the giant planet's structures, composition and extensive moon systems.
One focus of the study will be designing a common spacecraft platform that could be developed in two copies and launched to Uranus and Neptune for about $2 billion each, according to Jim Green, head of NASA's planetary science division.
But Green said scientists should look at scaled-back concepts that could be developed at less cost.
"We want to identify potential concepts across a spectrum of price points," Green said Monday in a meeting of a NASA-sponsored science working group devoted to outer planets research. "One of our (impediments) to make missions happen is the huge price tag it takes in order to be able to get out to the outer solar system."
The study is the first bureaucratic step in a multi-year effort involving independent cost and technical assessments, scientific peer review and federal budgeting before a mission to one of the icy giant planets goes from the drawing board to reality, Green said.
Results from the study will be presented to a panel of scientists seated by the National Research Council in the early 2020s. The NRC committee meets once per decade to map out the top priorities for the next 10 years of planetary science research, producing a report that ranks mission concepts for consideration by NASA decision-makers.
The space agency's policy is to follow the decadal survey's recommendations.
A mission to Uranus or Neptune will likely be a multibillion-dollar flagship-class mission in the mold of NASA's Cassini orbiter flying around Saturn and a recently-approved probe to repeatedly fly by Jupiter's icy moon Europa.
NASA's Voyager 2 spacecraft encountered Neptune in August 1989. Credit: NASA
NASA's budget for planetary science can only support development of one such costly mission at a time, so only low-level work on a follow-up flagship project is affordable until after the Europa mission departs Earth in 2022.
"Obviously, it's not going to be easy to be able, even after we get Europa under our belt, to actually execute on the next large mission, but we need to make progress to understand our science priorities and look at this in a way that will prepare us for the next decade, but also utilize new technologies and capabilities that have come up (since the last decadal survey)," Green said Monday.
The last decadal survey report issued in 2011 set NASA's foremost planetary science objectives as a Mars sample return mission and a probe to Europa.
NASA's next Mars rover set for launch in 2020 will collect and store rock specimens for retrieval and return to Earth by a future mission, fulfilling the first step in a multi-mission odyssey to bring back samples from the red planet's surface. And NASA formally approved the Europa flyby probe earlier this year to assess the icy moon's habitability.
A Uranus orbiter was third in line in the 2011 decadal survey, but NASA's budget will keep the mission grounded until at least the late 2020s. That means NASA's ultimate approval of the mission depends on it faring well in the next decadal assessment by the National Research Council.
It is likely to be up against strong backing for a robotic mission dedicated to Saturn's moon Titan, which has seas and rivers of liquid hydrocarbons like methane, and another flagship mission to Mars to pick up the samples collected by the 2020 rover.
A lander or rover mission to Venus may also gain support in the next decadal report. The surface of the sweltering cloud-shrouded world has not been explored since Soviet-era lander missions in the 1980s.
NASA is expected to request similar conceptual studies on other leading contenders for future flagship missions heading into the next decadal survey, but Uranus and Neptune are first in the lot.
A concept for a Uranus orbiter and atmospheric entry probe was evaluated during the last decadal survey report released in 2011. Credit: NASA/NRC Decadal Survey
Orbiters for Uranus and Neptune will almost certainly rely on nuclear batteries powered by plutonium, and U.S. government funding of additional production of space-grade plutonium ensures such projects will have the power resources they need, Green said.
Engineers pack pellets of plutonium-238, the isotope tailored for electricity in space, into radioisotope generators. The natural decay of plutonium-238 produces heat, which is transferred through thermoelectric couples to generate electricity.
"It would be after 2023, as we get into the next decade that we would consider using radioisotope power for those missions, if they survive the decadal process, which I'm sure they will," Green said Monday.
Nuclear power is required for probes in the far reaches of the solar system, where sunlight is insufficient for solar arrays. NASA's New Horizons mission to Pluto, the Cassini mission at Saturn and the Curiosity rover on Mars currently rely on plutonium power sources.
Uranus orbits about 1.8 billion miles from the sun, more than three times farther than Jupiter, and Neptune is positioned 2.8 billion miles away.
Other objectives of the JPL study include assessing how Uranus and Neptune research probes could benefit from advanced sensor technologies, such as compact instrumentation and high-resolution cameras. Green said the study will also examine how NASA's powerful Space Launch System, which is being considered for the launch of the Europa mission in 2022, could allow for bigger, more capable and less risky missions to Uranus and Neptune that could make the trip in a fraction of the time feasible if the probes used a smaller rocket.
"There is this underground sentiment that we do need to get back to the outer solar system, but it's just so hard," said Heidi Hammel, a planetary astronomer who is executive vice president of the Association of Universities for Research in Astronomy. "We're working on technology to make it not so hard and so expensive."
Neptune and its largest moon Triton are pictured in this view from NASA's Voyager 2 mission in 1989. Credit: NASA
NASA also tasked JPL to identify ways international partners could participate in the missions and to establish a science definition team for Uranus and Neptune.
Some scientists view Uranus and Neptune as the logical next step in the strategic exploration of the solar system, and orbiters to one or both of the huge planets could arrive about a half-century after their first encounters by NASA's Voyager 2 probe.
"The planetary decadal puts a Uranus mission very high," Green told reporters in July in a briefing during the New Horizons flyby of Pluto. "Even though those are giant planets — Uranus and Neptune — they have a lot of major compositional differences from the big gas giants — that are primarily hydrogen and helium — which is Saturn and Jupiter. We call those — Uranus and Neptune — ice giants because they have a lot of ammonia and other material."
Scientists believe Uranus and Neptune are composed mostly of rock and ice, with a dense, layered atmosphere. Researchers are not sure where they got so much ice, but some experts believe Uranus and Neptune were bombarded with frozen primordial objects from the Kuiper Belt, a ring of frigid proto-worlds beyond Neptune that contains Pluto and dozens more nation-sized dwarf planets.
Surprising discoveries by the New Horizons flyby of Pluto, revealing the diminutive icy world to show signs of apparent glacial flows and ongoing geologic activity, have renewed attention on the mostly unexplored far edges of the solar system, such as the Kuiper Belt.
"Our new frontier is the outer part of the solar system," Green said.
At least some of the outer giant planets' moons, such as Neptune's Triton, are likely intact remnants from the ancient Kuiper Belt that were captured billions of years ago.
"If we want to go back to a Kuiper Belt Object (after New Horizons), we may not have to go into the Kuiper Belt to get it," Green said in July. "We may want to go to Neptune to visit Triton, which is closer. Although Neptune is a heck of a distance away, it's still not as far as some of the Kuiper Belt Objects."
NASA created this size comparison chart for the solar system's giant outer planets based in imagery from the Voyager missions. Credit: NASA/JPL-Caltech
"I think the science case for a future mission to one — or both — of the ice giants is strong, and I do expect them to be well placed in the next decadal survey," said Mark Hofstadter, a planetary scientist who led studies for a Uranus mission in the late 2000s.
"The announcement yesterday from Jim Green means that the next decadal will be better positioned to identify a realistic and capable mission, and its cost," Hofstadter told Spaceflight Now.
For William McKinnon, a planetary geologist at Washington University in St. Louis, another visit to Uranus or Neptune would be fascinating, he tells Spaceflight Now.
But McKinnon, who currently analyzes fresh data on Pluto from New Horizons, brings up an often-overlooked concern among scientists working on probes to faraway destinations: It takes decades to design, build and fly such a mission, followed by more years of data crunching.
"An ice giant mission, presumably an orbiter, is, alas, over the horizon as far as my lifespan is concerned, so I salute those who will live to see it!"
© 2015 Spaceflight Now Inc.

NASA To Study Uranus, Neptune Orbiters
by Dan Leone — August 25, 2015
NASA has initiated preliminary studies of missions to either Uranus or Neptune, Jim Green (above), the agency's planetary science director, said Aug. 24. Credit: NASA
LAUREL, MD. — NASA began an early feasibility study for missions to the distant, mostly ignored ice-giants Uranus and Neptune, a senior agency official said here Aug. 24.
"I've asked [the Jet Propulsion Laboratory] to initiate an ice giant study," Jim Green, NASA's director of planetary science, said during a presentation to the agency-chartered Outer Planets Assessment Group, which met at the Johns Hopkins University Applied Physics Laboratory here.
A closeup of Uranus — from about 1 million kilometers away. Credit: NASA/Voyager 2
The study will run "at least a year" once JPL, Pasadena, California, stands up what is known as a science definition team, Green said. He advised scientists here who are interested in participating on the team to watch for a formal announcement NASA will publish "soon."
Green assigned a cost cap of $2 billion in fiscal year 2015 dollars to either orbiter mission.
The study is a long way from a NASA commitment to send a probe to either Uranus or Neptune: Largely unexplored bodies planetary scientists have long desired to observe more closely.
Storms on Neptune, last seen up close by Voyager 2 nearly three decades ago. Credit: NASA/Voyager 2.
No NASA mission to the ice-giants would launch until the late 2020s or 2030s; the JPL-led study is intended to inform the planetary science community as it prepares to write its next 10-year science roadmap, or decadal survey, that will be published by the National Research Council around 2022, Green said.
Green said the JPL team will answer very preliminary questions: A mission's addressable science objectives; required technology development; and whether the objectives are realistic given NASA's budget outlook and short supply of nuclear power systems. Green said a nuclear power source would be needed for any Uranus or Neptune mission.
Before NASA mounts a mission to either planet, Uranus and Neptune will again have to receive the planetary science community's endorsement as top destinations in the 2022 decadal.
"I'm sure they will," Green said. "They're very worthy."
NASA's Voyager 2 is the only spacecraft ever to get anywhere near Uranus and Neptune. The spacecraft snapped closeups of Uranus in 1986, and of Neptune in 1989.

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