From Spaceflight Insider: “Planetary scientists explore possible Kuiper Belt follow-up mission”


Spaceflight Insider

May 8th, 2017
Laurel Kornfeld

Artist’s concept of the New Horizons spacecraft during its encounter with Pluto. Image Credit: NASA / JHU-APL / SwRI

Less than two years after the New Horizons spacecraft’s historic Pluto flyby, a group of planetary scientists is taking the first steps toward a second mission to the Kuiper Belt.

NASA/New Horizons spacecraft

Kuiper Belt. Minor Planet Center

Such a mission could be a return to Pluto, this time with either a Cassini-type orbiter and lander or a first mission to another Kuiper Belt dwarf planet, Alan Stern of the Southwest Research Institute in Boulder, Colorado, said in a conversation with Spaceflight Insider.

NASA/ESA/ASI Cassini-Huygens Spacecraft

Stern, who is the principal investigator of New Horizons, noted that some 35 planetary scientists met in Houston, Texas, on April 24, to discuss possibilities for a follow-up mission.

The meeting was not a New Horizons event but an independent gathering of planetary scientists who had expressed interest in a variety of potential missions to the outer Solar System.

Stern compared the workshop to the ones planetary scientists held in the late 1980s that eventually led to New Horizons.

While the Pluto flyby yielded a wealth of information about the dwarf planet, its findings raised more questions than they answered, Stern emphasized.

“We surprised ourselves with how complex Pluto is,” he said, describing the mission’s discoveries as “a huge leap in our understanding.”

Among the questions raised by New Horizons are how Pluto can be so geologically active; what created Sputnik Planitia – the smooth, young terrain on the left side of Pluto’s heart – and whether the small world has a subsurface ocean.

Because the spacecraft was traveling so fast, its instruments were able to map only 48 percent of Pluto and its large moon Charon in high resolution.

Among the scientists who attended the workshop, there was significant debate as to whether a follow-up mission should be a return to Pluto with an orbiter or a sampling of the diversity of the Kuiper Belt by visiting one or more of its other dwarf planets.

These worlds have proven to be surprisingly diverse and heterogeneous, Stern noted.

The latter option would be an updated version of New Horizons, with three or four targets that would require three or four separate launches.

Returning to Pluto would require launching on a big rocket, such as the Space Launch System (SLS) that NASA is currently developing, and using a propulsion system like that used by NASA’s Dawn spacecraft to Vesta and Ceres.

The spacecraft would have to carry a large fuel tank because of the amount of fuel needed to put it into orbit around Pluto.

Using the SLS would likely reduce the travel time to Pluto from the nine-and-half-years that New Horizons took to about five or six years. However, the amount of slowing down required to get into orbit after arrival would increase the journey to somewhere between seven and nine years.

“You want to travel there quickly, then brake,” Stern emphasized.

However, once at the Pluto system, a spacecraft could use Charon’s gravity to power visits to the system’s four small moons much like Cassini used Titan’s gravity to alter its Grand Finale trajectory.

“You don’t need fuel once there because Charon is your motor. You could even fly out of orbit and do some Kuiper Belt exploration after (about) four years,” Stern said. “You’ll leave at a slow velocity because Charon has a low escape speed.”

Neptune’s moons Triton and Nereid are likely captured Kuiper Belt Objects, so they are also candidates for exploration.

Using a heavy launch vehicle and electric propulsion, a probe could travel extremely fast, even covering the nearly 100 Astronomical Units (AU, with one AU equal to the average Earth-Sun distance or 93 million miles) for a rendezvous with Eris.

A crucial step toward getting a mission off the ground is getting it prioritized in the Planetary Science Decadal Survey NASA conducts every ten years to select new missions.

The agency’s next Decadal Survey will take place in approximately two to three years, making now an ideal time to build support for a Kuiper Belt mission and generate interest in it through the media, he stated.

Over the next two years, scientists interested in this concept will hold more workshops where they will examine a variety of options. They will write papers outlining various proposals that will be presented to advisory groups such as NASA’s Outer Planets Assessment Group (OPAG) and Small Bodies Assessment Group (SBAG), which identify priorities for exploration in the outer Solar System and among small bodies such as asteroids and comets.

However, the goal is visiting one or more of the Kuiper Belt Objects large enough to be spherical, not an asteroid or comet.

The process will eventually include several hundred members of the planetary science community, who will examine potential science gains, the feasibility of each proposed mission, and mission costs, Stern said.

For each possible mission, this involves considering the type of propulsion to be used, whether electric or ballistic, flybys versus orbiters, and whether or not to use Jupiter gravity assists to speed up the trip.

Image Credit: NASA

Stern said: “We can’t go to the Decadal Survey with 100 projects. We need to determine which are feasible and what science comes out of them.”

Many proposals will gradually be whittled down to a few.

Outer Solar System missions require plutonium, which is currently in limited supply. However, the U.S. and European countries have recently begun producing plutonium again.

Any of the missions being discussed would likely launch in about 12 years, allowing sufficient time to ramp up plutonium production.

The next workshop on the project will be held at the 49th Meeting of the Division of Planetary Sciences of the American Astronomical Society this coming October.

Video courtesy of New Scientist

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