Technical Experts Weigh In On NASA's Asteroid Retrieval Mission

Technical Experts Weigh In On NASA's Asteroid Retrieval Mission

On Tuesday,  Ball Aerospace held the second “Target NEO” workshop on the technical challenges and opportunities of exploring Near Earth Objects (NEOs), especially asteroids and NASA’s new Asteroid Retrieval Mission (ARM).

The workshop was a follow-up to the February 2011 Target NEO workshop sponsored by the George Washington University Space Policy Institute and Ball Aerospace.  That workshop was in response to President Obama’s 2010 call to send humans to an asteroid by 2025. The agenda for that workshop centered around gathering information to achieve that goal.

Tuesday’s “Target NEO 2” workshop focused on the Obama Administration’s latest iteration of that goal—deploying a robotic probe to capture an asteroid, redirecting it into lunar orbit, and sending astronauts there to study and possibly extract a sample of it. This is variously referred to as the Asteroid Retrieval Mission, Asteroid Return Mission, or Asteroid Redirect Mission, and is part of what NASA calls an asteroid strategy that in turn is part of an asteroid initiative.

The six sessions featured a variety of policy, science, and management experts.

The workshop started off optimistically with a presentation by William Gerstenmaier, the NASA Associate Administrator for Human Exploration and Operations, on the current thoughts and capabilities for ARM. The proposed timeframe is to launch a robotic probe by 2017 to travel to the asteroid and capture it, with the possibility of redirecting it into lunar orbit and launching a crew to visit it in 2021, which is the first time the Space Launch System is scheduled to send an Orion spacecraft with a crew into space.

Gerstenmaier stressed that ARM is a valuable mission because it would build upon technologies that NASA has already marked as priorities and that are currently in development, such as solar electric propulsion. He made it clear that the main thrust behind this effort is not science, but rather demonstrating that the United States can send people to Mars by the 2030s.  He asserted that this mission would build off already-existing infrastructure and personnel, while at the same time expanding the country’s operational and technical capabilities in ways that activities on the International Space Station cannot.

Later sessions delved into questions about the technical and scientific feasibility of an asteroid retrieval mission. Determining how many NEOs are suitable for this mission requires a combination of modeling and observation. The criteria for a satisfactory target asteroid are tough: the orbit must be close to the Earth (less than about .05 astronomical units, or about 20 times the distance between the Earth and the Moon), have a low velocity relative to that of the Earth (less than about 2.5 kilometers per second) as well as a fairly circular orbit, and should not be tumbling or spinning very quickly. Not surprisingly, models suggest that an asteroid with these characteristics will be hard to find, even though William Bottke of Southwest Research Institute said that observations discover about eight times more ARM candidates than models predict. Still, out of the 1,000 near-Earth asteroids observed each year, only about 2.5 of those meet the criteria to be a potential target, Paul Chodas from the Jet Propulsion Laboratory (JPL), said.

A large mission design driver comes from the physical properties of the target asteroid, but even after a target is identified, which may be as late as 6 months before launch, various panelists showed that the size, mass, orbital path, and tumbling motion will still be very uncertain.  Andrew Rivkin of the Applied Physics Lab (APL) said that scientists have rarely been able to directly measure the size of an asteroid. Instead, the absolute magnitude, or brightness as seen from the earth, is used as a proxy for the size. Furthermore, if scientists cannot determine the composition of the target, the mass will be uncertain. Rivkin said this uncertainty might be by a factor of up to 25-30. Carlos Roithmayr from NASA’s Langley Research Center and Stephen Broschart from JPL reminded the audience that this greatly affects the propellant required for the mission; an asteroid that is too massive to retrieve with the planned fuel budget may render the mission impossible. The composition of the asteroid also affects the technology used on the spacecraft: a “sand bar” must be treated very differently than a rock.

Towards the end of the day-long workshop, panelists expressed mixed feelings about ARM.  Gentry Lee, Chief Engineer for the Planetary Sciences Directorate of JPL, reminded the audience that the uncertainties in the mission, such as mass and composition of the asteroid, would translate into the need for a time consuming and expensive test program prior to launch.  At the same time, Lee was hopeful that a mission like this could restore the type of collaboration among NASA’s field centers to what it was during the Apollo era in the 1960s and early 1970s.

Former astronaut Tom Jones pointed out that this mission could demonstrate U.S. leadership in space while at the same time providing an opportunity to forge international collaboration. He also believes it will generate excitement for space exploration from the public and Congress. Conversely, other panelists worried that the proposed schedule was too aggressive and the funding situation is questionable.   But Gentry Lee offered that perhaps some progress in the field of human spaceflight is better than being stalled; since this mission now has visibility and support from the administration, it may be worthwhile to pursue.

A written report from the workshop will be released in about a month. In the meantime, the public can comment on the draft, which will be uploaded onto the workshop website:

Editor’s Note: welcomes Gabriele Betancourt-Martinez as a correspondent for the website.   She is a third year PhD student studying astrophysics at the University of Maryland, College Park, and does her research at NASA’s Goddard Space Flight Center. Before starting graduate school, she was a Lloyd V. Berkner Space Policy Intern with the Space Studies Board of the National Academies, and a consultant for the European Science Foundation, European Space Sciences Committee in Strasbourg, France.  She has a B.S. in Astronomy and Physics from Yale University.

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