Commentary | What Is Wrong With Retrieving an Asteroid?

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Is the Obama administration’s proposed redirection of a small asteroid into lunar orbit, followed by a short visit by two astronauts, an endeavor “worthy of a great nation?” The Review of the United States Human Space Flight Plans Committee, the Augustine committee report, famously made that a test for considering large NASA projects.  

Many members of Congress do not think the asteroid redirection is a worthy goal — but it is the project our nation appears willing to pay for. 

The asteroid redirection is one of the cheapest scientifically and industrially meaningful human missions yet proposed. It is certainly better than the plan it displaces — putting the first human mission of the Orion deep-space capsule into a retrograde 70,000-kilometer halo orbit above the lunar surface. Without costing much more money, it enables human astronauts to do what they are good at — geological fieldwork — rather than what they are bad at — remote sensing. 

Missions more useful for the long term could include:

  • Building and operating a lunar base to practice living off the land on a nonterrestrial world.
     
  • A “PhD” mission to the martian moons Phobos and Deimos to demonstrate interplanetary travel and life support.
     
  • A second-generation space station, this time in a cislunar orbit, for practicing and demonstrating skills needed deeper in the solar system, and as a continuing market to help secure a commercial space transportation industry.

None of these can be financed with the congressionally mandated Space Launch System (SLS) consuming so much of the budget. Without an improbably large increase in NASA’s funding, there will be no money left over to develop deep-space infrastructure — habitats, landers or tugs — for the foreseeable future. Clear alternatives to the SLS exist, including operational or impending commercial launch vehicles like the United Launch Alliance Delta 4 Heavy or the Space Exploration Technologies Falcon Heavy. Using these would free up money for actual exploration, but doing so is politically unacceptable to members of Congress with large NASA human spaceflight facilities to keep busy developing new rockets. 

An asteroid redirection represents an exceedingly clever way out of this bind. It allows field geology and prospecting by on-site geologists at a price NASA can afford. More importantly, it is not hard to see some silver linings to the project. Setting aside the obvious benefits of giving the SLS and Orion something useful to do, successfully retrieving a large chunk of asteroid could have enormous value for future industrialization, planetary protection and especially for science. 

Materials splashed up from one asteroid in impacts end up on other asteroids. A large, pristine sample of one that has not been fused into an amorphous mass during entry into Earth’s atmosphere is likely to include smaller samples of many. Some of these secondary samples may have decipherable ages and, just possibly, provenances (the original asteroids they came from). 

Most asteroids are in stable orbits that thankfully do not come close to crossing Earth’s — which also means they are not the sources of most meteorites that fall to Earth. All our direct knowledge of asteroidal materials comes from meteorites derived from a very few asteroids, representing a highly limited sample of what is likely to be out there. For example, the HED (howardite-eucrite-diogenite) meteorites are thought to originate in the impact that created the south polar basin on the asteroid Vesta. A set of papers in Nature recently argued that the Chelyabinsk impact in Russia is likely to have originated on the 2-kilometer Asteroid 86039 within the past 40,000 years, and may have “sibling” fragments that could impact Earth in the future. 

Outside of a few examples like these, we have no samples of the vast majority of these relatively pristine relics from the solar system’s formation. 

Since asteroid orbits evolve over eons, meteorites that arrived on Earth in the distant past would have come from different source asteroids. Very old meteorites may represent different samples — but these meteorites will have been severely degraded or destroyed by terrestrial geologic activity.

A more diverse suite of samples would be preserved on weatherless asteroids that have been passively collecting debris, from slowly changing orbits, for the lifetime of the solar system. Any small asteroid retrieved for study by astronauts is likely to include a much wider collection of asteroidal material than we have now. It might well contain a surprise or two. 

Just as important, while the most delicate samples will never make it to Earth’s surface, fragile pieces of the first conglomerations of the pre-solar nebula could be the most interesting. Finding a well-preserved sample impact-splashed from another star system is a remote possibility. A human mission with geologists on site would be the most likely to recognize the unexpected. 

All of this will be of value to those interested in asteroid science; it will also be of interest to prospectors looking for water or heavy metals. They too might find rare materials that could be more valuable than the bulk water, oxygen and carbon that are known to exist.

The asteroid retrieval would demonstrate a number of skills useful or necessary for a future lunar, Mars or PhD base. These include: 

  • Deep-space propulsion, navigation and operations.
     
  • Space walks on a rugged and unknown surface with negligible gravity.
     
  • Practice at resource extraction and living off the land, especially if multiple asteroids are retrieved.
     
  • All-important radiation protection, whether through passive use of regolith or the development of new-technology active protection.
     
  • Grappling large uncooperative objects with loose, probably friable surfaces.
     
  • Moving very heavy cargo around the inner solar system: One identified candidate, asteroid 2009 BD, weighs approximately 325 metric tons.  

In the absence of additional resources for space exploration we should do the asteroid retrieval mission or something similar. It would give us a limited, but important, suite of deep-space operations and survival skills that we do not have today. It is already advancing the vital art of solar-electric propulsion. 

It may be a small step on the way to Mars, but it is a step. If the right discoveries are made, it just might be a giant one. 

 

Donald F. Robertson is a freelance space industry journalist based in San Francisco. For further examples of his work, see www.DonaldFRobertson.com.