[meteorite-list] Near-Earth Asteroids: The Third Option

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:09 2004
Message-ID: <200401261754.JAA19470_at_zagami.jpl.nasa.gov>

http://www.thespacereview.com/article/90/1

Near Earth asteroids: the third option
by Jeff Foust
The Space Review
January 26, 2004

For years, the debate about the future of human spaceflight has focused on two
destinations: the Moon and Mars. Proponents of a human return to the Moon have argued
that such a mission is far more feasible than sending people to Mars and could have
numerous scientific and even commercial benefits. However, they have also had to fight
against the "been there, done that" mindset that argues that since we went to the Moon
over three decades ago, a return would not be that effective in stimulating the public's
interest in space exploration. Mars advocates, usually marching under the banner of the
Mars Society, have tried to point out that a human mission could be done for far less than
what was proposed in the old Space Exploration Initiative and could answer fundamental
questions, such as whether life ever existed on the planet. The mixed track record of
robotic Mars missions, though, makes it difficult to shake the perception that a human
mission would be extremely risky. (See "Choosing our destination" in this issue.)

President Bush's new space initiative appears to
have resolved this debate, at least for the near term,
by emphasizing a human return to the Moon, while
offering Mars advocates a consolation prize of
eventual Mars expeditions at some point beyond
2020. While the Bush administration may be set on
this new initiative, there is no guarantee that this
vision will ever become reality. Public opinion is, at best, mixed on this plan, with many
concerned about the high costs-real or perceived-such a plan entails. With some
members of Congress, including some conservatives, expressing concern about rising
budget deficits, this new plan will be subject to considerable Congressional scrutiny in the
weeks to come. Even if it survives this near-term challenge, a new president taking office
in 2009, let alone 2005, could dramatically reshape-or stop-the plan with a minimum of
wasted effort even if it is carried out as planned over the next five years. (See "Looking
beyond vision", January 19, 2004.)

The plan, and the overall debate, has been predicated on the belief that the only two
destinations for humans beyond Earth orbit for the foreseeable future are the Moon and
Mars. It turns out this is not necessarily the case. A small group of people, including
planetary scientists and former astronauts, has argued for a different destination for
manned expeditions: one or more of the many asteroids that pass near the Earth. Such
missions could be affordable (relatively speaking), visit new destinations, carry out
important research, and also set the groundwork for more ambitious missions, like Mars.

Fear, greed, and curiosity

As of the end of last week, there were 2,682 known near Earth objects (NEOs), all but 49
of which are asteroids. (The remainder are comets in short-period orbits that cross or
approach the Earth's orbit.) Of those 2,682 NEOs, 693 are asteroids with diameters of
one kilometer or larger. While astronomers believe that they have identified about 70
percent of the population of those large NEOs, the number of smaller NEOs may be vastly
larger: over 100,000 with diameters exceeding 100 meters.

In addition to the incomplete catalogs of objects, there are large gaps in our understanding
of these bodies. Groundbased telescopes have allowed planetary scientists to crudely
classify these objects based on their spectra, and radar observations of some
close-passing NEOs have revealed their shapes. Only a handful of asteroids, near Earth
or otherwise, have been studied in detail by spacecraft, such as NASA's NEAR
Shoemaker mission that orbited and eventually landed on the NEO Eros. Japan last year
launched Hayabusa, the first mission designed to take samples of an asteroid and return
them to Earth.

Why study NEOs at all? Dan Durda, a planetary
scientist at the Southwest Research Institute in
Boulder, Colorado, and a proponent of human missions
to asteroids, provided a rationale that can be summed
up in three words: fear, greed, curiosity. Fear comes
form the fact that NEOs have, and will continue to,
collide with the Earth. Right now the emphasis is on simply finding NEOs and determining
which ones could pose a risk to the Earth in the future. If any do pose a major hazard, then
attention will have to turn to mitigating that threat, most likely by deflecting the object's
orbit. That will require significant knowledge of the asteroid and how to operate on it:
detonating nuclear weapons, a popular proposal for deflecting asteroids, might instead
simply break apart an object that is a loosely-bound rubble pile. "I don't want to invoke
Chicken Little," said Durda in a recent interview, "but it is a real threat."

Curiosity comes from the scientific study of NEOs, including work that can only be done on
the asteroid itself, preferably by people. Studying these objects, said Durda, offers a
window into the origins of the solar system, since these objects are virtually unaltered
since the formation of the solar system. Greed is linked to the wealth of resources, from
water ice and other volatiles to platinum-group metals, found on asteroids. Scientists and
science-fiction authors have long talked about mining asteroids: while there's no need for
these resources on Earth for the indefinite future, such spacebased resources may be
useful, if not vital, to any long-term settlement in space. Durda notes that NEOs, the
most easily accessible asteroids, are hundreds of times richer in unprocessed materials
than the Moon. "They're literally gold mines in the sky," he said. By contrast, the lunar
regolith "has a composition similar to mining slag."

Planning a mission

While there are a number of good reasons for visiting NEOs, what makes the case for
such missions-human in particular-so compelling is the accessibility of these bodies. The
proximity of these objects and their small size sharply reduce the delta-v-the change in
velocity-and thus the amount of propellant needed to reach them. In many cases, the total
delta-v for a NEO mission is less than a mission to the Moon. At a September 2002
conference on mitigating asteroid impact hazards in Arlington, Virginia, Durda described
an example of a mission to one NEO, 1991 VG. A round-trip mission lasting just 60 days
would require a total delta-v of 6.1 kilometers per second, approximately the same as a
one-way mission to the Moon. Extending the mission duration to 90 days decreased the
delta-v to 4.9 km/sec.

These factors put manned NEO missions almost entirely within the capacities and
experience of human spaceflight today. Durda envisions missions to nearby NEOs lasting
90-120 days, using hardware based on modules developed for the ISS with "a modest
investment in new technologies." The duration of a NEO mission is considerably less than
the six months crews are now spending on the ISS, although the station crews have the
advantage of regular resupply from Earth. The low surface gravity of asteroids-a
one-kilometer body has just a few thousandths the gravity of the Earth-will also remind
astronauts of working on the station. "All the EVA experience we have gained on ISS will
be applicable here," Durda said.

The new technologies required for human NEO
missions are, in large part, items also needed for lunar
or Martian missions: improved power systems,
including nuclear power; spacesuits that can handle
dusty environments, and radiation protection. The
extremely low gravity of asteroids would introduce
some unique issues, such as the need to anchor ships or even people to the surfaces of
these objects. However, Thomas Jones, a former shuttle astronaut with a PhD in
planetary science who has worked with Durda on human NEO mission plans, points out in
an interview that an asteroid mission would also makes things simpler. "You would not
need a beefy lander, just a mobile platform to ferry EVA astronauts over to the asteroid
and back," he said.

The cost of a human NEO mission hasn't been estimated in any detail, Jones said. He
guesses that a NEO program would cost less than the roughly $30 billion that has been
spent on the space station program to date. "This amount would be spent over ten years
to do not just one, but a series of asteroid round trips," he said. The same hardware
developed for those missions could also be used for lunar missions, he added, with the
addition of a lander.

Drawbacks

While human missions to NEOs sound compelling and straightforward, they are not
without a number of challenges. The asteroid environment will pose a number of
challenges, from its near-absence of gravity to rapid rotation rates that create day-night
cycles that last just a few hours. "The dynamics of moving around an object will be
counterintuitive," warned Durda. "You can't just hop from point A to point B."

Another issue is selling the mission to the public. Virtually everyone is familiar with the
Moon and Mars (although the familiarity may be grounded more in fantasy than fact) and
thus can grasp, to some degree, the idea of sending people to these worlds. However,
outside of a few, largely forgettable movies like Deep Impact and Armageddon, most of
the general public is likely unfamiliar with the idea of sending people to asteroids, near
Earth or otherwise. In the body of public opinion and knowledge, it would be difficult for a
small asteroid, perhaps still carrying an alphanumeric designation like 2000 SG344, to
compete with the Moon and Mars.

Durda, speaking at the 2002 asteroid mitigation conference, said that he thinks the public
would embrace a human NEO mission, regardless of how obscure the destination,
because of the spirit of adventure involved with any human exploration. "I guarantee to
you that the first time humans go beyond LEO to a small rock, the public is going to eat it
up," he said.

Perhaps the biggest challenge a human mission faces, though, is selling the need to send
humans in the first place. Some advocates of spacecraft missions to NEOs argue that
robotic missions can accomplish all the requirements-scientific, threat mitigation, and
utilization-for studying these objects for the foreseeable future. Air Force Brigadier
General Simon "Pete" Worden, an advocate of asteroid missions in general, was skeptical
about the benefits of human missions during a forum on planetary defense last week in
Washington organized by the Homeplanet Defense Institute. While calling the concept of
human NEO missions "cool", he warned about the cost and benefit tradeoffs. "My
experience with space programs is that whenever you put a person into a mission it is an
order of magnitude more cost," he said. "I can't imagine that these kinds of things
[asteroid missions] would benefit from some kind of human presence.

Durda notes that any human mission would be preceded by robotic reconnaissance, from
microsat orbiters to sample return missions. However, human geologists on an asteroid
will be far more efficient than their robotic counterparts. "You will never replace the
creativity and the intuition of the human mind," he said. "That is the true benefit of putting
humans in the environment."

Fitting missions into the new plan

For the near term, though, the debate over human expeditions to NEOs appears to be
academic. Asteroid missions don't figure into the president's new space initiative, at least
through 2020. Beyond that, though, advocates believe there is an opening for carrying out
these missions as part of preparation for a human Mars expedition. "You can choose
either the Moon or asteroids to build up experience for Mars," said Jones. "Asteroids are
natural stepping stones for Mars."

Jones is optimistic that NEO missions can be worked
into the overall Bush initiative. "There is nothing in
the President's plan which bypasses the asteroids,"
said Jones. "The lunar missions lead naturally to
expansion of our experience base to the NEOs. The
lunar hardware to be developed can be simply
augmented with additional propellant and life support
to enable months-long asteroid voyages. One of the major benefits of the President's plan
is that we will be building hardware and capability to take advantage of asteroidal
resources and to learn how to work on them."

Durda, in an interview several weeks before Bush unveiled his new plan, argued that, in
the end, it was more important for NASA to establish a new destination-driven program
for human exploration. "If we decide to go back to the Moon, I am fully behind it," he said.
Still, he hoped NASA would look for "something new and exciting, something beyond the
Moon but not quite as difficult as going to Mars."

With a new plan in place, but still subject to change by this or a future administration, that
opportunity to do "something new and exciting" may still present itself sooner rather than
later. "A bonanza of new knowledge, the basis for space commercialization, and planetary
protection," Jones summarized. "NEOs are a convincing combination."


Jeff Foust (jeff_at_thespacereview.com) is the editor and publisher of The Space Review.
He also operates the Spacetoday.net web site. He has also recently started a weblog titled
Space Politics to track space policy issues.
Received on Mon 26 Jan 2004 12:54:24 PM PST