On April 15, 2010, President Barack Obama gave a major speech at the Kennedy Space Center in Florida, announcing that the US would send astronauts to Mars by the mid-2030s. But in order to do so, NASA would first need to ramp up its capabilities through missions directed toward "a series of increasingly demanding targets," i.e. asteroids.
The President outlined a plan to send astronauts to an astroid for the first time by 2025. The vehicle for this historic mission would be the Orion spacecraft, originally designed as part of President Bush's vision for space exploration. The spacecraft would be launched aboard a heavy-lift vehicle, designated as the Space Launch System (SLS).
However, since most known asteroids reside in the asteroid belt between the orbits of Mars and Jupiter, reaching one of these asteroids would actually be a longer journey than reaching Mars. The SLS-Orion combination would not be capable of such a long journey. A smaller, but sizable, number of asteroids have orbits that bring them close to Earth. However, finding a suitable asteroid whose orbit would cross Earth's sometime in the 2020s was a difficult task.
Instead, NASA experts came up with a novel concept: a robotic mission to capture a small asteroid, then put it in orbit around the moon, where astronauts will visit it and return samples to Earth.
The Asteroid Redirect Mission (ARM) is the brainchild of Dr. John Brophy, a principal engineer at the Jet Propulsion Laboratory in Pasadena, Calif. Dr. Brophy led the team that developed the ion drive system that powers NASA's Dawn spacecraft (currently en route to the dwarf planet Ceres after visiting the asteroid Vesta in 2011). The ion drive uses electricity from solar arrays to ionize and accelerate an inert gas. Ion drives generate much less thrust than traditional rocket engines. In fact, Dawn's engines produce less than a third of an ounce of thrust. However, they are much more efficient, as measured in terms of specific impulse: Dawn's engines have a specific impulse of 3,100 seconds, compared to 452 seconds for the space shuttle's main engines. By providing a small but steady thrust over a long period of time, ion drives can produce a velocity change equal to that of much larger rocket engines, while using less propellant.
Dr. Brophy realized that a similar system could be used, not just to visit an asteroid, but to actually change its trajectory. Working with a small group of colleagues at NASA, he determined that retrieving a small near-Earth asteroid and bringing it to the International Space Station would be feasible. A follow-up study by the Keck Institute of Space Studies recommended putting an asteroid in lunar orbit instead.
As currently envisioned, the first stage of the ARM would consist of a robotic spacecraft, equipped with an advanced ion drive, to be launched before the end of this decade. In Option A the robotic spacecraft would capture an asteroid inside a gigantic inflatable plastic bag:
In Option B, the robotic spacecraft would snatch a boulder from the surface of a larger asteroid:
In either case, the spacecraft would carry the asteroid (or boulder) into orbit around the moon. An SLS-Orion spacecraft will then bring a crew of astronauts on a nine-day journey around the far side of the moon to rendezvous with the asteroid. The astronauts will leave their spacecraft to collect samples from the asteroid, then return to the spacecraft and head back to Earth.
Does this remind you a little of the 1998 films Deep Impact and Armageddon? Although the asteroids that are likely targets of the ARM are too small to present any threat to the Earth (about 30 ft in diameter), NASA says that the ARM will provide an opportunity to test technologies that could be used to defend our planet against much larger asteroids. In the boulder-retrieval option, the spacecraft will test an "enhanced gravity tractor" technique -- orbiting the asteroid for several months, during which time the spacecraft's gravitational pull will gently nudge the asteroid's trajectory.
The mission will also be an opportunity to test technologies that would be needed for a long-range space mission, such as a trip to Mars. For example, the ion drive used to power the robotic spacecraft could also be used for robotic cargo vessels that would resupply Mars-bound astronauts.
The ARM has come in for some harsh criticism. In an editorial for The Hill , US Rep. Lamar Smith (R-Texas), chairman of the House Science Committee, called the plan "costly and uninspiring." NASA's own Small Bodies Assessment Group has called the idea "very interesting and entertaining," but "not considered to be a serious proposal." And, in a 286-page report, the National Research Council says the mission is a dead end that won't lead humanity to Mars.
However, the mission also has many defenders. In an editorial astronaut Tom Jones and Planetary Society co-founder Louis Friedman argued that the ARM is a "challenging and innovative" mission that "may do much to restore near-term public interest in space exploration."
What do you think? Is the Asteroid Redirect Mission a good idea or a bad idea? Let us know in the comments section below.