OSIRIS-REx bound for 4.5 billion mile journey for some priceless pebbles
CAPE CANAVERAL, Fla. — Tomorrow evening, Thursday, September 8, 2016, NASA’s latest foray into space, a mission named OSIRIS-REx, is scheduled to launch from Launch Complex 41 at Cape Canaveral Air Force Station adjacent to Kennedy Space Center in Florida. While the objective of the mission might appear tiny, what the “might” possibly be is profound.
Its payload, which contains instruments, a sample acquisition mechanism, and a return capsule, will begin a 7-year journey to the Asteroid 101955 Bennu and back. Its goal is to study the remnant of our solar system’s early formation in detail and collect a sample of the asteroid’s surface material for return to Earth and intensive study.
The timeline for this mission is an example of just how long space exploration efforts take, from start to finish. Planning for OSIRIS-REx began 5 years ago, led by a team of scientists and engineers from the University of Arizona, and including scores of others from NASA, United Launch Alliance, and Lockheed Martin.
The spacecraft will take two years to chase down the asteroid, a year to map and explore the asteroid’s surface, and another 2 years to return, not to mention the years of subsequent analysis of the returned samples.
According to NASA, asteroids are metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. Known as “minor planets”, tens of thousands of asteroids congregate in the so-called main asteroid belt: a vast, doughnut-shaped ring located between the orbits of Mars and Jupiter. Asteroids are thought to be primordial material prevented by Jupiter’s strong gravity from accreting into a planet-sized body when the Solar System was born some 4.6 billion years ago.
Known asteroids range in size from the largest – Ceres, the first discovered asteroid in 1801 – at about 600 miles (966 km) in diameter down to the size of pebbles. Sixteen asteroids have diameters of 150 miles (241 km) or greater. The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun.
The OSIRIS-REx mission is slated to visit Bennu, a mid-sized asteroid about 1,640 feet (500 meters) in average diameter (about the height of World Trade Center destroyed in 2011). It travels at about 63,000 mph (102,998 km/h) – Earth travels at about 67,000 mph (107,826 km/h) – around the Sun every 1.2 years.
Bennu is considered a primitive asteroid that has not significantly changed in 4.5 billion years; it is carbon-rich and is thought to have a composition similar to that of Earth. In 2035, Bennu is predicted to come as close to our home world as 186,000 miles (257,495 km) – the Moon orbits Earth at a mean distance of 238,854 miles (384,399 km). At present, Bennu is about 340 million miles from our planet (3-and-a-half times the distance from the Earth to the Sun).
During a Sept. 6, 2016, press conference, Dante Lauretta, OSIRIS-REx’s principal investigator from the University of Arizona (Tucson) explained that Bennu was chosen for the target of this mission based on criteria including distance from Earth, its orbit isn’t too close to the Sun, has an orbital inclination of less than 10 degrees compared to our planet, and the possibility of having loose material on the surface. Five reasonably sized asteroids met those criteria, from which Bennu was chosen.
The OSIRIS-REx spacecraft that is being prepped to fly to Bennu weighs a bit over 2 tons (1,814 kg) and is roughly the size of a FedEx truck. It will be powered by two solar panels that will deploy after launch. The spacecraft’s payload includes a camera suite, three spectrometers, a laser altimeter, a sampling arm, and a sample return capsule. Lockheed Martin built the spacecraft with instruments produced by the University of Arizona, the Canadian Space Agency (OLA), Arizona State University, NASA’s Goddard Space Flight Center, and the Massachusetts Institute of Technology.
Lauretta describes the process in a NASA video: Engineers will activate thrusters with which to navigate the spacecraft very slowly toward the asteroid, and in about mid-2020, will slowly descend the spacecraft to the surface of the asteroid. Given that the probe will be traveling approximately 30 times faster that the fastest high-velocity rifle bullet – this is tricky indeed.
A robotic arm with a sampler head will then be deployed, allowing the disc-shaped sampler head (about 18” in diameter) to briefly contact the asteroid surface for 5 seconds or so. During that contact, compressed nitrogen gas will stir up the surface material (anticipated about 1 cm in diameter) that will be captured in a basket-like chamber.
Once engineers confirm that material has been collected, they will orient the spacecraft for its 2-year return to Earth. It will then conduct a fiery re-entry through the Earth’s atmosphere, with a parachute-assisted landing in the Southwest of the United States.
Only about 25 percent of the sample will be made available for immediate analysis. The remaining 75 percent will be preserved for future analysis by succeeding generations of scientists with more sophisticated technology.
Worried that Bennu or some other asteroid might someday smash into the Earth? NASA is keeping a close watch. Explains Lauretta on his website, “The tabulation of potential Earth impacts results in a cumulative impact probability of approximately 1 in 2700 sometime in the 2175–2196 time frame. The effect of a Bennu impact on Earth would be insignificant on a planetary scale. The Earth is not strongly disturbed by such an impact and loses negligible mass. The impact does not make a noticeable change in the tilt of Earth’s axis and it does not shift the Earth’s orbit noticeably. Local effects, however, would be much more noticeable.”
For Lauretta and the other team members working on this mission, tomorrow’s planned launch will not mark the culmination of five years of work, but rather the beginning of an odyssey of another seven years, awaiting the return of their precious treasure in 2023.
Jim Siegel comes from a business and engineering background, as well as a journalistic one. He has a degree in Mechanical Engineering from Purdue University, an MBA from the University of Michigan, and executive certificates from Northwestern University and Duke University. Jim got interested in journalism in 2002. As a resident of Celebration, FL, Disney’s planned community outside Orlando, he has written and performed photography extensively for the Celebration Independent and the Celebration News. He has also written for the Detroit News, the Indianapolis Star, and the Northwest Indiana Times (where he started his newspaper career at age 11 as a paperboy). Jim is well known around Celebration for his photography, and he recently published a book of his favorite Celebration scenes. Jim has covered the Kennedy Space Center since 2006. His experience has brought a unique perspective to his coverage of first, the space shuttle Program, and now the post-shuttle era, as US space exploration accelerates its dependence on commercial companies. He specializes in converting the often highly technical aspects of the space program into contexts that can be understood and appreciated by average Americans.