September 9, 2023



     In his Your Place in Space feature printed in The Planetary Report’s June Solstice 2023 edition, Bill Nye opened this special OSIRIS-REx issue with some reflections about the probe’s seven year journey.  As the president of The Planetary Society, Nye wanted to remind all the Society’s members that, “You share in missions like OSIRIS-REx.  You help make them happen.  You help these missions get funded, stay funded, and make it to the launch pad.  You also help spread awareness of these amazing missions and the things they teach us about the Cosmos, inviting new people to experience the joy of exploration and discovery.”  Does Nye sound a little excited about this mission?  Granted, having watched enough episodes of Bill Nye the Science Guy (his long-running show aimed at kids but educational for adults, also) has shown me that he   gets excited about all things science.  As the President of the PS, Nye manages to hold onto that excitement even when it takes a long time for a mission to be planned, executed, and evaluated.

     The return of OSIRIS-REx on September 24, 2023 makes this the right time to review why Bill Nye is so excited about a mission originally launched on September 8, 2016.  For the record, OSIRIS-REx is the shortened version of the probe’s full name:  the Origins Spectral Interpretation Resource Identification, Security-Regolith Explorer.  Yes, that is a mouthful, thus we will keep referring to it as either OSIRIS-REx or just O-REx.  The mission to the asteroid Bennu was accomplished in several stages.  After it was launched, O-REx began the journey by swinging past the Earth on September 17, 2017.  This gave the probe a gravitational boost to give it more  speed for the long trip.  The craft arrived at Bennu on December 3, 2018 where it began orbiting the asteroid for 505 Earth days (a year and a half).  During this time, it took pictures for mission controllers back on Earth who used them to find a suitable place to perform what Nye calls ‘a robotic arm scoop-up’.

     The asteroid Bennu’s name (actually, it is formally known as 101955 Bennu) was coined in 2013 by a nine-year old North Carolina boy named Mike Puzio.  As a third grader, he entered a ‘name the asteroid contest’ co-sponsored by The Planetary Society and the LINEAR asteroid survey (who had first discovered it).  Though it was originally called ‘1999 RQ 36’, Puzio suggested ‘Bennu’ because he thought the Touch-and-Go Sample Mechanism (or TAGSAM) (more on that in a bit) resembled the neck and wings of a gray heron, a bird often depicted in ancient Egyptian art.  To the Egyptians, Bennu was the living symbol of Osiris.  The shape of the asteroid also resembles an egg and Puzio’s suggested name connected enough dots to be picked over the thousands of other entries sent in.

     Nye further explained some of the mission’s elements as follows:  “The O is OSIRIS stands for Origins – our origins.  Asteroids come in a variety of types with a variety of characteristics.  Bennu, believed to have formed at the very beginning of our Solar System, has a great deal of carbon.  That suggests it may have organic compounds, which in turn suggests it may have some of the fundamental molecules found in the organisms that are alive today.  If we can find organic molecules aboard this species of asteroid, it may have remarkable implications about the origin of living things – like us.  The S in OSIRIS stands for Security.  We want to learn about the orbits of objects like Bennu so we can prepare in case there’s one incoming.  We want our home to be secure.  Stay tuned.  Bennu has a slim chance of impacting Earth in the year 2182.  With this mission, we’ll learn more about asteroids and their orbits and how they may cross ours someday.”

     Planetary Society members (and others) were offered an opportunity to join OSIRIS-REx on the journey to Bennu and back.  On board, it carries a microchip encoded with the names of the 442,803 who responded to the offer.  Somewhere in my archives I have a certificate stating that my name was included in this chip.  Whenever an offer like this came up to ‘join’ a space exploration mission, I passed it along to my students so there may very well be a few more names with an Ontonagon County connection on board.  Why does the PS have this longstanding tradition of collecting names to send aboard spacecraft?  As Nye points out, “We want to emphasize the fact that everyone on this planet has a role to play in space exploration and that when a mission heads out into the Cosmos, we go with it in spirit.

     Bennu is what is known as a ‘rubble-pile’ asteroid.  This means it isn’t exactly a solid object.  Bennu (and two other asteroids previously visited by probes from the Japanese Space Agency (JAXA) called Ryugu and Itokawa) consists of chunks of rock bound together gravitationally.  It is thought these rubble-pile objects are formed when the pieces of a larger asteroid destroyed in a collision come together.  When these pieces reassemble into another asteroid, the mass isn’t great enough to generate enough gravitational pull to solidify the particles.  As Kate Howelis writes in The Planetary Report, “Since Planets, moons, and asteroids have to all start from such smaller collections of material, rubble-pile asteroids might shed insights on the early stages of planetary formation.”

     Bennu orbits the Sun every 1.2 years and every six years, it makes its closest approach to Earth’s orbit passing some 186,000 miles from us.  When O-REx began orbiting the asteroid on December 31, 2018, it started mapping the surface so mission control could pick out potential sampling sites.  The first attempt to collect material from Bennu came on October 20, 2020.  Dante Lauretta, the mission’s principal investigator told The Planetary Reporter, “What surprised us was how loosely packed and fragile the surface was.  When the spacecraft made contact, it sank like two feet deep.  The robotic arm just plowed through with no resistance whatsoever.  It was shocking to us.  And we realized the material is very weak and breaks apart incredibly easily.”

     Two previous JAXA missions to collect material fired a projectile into the asteroids and collected particles ejected from the resultant crater.  O-REx used a different technique that allowed it to collect a larger sample than either JAXA probe.  The O-REx Touch-and-Go method used a burst of nitrogen gas to stir up material that was then collected with the robotic arm.  The goal of collecting at least 2 ounces was easily met even though it carried three additional nitrogen canisters in case the first pass was unsuccessful.  According to, O-REx was an historic, record setting mission:  Bennu is the smallest body a spacecraft has ever orbited (with a diameter of 1,640 feet) and O-REx performed the closest orbit ever of a small body, at just one mile from the surface.”  O-REx made its last flyover of Bennu on April 7, 2021 and departed on its trajectory back to Earth on May 20, 2021.

     The return trip won’t be like getting a FedEx or UPS delivery at your door.  When the O-REx vehicle approaches Earth on September 23, 2023, there will be a set of complex steps that will be needed to ensure the safe return of the Bennu samples.  When the craft is about four hours or 60,000 miles from the Earth, things will begin to happen.  Mike Moreau, the flight dynamics system manager at NASA’s Goddard Space Flight Center, is in charge of the team handling OSIRIS-REx’s navigation.  He explains, “You’re a third of the way to the Moon, and you just have this spring that is ejecting the [sample] capsule and giving it a spin.  We don’t do anything to control it,  It’s just like a really long three-point shot.” 

      Swapna Krishna (reporting for The Planetary Society) continues:  “The sample container itself doesn’t have any engines or thrusters.  The hard work to obtain a precision landing comes in the period before that separation.  At 14 days out from the sample return, O-Rex will fire its thrusters and perform a trajectory-correction maneuver, targeting a specific return area at the Utah Test and Training Range  80 miles SW of Salt Lake City.  “All the work to do the targeting is happening in those two weeks beforehand,” says Moreau.  Moreau’s team has spent the last year refining their navigation programming so by the time the craft nears the sample container separation phase, only minor adjustments should be needed to ensure they hit the target.  The landing area in question is an ellipse measuring roughly 12 by 50 miles.  Moreau continues, “It is kind of mind boggling that you release a thing on a spring 100,000 km (approximately 160,000 miles) from the Earth…and it’s going through a window that’s probably a couple of km (less than 2 miles) wide in the atmosphere to hit your target.”

     The return canister carrying the samples from Bennu is similar to the manned capsule that returned the astronauts from the Moon.  It has a blunt end and a nose cone but at just under 1 meter (3 feet) long, it is much smaller than the manned capsule.  Laurettta told The Planetary Reporter, “It’s got a heat shield with the nose cone that’s aerodynamically optimized for high velocity entry through the atmosphere.”  Traveling at 7.7 miles per second, it will make one of the fastest reentries in the history of space flight.  Friction with the thickening atmosphere generates a lot of heat that the shielded blunt end will dissipate to keep the cargo inside safe.  While the heat is being bled off, so is the capsule’s speed as it undergoes rapid deceleration.  Two minutes and 10 seconds after it enters the atmosphere, a drogue parachute will deploy to stabilize the container and around 1,000 meters (3,200 feet) the main parachutes will deploy.  The entire process from entry to landing will take approximately 13 minutes and once touchdown is achieved, the ground teams will spring into action.

     Lauretta and his team will be waiting in hangars at the Utah Test and Training Range which will put them less than an hour away from the landing zone which they will reach by helicopter.  He explained, “There will be four helicopters staged there.  In case of inclement weather, we’ll have ground track vehicles, so we will drive out, which will take a lot longer.  It doesn’t matter – rain or shine, whatever happens in Utah, we’re coming.”  The first to arrive will be the safety officer who will make sure the landing area is safe.  Soil, air, and anything else around the capsule will be sampled and photographed by the rest of the team.  The capsule will then be taken back to the hangar and housed in a portable clean room where it will have the back shell and heat shield removed as well as the avionics equipment.  The sample canister itself will be placed in a nitrogen rich environment before curation, much like the Apollo lunar samples were stored.  The nitrogen purge will keep out the terrestrial atmosphere and humidity.

     The canister, still bathed in nitrogen gas, will be flown to the Johnson Space Center in Houston.  Nicole Lunning, deputy OSIRIS-REx curator within NASA’s Astromaterials Research and Exploration Science Division is in charge of preserving the asteroid samples.  Lunning says, “The canister does not get opened until they get into the O-REx curation lab.  We actually will open the canister inside a nitrogen glove box.  We’ll basically have a very elaborate unboxing procedure,” Lunning joked before adding this step will take place nine or ten days after landing.

     Lauretta estimates there could be about 250 grams of sample to work with, an amount similar to the mass of a baseball.  “Having more sample than we know what to do with is the best-case scenario, “ says Lunning.  The mission’s goal was to collect at least 59.5 grams.  The materials will be closely analyzed at the NASA facility.  Eventually, smaller samples will be hand-carried to labs around the world as part of NASA’s Participating Scientist Program.  Many other samples will remain in the Johnson Space Center vault for future study.

     After the fly-by drop off in September, what will become of the O-REx probe?  It will continue on an extended mission and become OSIRIS-APEX (or APophis EXplorer.  It will target another near-Earth asteroid (and another potentially hazardous object) 99942 Apophis.

Apophis will make a very close pass to the Earth on April 13, 2029.  O-APEX will begin observing Apophis on April 8 of that year and make a planned rendezvous with the asteroid on April 21.  During the 18 months it orbits the new asteroid, O-APEX will use its thrusters to disturb the surface materials so a spectral study of the subsurface materials can be done.

     It has become commonplace for NASA, SpaceX, and other space related organizations to air live coverage of their major events.  No doubt the capsule recovery from the O-REx mission will be carried on one or more platforms live.  If one misses the big event on September 24, the event will be played and replayed on multiple platforms for quite a while.  Welcome back, O-REx and happy landings and good luck O-APEX on your continued journey.


Top Piece Video:  Okay space history buffs – this isn’t a song about O-REx, but hey, you can not go wrong with Telestar by the Tornados – love that organ sound!