Back in the 1930s, the German astronomer Karl Reinmuth discovered a near-Earth asteroid now called 1862 Apollo, which gave its name to the Apollo asteroids, all of them Earth-crossing and of high interest to those looking to plan asteroid missions. The number of known Apollo asteroids totals close to 7000. The one that gains our attention today is 101955 Bennu, for this is the target of the upcoming OSIRIS-REx mission, scheduled for launch on September 8.
Standing for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, OSIRIS-REx is a sample return mission that will, if all goes well, reach Bennu in 2018, surveying the asteroid from nearby space for 505 days in search of optimum sampling sites. The plan is for no actual landing but a very close approach in which the spacecraft’s extended robotic arm will attempt to gather the sample. The robotic arm (known as TAGSAM, for Touch-And-Go Sample Acquisition Mechanism) will collect between 60 and 2,000 grams of surface material.
Image: The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft will travel to a near-Earth asteroid, called Bennu (formerly 1999 RQ36), and bring at least a 60-gram sample back to Earth for study. The mission will help scientists investigate how planets formed and how life began, as well as improve our understanding of asteroids that could impact Earth. Credit: NASA/University of Arizona.
Like 2001 CQ36, which we talked about yesterday in relation to Deep Space Industries’ Prospector-1 mission, Bennu is a potential Earth impactor and thus offers dual service in terms of pure science and planetary defense. The asteroid has a diameter of approximately 500 meters and, as you can see from the images below, has been surveyed by the planetary radar facilities at both Arecibo and Goldstone. The low delta-v required to reach it from Earth orbit makes it a prime candidate for close study, and we should have samples by 2023.
Image: These radar images of Bennu were obtained by NASA’s Deep Space Network antenna in Goldstone, Calif. on Sept 23, 1999. NASA detects, tracks and characterizes asteroids and comets passing close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., commonly called “Spaceguard,” discovers these objects, characterizes some of them, and plots their orbits to determine if any could be potentially hazardous to our planet. Credit: NASA/JPL-Caltech.
One reason images like these are important is that the precise measurement of an asteroid’s trajectory depends upon the Yarkovsky effect, which depicts the forces upon a rotating object as it heats. The effect can be subtle but over time can make for serious changes in an asteroid’s orbit. The asteroid 6489 Golevka, as measured between 1991 and 2003, drifted 15 kilometers from its predicted position. When we’re dealing with nearby asteroids and trying to make sure they don’t present a hazard to Earth, small changes like this can obviously be critical.
Learning the exact shape of an asteroid, along with its orientation and albedo, helps us produce more accurate predictions. That makes the Yarkovsky effect anything but theoretical, and in fact there are proposed asteroid deflection schemes based on it, some focusing sunlight on the object, some changing a small asteroid’s albedo by painting the surface with reflective coatings. OSIRIS-REx, as part of its numerous studies at Bennu, will be measuring the Yarkovsky effect.
The scientific payoff should be impressive as we look to learn more about the formation and evolution of the Solar System. Asteroids are leftovers from the system’s earliest days, and as we’ve seen from the Deep Space Industries plans, they’re also packed with natural resources like water, organics and metals. A carbon-rich sample from Bennu will help us probe the regolith layer at the sample site and understand the chemistry and mineralogy of such objects.
OSIRIS-REx is scheduled to launch on Sept. 8, 2016, at 1905 EDT (2305 UTC).
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Delta-v to Bennu is about 5.1 km/s. A table of asteroid delta-vs can be found here.
The hydrazine monopropellant engine has an Isp in the low 200 seconds, not that much better than the estimated 200 seconds of the advanced DSI Comet-1 water propellant electrothermal engine.
I’m expecting the close up imaging to be spectacular. We’ll get to see the surface in unparalleled detail. Add in the spectrometer data for composition, and the mapping and this should be the most comprehensively mapped asteroid. And what surprises might the returned sample analysis find?
60 plus grams, outstanding!
This probe will also be carrying an Asteroid Time Capsule:
Great article as usual. And straight to the point . The Yarkovsky effect. Small over short periods and for larger ( km plus) NEOs but critically adds up over decades and can make all the difference especially in 100m class bodies like Bennu. These may not be “dinosaur killers” but can still back a big punch , serious megatonnage dependent on impact velocity.
It’s these NEOs that require long term surveys to accurately predict their position over long periods once discovered as things can change over time and what’s safe ( or risky) one decade , may not be the next. The Large Synoptic Survey Telescope of next decade may indeed locate 90% or so of even these low sized NEOs, but there will need to be a process of long term observation to keep the highest risk targets under tabs. Most especially for those objects that generally orbit within Earth’s orbit so are not easily imaged from ground based telescopes due to the presence of the Sun.
It’s for objects like this that the B612 Foundation conceived their Sentinel telescope and NEOCAM is amongst the favourites for the next round of Discovery concept missions. Both were designed to image in or around the Near infrared , where even dark coloured NEOs show up at 10 microns in particular , and are placed conveniently inside Earths orbit so they can look outwards. Sentinel near Venus’ orbit , NEOCAM at the Sun / Earth L1 Lagrange point about one million kms inward of Earth .
Sleep easier with these missions in place .
While I am of course very glad that we as a species are finally truly aware of the dangers of impacts from space, I will probably sleep a bit better once we set up an actual defense system against rogue planetoids and comets.
Just remember how much damage the relatively tiny meteor that hit Chelyabinsk in 2013 caused and there was virtually no way to detect that one in time.
I couldn’t agree more. It’s the “smaller” NEOs that pose the greatest threat . . It’s also one of the best cases of “forewarned is fore armed” . ( Continued ) Observation is critical , Yarkovsky effect and such like.
There are annual conferences involving the world’s experts in this area, three of whom, Henri Melosh, David Dearborn and Bie Wong ,all from the U.S. , lead in their field and although their opinions on how best to deal with the threat of NEOs vary to a degree ( with a big overlap ) . Their emails to me have helped reveal the common theme of not enough political awareness or interest in this critical matter. Internationally. Hence the B612’s Foundation’s excellent Sentinel telescope concept that would go along way to addressing the problem . Sadly it’s donations are not what they could be and a long way short of its half billion dollar cost . For six years operations.
The LSST at least should cover about 95 % of targets over time , it’s just those smaller asteroids whose orbits are internal to Earth’s and thus hidden by the Sun from Earth based scopes.
It’s decision time on the next round of the circa half billion ( ironically ) Discovery programme and I hope the NEOCAM is one of the two concepts selected. We all should as you say ! Only a two year primary mission to begin with , to help keep the bid’s operations costs down ( a ploy often used to seemingly keep costs down ) but can easily be extended and the results should then speak for themselves . The good news is that a lot of very good research has gone into varying Earth impacting deflection techniques and with warning there are numerous good ways of achieving very good defence even down to relatively short notice.
How big (or small) does an object have to be to merit calling an encounter a landing, vs. a docking or contact?
OSIRIS-REx is on its way to Bennu!
Thankfully the nearby explosion of SpaceX’s Falcon 9 rocket on September 1 did not affect the asteroid probe launch (and my condolences to the Amos 6 comsat):
OSIRIS-REx’s cameras see first light
Posted By Emily Lakdawalla
2016/09/29 08:34 UTC
As OSIRIS-REx speeds away from Earth, it’s been turning on and testing out its various engineering functions and science instruments. My favorite proof of a happy instrument is data, especially camera data, so I’ve really been enjoying the series of “first light” images that OSIRIS-REx has been sharing over the past few weeks.
Full article and images here:
StowCam also took an amazing shot of the space probe’s sample return capsule: