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OSIRIS-REx: Mission to an Asteroid

Why mount a mission to an asteroid? For one thing, some of them cross the Earth’s orbit, and that makes gathering knowledge about their composition essential to any future trajectory-altering operation. For another, the science return could be immense. These are unprepossessing objects, no more than chunks of rock and dust, but they can tell us much about the early Solar System. Moreover, getting to an asteroid, as NASA GSFC is now proposing to do with a mission called OSIRIS-REx, would allow us to examine samples in situ, something mission proponent Bill Cutlip finds more valuable than studying chunks of asteroids that fall to Earth in the form of meteorites:

“[Meteorites] are toasted on their way through Earth’s atmosphere. Once they land, they then soak up the microbes and chemicals from the environment around them.”

No, pristine is better, for we’re trying to learn about the earliest days of our system, the period of planetary formation and the origins of the organic compounds that resulted in life. An asteroid like 1999 RQ36, some 580 meters in diameter and the target of OSIRIS-REx, is debris from the solar nebula that gave birth to the Sun and planets about 4.5 billion years ago. Usefully, it seems to have undergone little alteration since that era, unlike asteroids that have suffered from collisions or grown large enough that their interiors became molten. Moreover, RQ36 is rich in carbon. Does it also contain organic molecules of the kind found in other meteorite and comet samples?

If the mission is approved, we’ll learn the answer to this and more, generating a complete map of the asteroid and its topography. The mission will include two infrared spectrometers, a light detection and ranging (LIDAR) instrument to bounce laser pulses off the surface, a mass spectrometer to separate and identify atoms and molecules, and a laser altimeter. Following evaluation from orbit, OSIRIS-REx will collect a surface sample that will be returned to Earth. The plan is to orbit the asteroid for about a year before selecting the sample site, allowing a thorough study of the surface. Sampling an asteroid could be tricky because of the fast rotation, making the operation more like the meeting of two spacecraft:

“Gravity on this asteroid is so weak, if you were on the surface, held your arm out straight and dropped a rock, it would take about half an hour for it to hit the ground,” says Joseph Nuth (NASA GSFC). “Pressure from the sun’s radiation and the solar wind on the spacecraft and the solar panels is about 20 percent of the gravitational attraction from RQ36. It will be more like docking than landing.”

But learning how to maneuver in proximity to an asteroid could be useful for future dealings with near-Earth objects. RQ36 has a slight but real chance of striking the Earth in the year 2170. One motivation for OSIRIS-REx is to measure the Yarkovsky effect, the slight push that occurs when an asteroid soaks up sunlight and emits heat. The uneven surface and variation in asteroid composition makes the Yarkovsky effect difficult to calculate, but if we ever need to change the trajectory of such an object, we’ll need to know how the effect changes its orbit. Adds Nuth: “It’s like trying to make a complex, banking shot in a game of pool with someone shaking the table and kicking the legs.”

If selected by NASA, OSIRIS-REx would be launched no later than December of 2018, but right now it’s one of three proposals chosen in late 2009 under NASA’s New Frontiers program. As for the acronym, it’s torturous indeed. O stands for origins (i.e., the origin of life), SI for spectral interpretation, RI for resource identification, S for security, and REx for regolith explorer. All of that in a single package, but hey, it’s not easy to choose a mission name, and once cobbled together, this one has a nice ring to it.


Comments on this entry are closed.

  • NS March 16, 2010, 1:27

    Well, since nobody responded, I’ll go a little OT and post this YouTube link about a proposed rendezvous mission (not a sample return) to a near-Earth asteroid:


  • UncleDan March 16, 2010, 9:12

    My two cents – while I am fascinated by the science from an asteroid mission, I would rather see a mission to Mars, Europa, or Enceladus to search for life or precursors to life. That, in my opinion, is the big prize.

  • Bounty March 16, 2010, 14:36

    I’m excited by the Dawn mission. It’ll be great to have a better idea of what our largest asteroids are made of.

  • Mark March 16, 2010, 16:06

    I too am a big fan of a manned Mars mission but there has got to be some interesting stuff out there on those asteroids too, there’s just so many of them. I bet if we looked at all of them we’d find at least a half-dozen Bracewell probes, silently monitoring the solar system for intelligent life and reporting back to their owners. Think about it, it makes sense. If you want your probes to be unmolested for as long as possible, why put them on the moon, or even Mars? You sprinkle them among the asteroids. There’s no one asteroid that’s more obvious than another as a place to explore. The moon’s obvious, Mars is obvious, but pick a handful of random asteroids, and you have a monitoring platform that’s unlikely to be molested even as we develop very advanced spacefaring capabilities, simply because there are so many and they’re so small.

    I also think it would be cool to watch a rock take a half hour to drop. It would be pretty hard to move around on such a rock, unlike what we see on the movies, where asteroids of course have earth-normal gravity. I’d volunteer for an asteroid mission myself except for two things. 1) I’m extremely claustrophobic and 2) I’m scared of the dark, and there’s an awful lot of dark out there.

  • Darnell Clayton March 16, 2010, 17:14

    It’s a shame that we have not YET found the time and funds to investigate at least one of these asteroids in the past few decades!

    After all, if we eventually do end up mining these rocks of metal and ice, it would be wise to become familiar with landing upon them and finding out how solid they are.

    If it were not for this recession, I would advocate NASA doing this now (either that or have one of the private companies explore that option).

  • Ron S March 16, 2010, 17:26

    “…there’s an awful lot of dark out there.”

    You’ll be in full sunlight, 24×7.

  • george scaglione March 17, 2010, 15:16

    uncle dan : yes while a mission to an asteroid would be a great thing,nonetheless the other missions you mention would without doubt be alot better yes now,someone educate me.we are talking manned missions are we not!? recently i made some comments on what i thought would be great stuff to do and was then told that,oooh errr ahhh george i was only talking unmanned! i had not properly understood. :( but either way it will be a beginning.just guess which one i am rooting for.thank you one and all your friend george