Yearly Archives: 2009

astronomy, satellite collision debris

Junk Orbits

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Messing up LEO and Endangering ISS

Recall a few weeks ago we had a little “oopsie” between a couple of satellites that resulted in both of them being broken apart into small chunks of debris. Some of that debris has started to fall through the atmosphere, and will likely burn up as it passes through or if any pieces survive and fall to Earth, they’d be “ghosts” of their former selves.

However, some of this material (tastefully renamed Micrometeroid Orbital Debris) could very likely pose a threat to the International Space Station. According to the NASA watch board NASA Spaceflight.com, the crew of the space station has been alerted that they may have to  move into the Soyuz capsule and possibly be prepared to leave the station due to a “red threshold late notice” they received about debris that could slam into the station. Given all the factors that affect the orbits of debris, it’s still not clear as of this morning (Thursday, March 12) whether the team will have to do this. (It’s getting clearer — see updates below.)

Note:  The piece of debris was a piece of a Payload Assist Module (got that info from the link above).  The ISS really dodged more than a bullet!

A satellite with a PAM-D upper stage attached. A piece of the PAM-D from the recently-collided Iridium satellite is what passed by the International Space Station today.
A satellite with a PAM-D upper stage attached. A piece of the PAM-D from the recently-collided Iridium satellite is what passed by the International Space Station today.

This problem raises the issue of just what we’ve done to junk up near-Earth space. It’s not just this satellite collision that groatied things up.  There has been space junk out there for years, ranging from stuff dropped during EVA missions to junk from intentionally destroyed satellites. It’s all out there, either raining down after years of atmospheric drag or plugging along in orbit, waiting for a chance collision with something like ISS or, worse, a shuttle or other launch vehicle ascending to orbit.

We’ve junked out Low Earth Orbit now — and there’s not a lot we can do to clean it up.  We have to dodge the junk in order to get to space, and once we’re there, we have to watch out for it.  Although space is big and the junk is small, this is still just a bit too much like the work-arounds we live with here on Earth to avoid drinking polluted water or breathing crappy air.

The good news  is, provided we don’t further scatter our stuff around LEO, given time and atmospheric drag and a few other factors, orbits will get clean again, but that’s little consolation to the folks who have to live with it (literally) on orbit.  Now we need to find ways to actively clean up LEO.

Late note: according to Nancy Atkinson over at Universe Today, the crew is shutting down hatches on ISS and will head for Soyuz from 16:30 to 16:45 GMT Thursday. The possible debris hit could be in as little as 40 minutes from now (now being around noon on the U.S. East Coast).

Even later note:  the piece passed by and didn’t hit the ISS.  We can all breathe again.

2009 dd45, asteroid

Revisiting the Celestial Drive-by

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More Data Yields Better Information

Remember that near-Earth asteroid that whizzed by us last week and caused a flurry of excitement? There was a lot of speculation about how much damage 2009 DD45 would have caused if it had hit our planet. Several of us wrote about that in a special New York Times blog discussion and there were numerous press reports about “‘Roid Rage” and so forth.

Well, with the passage of time and continuing observations of this tiny interloper, astronomers have been able to tighten up the size estimates on 2009 DD45. In a short note to subscribers of the NEO News listserv, scientist David Morrison reported:

Rick Binzel and colleagues observed DD45 in the infrared from Mauna Kea and reported as follows to the Central Bureau for Astronomical Telegrams: R. P. Binzel, M. Birlan, and F. E. DeMeo, Paris Observatory, made 0.8- to 2.5-micron spectroscopic measurements on Mar. 2.6 UT using the NASA Infrared Telescope Facility 3-m reflector on Mauna Kea. Absorption bands revealed at 1 and 2 microns show the characteristics of the S-type class of asteroids. Using the average albedo value of 0.36 for small NEAs in this class and based on its observed brightness, the diameter is estimated to be 19 +/- 4 m. This is near the lower size limit and, together with the stony composition, suggests that this object would likely have disintegrated too high to do any ground damage. Knowing the size also allows us to revise the estimate of how often a NEA of this size passes this close to Earth, to roughly once per year.

Asteroid Eros is a good example of a S-type asteroid; the chunk of rock that wandered past Earth last week is also an S-type asteroid. Courtesy NASA (click to embiggen).
Asteroid Eros is a good example of a S-type asteroid; the chunk of rock that wandered past Earth last week is also an S-type asteroid. Courtesy NASA (click to embiggen).

So, essentially what happened is that observers figured out what this object is made of — a stony mix of silicates and other rocky materials. We know how much light such materials can reflect (what their brightness, or albedo, is), and based on the observed brightnesses, astronomers were able to figure out a size of somewhere between 15-23 meters (roughly  50 to 75 feet) in diameter. That’s not large enough to make it safely through the atmosphere — this object would have burned up had it been on a collision course with Earth.

This illustrates the value of continuing observations of asteroids, or any celestial object for that matter. The more you observe, the more you learn and the more you ultimately know about an object.  No doubt continued observations of DD45 will refine its orbital parameters, its spin, and other factors about this piece of rock that orbits the Sun and occasionally comes close to Earth.