Whoops! (in the newspaper, in space ...)
I've learned to read news articles with a great deal of skepticism, because when I read about subjects I know personally, there are so many glaring errors. It is reasonable to infer that other subjects are reported just as inaccurately. Case in point:
Scientists estimate that there should be around 3,000 comets in the galaxy, but only 25 have so far been identified.
Heh!
There are way more than 25 comets known. Here's a 2005 NASA announcement about a single observatory that has been used to discover 1,000 comets.
(The newspaper article seems to be talking about old comets that no longer produce tails and are especially hard to detect, but that's not what it says. And I'm not even touching the apparent mixup of "galaxy" with "solar system".)
I suppose there is now a legitimate basis for editing Wikipedia to say that only 25 comets have ever been identified. Heh.
In other news ... two communications satellites smashed into each other yesterday at an altitude of 789 kilometers. (After my warning above about inaccuracy in media, I'll note that Bill Harwood is an excellent reporter who routinely seems to get everything right, from the details to the big picture.) This is the first time two large objects have collided in orbit. There have been a few previous minor incidents, such as an antenna getting clipped by a piece of space debris, plus a general peppering of dust-size space debris on orbiting satellites. What happened yesterday is at a whole different order of magnitude.
Orbital velocity is around 25 feet per millisecond, so satellite collisions are fast. The satellites don't smash into each other, they melt instantly and pass through each other. Both satellites have disintegrated into an orbiting debris cloud, basically high-velocity shrapnel. And this is in a very bad place, because debris at that altitude will stay in orbit for a very long time, and that part of space is heavily populated (weather satellites, astronomy satellites, etc). Below about 500 km, the thin traces of Earth's upper atmosphere brings down anything that is not being actively kept in space; above about 1,500 km, there are few satellites and they're widely spaced (with the exception of the geosynchronous ring). A long-standing fear in the space community has been a chain reacton, where debris from one collision hits another satellite creating more debris, etc. This is the altitude range where collisions are most worrisome.
For reference, the Chinese ASAT test happened at a similar altitude. They shot a missile into one of their weather satellites, and about 10-15 percent of everything tracked in orbit is debris from this one weapons test. (In contrast, the US shootdown of a failed and potentially hazardous military satellite happened so close to the atmosphere that all the debris has already come down from space, leaving no long-term debris hazard to other satellites.)
Oh, I should mention what the satellites were in yesterday's collision. One was an active Iridium communicatons satellite, the other was a dead Russian military communications satellite. At that altitude, unused satellites, rocket stages or other debris can remain in orbit for hundreds of years.
Scientists estimate that there should be around 3,000 comets in the galaxy, but only 25 have so far been identified.
Heh!
There are way more than 25 comets known. Here's a 2005 NASA announcement about a single observatory that has been used to discover 1,000 comets.
(The newspaper article seems to be talking about old comets that no longer produce tails and are especially hard to detect, but that's not what it says. And I'm not even touching the apparent mixup of "galaxy" with "solar system".)
I suppose there is now a legitimate basis for editing Wikipedia to say that only 25 comets have ever been identified. Heh.
In other news ... two communications satellites smashed into each other yesterday at an altitude of 789 kilometers. (After my warning above about inaccuracy in media, I'll note that Bill Harwood is an excellent reporter who routinely seems to get everything right, from the details to the big picture.) This is the first time two large objects have collided in orbit. There have been a few previous minor incidents, such as an antenna getting clipped by a piece of space debris, plus a general peppering of dust-size space debris on orbiting satellites. What happened yesterday is at a whole different order of magnitude.
Orbital velocity is around 25 feet per millisecond, so satellite collisions are fast. The satellites don't smash into each other, they melt instantly and pass through each other. Both satellites have disintegrated into an orbiting debris cloud, basically high-velocity shrapnel. And this is in a very bad place, because debris at that altitude will stay in orbit for a very long time, and that part of space is heavily populated (weather satellites, astronomy satellites, etc). Below about 500 km, the thin traces of Earth's upper atmosphere brings down anything that is not being actively kept in space; above about 1,500 km, there are few satellites and they're widely spaced (with the exception of the geosynchronous ring). A long-standing fear in the space community has been a chain reacton, where debris from one collision hits another satellite creating more debris, etc. This is the altitude range where collisions are most worrisome.
For reference, the Chinese ASAT test happened at a similar altitude. They shot a missile into one of their weather satellites, and about 10-15 percent of everything tracked in orbit is debris from this one weapons test. (In contrast, the US shootdown of a failed and potentially hazardous military satellite happened so close to the atmosphere that all the debris has already come down from space, leaving no long-term debris hazard to other satellites.)
Oh, I should mention what the satellites were in yesterday's collision. One was an active Iridium communicatons satellite, the other was a dead Russian military communications satellite. At that altitude, unused satellites, rocket stages or other debris can remain in orbit for hundreds of years.