A NewScientist.com summary of Wednesday’s House Armed Services Committee strategic forces subcommittee hearing on “space and U.S. national power” plays up the worst-case scenario of an attack on US civil and military satellites:
If the US does not protect its Earth-orbiting satellites, the equivalent of a car bomb in space could take the economy back to the 1950s, according to witnesses testifying in Washington DC earlier this week.
The article goes on to discuss the effects of detonating a nuclear weapon in low Earth orbit, a move that could devastate the satellites there. However, as the witnesses at the hearing pointed out, most major communications satellites are not in LEO but in GEO, which is much harder to reach (the exceptions are the ORBCOMM, Iridium, and Globalstar satellite constellations), while navigation satellites are in MEO, which is also difficult to reach. It still makes for a very bad day for satellites (and astronauts) in LEO, but it doesn’t necessarily “take the economy back to the 1950s”. That makes the doomsday scenario hyped by NewScientist.com less of a worry that more conventional attacks on specific satellites, through anti-satellite weapons, terrestrial jamming, or attacks on ground stations.
> However, as the witnesses at the hearing pointed out, most major communications satellites are
> not in LEO but in GEO, which is much harder to reach (the exceptions are the ORBCOMM, Iridium,
> and Globalstar satellite constellations), while navigation satellites are in MEO, which is also difficult to reach.
A nuclear weapon doesn’t have to reach GEO or MEO. All it needs to is reach orbital altitude, not orbital velocity.
And it doesn’t even have to reach orbital altitude — just the charged particles do. Exploding the bomb at high magnetic latitude, above the atmosphere, will cause the electrons and positrons to spiral out to much higher altitude.
The results of the early US and Soviet out-of-atmosphere tests (the US series including STARFISH comes to mind, and the Soviets launched a bunch from Novaya Zemla to the regions of the open magnetic field lines) indicate there would be more limited problems. The results of such an explosion at the altitude of a satellite with a low apogee/perigee would be devastating to satellites such as the Space Station but would not be harmful to most other satellites. The sun-synchronous NOAA satellites might be at some risk, but the Iridium and other medium height satellites would be unaffected. All geosynchronous satellites would be well above the effects.
Most geosychronous satellites are armored against charged particles anyway, since they can be assumed to be outside of the Earth’s protective magnetic shield at some point in their operational lives.
For a low latitude explosion, the cascade of charged particles would be trapped in a band of latitudes about the equator – and would spread around the world in a belt. The particles would have a hard time crossing magnetic field lines in general.
For an explosion above the Arctic or Antarctic, the charged particles would be quickly ducted either into the atmosphere or out into the magnetotail.
I would not want to be an astronaut on the Station – and some low altitude satellites would be fried – but the most probable nuclear explosion in near space would not directly affect our economy. Other than increasing defense budgets again.
a few thoughts on this:
1) The US military is increasingly reliant on commercial satellites. I presume these are unhardened.
2) The Galaxy IV failure (http://en.wikipedia.org/wiki/Galaxy_IV) suggests to me that picking a small number of key satellites can have a sufficiently crippling effect.
3) What stops some amateur group or unfriendly government from launching a handful of parasitic microsats and sending some to GEO? What trajectories could be used? Could we even track something the between the size of a coke can and a shoe box in the vicinity GEO? If there were already something there, how would we know?
Charles: explosions above the latitude at which magnetic fields lines connect to the magnetotail would cause the plasma to rapidly escape. Explosions at low latitude would trap the plasma at low altitude.
The concern would be explosions at latitudes between these. There is a latitude where the magnetic field lines go out to the position of GPS satellites, for example.
The explosions would probably have to be thermonuclear to really have a significant effect. Starfish was a 1.4 megaton explosion. The stored magnetic energy in the external portion of the Earth’s magnetic field is about 200 megatons, so to get significant plasma beta (ratio of plasma pressure to magnetic pressure) you’d need rather hefty explosions (although damage to satellites could occur even at lower average beta.)
What stops some amateur group or unfriendly government from launching a handful of parasitic microsats and sending some to GEO? What trajectories could be used?
That they don’t exist yet..?
Prove it.
Prove what? The non-existence of a fictitious threat that you think my tax dollars should be wasted to defend against?
The onus is on YOU to prove they exist.
Otherwise, the following argument has as much validity:
we should spend precious space $ to defend against the impending invasion by the space alien fleet which is due to attack soon by building a giant fleet of space laser platforms.
Prove that the space alien fleet does NOT exist. Don’t tell me that you can’t find it, prove to me it DOESN’T EXIST.
I think that most would agree that I should prove it does exist…
Just another example of the liberals who would have us cut-and-run from the alien fleet menace. We’re fighting them in space so we don’t have to fight them here.