Blitzen
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kaboom
If a communications satellite, one of the largest comm sats, somehow crashed to Earth and landed in a city, how much damage are we imagining would occur?
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7/3/2009, 9:36 pm
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Reythia
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Re: kaboom
Hmmmm... I'm not actually sure.
Here's a good site for something similar: the crashing of an asteroid: Determining the Damage of an Asteroid Impact
Like they say there, we usually calculate devastation in terms of energy released (commonly measured as the equivalent blast in kilos or tons of TNT). The energy released depends on two things (roughly): the mass of the object at the time of impact, and the speed at which it's moving.
Thing is, a satellite that's come through the whole atmosphere at God-knows-what angle and inclination could have a wide range of speeds and masses. I guess the first question's I'd ask are:
1.) What altitude and inclination (angle from the equator) did the satellite normally orbit at?
2.) What pulled it off that orbit? Is it just decay? Was its orbit intentionally changed? Did aliens push it?
3.) How much of the atmosphere did it pass through prior to hitting the city? That is, did it come in at an angle -- thereby going through a lot more air -- or did it come straight down?
Also, I should add that these numbers are sort of general, since the WAY it hits the ground could have a big effect. For example, a grazing blow would probably cause more damage than a direct hit that simply plowed into the ground. And hitting water has a very different effect than hitting ground. Also, if you're in a seismically-unstable place, a big enough impact could set of earthquakes -- though I suspect that's more of a problem for large (km-wide) asteroids than satellites only a few meters long.
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7/3/2009, 11:06 pm
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QS2
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Re: kaboom
Well to help out a bit, the largest comm sat in existence is a bit short of 7 tons and none of them have enough fuel to really slow there orbits all that severely. So they'd usually come in pretty shallow I imagine. So As a rough guess, I would thus say that even the biggest one would only do fairly limited damage, even assuming a worst case scenario. (Mostly because it wouldn't come through the atmosphere without losing a ton of speed and mass)
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7/4/2009, 11:05 pm
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BaneBlade
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Re: kaboom
quote:
Reythia wrote:
The energy released depends on two things (roughly): the mass of the object at the time of impact, and the speed at which it's moving.
That part is key. While you might think that the heat caused by re-entry would be the only factor, if the satellite has a shape that isn't very aerodynamic, and unsuited to the stresses of drag, then drag can have a very disruptive effect on it. Using one of the old MILSTARs as an example, I wouldn't expect the solar panels to last long, before they are ripped off.(In a general way air resistance is proportionate to velocity. I'm generalizing since re-entry vechicles are usually high-drag but have low ballistic coefficients in an effort to slow them down. ) Additionally that drag can impart an unstable trajectory. Simply spinning an object through the air at sufficient velocity can cause it to break apart. That effect is more disruptive is the object is long and narrow, like our MILSTAR sans panels. Protruberences will not fair well either. Whereas Rey's sat being more trapezoidal and most of the equipment being encased within the main body, would handle the spin better.
A good reference would be to look at Columbia. I'm not sure NASA has actually released data on it's trajectory when the structure reached the point of catastrophic failure, but it was under Mach 19, under 210,000 feet, in a shallow descent, IIRC.
The debris field was spread across three states. It was designed for re-entry. A solid, monolithic object would likely reach "dirt" with more of it's structure intact.
Last edited by BaneBlade, 7/5/2009, 8:26 am
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7/5/2009, 3:09 am
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Reythia
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Re: kaboom
quote:
BaneBlade wrote:
Whereas Rey's sat being more trapezoidal and most of the equipment being encased within the main body, would handle the spin better.
*hugs* Awwww! Bane remembered my satellite! I feel so loved!
But yes, I agree. An uncontrolled re-entry could easily destroy the whole thing, or at least break it into little bitty chunks. Remember when the space station Mir re-entered the atmosphere? Well, most satellites are about equally as non-aerodynamic.
Also, QS2 is right about this:
quote:
none of them have enough fuel to really slow there orbits all that severely. So they'd usually come in pretty shallow I imagine.
I hadn't thought about the fuel part, but that's 100% true. Of course, if an external force slowed/turned the satellite, this could be irrelevant.
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7/5/2009, 8:45 pm
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QS2
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Re: kaboom
I had thought of a natural force slowing it down, but the only one I could think of was some rock whizzing by. And any rock able to slow it down enough to fall down at a sharp angle would almost certainly totally obliterate it. Thus rendering the entire question moot. 
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7/5/2009, 9:58 pm
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Reythia
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Re: kaboom
quote:
QS2 wrote:
I had thought of a natural force slowing it down, but the only one I could think of was some rock whizzing by. And any rock able to slow it down enough to fall down at a sharp angle would almost certainly totally obliterate it. Thus rendering the entire question moot.
Yeah, I thought immediately of the semi-recent satellite crash, but again, that would tend to make many little harmless-to-the-ground pieces.
On the other hand, if it's for a scifi story, anything is possible!
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7/6/2009, 3:46 am
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Reythia
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Re: kaboom
Ooooooooo.... Meadows blew up the Moon!! Impressive! 
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7/6/2009, 4:03 pm
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David Meadows
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Re: kaboom
It was an accident 
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7/6/2009, 4:11 pm
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QS2
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Re: kaboom
I don't suppose you had any more such 'accidents' right? 
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7/6/2009, 8:26 pm
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Firlefanz
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Re: kaboom
quote:
David Meadows wrote:
It was an accident
That's what they always say.
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7/6/2009, 9:20 pm
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Blitzen
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Re: kaboom
Thanks guys.
My laptop died, so I'm on the netbook and the internet is playing funny buggers, but whilst I'm here I'll check over what you've given me,
Cheers.
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7/6/2009, 10:15 pm
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Blitzen
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Re: kaboom
Do satellites only orbit the equator?
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7/7/2009, 10:30 am
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David Meadows
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Re: kaboom
Satellites can orbit pretty much anywhere you want. Geostationary satellites, which maintain position above a single point on the Earth's surface (such as the Sky TV satellite, which has to be a constant spot so you can point your dish at it), must be above the equator. But any satellite which moves across the sky (such as the CIA mind control lasers) can be at any orbital inclination, all the way up to polar orbits.
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7/7/2009, 11:24 am
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Reythia
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Re: kaboom
Correct.
The orbit your satellite is in depends on the job you want it to do. For example, a lot of science satellites are interested in what's happening in Antarctica and Greenland, so they tend to be in polar orbits. Satellites measuring sea-height and some types of photographic satellites need to be in solar-synchronous orbits, so that each day they see the same spot of land at the same time of day. Many types of satellites are set in orbits that give them a 'repeat pattern', where they cross the same set of ground locations every N days.
Communications satellites are typically arranged in what's called a 'constellation' -- a collection of satellites, spaced out so they surround the Earth in a known pattern. The pattern (and thus each individual orbit) depends on where you want your communications to reach. If your target audience is in the low latitudes, then it'd be okay to have an equatorial or near-equatorial orbit (we'd say the orbit has 'low inclination'). But if you want to hit a mid-latitude, you'd need a non-equatorial orbit in order for the people on the ground to be able to receive information from the satellite, and vice versa.
Most of these orbits are circular, since that's both more stable and takes less energy to get the satellite into. But the Russians had a tough time when they first went to launch their communications networks, since they needed to have access to them from the very high north latitudes. So they developed an orbit that's highly elliptical (with apogee above Russia) and highly inclined (ie: goes closer to the poles). This meant that it zipped quickly around the rest of the planet (since it was lower and faster-moving there) and spent most of its time over the then-USSR (since it was higher up and slower-moving there). Here's a picture of that style orbit, called a "Molniya Orbit":
Molniya Orbit
So, in short: no, most satellites aren't equatorial ones.
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7/7/2009, 4:13 pm
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QS2
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Re: kaboom
An interesting way to optimize satellite time over the areas most relevant to you. 
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7/7/2009, 5:39 pm
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Reythia
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Re: kaboom
Yep. And an old one -- it's from way back in the 60s.
There are a lot of neat tricks you can play with orbits, really. Of course, I'm a geek to say so!
By the way, Meadows, I'm still not convinced that Moon thing was ENTIRELY accidental! 
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7/7/2009, 9:46 pm
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Pastor Rick
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Re: kaboom
I just spent an hour over there till I finally destroyed the earth with the moon crashing into us! I am a tad worried about MIR since it weighs in at 145 Tons...
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7/8/2009, 5:54 am
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BaneBlade
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Re: kaboom
quote:
Pastor Rick wrote:
I am a tad worried about MIR since it weighs in at 145 Tons...
Worry not, it's already down. And I didn't even get my free Taco. 
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7/8/2009, 6:24 pm
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Reythia
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Re: kaboom
Taco???
Though, about Mir, remember that they DID intentionally crash it over the ocean. So while we can be sure the pieces that hit the ground (well, water) weren't huge, I don't really have a good feel for how big they really were.
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7/8/2009, 10:11 pm
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BaneBlade
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Re: kaboom
quote:
Reythia wrote:
Taco???
Taco Bell- MIR Promotion
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7/9/2009, 1:04 am
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Reythia
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Re: kaboom
AH. I totally missed that, at the time. Good thing it didn't land on them, or I'd have been out a taco!
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7/9/2009, 3:40 pm
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