FRIHOST • FORUMS • SEARCH • FAQ • TOS • BLOGS • COMPETITIONS
You are invited to Log in or Register a free Frihost Account!


NASA satellite coming down to earth





Adiiforu
Did you guys know about the satellite that fell on earth today, reportedly fell from Canada to Africa NASA said it is difficult to locate the satellite.
loremar
I hope no animal was killed in the crash. Except for cockroaches. I hate cockroaches.
Peterssidan
Apparently satellites fall down quite often but most of them never reach the ground.
odayguide
why it's out of control.
kelseymh
odayguide wrote:
why it's out of control.


UARS was at the end of its life. No more power, no more station-keeping propellant. Consequently, as the atmosphere expanded and contracted over time (seasonally, solar cycles, etc.), UARS was gradually slowed down with no way to push itself back up. Eventually, it slowed sufficiently to enter thicker atmosphere and burn up.
Nameless
Sorry guys. This was my bad, I let that one by. *sheepishly puts away baseball mitt*
ocalhoun
I hope it wasn't one of the nuclear powered ones.

Which begs the question, what do they do when one of those runs out of propellant. (And yet, is still very radioactive.)
kelseymh
ocalhoun wrote:
I hope it wasn't one of the nuclear powered ones.

Which begs the question, what do they do when one of those runs out of propellant. (And yet, is still very radioactive.)


RTGs (radioisotope thermal generators) are not used for Earth-orbiting satellites. They are only used for long-duration missions at distances where solar power generation is impossible or infeasible.

In any event, the devices are not particularly radioactive. They are powered by non-weapons-grade plutonium, and operate by capturing the heat (yes, regular ordinary heat) from radioactive decay in the block of material. There is little to no induced activation (the alphas are absorbed in the chunk of plutonium itself, which is where the heat originates). Plutonium is most dangerous simply as a heavy metal, not as a radiation per se.
_AVG_
This has been making the news since the last 3 days now ... I think it had fallen earlier (but they couldn't pinpoint its location exactly) ... now we know it's landed in Canada. No one was hurt
ocalhoun
kelseymh wrote:

RTGs (radioisotope thermal generators) are not used for Earth-orbiting satellites. They are only used for long-duration missions at distances where solar power generation is impossible or infeasible.

Ah, that's comforting to know, but has it always been that way?
I thought I remembered reading somewhere that they used to be more common before some treaty banned them.

And yeah, I did know what they were called and that they were heat-driven... but I didn't know that their radiation risk was low... I thought it was still pretty high.
kelseymh
ocalhoun wrote:
kelseymh wrote:

RTGs (radioisotope thermal generators) are not used for Earth-orbiting satellites. They are only used for long-duration missions at distances where solar power generation is impossible or infeasible.

Ah, that's comforting to know, but has it always been that way? I thought I remembered reading somewhere that they used to be more common before some treaty banned them.


I can't find any evidence of treaties. You might be thinking of the atmospheric test ban treaty (1963), which had the side effect of terminating Project Orion (Freeman Dyson's atomic-bomb powered spaceship Smile ).

I think use of RTGs in earth-orbiting satellites fell out of favor because of the perceived hazards of re-entry breakup (despite the "success" when Apollo 13 re-entered the atmosphere and it's RTG fell into the Pacific Ocean intact, as designed). Also, improved technology for solar power generation means that modern satellites can use smaller panels to obtain the same power levels.

Quote:
And yeah, I did know what they were called and that they were heat-driven... but I didn't know that their radiation risk was low... I thought it was still pretty high.


Well, my own information turns out to be limited. The Wikipedia article points out that a number of different isotopes have been used in RTG's over the years, including Sr-90 and Po-210. Both of those are extremely nasty (shorter half-lives), and do have to remain encapsulated until they decay away. Thanks for the good question, to get me to update my knowledge Smile
Josso
It's come down now, and they don't know where it went down... which I find unusual seeing as it was being tracked by the US air force - who have access to some of the most advanced radar and other debris-tracking-type technology.
ocalhoun
Josso wrote:
It's come down now, and they don't know where it went down...

I suspect that by 'don't know where', they can't pinpoint it precisely enough to be able to find it on the ground.

Their tracking equipment probably tracks it only to a certain minimum altitude, and is unable to track it lower than that... which would leave an area of doubt about where exactly it landed, while still allowing them to know very well the general area it is in.
Peterssidan
NASA wrote:
NASA’s decommissioned Upper Atmosphere Research Satellite fell back to Earth at 12 a.m. EDT (0400 GMT), as Friday, Sept. 23, turned to Saturday, Sept. 24 on the United States east coast. The Joint Space Operations Center at Vandenberg Air Force Base in California has determined the satellite entered the atmosphere over the Pacific Ocean at 14.1 degrees south latitude and 189.8 degrees east longitude (170.2 west longitude). This location is over a broad, remote ocean area in the Southern Hemisphere, far from any major land mass. The debris field is located between 300 miles and 800 miles downrange, or generally northeast of the re-entry point. NASA is not aware of any possible debris sightings from this geographic area.
It crashed in the Ocean so not very strange that they haven't found any parts of it yet. Do they even search for the debris? Will any of it float or is it just metal left when it reach the surface?
ocalhoun
Peterssidan wrote:
Will any of it float or is it just metal left when it reach the surface?

If they didn't make any attempt to slow the descent, then the final impact would pretty much destroy anything the atmosphere didn't already burn away.

I'd be extremely surprised if any part of it managed to land in a still-recognizable form.
SonLight
If the satellite was large enough to leave a "debris field" and was left to run out of fuel, then it appears NASA had no control over where it landed and just got lucky it was over the ocean. It seems to me that it should not have been allowed to run completely out of fuel, but directed to a known area where the risk of harm was minimized.

On the other hand, they may have been able to predict where it would land before it ran out of fuel. With a landing over remote ocean and with a warning to ships to avoid the area the risk of damage would be extremely remote. If satellites are allowed to just fall wherever they wind up after they run out of fuel, the chance of damage would still be small but that chance should be avoided unless the satellite is expected to burn up during reentry or there is an accident that prevents a controlled descent.
Related topics
What Is Your Favorite Time Of Year
LOST
is Space exploration worth it?
science vs. religion
empty space is best outside your head
Love Lust and Age
Why did the chicken cross the road?
Bible Verses: Do Disbelievers Go To Hell?
Poem Inner Woods
Do you believe in Aliens ?
Can we create ice berg?
What if your belief was PROVEN wrong?
Obama - the truth part 1
Height of a Mountain...
Reply to topic    Frihost Forum Index -> Science -> The Universe

FRIHOST HOME | FAQ | TOS | ABOUT US | CONTACT US | SITE MAP
© 2005-2011 Frihost, forums powered by phpBB.