Posted by
Hemos
on from the checking-things-out dept.
hubie writes "The NEAR spacecraft flew by the asteroid Eros at a closest approach of only 3 miles! Despite what the story says, that is much less than the altitude of a commuter aircraft. Stay tuned for some expected cool closeup shots."
This is extremely dangerous. With the low (almost nil) gravity on Eros, an alien lifeform can easily knock down our probe with nothing more than a well-aimed rock. I consider it a serious lapse of judgement in our elected officials to allow NASA to spend billions on such a risky endeavour.
I propose a Congressional panel to carefully scrutinize NASA's policies in regards to alien surface-to-air defenses, and whether the NEAR probe and others (Cassini! The Saturnians are watching!) are unjust provocations to our extra-terrestrial brethren.
I, for one, would like to welcome our new overlords, and would like to remind them that as a loyal Slashdot reader, I can be instrumental in rounding up the open-source zealots to toil in their salt mines.
This is extremely dangerous. With the low (almost nil) gravity on Eros, an alien lifeform can easily knock down our probe with nothing more than a well-aimed rock. I consider it a serious lapse of judgement in our elected officials to allow NASA to spend billions on such a risky endeavour.
How could any right-thinking red-blooded American like yourself just lie down and accept the threat from these alien sons of bitches? Surely you're not going to let this threaten democracy and our way of life? Show some true Yankee grit and tell NASA and the Air Force to put a nuke right up their ugly green ass:)
--
Any sufficiently advanced technology is indistinguishable from a rigged demo --Andy Finkel (J. Klass?)
Following closely in the orbit of Eros is another asteroid, named Phallus. Astronomers are unsure of the makeup of this asteroid, as it changes size and orientation periodically, growing larger and more vertical as it nears Eros.
Actually, the article is right on that nit...
by
Tau+Zero
·
· Score: 2
Commuter aircraft generally don't fly terribly high; they're often on relatively short hops and don't have any reason to fly at the kinds of altitudes typical of airliners. When it costs more time and maybe fuel to climb higher, or the upper levels are full of 757's and DC-10's and ACT won't clear you upwards, it makes no sense to even try. --
-- Time is Nature's way of keeping everything from happening at once... the bitch.
Re:Actually, the article is right on that nit...
by
Alioth
·
· Score: 2
Not really.
Commuter aircraft these days are typically things like ATR-42s and bigger. Unless the trip is really short, they usually fly at FL180 (18,000 ft) and above. Turbines are just thermodynamically a lot more efficient higher up. Virtually all commuter airlines are running turboprops. True - Redwing Airlines in Missouri, whose fleet consists of a single piston powered Piper Seneca (unpressurized) aren't going to be flying that high, but the majority of commuter airliners will be up that high so that their turbine engines at least get good fuel economy. The commuter airlines that operate the new regional jets will be up at FL250 (25,000') and higher, rubbing shoulders with their major airline brethren.
Also, ATC is there to serve us, and not the other way around. If you ask, ATC will normally give, especially once you're out of the busy terminal area. ATC in the United States are very good at working with the pilots to get them what they need.
> Holy cow! It's a rock! And it's in space! And it's got holes in it! And now we've got pictures!
Believe me, if Eros had holes in it, as opposed to craters, I'd be phoning my broker with SELL orders, and then practicing up on my Wing Commander and other 3D space-combat game skills.
Cripes, didn't anybody here read Ender's Game? The buggers are out there, I tell you! They're out there!
They said that 3 miles was about as high as a
commuter aircraft. Commuter aircraft are
the smaller passenger aircraft generally operated
in the US by regional airlines, and 3 miles is
reasonably close to how high they fly. They
were not talking about the large airliners
that generally fly roughly 6-8 miles high.
--
-- "Ever wonder why the SAME PEOPLE make up ALL the conspiracy theories?"
as a kid i was a huge space fan. Im always fascianted to look at pictures of stuff in space. I used to just flip endlessly through astronomy magazines and books just looking at the cool galaxies and stuff. what saddens me though, is how little interest society has on the space program these days. These people are literally risking life and limb in the name of bettering society. Many common day items are spun off from the space program. I feel like im the only one watching the lift offs of the space shuttle. I hope the populace regains its interest in the space program, it'ld seem like such a waste if they didnt
"sex on tv is bad, you might fall off..."
--
I lost my concept of community when my community lost all concept of me.
The NEAR spacecraft, and the information that it is gathering, are probably one of the most worthwhile missions that NASA has ever had. The detailed look at Eros that it is providing will fill in a lot of details about our scientific knowledge of asteroids.
You can expect to see similiar missions to asteroids in the coming years. SpaceDev, a publicly owned company, is proposing NEAP, the Near Earth Asteroid Prospector. This probe, tentatively scheduled to launch in 2003, was originaly planned to visit the Near Earth Asteroid (NEA) Nereus. Recent discovery of hundreds of previously unknown NEA's may cause SpaceDev to delay the mission, and redirect the probe to some better target asteroid.
Additional missions? None scheduled yet. But you can bet they'll happen. The accessable resources of the asteroids have an estimated dollar value of about $100 Billion per person currently living on Earth. Someday soon, someone is going to dig into that Bonanza.
I agree! Now, why is it that the NASA homepage starts with links to speeches by NASA bureaucrats, and not to these amazing close-up photos of Eros? In fact, there are no links to NEAR anywhere on the homepage. In fact, there are no links to NEAR even on the "Hot Topics" page. Of course, you can still get directly to the bureaucrat speeches from there. Cause that's a pretty hot topic. Probably you'll all want to do that right away. Yeah. I'm thinkin' those speeches are gonna get purdy damn Slashdotted in jusasec here. Uh-huh.
Eros Photographed, Buggers Discovered!!!
by
Sir.Cracked
·
· Score: 5
In a leak from the Defense Department, the first Photos of Eros revealed a race of insectoid beings that insider's are calling Buggers. Speculation is flying as to how to deal with the threat, with one idea of gathering all the most brilliant children up and putting them on a space station to train as generals. More at 11.
If you don't know what I'm talking about, read Ender's Game
-- Where are we going, and why am I in this handbasket?
pictures and project home page
by
pigpen_
·
· Score: 2
The project home page has a lot of great photos and also daily updates on the project.
--
lukas
-- Zambozay! My brain must've been eatin' a sandwich!
Did anyone read about the Plutino rock they found between Neptune and Pluto? I love space.
False alarm. They found it was an escaped diamond from one of Liz Taylor's rings.
Near skirts?! Eros!? Closeup shots!?
And I thought/. wasn't a pr0n site...
--
--
A feeling of having made the same mistake before: Deja Foobar
Downloaded the movie!!!
by
GReaToaK_2000
·
· Score: 2
DAMN!!!!
If that movie is to scale... That asteroid is pretty big.
I am thoroughly impressed and I like the NEAR team "spokes person" saying that the good news was they didn't hit it and there was no bad news. I think we are getting there. This is great.;)
1996 launch date means probably 1993 technology. I can live with that. I know that 8051 is the processor they used for the Patriot missle and that did a good job of hitting skuds. Therefore even if they used a 68K or 386/486 hardened for space that would be great... That might explain why they were able to avoid getting to NEAR the asteroid.;) It is probably something thing like 486 or 68K or ASIC which is good. This is only a guess considering the pentium was being hardened for space about 2.0 years ago.
I am excited, this is REALLY good news.;)
Good WORK!!!
Re:Downloaded the movie!!!
by
GReaToaK_2000
·
· Score: 2
Flight Computer...
Honeywell MIL-STD-1750A 9MHz
512K RAM
256K EEPROM
16K PROM
Attitude Computer...:-)
Harris RTX2010 6MHz
64K RAM
64K EEPROM
2K PROM
For those that care. The specs for these processors are impressive.;)
NASA is underfunded!
by
Anonymous Coward
·
· Score: 2
it's about time nasa realized that it's alot more cost effective to come close to heavenly bodies than it is to crash into them. If I have to read one more "NASA to crash probe into _______" i'm going to scream! I mean, in the interest of science, crashing probes into distant moons or planets may be educational, but for the hundreds of millions of dollars spent on such missions, it seems the money would be better spent feeding homeless people, coming up with alternatives to petrochemicals to fuel our vehicles, buying everyone in the USA a puppy, or any of those things that would really make an impact in our society.
I probably shouldn't even respond to a post this ignorant, but I can't resist.
First off, the only probes that have been "crashed" into anything (with the exception of probes which are at the end of their useful life) have been called "landers". Any crashes have been purely unintentional!;-)
Secondly, in those rare cases where a probe is sacrificed in a hostile environment (the upcoming drop of a Cassini module into Jupiter comes to mind), expending the probe is the only way to get any scientific data at all Believe me, the scientists involved would love to extend the useful lifetime of any probe if possible.
Regardless, it's hard to argue that NASA spends too much money - NASA's budget is tiny compared to what is spent on defense, for instance. The payoff from technologies and basic science sponsored by NASA is certainly far beyond anything we're likely to see from other government agencies. That said, I'd certainly like to see more private companies getting involved in space exploration.
Did anyone else laugh at the description of the "bird's eye view of the asteroid"? (South Saddle.) I had a fleeting image of some poor confused crow seeing this view as it flailed about with its useless wings and its last breath blew out into the vacuum.
It is generally accepted that the Patriot missiles failed to have any significant success against Scuds. Some analysts have suggested that not one Scud was intercepted.
Look here for the official story, or here for another analysis.
But the really interesting report is the Postol/Lewis analysis, including detailed analysis of video evidence, is here
In the interests of balance, This is a response to it.
What's the big deal? We all know Han Solo landed his modified freighter, the Millenium Falcon, right inside a big asteroid, and it was much cooler looking than this one.
Plus he was being chased by hostile foes through a dangerous asteroid field, and escaped from the giant worm which was living in the asteroid, which is why you won't see anyone making a movie about the NEAR spacecraft.
What processors NEAR runs off of..
by
eples
·
· Score: 3
Well you couldn't be more wrong about what processors are in this sucker!
There's actually 7 on-board, 6 of them are Harris
RTX2010's (Harris is now Intersil). This processor can do 6 MIPS at 8MHz..
There is also one Honeywell
1750A that runs the flight program. (2.5 MIPS - The military hybrid of this
chip also runs Linux ;.)
I quote from the above.PDF: "All processors are Harris RTX2010's except the G&C subsystem Flight
Computer which is a Honeywell 1750A."
It's not much less than a commuter aircraft, unless you commute accross the Atlantic. Short-distance aircraft don't go to 10km altitude like long-distance aircraft, because for short distances it's not worth it (the cost of climbing to that altitude is more than the gain you get from flying in thin air/strong wind). 5 km is about right for a commuter.
If you look at frames 43, 44 & 45 of this orbital animation of eros you can clearly see a huge boo-scary tortured-looking face on the surface!
I know it's a meritless thing to point out and has no real scientific significance (like the infamous "face on Mars"), but considering that:
It's named after the Greek god of love (dual entendre, anyone?)
It's shaped like a loaf
It's almost Hallowe'en
...I found it pretty funny on three separate levels, which could lead to some great Onion-esque headlines...
Following Probe, Lusty Anthropomorphic Asteroid Hurtles Toward Uranus
Mister Hanky's Mothership Arrives
Approaching Space Demon "Eros" Denies Connection to Ancient Ones, Intention to Destroy Earth
Well, so much for NASA's latest rhetoric. Later on today they are going to announce their proposed 2005 Mars Mission that is going to be a throwback to the old days. Supposidly they're giving up on cheap hardware and going back to the heavy duty gear. Ah well, it's kind of sad to see something like NEAR work so well and at the same time have 2 failures in the last year. Maybe NASA should be more careful in who they pick as their contractors - it sounds like you guys did a really good job.
These guys are the ones who built near. more nice pictures and some videos.
Near stuff.
Re:Good going Noam and the NEAR Team!
by
Tackhead
·
· Score: 3
> This project is one example of an effective, efficient, non-disasterous project that demonstrates that
space can be done for cheap cost [... ]
Agreed. NEAR is an awesome bit of work. Though the mission came extremely close to disaster. The reason we're reading about this in 2000 is because they damn near lost the spacecraft on first approach, and executed a miraculous recovery. It delayed the mission a year (waiting for the next orbit), but it didn't cost us much in terms of scientific return at all.
It's also a great demonstration of the fact that if you're in orbit around something - thinking of NEAR, Eros, and the Sun - whether you throw an object "up" or "down" makes no difference, it'll intersect your position next orbit.
That is, if you want to go "up" or "down" and you're in orbit, you thrust "forward" or "back". The EROS recovery was basically "screw it, don't waste fuel chasing the rock this year, because if we just relax, Newton will put us back on target for another encounter next year")
Re:Can objects orbit at really low altitudes? cm?
by
Mad+Hughagi
·
· Score: 2
Actually...
Both of your descriptions are accurate, it is just that you are describing different things. The parent post is talking about an object that is allready in a stable orbit. In that case if you increase the tangential component of your velocity you would move into a higher orbit. What you are describing is the tangential velocity required to maintain a stable orbit, which is also true.
Just because something doesn't make sense at first doesn't mean that it is wrong, maybe you just haven't wrapped your head around it properly.
The law in question was repealed in 1991 without any fanfare. You're now free to touch aliens all you want, as long as you make sure they aren't same-sex or under-age aliens.
Well, the last intentional crash of a probe was the Lunar Prospector, which was a wildly successful mission. NASA achieved all their goals including more accurate mapping of the moon than ever before, and once the mission was over the Prospector would have become so much space junk.
Except there's been a speculation about the moon that's lasted since we first began studying it in earnest. Does the moon have any water, even in crystaline form? They decided to sacrifice a sentimental piece of space junk to observe the impact and do a spectral analysis of the resulting shower of debris. Unfortunately, the results were negative. No water on the moon, at least in the region they hit.
What if they had? Well, water is a fundamental requirement for life, as well as one of the ingredients they use for propellant in outer space. So if they'd found ice on the moon it would have increased the chances of a lunar base by a large percentage, meaning we'd have a relatively convenient launching base for the exploration of the rest of the solar system. So don't knock it: there was a point to it.
As for the unintentional crashes, all I can say is that when you mix up your math you get all sorts of problems. NASA got too cocky and skimped on their error-checking in their haste to get projects out the door. They're paying for that, but I still support them. In times of peace, the kind of technological breakthroughs we've experience can at least in part be due to the push for space exploration. That air conditioning unit you can't live without? Space exploration. Minaturization of technology? Space exploration. Don't think that just because we're putting money into a project that doesn't provide immediate gratification (except for those astronomy buffs among us), we're not also researching a better way of life for everyone. If they figure out efficient waste recycling, it'll have benefits for the entire world.
-- There is no problem which cannot be resolved by the judicious use of firepower.
Mind you the orbital speed at such a low gravity approximates walking speed.
Not according to this NASA page; the escape velocity is around 22 MPH (from where on the asteroid, they don't say). Divide by sqrt(2) to get the surface-skimming orbital velocity for a spherical body (yeah, right) and it comes out to about 15 MPH. Definitely a fast run, not a walk. I have not run the numbers to see where on Eros that escape velocity figure would apply, but if it's at either of the ends the rotational velocity (33 km * 3.14 / 5.27 hours = 19.7 km/hr = 12.2 MPH) would give you well over half of it.
If you want to try working out the orbital speeds yourself, you'll need the gravitational constant G (6.67 * 10^-11 N m^2/kg^2) plus the mass and dimensional data on the NASA page linked above.
I find it interesting that you could land on Eros with the equivalent of a big pogo stick, and launch yourself to escape velocity the same way. --
-- Time is Nature's way of keeping everything from happening at once... the bitch.
You are right about being able to orbit at any altitude, of course, friction of the atmosphere would become significant at lower altitudes.
You were only partially right when you said that the earth's gravity pulls at 9.8 m/(s^2), actually, according to Universal Gravity, two bodies will attract eachother with a force governed by the following equation:
F=(G M m)/(r^2)
Where F is the force of attraction, G is the gravitational constant (about 6.67*10^-11 m^3/(kg/s^2)), M and m are the masses, and r is the distance between the the two bodies' centers of gravity.
That is all well and good, but it dosen't tell us what the force of attraction for the earth is. To discover that, we have to use another equation, Newton's second law:
F= m a
Where F is force, m is mass, and a is (you gussed it) acceleration.
We can set F equal to F and yeald:
m a = (G M m) / r^2
We can cancel out the two small 'm's to get:
a = (G M) / r^2
We need a 'r' and a 'M', so I will now stipulate that the radius of the earth is about 6.38*10^6 m and that the mass of the earth is 5.98*10^24 kg. An abitious slashdoter could most likely find much more accurate figures, but these will fit our purposes. Consequently, we can find the acceleration due to gravity with:
a = (6.67*10^-11 * 5.98*10^24) / ((6.38*10^6)^2)
a = 9.799 m/(s^2)
I hope you can see that 'a' would be significantly less were an object higher (say, 500km) from the surface of the earth, as 'r' would increase:
a = (6.67*10^-11 * 5.98*10^24) / ((6.38*10^6 + 500*1000)^2)
a = 8.427 m/(s^2)
Back to the original question: How fast must an object to travel to orbit the earth at the surface? To answer that, we have to call apon yet another equation, that of centripical acceleration in circular motion:
a = (v^2) / r
We know that the centripical acceleration is the acceleration due to gravity, which we found to be 9.799 m/(s^2) at the surface of the earth, and we know 'r' to be the radius of the earth, so to find 'v' (velocity) we could have:
v = sqrt( a r )
v = sqrt( 9.799 * 6.38*10^6)
v = 7906.81 m/s
v = 7.907 km/s (*)
As you can see, this is significantly less than your figure of 30,000 km/s!
(*) Us Americans, who's brains have been destroyed by the English System, would get more sense out of 17,687 mi/hr.
--
Jordan Bettis
``Wherever you go, there's another stupid sigfile quote.''
Slashdot Mirror
I propose a Congressional panel to carefully scrutinize NASA's policies in regards to alien surface-to-air defenses, and whether the NEAR probe and others (Cassini! The Saturnians are watching!) are unjust provocations to our extra-terrestrial brethren.
I, for one, would like to welcome our new overlords, and would like to remind them that as a loyal Slashdot reader, I can be instrumental in rounding up the open-source zealots to toil in their salt mines.
Any ideas to what shape an asteroid named "Eros" would be?
- I don't care if they globalize against free speech. All my best free thoughts are done in my head.
Commuter aircraft generally don't fly terribly high; they're often on relatively short hops and don't have any reason to fly at the kinds of altitudes typical of airliners. When it costs more time and maybe fuel to climb higher, or the upper levels are full of 757's and DC-10's and ACT won't clear you upwards, it makes no sense to even try.
--
Time is Nature's way of keeping everything from happening at once... the bitch.
images here.
Here's a number of pictures of it:
http://nssdc.gs fc. nasa.gov/planetary/mission/near/near_eros.html
Enjoy =)
---
They said that 3 miles was about as high as a commuter aircraft. Commuter aircraft are the smaller passenger aircraft generally operated in the US by regional airlines, and 3 miles is reasonably close to how high they fly. They were not talking about the large airliners that generally fly roughly 6-8 miles high.
-- "Ever wonder why the SAME PEOPLE make up ALL the conspiracy theories?"
The altitude at which you look down out the airplane window and it looks like SimCity.
as a kid i was a huge space fan. Im always fascianted to look at pictures of stuff in space. I used to just flip endlessly through astronomy magazines and books just looking at the cool galaxies and stuff. what saddens me though, is how little interest society has on the space program these days. These people are literally risking life and limb in the name of bettering society. Many common day items are spun off from the space program. I feel like im the only one watching the lift offs of the space shuttle. I hope the populace regains its interest in the space program, it'ld seem like such a waste if they didnt
"sex on tv is bad, you might fall off..."
I lost my concept of community when my community lost all concept of me.
The NEAR spacecraft, and the information that it is gathering, are probably one of the most worthwhile missions that NASA has ever had. The detailed look at Eros that it is providing will fill in a lot of details about our scientific knowledge of asteroids.
You can expect to see similiar missions to asteroids in the coming years. SpaceDev, a publicly owned company, is proposing NEAP, the Near Earth Asteroid Prospector. This probe, tentatively scheduled to launch in 2003, was originaly planned to visit the Near Earth Asteroid (NEA) Nereus. Recent discovery of hundreds of previously unknown NEA's may cause SpaceDev to delay the mission, and redirect the probe to some better target asteroid.
Additional missions? None scheduled yet. But you can bet they'll happen. The accessable resources of the asteroids have an estimated dollar value of about $100 Billion per person currently living on Earth. Someday soon, someone is going to dig into that Bonanza.
In a leak from the Defense Department, the first Photos of Eros revealed a race of insectoid beings that insider's are calling Buggers. Speculation is flying as to how to deal with the threat, with one idea of gathering all the most brilliant children up and putting them on a space station to train as generals. More at 11.
If you don't know what I'm talking about, read Ender's Game
Where are we going, and why am I in this handbasket?
The project home page has a lot of great photos and also daily updates on the project.
--
lukas
Zambozay! My brain must've been eatin' a sandwich!
False alarm. They found it was an escaped diamond from one of Liz Taylor's rings.
Near skirts?! Eros!? Closeup shots!?
And I thought
--
A feeling of having made the same mistake before: Deja Foobar
If that movie is to scale... That asteroid is pretty big.
I am thoroughly impressed and I like the NEAR team "spokes person" saying that the good news was they didn't hit it and there was no bad news. I think we are getting there. This is great. ;)
1996 launch date means probably 1993 technology. I can live with that. I know that 8051 is the processor they used for the Patriot missle and that did a good job of hitting skuds. Therefore even if they used a 68K or 386/486 hardened for space that would be great... That might explain why they were able to avoid getting to NEAR the asteroid. ;) It is probably something thing like 486 or 68K or ASIC which is good. This is only a guess considering the pentium was being hardened for space about 2.0 years ago.
I am excited, this is REALLY good news. ;)
Good WORK!!!
I probably shouldn't even respond to a post this ignorant, but I can't resist.
First off, the only probes that have been "crashed" into anything (with the exception of probes which are at the end of their useful life) have been called "landers". Any crashes have been purely unintentional! ;-)
Secondly, in those rare cases where a probe is sacrificed in a hostile environment (the upcoming drop of a Cassini module into Jupiter comes to mind), expending the probe is the only way to get any scientific data at all Believe me, the scientists involved would love to extend the useful lifetime of any probe if possible.
Regardless, it's hard to argue that NASA spends too much money - NASA's budget is tiny compared to what is spent on defense, for instance. The payoff from technologies and basic science sponsored by NASA is certainly far beyond anything we're likely to see from other government agencies. That said, I'd certainly like to see more private companies getting involved in space exploration.
Have a nice terrestrial rotation.
Did anyone else laugh at the description of the "bird's eye view of the asteroid"? (South Saddle.) I had a fleeting image of some poor confused crow seeing this view as it flailed about with its useless wings and its last breath blew out into the vacuum.
Maybe I'm just too damn literal.
Look here for the official story, or here for another analysis.
But the really interesting report is the Postol/Lewis analysis, including detailed analysis of video evidence, is here
In the interests of balance, This is a response to it.
What's the big deal? We all know Han Solo landed his modified freighter, the Millenium Falcon, right inside a big asteroid, and it was much cooler looking than this one.
Plus he was being chased by hostile foes through a dangerous asteroid field, and escaped from the giant worm which was living in the asteroid, which is why you won't see anyone making a movie about the NEAR spacecraft.
Well you couldn't be more wrong about what processors are in this sucker!
There's actually 7 on-board, 6 of them are Harris RTX2010's (Harris is now Intersil). This processor can do 6 MIPS at 8MHz.. There is also one Honeywell 1750A that runs the flight program. (2.5 MIPS - The military hybrid of this chip also runs Linux ; .)
I quote from the above
"All processors are Harris RTX2010's except the G&C subsystem Flight Computer which is a Honeywell 1750A."
Nice little satellite for early 90's.
I'm a 2000 man.
It's not much less than a commuter aircraft, unless you commute accross the Atlantic. Short-distance aircraft don't go to 10km altitude like long-distance aircraft, because for short distances it's not worth it (the cost of climbing to that altitude is more than the gain you get from flying in thin air/strong wind). 5 km is about right for a commuter.
If you look at frames 43, 44 & 45 of this orbital animation of eros you can clearly see a huge boo-scary tortured-looking face on the surface! I know it's a meritless thing to point out and has no real scientific significance (like the infamous "face on Mars"), but considering that:
- Following Probe, Lusty Anthropomorphic Asteroid Hurtles Toward Uranus
- Mister Hanky's Mothership Arrives
- Approaching Space Demon "Eros" Denies Connection to Ancient Ones, Intention to Destroy Earth
Just look at it already, you'll see what I mean: http://n ssd c.gsfc.nasa.gov/planetary/image/near_20000919_larSnickersnee3: Build your own 3-watt Luxeon Star headlamp from scratch
UBU
These guys are the ones who built near. more nice pictures and some videos. Near stuff.
Agreed. NEAR is an awesome bit of work. Though the mission came extremely close to disaster. The reason we're reading about this in 2000 is because they damn near lost the spacecraft on first approach, and executed a miraculous recovery. It delayed the mission a year (waiting for the next orbit), but it didn't cost us much in terms of scientific return at all.
It's also a great demonstration of the fact that if you're in orbit around something - thinking of NEAR, Eros, and the Sun - whether you throw an object "up" or "down" makes no difference, it'll intersect your position next orbit.
That is, if you want to go "up" or "down" and you're in orbit, you thrust "forward" or "back". The EROS recovery was basically "screw it, don't waste fuel chasing the rock this year, because if we just relax, Newton will put us back on target for another encounter next year")
Both of your descriptions are accurate, it is just that you are describing different things. The parent post is talking about an object that is allready in a stable orbit. In that case if you increase the tangential component of your velocity you would move into a higher orbit. What you are describing is the tangential velocity required to maintain a stable orbit, which is also true.
Just because something doesn't make sense at first doesn't mean that it is wrong, maybe you just haven't wrapped your head around it properly.
UBU
The law in question was repealed in 1991 without any fanfare. You're now free to touch aliens all you want, as long as you make sure they aren't same-sex or under-age aliens.
-- Anne Marie
Well, the last intentional crash of a probe was the Lunar Prospector, which was a wildly successful mission. NASA achieved all their goals including more accurate mapping of the moon than ever before, and once the mission was over the Prospector would have become so much space junk.
Except there's been a speculation about the moon that's lasted since we first began studying it in earnest. Does the moon have any water, even in crystaline form? They decided to sacrifice a sentimental piece of space junk to observe the impact and do a spectral analysis of the resulting shower of debris. Unfortunately, the results were negative. No water on the moon, at least in the region they hit.
What if they had? Well, water is a fundamental requirement for life, as well as one of the ingredients they use for propellant in outer space. So if they'd found ice on the moon it would have increased the chances of a lunar base by a large percentage, meaning we'd have a relatively convenient launching base for the exploration of the rest of the solar system. So don't knock it: there was a point to it.
As for the unintentional crashes, all I can say is that when you mix up your math you get all sorts of problems. NASA got too cocky and skimped on their error-checking in their haste to get projects out the door. They're paying for that, but I still support them. In times of peace, the kind of technological breakthroughs we've experience can at least in part be due to the push for space exploration. That air conditioning unit you can't live without? Space exploration. Minaturization of technology? Space exploration. Don't think that just because we're putting money into a project that doesn't provide immediate gratification (except for those astronomy buffs among us), we're not also researching a better way of life for everyone. If they figure out efficient waste recycling, it'll have benefits for the entire world.
There is no problem which cannot be resolved by the judicious use of firepower.
If you want to try working out the orbital speeds yourself, you'll need the gravitational constant G (6.67 * 10^-11 N m^2/kg^2) plus the mass and dimensional data on the NASA page linked above.
I find it interesting that you could land on Eros with the equivalent of a big pogo stick, and launch yourself to escape velocity the same way.
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Time is Nature's way of keeping everything from happening at once... the bitch.
You are right about being able to orbit at any altitude, of course, friction of the atmosphere would become significant at lower altitudes.
You were only partially right when you said that the earth's gravity pulls at 9.8 m/(s^2), actually, according to Universal Gravity, two bodies will attract eachother with a force governed by the following equation:
F=(G M m)/(r^2)
Where F is the force of attraction, G is the gravitational constant (about 6.67*10^-11 m^3/(kg/s^2)), M and m are the masses, and r is the distance between the the two bodies' centers of gravity.
That is all well and good, but it dosen't tell us what the force of attraction for the earth is. To discover that, we have to use another equation, Newton's second law:
F= m a
Where F is force, m is mass, and a is (you gussed it) acceleration.
We can set F equal to F and yeald:
m a = (G M m) / r^2
We can cancel out the two small 'm's to get:
a = (G M) / r^2
We need a 'r' and a 'M', so I will now stipulate that the radius of the earth is about 6.38*10^6 m and that the mass of the earth is 5.98*10^24 kg. An abitious slashdoter could most likely find much more accurate figures, but these will fit our purposes. Consequently, we can find the acceleration due to gravity with:
a = (6.67*10^-11 * 5.98*10^24) / ((6.38*10^6)^2)
a = 9.799 m/(s^2)I hope you can see that 'a' would be significantly less were an object higher (say, 500km) from the surface of the earth, as 'r' would increase:
a = (6.67*10^-11 * 5.98*10^24) / ((6.38*10^6 + 500*1000)^2)
a = 8.427 m/(s^2)Back to the original question: How fast must an object to travel to orbit the earth at the surface? To answer that, we have to call apon yet another equation, that of centripical acceleration in circular motion:
a = (v^2) / r
We know that the centripical acceleration is the acceleration due to gravity, which we found to be 9.799 m/(s^2) at the surface of the earth, and we know 'r' to be the radius of the earth, so to find 'v' (velocity) we could have:
v = sqrt( a r )
v = sqrt( 9.799 * 6.38*10^6) v = 7906.81 m/s v = 7.907 km/s (*)As you can see, this is significantly less than your figure of 30,000 km/s!
(*) Us Americans, who's brains have been destroyed by the English System, would get more sense out of 17,687 mi/hr.
Jordan Bettis
``Wherever you go, there's another stupid sigfile quote.''