Astronaut space dump pong-bomb frag shower today An old fridge thrown off the International Space Station last year is set to re-enter the Earth's atmosphere shortly, according to reports, delivering a volley of 100mph space frag debris to an as-yet unknown impact site. The refrigeration unit in question is the Early Ammonia System (EAS), a 1400lb tank intended to furnish …
Just because the article contains such linguistic gymnastics as "This has got a very low likelihood that anybody will be impacted by it,", instead of the easier "we don't think it will hit anyone", is it really necessary for the headlines to compete for a prize for lack of meaning?
Although given the logic behind this gem: "If anybody found a piece of anything on the ground Monday morning, I would hope they wouldn't get too close to it." you've got to wonder who writes this stuff.
> There were never any plans to engage the innocuous coolant assembly with a volley of missile-defence interceptors
Did the author mean "noxious" rather than "innocuous"?
And can anyone explain why this sort of space junk isn't propelled in the direction of The Sun (no, not the tabloid 'newspaper'!), just like we always used to throw stuff into the wide, wide, ocean, confident in the knowledge that it was So Big that no harm would result?
On the assumption we're going to keep chucking large lumps back down to earth, would it be practical to have a rocket pack, which could be 'joined' to such stuff, and used to make a more predictable impact area ?
I'd imagine over a year, a very low amount of thrust, maybe even from solar cell's would be sufficient ?
"And can anyone explain why this sort of space junk isn't propelled in the direction of The Sun"
You're new to this gravity and orbit thing arent you?
A sodding great rocket burns hundreds of tonnes of fuel and it just gets into low earth orbit.
Yet some dude on the the end of a robot arm is supposed to throw it into the sun?
Can someone explain why we dont launch satellites by throwing them really hard into the sky? If we did it at night then you can see space so it should work.
AC wrote:
"Can anyone explain why this sort of space junk isn't propelled in the direction of The Sun"
Even in orbit the gravitational force is still significant, it's just balanced by the centripetal force. Achieving escape velocity would require a sizeable push (which will affect your orbit). And you're more likely to hit the moon or another planet than ever reach the sun.
If you fall from outer space, even halfway out to the moon, your velocity (should you survive the heat of reentry) will be about 120mph near the ground.
Terminal velocity.
The only way to go faster than that is
1 to be so massive the atmosphere can't slow you down. I don't think this is going to be a problem. If their brountouts are producing multi-kiloton jobbies, there are other issues at stake
2 have a jetpack. If they are tying scramjets to their Inter Continental Bum Missiles, they seriously need to get out more.
> Even in orbit the gravitational force is still significant, it's just balanced by the centripetal force.
No.
In this particular case, the gravitational pull of the Earth *is* the centripetal force that acts on said orbiting object. Imagine that gravity suddenly failed... no centripetal force, so said object carries on in a straight line, i.e. at a tangent to the previous circular orbit.
What you mean is that the gravitational acceleration of the object for that particular orbit is equal to the value for centripetal acceleration (the rate of change of tangential velocity) that keeps the object's distance from the Earth constant: the radial rate of descent is zero.
"But still, it is a large object and pieces will enter and we just need to be cautious."
So we should have all spent the day looking for lumps of space debris heading towards us at 100mph?
From this statement we can presumably infer that if anyone did get hit by a lump of stink tank then they've only got themselves to blame.
NASA. You gotta love 'em.
I think the clue was in the word 'propelled' - I was hardly suggesting that an astronaut should give a gentle push to this chunk of space stuff, and expected it to whiz off sun-wards.
Perhaps someone knowledgeable (like a few of the subsequent posters?) could assess how much effort would be required to break it out of orbit and direct it towards the sun?
Nick wrote:
"Even in orbit the gravitational force is still significant, it's just balanced by the centripetal force."
William Old replied:
"In this particular case, the gravitational pull of the Earth *is* the centripetal force that acts on said orbiting object."
I'll admit that I was rather imprecise with my language.
However, I wouldn't say that "the gravitational pull of the Earth is the centripetal force". One is a force, the other is a requirement for the orbital motion.
If we're going to nit-pick then I would say that gravity *provides* the centripetal force.
You are right that the terminal velocity of a skydiver is about 120mph, but that's because skydivers are particularly un-aerodynamic things.
My conjecture is that a large stinky space fridge would be quite a bit more aerodynamic than a man. For example, I went to NASA's online terminal velocity calculator here:
http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html
And I entered a weight of 15lb (like the article suggests), a cross-sectional area of 0.25 sq ft (a guess) and a drag coefficient of 2.1 (what Wikipedia suggests as the Cd of a "smooth brick").
Falling from 60,000 feet, that gets up to a fairly decent 345mph.
You can have all sorts of fun lobbing large imaginary objects from space to the ground. I reckon a Toyota Prius (Cd 0.26, mass 2921lb, cross-sectional area about 25 sq ft) would hit the deck at a monster 1306mph, which is a fair bit better than it can manage down the M4.
So thanks for the science lesson, but I think we have to dig deeper. What is NASA not telling us?
The ISS orbits at about 7km/second tightly round the Earth. Escape velocity at that altitude is around 11km/second.
So escaping Earth's orbit from ISS requires about 4km/second of velocity change. Now for some super simple math:
exhaust velocity * ln ( loadedWeight / emptyWeight ) = our capacity for velocity change i.e. delta-v
Let's assume a simple, bog standard, hypergolic hydrazine+nitro rocket cause it's cheap and simple. The exhaust velocity is about 2 km / second.
To reach escape velocity you would need about 7 times the fridge & rocket's weight in fuel.
Tank and all we're talking about a rocket far bigger than the fridge itself!
If you double that fuel you can get around 5.5km/second of capacity for velocity change, which is enough to leave earth orbit, into a solar orbit, then perform a second burn a half year later to change your orbit so it doesn't cross paths with Earth. Probably.
But you didn't want in space for a super long time, you want the Sun!
Earth orbits the Sun at about 29km/second. To de-orbit the sun you need to pretty much get rid of all of this speed. That's a velocity change of almost 29km/second. Maybe slightly less.
Those epic, giant launch vehicles? They can put out around 10km/second of delta-v.
There's absolutely no way a hypergolic rocket is sending you into the Sun. Even an efficient, cryogenic fuelled (lox-hydrogen) rocket won't do it for you.
To manage 29km/second you'll need a super efficient ion propulsion.
This basically amounts to installing a (probably expensive) engine, all the equipment for a satellite, and set of solar panels onto the fridge and programming it to set sail for fiery doom.
OR you could just fling it onto the Earth.
" I think the clue was in the word 'propelled' - I was hardly suggesting that an astronaut should give a gentle push to this chunk of space stuff, and expected it to whiz off sun-wards.
Perhaps someone knowledgeable (like a few of the subsequent posters?) could assess how much effort would be required to break it out of orbit and direct it towards the sun?"
Sure thing. According to the article, the tank is 1400 lbs (call it ~600 kg) and tudelft.nl lists impulsive shot (i.e. all the delta v is applied in a short time period) delta v for LEO to escape velocity as 3.2 km/sec. From kinetic energy = 1/2 mv^2, this gives us 300 * 3200 * 3200 or ~ 3 gigajoules (roughly 850 KWh) of energy. From there, if you were to kill off your orbital velocity around the Sun, then the Sun's gravity would take over and the tank would fall into the Sun. I didn't see any delta v listed (Solar impact is not a very popular space probe mission), but I can't see it as being worse than Earth's orbital velocity of ~30 km/sec which would require about 270 gigajoules (75000 KWh). In other words, I think you could safely characterize the energy requirements for solar impact as a "sh*t load"
Even if you used some really fancy orbital slingshot trajectory work to reduce the solar impact delta v to little more than Earth escape delta v, you would still have to bring up a rocket motor and reaction mass (at a price of ~ $10,000 a pound or more) to manage this. Executive summary- using the Sun as a trash disposal is extremely expensive.
NASA's calculator is only accurate for objects falling vertically, so if you lifted a Prius up to (say) 100,000 feet in a balloon and then dropped it, it would indeed reach a terminal velocity (the speed at which air resistance balances weight) of 1,300mph. But our pong-bomb will reach the upper atmosphere with an (almost) horizontal component of orbital speed - say 17,500mph.
My powers are too weak to calculate whether air resistance will have time (free fall to earth in a vacuum from 100,000 feet is about 80 seconds - reentry times are typically around a couple of minutes) to scrub off all this horizontal speed, but I observe that meteors (which admittedly reach the atmosphere with 2-3x greater speed) don't land vertically.
Yes, just like on Earth so it is in Heaven. You pitiful little meatsacks strewing you garbage all over the place.
I shall now double my efforts in the lobbying of the Galatic Council to keep you vermin in your own solar system. Yes, the cost of a Dyson Sphere is astronomical but it will be worth it, at the very least the place will be tidy.
Smell you later, smell you later forever.
"My conjecture is that a large stinky space fridge would be quite a bit more aerodynamic than a man. For example, I went to NASA's online terminal velocity calculator here:"
Actually the human body is suprisingly aerodynamic. One reason may be why the aquatic ape idea is true. Scuba divers (especially those spellunking) KNOW to a great degree how much harder it is to push yourself backwards through water because that way is not as aerodynamic as going head first.
Add to that jobbies float probably even better than the human body does and this frigde won't be 100% jobbie, and you have a shape that is much LESS aerodynamic than a skydiver and less dense along with it (though of greater volume, maybe). A terminal velocity of less than 120mph seems acceptable.
And these are (for ones that get to the ground) going at MUCH higher velocities and are much heavier.
1/2 Mv^2
But the dissipation is proportional to the force times distance. The drop of energy then is proportional to velocity, not velocity squared.
So if you go fast enough the atmosphere will not be able to bleed off enough energy before you smack into the ground.
Add to this the problem of orbital mechanics. You can't just shoot the shit at the sun, since as it gets closer, the conservation of angular momentum means that the lateral velocity increases quickly.
And since the sun is only half a degree, that's REAL easy to miss.
And so what you may end up with is a shit comet whipping round the sun-earth distance and eventually we smack into the turdish meteor as we go round the sun.
Net effect: naff all.
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