The point is by dropping the trash’s velocity to 18 km/s from 30 km/s it’s still orbiting the Sun. It now has an orbital apoapsis (farthest from Sun) of 1 AU where it moves at 18 km/s and a periapsis (closest to Sun) of 0.3 AU where it’s travelling at 80 km/s.
You basically have to shed all of your velocity to get your periapsis to within a solar radius at which point you’d have been better off trying to fire it into deep space.
The problem with doing this to reach the Sun is that you probably can’t get much closer than the orbit of Mercury, at least not for any reasonable (i.e. human lifetime) intervals. The reason for this is that you can only get so much momentum transfer from a gravitational swingby maneuver based upon the relative velocities of the planet and spacecraft and how closely the spacecraft can approach the planet while still having sufficient momentum to leave the sphere of influence (else it falls into orbit of the planet). The slower the spacecraft is going, the fewer opporunties it would have to make those kind of swingby intercepts. The reasons for this may not be immediately clear from everyday terrestrial experience so I’ll expand.
When you decide to go from one city to another–say, London to Kolkata–you know that you’ll be travelling a fixed distance (roughly 6500 km) which takes a relatively consistent amount of energy depending on your mode of transportation. Although there is a minor difference in energy state between the two locations because of the different latitudes (51.5 deg N versus 22.7 deg N) the amount of difference in potential and kinetic energy is negligible compared to the losses due to drag and lift required to fly between the two cities. However, when going from one celestial body to another–say, Earth orbit and Saturn–you have to account for the fact that the distance between the bodies is constantly changing but that their relative energy states also changes radically through their respective orbital positions. The fact that the energy losses due to drag in interplanetary space are almost negligible doesn’t even begin to make up for the fact that the difference in energy states (based upon how fast and what direction the planets are moving with respect to one another, and their distances from the Sun) are enormously beyond what it takes to travel from any point on Earth to any other point.
Getting back to going to the Sun, given an indefinite amount of time and propellant budget you could probably plot some course which would eventually null out the orbital momentum of the spacecraft sufficient that it would begin to graze the photosphere of the Sun and eventually disintegrate, but the interval would be on the order of tens of thousands of years with a hugh dispersion in the possible spacecraft trajectory which would require active control to fine tune. (So far, our record for an operating spacecraft is 36 years–the Voyager 1 and 2 probes, with the next longest being Pioneer 6 solar orbiting probe launched in 1966 and last telemetry receieved in 2000–so the notion of trash barges being directed into the Sun over a span of eons is far-fetched to say the least.) In fact, the easiest way to get something to the Sun isn’t to fly inward, but go outward; it is possible to fly a trajectory to Jupiter which makes a long, slow pseudo-lissajous orbit that nulls out the majority of orbital speed at that point, essentially leaving the spacecraft free to fall into the Sun. Depending on the configuration of the planets, this might take as little as four or five years. I know it seems totally counterintuitive that the fastest way to get to a destination is to go the opposite direction, but that’s orbital mechanics for you. The first rule of orbital mechanis should be, “Everything you know is wrong.”
Setting aside the misconceptions and conflation of global climate change with rubbish/hazardous waste, there are two things to note. First of all, the rotation of the Earth would only be affected by the change in moment of inertia and momentum transfer of the material placed into orbit or space, and since most of the impulse to place a satellite in orbit comes from the rocket, the change in rotational momentum is small. (Technically, the propellant, once expelled does impart some momentum on the atmosphere, which is part of the Earth, but it is far from an ideal elastic interaction and can be assumed to be essentially converted to heat, which has no direction.) It should also be noted that the entire crust of the Earth is a tiny fraction of 1% of the total mass of the Earth; despite being at the outer fiber (greatest distance from the center) and having the greatest effect on the rotational inertia of the planet, removing the entire crust (much less the tiny part of it that we have deemed to be “waste”) would have almost a negligible impact on the total angular momentum of the Earth.
Second, that stuff which you call “waste” today may well be “raw materials” or “energy sources” for future generation. Today, we eat food and drink contained in steel and aluminum cans, with only a modest portion recycled despite the fact that those are irreplaceable mineral resources which future generations will likely need. Similarly, the fuel material used in nuclear powerplants (uranium) is almost exclusively used in a “once through” cycle which doesn’t even extract 1% of the total available energy in a full burnup fuel cycle. Dumping “nuclear waste” (expended fuel elements) in deep mine, into ocean trenches, or otherwise making it completely inaccessible is like taking a 24k gold ingot, using it to wipe your ass, and then throwing it in the latrine. Not only will expelling material out into space or to the Sun not only address climate change or pollution effectively, it also deprives future generations of valuable and already partially processed resources.
Stranger
I think what you’re imagining is that, you have a barge of trash. You launch it from Earth. It’s now in space, orbiting the sun at the same speed as the Earth (give or take). Now you fire the rockets again, slowing down the garbage barge. Since it’s not traveling fast enough to orbit the Sun like the Earth does, it starts to fall toward the Sun. It travels a long spiral path, and eventually hits the outer layers of the Sun, where it bursts into pretty colored flames.
The trouble is that spiral orbits can’t happen (unless you’re orbiting inside the atmosphere). I blame Star Trek for this, every time the engines fail the Enterprise starts spiraling into the planet below. Except that won’t happen. All orbits are parabolic (you throw a baseball into the air, it flies up then falls down), or hyperbolic (you throw a comet towards the Sun from interplanetary space, it curves towards the Sun and then flies back out into interplanetary space), or elliptical (circles are just really regular ellipses).
If you slow down something orbiting the Sun at around the orbit of Earth, it creates a new orbit–a less circular one. But it will eventually fall back to the same height it had before, before falling back towards the Sun again. Think of Halley’s comet. It spends 75 years out in the outer reaches of the solar system, falling slowly towards the Sun. But as it gets closer and closer to the Sun it starts falling faster and faster. If it doesn’t actually hit the Sun, it whips around the sun at high speed and zips back out into the outer solar system. When it’s near the Sun it’s going really fast, and since it’s energy is conserved that energy doesn’t go anywhere. It’s outer journey is just like the fall towards the Sun, only in reverse.
Thank you Lemur, this is exactly what I’m imagining. And I appreciate your taking the time to try to explain it to me. But I have to admit that it seems counter-intuitive to me. I guess I’m a victim of **Stranger’**s ‘First Rule of Orbital Mechanics’. In addition to the Star Trek Phenomenon you mentioned, I also have visions of those bowling balls on trampolines sucking the smaller balls to them. I know there is no friction in space but still it’s a powerful graphic.
Anyway, thanks again. I shall fill this under ‘shit I’m probably never going to understand’.
A bit of a hijack, but … is this done already? If not, why not? It takes a tremendous amount of energy to dig that big of a hole, and the surrounding environment is often shot to hell anyway.
Because the end waste isn’t generally in the same place where you extracted the raw materials, and in the intervening time you tend to be extracting more materials from the mine. In the case of hazardous minerals, in their natural state they are often bound up with other materials that makes them relatively benign, or at least not prone to leeching into groundwater and air, whereas the waste products are often in a form that makes them readily mix with the environment. (Coal or petroleum into CO[sub]2[/sub] is perhaps the most extreme example of this; in the natural state, it is almost completely inert and buried in the ground; the final waste is distributed in the atmosphere and extremely difficult to extract and sequester.)
It is also important to keep in mind that most hazardous wastes are not from the end product themselves but from the processing necessary to produce useful products. Dioxins, for instance, are not found in any significant quantity in any product, but were used in processing nearly all textiles, paper products, pesticides, and other commercial and consumer goods through the 1980s. This same problem is often ignored in superficial analyses of the hazards and pollution of the nuclear fuel cycle; while the expended fuel elements and low level waste produced by handling is relatively easy to sequester and control, all of the solvents and waste produced during the processing cycle remains a substantial problem, which argues toward nuclear fuel cycle technologies that minimize processing to reduce the total lifecycle costs and hazards.
“Garbage”, like in-laws, don’t just “go away” because you put them out of sight, not even in space. One of the growing problems in the nascent space industry is what is going to happen once there are a bunch of commercial smallsat and microsats in orbits that don’t decay within a few years and the resulting contamination and debris hazards at LEO space.
Stranger
The easy part to understand is that as the garbage barge falls toward the sun it starts going faster and faster and faster. But it’s still got the same sideways vector it had way out in Earth orbit, only a little bit less. So as it’s falling toward the Sun, it’s still moving away from the Sun. So it is sure to miss the Sun, unless you completely stopped it dead in its tracks with your rocket blast.
Now, as it falls toward the Sun and misses, it’s going really fast, so it swings waaaaaaay back out into space again, getting slower and slower and slower…until it falls back towards the Sun again. But it’s going to miss again. It is going to miss every time, because it will always have that sideways movement, unless you fired your rockets hard enough to totally kill that sideways movement. And note that we don’t actually have any rockets powerful enough to actually do this, it would take a tremendous amount of energy to stop something moving as fast as something in Earth’s orbit, which is 29,000 meters per SECOND.
Think of it like a roller coaster. The roller coaster faaaaaallls all the way down the hill, but that gives it enough energy to roll all the way back up the next hill. Except in space there’s no friction, so it will never stop falling down the hill and rolling up the next and falling back down.
