With the “periodically re-intercepting” coming at a period of around an hour and a half, if you’re in low Earth orbit.
OK, one more and then I’ll bow out and go sit in the corner and chew on my bone. I’m in the Shuttle in a perfectly circular orbit around the Earth. If I understand this diagram correctly, when I throw the tile I will force it into an orbit whose eccentricity is some nonzero value. No matter how hard I throw it, unless it catches air it’s not going to hit the ground. The tile and I will continue to orbit the Earth together, and at various times I will be able to spot it above me, below me, behind me, and ahead of me. And it might eventually come back and hit me in the head.
Yes, that’s all correct, now.
This blows my mind. On the flash demo, my planet crashes into the sun frequently if I dont impart enough initial velocity. Isnt’ this what would also happen with the trash? I dont get how objects wouldn’t just get pulled into the sun if we aimed it correctly. Like, enough energy to escape the earth’s orbit, then aim it straight at the sun (or the equivalent accounting for gravity). I understand that everyone in this thread is saying that is not how it works. I tried to read the Kepler’s law entry in Wiki but it’s over my head.
If this is the simplest explanation, I’m not getting it.
It’s the same idea as the ISS guy throwing a wrench at the Earth. For simplicity let’s assume that the ISS is in a circular orbit. Since the ISS is going in a circle, the change in distance between the surface of the Earth and the ISS is always zero. There is zero velocity toward the Earth, all of its velocity is perpendicular to the Earth, keeping it in orbit.
Now let’s say you throw a wrench toward the Earth. Let’s be generous and say that you have a mean fastball, and you throw the wrench down at 100 mph. That seems pretty fast on our scale. But meanwhile your, and the wrench’s, horizontal velocity is 17,000 mph. Any reasonable speed you can part with the wrench will pale in comparison to its horizontal speed, and so if you look at the problem on the scale of the entire Earth, the orbit just becomes shifted a tiny fraction.
It’s the same deal with Earth and the sun. The Earth’s horizontal velocity with respect to the sun is a mean 66,000 mph. We’re nowhere near capable of launching anything comparable to such a speed.
The problem is with the “aim it straight at the Sun”. You can only aim it curved, and basically all curves will miss the Sun. To aim it straight, you’d first have to “stop” it in its (Earth-like) solar orbit, which takes a ridiculous amount of energy.
(I’m no expert, I’m just trying to rephrase what the people-who-understand have told us above.)
Even those are ‘resources’, possibly very hard-to-replace ones. Someday we may have the technology to recycle or re-process them into something usable.
Many of the old garbage landfills are now looked at as potential mine sites, since they contain materials (aluminum cans, copper, etc.) that could be reused cheaper than mining new materials.
You are conflating two different things here: escape from the Earth’s sphere of influence (the approximate spheroid in which the gravity field of the Earth has more influence (SOI) than that of the Sun), and eliminating the tangential “orbital” speed that the object has initially from starting at Earth of 30 km/s.
Breaking away from the Earth’s SOI isn’t terrifically hard; at low Earth orbit (LEO) the escape speed is about 7 km/s, which is achievable by small (>6000 kg) payloads using a high efficiency transtage like the Centaur upper stage. Alternatively, if you aren’t in a hurry, you can “nudge” the stage into progressively higher orbits by performing short thrust impulses at the low apsis (perigee, the lowest point of approach in the elliptic orbit), which will raise the injection apsis (apogee) higher were escape speed is lower, until your orbital speed at apogee exceeds escape speed, as will be done with the upcoming Lunar Atmosphere and Dust Environment Explorer (LADEE) mission.
Nulling out the solar orbital speed of nearly 30 km/s, on the other hand, is phenomenally difficult. Although it is less than solar escape speed at Earth’s orbit (~42 km/s), you can achieve solar escape by the method outlined above for gradually escaping Earth’s SOI, plus you can use derived impulse from close approaches to the massive outer planets via gravitationaly swing-by maneuvers, which is what makes it feasible to explore the outsystem. (I wrote a Mailbag column on swing-bys a few years ago but it seems to have been subsumed by the aether.) However, to subtract the 30 km/s orbital speed requires mostly direct thrust. You can perform swing-bys to subtract momentum from your craft and perform retrograde burns at the low apsis (perihelion in this case) but you are starting from a nearly circular orbit. Chronos is correct in stating that the Sun is, in terms of minimum energy, the most difficult point to reach in the Universe. Given no time constraints, it literally takes less energy to direct a vessel to any other point in space.
The animation linked below exaggerates the size of the Sun relative to an orbital path by many orders of magnitude, so it seems easy to make the object crash into the surface. However, bear in mind that your starting velocity should be lateral (or very nearly for any chemical propulsion method) to the line from your starting point to the Sun. Using a solar sail to progressively reduce orbital speed as suggested previously is the only practicable method, and this still assumes that you can apply enough energy to first extract your payload from Earth’s SOI.
While I agree that launching waste into space isn’t a remotely practical solution, if you assume that you already have that capability then it is merely a matter of developing a mining and refining infrastructure to extract resources from extraplanetary sources. There are vastly more mineral, energy, and radioisotope resources available in space than could ever be feasibly extracted on Earth, and they can be extracted without any concern over environmental contamination. (Even the most ardent environmentalist can’t be too concerned over strip mining a lifeless asteroid millions of miles from any kind of habitat for resources.)
About the only common material that is literally cheaper (in terms of energy) to recycle rather than mine is aluminum, due to the difficulty of extracting the raw element from bauxite. Many of the rare earth elements are also easier to recover than extract, but with nearly limitless solar energy and no concerns about runoff or wastage it may well be easier to extract these from space sources rather than recycle them on Earth. The real reason for recycling materials is because we currently only have access to the limited amount of material available in the upper crust of the Earth’s surface, but even a single small metals-rich asteroid could provide more iron, copper, nickel, platinum, and other metals than all of the mines extant on Earth.
Stranger
Imagine if we dumped all of our trash beside the roads and in the medians rather than hiding it away (like is space.) It wouldn’t take long for the amount of trash we create to be seriously addressed. It’s not like we use that land for anything anyway. Every time I hear of some new place we could hide our trash so we don’t have to think about it I cringe.
Even if we could shoot trash into the sun for zero cost it would just lead us to be even more wasteful. Before long we would be pitching whole buildings off of the Earth rather than bother taking them down.
The animation doesn’t have things in the proper proportions:
-their sun is 40 pixels wide.
-their “garbage” is 20 pixels wide (half a solar diameter)
-their viewing area is 325 pixel-widths from center to corner (~8 solar diameters)
The real sun is 870K miles across, your garbage scow is maybe a couple of miles across, and it starts out at earth’s orbital radius, 93M miles away. So let’s remake the simulation in the proper proportions:
-the sun is still 40 pixels wide.
-your garbage scow is a fraction of a pixel wide.
-your starting point is 4300 pixels away from the center of the screen. My PC’s display is 1280 pixels wide, so in my case, I’d be dumping my sub-pixel garbage from 3.3 screens away.
To get a collision, you need to put an object into a highly elliptical orbit whose trajectory takes it through the body being orbited. Now that you can appreciate the scales involved - planets and suns are very small compared to the distances between them - maybe it’s easier to see how it will be difficult to hit the sun.
More to the point, it’s not difficult technically - it’s just that when you’re starting out with the earth’s orbital speed, you have to remove a very, very large tangential velocity to achieve the desired highly-elliptical orbit that will cause your garbage to impact the sun, and that takes a big-ass rocket.
Thank you for the informative lesson. The scale thing really helps visualize what’s happening better.
Am I correct in thinking that if our theoretical garbage pile was much larger, it would be easier to hit the sun? Like say, 1/2 the size of the sun?
The funny thing is, all the talk about slingshotting, that part totally made sense from all my years of watching Star Trek.
But impractical, though. I mean, we’ve not been there often, for long, or recently, though I misremember the specifics. :dubious:
The biggest problem with materials mined in space is getting them back to Earth’s surface. Even if we’re cheaply producing megatons of iron and aluminum in space, the primary use for those materials will have to be in space, rather than on Earth. I guess if we’ve got some space elevators running we’ll want to send the same amount of mass down to Earth as we send up from Earth. So unless we’re sending megatons of something into space we aren’t going to be sending megatons of processed material back to Earth.
This is assuming we don’t just drop the stuff and recover the metals from the crater. A lot of beautiful sunsets in our future if we go that route.
It would be a little easier, but keep in mind that the Earth-sun distance is over 100 sun diameters, so even sending something the size of the sun from Earth to collide with the sun is really tricky.
Why not send more mass down than is sent up? The force imbalance could be used to generate electricity. Talk about a renewable resource…
It can be drop it into the ocean using a blunt-arsed ablative heat shielded capsule to slow it to a subsonic, non-tsunami-inducing speed, and recovered via standard underwater salvage processes. But I agree that the primary utility in having a space mining and manufacturing infrastructure is to support permanent human habitation in space, and in fact is a prerequisite for this.
Stranger
Because that would pull the space elevator into space. Newton’s laws.
You could actually use a space elevator to produce usable energy, by effectively stealing some of the Earth’s rotational energy. Now, the Earth has a huge amount of rotational energy, but it’s still, strictly speaking, a finite resource, so it’s probably better to keep things balanced just as a matter of principle.
That said, though, it’s not like it’d be hard to get equal masses going both ways. Iron and other metals are cheap in space but valuable on Earth, while water is cheap on Earth but valuable in space. Or if you’re worried about using up the oceans, just plain rock.
Yes, but they are out in space. We need them here on earth.
So for this to be feasible, you would also have to assume that we have the capability to somehow transport those refined extra-planetary resources down to the earth’s surface, and cheaply. (Which might be valid, someday.)
While I agree that the sun is literally the most energetically difficult place to reach from earth in the universe, given no time constraints, I don’t feel that imparting 37 km/s to a payload is technologically insurmountable, even by today’s standards. Get an ion drive out of earths orbit and into an orbit around the sun using conventional rocketry, and gradually slow yourself relative to the sun such that your orbit becomes more and more elliptical with each revolution. Eventually, you will fall into the sun.
My interest is piqued, but admittedly this isn’t my field of expertise. Could someone crunch the numbers to determine the mass of propellant needed to accelerate a theoretical vehicle with a total mass of 10000 kg to a velocity of 30 km/s assuming a specific impulse of 30,000 s (the reported maximum specific impulse of VASIMR). Would the mass of propellant be less than the total mass of the vehicle? If the required mass is more than the mass of the vehicle then it is impossible without further improvements to technology. I’d do it myself, but I have no head for physics.