In theory

[Chik Sneadlov]

Lets say your planet has an atmosphere 100,000 feet thick and you're stuck in orbit at 100,009. The atmosphere and your orbit are precise and they never vary. You're out of fuel and doomed to circle the planet for eternity so in desperation you tie pieces of your clothes together along with some rope you find on board and you hang it out of the capsule which is as light as they get. The dirty laundry rope you made is long enough that twenty feet of it dips into the highest part of the thin atmosphere. I think you could slow yourself enough that eventually your ship would sink into the thicker atmosphere. After awhile you'd be low enough to pop a chute and land. Its just a matter of how long this would take or if the rope would burn up, but I'm assuming the atmosphere would be very thin at that point so your rope would not heat up much. 

[DDE]

5 minutes ago, Chik Sneadlov said:

but I'm assuming the atmosphere would be very thin at that point so your rope would not heat up much. 

Quite naively. The upper atmosphere may be rarified but it’s extremely hot, and the reentry plasma is hottest up high.

[Starman4308]

Real world atmospheres do not work that way. They continue up indefinitely, though eventually it just merges with the interplanetary medium. The strict cutoff in KSP is a game mechanic to permit time warp for LKO satellites.

What you would have in this scenario is a slowly decaying orbit, that may either strip off the heatshield or simply take too long to decay, running you out of life support supplies.

[PB666]

1 hour ago, Chik Sneadlov said:

Lets say your planet has an atmosphere 100,000 feet thick and you're stuck in orbit at 100,009. The atmosphere and your orbit are precise and they never vary. You're out of fuel and doomed to circle the planet for eternity so in desperation you tie pieces of your clothes together along with some rope you find on board and you hang it out of the capsule which is as light as they get. The dirty laundry rope you made is long enough that twenty feet of it dips into the highest part of the thin atmosphere. I think you could slow yourself enough that eventually your ship would sink into the thicker atmosphere. After awhile you'd be low enough to pop a chute and land. Its just a matter of how long this would take or if the rope would burn up, but I'm assuming the atmosphere would be very thin at that point so your rope would not heat up much. 

Things don't hang in space they drift. A space craft is orbit follows the following logic w²r = u/r². Since all particle on the craft mean the same criteria. If you push a sheet out of the space craft in a downward direction in 1/2 an orbit it will be the maximum distance that it went down but above the spacecraft.

Since there is no way to precisely confine a gaseous atmosphere, the ship will experience drag anyway, however, the best way to enter faster is to turn the ejection surface to in the prograde direction, take half the ejection mass (say a bag filled with toilet waste and old spent CO2 absorption cartridges), while tied to ship expel waste into space. [Throw the waste in the direction of the velocity vector, the prograde direction]

If your vessel weighs 20 tons and you expel 5 kg of mass at 5 meters per second. This means you have given the ship .00125 meters per second of retrograde speed. If this were to occur above Earth at 30483 meters then its radius is 6401483 meters from earths center of mass. The vehicle would be traveling at 7890.93725 m/s, lowering its speed to .00125 would drop the speed to 7890.93225. Specific Orbital energy equation allows us to calculate a . . SKE-SPE = -u/2a. a = -u/(2*(SKE-SPE)). Once the mass is expelled its current radius becomes the apogee, this is because it previously was a circle, but now that it moving slower its radius will fall from that point, a then went from 6401483 to 6401480.97. However a is not the perigee, its halfway in radius between the apogee and perigee so at perigee you would be 6401478.94 (30478.94 meters in altitude, 99996.54 feet.

Oh and btw without fuel the vehicle no longer has RCS thrusters so it cannot turn without reaction wheels and eventually they will max out, so more than likely the vessel will burn up upon entry.

 

 

[NSEP]

Atmospheres don't end at a specific altitude, it slowly fades away the higher you go. 

[YNM]

It depends, to be honest.

 

What's your theory ?

- Does the rope stays "magically" straight ?

- Does the atmosphere "magically" dissappears altogether at a certain altitude ?

There's some possibility that the rope would just buckle up "out of the atmosphere" ; on the other hand atmospheres are not really a "solid" thing (heheh), technically there're atmosphere even in interstellar space (gas clouds), and near every space bodies the atmosphere just gets less and less dense up until a range of density at some distance.

Edited December 19, 2017 by YNM

[Lukaszenko]

Your orbit would degrade and you would sink into the lower atmosphere (or at least parts of you). The problem is that once you hit enough atmosphere, your trajectory quickly degrades and puts you into a steep path to the denser parts...but, much steeper and hence quicker than you want to give you enough time to shed your speed and heat. The result is that you DON'T shed enough speed and heat and you either burn up or break up, or some combination of both. 

[Chik Sneadlov]

8 hours ago, Chik Sneadlov said:

Lets say your planet has an atmosphere 100,000 feet thick and you're stuck in orbit at 100,009. The atmosphere and your orbit are precise and they never vary.

The title is "In theory" and I clearly set some "rules" for this hypothetical situation right there. In this problem the atmosphere and orbit are precise and they never vary. It doesn't matter how the real world really is, this is a hypothetical question. So in this place the atmosphere does end at exactly 100,000 feet. The orbit is circular and exactly 100,009 feet. 

 

6 hours ago, PB666 said:

Things don't hang in space they drift. A space craft is orbit follows the following logic w²r = u/r². Since all particle on the craft mean the same criteria. If you push a sheet out of the space craft in a downward direction in 1/2 an orbit it will be the maximum distance that it went down but above the spacecraft.

Since there is no way to precisely confine a gaseous atmosphere, the ship will experience drag anyway, however, the best way to enter faster is to turn the ejection surface to in the prograde direction, take half the ejection mass (say a bag filled with toilet waste and old spent CO2 absorption cartridges), while tied to ship expel waste into space. [Throw the waste in the direction of the velocity vector, the prograde direction]

 

 

 

I'm no expert and I'm not orbiting when I drive a car, but let me just point out that there is gravity, which pulls towards the center of the earth and 100,000 feet probably doesn't affect gravity much so wouldn't anything "dropped" out of a spacecraft also be pulled toward the center of the earth? Your reply makes it sound as though the rope and clothing would go up and away from earth and back. Then you assumed I "pushed" which sounds like you're thinking of every action causes an equal and opposite reaction. 

If I'm driving in a car I'm above the earth by about 3 feet and if I'm going 30mph and I let a piece of rope hang out it might drift back, but that's because its hitting the atmosphere. In my original situation I'm in the precise space vacuum so there is nothing to drag the rope back. As long as the rope is in vacuum it should hang perpendicular to the ship pointing at the center of the earth. If I drop it even further, lets say to exactly 99,999 feet it will hit the top 1 foot of very thin atmosphere. I can see this would cause the rope to drift back but its because it is encountering atmosphere. 

Is there gravity just above the atmosphere? I would say yes, but your response seems to ignore gravity while focusing on other parts of Newton's laws, like the reaction of the craft to me "pushing" the rope out. I don't have to push the rope. It falls because of gravity. I just release the rope and "toilet waste". Also, why do people assume I don't pull the rope back in if it starts to heat up? The air at the top is very, very thin, I doubt it will heat rope up much in a second and it will drag back just like if I was hanging a rope out my car window because it encountering friction with the air whereas my space vehicle is not yet encountering friction. It is still in a vacuum. Eventually, it will slow because of the drag of the rope, but that will take quite a bit of time, assuming the ship and I are of substantially greater mass. And sure, once the ship starts to hit the atmosphere it will slow even more and fall even more and heat up dramatically but that will take awhile. 

Can we agree that a 8 foot rope hanging from a craft in vacuum hangs straight down from a ship in vacuum when we are at an altitude of 100,009? The rope would not drift back or up at all since it is in a perfect vacuum even though it and the ship are moving thousands of mph.

The first thing I looked up was the temperature at high altitudes and I was shocked to find that there are places with very high temperatures. Most places high up are very cold. I don't know how big these high temperature areas are or widespread. I don't think they belong in this problem because they aren't uniform and they don't have much to do with gravity, vacuums and orbits. How could any space program survive if the earth's high atmosphere is full of vast areas at 3000 degrees F? Sure, ships heat up as they reenter but that's because of friction with atmosphere the result of an object hitting something at high speed. 

[PB666]

1 minute ago, Chik Sneadlov said:

The title is "In theory" and I clearly set some "rules" for this hypothetical situation right there. In this problem the atmosphere and orbit are precise and they never vary. It doesn't matter how the real world really is, this is a hypothetical question. So in this place the atmosphere does end at exactly 100,000 feet. The orbit is circular and exactly 100,009 feet. 

 

I'm no expert and I'm not orbiting when I drive a car, but let me just point out that there is gravity, which pulls towards the center of the earth and 100,000 feet probably doesn't affect gravity much so wouldn't anything "dropped" out of a spacecraft also be pulled toward the center of the earth? Your reply makes it sound as though the rope and clothing would go up and away from earth and back. Then you assumed I "pushed" which sounds like you're thinking of every action causes an equal and opposite reaction. 

If I'm driving in a car I'm above the earth by about 3 feet and if I'm going 30mph and I let a piece of rope hang out it might drift back, but that's because its hitting the atmosphere. In my original situation I'm in the precise space vacuum so there is nothing to drag the rope back. As long as the rope is in vacuum it should hang perpendicular to the ship pointing at the center of the earth. If I drop it even further, lets say to exactly 99,999 feet it will hit the top 1 foot of very thin atmosphere. I can see this would cause the rope to drift back but its because it is encountering atmosphere. 

Is there gravity just above the atmosphere? I would say yes, but your response seems to ignore gravity while focusing on other parts of Newton's laws, like the reaction of the craft to me "pushing" the rope out. I don't have to push the rope. It falls because of gravity. I just release the rope and "toilet waste". Also, why do people assume I don't pull the rope back in if it starts to heat up? The air at the top is very, very thin, I doubt it will heat rope up much in a second and it will drag back just like if I was hanging a rope out my car window because it encountering friction with the air whereas my space vehicle is not yet encountering friction. It is still in a vacuum. Eventually, it will slow because of the drag of the rope, but that will take quite a bit of time, assuming the ship and I are of substantially greater mass. And sure, once the ship starts to hit the atmosphere it will slow even more and fall even more and heat up dramatically but that will take awhile. 

Can we agree that a 8 foot rope hanging from a craft in vacuum hangs straight down from a ship in vacuum when we are at an altitude of 100,009? The rope would not drift back or up at all since it is in a perfect vacuum even though it and the ship are moving thousands of mph.

The first thing I looked up was the temperature at high altitudes and I was shocked to find that there are places with very high temperatures. Most places high up are very cold. I don't know how big these high temperature areas are or widespread. I don't think they belong in this problem because they aren't uniform and they don't have much to do with gravity, vacuums and orbits. How could any space program survive if the earth's high atmosphere is full of vast areas at 3000 degrees F? Sure, ships heat up as they reenter but that's because of friction with atmosphere the result of an object hitting something at high speed. 

Gravity is a faux force, just as centripetal acceleration is a faux force, in a circular orbit the two faux forces cancel each other.
Lets sat you wanted something to fall say 30 feet in space, like throwing an anchor. You throw the anchor behind the craft, not under it, provide it with enough rope and it will fall because now gravity is stronger than the centripetal force. As it falls it will speed up and eventually be under the craft. If you though the anchor down it will end up in front of the craft, if you through it in front of the craft it will end up over.

Here is the equation you want.

V2= u (2/r - 1/a). If you throw something down you don't change a, you change e. If you throw it behind, you change a and since you would be at forced change at apoapsis then periapsis must change. By the same token your ship will gain a, which means it would be harder for it to enter the atmosphere, as the object is falling your ship is speeding up, so the rope should be very long.

The foolproof way of causing the ship to enter the atmosphere is the way I describe, toss some weight faster than the ship and the ship will slow down and fall into the atmosphere.

The reason that very high altitudes are hot is that they are being bombarded with energetic particles from space. You really don't care about the heat of space because heat density is so low. What you care about is the heat the velocity your craft creates. However there are ways to control this heat.

1. Reentry angle is oblique, this means craft slows down at higher atmosphere.
2. The shielded areas of the spacecraft can be tilted to provide lift. Just as in number 1 reducing that -verticle velocity can reduce the rate at which the space craft encounters denser gas at higher speed.
3. Thicker shields or wider shields.
4.  retrograde thrust.

 

 

[sevenperforce]

4 minutes ago, Chik Sneadlov said:

The title is "In theory" and I clearly set some "rules" for this hypothetical situation right there. In this problem the atmosphere and orbit are precise and they never vary. It doesn't matter how the real world really is, this is a hypothetical question. So in this place the atmosphere does end at exactly 100,000 feet. The orbit is circular and exactly 100,009 feet. 

I'm no expert and I'm not orbiting when I drive a car, but let me just point out that there is gravity, which pulls towards the center of the earth and 100,000 feet probably doesn't affect gravity much so wouldn't anything "dropped" out of a spacecraft also be pulled toward the center of the earth? Your reply makes it sound as though the rope and clothing would go up and away from earth and back. Then you assumed I "pushed" which sounds like you're thinking of every action causes an equal and opposite reaction. 

If I'm driving in a car I'm above the earth by about 3 feet and if I'm going 30mph and I let a piece of rope hang out it might drift back, but that's because its hitting the atmosphere. In my original situation I'm in the precise space vacuum so there is nothing to drag the rope back. As long as the rope is in vacuum it should hang perpendicular to the ship pointing at the center of the earth. If I drop it even further, lets say to exactly 99,999 feet it will hit the top 1 foot of very thin atmosphere. I can see this would cause the rope to drift back but its because it is encountering atmosphere. 

The rope will not hang perpendicular to the ship, because both the rope and the ship are in free-fall. Gravity is not pulling the rope toward the center of the Earth any differently than it is pulling the ship toward the center of the Earth.

In reality, there will be tiny tidal effects which would tend to pull the entire ship into a radial orientation relative to the ground, but there is no source of differential gravitational force which would "tug" on the rope.

4 minutes ago, Chik Sneadlov said:

Is there gravity just above the atmosphere? I would say yes, but your response seems to ignore gravity while focusing on other parts of Newton's laws, like the reaction of the craft to me "pushing" the rope out. I don't have to push the rope. It falls because of gravity.

Again, the rope will not fall. The rope is already falling, and it is falling along with the spacecraft.

4 minutes ago, Chik Sneadlov said:

I just release the rope and "toilet waste". Also, why do people assume I don't pull the rope back in if it starts to heat up? The air at the top is very, very thin, I doubt it will heat rope up much in a second and it will drag back just like if I was hanging a rope out my car window because it encountering friction with the air whereas my space vehicle is not yet encountering friction. It is still in a vacuum. Eventually, it will slow because of the drag of the rope, but that will take quite a bit of time, assuming the ship and I are of substantially greater mass. And sure, once the ship starts to hit the atmosphere it will slow even more and fall even more and heat up dramatically but that will take awhile. 

Can we agree that a 8 foot rope hanging from a craft in vacuum hangs straight down from a ship in vacuum when we are at an altitude of 100,009? The rope would not drift back or up at all since it is in a perfect vacuum even though it and the ship are moving thousands of mph.

No, it will not hang in any sense whatsoever.

4 minutes ago, Chik Sneadlov said:

The first thing I looked up was the temperature at high altitudes and I was shocked to find that there are places with very high temperatures. Most places high up are very cold. I don't know how big these high temperature areas are or widespread. I don't think they belong in this problem because they aren't uniform and they don't have much to do with gravity, vacuums and orbits. How could any space program survive if the earth's high atmosphere is full of vast areas at 3000 degrees F?

The average temperature of the diffuse gas in the thermosphere is around 2500 degrees, but the air pressure is so negligible that there is no meaningful heat transfer between objects and the air around them. Even though the temperature is technically very high, you are almost perfectly insulated by a vacuum and so it's effectively very cold.

Counter-intuitive, I know, but it's the same principle as someone dipping his hand in water and then dunking it in molten lead. The water boils and expands so fast that it holds the molten lead away from your hand, so the heat cannot be transferred to you. Similarly, the gas molecules in the thermosphere have a LOT of kinetic energy due to solar radiation, but there is so much space between molecules that very little of that kinetic energy is transferred to objects as heat.

Of course, the lack of heat transfer goes both ways. We say it's "cold" in space because objects lose thermal energy by blackbody radiation faster than they gain thermal energy by collisions with gas molecules, but it isn't cold in the sense that objects in space instantly freeze. If you step into a freezer, you feel cold because your body begins losing thermal energy to the frigid air, but there aren't enough molecules in space to lose energy to, so you don't gain energy or lose energy. 

Objects that produce their own internal heat, like the ISS and the astronauts it contains, are so well-insulated by vacuum that they will rapidly overheat if radiators are not used to radiate away that thermal energy in the form of blackbody radiation. The rate of heat transfer by blackbody radiation depends on the emissivity of the material and the material's surface area, which is why big thin metal panels are so great at radiating away heat.

4 minutes ago, Chik Sneadlov said:

Sure, ships heat up as they reenter but that's because of friction with atmosphere the result of an object hitting something at high speed. 

Slightly pedantic, I suppose, but ships heat up not due to friction but due to compression. When you compress an ideal gas, its temperature increases, because you have the same amount of thermal energy packed into a smaller volume. A re-entering spacecraft is traveling so fast that the air cannot get out of the way, so it is compressed. The air is compressed so rapidly and thoroughly that the kinetic energy of the molecules exceeds their ionization energies, causing them to flash into plasma. As tongues of plasma come into contact with the surface, they transfer their heat to that surface by a combination of conduction and radiation, eating away at it. 

Modern heat shields are typically phenol-impregnated carbon. Phenol is a volatile organic compound (responsible, incidentally, for the unique flavor present in Islay scotch) that is stable to reasonably high temperatures and then rapidly evaporates. The heat transferred by the re-entry plasma causes the phenol to evaporate, bleeding into a boundary layer that insulates the shield, not unlike the water on a person's hand boils away and insulates them from the molten lead in the example above. The carbon shield underneath doesn't really burn as much as it just slowly bakes in the radiated heat from the plasma.

 

[K^2]

21 hours ago, YNM said:

- Does the rope stays "magically" straight ?

That part actually isn't a problem. If you let out a length of rope out of your ship, it will either hang straight down or straight up due to tidal forces. It might take a while to settle, since these forces are pretty small. But so is drag at the edge of atmosphere.

[Green Baron]

For tidal forces e.g. from tidal waves of the oceans or the influence of other bodies (sun/jupiter) to be effective the rope must be rigid for the forces to get a grip on the craft. Or, the roche limit for a rope is far out :-) It'll rather begin a chaotic dance between straightening and coiling up while hanging down/staying behind or going up/being in front while minuscule gravity differences and forces between the fibres like electro-statics and mechanical elements from "remembered" former states play with each other.

But, well, anyway, we are willingly ignoring physics/astronomy/atmosphere as well as house keeping habits ... :-)

Edited December 20, 2017 by Green Baron

[sevenperforce]

2 hours ago, K^2 said:

That part actually isn't a problem. If you let out a length of rope out of your ship, it will either hang straight down or straight up due to tidal forces. It might take a while to settle, since these forces are pretty small. But so is drag at the edge of atmosphere.

Tidal forces will have an effect on the ship as a whole. Unless there's some magical station-keeping force (KSP-style infinite reaction wheels and an RTG) keeping the spacecraft oriented prograde, then tidal forces will tend to pull the whole thing into a single equilibrium position as it orbits.

[YNM]

3 hours ago, K^2 said:

That part actually isn't a problem. If you let out a length of rope out of your ship, it will either hang straight down or straight up due to tidal forces. It might take a while to settle, since these forces are pretty small. But so is drag at the edge of atmosphere.

Yeah, just realized that. Maybe it'll settle somewhat on a quasi-stable state where it has a very slight bend.

So I guess it's quite inevitable then.

Edited December 20, 2017 by YNM

[Nibb31]

Deorbit by tether is actually a thing.

[Green Baron]

Yeah, a theoretic thing, with a mass at the other end, rotating to keep it straight, and a conductive tether interacting with earth's magnetic field like a current brake. Did i understand that right ?

The washing line can only be used as a brake if thrown out prograde.

[PB666]

On 12/20/2017 at 5:57 AM, K^2 said:

That part actually isn't a problem. If you let out a length of rope out of your ship, it will either hang straight down or straight up due to tidal forces. It might take a while to settle, since these forces are pretty small. But so is drag at the edge of atmosphere.

Actually no, since initially there is no force acting on the rope, the ropes straitness will be governed by internal forces like tension that remains after it was last coiled, it would want to sort of coil back to that shape. Of course you could run the rope through a steamer to make sure all the tension is released.

My idea is best, throw it backwards and let its w²r + g pull it down under the ship, as it entered the atmosphere the drag would pull it backwards. In this fairy-tail his atmosphere is not a grade it immediate, so chances are the 'knot board' at the end of the rope would bounce up and down each time tossing a little energy. The rope would have to be slacked out and then slowly pulled back otherwise the impact energy would cause it to pull the rope over the ship and slam back into the atmosphere.   

[Nuke]

ive always wondered if airfoils would function at such high velocities. if a bit of down force could be generated to hold the 'rope' in the atmosphere long enough for drag to bring the whole ship into the atmosphere. would need to be a hypersonic wing design, possibly just a peice of wood out of one of the seats (they wouldnt use wood but lets say this spacecraft is made by ikea) wittled into a triangular shape with a bit of a curve on one side to form a crude delta wing, with maybe a couple stabilizer fins glued on. and then through some feat of engineering the precise center of lift on the foil is found and attached to said "rope". fishing boats use something similar to improve stability.

Edited December 22, 2017 by Nuke

[ARS]

Suddenly I am thinking about feasibility of space elevator

[GoSlash27]

One does not simply "hang things" in orbit.

Anyone Remember that shuttle mission where they attempted to generate electricity using a tether? That got ugly in a hurry...

Best,
-Slashy

[DerekL1963]

On 12/21/2017 at 4:11 AM, Nibb31 said:

Deorbit by tether is actually a thing.

Well, it's theoretically a thing.  Experiments with using actually using tethers on orbit have not in general fared well.   If anyone's actually used one, I can't find any traces thereof.  (Lots of bold predictions, no actual data.)

[mikegarrison]

On 12/19/2017 at 12:31 PM, Chik Sneadlov said:

The title is "In theory" and I clearly set some "rules" for this hypothetical situation right there. In this problem the atmosphere and orbit are precise and they never vary. It doesn't matter how the real world really is, this is a hypothetical question. So in this place the atmosphere does end at exactly 100,000 feet. The orbit is circular and exactly 100,009 feet.

Your basic problem is that you posted some completely non-physical premises and then asked for a physics answer. That doesn't work.

Even in simplified physics problems (neglect friction, etc.) you can't ask things like "neglecting gravity, how long will it take someone to fall from the top of a cliff?" If the thing you are neglecting (atmospheric drag in your case) is also the thing you are asking about, how can that possibly work?

Edited December 23, 2017 by mikegarrison

[ARS]

13 hours ago, GoSlash27 said:

Anyone Remember that shuttle mission where they attempted to generate electricity using a tether? That got ugly in a hurry...

Uuum... Which one? I kinda never heard about that?

[Chemp]

2 hours ago, ARS said:

Uuum... Which one? I kinda never heard about that?

STS-75

[ARS]

Regarding OP's question, there's some things that I'd like to point out:

1.There's no precise boundary of atmosphere. There's no thin upper one and thick lower one. The atmosphere extend upwards and blends with space medium, making the question of thick and thin layer kinda not making any sense

2.Reentry does not work that way. You are in highspeed free fall state while in orbit, so when you are entering atmosphere, you did it at speed so high that the air molecules in front of the capsule doesn't have enough time to displace and thus being compressed. This compression generates heat so high that the air turns into plasma, which is what becomes a hazard to your craft. Sticking something outside your capsule, even if you are in orbit and it touches the atmosphere, won't even make it on fire

3. You cannot hang something on space. The rope that being hanged outside won't stay straight downwards towards the planet. Remember, you are in orbit, you still have orbital velocity, that does not mean your craft stay static and any stuff you throw outside will drop straight downwards. The rope would be trailing behind your craft. And even if you attach makeshift "parachute", it won't work since you are in orbit, there are not enough gases to slow your craft

I assume that OP thinks that atmosphere is like water where there's a clear boundary between water and air above, and thinks as if you are on a hovering vehicle that cannot stop, so you throw a makeshift parachute into water and let the water slow the craft, pulling the vehicle towards water surface where friction can slow it down to a dead stop. Unfortunately, real life atmosphere does not work that way