Only once in history has anyone managed to successfully skydive from over 100k feet in altitude: Colonel Joseph Kittinger, who had the backing of the United States Airforce.
Nick Piantanida made an attempt in 1966. Freefalling from perhaps as high as 120k feet, his mask depressurized at around 57k feet and he suffered brain damage from lack of oxygen. He remained in a coma for the last four months of his otherwise uneventful life.
Several others are planning attempts to break the record. I assume that one of them will succeed within the next five years. Possibly, one or more of them will die in the attempt, but I doubt it. And when they don't...
Let's discuss the components needed to bring near-space skydiving to the masses. And by masses, I mean up-to a hundred people a year.
Using a balloon like this:
http://www.csbf.nasa.gov/balloons.html
These use helium, which costs $60-$65 per thousand cubic feet. That doesn't sound like all that much, but consider that it needs almost 40 million cubic feet of the wispy stuff. That's $2.6M just for helium. Hydrogen, on the other hand, can be produced for around $2.50 per thousand cubic feet. In other words, for around $100k. Hydrogen is also 7% lighter. So, instead of an 8,000lb payload, you could go with 8560lb. This additional payload would be useful for the (hopefully) reusable emergency equipment that it would be nice to take along. It could even be used to accommodate electrostatic dispersal equipment (a network of fine, slightly-charged metal wires running through the interior of the balloon). I've never actually heard of anyone using active suppression in a balloon, so feel free to look into it.
Yes, hydrogen is risky compared to helium. Certain contingencies would require thoughtful preparation. Passengers would be trained to abandon ship at any time. Low-level disasters would actually be far more dangerous than high-altitude failures. Near the ground, spacedivers would wear large BASE jumping chutes. If the lifting envelope lit off only five hundred feet above the ground the twelve spacedivers would need to leave the gondola simultaneously. Thus, they would be too close together to release their chutes without interfering one with another. This could be solved with rocket dispersal packs. Each spacediver would be shot away from the gondola on a different trajectory. This would have the added benefit of getting the spacediver out of the path of the falling gondola. Who wants to land safely only to be squashed by falling debris? The fireball wouldn't be much of a problem (aside from being a fireball), since burning hydrogen flames upward. The falling gondola would pose a problem. To preserve the equipment carried aboard, the gondola would deploy a parachute of its own. If, for any reason, a spacediver failed to detach from the gondola, the gondola's own chutes would open a new survival path.
Spacedivers would wear heated, pressurized suits. Spacesuits. The gondola would also have a chamber that could be pressurized to normal atmospheric pressure and used for emergencies. It would also carry a pair of emergency back-up suits (in case you pick up hitchhikers on you way to the edge of space). If a spacediver became incapacitated and unable to complete their dive, they would take refuge, along with an attending medic, inside the safety chamber. This would either detach and ride down on its own chutes while the remaining spacedivers complete the program, or it could remain attached to the gondola and ride down at the end. This would depend entirely on the individual circumstances.
For the middle part of the ascent, spacedivers might gather together in the unpressurized safety chamber, or in a thermally insulated unpressurized tent. This would allow spacedivers to conserve heat and converse during the hours-long ascent. What would they talk about? Probably baseball.
Before making the ascent, spacedivers would breath pure oxygen for several hours, thereby removing dissolved nitrogen from their blood. Most likely, they would breath only a partial atmosphere (equivalent to the top of Everest, for instance) of pure oxygen during the entire flight program.
During the ascent, spacedivers would hook into a shared oxygen supply aboard the gondola. They would have individual oxygen tanks as well- carried on their persons at all times- which would provide emergency back up in the event that the shared supply failed. If the shared supply did fail, spacedivers would immediately return to earth.
Different parachute programs would be designed for jumps from different altitudes. Spacedivers would be trained for all possible jump parameters.
Jumping from over 100k feet would involve extremely high speeds. Colliding with another spacediver would likely segue seamlessly to death. Therefore, jumps would be staggered to prevent this undesirable scenario. Divers would pay a premium for the last (highest) jump slots. Each spacediver would also be assigned a vector, which, properly followed, would take her away from her fellow divers.
Spacediver landing zones would be spread out over a large area, as much as two hundred miles in diameter. Each spacediver would be provided with a retrieval team. Retrieval teams would be dispersed over the retrieval area and would arrange between themselves to retrieve diver closest to themselves without neglecting any. Divers would be equipped with mapping GPS and would be in general radio contact. Once a retrieval team had been assigned to a diver, the diver would switch to a direct channel. Automatic GPS locators would allow recovery even if the diver was unconscious or "other." Spacedivers should be adept at controlled flight and able to choose their landing area from high altitude.
A total payload of 8650lbs would allow for a 1800lb gondola frame built of carbon composites to sustain moderately high impact; 1400lbs of oxygen equipment; 350lbs each for twelve spacedivers (include the diver herself, suit, four main chutes, and diving oxygen), plus an additional 1360lbs for individual emergency chutes, dispersal rockets, pressurized safety chamber, two extra suits, and the gondola's own recovery chutes. This leaves a 500lb margin that could be used (just as an example) for baseball equipment.
Disclaimer: the gondola wouldn't provide very much of an outfield due to being the size of a small truck.
The gondola would be hexagonal, semi-rigid, and have three concentric zones. The outer layer is the jump platform. This would be open to the air. The middle layer, is an unpressurized, insulated solar tent. This would provide shelter from the blistering cold during the long ascent. In the center of the gondola would be the emergency pressure chamber. It would be large enough for two people to change into the back-up suits simultaneously, or for divemaster / medic to attend to a prone patient.
One divemaster would accompany each group. The divemaster would be the last to leave the gondola under normal circumstances. Under abnormal circumstances, the company would go out of business. This is a very dangerous idea.
Total costs:
Development: $6.3M (includes all administrative costs). $1.8M for entire parachute development program (run concurrent with test dives). Up-to $300k for hydrogen production plant. $600k for each of two gondolas, $800k for sixteen suits ($50k * 16). $1.8M for up to six test flights ($300k * 6). $400k for facility (rent is cheap in the desert, right?). Recovery vehicles would be provided by subcontractors paid $2k each per recovered spacediver / nothing if spacediver not actually recovered.
Per flight costs:
Disposable balloon envelope (recyclable): $20k
Hydrogen gas: $120k
Training: $16k
Retrieval teams: $2k / team = $24k.
Equipment retirement: $20k
Administration: $50k
Unavoidable insurance costs: $40k
Total per flight: $290k
Client cost per flight: $90k x 11 = 990k
Profit per flight: $700k.
Number of flights to recover development costs: 9
Two flights per month from May through October allows to become profitable after the first year and a half of operation. Prices could be lowered afterward to better accommodate supply / demand.
I have now extracted as much fun from this idea as I'm ever likely to extract.
Thursday, May 26, 2011
Planetary-Scale Engineering Using Relativistic Hulks
According to special relativity, a container of hot gas, in which individual particles are moving rapidly within the system, will weigh every so slightly more than a container of cold gas. This is because, the faster a mass moves relative to rest, the more mass it has (from it's own frame of reference, there is no change). Objects weigh more in proportion to the fraction of the speed of light, seeming to approach infinity as the fraction approaches unity. See my previous post for tons of mathematical examples of this effect. Cosmic rays, for instance, are lightweight particles (electrons and atomic nuclei) that have been made heavy through acceleration.
I'm going to use this concept as the basis for a mega engineering thought experiment. One of the requirements of this thought experiment is that we have access to unlimited drive energy onboard a starship. There is no known way to achieve this, and no terribly realistic ideas for fixing this particular inconvenience. Therefore, the source of drive energy is in the realm of pure science fiction. The idea described here doesn't work with ram scoops, antimatter rockets, or interstellar lasers driving solar sails. It requires something exotic like stretching and exploiting the zero-point energy gradient, tuning into blackholes via a holographic hack, or blocking gravity in one direction, thereby causing the weight of the unblocked universe to pull the ship toward itself. I won't bother to discuss it any further here, other than to ask that you assume the unassumable before we continue.
Imagine that you have an extra-impossible starship. Imagine also that you can accelerate that ship very close to the speed of light. That ship will rise in mass and exert significant gravitational influence on its surroundings. By accelerating to high relativistic speeds, the mass, and therefore the gravitational influence, will both increase, approaching infinity at around half the rate of the increase in velocity (in other words, you'll never achieve infinite mass through acceleration, ie, going from lower velocity to higher velocity to even higher velocity.)
Imagine if you were to pass by an asteroid, comet, or even a small moon traveling at a high percentage of the speed of light. You could, according to this idea, cause a gravitational pull on the side that the ship passed by. By doing flybys with many heavy fast ships, you could nudge your target off its original orbit. With careful planning, via advanced simulation, you could engage not just in terraforming, but solarforming- the modification of a solar system to make it more inhabitable.
For instance, imagine a planet is already in the right approximate location, but its precession and eccentricity are out of synch, disallowing regular seasons. Using this method, you could flatten the eccentricity by nudging the planet toward its star while at apogee (greatest distance from the center of orbit). You'd do this by passing your ship between the planet and the star. Alternately, you could pass on the the far side while the planet is at perigee. You could also speed or slow the orbit of the planet by passing in front or behind. By using multiple ships and multiple pass-bys, you could fine-tune the orbit.
On the down side, a point mass passing close to a target would exert massive tidal forces. The most powerful effects would also be the most violent. The surface would be more affected than the core, and the overall effect would be like trying to move a pumpkin by hitting it with a sword. Close flybys would affect rotation more than location (useful for changing the length of the day). Really close fly-bys would rip mountains up by their roots and strip away half the atmosphere.
To be most useful, the virtual masses involved would have to be planetary themselves, and be kept at a safe remove. The effect would come and go very quickly- in a matter of seconds- further dampening the effect.
How heavy, and how fast? For example, a "ship" weighing around 8,500kg (a small commercial truck) moving at 0.999999999999999999999999% of the speed of light (impossible) would effectively weigh as much as the earth when measured from the rest frame (~6e+24kg). Flying something like that through our solar system would have a very disturbing effect. It would cause earthquakes, volcanism, tidal waves- literally- and high velocity winds. Better to use it on planets that aren't yet inhabited.
Would this be a practical approach? No!!! It gets more and more practical the less and less realistic it is (ie, with large masses, higher velocities, and greater standoff). It's a thought experiment that assumes that literally unlimited energy for acceleration is available and can be translated into terrifying, unsurvivable amounts of acceleration. However, if you had access to that much energy, there would be much more efficient ways to use it. You could attach a many of these fanciful drives to the planet directly, or you could use their driving principle at a more fundamental level to get the same effect.
The one advantage is that the above technique uses minimal infrastructure- a single starship run by a single advanced autopilot operating on an extremely precise simulation.
But really, building extensive infrastructure shouldn't be a problem if you're moving planets around, right? Come on.
I'm going to use this concept as the basis for a mega engineering thought experiment. One of the requirements of this thought experiment is that we have access to unlimited drive energy onboard a starship. There is no known way to achieve this, and no terribly realistic ideas for fixing this particular inconvenience. Therefore, the source of drive energy is in the realm of pure science fiction. The idea described here doesn't work with ram scoops, antimatter rockets, or interstellar lasers driving solar sails. It requires something exotic like stretching and exploiting the zero-point energy gradient, tuning into blackholes via a holographic hack, or blocking gravity in one direction, thereby causing the weight of the unblocked universe to pull the ship toward itself. I won't bother to discuss it any further here, other than to ask that you assume the unassumable before we continue.
Imagine that you have an extra-impossible starship. Imagine also that you can accelerate that ship very close to the speed of light. That ship will rise in mass and exert significant gravitational influence on its surroundings. By accelerating to high relativistic speeds, the mass, and therefore the gravitational influence, will both increase, approaching infinity at around half the rate of the increase in velocity (in other words, you'll never achieve infinite mass through acceleration, ie, going from lower velocity to higher velocity to even higher velocity.)
Imagine if you were to pass by an asteroid, comet, or even a small moon traveling at a high percentage of the speed of light. You could, according to this idea, cause a gravitational pull on the side that the ship passed by. By doing flybys with many heavy fast ships, you could nudge your target off its original orbit. With careful planning, via advanced simulation, you could engage not just in terraforming, but solarforming- the modification of a solar system to make it more inhabitable.
For instance, imagine a planet is already in the right approximate location, but its precession and eccentricity are out of synch, disallowing regular seasons. Using this method, you could flatten the eccentricity by nudging the planet toward its star while at apogee (greatest distance from the center of orbit). You'd do this by passing your ship between the planet and the star. Alternately, you could pass on the the far side while the planet is at perigee. You could also speed or slow the orbit of the planet by passing in front or behind. By using multiple ships and multiple pass-bys, you could fine-tune the orbit.
On the down side, a point mass passing close to a target would exert massive tidal forces. The most powerful effects would also be the most violent. The surface would be more affected than the core, and the overall effect would be like trying to move a pumpkin by hitting it with a sword. Close flybys would affect rotation more than location (useful for changing the length of the day). Really close fly-bys would rip mountains up by their roots and strip away half the atmosphere.
To be most useful, the virtual masses involved would have to be planetary themselves, and be kept at a safe remove. The effect would come and go very quickly- in a matter of seconds- further dampening the effect.
How heavy, and how fast? For example, a "ship" weighing around 8,500kg (a small commercial truck) moving at 0.999999999999999999999999% of the speed of light (impossible) would effectively weigh as much as the earth when measured from the rest frame (~6e+24kg). Flying something like that through our solar system would have a very disturbing effect. It would cause earthquakes, volcanism, tidal waves- literally- and high velocity winds. Better to use it on planets that aren't yet inhabited.
Would this be a practical approach? No!!! It gets more and more practical the less and less realistic it is (ie, with large masses, higher velocities, and greater standoff). It's a thought experiment that assumes that literally unlimited energy for acceleration is available and can be translated into terrifying, unsurvivable amounts of acceleration. However, if you had access to that much energy, there would be much more efficient ways to use it. You could attach a many of these fanciful drives to the planet directly, or you could use their driving principle at a more fundamental level to get the same effect.
The one advantage is that the above technique uses minimal infrastructure- a single starship run by a single advanced autopilot operating on an extremely precise simulation.
But really, building extensive infrastructure shouldn't be a problem if you're moving planets around, right? Come on.
Friday, May 13, 2011
Virtual Hyperspace
Imagine that you want to travel to a distant star, some 10 lightyears away, and then come back to earth.
Let's assume that you have a spaceship capable of accelerating at 100 gee. Let's also assume that you can handle the acceleration. You'd spend half the journey (5 ly) accelerating, and half deccelerating at the same speed. Your 10 lightyear journey would be over in 50 days of shipboard time. You'd be 50 days older, while, back on earth, about 10.01 years would have passed. Let's assume that you then spend ten days at your destination, get in your ship, and return to earth using the same velocity envelope.
When you arrived back on earth, everyone you'd left behind would be 20.07 years older. You'd be 110 days older.
If, however, you could arrive back at earth only 110 days after you'd left- thereby synchronizing your perceived passage of time to the rest frame, you'd effectively be making the trip instantaneously (minus 50 days per leg). I'll explain how a little later. You'd be engaging in interstellar time stoppage. You'd almost be time traveling. You'd be able to deliver information about a distant place a whole ten years earlier than it could have arrived by radio. As long as you didn't get it there before you left- obviating the need to make the trip, you wouldn't be violating causality. The information would be between 50 and 60 days old from the standpoint of a single universal frame of reference- a reference we'll call "hypertime." If the distance between the two locations was less, then the gap in time would also be less. If you collapsed the distance to zero, you'd collapse the gap to zero (simultaneous time and place)- you'd never actually get information earlier, from the hypertime perspective, than it was actually produced. The only reason causality wouldn't be breached is because you never actually traveled faster than light. Traveling faster than light goes beyond the instantaneous. It is tantamount to traveling back in time.
How to do it though?
Assume that, before we leave, we built an Einstein-Rosen bridge, using matter with negative mass to keep it open, and take one end of the bridge with us. That's a massive assumption, but as long as building such a bridge is possible, then the assumptions that follow are sound.
We take one end of the bridge to a distant planet, some 10 light years away. We now have a wormhole. If we were to travel through the wormhole, we'd appear instantly back on earth. Let's assume, as Stephen Hawking has, that the act of traveling through it causes a feedback cascade that collapses the bridge, making travel across space impossible. Let's say that the most we can hope for is to keep the bridge open at a distance. Being able to travel through a wormhole at all involves a massive assumption that is probably wrong. However, without it, there's no point in continuing.
We spend ten days at our destination, and then we travel home at 100 gee, arriving fifty days later according to the ships clock.
The mobile end of the ER bridge is then reunited, in terms of literal proximity, with the stationary end. The stationary end is now 20.07 years older. The mobile end is 110 days older. By traveling through the bridge at this point, we emerge on the other side a mere 110 days after we left. We travel back in time- but it's not our own time we travel back into because were weren't around. Assuming that going through the bridge is done in a way that doesn't challenge causality, then it might be allowed. On the other hand, if we travel through and then destroy the bridge, which must continue to exist for another twenty years, or otherwise interfere with crossing through it in the future, then we've created a forbidden paradox. Or, let's say that 20 years later, we choose not to go through the bridge to emerge 20 years earlier. Again, a paradox. However, it's conceivable that we could design a system that would insulate us from paradoxes.
For instance, imagine that the ER bridge could not be accessed without being linked with the missing half. Travel and communication through it wouldn't be possible, but the two ends would still age differently. What if the ship were designed in such a way as to make it impossible to leave the ship without traveling through the ER bridge? Or, even better, a design that physically forces you to travel through when the side are connected. If these decisions were made in advance, and insulated from influence, then the spectre of free-will tampering wouldn't have to emerge.
Perhaps what we need is two bridges.
You go through the first to enter the ship at the beginning of the trip. When the ship physically detaches itself, the stationary end closes and the mobile end opens onto a second bridge which is entirely contained on the ship. Ideally, there would be a neutral region between these, but it is also conceivable that no neutral area exists, and that the bridge is effectively continuous with three sections and two areas where it is stretched across cosmic distances- one for each leg of the trip. The occupants live inside the second half of the bridge- the one that isn't being stretched during the first transit. Once they arrive, they leave the ship via the second bridge, opening it onto the distant planet. When they depart, they leave half of the second bridge behind, closing it from within as they depart to prevent it from being destroyed by a paradox-forbidding cascade. This allows the ship to return again to that distant planet with the same benefit of near instantaneous travel. Limited virtual simultaneity is established between the two locations, though this is different from the simultaneity of hypertime.
When they arrive back on earth, we make it so that the only way to exit the ship is via the local bridge, opening it from within. As long as no one who remained on earth can enter the ship by other means and exit via the wormhole, no actual time travel is possible. If we say that time travel is impossible as a basic requirement of the universe, then we could assume that this is prevented by stating that it is simply impossible to do that. Also, that it is impossible to travel through an ER bridge over great distances, and that it is impossible to enter an ER bridge that is not linked locally (same thing, said twice). If we disallow the breakdown of causality, but not the existence of an ER bridge, then this constraint allows for hyperspace-like travel despite never entering into a literal "hyperspace" other than the strange area within the ER bridge itself.
This scenario assumes a very particular type of ER bridge- one with non-trivial length and extradimensional topology not normally required by an ER bridge. In essence, it needs to have regions that extend beyond the point where the stretch is taking place. It needs to be cut off from normal space, and for its contents to be separated from normal space by the wall of the ER bridge, even though, if traveling through the wall of the bridge were possible, they would simply emerge somewhere in deep space (wherever the ship carrying the bridge happened to be located at the time).
To make the proposition even more elegant, we'd have to say that the ship itself either penetrates the wall (by field or substance), or that the ship can travel through the ER bridge, or is, perhaps, constantly within it, or within the neutral area between two bridges. However, penetrating the wall in any way violates the nature of the allowability of the ER bridge (see above). Therefore, the only solution that doesn't leave a starship parked out in space 20 years later is for the ship to travel through the bridge itself. That means that the bridge would have to be moved, ie carried, from within the bridge itself. This is a problem, since the ship needs to be able to interact with external reality in order to move relative to it.
Assuming you could do that, you've got yourself some hyperspace.
Let's assume that you have a spaceship capable of accelerating at 100 gee. Let's also assume that you can handle the acceleration. You'd spend half the journey (5 ly) accelerating, and half deccelerating at the same speed. Your 10 lightyear journey would be over in 50 days of shipboard time. You'd be 50 days older, while, back on earth, about 10.01 years would have passed. Let's assume that you then spend ten days at your destination, get in your ship, and return to earth using the same velocity envelope.
When you arrived back on earth, everyone you'd left behind would be 20.07 years older. You'd be 110 days older.
If, however, you could arrive back at earth only 110 days after you'd left- thereby synchronizing your perceived passage of time to the rest frame, you'd effectively be making the trip instantaneously (minus 50 days per leg). I'll explain how a little later. You'd be engaging in interstellar time stoppage. You'd almost be time traveling. You'd be able to deliver information about a distant place a whole ten years earlier than it could have arrived by radio. As long as you didn't get it there before you left- obviating the need to make the trip, you wouldn't be violating causality. The information would be between 50 and 60 days old from the standpoint of a single universal frame of reference- a reference we'll call "hypertime." If the distance between the two locations was less, then the gap in time would also be less. If you collapsed the distance to zero, you'd collapse the gap to zero (simultaneous time and place)- you'd never actually get information earlier, from the hypertime perspective, than it was actually produced. The only reason causality wouldn't be breached is because you never actually traveled faster than light. Traveling faster than light goes beyond the instantaneous. It is tantamount to traveling back in time.
How to do it though?
Assume that, before we leave, we built an Einstein-Rosen bridge, using matter with negative mass to keep it open, and take one end of the bridge with us. That's a massive assumption, but as long as building such a bridge is possible, then the assumptions that follow are sound.
We take one end of the bridge to a distant planet, some 10 light years away. We now have a wormhole. If we were to travel through the wormhole, we'd appear instantly back on earth. Let's assume, as Stephen Hawking has, that the act of traveling through it causes a feedback cascade that collapses the bridge, making travel across space impossible. Let's say that the most we can hope for is to keep the bridge open at a distance. Being able to travel through a wormhole at all involves a massive assumption that is probably wrong. However, without it, there's no point in continuing.
We spend ten days at our destination, and then we travel home at 100 gee, arriving fifty days later according to the ships clock.
The mobile end of the ER bridge is then reunited, in terms of literal proximity, with the stationary end. The stationary end is now 20.07 years older. The mobile end is 110 days older. By traveling through the bridge at this point, we emerge on the other side a mere 110 days after we left. We travel back in time- but it's not our own time we travel back into because were weren't around. Assuming that going through the bridge is done in a way that doesn't challenge causality, then it might be allowed. On the other hand, if we travel through and then destroy the bridge, which must continue to exist for another twenty years, or otherwise interfere with crossing through it in the future, then we've created a forbidden paradox. Or, let's say that 20 years later, we choose not to go through the bridge to emerge 20 years earlier. Again, a paradox. However, it's conceivable that we could design a system that would insulate us from paradoxes.
For instance, imagine that the ER bridge could not be accessed without being linked with the missing half. Travel and communication through it wouldn't be possible, but the two ends would still age differently. What if the ship were designed in such a way as to make it impossible to leave the ship without traveling through the ER bridge? Or, even better, a design that physically forces you to travel through when the side are connected. If these decisions were made in advance, and insulated from influence, then the spectre of free-will tampering wouldn't have to emerge.
Perhaps what we need is two bridges.
You go through the first to enter the ship at the beginning of the trip. When the ship physically detaches itself, the stationary end closes and the mobile end opens onto a second bridge which is entirely contained on the ship. Ideally, there would be a neutral region between these, but it is also conceivable that no neutral area exists, and that the bridge is effectively continuous with three sections and two areas where it is stretched across cosmic distances- one for each leg of the trip. The occupants live inside the second half of the bridge- the one that isn't being stretched during the first transit. Once they arrive, they leave the ship via the second bridge, opening it onto the distant planet. When they depart, they leave half of the second bridge behind, closing it from within as they depart to prevent it from being destroyed by a paradox-forbidding cascade. This allows the ship to return again to that distant planet with the same benefit of near instantaneous travel. Limited virtual simultaneity is established between the two locations, though this is different from the simultaneity of hypertime.
When they arrive back on earth, we make it so that the only way to exit the ship is via the local bridge, opening it from within. As long as no one who remained on earth can enter the ship by other means and exit via the wormhole, no actual time travel is possible. If we say that time travel is impossible as a basic requirement of the universe, then we could assume that this is prevented by stating that it is simply impossible to do that. Also, that it is impossible to travel through an ER bridge over great distances, and that it is impossible to enter an ER bridge that is not linked locally (same thing, said twice). If we disallow the breakdown of causality, but not the existence of an ER bridge, then this constraint allows for hyperspace-like travel despite never entering into a literal "hyperspace" other than the strange area within the ER bridge itself.
This scenario assumes a very particular type of ER bridge- one with non-trivial length and extradimensional topology not normally required by an ER bridge. In essence, it needs to have regions that extend beyond the point where the stretch is taking place. It needs to be cut off from normal space, and for its contents to be separated from normal space by the wall of the ER bridge, even though, if traveling through the wall of the bridge were possible, they would simply emerge somewhere in deep space (wherever the ship carrying the bridge happened to be located at the time).
To make the proposition even more elegant, we'd have to say that the ship itself either penetrates the wall (by field or substance), or that the ship can travel through the ER bridge, or is, perhaps, constantly within it, or within the neutral area between two bridges. However, penetrating the wall in any way violates the nature of the allowability of the ER bridge (see above). Therefore, the only solution that doesn't leave a starship parked out in space 20 years later is for the ship to travel through the bridge itself. That means that the bridge would have to be moved, ie carried, from within the bridge itself. This is a problem, since the ship needs to be able to interact with external reality in order to move relative to it.
Assuming you could do that, you've got yourself some hyperspace.
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