Timeline for What could prevent a sentient species from going to space?
Current License: CC BY-SA 3.0
32 events
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| Jul 6, 2017 at 20:47 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 30, 2016 at 4:41 | comment | added | Benito Ciaro | Granted the question mentioned 'human-like' species but, if a species had bodies capable of withstanding high Gs, a railrun launch to orbit might be feasible, bypassing the chemical rocket equation completely. | |
| Jun 27, 2016 at 9:34 | comment | added | Luaan | Yes, but most of that 6% is dead weight for anything you want to do in space. Measuring "initial mass delivered to LEO" is kind of like measuring gas mileage - the more gas you burn, the better the car, right? Payload is the important bit. You might say that the shuttle itself is kind of part of the payload (due to its reusability), but that's only useful if the savings of the shuttle's reusability is higher than the cost of the fuel needed. Turns out this was never true of the american shuttle, which is why everyone else kept using rockets (and now, reusable rockets). | |
| Jun 27, 2016 at 9:23 | comment | added | Gary Walker | @Luaan -- And yet, the Saturn V had a worse payload ratio in terms of fraction of initial mass delivered to LEO(5%) than the shuttle (6%). I clearly identified both the official payload an the total mass in LEO in my answer. Pulsed nuclear would clearly get you into orbit even if earth was several times heavier. We don't use it, and would neither would another planet unless the advantages were thought to outweigh the disadvantages, such as having to explode 800 nuclear bombs to reach LEO. | |
| Jun 27, 2016 at 8:58 | comment | added | Luaan | I wouldn't use the space shuttle for comparison at all - its design requirements weren't centered around an optimal payload/fuel ratio. The much less complex Saturn V rocket has a launch mass of 3 000 tons (just 50% more than the shuttle) with 140t payload to LEO (about four times more than the shuttle). And if we didn't have enough power in chemical rockets, you can bet your ass we would use nuclear propulsion. After all, we're still using coal power plants despite the massive amounts of radiation and other pollutants they release. Energy is the great civilization enabler. | |
| Jun 27, 2016 at 6:54 | vote | accept | Pavel Janicek | ||
| Jun 27, 2016 at 4:28 | comment | added | Russell Borogove | The SR-71 flies around mach 3. Orbital speed is about 8 times that. | |
| Jun 25, 2016 at 5:36 | comment | added | Gary Walker | @MichaelHampton -- no, the Apollo program was not even remotely close to being as expensive as it would have been on an earth with double the mass. Apollo would have cost many thousands or even million times more. And, no, I cannot envision that it would happen under those conditions | |
| Jun 25, 2016 at 4:25 | comment | added | Michael Hampton | You "cannot envision anyone doing such a thing" due to "national pride, or a publicity stunt"? It's happened before, albeit on this planet. | |
| Jun 25, 2016 at 2:04 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 24, 2016 at 9:59 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 23, 2016 at 0:50 | comment | added | Scott | Making the atmosphere thicker would have a similar effect, IIRKSPC | |
| Jun 22, 2016 at 17:13 | comment | added | njzk2 |
about planes because they don't have to carry their own oxidizer. also, lift, and also, Isp of jet engines is ~1 order of magnitude higher than that of rocket engines.
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| Jun 22, 2016 at 16:48 | comment | added | Gary Walker | @James_pic -- planes have other advantages too, such as not having to reach orbital velocity, in-flight refueling, acceleration of the ambient air to provide thrust, etc. not carrying oxidizer was meant only to state only them major characteristic that distinguishes from rockets. | |
| Jun 22, 2016 at 16:31 | comment | added | James_pic | Planes have a bigger advantage than a ready supply of oxidiser. Rockets (and anything else that operates in space) are propelled entirely by their exhaust gas, which is a finite resource. Even if you've got a limitless supply of energy, once you're out of exhaust material, you can't go anywhere. Planes, on the other hand, can be designed to keep going for as long as they've got an energy supply. | |
| Jun 22, 2016 at 14:23 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 22, 2016 at 11:05 | comment | added | Tomáš Zato | This answer adresses the issue of getting into space pernamently. However this does not affect temporary reaching space, such as when using balloons or airplanes (think fish jumping out of water). | |
| Jun 22, 2016 at 1:10 | comment | added | Aron | @MichaelKarnerfors Obligatory xkcd reference what-if.xkcd.com/58 You should read the whole article to correct you understanding of orbits. A balloon does nothing. That's why we don't launch on top of Everest and almost exclusively launch at sea-level. | |
| Jun 21, 2016 at 20:55 | comment | added | Perkins | An elevated platform doesn't buy you much because gaining altitude is cheap compared to attaining orbital velocity. A moving launch platform, however is a different matter. The more of your velocity you can attain while still using oxidizer you don't have to carry the more efficient your launch will be. The SR-71 flew high and fast enough that the flightsuits of its crew were practically the same as for the shuttle. Just need to cram in enough of a rocket engine to go the rest of the way. | |
| Jun 21, 2016 at 19:54 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 21, 2016 at 19:48 | comment | added | jpmc26 | @Mat'sMug Not if your employees are already up there, I guess. | |
| Jun 21, 2016 at 19:48 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 21, 2016 at 17:30 | comment | added | vsz | @MichaelKarnerfors : sorry, but you're wrong. You will not reduce the costs by any significant margin by launching from an elevated platform. Most of the energy required for the orbit is spent achieving the huge velocity, very little of it is used to gain altitude. | |
| Jun 21, 2016 at 16:50 | comment | added | joojaa | heavier planet means easier ballooning. | |
| Jun 21, 2016 at 12:15 | comment | added | MichaelK | No offense taken. :) Yes but we are not talking fuel efficiency here now. We are talking about the feasibility of getting into space. At what gravity can we no longer beat The Tyranny, even if we do go for air launched platforms? | |
| Jun 21, 2016 at 12:12 | comment | added | Gary Walker | Not my intent to insult you but the NASA calculations for launching from even 35 km suggest a 25% decrease in fuel for LEO. I consider this a minor improvement in light of a planet that has 25 percent more mass as high balloon launch will necessarily be micro sats, or an exceedingly expensive balloon launch. We never even considered microsats until we had considerable experience with the advantages of satellites. The initial horizontal velocity component advantage is quite small (less than 1% as you are less than 1% higher). Perhaps we only differ in what is considered a minor improvement. | |
| Jun 21, 2016 at 11:52 | comment | added | MichaelK | You start well above the thickest part of the atmosphere and get a nice horizontal part of your orbital speed for "free". Feel free to do the numbers if you like and see what this means in the struggle against The Tyranny. | |
| Jun 21, 2016 at 11:48 | comment | added | Gary Walker | Actually, if you do the math, you will find that staring from a 10 km or 20 km altitude is not actually a big advantage. Mt. Kilimanjaro would seem like an excellent starting place, yet nobody uses it. I chose 25% earth mass increase because it overcompensates for minor improvements. Sic Semper Tyrannis | |
| Jun 21, 2016 at 11:09 | comment | added | MichaelK | The Tyranny of the Rocket Equation applies only if you start from the ground. If you use an airborne launch platform — which is tecnically more difficult than just tacking on more fuel and starting from the ground, but none-the-less feasable — then you drastically reduce the impact of The Tyranny. Also if you increase gravity, then you also increse the density of the atmophere, which makes for more efficient airborne launch platforms. | |
| Jun 21, 2016 at 10:42 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 21, 2016 at 10:37 | history | edited | Gary Walker | CC BY-SA 3.0 |
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| Jun 21, 2016 at 10:22 | history | answered | Gary Walker | CC BY-SA 3.0 |