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Steam Shuttle
use of steam as an ablative, retro-rocket and directional control during re-entry | |
A system consisting of a controlled waterflow to contiuous compartments in the wings/belly/nose, which releases steam through perforations in the skin.
From storage reservoir(s), controlled amounts of water are pumped to the areas of the Shuttle that bear the brunt of re-entry. When the area is heated
by friction, the water boils and is released through perforations in the skin. The phase-change from water to steam removes heat, the ejection of the steam removes the heat permanently, and the ablated steam is also further heated by some air that would be hitting the skin, thus removing even more (potential) heating.
Further benefits to the Shuttle: partial retro-rocket; can provide directional control/stability.
Benefits to the space program: low/high-weight payload flights can be normalized and weight-balanced by auxiliary water-tanks (or lack of same); excess water can be reservoired at or near the Space Station and then used if a heavily laden Shuttle comes up without water.
For safety reasons, the new Shuttle should be designed to easily with stand a re-entry "dry" in case of catastrophic failure of the system; the extra cost/weight of a more robust design is easily offset by the reduced maintenance. Of course the compartments have a safety pressure-valve and the hull compartments and pipes are dry prior to re-entry (preventing ice blockage).
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//the new Shuttle should be designed to
withstand one or two re-entries "dry" in
case of catastrophic failure// So, a full
conventional heat-shield, then? And why
"two"? |
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Have you made a calculation of the mass
of water that would need to be vaporised? |
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original post changed to be more understandable. |
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And yes, a lightweight emergency heat shielding or more thermodynamically robust intrinsic design that would *not* have to be maintained or replaced unless there's a failure of the main system on the previous flight. |
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While true a simplistic calculation of kinetic energy vs. latent heat of evaporation yields a ridiculously large figure, I doubt that that's even close to the same order as the amount actually required. |
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Probably cheaper to carry the weight as a second layer of tiles rather than water. After all, if there's water left over I'd think you'd want to leave it in space, given how much effort you put in to getting it there to begin with. Lastly, it seems likely that skidding on a layer of water vapor would change the dynamics of reentry. |
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I keep finding a quoted mass for the Shuttle as 2,029 tonne. Ah, that includes fuel at takeoff. |
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Landing weight equals 104,000 kg = 104,000,000 grams
Specific heat of water 1 cal/degC/gram
Heat of vaporisation of water 586cal/gram
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Let's assume we start at about 7degC and heat the water up as we go in. 1 cubic metre of water will require 679 million calories to vaporise. |
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The shuttle will be travelling at about Mach 18 on re-entry, as I recall. That's about 5,940 metres per second (if we take Mach as a standard 330m/s). |
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To decelerate the shuttle to say 200m/s we have to apply 596,960,000 Nm of force. |
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You're gonna need a lot of water. |
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//You're gonna need a lot of water// |
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I did (a simplified version of) that calculation too, but there's also some other major factors; the kinetic energy transference is not simply water evaporating from 100C liquid to 100C gaseous. |
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- heating of the mass of the shuttle's skin absorbs alot of joules (which is then slowly dissipated later on)
- heating of the atmosphere directly from the skin (in low pressure areas)
- heating of atmosphere directly from the ejected superheated steam
- further heating of the already ejected superheated steam from the atmosphere. |
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Anybody got a url or cite for how many joules the current tiles ablate ? |
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This is kind of baked, but they use a solid to phase change instead of water. The old space capsule used this system. I'm sure the material used a lot more energy to phase change than water, used less weight. |
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//Anybody got a url or cite for how many joules the current tiles ablate ?//
The tiles don't ablate, they insulate. |
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the advantage of liquid over solid is the same reason as liquid-fueled rockets over solids : greater control and less susceptibility to physical defects... of course the best would be a non-viscous liquid with a very high latent heat index on evaporation, but water has the advantage of being multi-purpose, non-reactive with the atmosphere and environmentally friendly. |
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A shuttle that sweats? Nice. Too bad we can't use that heat for something. |
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