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Thread: What mass to weight ration would create unproblematic heat, on re-entry?

  1. #1
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    What mass to weight ration would create unproblematic heat, on re-entry?

    Say, a large plastic bubble, in the order of 20-100m diameter..

    And what type of plastic could be used, and would it, or could it be coated in hear resistant material..of a thin nature..?
    Formerly Frog march.

  2. #2
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    Quote Originally Posted by WaxRubiks View Post
    Say, a large plastic bubble, in the order of 20-100m diameter..

    And what type of plastic could be used, and would it, or could it be coated in hear resistant material..of a thin nature..?
    At any given elevation, the weight of a body is mass times gravitational acceleration at that elevation. Thus the mass to weight ratio will be independent of the size, mass, density, etc.

    My educated guess is that's not what you meant. Is that correct? If so, perhaps you could revise your choice of words.

    In principle, if I am not mistaken, a large body of ultra-low mass could be gently slowed down by the upper wisps of atmosphere, and perhaps settle toward the Earth without being scorched. I have no means of calculating the quantitative details. If the density is low enough it will float at a height where the air is at the same density.

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    Off topic: I'm glad I'm not the only one who types "ration" when I mean "ratio".
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  4. #4
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    These inflatable re-entry systems were all the rage in the 1960s.
    FIRST and MOOSE and SAVER will give you an idea of the sort of things considered in this category.

    Grant Hutchison
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    Oh, and take a look at this JPL document (50KB pdf) on the use of ballutes for aerocapture.

    Slow yourself in the outer edges of the atmosphere, ditch the ballute and then Kittinger down from there.

    Grant Hutchison
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    Quote Originally Posted by grant hutchison View Post
    Oh, and take a look at this JPL document (50KB pdf) on the use of ballutes for aerocapture.

    Slow yourself in the outer edges of the atmosphere, ditch the ballute and then Kittinger down from there.

    Grant Hutchison
    I applaud you, sir, for the use of "Kittinger" as a verb.

    I'm not entirely clear whether the OP was referring to reentry from orbital velocity or just straight down. The latter is far easier.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

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    Quote Originally Posted by Trebuchet View Post
    I applaud you, sir, for the use of "Kittinger" as a verb.
    I originally wrote kittinge, that being what a kittinger does, but decided it was a little obscure.

    Grant Hutchison
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  8. #8
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    I wonder if there is a way to slow without much in the way of heating at all.

    The idea of a backspun flyby rotorvator--as part of an asteroid bola--two bodies orbiting--one with a tail that back spins down.

    There a soft drop or skyhook up is possible.

    Or, if the tether very strong and the mass not large, some structure below the ocean could open and the drag on the body felt strongly--but not enough time for heating. Trying to find a way to avoid heat shields and rockets altogether at some point.

  9. #9
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    I had the idea of a giant re-entry bubble from reading about this:

    Japanese scientists and origami masters considered in 2008 launching a flotilla of paper planes from space.[1] The launch was tentatively slated for 2009[2] from the International Space Station[3] 250 miles above Earth. However, the planes' developers, Takuo Toda (see paper plane world records) and fellow enthusiast Shinji Suzuki, an aeronautical engineer and professor at Tokyo University, postponed the attempt after acknowledging it would be all but impossible to track the planes during their week-long journey to Earth, assuming any of them survived the searing descent. The developers continue, in 2009, with hopes that China or Russia will back further efforts on the project.[4]
    Some 30[3] to 100[4] planes had been considered to make the descent, each gliding downward over what was expected to be the course of a week to several months. If one of the planes survived to Earth, it would have made the longest flight ever by a paper plane, traversing the 250 mi./400 km. vertical descent. In a test in Japan in February 2008, a prototype about 2.8 inches long and 2 inches wide survived Mach 7 speeds and temperatures reported to be 200C in a hypersonic wind tunnel for 10 seconds. Materials designed for use in conventional reentry vehicles, including ceramic composites, withstand temperatures on the order of 2200C.[5] The 30 cm planes were to have been made from heat-resistant paper treated with silicon.[4]
    As the Japanese/JAXA project was outlined, scientists would have had no way to track the airplanes or to predict where they might land; and as 70% of the Earth's surface is covered in water, the craft would have anticipated a wet reunion with the planet. Each plane, however, would have borne a request in several languages asking its finder to contact the Japanese team. Should one of the airplanes thus have made its way home, its journey would have helped to demonstrate the feasibility of slow-speed, low-friction atmospheric reentry. Critics have suggested that even a successful demonstration would lack probative impact beyond the realm of diminutive sheets of folded paper—they can only fall.[6] Supporters countered that the broadening of knowledge was justification enough.
    https://en.wikipedia.org/wiki/Paper_...hed_from_space

    If there were a reward for returning the paper aeroplane then they might get a few back.

    3/10 of the world is land, so release a hundred planes and 30 should end up on land.
    Formerly Frog march.

  10. #10
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    Quote Originally Posted by grant hutchison View Post
    These inflatable re-entry systems were all the rage in the 1960s.
    FIRST and MOOSE and SAVER will give you an idea of the sort of things considered in this category.
    Nice. I don't remember seeing FIRST before. I do remember the Paracone concept, which wasn't an inflatable, but was similar to these with a large surface area for emergency reentry.


    Quote Originally Posted by grant hutchison View Post
    Slow yourself in the outer edges of the atmosphere, ditch the ballute and then Kittinger down from there.
    Or perhaps one could Gagarin down. Gagarin only parachuted from 20,000 feet, but it was parachuting from a vehicle that had actually been in orbit, and the Vostok doesn't seem that far from some of these concepts.

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