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Space Shuttle, thermal energy transfer, book makes no sense

  1. Oct 29, 2015 #1
    1. The problem statement, all variables and given/known data
    Space shuttle enters the atmosphere.
    (i) What happens to the transferred energy?
    (ii) how do the high temperatures generated in the shuttle enters the Earth atmosphere relate to the material used for the underside of the shuttle surface? Why is the underside not made from aluminium or iron?

    2. Relevant equations
    Work and power chapter in the book.

    3. The attempt at a solution
    (i) THIS IS MY ANSWER : The energy is created by friction from the surrounding gases in the atmosphere. Energy is also transferred to same gases in the atmosphere. Some energy is absorbed by the tiling on the on the under-surface of the shuttle.

    BOOK ANSWER:Series of the manoeuvres used before landing to get rid of excess energy.

    The book answer makes no sense to me.

    (ii)
    The tiling under the shuttle will be matte black and a poor conductor of thermal energy.

    A black surface emits thermal (infrared) radiation well so the heat will be transferred to the atmosphere. A black body also absorbs radiation but because it is a poor conductor it should emit more than it absorbs thereby keeping the shuttle cool.

    A steel or iron under-surface is not used because metallic structures will conduct thermal (infrared) radiation and become very hot and may melt. Metallic structure will not emit radiation.

    MY OWN QUERY: I'm confused why metallic structures do not emit heat radiation when they can absorb it (and get hot). Isn't the heat behaving like electricity i.e. electricity is conducted through metal easily and if someone touches the metal they absorb the electricity that has been emitted (and they get a shock). I know I'm wrong somewhere in this statement but can't see quite where so I would be grateful if someone could clarify what I should be thinking. Thank you
     
    Last edited: Oct 29, 2015
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  3. Oct 29, 2015 #2

    HallsofIvy

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    "Series of the movers"? Does your text really use that phrase? Perhaps a "series of moves" was intended- the shuttle dips down into the atmosphere, so that some speed is converted to heat, then back out of the atmosphere to radiate that heat into space, back into the atmosphere, etc.
     
  4. Oct 29, 2015 #3

    SteamKing

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    While most metals are good conductors of heat, that does not necessarily imply that metals will absorb and then re-radiate heat absorbed with equal facility, such that the temperature of the metal does not change.

    In particular, the radiation of heat from the metal back into the surroundings is proportional to the fourth degree of the absolute temperature of the metal (T4) and to an elusive quantity called the emissivity, which varies according to certain physical properties of the material doing the radiating. When the temperature of the metal is almost identical to the temperature of its surroundings, very little heat transfer by radiation occurs.

    https://en.wikipedia.org/wiki/Heat_transfer

    The reason metal is used in most structures is that it provides a high strength to mass ratio. However, as the temperature of metals increases, the strength of the material is also reduced. If the strength of a metal structure is reduced below a certain point, failure of the structure can be expected. That's why metal structures and parts exposed to high temperature environments are over-designed and cooled where possible, to insure that failure will not occur when the local temperature of the metal is elevated.

    Most structural steels, for example, lose a lot of their strength if the temperature goes much above 1000° F (approx. 550° C), unless special and expensive alloys are used. Aluminum is even more susceptible to failure at high temperature because its melting point (660° C) is much lower than that of iron (1538° C), the primary constituent of steel.
     
  5. Oct 29, 2015 #4
    My mistake. Was meant to be series of manoeuvres used before landing to get rid of excess energy.
     
  6. Oct 29, 2015 #5
    Thank you so far. So was my answer to part (i) acceptable? The book answer about "manoeuvres" I think is off the plot considering its a High School Physics book and the chapteris about work & power and the only formula they've mentioned so far is W=Fd
     
  7. Oct 29, 2015 #6

    SteamKing

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    Well, when the Shuttle re-enters the atmosphere, it is an unpowered glider traveling at nearly 18,000 mph. If you haven't guessed yet, that's waaaaay too fast to land. Since the speed of the shuttle must be reduced to about 200 mph or thereabouts to land safely like a conventional aircraft, the Shuttle must glide a long distance so that atmospheric drag can bleed off the kinetic energy produced by the immense speed of the craft. Executing a series of maneuvers while airborne further reduces the speed of the craft without extending the gliding distance. It is important that the Shuttle reach approximately the proper landing speed at approximately the right location, or a crash could occur, if the shuttle does not retain enough energy to approach the landing field.

    https://en.wikipedia.org/wiki/Space_Shuttle#Re-entry_and_landing

    The energy which is created by friction with the atmosphere will be created regardless, due to the speed of the Shuttle on re-entry, and must be dissipated, lest the Shuttle burn up, like Columbia did in 2003.
     
  8. Oct 29, 2015 #7

    DrClaude

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    Note also that friction is not the main source of the heat produced when the shuttle reenters the atmosphere, as https://www.quora.com/Why-does-a-spacecraft-heat-up-during-reentry [Broken]
     
    Last edited by a moderator: May 7, 2017
  9. Oct 29, 2015 #8
    The book answer is nonsense.

    The banking turns are not to get rid of the kinetic energy directly, but to control the rate of descent.
    The space shuttle is designed to fly with a 40 degree nose up attitude. If the shuttle would fly with wings level all the time, it wouldn't descend fast enough.
    By banking up to 70 degrees the upward component of the drag force will reduce and the shuttle will descend faster. This will of course increase the drag, and decrease the kinetic energy of the shuttle faster.

    The tiles have to be very light, withstand high temperatures and be a very poor conductor of heat.
    Any metal would be too heavy and conduct heat too well.
     
  10. Oct 30, 2015 #9
    So this is my final answer i think after taking information from all your posts. Comments welcome

    (i) What happens to the transferred energy?
    The energy (that is in part created by friction from the surrounding gases in the atmosphere) is transferred to same gases in the atmosphere. Some energy is absorbed by the tiling on the on the under-surface of the shuttle (so they will become hot).

    When re-entering the the atmosphere, the shuttle will be traveling very fast (18,000 mph). So to reduce its energy (i.e slow it down to a manageable landind speed of 200mph)
    the Shuttle must glide a long distance around Earth so that atmospheric drag can bleed off the kinetic energy. By performing a series of maneuvers while airborne the pilots can reduce the kinetic energy (and hence its speed further). So the transferred energy is lost to the atmosphere



    (ii) How do the high temperatures generated in the shuttle enters the Earth atmosphere relate to the material used for the underside of the shuttle surface? Why is the underside not made from aluminium or iron?

    The tiling under the shuttle will be matte black, light weight and a poor conductor of thermal energy. A black surface emits thermal (infrared) radiation well so the heat will be transferred to the atmosphere. A black body (the tiles) also absorbs radiation but because it is a poor conductor it should emit more than it absorbs thereby keeping the shuttle cool. A steel or iron under-surface is not used because metallic structures will conduct thermal (infrared) radiation and become very hot and may melt. Metallic structure are also heavy.
     
  11. Oct 30, 2015 #10

    rcgldr

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    Summary: Most of the heat during re-entry is due to compression, not friction.

    Almost all of the kinetic and gravitational potential energy is converted into heating of the atmosphere. Some of if it is converted into mechanical energy of the air. The downwards component of force eventually results in a impulse imparted through the atmosphere onto the ground. The horizontal component of force would result in a slight change in wind speed.

    Wiki article about the Space Shuttle thermal protection system:

    http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system

    The 40 degree nose up attitude was used during initial re-entry to increase braking and reduce re-entry heating. The S turn maneuvers were done while still at 40 degree pitch up attitude and high speed, with steeply banked turns (70 degrees) to allow the shuttle to continue to descend in spiral arcs rather than maintain or perhaps increase altitude due to the 40 degreee nose up attitude. The attitude was kept at 40 degrees pitch up (nose up relative to flight path) during these turns, so no additional drag or g forces were produced by the S turn maneuvers, other than the fact that the atmoshpere denisty increases as the shuttle descends. So the purpose of the S turns was to reduce gravitational potential energy (decrease altitude) while continuing to reduce kinetic energy due to drag.

    Once the shuttle goes into a traditional glide mode, it needs to be significantly nose down. Even at sub-sonic speeds, during final approach, it's best lift to drag (glide) ratio is only about 4.5 to 1. It only noses up just before landing to reduce decent rate (and also forwards speed) for touch down. Wiki article:

    http://en.wikipedia.org/wiki/Space_Shuttle#Re-entry_and_landing
     
    Last edited: Oct 31, 2015
  12. Oct 31, 2015 #11
    Thanks for all the replies everyone. Please can I say that I've been posting on this forum quite often and find it difficult to get an answer at my level of understanding. I just have to keep an eye on the replies and hope among the paragraphs is a sentence that I can understand. This is NOT a criticism ... the posters are just gifted at physics and what you write makes sense to physicists. I'm only High School physics level


    I posted this earlier:

    (i) What happens to the transferred energy?
    The energy (that is in part created by friction from the surrounding gases in the atmosphere) is transferred to same gases in the atmosphere. Some energy is absorbed by the tiling on the on the under-surface of the shuttle (so they will become hot).

    When re-entering the the atmosphere, the shuttle will be traveling very fast (18,000 mph). So to reduce its energy (i.e slow it down to a manageable landind speed of 200mph)
    the Shuttle must glide a long distance around Earth so that atmospheric drag can bleed off the kinetic energy. By performing a series of maneuvers while airborne the pilots can reduce the kinetic energy (and hence its speed further). So the transferred energy is lost to the atmosphere

    (ii) How do the high temperatures generated in the shuttle enters the Earth atmosphere relate to the material used for the underside of the shuttle surface? Why is the underside not made from aluminium or iron?

    The tiling under the shuttle will be matte black, light weight and a poor conductor of thermal energy. A black surface emits thermal (infrared) radiation well so the heat will be transferred to the atmosphere. A black body (the tiles) also absorbs radiation but because it is a poor conductor it should emit more than it absorbs thereby keeping the shuttle cool. A steel or iron under-surface is not used because metallic structures will conduct thermal (infrared) radiation and become very hot and may melt. Metallic structure are also heavy.

    Can someone just mark it / comment on what I've deduced so far. Thanks in advance for your generosity
     
  13. Oct 31, 2015 #12

    rcgldr

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    Most of it heats up the atmosphere, a small part of it goes into mechanical energy of the air. The shuttle also gets hotter, but eventually that heat also goes into the atmosphere (some of it after landing).

    Holding the pitch attitude at 40 degrees (nose up relative to flight path) provides high drag and less overall heating. The maneuvers, four S turns with about 70 degree banking, are also done with pitch attitude at 40 degrees, so the g forces in the turns and drag remain about the same, but the banked turns allows the shuttle to continue downwards in spiral arcs rather than holding at level flight or possibly climbing, so the point of the maneuvers is to lower the altitude and descend into higher density air, which produces more drag for a given speed. During the S turn maneuves, the decrease in gravitational potential energy corresponds to increased speed and kinetic energy compared to level flight, but any increase in speed would produce more drag. The drag is sufficient that the speed continues to be decreased during the S-turns, but at a slower rate than level flight.

    Wiki article:

    http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system
     
    Last edited: Oct 31, 2015
  14. Oct 31, 2015 #13
    Thanks rcgldr.

    About the info in the link:
    http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system

    Is there a more generic, non-specific answer to my question? Just one or two sentences.Its all tough reading.

    I said this earlier:

     
  15. Oct 31, 2015 #14

    Mister T

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    Terminology nightmare. The shuttle collides with air molecules. When a fast-moving billiard ball collides with a slow-moving one, the fast one loses energy and the slow one gains energy.

    In the same way the shuttle loses kinetic energy and the molecules of the air and the shuttle underbelly gain kinetic energy.

    Macroscopic kinetic energy (mechanical energy) is converted to microscopic kinetic energy (internal energy).
     
  16. Oct 31, 2015 #15
    Fantastic. So my answer to the question at the top (Space shuttle enters the atmosphere (i) What happens to the transferred energy?) will now be:

    "The kinetic energy of the space shuttle will be transferred to the air molecules so will eventually slow down to a safe landing speed. As the shuttle loses energy, the air molecules will be gaining energy when the are hit by the shuttle in the same way that "when a fast-moving billiard ball collides with a slow-moving one, the fast one loses energy and the slow one gains energy". The air molecules gain heat and speed".


    As the shuttle enters the atmosphere the it gets hot on the under-surface. WHY(??) when we've just said that the energy is being transferred to the air molecules?
     
  17. Oct 31, 2015 #16

    Mister T

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    I thought you were trying to understand an answer you had already submitted, not formulate a new one. I wouldn't have given you the answer if I'd have known I was writing your answer for you.

    Not we, me. I said that, not you. Why do you think the tiles are needed?
     
  18. Nov 1, 2015 #17
    Your're helping me learn Mister T. I think I've tried enough trying to decipher an answer from all the posts. Most posters on this forum talk in riddles, trying to get you to work the answer out. Sometimes one can't do this and just need a helping hand. Mister T thanks for your post that helped me to understand

    Yes YOU indeed said that, alone. I said "we" in haste ..... I was just in the moment .... and thought I was doing the thinking .... but you correctly point out the thoughts were all yours. Credit to you Sir .... you have a fine mind.

    Now about the tiles .... they exist to absorb the heat transferred to them when they collide with the air molecules that have become hot from the energy they gained when the shuttle collided with them
     
  19. Nov 1, 2015 #18

    JBA

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    There is a lot of discussion included in the above posts about how the heat is created; but, if you review your problem statement, you will find that is not one of the questions you are being asked to discuss. You have developed a reasonable response to the problem questions, so I suggest you address only those issues in your response; plus, a brief statement about the actual purpose of the maneuvres including a verifying reference in that part of your response.
     
  20. Nov 1, 2015 #19

    Mister T

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    What do you mean by a molecule "becoming hot"? And when you say "absorb heat" remember that heat is transferred only when there's a temperature difference.

    When something becomes hot it's because it has more internal energy. Heat is not the only way to increase the internal energy. (And as an aside totally irrelevant to this discussion, an increase in internal energy doesn't necessarily mean there's an increase in temperature).
     
  21. Nov 1, 2015 #20

    Mister T

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    I agree.

    Do you now see how those maneuvers increase the effect you talked about in your original answer? It was not my intention to get you to change your answer, only to get you to see the connection between your answer and the book's answer.

    You do still need to address why tiles are used instead of aluminum plates. Do it in a simple and direct way. Turn in your answer, not mine. Yours will look like it came from you. Mine will look like it came from someone else.
     
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