Author Topic: Reentry possible? (Read 3343 times)

Neil Obstat · « **Reply #20 on:** October 16, 2018, 11:03:22 AM »

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The heat shield uses a titanium skeleton that provides the interface points with the crew module and adds strength to the heat shield required for it to withstand the impact with the water at splashdown.
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Why does the heat shield need to survive impact with water at splashdown? Isn't the purpose of the heat shield to survive re-entry heat of friction with the atmosphere? When splashdown occurs, there is no more atmosphere friction to be concerned with, so why is the heat shield still important?
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Stanley N · « **Reply #21 on:** October 17, 2018, 11:27:00 PM »

Quote from: Struthio on October 13, 2018, 09:52:59 PM

Now let's descend down to sea level. Given the unrealistically high 20min or 1200s of travel time, and assuming unrealistically that braking power is constant, braking power is

P = 75GJ / 1200s = 62.5MW

The corresponding temperature (Stefan Boltzmann law) is

2854K or 2580°C.

This is, I think, the place you should look into more. You're using the equation for radiative heat transfer, as if the reentry vehicle heats up to this temperature and disperses heat by black body radiation.

The vehicle heats up from the heat generated by the bow shock (of a blunt body reentry vehicle). This happens over a large area. Heat is transferred to the vehicle mostly by convection, with some by radiation. The heat load the vehicle has to handle is only a fraction of the overall energy dissipated in losing kinetic energy - most of that energy goes to the atmosphere.

Struthio · « **Reply #22 on:** October 17, 2018, 11:56:00 PM »

Quote from: Stanley N on October 17, 2018, 11:27:00 PM

This is, I think, the place you should look into more. You're using the equation for radiative heat transfer, as if the reentry vehicle heats up to this temperature and disperses heat by black body radiation.

The vehicle heats up from the heat generated by the bow shock (of a blunt body reentry vehicle). This happens over a large area. Heat is transferred to the vehicle mostly by convection, with some by radiation. The heat load the vehicle has to handle is only a fraction of the overall energy dissipated in losing kinetic energy - most of that energy goes to the atmosphere.

I assume that the heat shield is ideal and emits all friction energy in form of radiation. Doing this, the surface of the heat shield has the Boltzmann-temperature.

Alternatively, part of the energy/power may heat the vehicle. But that would have to be a small fraction of the 62.5MW which does not really make difference.

happenby · « **Reply #23 on:** October 18, 2018, 12:22:36 PM »

Origen called the firmament “without doubt firm and solid” (First Homily on Genesis, FC 71). Ambrose, commenting on Genesis 1:6, said, “the specific solidity of this exterior firmament is meant” (Hexameron, FC 42.60). And Saint Augustine said the word firmament was used “to indicate not that it is motionless but that it is solid and that it constitutes an impassible boundary between the waters above and the waters below” (The Literal Meaning of Genesis, ACW 41.1.61).

Struthio · « **Reply #24 on:** October 18, 2018, 04:57:51 PM »

Quote from: happenby on October 18, 2018, 12:22:36 PM

Origen called the firmament “without doubt firm and solid” (First Homily on Genesis, FC 71). Ambrose, commenting on Genesis 1:6, said, “the specific solidity of this exterior firmament is meant” (Hexameron, FC 42.60). And Saint Augustine said the word firmament was used “to indicate not that it is motionless but that it is solid and that it constitutes an impassible boundary between the waters above and the waters below” (The Literal Meaning of Genesis, ACW 41.1.61).

What does that have to do with the question whether a reentry from a low orbit is possible?

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Author Topic: Reentry possible? (Read 3343 times)

Neil Obstat

Re: Reentry possible?

Stanley N

Re: Reentry possible?

Struthio

Re: Reentry possible?

happenby

Re: Reentry possible?

Struthio

Re: Reentry possible?