Author Topic: Heatshields for aerocapture and reenetry  (Read 2133 times)

Offline alexterrell

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Heatshields for aerocapture and reenetry
« on: 10/25/2009 03:28 PM »
What is the difference in heat shield requirements and cosntructions for different demands?

For example, in terms of Joules / Kg converted from kinetic and gravitational energy to heat:
1. LEO reentry, 7km/s -> 0, =24.5MJ/kg
2. Escape velocity reentry, 11km/s -> 0, = 60.5MJ/kg
3. Aerocapture, 12km/s -> 11km/s, = 11.5MJ/kg.
4. Aerobraking, 11km/s -> 7km/s, 26MJ/kg

I assume in all these cases most of the heat is transferred to air molecules, and most of the rest is radiated away. Only a fraction is conducted away from the heatshield.

Are the ratios similar for different types of reentry?

Could the Spacex Dragon Heatshield, designed for Case 1 above, be used for Case 4?

Can Case 2 be done as Case 4, followed by a cooling period, followed by Case 1?

Offline Danny Dot

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Re: Heatshields for aerocapture and reenetry
« Reply #1 on: 10/25/2009 08:31 PM »
What is the difference in heat shield requirements and cosntructions for different demands?

For example, in terms of Joules / Kg converted from kinetic and gravitational energy to heat:
1. LEO reentry, 7km/s -> 0, =24.5MJ/kg
2. Escape velocity reentry, 11km/s -> 0, = 60.5MJ/kg
3. Aerocapture, 12km/s -> 11km/s, = 11.5MJ/kg.
4. Aerobraking, 11km/s -> 7km/s, 26MJ/kg

I assume in all these cases most of the heat is transferred to air molecules, and most of the rest is radiated away. Only a fraction is conducted away from the heatshield.

Are the ratios similar for different types of reentry?

Could the Spacex Dragon Heatshield, designed for Case 1 above, be used for Case 4?

Can Case 2 be done as Case 4, followed by a cooling period, followed by Case 1?

If you convert to imperial for me I can help you out.  I am too busy to do the conversion that is needed for me.  I don't think metric.

Danny Deger
Danny Deger

Offline alexterrell

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Re: Heatshields for aerocapture and reenetry
« Reply #2 on: 10/26/2009 09:06 AM »
What is the difference in heat shield requirements and cosntructions for different demands?

For example, in terms of Joules / Kg converted from kinetic and gravitational energy to heat:
1. LEO reentry, 7km/s -> 0, =24.5MJ/kg = 2.65 M Calories / lb
2. Escape velocity reentry, 11km/s -> 0, = 60.5MJ/kg = 6.5 M Calories / lb
3. Aerocapture, 12km/s -> 11km/s, = 11.5MJ/kg = 1.24 M Calories / lb
4. Aerobraking, 11km/s -> 7km/s, 26MJ/kg = 2.81 M Calories / lb

I assume in all these cases most of the heat is transferred to air molecules, and most of the rest is radiated away. Only a fraction is conducted away from the heatshield.

Are the ratios similar for different types of reentry?

Could the Spacex Dragon Heatshield, designed for Case 1 above, be used for Case 4?

Can Case 2 be done as Case 4, followed by a cooling period, followed by Case 1?

If you convert to imperial for me I can help you out.  I am too busy to do the conversion that is needed for me.  I don't think metric.

Danny Deger
Not sure what the right units are but I had a go above. (Metric is so much easier because KE = 1/2 mv^2 with no constants to worry about).

Point is, return from High Earth Orbit has double the heat of return from Low Earth Orbit. So could you take the heatshield of a Dragon for example, and use it for Aerobraking HEO -> LEO. (25,000mph -> 15750mph)?

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