AEM_360_Homework#5

AEM 360 ASTRONAUTICS Homework #5 – Rockets Name: none 1. Circle the most correct answer for each question. 2. Provide a reference from the course text (chapter and page number). For questions involving calculations, please show your work. 1. ( 8 points ) A 1.5 m 2 spacecraft radiator with an emissivity, ε, of 0.75 ejects 110 joules of heat per second (i.e, watts). What temperature must it be in degrees Celsius? Given : Stefan-Boltzmann constant, σ = 5.67 × 10 –8 W / m 2 K 4 ° C = K - 273.15 a. -59.72° C b. 203.78° C c. -69.37 K d. -69.37° C Reference: Ch. 13, Pg. 469 2. (4 points) Heat pipes are a means of internal active thermal control that provide a heat conduction path inside a spacecraft. They transfer heat based on the a. latent heat of fusion, the principle of storing additional heat in a liquid as it changes phase to a vapor. b. latent heat of vaporization, the principle of storing additional heat in a liquid as it changes phase to a vapor. c. latent heat of fusion, the principle of storing additional heat in a solid as it changes phase to a liquid. d. latent heat of vaporization, the principle of storing additional heat in a liquid as it changes phase to a solid. 1 E = 110 1.5 = 73.33 73.333 = ( 0.75 ) ( 5.67 ∗ 10 − 8 ) ( T + 273.15 ) 4 T =− 69.37 o C

Reference: Ch. 13, Pg. 472 3. (5 points) Space Shuttle space suits operated at a pressure of only 29.6 kPa (4.3 psi). Therefore, at 12 hours before extravehicular activity (EVA, or spacewalk), air pressure inside the Shuttle was lowered from its normal near-sea level pressure to 70.3 kPa (10.2 psi) to avoid ________________; the EVA astronauts also had to breathe pure oxygen for 3-4 hours to purge nitrogen from their bodies to avoid nitrogen bubbles in the blood, which can cause_______________. a. decompression problems ; the bends. b. depression problems; the bends. c. compression problems; the leans. d. decompression problems; the leans Reference: Ch. 13, Pg. 474 4. ( 7 points ) A cylindrical rod 10 m long at room temperature, 21° C, has a coefficient of thermal expansion, α, of 2.22 x 10 -7 /°C . What will its change in length, ΔL, be at 50° C? What will the strain, ε, be? a. ΔL = 6.438 x 10 -5 m; ε = 6.438 x 10 -6 b. ΔL = -8.795 x 10 -8 m; ε = -8.795 x 10 -7 c. ΔL = 8.795 x 10 -5 m; ε = 8.795 x 10 -6 d. ΔL = -6.438 x 10 -5 m; ε = -6.438 x 10 -6 Reference: Ch. 13, Pg. 487 5. (5 points) Which statement about the launch vehicle acceleration profile shown below is false ? a. The two peaks on the left indicate dual solid rocket strap-on boosters. b. The long red line from before 5.0 min to after 15.0 min represents a relatively low thrust third stage. c. The maximum g-loading on the vehicle is more than 4.0 g’s d. The two peaks on the left indicate increasing acceleration due to decreasing propellant mass with near constant thrust. 2 ΔL = ( 10 ) ( 2.22 ∗ 10 − 7 ) ( 50 − 21 ) = 6.438 ∗ 10 − 5 m ε = 6.438 ∗ 10 − 5 10 = 6.438 ∗ 10 − 6