Rocket Propulsion

Ft

=

mv

So:•F = engine thrust t = time to burn fuel•m = mass of fuel burnedv = exhaust gas velocity

Which Rocket Accelerates faster?A B

Demo – F14

Rocket PropulsionExample 1: A rocket burns fuel at a rate of 1.2 kg/s, with an exhaust velocity of 1250 m/s. What thrust does it develop? (1500 N)

Rocket PropulsionExample 2: A model rocket engine develops 12.0 N of thrust with an exhaust velocity of 718 m/s. What is its fuel burn rate?What is the rocket’s initial acceleration if it has a mass of 238 g? (0.0167 kg/s, 40.6 m/s/s)

A certain rocket engine burns .0352 kg of fuel per second with an exhaust velocity of 725 m/s. What thrust does it generate?

25.5 N

The Saturn V’s first stage engines generated 33.82 MN of thrust (33.82 x 106 N) with an exhaust velocity of 2254.7 m/s. What was its fuel burn rate?

15,000 kg/s

A D12 engine generates 11.80 N of thrust burning fuel at a rate of .0143 kg/s. What is the exhaust velocity? If the rocket has a mass of 139 grams, what is the initial upward acceleration?

825. m/s, 75.1 m/s/s

Rocket Propulsion

© Microsoft Encarta

Solid Fuel Engine:

Rocket Propulsion

© Microsoft Encarta

Solid Fuel Engine: Thrust of the Engine:F = mv t

•Big v means big F •Big v also means lots of pressure•Danger Will Robinson!

© Estes

Lookout!m = .5 kg, Ft = 20 NsFt = m v20 Ns = .5kg vv = ? (x 2.237 for mph)

© Estes

Rocket Propulsion

© Microsoft Encarta

Liquid Fuel Engine:

•How do you keep it from tipping?•Why the “steam” coming off?

Saturn V Animation (Flash in IE)

Saturn V Rocket - Apollo missions

First stage

Second stage

Third stageL.E.M

Command Module

Escape Tower

Ion Propulsion systems Low thrust/high Δv20-50 km/s exhaust velocityDawn

Gridded Xenon ion drive (Like Dawn has)

where’s the power come from?

The Dawn spacecraft has a mass of about 770 kg, and an ion drive with an exhaust velocity of 35,000 m/s that generates about 92 millinewtons of thrust. (.092 N)

How what is the “burn” rate for this engine? (2.6E-06 kg/s)

How big a change in velocity can 50 kg of fuel give the spacecraft?The final mass will be 770 – 50 = 720 kg, on the average the spacecraft will have a mass of 745 kg (2350 m/s)