MAE 4262: ROCKETS AND MISSION ANALYSIS Rocket Equation and Losses Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk 1 ROCKET EQUATION: IMPORTANT TRENDS 2 TYPICAL V MISSION REQUIREMENTS
3 http://www.strout.net/info/science/delta-v/intro.html V CAPABILITY FOR VARIOUS ROCKETS REF: Space Propulsion Analysis and Design, by Humble, Henry and Larson 4 TYPICAL PERFORMANCE PARAMETERS (T and Isp) GRAVITY Remember that gravity on Earth (~ 9.81 m/s2) may be calculated fundamentally
Average radius of the Earth ~ 6,378 km or 3,963 miles Mass of the Earth ~ 5.9742x1024 kg F mg GMm R2 Re g g e Re h 2
Some typical values for Earth: High power amateur model rocket ~ 100,000 ft, 30.5 km, 19 miles g/ge = 99% Shuttle in LEO (altitude of 300 km, 186 miles) g/ge = 91% Satellite in GEO (altitude of 42,000 km, 26,000 miles) g/ge = 1.7% Note that the radius of the moon is about 1,737 km and mass is 7.36x1022 kg So g on the surface of the moon is about 1.62 m/s2 6
COMPARISON OF GRAVITY, DENSITY AND PRESSURE VERSUS ALTITUDE 1.00 Gravity Density Pressure Gravity 0.90 Percent of Sea Level Static Value 0.80 0.70
0.60 0.50 0.40 Pressure 0.30 Density 0.20 0.10 0.00 0 100
200 300 400 500 600 700 800 900
1000 Altitude, km 7 COMPARISON OF GRAVITY, DENSITY AND PRESSURE VERSUS ALTITUDE 1.00 Gravity 0.90 Density
Percent of Sea Level Static Value 0.80 0.70 Pressure 0.60 Shuttle 0.50 0.40 0.30 LEO
0.20 Gravity Density Pressure 0.10 0.00 1 10 100 Altitude, km
1000 8 WHAT IS ACTUAL SCALE OF ORBITS? NOT EVEN CLOSE TO SCALE WHAT IS ACTUAL SCALE OF ORBITS? GEO EARTH LEO, 300 km
WHAT IS ACTUAL SCALE OF ORBITS? GEO LEO EARTH TYPICAL DRAG VARIATION FOR ROCKETS 12 Variation of lift and drag coefficient with Mach number of V-2 rocket missile based on body cross-sectional area with jet off 13
DRAG: SUPERSONIC MISSILE EXAMPLE 14 COMMENTS: LAUNCH FROM SURFACE OF EARTH To get to orbit (or to escape), direction of travel must be parallel to Earths surface (not perpendicular) We launch vertically off the surface of the Earth, WHY? Gravity
When rocket is vertical, gravity is acting against T and V Drag V2 dependence: Drag as rocket accelerates Large effect in lower atmosphere Acceleration of vehicle is almost constant even though mass is changing Density dependence: very rapidly in atmosphere (/S.L. ~ 1% at 100,000 ft) All rocket pass through condition of maximum dynamic pressure (MAX Q) Many rockets stay vertical through this part Get through atmosphere as quickly as possible BUT before rocket really starts to speed up 15
COMMENTS: LAUNCHERS Need certain velocities to get to space (and stay in space), escape, insertion, transition velocities, etc. give V requirements Dont want to carry fuel (heavy fuel is working against you) Burn fuel early in flight high accelerations, V2 Atmosphere is counter argument: drag, dynamic pressure
Why not launch horizontal? Less gravity loss Drag loss is high, more time in atmosphere Lots of structural stress Launch might look different on moon Vertical launch segment: Get out of dense atmosphere quickly, but still at relatively low speed Dont spend too much time here (vertical segment contributes nothing to eventual vertical orbital velocity) Highest gravity losses, but sustain them to get lower density then really increase V 16
Variation in air density (), velocity (V), altitude (h), and dynamic pressure (q) during a Space Shuttle launch 17