CL and CD are lift and drag coefficients, respectively. For airplanes and winged missiles the area A is understood to mean the wing area. For wingless missiles or space launch vehicles it is the maximum cross-sectional area normal to the missile axis. The lift and drag coefficients are primarily functions of the vehicle configuration, flight Mach number, and angle of attack, which is the angle between the vehicle axis (or the wing plane) and the flight direction. For low flight speeds the effect of Mach number may be neglected, and the drag and lift coefficients are functions of the angle of attack. The variation of the drag and lift coefficients for a typical supersonic missile is shown in Fig. 4-3. The values of these coefficients reach a maximum near a Mach number of unity. For wingless vehicles the angle of attack a is usually very small (0 < a < Io). The density and other properties of the atmosphere are listed in Appendix 2. The density of the earth's atmosphere can vary by a factor up to two (for altitudes of 300 to 1200 km) depending on solar activity and night-to-day temperature variations. This introduces a major unknown in the drag. The aerodynamic forces are affected by the flow and pressure distribution of the rocket exhaust gases, as explained in Chapter 18.
For space launch vehicles and ballistic missiles the drag loss, when expressed in terms of Aw, is typically 5 to 10% of the final vehicle velocity increment. This relatively low value is due to the fact that the air density is low at high altitudes, when the velocity is high, and at low altitudes the air density is high but the flight velocity and thus the dynamic pressure are low.
Gravitational attraction is exerted upon a flying space vehicle by all planets, stars, the moon, and the sun. Gravity forces pull the vehicle in the direction of the center of mass of the attracting body. Within the immediate vicinity of the earth, the attraction of other planets and bodies is negligibly small compared to the earth's gravitational force. This force is the weight.
If the variation of gravity with the geographical features and the oblate shape of the earth are neglected, the acceleration of gravity varies inversely as the square of the distance from the earth's center. If R0 is the radius of the earth's surface and g0 the acceleration on the earth's surface at the earth's effective radius R0, the gravitational attraction g is
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What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.