Atmospheric and Aerodynamic Factors
This is an interactive program in which you can investigate changes in the atmosphere and their effects on aerodynamic variables. It uses mathematical models of the standard atmosphere of the Earth and Mars. You can find the equations for the standard Earth atmosphere on this website in both English units and metric units. Similar information is available on the Martian atmosphere. Based on your input velocity, the program also calculates the Mach number, dynamic pressure, and stagnation, or total temperature on your rocket. The stagnation temperature is the temperature of the airflow at a stagnation point, such as the leading edge of the nose cone.
Please note: the simulation below is best viewed on a desktop computer. It may take a few minutes for the simulation to load.
Properties of the Atmosphere
The pressure, temperature, and density of the atmosphere constantly change. At any one time, there are great variations in the properties of the atmosphere, depending on location around the planet and height above the surface of the planet. The mathematical models used in this simulator show an average variation of properties of the atmosphere at various heights, but not at various locations. The simulator will not predict the temperature or pressure at any single location at any time. But it will help us understand the relations among the values of a given variable at different heights. The simulator can also demonstrate the relative magnitude of the variables on Earth and Mars.
The simulator is divided into three main sections:
- On the left is the graphic showing the altitude of interest and the velocity of your rocket. You can set the altitude by clicking on the rocket image, holding the mouse button down, and moving the rocket to a new location. The altitude roughly corresponds to the base of the rocket image. The velocity is set by the slider at the left. Click on the yellow bar and slide it to your desired velocity.
- At the upper right are the input selection buttons and text fields. You can choose to look at rockets on Earth or Mars, and you can display the input and output in either English or metric units. You can also input desired values of altitude and velocity using the white input boxes. Simply backspace over the current value, enter a new value, then hit Enter to send the value to the program.
- The lower right portion of the simulator provides output information. You can display either the temperature, pressure, density, speed of sound, dynamic pressure, force ratio, Mach number, or total temperature on your rocket in the output box. Output gauges also display the atmospheric temperature and pressure. The speed of sound depends on the type of gas in the atmosphere (nitrogen and oxygen for the Earth and carbon dioxide for Mars) and on the square root of the temperature of the gas. The dynamic pressure depends on the gas density and the square of the velocity and is an important design constraint on full-scale rockets. You can make a comparison of the aerodynamic force generated on a rocket at two altitudes. The force ratio displayed here compares the aerodynamic force generated by a given rocket design, at the specified velocity, at the selected altitude (and the planet) to the force generated by the same rocket, at the same velocity, at sea level on the Earth. You can compare the Mach number of a rocket at two altitudes or on different planets. The Mach number is computed at the specified altitude and velocity. Since the speed of sound depends on the temperature and the gas, you will note some important differences in Mach number. As the Mach number gets closer to (or exceeds) one, compressibility effects, like shock waves and wave drag, become more important to the rocket. Finally, the program determines the stagnation, or total temperature, which occurs on the nose of your rocket. The total temperature depends on the local, atmospheric, static temperature and the velocity of the rocket.