GDP-Light

The Grain Design Program (GDP) is a software package to design rocket motors and other gas generating devices. GDP comes in two versions. The Light version (GDP-Light) has the following features:

Capable of calculating ALL 2D-grains, like stars, moonburners, slotted grains, BATES grains, etc. Geometries are devided into 4 categories:

	Simple stars are treated analytically.
	Simple cylinders (like BATES), treated analytically.
	All other shapes are calculated graphically. The user provides a file (.pcx, .gif, or .bmp) of the grain. GDP automatically finds burning areas and calculates burnback ! This options allows full burn-back, including slivers. Even cracks can easily be drawn with a drawing program, and modeled.
	Tabular input allows grain input by entering burning area and burning volume as function of burn depth.

All images on this page can be enlarged by clicking on the image.

Modular motor configuration. Each design may consist of several segments (grains). Each grain can be selected from one of the three groups above. The screen copy below shows the main grain edit menu. In this case the rocket consists of three different segments. Detailed information of the current segment is shown together with a picture of the current design on scale.

Segment editing allows copying and modifying of all other elements already in the design. Burn-back of each segement can be carried out, before calculating the complete design. In this way each segment can be evaluated individually. The picture below shows the burn-back of a star-grain. The grain was drawn in a CAD program, and then exported to a .pcx file. Note the full burn-back, including slivers. Calculations can be interrupted (and resumed) to show the obtained segment characterists.

Propellant burn rate and thermophysical characteristics are inputted in the propellant menu. The temperature sensitivity is used to evaluate motor performance at different ambient temperatures. Different burn rate equations can be used in different pressure intervals (e.g. for slope-breaks in the burn-law).

The nozzle is defined by a diameter or effective surface. Other input values may include expansion ratio, divergence angle, efficiency, discharge coefficient and diaphragm burst pressure.

Ambient conditions are given by ambient pressure and temperature.

After all data is fed into GDP, the program calculates the burn-back of the motor. Calculation results are presented as graphs, or summarized in a report file. The plots may contain properties from the following list:

	Pressure
	Mass flow
	Thrust
	Thrust coefficient
	Nozzle exit pressure
	Total impulse
	Expelled mass
	Burn area
	Burn rate
	Free volume
	Specific impulse
	Total impulse

The x-axis is usually time, but also may be one of the quantities of the above list. A typical example is shown below.

	User can select between SI or US input and output at any time.
	Export graphics to printer or file. Text output of all input and calculated data to printer or file.
	Graphical user-interface.
	Context sensitive help.
	Note that in GDP-Light the total propellant mass is limited to 150 kg (this eliminates an export license).

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