The Restrictions File

The restrict.par file contains all restrictions except the Star Sensor 1.3 and the High-Gain Antenna down-link restrictions. Except for the first line, these restrictions may be entered in any order. The first line, however, must always be the Monitoring star sensor restriction 2.5. A maximum of twenty lines will be read from this file by uvplot. The contents of restrict.par as supplied with the distribution disk are shown in Table 5. There are three basic types of restrictions which may be defined in restrict.par, which may be seen in this Table:

  
Table 5: Contents of the restrict.par file used in uvplot, ground and allsky

1) ANGLES BETWEEN A GIVEN VECTOR AND THE SUN, MOON, AND EARTH VECTORS

The first three lines are examples of the simplest form of restriction, that of a vector in the satellite frame being required to exceed (or be within) a given angle with the vectors pointing to the sun, moon, or earth. This type of restriction requires only one line to define. The first three numbers in the line are the coordinates of the restriction vector, in the satellite frame (see Figure 1), and the next three numbers contain the minimum angles allowed between that vector and the sun, moon, and earth. The restriction vector is always a unit vector. For example, the first line specifies that the x-axis of the satellite must be pointing at least 60 away from the edge of the sun disk, at least 20 away from the edge of the moon disk and at least 30 away from the earth disk. The second line is the restriction that the z-axis of the satellite must be pointing at least 100 away from the sun.

If a restriction is such that the vector must lie within a certain number of degrees of a celestial body (as is the case for the sun for power production, for example), the specified angle is negative. For example, if instead of requiring that the z-axis be pointing at least 100 away from the sun, it were required that the z-axis were pointing at most 100 away from the sun, this line would have been entered:

0 0 1 100 0 0

2) PROJECTION OF A GIVEN VECTOR ONTO A SPECIFIED PLANE

The fourth and fifth lines of Table 5 comprise an example of a restriction involving a projection. This type of restriction is defined using two lines. The first three numbers of the first line indicate the principle plane onto which a vector is to be projected. These numbers may be either 0, 1, or 0.5. 0 indicates that the projection plane does not contain that component, whereas 1 indicates that it does. 0.5 indicates that the projection plane in that component is a semi-plane, either positive or negative. For example, line four specifies that the projection plane is the y-z plane, whereas line six specifies that the projection plane is the x-z semi-plane with z<0. The next three numbers of the first line indicate which of the vectors - sun, moon, or earth - is to be projected onto the specified plane. These numbers may be either a 0 (do not project) or a 1 (do project). The seventh column is a flag indicating the type of restriction being specified, and must be a 1. The first three numbers in the second line (for example, line 5 in Table 5) are the components of the vector, in the satellite frame, which is to be compared with the projected vector. The next three numbers of this second line contain the minimum permitted angles. For example, the restriction outlined in lines four and five of this file specify that the angle between the z-axis of the satellite and the projection onto the y-z plane of the vector pointing from the satellite to the sun must exceed 145.

3) COMPARISON OF A VECTOR WITH A PLANE

The third type of restriction involves the comparison of a vector with a specified plane in the satellite frame of reference. This restriction needs only one line to define. The first three numbers in the line specify the plane in the satellite frame in the same format as the projection plane was indicated in the first line of the two-line projection restriction specification described above. The next three numbers are the minimum permitted angles between that plane and the vectors pointing toward the sun, moon, and earth disk edges, respectively. The seventh entry in the line is a flag indicating the type of restriction being specified, and must contain a 2. For example, line eight of this file represents the restriction that the vector pointing toward the sun must be within 30 of the x-z semi-plane with z<0.

The specified angles may indicate either a minimum or a maximum permitted angle between the restriction vector and the sun, moon, or earth vectors. If the angle is positive, it is considered a minimum angle (the actual angle must be greater than the angle given) but if it is negative, it is considered a maximum angle (the actual angle must be less than the absolute value of the angle given).