SET BOUNDS

Syntax

   SET BOUNDS (1:2){ FROM @calendar
                   | TO   @calendar }
 
   SET BOUNDS (1:1){ USING (1:)\body
                   | USING ALL
                   | USING EPHEMERIS     }

Description

The SET BOUNDS command changes the endpoints of the default interval (the single interval contained in the default schedule).

The default interval defines the default search interval for the FIND command.

The initial default interval is

   FROM 1998 OCT 01 00:00:00.000 (TDB)
   TO   2001 OCT 01 00:00:00.000 (TDB)

Epochs

Either endpoint, or both, may be specified explicitly.

Bodies

The default interval may be defined implicitly by specifying (USING) a list of ephemeris bodies. The program determines the largest interval for which ephemeris data are available for every body in the list, and this interval becomes the default interval. This guarantees that states for the objects in the list will be available throughout the default interval.

Conceptually, the program constructs a schedule for each body containing intervals for which ephemeris data for the body are available, then forms the intersection of all the schedules. The default interval is the largest interval in the intersection.

When specifying a list of bodies, it is important to include all of the bodies that may be needed. For example, the command

   FIND TITAN_SCHEDULE SEPARATION OF CALLISTO IO FROM EARTH
        LESS THAN 30 ARC SECONDS
        STEP SIZE 20 MINUTES;

needs to determine the state of Earth in order to allow sufficient padding for light-time corrections. This requires the use of Earth (399) and the Earth-Moon Barycenter (3). Furthermore, the location of the Io, Jupiter, Callisto and the Jupiter Barycenter (10) are needed in the computation of the separation of Io and Callisto.

When specifying a list of bodies, the following rules of thumb should be followed:

1.

2.

The SET BOUNDS USING ALL command is equivalent to listing every body (including designated objects) for which ephemeris data are available.

The SET BOUNDS USING EPHEMERIS command is equivalent to listing every body (excluding designated objects) for which ephemeris data are available.

Light-time

When a list of bodies is specified, the initial endpoint of the interval for each body is incremented by the one-way light-time from Earth to the body. These intervals are intersected to determine the schedule during which the set of bodies can be used. The largest of these intervals becomes the default interval. The light-time correction is necessary to allow apparent states to be computed during searches.

Examples

Example 1

In the following example, the bounds of the default schedule are set just before executing a FIND command. Since no search schedule is specified, the search is confined to the default schedule.

   SET the BOUNDS
   FROM 1991-JAN-1 TO 1991-FEB-4 3:00:00;
 
   FIND OCC OCCULTATION OF SAT BY PLN FROM EARTH
   STEP SIZE LENGTH;

Example 2

In the following example, a planning session involving observations of the Galilean satellites of Jupiter from HST begins by using these bodies to define a default search interval.

   SET BOUNDS USING
        HST
        JUPITER JUPBARY
        IO EUROPA GANYMEDE CALLISTO
        EARTH EMBARY SUN;

Note that the Sun and the Earth-Moon barycenter are included in the list, in accordance with the rules of thumb described earlier.

Notes

To see the endpoints of the default interval,

   SHOW BOUNDS;