Measuring Response Time

The Response Time figure of merit (FOM) measures the time between a request for coverage of a point and the time at which coverage is achieved. The dynamic definition of Response Time is the time until the next access begins. The value is zero (0) if the point is currently in access, and 1000000 seconds if the current animation time is later than the end of the last access period. Options for the static definition of Response Time are described in the following table.

Compute options for Response Time

Option	Description
Average	This is the average response time over the entire coverage interval, computed as:
Maximum	This is the maximum response time over the entire coverage interval. It is useful in determining the length of the longest gap between coverages.
Minimum	This is the minimum response time over the entire coverage interval. The value is 0 if any accesses exist for the grid point.
Percent Below	The value computed indicates that the point has a Response Time of at most R, X percent of the time, where R is the computed value and X is a Percent Level you specify.
Percent Below Gaps Only	The computed value indicates that the point has a response time of at most R, X percent of the time when in a coverage gap, where R is the computed value and X is a Percent Level that you specify.

STK's Coverage capability uses an "optimistic" algorithm when coverage gaps that share a boundary with the coverage interval exist. The span of the coverage gap is measured using the coverage interval bound. This is important for the correct interpretation of the Age Of Data, Revisit Time, Time Average Gap, and Response Time figures of merit.

Use the Min # Assets text box to enter the the minimum number of assets required for the Coverage object.

Limitation on using Response Time FOM

If you choose Response Time as the FOM for your coverage object, you cannot use a Chain object in the Coverage definition. This is because the Chain object by definition is only valid for simultaneous access. For example, you could create a Chain object with an Area Target and some sensors on a Satellite, assigning the Chain to a Coverage with the Area Target as the grid. You could then assign a ground station (far from the target) as the receive field. However, since the Satellite cannot access the Area Target when in view of the ground station, a Response Time FOM would not produce any meaningful results. In this case, you should use a Constellation object for the sensors and Area Target.

Displaying Response Time in a graphics window

STK uses graphics to represent the static and dynamic value of Response Time, but only during animation. If you select the Satisfaction check box, the graphics follow the general behavior for satisfaction graphics. If you do not select the check box, the graphics appear as described in the following table:

Static or Animation?	Grid points highlighted if they...
Static	are in a coverage gap at least once during the coverage interval
Animation	are currently in a coverage gap

The Satisfaction Threshold value is the time between a request for coverage of a point and the achievement of that request. The default behavior for this Figure Of Merit corresponds to a Satisfaction setting of Greater Than 0.