Hi!
I am now working on the access computing concerning multiple objects and sensors.
For example,I have two ground stations with multiple sensors,and two satellite with multiple sensors. To compute access time between each sensor on the ground to each sensor on the satellite, I think it will be more effecient to compute them in one propagator.But I’m not sure if I can use the event handler mechanism to compute all the accesses in one time while recording the in/out time amd az/el/range data.
Did anyone have this kind of problem before?Any help would be really appreciated!
Hi AstoL,
Since you have only one satellite it is possible compute all those quantities in one pass of one propagator using a combination of EventDetectors and StepHanders. One could add a step handler for az, el, range from each ground site and an event detector to determine access times for each ground site.
In terms of efficiency step handling is O(jk) where j is the number of steps and k is the number of step handlers. Event detection is roughly O(n + nm + ml) where n is the number of events, m is the number event detectors, and l is (propagation duration / max check). The n term represents the number of calls to the root finder and the other terms are g function evaluations searching for sign changes. The reason for the nm term is that there are ordering guarantees for events detected by a single propagator, but those guarantees do not apply for events detected by different propagators. So one must balance the cost of event detection with the cost of propagation. E.g. if one had thousands of event detectors in one propagator it would probably be better to split them up among different propagators, but if one had one event detector in each of a thousand propagators it would probably be better to combine some.
If you’re looking for more efficiency there was another proposal on this forum a while ago about faster event detection without ordering guarantees. The there would be no nm term in the cost of event detection and event detection efficiency would be equivalent whether in a single propagator or split among many.
Regards,
Evan
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Thank you for your advice!
I now realize that it’s quite a complicated problem to write a common function to compute accesses between multiple sensors with multiple constraints(i.e. elevation,sensor pointing,sensor shape ).It may take my some time to test the code,hope I could discuss with you about this issue latter.
In addition,do you have any example about access computation with sensor pointing constraints on the satellite?That might be a great help to me!