The Orbit Planner (click here to see the movie) is the tool that allows packing exposures into orbits. The tool will allow you see how your exposures will be placed in each orbit, and allow you to manipulate the exposures to place them in the order and orbit you desire.

Note that this tool is for planning purposes only, and while your exposures will execute in the order you specify, there is no guarantee that your exposures will occur in the orbits you specify (e.g. exposures may be shifted depending on when it is actually scheduled). If you need exposures to occur without gaps (due to occultations or SAA passages), you need to use the Exposure Sequence capability, which will force the exposures to occur without interruption; see separate documentation and movie on creating Exposure Sequences.

Before initiating the Orbit Planner, you should select the visit(s) you wish to process; note that there is a Run All Tools button that will process multiple visits through all tools in a batch run. You can select your visit(s) by either selecting the Visit container or any exposure in the visit in the Hierarchical (Tree) Editor; selecting the Visits container will select all visits in the proposal for processing. Then select the Orbit Planner button at the top of the display, which will initialize the tool. Note that the title is in red, and that the Update Display button is active (and red) - this indicates that the display is out of date. There is also a mini-spreadsheet available for editing exposure attributes without toggling to the Form Editor.

Processing the visit

To process the visit(s), hit the Update Display button. Note that the screen greys out during processing, and the Progress Wheel spins. When complete, the orbit structure is displayed. The title is now shown in black, and the Update Display button is inactive - this indicates that the display is now up-to-date. If multiple visits were processed, select the visit you want to see in the Visits to Process area.

Each exposure is labeled in the display, and by placing your cursor on the label or the exposure, a tool-tip will appear which gives more details. The tool-tip displays the configuration, exposure time, start time, overhead, and the total duration (i.e. exposure time + overhead). You can change the timeline to be displayed in minutes instead of the default seconds.

Orbit Packing

There are 2 ways to pack your orbits. To manually pack the orbits, you can use the mini-spreadsheet to revise the exposure times. In the example, there was 698s of unused orbital visibility in orbit 1. This time will be added to exposure2 (900+698=1598), and the Orbit Planner rerun. Note that multiple changes can be made before updating in the Orbit Planner.

Note that there is now a orbital visibility overrun of 100s, which is due to a typo (1698s instead of 1598s). The diagnostic can be seen in the tree editor, the Visits to Process area, and in lower right corner (which will bring up the diagnostic browser; see separate documentation and movie on the tool). One would have expected Exp 2 to have been placed in the subsequent orbit, which would have caused the orbit structure of orbit 2 to be revised, and you would have a cascading effect due to the simple math error. With APT, each exposure is assigned an orbit number (either manually or automatically by the software), and that forces each exposure to stay in that orbit even if the exposure goes into occultation; see separate documentation and movie on orbit numbers for more information on this concept.

If we now subtract 100s from Exp 2 and rerun the Orbit Planner, there is now no unused orbital visibility.

Note that the overhead time for some exposures is a function of the exposure time (e.g. as the exposure time is reduced, so is the overhead time), which could result in remaining unused orbital visibility. It is possible to iterate further to attempt to fully pack the orbit, but since the orbit is approximate (i.e. the true orbital visibility of your target depends on exactly when it is observed, whereas the orbital visibility used in APT is an average value), it is not worth any effort to pack the last couple of seconds.

A second way to pack your orbits is to use the Auto-Adjust capability (see separate documentation and movie for more information on this concept). With Auto-Adjust, you select the sub-exposures in each orbit that you wish to expand, and APT will divide the Unused Orbital Visibility equally among those sub-exposures.

Last modified: May 6, 2014.