Miscellaneous

This page describes miscellaneous concepts relating to the OrbitPy package.

Todo

OUTDATED. REVISION NECESSARY.

Issues with the above coverage calculation approach

Current implementation works well only for:

  1. Instruments whose required observation time < propagation step-size. For scanning type instruments (like pushbroom sensors, stripmap SARs) this condition would be met. But this condition cannot be met for instruments like Matrix imagers, radiometers which require the entire sensor FOV to be focused on the scene.

  2. Whose FOV << FOR.

First one is not realistic if the minimum exposure/ dwell time of instruments (required in radiometers) is to be considered. Second one is not realistic assumption for instruments having a wide-swath.

The access file generated by the orbit and coverage is quite naive. It indicates if the ground-point can be accessed at some instant of time. However, what we require are the imaging opportunities, where a imaging opportunity is defined as:

Outlier grid-points: The area around the grid-point should be able to be observed, not just the point. Not realistic for instruments with large FOV.

_images/outlier_grid_points.png

Issue of the outlier grid-points

Common issues:

Issue

  • The area around the ground-point is not the same at each observation, especially for rectangular FOV sensors.

_images/different_observation_areas.png

Issue of the different observation areas when observation is made with footprint aligned to the ground-track.

Unclassified

With respect to integration in DSHIELD, the outputs/ functions of the package are used by other modules of DSHIELD as follows:

Integration to other modules

Data output

the other module

Satellite States, Grid Points

ACS module

Intersatellite comms

Comm Module

Ground-station comms

Ground module

Access Opps with Observation quality

Planner

The input to the first three items is straightforward and can be used directly from the current implementation. The last item however has issues. The raw access outputs are naive, and need to be filtered, post-processed to imaging opportunities (raw access vs imaging opps).

Issue #1

Consider a 5 second mission, the desired output from the Orbits to the Planner would be as follows:

Time, (Grid-points, Observation Quality)
1,    (10,2) (45,1) (100,1) (210,4)
2,    (10,3) (45,2) (100,2) (210,3)
3,    (10,4) (45,3) (100,3) (210,2)
4,    (10,3)        (100,4) (210,1)
5,    (10,1)        (100,5)

Where a observation is defined as taking an image/ reading around the respective ground-point:

_images/valid_vs_invalid_obs.png

Valid vs Invalid observations

In order to deal with the above issue, the observation is deemed to be made with the pointing axis pointed to the GP (and hence the missle of the observation). While this flows naturally when calculating coverage from pointing-options, it is not natural for the case of coverage calculated from grid-points. See Correction of access files for purely side-looking instruments with narrow along-track FOV.

Issue #2

A similar issue exists in the time domain:

Time,Access,Imaging Opp
98,No, No
99,No, No
100,Yes, No
101,Yes, No
102,Yes, No
103,Yes, Yes iff t= 104, are free
104,Yes, Yes iff t= 103, 105 are free
105,Yes, Yes iff t=103, 104, 106 are free
.,.,,
.,.,,
.,.,,
.,.,,
115, Yes,No
116, No,No
_images/outlier_times.png

Valid vs Invalid obs times

To deal with the above issue, a constraint condition such as that shown in the table is implicit in the provided imaging oppurtunities table.