AERO4701 Space Engineering 3 – Week8

Attitude Determination and Remote Sensing

AERO4701 Space Engineering 3 – Week 8

AERO4701 Space Engineering 3 – Week8

Course So Far …

• Orbital Mechanics, Perturbations• Global Positioning System• Satellite Attitude Determination• Introduction to Data Fusion

AERO4701 Space Engineering 3 – Week8

Overview

• First Hour– Satellite Pointing and Geo-location– Earth Viewing Geometry– Mapping and Pointing Budgets

AERO4701 Space Engineering 3 – Week8

Remote Sensing

AERO4701 Space Engineering 3 – Week8

Resolution and Swath Width

AERO4701 Space Engineering 3 – Week8

Measures of Coverage

• Percentage coverage –number of times a point is observed

• Maximum Coverage Gap

• Mean Coverage Gap

• Time Average Gap – mean gap / time

• Mean response time –average time from when we receive a random request to observe a point until it is observed

AERO4701 Space Engineering 3 – Week8

Geo-location from remote sensor observations

• Using Radar:

AERO4701 Space Engineering 3 – Week8

Geo-location from remote sensor observations

• Using Camera (can compute by assuming the earth in spherical and finding the intersection of the line of sight and the Earth’s surface):

• Substitute 3 equations into equation for the Earth’s sphere:

AERO4701 Space Engineering 3 – Week8

Geo-location from remote sensor observations

AERO4701 Space Engineering 3 – Week8

Earth Viewing Geometry

AERO4701 Space Engineering 3 – Week8

Single View Coverage

AERO4701 Space Engineering 3 – Week8

Earth Viewing Geometry

AERO4701 Space Engineering 3 – Week8

Earth Viewing Geometry - Example

• Calculate the coverage of a single sensor observation of a nadir pointing sensor with a field of view of 47o from a satellite at an altitude of 800km

• ρ = sin-1(6378/(6378+800)) = 62.6914o

• ε = cos-1(sin(47o/2)/sin(62.6914o)) = 63.3360o

• λ = 90o – ε – η = 3.1640o

AERO4701 Space Engineering 3 – Week8

Earth Viewing Geometry - Example

AERO4701 Space Engineering 3 – Week8

Mapping and Pointing Budgets• Pointing Tasks: instruments towards ground,

communications antenna pointing• Mapping Tasks: climate, atmospheric and ocean

studies, monitoring of bushfires and other natural disasters, surveillance

• We want to determine what sensing, timing and system accuracies are needed to achieve a given mapping or pointing accuracy

AERO4701 Space Engineering 3 – Week8

Error Sources

AERO4701 Space Engineering 3 – Week8

Error Sources

AERO4701 Space Engineering 3 – Week8

Mapping and Pointing Errors

AERO4701 Space Engineering 3 – Week8

Mapping and Pointing Errors

• Attitude Errors and Target Altitude Errors: as ε->0o, errors in mapping becomes large

• Generally larger errors for larger altitude Rs

AERO4701 Space Engineering 3 – Week8

Example Mapping Errors

AERO4701 Space Engineering 3 – Week8

Example Mapping Errors

AERO4701 Space Engineering 3 – Week8

Example Pointing Errors

AERO4701 Space Engineering 3 – Week8

Remote Sensing Mission Design

• Need to balance sensor coverage and accuracy• Coverage effected mainly by orbital parameters (altitude

etc.)• Accuracy effected by positioning and attitude

determination errors but also by orbital parameters• Trade-off between coverage, accuracy, orbit, quality/cost

of attitude determination hardware

• Next week: design case studies looking into the design process for several satellite missions