lecture09 - Satellite centered coordinate systems The final...

This preview shows pages 1–6. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Satellite centered coordinate systems The final two coordinate systems we’ll discuss, RSW and NTW, are satellite-centered, • Type: usually Cartesian. • Center: satellite position. • Orientation: polar axis ˆ W = ˆ h perpendic- ular to orbital plane, RSW principal axis ˆ R = ˆ r , NTW second axis ˆ T = ˆ ˙ r . RSW is satellite radial , NTW is satellite normal coordinates. RSW is sometimes called Local Vertical Local Horizontal (LVLH) though it’s not precisely gravitationally horizontal. For circular orbits, they are the same, but ex- cept at perigee and apogee for non-circular or- bits they are not, because r and ˙ r are not per- pendicular. L. Healy – ENAE404 – Spring 2007 – Lecture 9 (Feb. 22) 1 In-track, cross-track When describing the position of a satellite, one often hears the terms • in-track : ˆ T direction, • along-track : ˆ S direction, • cross-track : ˆ W direction, usually in the context of errors. In-track and along-track are usually timing errors, because they are basically the velocity vector direction. Cross-track errors are either positioning or per- turbation computation errors, and are usually much smaller than cross track errors. L. Healy – ENAE404 – Spring 2007 – Lecture 9 (Feb. 22) 2 Flight-path angle Ref.: Curtis Sec. 2.4, pp. 48–50 Related to the RSW/NTW distinction is the concept of flight-path angle , γ . This is the angle that the velocity vector ˙ r makes with the local horizontal, the perpendicular to position vector. See Figure 2.11. In other words, it is the angle between ˆ S and ˆ T , note positive is clockwise. • For a circular orbit, the flight-path angle is always zero, because the velocity vec- tor is always perpendicular to the position vector. • For an elliptical (non-circular) orbit, it is positive from perigee to apogee, and neg- ative from apogee to perigee. L. Healy – ENAE404 – Spring 2007 – Lecture 9 (Feb. 22) 3 Picture of RSW vs. NTW R S N T Note that the positive sense of the flight-path angle from ˆ S to ˆ T is clockwise, but positive rotation about ˆ W (out of plane towards you) is counterclockwise. L. Healy – ENAE404 – Spring 2007 – Lecture 9 (Feb. 22) 4 Flight-path angle computation The tangent of the flight-path angle is the ratio of velocity along the radial vector v r , and perpendicular to it, v ⊥ . The prependic- ular component is the speed times the angular rate, and the radial speed is the time rate of change of the distance, both computed pre- vously (Lecture 8, p. 13) v r = ˙ r = s...
View Full Document

This document was uploaded on 04/27/2011.

Page1 / 22

lecture09 - Satellite centered coordinate systems The final...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online