The 66 low-orbit satellites in the Iridium project are divided into six necklaces around the ear

The 66 low-orbit satellites in the Iridium project are...

Key Concepts

Satellite Constellation

A satellite constellation is a group of satellites working in concert to provide global or regional coverage. In systems like Iridium, satellites are arranged in multiple orbital planes or 'necklaces' to ensure that at any given time, a transmitter on Earth has access to a satellite for communication. This arrangement underpins the concept of continuous coverage which is essential for seamless handoffs.

Orbital Period

The orbital period is the time a satellite takes to complete one full orbit around Earth. In the context of the problem, the specified 90-minute period is key to determining how frequently the satellites move in and out of view relative to a stationary transmitter. This timing directly influences the rate at which a handoff between satellites might be required.

Handoff

Handoff refers to the process of transferring an active communication link from one satellite to another as the satellites move. For a stationary transmitter, the handoff interval is determined by both the satellite’s orbital mechanics and the layout of the constellation. Understanding handoffs is critical for maintaining an uninterrupted service.

Satellite Coverage Footprint

The satellite coverage footprint is the region on Earth's surface that can be served by a satellite at any given time. This concept is important because as satellites travel in their orbits, their footprints shift, requiring handoffs to other satellites to maintain continuous coverage for a fixed point on the surface.

Transcript

00:01 The global positioning system, gps, uses a constellation of some 30 satellites to provide accurate positioning for any point on earth.

00:15 Gps receivers time radio signals traveling at the speed of light from three of the satellites to find the receiver's position.

00:25 Signals from one or more additional satellites provide corrections, eliminating the need for high accuracy clocks in individual gps receivers.

00:39 Gps satellites are in circular orbits at an altitude of 20, and i'm making sure that i'm reading this correctly, 20 ,200 kilometers.

00:56 And that is altitude.

00:59 What's the approximate orbital period of gps satellites? so we're given an equation in the textbook that says t squared equals, can't rate equals.

01:20 4 pi squared r cubed over gm.

01:31 So t is the square root, taking the square root of both sides of 4 pi squared r cubed.

01:44 So we're given an altitude.

01:47 The altitude that we're given is 20 ,200 kilometers.

02:01 So that would be 20 ,200 meters.

02:02 So that would be 20 ,200 ,000 meters.

02:05 So r cubed, that would be the distance from the center of the earth.

02:10 We're going to have to add the radius of the earth, which is 6 .37 times 10.

02:28 To the sixth power onto the altitude.

02:39 So the altitude is 20 .2 times 10 to the sixth power.

02:49 That is quite an altitude.

02:51 That's much greater than the radius of the earth.