operations tracking (cont’d)

Unit 4, Chapter 13, Lesson 13: Space Operations 1

OperationsTracking (cont’d)

• Figure 13-12 shows the Iridium ground station in Yellowknife, Canada which is one of several that tracks the Iridium constellation of sixty-six satellites.


OperationsCommand and Control

• Commands are instruction sets telling the onboard computers to take some action or update some critical part of the software.

• Commands can tell the spacecraft to charge batteries, fire rockets, or point at a new target.

• Commands can either be real-time or stored.– Real-time commands implemented on receipt– Stored commands carried out

• At a time an operator determines• After a certain event


OperationsCommand and Control (cont’d)

• Important commands are sent in two stages:– The command travels to spacecraft through an uplink.– The communication subsystem echoes it back to the operators

through the downlink.– After operators confirm the command received is the one sent, they

send a second command to enable it in the spacecraft’s onboard software.

• Two stage commands ensure important information doesn’t get garbled during transmission and provides some security from outside interference.



• Because the spacecraft communication links are so important to mission performance, most spacecraft have built-in commands to follow if they lose a communication link.

• A simple timing switch or “watch-dog timer” onboard keeps track of the time a spacecraft goes without communication.

• If this time exceeds a certain preset amount, the spacecraft puts itself into a “safe mode” to make it easier to restore the communication link and resume the mission.


CommunicationElements of Communication

• Radio communication is like carrying on a conversation in several key ways:– Distance– Language– Speed– Environment



Distance

• For a conversation, participants should be within hearing distance so each person’s words reach the other.

• The more distance between participants, the louder they must talk to be heard.

• If they are too far away to hear each other, they can’t communicate.

• To communicate effectively from one spacecraft to another or to a ground station, we must consider the distance or range between the speaker (called the transmitter) and the listener (called the receiver).



Language

• For a conversation, the language must be one that both participants can understand and speak fluently.

• For radio communications, the transmitter and receiver must understand the language or code that each uses.



Speed

• In a conversation if people speak too rapidly, it’s hard to process the words fast enough to understand their message.

• For radio communication, the receiver must handle the transmitter’s message speed or data rate.



Environment

• If a conversation occurs in a crowded football stadium, the crowd generates noise. To overcome the noise, participants must talk louder—increase the strength of their signal.

• For radio communication, the signal strength must be higher than the noise level—the signal-to-noise ratio must be greater than one.

• The important quantity for communication is the ratio of the volume of your speech to the volume of their noise.


Communication (cont’d)

• The receiver must handle the transmitters message speed or data rate.

• The volume or signal strength at the receiver must be higher than the overall noise in the system.



• When turned on, the car radio receives signals from the radio station in the form of electromagnetic (EM) radiation.

• EM radiation comes from an accelerating charge.• As charges accelerate in the radio station’s transmitter

antenna, an electric field forms and induces a magnetic field.

• The magnetic field induces an electric field.• The frequency at which this charge accelerates

determines the frequency of the EM radiation. The faster the charge accelerates, the higher the frequency.


CommunicationCar radio example

• A radio station broadcasts carrier signal at specified frequency regulated and licensed by the Federal Communication Commission (FCC).

• The transmitter then places the message being sent on top of carrier signal, using some type of modulation. We’re most familiar with: – amplitude modulation (AM)– frequency modulation (FM)

• Signal travels from station antenna to car antenna.• Receiver re-translates it to the original signal and separates message

from the carrier signal (demodulates).• Receiver amplifies the original signal and—behold—music comes

from the speakers.


CommunicationCar radio example (cont’d)• Spacecraft applications use other schemes as well.

• This signal travels outward from the station’s antenna and hits the car radio’s antenna. There more charges accelerate.

• The receiver detects this charge movement in the antenna and re-translates it to the original signal.

• The receiver “demodulates” the AM or FM signal to separate the message from the carrier signal.


CommunicationCar radio example (cont’d)


CommunicationBasic Principles

• Similar to a radio transmitter, a light bulb emits EM radiation, but at a different frequency—visible light.

• A light bulb placed in the center of a room radiates outward in all directions (assuming it’s a perfect bulb with no light blockage).


OperationsTracking (cont’d)

• Figure 13-12 shows the Iridium ground station in Yellowknife, Canada which is one of several that tracks the Iridium constellation of sixty-six satellites.


OperationsCommand and Control

• Commands are instruction sets telling the onboard computers to take some action or update some critical part of the software.

• Commands can tell the spacecraft to charge batteries, fire rockets, or point at a new target.

• Commands can either be real-time or stored.– Real-time commands implemented on receipt– Stored commands carried out

• At a time an operator determines• After a certain event



• Important commands are sent in two stages:– The command travels to spacecraft through an uplink.– The communication subsystem echoes it back to the operators

through the downlink.– After operators confirm the command received is the one sent, they

send a second command to enable it in the spacecraft’s onboard software.

• Two stage commands ensure important information doesn’t get garbled during transmission and provides some security from outside interference.



• Because the spacecraft communication links are so important to mission performance, most spacecraft have built-in commands to follow if they lose a communication link.

• A simple timing switch or “watch-dog timer” onboard keeps track of the time a spacecraft goes without communication.

• If this time exceeds a certain preset amount, the spacecraft puts itself into a “safe mode” to make it easier to restore the communication link and resume the mission.



• Radio communication is like carrying on a conversation in several key ways:– Distance– Language– Speed– Environment



Distance

• For a conversation, participants should be within hearing distance so each person’s words reach the other.

• The more distance between participants, the louder they must talk to be heard.

• If they are too far away to hear each other, they can’t communicate.

• To communicate effectively from one spacecraft to another or to a ground station, we must consider the distance or range between the speaker (called the transmitter) and the listener (called the receiver).



Language

• For a conversation, the language must be one that both participants can understand and speak fluently.

• For radio communications, the transmitter and receiver must understand the language or code that each uses.



Speed

• In a conversation if people speak too rapidly, it’s hard to process the words fast enough to understand their message.

• For radio communication, the receiver must handle the transmitter’s message speed or data rate.



Environment

• If a conversation occurs in a crowded football stadium, the crowd generates noise. To overcome the noise, participants must talk louder—increase the strength of their signal.

• For radio communication, the signal strength must be higher than the noise level—the signal-to-noise ratio must be greater than one.

• The important quantity for communication is the ratio of the volume of your speech to the volume of their noise.



• The receiver must handle the transmitters message speed or data rate.

• The volume or signal strength at the receiver must be higher than the overall noise in the system.



• When turned on, the car radio receives signals from the radio station in the form of electromagnetic (EM) radiation.

• EM radiation comes from an accelerating charge.• As charges accelerate in the radio station’s transmitter

antenna, an electric field forms and induces a magnetic field.

• The magnetic field induces an electric field.• The frequency at which this charge accelerates

determines the frequency of the EM radiation. The faster the charge accelerates, the higher the frequency.


CommunicationCar radio example

• A radio station broadcasts carrier signal at specified frequency regulated and licensed by the Federal Communication Commission (FCC).

• The transmitter then places the message being sent on top of carrier signal, using some type of modulation. We’re most familiar with: – amplitude modulation (AM)– frequency modulation (FM)

• Signal travels from station antenna to car antenna.• Receiver re-translates it to the original signal and separates message

from the carrier signal (demodulates).• Receiver amplifies the original signal and—behold—music comes

from the speakers.


CommunicationCar radio example (cont’d)• Spacecraft applications use other schemes as well.

• This signal travels outward from the station’s antenna and hits the car radio’s antenna. There more charges accelerate.

• The receiver detects this charge movement in the antenna and re-translates it to the original signal.

• The receiver “demodulates” the AM or FM signal to separate the message from the carrier signal.


CommunicationCar radio example (cont’d)


CommunicationBasic Principles

• Similar to a radio transmitter, a light bulb emits EM radiation, but at a different frequency—visible light.

• A light bulb placed in the center of a room radiates outward in all directions (assuming it’s a perfect bulb with no light blockage).


CommunicationBasic Principles (cont’d)

• The light’s intensity or brightness at some distance from the bulb is called the power-flux density (“F” in Figure 13-14). – The farther away from the light

bulb we go, the dimmer it appears.

– In other words, the power-flux densityperceived as brightnessdecreases the farther we go from the light bulb.

– Radiation (“R” in Figure 13-14), moving equally in all directions as in the light-bulb example, is called omni-directional.


CommunicationBasic Principles—Gain

• To increase the brightness or power-flux density in only one direction using the same bulb would require the light to be focused, as in a flashlight.

• Putting a parabola-shaped mirror on one side of the light bulb will focus its light.

• Most of the light in one direction reflects off the mirror and heads in the opposite direction, creating a directed beam of light—a spotlight—rather than an omnidirectional source.


CommunicationBasic Principles—Gain (cont’d)

• In this way, most of the light energy is concentrated into a smaller area, resulting in a brightness in one direction that is much, much greater than it was when the bulb gave off light in all directions.

• This “gained” extra power density by using the parabolic mirror illustrates the basic principle of an antenna.

• Spacecraft often rely on specially designed “dish” antennas to let us focus the energy on a particular point of interest such as a receiving antenna.

• Ground stations usually use another directional (dish) antenna to better receive the signal, as well as transmit commands back to the spacecraft.


Satellite Control Networks

• The Spaceflight Tracking and Data Network (STDN) mostly tracks and relays data for the Space Shuttle and other near-Earth missions.– STDN includes ground-based antennas at White

Sands, New Mexico.– Space-based portions use the Tracking and Data

Relay Satellites (TDRS) in geostationary orbits.


Satellite Control Networks (cont’d)

Tracking and Data Relay Satellite’s (TDRS) Second Terminal


Satellite Control Networks (cont’d)

• The deep-space tracking network (DSN)– Includes very large

antennas (more than 70 meters in diameter).

– Tracks and enables operators to receive data from interplanetary missions.

Deep Space Network (DSN)

operations tracking (cont’d)

Documents

space operationsunit

spacecraft communication

realtime commands

stage commands

receiptstored commands

builtin commands

communication subsystem

hearing distance