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2. The characteristics of the tasks of several typical carrier rocket and spacecrafts



This lecture mainly talks about several typical space missions to introduce their characteristics of control.

2.1 carrier rocket

Measurement and control of launch vehicle mainly happens during its powered phase and the availabilities of Measurement and control system are evaluated only when the rocket is in its emission period. The powered phase is generally defined as the period of time from the start of the rocket launching to the separation of the rocket and the satellite. Measurement and control for carrier rocket of its powered phase includes the following contents.

(1)Tracking: the measurement of the instantaneous position and velocity of a carrier rocket which is also called exterior trajectory measurement

(2)Telemetry: the remote measuring of the internal parameters, environmental parameters and independent navigation positioning data of a flying rocket by radio

(3)Telecontrol: safety control. The flying rocket will be exploded through the instructions from radio remote control apparatus when it is abnormal and may endanger the safety of the ground.

Safety control happens only in real time. Telemetry and tracking functions can not only provide correct measurement results in real time for safety system decision but also make integrated information processing after the flight to provide a basis for evaluating the performance of the rocket and improving its design.

The flight during the powered phase with its short distant is not long, and therefore the measurement and control of the powered phase has the following characteristics.

(1) Measuring time with its short measuring distance is not long.

(2)The key of the measurement and control is trajectory measurement with high measurement precision by complex trajectory measurement system.

(3) Telemetry task is relatively simple. The amount of remote transmission information is not large, but there are many kinds of the information.

(4) The tasks of control are simple. The safety control for the carrier rocket and the astronauts (Manned space mission) is the only task.

(5) Strong real- timeliness. The measurement and control system must provide the flight trajectory and the important engineering parameters timely and correctly as the basis for security decision of the launching site. The time from the measurement and control system capturing the goal and outputting the measurement information to the computer processing for a variety of information according to its qualification is generally within hundreds of milliseconds.

(6) The time relations between the various control information are very strict, and the timing and frequency calibration precision provided by the unified time system should be


very high to ensure the trajectory measurement with high precision.

(7)Accuracy requirement of the factors influencing the measurement accuracy such as site survey and modification of radio-wave is also high.

2.2 low earth orbit (LEO) satellite

LEO satellite project consists of a satellite, a carrier rocket, launching site, measurement and control, operation control and application systems. The orbit characteristics of a LEO satellite determines its measurement and control characteristics: (1) the orbit coverage rate by the ground control network is low; (2) Accuracy requirements of the orbit and attitude measurements are high; (3) The reception of the telemetry data is difficult; (4) The storage type remote control is adopted; (5) Time comparison between satellite and ground is frequent.

In order to making the task analysis and plans, the whole process of the satellite life(from launching to the end) is divided into 4 stages, including launching to orbit, early orbit, long-term operation and return.

Stage of launching to orbit: starting from the carrier rocket launching, then the satellite rocket separation, to the satellite getting into early orbit.

Stage of early orbit: starting from the satellite getting into early orbit after its separation from the rocket to the satellite delivered to users.

Stage of long-term operation: also called long term business application stage, starting from the satellite delivered to users to the end of its working life.

Stage of return: starting from the landing operation of a returnable satellite to the re-entry module’s landing and recovery.

2.3 geosynchronous satellites

The orbit of a geosynchronous satellite is geosynchronous, and the rocket will only get the satellite into a large elliptical transfer orbit or a nearly circular parking orbit near the earth. Then the satellite will be accelerated into the large elliptical transfer orbit by the perigee engine and then to geosynchronous orbit by the apogee engine.

Many Swingbies and Orbit maneuver corrections will be needed before the satellite getting into its working orbit. That is the satellite will go through a geosynchronous transfer orbit (GTO, or called the transition orbit), drift orbit (DO, or called quasi synchronous orbit) and designated capture process before it finally gets into the fixed position. Fig 1 shows the whole process.

Fig 1 Schematic diagram of a geostationary satellite orbits

Measurement and control of a geostationary satellite has the following characteristics.






(1) The flight of the powered phase and foreign earth stations are needed.

(2) The duration of Measurement and control is long when the satellite is in the early orbit and the operation of it is complex.

(3) The duration of long-term operation measurement and control is even longer, but the measurement and control network is simple.

2.4 Manned space mission

Manned space flight is the space activity within which the human beings are engaged in a variety of detections, tests, research, military and productions in space by driving and riding the spacecraft. Manned space system generally consists of the manned spacecraft, launch vehicles, launching site, landing site, communication network, the astronaut system and the application system.

According to the special mission and requirements for manned flight and orbital characteristics, its orbit can be divided into ascent period, on-orbit operation period and return period.

(1) Ascent period. It is the flight period starting from the carrier rocket launching to the spacecraft’s separation from the rocket. The manned spacecraft is sent into the fixed orbit by the power from the carrier rocket in this period. The safety of astronauts and the implementation of emergency rescue plan must be ensured first once some serious accident happens.

(2) On-orbit operation period. It is the flight period starting from the spacecraft getting into its orbit to the attitude control for the spacecraft return. Emergency return measures must be taken in this period to make sure astronauts return safely to the ground once the spacecraft failure endanger the safety of astronauts.

(3) Return period. It is the flight period starting from the attitude control for the spacecraft return to the return capsule landing safely.

The characteristics of the manned space engineering have a significant impact on the design of measurement and control network.

Its main characteristics are as follows:

(1) High reliability; (2) Strong real-time; (3) High orbit coverage rate; (4) Multi functions and large volume of data.

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