Space Systems Engineering

Transcription

1 Space Systems Engineering This course studies the space systems engineering referring to spacecraft examples. It covers the mission analysis and design, system design approach, systems engineering process and methodology, and management needed for space development. (Lecture Note) This note adopted from many books called out in the References. The author deeply appreciate specifically to authors, J.R.Wertz, et al. of Ref.2[SMAD]. Vol.9 Revision C 14. Mission Operations 15. Ground System Design and Sizing August 21, /16

2 14. What is Mission Operations? Mission operation is the collection of activities performed by operations teams during the flight phase of the mission, together with the operations design activities they perform pre-launch. They include development of a mission operations concept, policies, data flows, training plans, staffing plans, and cost estimates. The mission operations system is the integrated system of people, procedures, hardware, and software that must cooperate to accomplish these tasks. Mission operations focuses on the period after launch. But substantial work must be done during all phases of mission design and development to prepare for operations. We must distinguish between the mission concept and mission operations concept. Mission concept means how we conduct the overall mission and how the elements of the mission fit together, while, Mission operations concept means how we do operations to carry out the mission objectives. We define 13 key functions performed by mission operations (see Fig. 14-1), and discuss how they combine to meet the mission operations concept. Figure 14-1 overviews a mission operations system that carries out the mission operations concept. This system processes information and controls the ground and space assets, so users and operators get needed information and services. 2

3 Most missions today focus on providing information to users or customers --- the downlink Developing a Mission Operation Plan For unmanned space missions the Mission Operations Plan (MOP) describes in operators and users terms the operational attributes of the flight and ground-based elements. Table 14-1 outlines the steps needed to develop a useful MOP. 3

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5 14.2 Space Mission Operations Functions Table 14-3 summarizes the attributes of 13 functions shown in Figure For small projects, members of a single team may do these tasks. 5

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7 15 Ground System Design and Sizing A ground system is ; (1) supports the space segment (spacecraft and their payloads), and (2) relays to users mission data generated by onboard instruments and received from the spacecraft. Table 15-1 summarizes these functions and corresponding options. 7

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9 a. Ground stations acquire mission data from a spacecraft and its instruments and transfer it to the data users. The ground system also supplies any telemetry and tracking information the data users may need. b. Ground Systems consist of Ground Stations and Control Centers working together to support the spacecraft and the data user. Figure 15-1 shows how these segments interact. Generally, the ground system commands and controls the spacecraft based on requests from the data user to the control centers. Users do not send commands independently to the spacecraft except for communications satellite. Because its overall health depends heavily on the state of individual instruments and systems. 9

10 15.1 A Ground System s Basic Elements Figure 15-2 shows the Ground System consists of mission elements and facility elements. a. Mission Elements control the space segment or handle mission data as a main body of the Ground System. b. Facility Elements support or are otherwise ancillary to mission elements. Both contain mixes of various hardware, firmware, and software. Mission operations coordinates activities for the ground system, and command and control of the spacecraft. 10

11 The Ground Station is the Earth-based point of communication with the space segment for control and, typically, user data. Figure 15-3 shows the basic Ground Station, which consists of the following components. (a) The single Antenna System includes the antenna and mount, its associated electromechanical actuators, the consoles and servo circuitry which control the antenna, and the feeds and transmission lines which carry RF signals to and from the RF equipmens. (b) Autotracking refers to the use of the received spacecraft signal itself to steer the antenna. (c) The Receive RF Equipment is generally in suites of racks, located to minimize transmission-line losses to the antenna. (d) Also in racks near the antenna system, the Transmit RF Equipment accepts tracking and command signals from the ground system s TT&C component and modulates them onto the RF uplink, which it also generates. (e) After the RF receive equipment demodulates the signals, the Mission Data Recovery Equipment conditions the mission data before relaying it to data users and ground system components. (f) The Data User Interface connects the mission data recovery equipment and the data user. 11

12 (g) The Telemetry, Tracking, and Command (TT&C) equipment conditions and distributes received telemetry and tracking signals. ( 認証する ) It also electrically formats, authenticates, and times transmitted command and tracking signals. It usually processes these tracking signals and data on the antenna-pointing angle to inform users about range, range rate, and spacecraft position. (h) The Station Control Center controls the configuration of, and the interconnects between the ground station components. 12

13 Following three types of control centers are found within ground systems for such a complex system like a manned ISS system operations. In simpler systems, we may merge the MCC with the SOCC, or all of them. (1) The Spacecraft Operations Control Center (SOCC) monitors and commands the spacecraft bus and common systems. While the onboard instruments or payloads are controlled by the POCC, as discussed below. The SOCC analyzes spacecraft telemetry and, when necessary, telemetry and mission data from instruments which can affect the spacecraft s attitude and dynamics. As the only ground system element that directly commands the spacecraft, it coordinates and controls POCC access. (2) The Payload Operations Control Center (POCC) analyzes telemetry and mission data from onboard payload instruments and issues commands to these instruments. Its command depend on approval by the mission control center(mcc), with coordination from the SOCC. We may use mutiple POCCs when several onboard instruments require careful independent supervision or when we need a backup for redundancy or survivability. 13

14 (3) The Mission Contrl Center (MCC) plans and operates the entire space mission, including the configuration and scheduling of resources for both space and ground system. It computes and issues information needed by ground system elements and data users, such as data on the spacecraft s orbit, ground station pass times, and antenna pointing angles. Figure 15-5 show the example of physical layout of a simple ground system with its data users colocated. This allows to eliminate the need for long-distance communications links between them. Such a system can provide low-coverage support of up to several spacecraft in low-earth orbit on a timeshared basis, or virtually 100% coverage for a single spacecraft in geostationary orbit. 14

15 15.2 Satellite Communication Links We may use satellites to provide communications between remote ground system elements and data users. Table 15-3 shows several geostationary communications satellites typically used by ground systems with elements around the world. (Most of them are out of date. Table should be updated.) In general, portions or all of the available transponder bandwidth may be leased. 15

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