Micromaps host Satellite Design Proposal



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1.2 Scope


The focus of this proposal is the design of a satellite that is capable of supporting the MAPS instrument and mission. The structure of this satellite, as well as all internal and external subsystem components are designed and sized. The satellite must carry the necessary power generation and energy storage systems. The ADCS is designed to fulfill MAPS orientation requirements. The method of ground communication is chosen for adequate transmission of necessary data.

The design process begins with an established nanosatellite design. This design is modified in all respects to fulfill our scope. The MAPS host satellite design must be complete by the end of the current semester. HokieSat provides a first iteration on the desired satellite, therefore allowing for a complete design in the time allotted. Launch vehicle suggestions are included in the scope of the project; however, this design does not limit launch vehicle selection.


1.3 Needs, alterables, and constraints


This satellite needs to integrate the MAPS instrument into a modified HokieSat design, which must perform all bus functions, access groundstations periodically, and maintain an orbit that allows fulfillment of the instrument’s science goals over a three year lifetime. The subsystems and operations are alterable within the limits set forth by the list of constraints. Other alterables include the launch vehicle selection, addition of a camera, the use of AMSAT broadcasting, and the solar array design. All needs, alterables, and constraints are listed in Table 1.

Table 1: List of needs, alterables, and constraints for host satellite design



Category

Element

Needs:

Perform all bus functions




Integrate MAPS into a design similar to HokieSat




Access necessary groundstations periodically




Maintain an orbit to fulfill required science goals




Three year lifetime

Alterables:

Camera




Solar cell mounting




AMSAT broadcasting




Launch vehicle

Constraints:

Nadir pointing +/- 2.5o




At least one year lifetime




Orientation of instrument with respect to orbital reference frame

1.4 Value system design


The value system design (VSD) is used to evaluate iterations on the HokieSat design. The VSD puts all mission objectives into a hierarchy beginning with the top-level objective: optimize the satellite design. Maximizing the performance objectives and minimizing the cost objectives optimizes the satellite design. The performance and cost objectives are described in this section.

The main objective of this satellite is to support the MAPS instrument. Below the top-level objective are two second-level mission objectives: maximize performance and minimize cost. The performance objectives are gathered from the instrument requirements placed on each subsystem, found in the interface control document (ICD, Reference 20). Each subsystem achieves these objectives in different ways. Table 2 depicts the interactions between subsystems and mission objectives. Figure 1 illustrates the entire objective hierarchy.



Table 2: List of objectives and their associated subsystems

Objective

Relevant subsystem

Maximize performance




Minimize pointing error

ADCS

Maximize data to LaRC

COMM

Maximize quality of data to LaRC

All

Maximize power efficiency

Power

Maximize lifetime

All

Minimize excess strength/stiffness

Structures

Maximize external surface area

Structures

Maximize coverage

ADCS

Minimize radiation effects

ADCS

Maximize attitude stability

ADCS

Minimize position error

GN&C

Minimize cost




Minimize launch cost

All

Minimize production cost

All

Minimize operational cost

All

Minimize mass

All


Figure 1: Objective hierarchy chart

This objective hierarchy is further divided into sub-levels of performance and cost that are associated with measures of effectiveness (MOEs). For example, a MOE for the ADCS is pointing error of the satellite. This MOE is minimized to achieve greater precision in attitude maneuvers. The communications subsystem maximizes data quality transferred to ground stations as one of its performance objectives. An objective of the structural engineers is to maximize the available surface area to allow for body mounted solar cells.

Several performance MOEs are comprised of separate quantities. The performance of the satellite structure accounts for material strength and stiffness. These quantities depend on material characteristics. Maximizing the efficiency of the power system depends on all internal components of the satellite such as the computer, ADCS components, and the MAPS instrument. The communications system performance also depends upon factors, which affect the entire satellite, such as the radiation dose.



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