1

Commercial

Shared STS TOS

Shared

STS Integral Propulsion

Through FlreSa!

Shared Shared STS STS

TOS Integral Propulsion

Fig. 2-4. FlreSat Trade Tree. Only some of the launch options are listed. Other mission elements are largely independent of the trade tree options. The goal Is to create drastically different options for comparison.

TABLE 2-7. Two of the Six Preliminary FlreSat Mission Concepts. See the trade tree in Fig. 2-4 for the other options.

Element

Option 1

Option 6

Mission Concept

IR detection of fires with results put on a map and transmitted

IR detection of fires with results put on a map and transmitted

Subject

Characteristics defined by the specification

Characteristics defined by the specification

Payload

Small-aperture IR

Large-aperture IR

Spacecraft Bus

Small, 3-axis

Mid-size, 3-axis

Launch System

Pegasus

STS, integral propulsion

Orbit

Low-Earth, 2 satellites, 2 perpendicular polar planes

Geosynchronous, 1 satellite centered over west coast of U.S.

Ground System

Single, dedicated ground station

Single, dedicated ground station

Communications Architecture

TDRS data downlink; commercial links to users

Direct to station; results relayed to users via FlreSat

Mission Operations

Continuous during fire season, partial otherwise

Continuous during fire season, partial otherwise

Step E. Look for other alternatives. Defining alternative architectures cannot be purely mechanical. For nearly any mission, we may find new and better ways of doing anything the basic elements do. A new, low-cost launch vehicle may dramatically change the available design alternatives. Alternative definitions of the subject or user may allow major performance improvements or cost reductions. For example, as an alternative mission concept we could detect forest fires by using small sensors spread throughout the forests being monitored and simply use the satellite system to interrogate the sensors and provide the data to the users. Chapter 22 further explores this low-cost alternative. The key point is that alternatives nearly always exist We must look carefully for them and be willing to revise normal requirements and constraints to meet our fundamental mission objectives.

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