02 Design

Designing Human Space Missions (Ch. 2): 

Designing Human Space Missions (Ch. 2) Objectives Identify important characteristics of Mission Concepts and Architectures Discuss the process of defining system level requirements based on top level mission objectives

The Design Process: 

The Design Process Goal is to select the best overall design for a human space mission and provide traceable rationale for the decisions Begins with Concept Exploration and Requirement Definition Establishes ROM cost / mass The Mission Concept is the core of the Architectural Plan it applies the Mission Objective Statement

Systems - What do we need?: 

Systems - What do we need? Launch Vehicle Orbit Adjust and De-orbit Engines (OMS) Attitude Control (RCS) Guidance, Navigation, and Control (GNC) Mechanical Systems (Mech) Electrical Power System (EPS) Environmental Control and Life Support System (ECLSS) * EVA Systems (EVAS) * Auxiliary Power Unit (APU) Communications System (COMM) Data Processing System (DPS) Caution and Warning (C&W) * Unique to human spacecraft

Characterizing the Subsystems: 

Characterizing the Subsystems Overall vehicle(s) configuration Mass Properties (system, consumables, CG) Safety features (abort scenarios) Power (ave, peak, A, V, W) and distribution Computers, C3, sensors, data rates ECLSS including thermal EVAS (suit, AL, tools, rovers)

Slide5: 

Define broad mission objectives Define mission requirements and constraints Develop alternate concepts and architectures Identify critical system drivers (mass) Select baseline mission Define systems requirements Document choices and rationale Integrate and iterate…

2.1 Define Mission Objectives: 

2.1 Define Mission Objectives First step – broad goals that the system must meet, overall purpose of the mission ‘Qualitative’ for the most part at this point Primary, secondary and non-technical objectives hidden agendas (political, social or cultural)

Define Mission Requirements and Constraints: 

Define Mission Requirements and Constraints Transforms the broad mission objectives into quantifiable design parameters in terms of specific requirements and constraints ESAS Report was the baseline for Constellation

Space Exploration Policy: 

Space Exploration Policy Space Transportation Supporting Exploration Develop Crew Exploration Vehicle (CEV) Initial test flight by 2008 Support human missions by 2014 Separate ISS crew and cargo missions Number of crew? Duration of mission? Destination? Number of vehicles?

Requirements: 

Requirements Functional – what (basic I/Os) Operational – how (P, M, V, crew time, etc.) Constraints – limits (cost, schedule, technology) Level 0, 1, 2, 3, and 4 First iteration of requirements comes from objectives and insight Negotiations between customer and designers start here ‘fixed price’ or ‘cost plus’ makes a big difference!

Attributes of a ‘Good Requirement’: 

Attributes of a ‘Good Requirement’ Achievable Affordable Objectively verifiable, preferably quantitatively – are you building the thing right? Validateable – are you building the right thing? Unambiguous Complete and contain all mission profiles, ops and maintenance concepts Expressed in terms of ‘need’, not ‘solution’ (addresses why and what, not how) Consistent with other requirements Appropriate for the level of system hierarchy

Examples of Top Level Requirements: 

Examples of Top Level Requirements Science and exploration goals identified Duration, logistics, survivability, mission ops, C3, interfaces, cost, schedule, regulations, political, environmental, COTS, human capabilities Human space missions depend as much on political, legal and economic elements as technological challenges

Project Constellation Requirements: 

Project Constellation Requirements Level 0 Requirements Implement a safe, sustained and affordable program to extend human presence across the solar system and beyond Acquire transportation systems to deliver crew to exploration destinations and return them safely to Earth Complete ISS by end of the decade Pursue international participation Pursue commercial opportunities related to ISS and beyond Inspire the nation Source: Level 0 Exploration Requirements for the National Aeronautics and Space Administration

Alternative Mission Concepts and Architectures: 

Alternative Mission Concepts and Architectures Top down (goal driven) or bottom up (technology enabled) Basic purpose is to quantitatively compare alternatives in terms of cost / benefit analysis Cost is often normalized to launch mass Equivalent System Mass approach

Common Options: 

Common Options Location – transfer orbit, surface, parking orbit ECLSS closure – breakeven point? Structure and configuration Some power options Batteries Fuel Cells Photovoltaics (solar panels) Radioisotope Thermoelectric Generator (RTG) Wind, geothermal, etc.

Common Options (contin.): 

Common Options (contin.) Propulsion Attitude and control ISRU Mobility EVA Rover (pressurized on non?) Assembly plan Logistics plan

System Drivers and Critical Requirements : 

System Drivers and Critical Requirements System drivers = design parameters that influence cost (mass), performance, risk or schedule Examine factors and look for hidden drivers EVA assembly and maintenance analysis Common drivers Number of crew Number of launches and s/c System mass / pressurized volume required Power Data rate and C3 Schedule and Ops

Putting it all together: 

Putting it all together Evaluate concepts Consider reliability (MTBF) and Failure Modes Estimate life cycle costs Parametrically estimate system mass