483 Lecture. Space Mission Requirements. February11, Definition Examples Dos/ Don ts Traceability

Transcription

1 483 Lecture Space Mission February11, 2012 Photo Credit::

2 What s a Requirement? ification? Requirement A concept independent statement of a mix of needs, wants, constraints, and sometimes preferred solution A description of functional, performance, physical, and interface characteristics and constraints for a product or service ification A concept dependent document that describes the exact functions and performance required to implement a selected concept A collection of requirements for a single system or function, including the qualification conditions for each requirement

3 Example Good Requirement Defines type To be verb The C&DH subsystem shall be able to download all housekeeping telemetry using the 20 kbps downlink. Defines a positive end result Performance criteria The challenge is to seek out the user type, end result, and success measure in every requirement you define

4 Flow Example System Document Launch on Delta II System ( A ) ification System ( A ) ification Launch Satellite on a Delta II LV Launch Satellite on a Delta II LV Space Segment Space Segment Mass 2650 kg Mass 2650 kg System Development ( B ) ification System Development ( B ) ification Launch 2700 kg Satellite into Sun Launch 2700 kg Satellite into Sun synchronous orbit synchronous orbit Launch Segment Launch Segment Launch 2700 kg into Launch 2700 kg into Sun synch orbit Sun synch orbit Ground Segment Ground Segment N/A N/A Bus Bus Mass 1100 kg Mass 1100 kg Mass Margin Mass Margin Space Segment Space Segment Initial = 400 kg Initial = 400 kg Payload Payload Mass 1150 kg Mass 1150 kg P/L Adapter P/L Adapter ification ification Mass 50 kg Mass 50 kg Structures and Structures and Mechanism Mechanism Mass 325 kg Mass 325 kg C&DH/TT&C C&DH/TT&C Mass 50 kg Mass 50 kg Propulsion SS Propulsion SS Mass 175 kg Mass 175 kg EPDS EPDS Mass 325 kg Mass 325 kg ADCS ADCS Mass 225 kg Mass 225 kg Propellant Mass 100 kg Telescope Telescope SS SS Mass 500 kg Mass 500 kg Instrument Instrument SS SS Mass 250 kg Mass 250 kg Optical Bench Optical Bench & Structures & Structures SS SS Mass 250 kg Mass 250 kg P/L Control & P/L Control & Data Handling Data Handling SS SS Mass 150 kg Mass 150 kg A6917_168B[ISO] vsd/wise /2/99

5 Use of shall, will, should, and may Use shall whenever a specification expresses a provision that is binding Use should and may when necessary to express non-mandatory provisions The verification method is N/A Will can be used to express a declaration of purpose on the part of the customer It may also be necessary to use will in cases where the simple future tense is required - Power for the motor will be supplied by the ship. Remember The customer will The contractor shall Be consistent in word use for mandatory requirements Be equally consistent in word use for optional requirements

6 Properties of good requirements ify what s essential to perform mission Necessary- capability, physical, or quality Concise Implementation-free ifies the function, not design Attainable Complete- standalone Unambiguous Verifiable- by test, demonstration, analysis, inspection Consistent Traceable Slide source: SMAD Ch. 4 and AOSS 583 Course Notes 2012

7 Properties of bad requirements Dictates design Imposes needless constraints Anything referring to objectives/ goals Minimize/ Maximize Bad terms to use Rapid User-friendly Easy Sufficient Adequate Quick Flexible And/Or Slide source: SMAD Ch. 4 and AOSS 583 Course Notes 2012

8 Requirement - NEED MORE System Segment Component Process (SPS) Industry specifications and standards are available in the public domain Military: NASA: Material

9 Science Matrix (in teams) 3:50-4:20 What is a Science Matrix (STM)? Simple, quick description of mission goals and implementation Overview of what the mission will accomplish Demonstrates traceability- how downstream decisions are driven by program, mission, and science objectives Famous JPL quote: Who is Mr./ Mrs. Moneybags? (usually drive program objectives) Elements of STM: Program Objectives Mission and Science Objectives Measurement Objectives Measurement Instrument Science Products Spacecraft, Ground System, Mission Operations What do you need to do? How are you going to accomplish it? Task: Develop an STM for the Mission concept you are assigned Reference available on CTools here: AEROSP W12 Resources / Readings and References / Mission Design/ WEISS_Science Matrix_JPL_2009.pdf

10 Example STM: DUST Mission Program Objectives: Study space weather with multiple in-situ satellites Mission and Science Objectives Measurement Objectives Measurement Instrument Science Products Spacecraft (ex.) A) Study Measure global atmospheric atmospheric density in LEO to density on a re-entry altitudes small-scale Multiple spatial/temporal in-situ measurements (accuracy ~10-12 kg/m 3?) * Wind Temperature Sensor (WTS)* measures neutral density Spatially and temporally distributed measurements to generate Maps/Models of atmospheric densities (particularly at low altitudes) Sufficient power, (1 W average), attitude knowledge (to 1 deg),. Measure atmospheric density on a large-scale Knowledge of s/c attitude (passive control/determination?), Multiple in-situ GPS and/or Groundbased measurements tracking Spatially and temporally distributed measurements of satellite locations-> drag effects->maps/models of GPS receiver, atmospheric densities (particularly at Sufficient power, (1 low altitudes) W average), B) Study electron density which interfere with communication/g PS in LEO to reentry altitudes Measure global electron density on a small-scale electron temperature, electron density, and electric potential Langmuir probe Spatially and temporally distributed measurements to generate Maps/Models of electron densities (particularly mid-latitude), plumes/scintillations, small scale instabilities (particularly at low altitudes) Sufficient power, (1 W average), attitude control (1 deg), knowledge (0.1 deg), OTHERS? *WTS (from WINCS) is a miniature instrument to measure the wind, temperature and atomic densities of the local neutral atmosphere. This instrument includes a unique imaging capability which can measure the number density across a 16 pixel fan, allowing the determination of not only the composition of the local atmosphere, but also the presence of any horizontal cross-track winds

11 What are requirements? Two types: Functional- what does the system need to do? Operational- how is the system going to accomplish it should answer the question: Are the main goals being accomplished? [Reno s 483 Talk] Does the design provided required functions? Is the design robust over time/ conditions?