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Published on January 16, 2008

Author: Terenzio

Source: authorstream.com

Plats du jour:  Plats du jour 9 Thermal Principles (March 20) Convection, Conduction, Radiation in the spacecraft environment Heat capacity and other simplifying considerations Minimalist’s FEA: MOST Hints from Heloise 10 -Thermal / Mechanical Design. FEA. 2 x PDRs (Joel Pedlikin - April 3) 11 - Project Management, Cost & Schedule 2xPDRs (April 10) 11.5 Digital & Special 4/17 12 - Design work (April 24) 13 - Presentations (May 1) 1 - Introduction 2 - Propulsion & ∆V 3 - Attitude Control & instruments 4 - Orbits & Orbit Determination 5 - Launch Vehicles 6 - Power & Mechanisms 7 - Radio & Comms 8 & 9 Reliability (March 13 & 20) Circles, Ellipses and Beyond:  Circles, Ellipses and Beyond r a rp v b Hyperbolic Asymptote Ellipse: Transfer, Molniya, Reconnaissance orbits Comets, Asteroids Real Planets, Moons, LEOs, GEOs Kepler’s 2nd law e = c / a r = p / [1+ e cos(v)] c Orbit Elements: a (or p), e (geometry) plus i p= a(1-e2) Ω (longitude of ascending node) w (argument of periapsis, ccw from Ω) tp, q0 … (epoch) Last week: Reliability:  Last week: Reliability Leads to What & Have in common Reliability arithmetic = probability theory:  Reliability arithmetic = probability theory Chances of: Flipping Heads: 1x: 0.51 = 0.5 2x 0.52 = 0.25 3x: 0.53 = 0.125 4x: 0.54 = 0.0625 (one out of 24 = 1:16) Chances of: Rolling one (snake eye) 1x: (1/6)1 = 0.1667 2x: (1/6) 2 = 0.02778 3x: (1/6) 3 = 0.004630 4x: (1/6)4 = 0.000772 (one out of 64 = 1: 1296) Expected Value = P(success) x Payoff • Bet on one roulette slot: 1/36 x 35x bet = 35/36 •  Lottery: 1: 10,000,000 x $10,000,000 = $1 (but tickets are $2) • Insurance: Premium is always > EV • Betting: Jackpot is always << EV => Why buy insurance or bet? Burglar Alarm Paradox:  Burglar Alarm Paradox Burglar Alarm Reliability: 99.9% • False alarm happens 1:1,000 days (3 years) Chance of being robbed: 1: 100,000 houses (or cars) P(alarm goes off due to robbery): Assume alarm sounds: P(Robbery) = 0.00001 P (False) = 0.001 => P(False) / P(Robbery) = 0.001 / 0.00001 = 100 : 1 ->100 false alarms for every real robbery <- If Alarm lives 10 years and false alarm costs $100: Cost = $100 x 0.001 x 365 x 10 + $(buy and keep alarm) = $365 + ($250 + $10 x 12 x 10) = $1815 = Cost Expected Value = 0.00001 x 365 x 10 x uninsured deductible (maybe $25k) = $912.50 = EV A World of Burglar Alarms:  A World of Burglar Alarms Any test performed a large number of times looking for an unlikely result: - Engineers’ warnings about unsafe vehicles, bridges… - Corporate whistle blowers - Mammography & other cancer screenings - Pregnancy & AIDS home tests - The latest advice on Butter, Margarine, blue-green algae, wheat grass, 8 liters of water per day… - Self test (eg in BMWs & VWs) - Owning a gun and keeping it in home, glovebox, pocket - S - Class parts: screening for defects - X-ray screening of parts / bombs - Twin - engine aircraft (depends on pilot) - Terrorist Alerts (high-res burglar alarm analogy) - Uninteruptable PS and 9V batteries in clock radios Weakest Link? Small Satellite Historical Survey results: 1956 - 1996:  Weakest Link? Small Satellite Historical Survey results: 1956 - 1996 Ground Rules: Small defined as < 150 kg. Exceptions for a few (<5) larger payloads which had dedicated Scout / Pegasus launches 456 Missions counted - all flown between 1956 and 1996. Multiple deployments of identical satellites were counted as 1 mission Note: Some countries may not have reported all launch and/or spacecraft failures The Statistics: 310 Spacecraft inserted successfully in orbit: 69% insertion reliability Failures include separation systems, upper stage engines, launch failures. Of 310 inserted successfully, 293 (95%) performed mission successfully If launches are historically 85% to 90% reliable, then mechanisms other than launch and the satellite are only about 80% reliable (the least reliable link in the chain). My Conclusions: This weakest link is separation and deployment mechanisms Launch reliability: 90%. Separation reliability: 80% Spacecraft reliability: 95%: Are we overspending on spacecraft reliability? Are small spacecraft more reliable than conventional ones despite decreased attention to traditional space product assurance methods? REAL THREATS:  REAL THREATS Funding Optimize what? P(corporate survival) vs. P(Program Survival) Promote, utilize foreign partners (space station strategy) Discipline: don’t blow the budget - cut requirements Team Performance Provide lots of feedback, + and -. Don’t skimp on tools, provide goodies Enforce buddy system, don’t hire stars Don’t demand paper Supply food Requirements Creep Accept no free features! Beware of, in fact, avoid at all costs, features justified on the basis of “easy”, “automatic”, “built in” or “useful next program” (even if the adjective “really” is appended) Don’t improve the design, extend test specs and duration Due Tonight (Thursday, March 20):  Due Tonight (Thursday, March 20) Reading on Reliability: SMAD 19.2 (15 Pages worth reading / skimming) TLOM 15 (clean rooms etc.) Reading on Thermal Design SMAD 11.5 (31 pages worth reading + good ref. Data) TLOM 10 Mission Success / Reliability plan (Electronique svp) Designing in Reliability - Mission Definition Insurance - Risk mitigation Estimate lifetime, P(Success) - Test Plan Due Thursday, April 3:  Due Thursday, April 3 Reading on Structural Design SMAD 18.3 (10 easy pages on structural requirements) Review/use SMAD 11.6 (36 pages on Structural analysis) For 4/10: Reading on Project Management: SMAD Chapter 23 (9 easy pages) TLOM ? Budgets Link - Bits (how many you need) Power - Mass $ (for key components +?) - ∆V (station keeping / ACS…) Thermal - schedule and labor (ROM) Conduction:  Conduction the primary heat transfer mechanism within a satellite Convection:  Convection the least significant heat conduction mechanism within a satellite Q: Why do we care about convection? A: We don’t - there is no flowing medium to conduct heat - but note that in an atmosphere + g-field, there is. A’: Putting a terrestrial device in a pressurized container may not be enough - you need a fan too. Even then, some part won’t get fanned and will overheat. A’’: Convective heat flux - without even a fan - is typically 10x to 100x conductive heat flux. Radiation:  Radiation the only way to lose or gain thermal energy => Heaters are futile??? Heat Capacity / Thermal Inertia:  Heat Capacity / Thermal Inertia µS/C Simplifications: thermal model:  µS/C Simplifications: thermal model Case Study: MOST thermal model:  MOST (Microvariability and Oscillations of STars) in development at University of Toronto. MOST is about the size of a briefcase and points one major face at the sun. (back side shown including marmon ring) Case Study: MOST thermal model More µSC Simplifications:  More µSC Simplifications Thermal Tools & Tactics:  Thermal Tools & Tactics

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