Скачать презентацию Plats du jour 9 Thermal Principles March

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• Количество слайдов: 18

Plats du jour • 9 Thermal Principles (March 20) • 1 - Introduction • 2 - Propulsion & ∆V • 3 - Attitude Control & instruments • 4 - Orbits – Convection, Conduction, Radiation in the spacecraft environment – Heat capacity and other simplifying considerations – Minimalist’s FEA: MOST – Hints from Heloise & Orbit Determination • 5 - Launch Vehicles • 6 - Power & Mechanisms • 7 - Radio & Comms • 8 & 9 Reliability (March 13 & 20) • 10 -Thermal / Mechanical Design. FEA. 2 x PDRs (Joel Pedlikin - April 3) • 11 - Project Management, Cost & Schedule 2 x. PDRs (April 10) • 11. 5 Digital & Special 4/17 • 12 - Design work (April 24) • 13 - Presentations (May 1) Engineering 176 Meeting #9

Circles, Ellipses and Beyond Ellipse: ptot e Transfer, Molniya, Reconnaissance orbits sym Comets, Asteroids ic A Real Planets, Moons, LEOs, GEOs r = p / [1+ e cos(v)] Orbit Elements: a a (or p), e (geometry) plus i p= a(1 -e 2) Ω (longitude of ascending node) w (argument of periapsis, ccw from Ω) tp, q 0 … (epoch) Meeting #9 Engineering 176 r b c v rp Hyp e=c/a erbo l Kepler’s 2 nd law

Last week: Reliability Leads to What & Engineering 176 Meeting #9 Have in common

Reliability arithmetic = probability theory Chances of: Flipping Heads: Chances of: Rolling one (snake eye) 1 x: 0. 51 = 0. 5 1 x: (1/6)1 = 0. 1667 2 x 0. 52 = 0. 25 2 x: (1/6) 2 = 0. 02778 3 x: 0. 53 = 0. 125 3 x: (1/6) 3 = 0. 004630 4 x: 0. 54 = 0. 0625 (one out of 24 = 1: 16) 4 x: (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 35 x bet = 35/36 • Lottery: 1: 10, 000 x \$10, 000 = \$1 (but tickets are \$2) • Insurance: Premium is always > EV • Betting: Jackpot is always << EV => Why buy insurance or bet? Engineering 176 Meeting #9

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

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 9 V batteries in clock radios Engineering 176 Meeting #9

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? Engineering 176 Meeting #9

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 Engineering 176 Meeting #9

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 – Insurance – Estimate lifetime, P(Success) Engineering 176 Meeting #9 - Mission Definition - Risk mitigation - Test Plan

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 Power \$ (for key components +? ) Thermal Engineering 176 Meeting #9 - Bits (how many you need) - Mass - ∆V (station keeping / ACS…) - schedule and labor (ROM)

Conduction the primary heat transfer mechanism within a satellite Engineering 176 Meeting #9

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 10 x to 100 x conductive heat flux. Engineering 176 Meeting #9

Radiation the only way to lose or gain thermal energy => Heaters are futile? ? ? Engineering 176 Meeting #9

Heat Capacity / Thermal Inertia Engineering 176 Meeting #9

µS/C Simplifications: thermal model Engineering 176 Meeting #9

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) Engineering 176 Meeting #9

More µSC Simplifications Engineering 176 Meeting #9

Thermal Tools & Tactics Engineering 176 Meeting #9