Plats du jour

• 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 14 & 19) Engineering 176 Meeting #9 • 9 Thermal Principles (March 19) – Convection, Conduction, Radiation in the spacecraft environment – Heat capacity and other simplifying considerations – Minimalist’s FEA: MOST – Hints from Heloise • 10 (11?) -Thermal / Mechanical Design. FEA (Joel Pedlikin - April 4 or 11) • 11 (10?) - Project Management, Cost & Schedule (April 18) • 12 - Design work +digital (April 25) • 13 - Presentations (May 2 or … )

Last week’s note on do-ability

• Orbital Rockets - barely do-able and for 10,000 years, not do able. 100 years from now, might be as easy as flying a Cessna to 10kft.

• Television - barely do-able in 1940s • Flight- barely do-able: Lindberg and Earhardt • Digital graphics - JPL IPL - famous in 1980s • Radios: barely do-able in Marconi era • Maybe we will say the same, 50 years from now, about … - personal satellite comms - earth services from space (light, power) - space billboards

Critical step is finding out what

’

s missing

Engineering 176 Meeting #9

Feynman on do-ability

• There was a time we didn ’ t understand even how gravity behaved • Then we modeled it (Kepler) but didn ’ t have a law of gravitation • Now we have the law of gravitation, ( but not the physics) • Understand large scale (planets, stars) ( Newton and Einstein) • Understand meso scale (atoms to planets) (Newton and Planc et al.) • Do not understand sub-proton / sub-neutron scale • QED was the first successful attempt to describe behavior of sub-nuclear particles (Feynman Nobel) Engineering 176 Meeting #9

Circles, Ellipses and Beyond

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

)]

b

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) t

p

, q

0

… (epoch) Engineering 176 Meeting #9

c r

v

r p

Vernal Equinox

(‘02 March 20, 2:16 pm)

Too many days Every 4th year correction is the Julian Calendar leap year - but it’s slightly to much - the equinox slips earlier - the calendar pages turn too slowly

Engineering 176 Meeting #9

Skip a leap Don’t Skip a leap Skip a leap Julian -> Gregorian subtracts leap years on centuries (00 years) except 400, 800) (next one to skip is in 2100 - see you there!)

Last week: Reliability

Leads to What &

Engineering 176 Meeting #9

Have in common

Real World FMECA Stats.

Chances of: Flipping Heads: 1x: 0.5

1 = 0.5

2x 0.5

2 = 0.25

3x: 0.5

3 = 0.125

4x: 0.5

4 = 0.0625

(one out of 2 4 = 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 6 4 = 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 = (but tickets are $2) $1 • 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 < 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) =

Engineering 176 Meeting #9

$912.50 = EV

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 at home, in car, in pocket - S - Class parts: screening for defects - X-ray screening of parts - Twin - engine aircraft (depends on pilot) - Terrorist Alerts (high-res burglar alarm analogy) - Uninteruptable PS and 9V batteries in clock radios

Engineering 176 Meeting #9

Real World FMECA Stats.

• Interconnections and interactions (some unknown), dominated by human factors, dominate risks • Same principles apply inside each black box

Engineering 176 Meeting #9

Ie - if we knew how to do this, automobile and drug recalls would be unknown

Real World Reliability How others do it – Systems Redundancy, subsystems degrade gracefully (reliability of species, not individual survival) “ In three words I can sum up everything I've learned about life: it goes on. - Robert Frost (1874-1963) – Balance: • too much defense vs. too little • Longevity vs. reproduction • Trial & error in real world • Consumer Products • run & fight vs. reliability • Think vs. do • learning/adaptation vs. Q – Redundancy is rare – Protect from user - Repair / Replace easier - Routine Maintenance – Product Evolution, not revolution • No user-serviceable parts • Limited control / access • Safety interlocks • Field xperience / statistics • Manufacturing process investment (automated test & cal) – Define “reliability” (e.g. “don’t kill people”) Engineering 176 Meeting #9

Real World Reliability: how we (should) do it • Avoid poor design: • Highest quality engineering team • People (not parts) who have done it before • Buddy system • real world testing based on engineering, not specs/politics • Redundancy for known problem components (batteries) • Special treatment for special parts (DC/DC converters, electrolytic capacitors): – Select / deselect vendors based on experience – Subject all to discrete component tests – Careful visual inspection • All Compoments: verify environment specs + test • Remove hardware (use software): – Packet creation / disassembly - Attitude Determination – Charge control – Antenna pointing - Fine pointing of optics - Is this trip necessary?

(use computers, drop towers, balloons, aircraft) 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 – 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 (see King ’ s Funnel) – 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

Ghosts of Programs Past

Software design and operator errors caused Clementine to accidentally exhaust all its propellant, ending its Mission.

HETE was stranded alive inside rocket launch envelope TRW’s Lewis (left) failed within a few days on orbit due to design and operator errors. Orbital’s Clark (right), Lewis’ “twin”, was cancelled mid-program due to budget overruns

Engineering 176 Meeting #9

JAS-1 underestimated power budget - survived with limited operations. Replaced by JAS-2 A poorly designed fuel system destroyed mars observer just upon reaching its destination.

Due Tonight (Tuesday, March 19)

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

Due Thursday, April 4

• Reading on Project Management: – SMAD Chapter 23 (9 easy pages) – TLOM ?

• Reading on Structural Design – SMAD 18.3 (10 easy pages on structural requirements) – Review/use SMAD 11.6 (36 pages on Structural analysis) • 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 small satellite

o

Q = A



²T / L

Big Big vs. Small Satellite Conduction Examples

²T = Q L / A  L=4m; A=10 -2m 2; Q  solar area = 16 m 2

Small

²T = Q L / A  L=.5m; A=10 -3m 2; Q  solar area = .25 m 2 Engineering 176 Meeting #9

Convection

the least significant heat conduction mechanism within a small satellite Engineering 176 Meeting #9 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

the only way to lose or gain thermal energy

Engineering 176 Meeting #9

Heat Capacity / Thermal Inertia

²T = temperature change in time t c = heat capacity (J / kg K) m = mass (Kg) For T in equilibrium in umbra @ 10C, in sun additional heat flux could be ~ 130 W => new equilibrium temp is 50C! But: • Q = 130W; • C (typical) 1000 J / kg C and • t (in sun) ­ 3600s • m ­ 100 kg => ²T = 130 x 3600 / 1000 x 100 = 4.7C

Moral of the story: Don’t isolate satellite parts and then thermostat them - or you’ll need to.

Engineering 176 Meeting #9

µ

S/C Simplifications: thermal model

Small Thermal Model Large Satellite: - 400 to 4000 node model: Do you believe it? How to test it? Time and $ to create it and test facilities to verify it.

Engineering 176 Meeting #9 1) 1000 W/m 2 2) A = 1 m2  =  o 3)  = x,  = y y 4) Tair , Vair 5) T,  sand , Tlake __________________ Solve a few balance equations; - intuitive and understandable - easy ¦ for resonable results - straightforward verification of individual box models Small Satellite: - 10 to 20 node model: runs on Excel - use large models for fine tuning and extra precision

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)

M OST Heat Transfer Solver M ajor Face Area = Solar Panel abs & emm = Is = 1350 x abs. x A = Width (front to back) = M aterial: 6061-T6 Aluminum Back side thermal emm = 0.6

0.85

688.5

0.1

167 0.5

m 2 Watts meter W / m K # of structural members 3 Length of structure 0.77

m T hickness of structure 0.003

T hermal Conductance = A



/ L = m 11.642

w / K T (s) (Guess) 373 323 365 355 356 357 Qr (s) radiate to sun 560 315 513 459 464 Qr (b) Abs - (r-t-s) 129 374 175 229 224 T (b) to radiate 295 385 319 341 339 337 ²T to radiate 78 -62 46 14 17 20 Qc(s->b) (conductive) 909 -722 540 166 201 236 ²T reqd.

comment Conduct->radiate 11 32 15 20 19 19 front way hot front way cold Front smidge hot front bit cold front bit cold Ahhhhh!

More

µ

SC Simplifications

Engineering 176 Meeting #9

Thermal Tools & Tactics

Engineering 176 Meeting #9