Plats du jour

1
Plats du jour

• 9 Thermal Principles (March 19)
• Convection, Conduction, Radiation in the
  spacecraft environment
• Heat capacity and other simplifying
  considerations
• Minimalists 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)

• 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)

2
Last weeks 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
  billboardsCritical step is finding out whats
  missing

3
Feynman on do-ability

• There was a time we didnt understand even how
  gravity behaved
• Then we modeled it (Kepler) but didnt 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)

4
Circles, Ellipses and Beyond
Ellipse Transfer, Molniya, Reconnaissance
orbits Comets, Asteroids Real Planets, Moons,
LEOs, GEOs Keplers 2nd law e c / a r p /
1 e cos(v)
Hyperbolic Asymptote
r
b
v
rp
a
c
Orbit Elements a (or p), e (geometry) plus ip
a(1-e2) ? (longitude of ascending node) w
(argument of periapsis, ccw from ?) tp, q0
(epoch)
5
Vernal Equinox (02 March 20, 216 pm)
Too many days
Dont Skip a leap
Skip a leap
Skip a leap
Every 4th year correction is the Julian Calendar
leap year - but its slightly to much - the
equinox slips earlier - the calendar pages turn
too slowly
Julian -gt Gregorian subtracts leap years on
centuries (00 years) except 400, 800) (next one
to skip is in 2100 - see you there!)
6
Last week Reliability
Leads to
What Have in common
7
Real World FMECA Stats.
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 24 116)
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
gt EV  Betting Jackpot is always ltlt EV gt Why
buy insurance or bet?
8
Burglar Alarm Paradox
Burglar Alarm Reliability 99.9 False alarm
happens 11,000 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 gt P(False) / P(Robbery) 0.001 / 0.00001
100 1 -gt100 false alarms for every real
robbery lt-
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
9
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
10
Real World FMECA Stats.
Interconnections and interactions (some
unknown), dominated by human factors, dominate
risks Same principles apply inside each black
box
Ie - if we knew how to do this, automobile and
drug recalls would be unknown
11
Real World ReliabilityHow 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 run fight
  vs. reliability
• Longevity vs. reproduction  Think vs. do
• Trial error in real world  
  learning/adaptation vs. Q
• Consumer Products
• Redundancy is rare - Repair / Replace
  easier
• Protect from user - 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. dont kill people)

12
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 - Fine pointing of optics
• Antenna pointing - Is this trip necessary?
  (use computers, drop towers, balloons,
  aircraft)

13
Weakest Link? Small Satellite Historical Survey
results 1956 - 1996

• Ground Rules
• Small defined as lt 150 kg. Exceptions for a few
  (lt5) 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?

14
REAL THREATS

• Funding
• Optimize what? P(corporate survival) vs.
  P(Program Survival)
• Promote, utilize foreign partners
• Discipline dont blow the budget - cut
  requirements
• Team Performance
• Provide lots of feedback, and -. Dont skimp
  on tools, provide goodies
• Enforce buddy system, dont hire stars (see
  Kings Funnel)
• Dont 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)
• Dont improve the design, extend test specs and
  duration

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16
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 - Mission Definition
• Insurance - Risk mitigation
• Estimate lifetime, P(Success) - Test Plan

17
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 - Bits (how many you need)
• Power - Mass
• (for key components ?) - ?V (station keeping /
  ACS)
• Thermal - schedule and labor (ROM)

18
Conduction
the primary heat transfer mechanism within a
small satellite
19
Convection
the least significant heat conduction mechanism
within a small satellite
Q Why do we care about convection? A We dont
- 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 wont get
fanned and will overheat. A Convective heat
flux - without even a fan - is typically 10x to
100x conductive heat flux.
20
Radiation
the only way to lose or gain thermal energy
21
Heat Capacity / Thermal Inertia
22
µS/C Simplifications thermal model
23
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)
24
More µSC Simplifications
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Thermal Tools Tactics