Transcript Emerging Spacecraft Technologies and Applications

Plats du jour
• 9 Thermal Principles
(March 20)
• 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)
– 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)
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)]
Orbit Elements:
a
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)176 Meeting #9
Engineering
r
b
c
v
rp
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)
1x: 0.51 = 0.5
1x: (1/6)1 = 0.1667
2x
0.52 = 0.25
2x: (1/6) 2 = 0.02778
3x:
0.53 = 0.125
3x: (1/6) 3 = 0.004630
4x:
0.54 = 0.0625
(one out of 24 = 1:16)
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?
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) = $912.50 = EV
Engineering 176 Meeting #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 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
Engineering 176 Meeting #9
Weakest Link?
Small Satellite Historical Survey results: 1956 - 1996
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Ground Rules:
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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:
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310 Spacecraft inserted successfully in orbit: 69% insertion reliability
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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:
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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
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Team Performance
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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
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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
o
Q = A  ²T / L
Big vs. Small Satellite Conduction Examples
Big
Small
²T = Q L / A 
L=4m; A=10 -2m 2; Q  solar area = 16 m 2
Engineering 176 Meeting #9
²T = Q L / A 
L=.5m; A=10 -3m 2; Q  solar area = .25 m 2
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.
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
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
µS/C Simplifications: thermal model
Small Thermal Model
1) 1000 W/m 2
2) A = 1 m 2  = o
3)  = x,  = y y
4) Tair , Vair
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
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)
MOST Heat Transfer Solver
Major Face Area =
0.6
2
m
# of structural members
Solar Panel abs & emm =
0.85
Is = 1350 x abs. x A =
688.5
Watts
0.1
meter
167
W/mK
Width (front to back) =
erial: 6061-T6 Aluminum
Back side thermal emm =
3
Length of structure
0.77
m
Thickness of structure
0.003
m
Thermal Conductance = A
/L=
11.642
w /K
0.5
T (s)
Qr (s)
Qr (b)
T (b)
²T
(Gues s )
r adiate to s un
Abs - (r-t-s )
to r adiate
to r adiate
373
560
129
295
78
909
11
front way hot
323
315
374
385
-62
-722
32
front way cold
365
513
175
319
46
540
15
Front smidge hot
355
459
229
341
14
166
20
front bit cold
356
464
224
339
17
201
19
front bit cold
337
20
236
19
Ahhhhh!
357
Engineering
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219 #9
Qc(s->b)
²T reqd.
comment
(conductive ) Conduct->r adi ate
More µSC Simplifications
Engineering 176 Meeting #9
Thermal Tools & Tactics
Engineering 176 Meeting #9