Mission Attrition

1
MissionAttrition
Gets used Works Launched Not preempted Tech
Success Stay Committed Committed
Resources Affordable (ROIgt1) Designs Good
Ideas Ideas Not yet Ideas
1s 10s 100s 1000s 10,000s 105
106
2
The Lineup

• 7 - Radio Comms (3/6)
• Radio Concepts
• Spectrum usage
• Link margin Orbits
• Modulation
• Antennas
• 8 - Thermal / Mechanical Design. FEA (3/20)
• 9 - Reliability (3/13)
• 10 - Digital Software
• 11 - Project Management Cost / Schedule
• 12 - Getting Designs Done
• 13 - Design Presentations

• 1 - Introduction
• 2 - Propulsion ?V
• 3 - Attitude Control instruments
• 4 - Orbits Orbit Determination
• 5 - Launch Vehicles
• 6 - Power Mechanisms(finish tonight)
• CoDRs(final 2 tonight)

3
Design Roadmap
You Are Here
Define Mission
Concept
Solutions Tradeoffs
ConceptualDesign
Requirements
Analysis
Next week I want you to visit here
Top Level Design
PartsSpecs
Suppliers / Budgets
MaterialsFab
Iterate Subsystems
Final Performance Specs Cost
Detailed Design
4
Last week Power
5
And...Deployables

• Definitely not moving - for a long (or too long)
  time
• 1-g vs. 0-g ( vacuum) matters
• Tolerance v. launch loads
• Vacuum welds, lubricants, galling
• Creating friction - rigging
• Static strength, dynamics, resonance
• Safety inhibits (its physical)

Galileo didnt x 1

• Flaws, cracks, delamination, vibration
  loosen/tighten
• Minute population test experience (the Buick
  antenna)
• Total autonomy
• High current actuation
• Statistics - ways to work v. not

Freja did x 8
6
Due tonight

• Preparation Radios Comms
• SMAD Chapter 13
• TLOM Chapters 7,8,9

• Technical requirementsCreate a list of
  technical requirements - even if it has TBDs in
  it. ( revisit mission rqts)

• Systems design / CoDRcreate a good looking
  cartoon set of the spacecraft, orbit and ground
  segments

• Tools selection
• Finite element
• Design and layout
• Presentation Graphics

• Tech Design / Analysis / Suppliers
• Structure / Thermal
• Design and layout
• Orbit / Launch
• ACS / Propulsion //

• Something Physical

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The plan for March 13

• Part 1 (assignment) Radio Strategy - what
  why why not the other options Spacecraft Tx
  Power, modulation, antenna selection, l same
  for Ground Station Up and down link calcs

• Part 2 (reading on reliability)
• SMAD 19.2 (15 Pages worth reading / skimming)
• TLOM 15 (clean rooms etc.)
• Part 3 Design
• What you are going to build
• Requirements Document

• Tech Design / Analysis / Suppliers
• Structure / Thermal
• Design and layout
• Orbit / Launch
• ACS / Propulsion

8
Electromagnetic Spectrum Map
100 GHz 10 GHz 1 Ghz 100 MHz 10 MHz 1
MHz 100 KHz 10 KHz 1 KHz 100 Hz 10 Hz
- SHF and some radars 15 - 50 GHz - UHF /
L-band Television, spacecraft, cordless
cellular 500 MHz to 1 GHz - Short Wave radio
International broadcast, amateur HF, worldwide
non-satellite comms 1.6 Mhz to 50
MHz Telephone / RTTY baseband 2400 - 9600
HzPower transmission 60 Hz
- (3 - 30) Millimeter wave / blackbody radiation
(10 - 100GHz) - Microwave Terrestrial
satellite, µwave ovens, Radio Astronomy1 GHz -
15 GHz - VHF FM radio, Taxi, Air Traffic, Air
Nav, VHF Amateur radio, Little LEOS50 MHz to
500 MHz - AM Radio, medium and long wave 180
KHz to 1.6 MHzVLF Comms (eg submarines)100
- 5000 Hz
1 cm 1 m 100m 10 km 1000 km (l)
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Some Radio Facts (?)

• 100 KHz is the low end of the useful radio band
• 100 MHz is low end of useful satellite lt --- gt
  earth links
• Light and heat are alternatives to radio -and
  no license required
• Radio is barely possible 0.5 W _at_ 2000 km yields
  4 x 10-14 W/m2
• Propagation goes as 1/r2
• Since EIR, for a 50W antenna, that signal is a
  µV varying at gt 109/second
• Bandwidth and data rate are proportional -
  mostly Shannons Law R(max) Blog2( 1 C
  / N )

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Spectrum Trades
Spectrum Region Pros Cons Below 100
MHz ( ) Ionosphere
blocks HF / VHF  Limited bandwidth l gt 3m
Big antennas 100 - 500 MHz Best
link with omnis Antennas are large VHF / UHF
Low cost RF components  Hard to provide
gain 3m gt l gt 60 cm Highest h
(80)  Limited bw (kbit/s) 1 - 2.5
GHz  Commercial gear plentiful  Crowded! L
S Bands  Good bw (Mbit/s)  Usually
requires 30 cm gt l gt 12 cm Good Tx h (60)
gain antennas  Small, low cost
antennas 8 - 10 GHz Small, high gain
antennas  Higher cost X - band  Less
Crowded Lower h (lt50) l - 3 cm  High bw
(many Mbit/s)   Some Wx sensitivity 25
GHz  Huge bw (Gbit/s)  Wx
sensitive SHF  Very high gain antennas
Slant angle limited l - 1.5 cm  Easiest
license to obtain  High Cost  Low h
(lt30)
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Data Rates

• Whats in a baud?
• 1 to 100 basic pager
• 100 to 1k messaging pager
• 1k to 10k fax, email, voice
• 10k to 100k web surfing, picture phone, digital
  radio
• 100k to 1M Digital LDTV
• 1M to 10M Digital HDTV
• 10M to 1B Data, multiplexing and multi channel
  of above

• Spacecraft data rates
• Amsat 10k
• Advanced micros 1M
• Small Sats (Iridium) 10M -
  100M
• Big satellites gigabits per second

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Modulation

• AM not inherently digital, low efficiency
• FM Easy lock where power is not critical
  (uplinks)
• BPSK QPSK Inherently Digital and efficient
• Spread Spectrum Low efficiency, bulletproof

Phase Shift
Interpretation
0
0 , 0
90
0, 1
180
1, 1
270
1, 0
360
0, 0
(Same as 0)

• Ranging
• Round trip time measurement
• good to bit rate i.e. 106 gt 100 m (maybe 10m)
• Doppler Typically 500m to 10 km
• Note Repeated measures of range and time
  allows orbit solution

• To Avoid
• Multiple Modulation Schemes
• subcarriers etc. (not info dense)

13
Attrition II
Field degradation Worst case link Eb / No (error
spec) Demodulation Modulation Noise(Tr, a, sky)
BW No Receive Aperture Absorb, polarize 4?r2 ( -
Gt ) Line / feed lossesBit rate Eb Transmitter
nWatts
100 102 104 106 108
1010 1012
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Notes on Links and Link Margins
The Link Equation objective Eb / Nb large
enough to detect the signal within a specific
level of uncertainty (error rate) Eb / Nb
Power x Lossl x Gaint x Ls x La x Gr
k x T x R where Lossl line loss
k Boltzmanns const. Gaint transmit
antenna gain T Temp (K) Ls space
loss (spreading) R Data Rate La
path attenuation Gr receive antenna
gain But... Gr is not real - it is
defined as the ratio of real aperture to
aperture of an isotropic antenna, l2/4p So
really it is a measure of area ratio, not gain.
Rx Antenna as noise reducer. Question Why is
R in the denominator (the No part?)
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(more) Notes on Links and Link Margins
How much margin do you need? - whats the
actual local horizon? - whats the penalty for
losing lock sometimes?  Local obstructions are
a factor - especially when snow covered
Variable data rate  Some tradeoffs - sun vs.
earth pointing - sun tracking PV array vs. earth
tracking antenna - data rate vs. contact
duration ( of GSs) - GS vs. satellite gain -
compression (CPU cost) vs. downlink rate  Its
amazing the link works at all...
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Orbit Implications for Comms

• LEO has 1600x easier link
• 3x (10dB) smaller antenna (50x lighter)
• 10x lower power
• 3x (10dB) smaller GS antenna

• But
• Need 10x more satellites, 5x more launches
• Reconstitution hassles
• Global Coverage! (whether you want it or not)
• Constellation Management
• Cross Linking, switching, handoffs

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Escort Link
36,000 km
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The costs of bit rate, small user terminals and
large coverage area
Availability
- Global Mobile - Many Locations - Fixed
Location

• Power a baud (bit rate)
• Power a (1/antenna dia)2
• Power a Service Area
• Power a obstacles (windows, roofs)
• Service Area a orbit altitude
• Mass a (Antenna dia)3

- Video - CD radio - Telephone - Paging
Laptop- Cell Phone - Wristwatch -
Bandwidth
Portability
Spacecraft Cost
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Ground
Elements
Station
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Antenna Strategies

• Omni (Sputnik)- 0 dB gain (or less)- Requires
  gt1 antenna- Interference fringes- Downlink
  power?

• Sector (HETE) 3 - 6 dB gain (or less)
  Requires gt1 antenna Active Control but no ACS
  impact

Directional (Pioneer)- huge gain 24 dB typ.
- requires gt1 just in case- Major ACS impact-
Steerable?
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Link design

• Start with Spacecraft
• Whats the critical link
• Up or down?
• What data rate required
• Frequency considerations
• GS limitations (power, gain)
• Eventually, pin down all but one or two variables
  e.g.
• Space antenna gain
• Modulation method
• Then do a trial link and iterate
• Note All user links need lots of margin - 10 dB
  good, 20 dB better

• Some tricks
• How reliable does the link need to be? What
  error rate?
• Coding requires only computation
• How close to the horizon can your GS see?
• Is one link critical, the other not?
• Differentiate master GS from user terminals
• Burst mode power can be higher - use batteries
• Scanning a high-gain antenna
• Spread spectrum - hurts link but helps sharing
  and security (whats in rqts?)