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Seminar 12The Future of Space Flight

Telemetry, Communications, & TrackingRobert Stengel

FRS 148, From the Earth to the Moon Princeton University

Copyright 2019 by Robert Stengel. All rights reserved. For educational use only.http://www.princeton.edu/~stengel/FRS.html

EntrepreneurshipGovernment-Funded Projects

Cost GrowthMarkets

Antennas and Signal PropagationSignal Detection and Noise

Deep Space Network1

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Commercial Space Transportation:Industry Trends, Government Challenges, and International Competitiveness Issues, GAO 12-836T, 2013 [https://www.gao.gov/assets/600/591728.pdf]

Pathways to Exploration: Rationales and Approaches for a U. S. Program of Human Space Exploration, National Research Council, 2014 [https://www.nap.edu/catalog/18801/pathways-to-exploration-rationales-and-approaches-for-a-us-program]

Resources

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https://en.wikipedia.org/wiki/Arianespacehttps://en.wikipedia.org/wiki/Asteroid_impact_avoidancehttps://en.wikipedia.org/wiki/B612_Foundationhttps://en.wikipedia.org/wiki/Bigelow_Commercial_Space_Stationhttps://en.wikipedia.org/wiki/Blue_Originhttps://en.wikipedia.org/wiki/Chinese_space_programhttps://en.wikipedia.org/wiki/Colonization_of_the_Moonhttps://en.wikipedia.org/wiki/Commercial_Crew_Developmenthttps://en.wikipedia.org/wiki/Future_of_space_exploration

Resources

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https://en.wikipedia.org/wiki/Japanese_space_programhttps://en.wikipedia.org/wiki/List_of_government_space_agencieshttps://en.wikipedia.org/wiki/List_of_private_spaceflight_companieshttps://en.wikipedia.org/wiki/Private_spaceflighthttps://en.wikipedia.org/wiki/Space_debrishttps://en.wikipedia.org/wiki/Space_industry_of_Russiahttps://en.wikipedia.org/wiki/Space_tourismhttps://en.wikipedia.org/wiki/SpaceXhttps://en.wikipedia.org/wiki/The_Planetary_Societyhttps://www.nasa.gov/about/whats_next.htmlhttps://www.nasa.gov/exploration/systems/sls/overview.html

Resources

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Discussion Topics§ Perpetuating the human race throughout

the solar system/galaxy§ Colonization of Moon and Mars§ International cooperation and competition§ AI§ Business opportunities§ Space tourism§ Aerospace planes§ Astronomical satellites§ Deep space probes

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Discussion Topics§ Critical programs

§ Weather/Earth resources satellites§ Communications satellites§ Asteroid defense§ Surveillance

§ Launch vehicles§ Expendable§ Reusable§ Commercial

§ Rocket propulsion§ CubeSats§ Space junk

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Discussion Topics§ Federal space programs

§ Civilian§ Military

§ Weaponization of space§ Commercial space development

§ Mining asteroids and the Moon§ Sub-orbital hypersonic transportation§ Risk-taking§ Human spaceflight

§ Travel to Moon and Mars§ Farther?§ Extended weightlessness§ Radiation exposure

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Telemetry, Communications, & Tracking

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Antenna Gain• Isotropic (uniform) radiation of power, P, from the center

of a sphere of radius, r• Power per unit area (power density) of sphere�s surface

p = P 4πr2

• Power received from isotropic radiator over area, S

PS = Spψ = beamwidth half-angle

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Antenna GainPower received over area, S, if all power is

focused uniformly on that area by antenna with gain, G

�

PS = GSpS = P

• Power density in S with idealized focused antenna

�

pS = P GS• Idealized antenna gain

�

G = PSpS

= 4πr2

S10

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Relationship of Antenna Area and Signal Wavelength to Antenna Gain

�

Geff =4πAeff

λ2

c = speed of light ≈ 3×108m / sf = carrier signal frequency,HzAeff = effective antenna area,m

2

λ = carrier signal wavelength,m= c / f

Effective antenna gain (transmitting or receiving)

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Relationship of Antenna Area and Signal Wavelength to Antenna Gain

Power received from the transmitter

�

Pr = prAr = GtPtAr

4πr2

pr = power density at receiving antennaAr = effective area of receiving antennaGt = gain of transmitting antenna

Pt = transmitted powerr = distance between transmitting and receiving antennas

Power ratio

�

Pr(watts)Pt (watts)

= GtAr

4πr212

Power Ratio (decibels, dB) = 10 log10Pr (watts)Pt (watts)

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Antenna Characteristics

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Typical Antenna Pattern• Gain vs. angle from boresight axis (2-D)• Geff is average gain over beamwidth• Beamwidth variously defined as –3 dB cone

angle or half-angle

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Characteristics of Typical Spacecraft Antennas

Conical log spiral antenna

Gain(dBi) ! 10 log Antenna GainIsotropic Antenna Gain

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Alternative Expressions for Power Ratio

Pr (watts)Pt (watts)

= GtAr4πr2

= AtArλr( )2

=

AtAr f2

cr( )2= GtGrλ

2

4πr2= GrAt4πr2

Power ratio in decibels

10 log10PrPt

⎛⎝⎜

⎞⎠⎟(dB) =

Gt (dB)+10 log10 Ar (dB)−10 log10 4π (dB)− 20 log10 r(dB)16

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Detected Power

�

PrPt(dB) = Pr

Pt

⎛

⎝ ⎜

⎞

⎠ ⎟ ideal

(dB) − Absorbtion(dB) − Rainfall(dB)

± Multipath(dB) −CrossPolarization(dB)

Pr = Pcarrier + Pinformation ≈ PcarrierPd = Pr + Pn

• Receiver�s detected power from– transmitter�s carrier signal– information signal– noise

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Noise Sources

Receiver thermal and �front end� noiseAtmospheric, cosmic, solar, and man-

made noisePn =

Pnreceiver + Pnatmosphere + Pnsolar + Pncosmic + Pnman−made18

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Receiver NoisePn = kTW (watts)

T = 290 10NF (dB)/10 −1( )= 290 F −1( )

�

k = Boltzmann' s constant =1.38 ×10−23w − s /°KT = effective receiver temperature,°KW = bandwidth,HzNF = receiver noise figureF = receiver noise factor

Power and temperature

Power density No = Pn /W= kT (watts /Hz) 19

Receiver Noise

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Solar NoiseNoise proportional to (wavelength)n or 1/(frequency)n

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Cosmic and Atmospheric

NoisePn ∝λ n

∝ 1 f n

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Signal-to-Noise Ratio and Information Content

�

SN

= Pr(watts)Pn (watts)

�

SN

dB( ) = Pr(dB) − Pn (dB)

�

Pr(dB) ≡10logPr(watts)1watt

⎛

⎝ ⎜

⎞

⎠ ⎟ Channel capacity

C bits / s( ) =W log2S + NN

⎛⎝⎜

⎞⎠⎟

=W log2SN

+1⎛⎝⎜

⎞⎠⎟

�

W = bandwidth,Hz23

Information Bandwidthfc = carrier frequency,Hz

W = Δf = f2 − f1 = information signal bandwidth,Hz

• Low-frequency information signal superimposed on (i.e., modulates) high-frequency carrier radio signal for transmission

• Information signal formats– Analog (continuous)– Digital (discrete)– Digitized analog (i.e.,

A/D conversion)

Power spectral density of transmitted signal

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Signal-to-Noise Ratio per Bit, Eb/No

�

S = received signal powerN = received noise powerW = bandwidth of receiverR = data bit rate

�

Eb : energy per bitNo : noise power spectral density

�

Eb

No

= SNWR

How would you express this in decibels?

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Link Budget for a Digital Data Link

Eb

No

=

PtLlGtLsLaGr

kTsR

�

Pt = transmitter powerLl = transmitter − to− antenna line lossGt = transmit antenna gainLs = space lossLa = transmission path lossGr = receive antenna gaink = Boltzmann' s constantTs = system noise temperature

�

Eb

No

= SNWR

Link budget design goal is to achieve satisfactory Eb/No by choice of link parameters

… in decibels?

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Typical Spacecraft System Noise Temperature

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Free-Space Laser Communication• Diffraction limit of electro-magnetic beam

is proportional to λ/d• λ = Wavelength• d = aperture (diameter) of beam source• Radio frequency wavelengths: cm – m• Optical wavelengths: μm• Up to 106 less beam spread for optical

communication

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Lesh, JPL, 1999 29

Optical Communication Advantage Compared to Ka-Band RF

(One-Way Pluto example, same power input)dB Factor Comparison13 Data Rate Increase 4.9 kbs vs. 270 bps26 Smaller Spacecraft

Aperture10 cm vs. 2 m

4 Less Transmitted Power Required

1 W vs. 2.7 W

7 Lower Transmitter Efficiency

5% vs. 28%

2 Lower System Efficiencies

24% vs. 40%

3 Atmospheric Loss -10 Smaller Ground

Station10 m vs. 34 m

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Good News/Bad News for Optical Communication

• Good news• Higher bit rates possible• Optical beams are narrower• Energy concentrated on receiver

• Bad News• Optical beams are narrower• Narrow beams must pointed more precisely• Must track intended receiver• RF may be preferred for acquisition,

command, and tracking• Effects of cloud cover

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LADEE Lunar LaserComSpace Terminal

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LADEE LaserCom Components

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Deep Space Network• Radar tracking (range,

elevation, and azimuth)• Radiated signal power drops

off as 1/r2• Reflected return signal power

drops off as 1/r2• �Skin track� return signal

power drops off as 1/r4

• Beacon (or transponder) on cooperative target– Receives radiated signal– Re-transmits fresh signal

• Known time delay• Different frequency

– Return signal power drops off as 1/r2

Goldstone 70-m Antenna

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Deep Space Network Coverage

JPL Control Center

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Communications Geometry• Ground station communication and tracking limited by its minimum

elevation angle, γ• Fixed (non-steerable) antenna must have sufficient beamwidth to transmit

or receive• Antenna gains and radiated power must be adequate, given slant range

and noise environment

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Beamwidth Coverage

• Broad or narrow coverage may be desired

�

ψ(cone) ≈ 21fd,deg

f = carrier signal frequency,GHzd = reflector diameter,m

Beamwidth of reflector antenna

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One-Way Radio Communication Calculation Nomogram (GE, 1960)

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One-Way Radio Communication Calculation Nomogram (GE, 1960)

NomogramComponents

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Atmospheric Attenuation, Multipath, and Ionospheric Effects on Space-Earth

CommunicationPrPt(dB) = Pr

Pt

⎛⎝⎜

⎞⎠⎟ ideal

(dB)− Absorbtion(dB)− Rainfall(dB)

±Multipath(dB)−CrossPolarization(dB)

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Analog Amplitude, Frequency, and Phase Modulation of Carrier Signal

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Digital Amplitude-, Frequency-, and Phase-Shift Modulation of Carrier Signal

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Bit Error Rate vs. Eb/No• Goal is to achieve

lowest bit error rate (BER) with lowest Eb/No

• Implementation losses increase required Eb/No

• Link margin is the difference between the minimum and actual Eb/No

• BER can be reduced by error-correcting codes– Number of bits

transmitted is increased

– Additional check bits allow errors to be detected and corrected

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Supplemental Material

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Electric and Magnetic Fields of a Dipole Antenna

http://en.wikipedia.org/wiki/Antenna_(radio) 47

Communications Carrier Frequencies

DSCS-3

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Typical Command and Telemetry Characteristics

TDRS

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Typical Communication Satellite Transponder Characteristics

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