10/25/2011

1

SPACECRAFT SUB-SYSTEMS

DESIGN

D.J.P. Moura

SPACECRAFT ARCHITECTURE (system level)

SPACECRAFT

PAYLOAD PLATFORM

STRUCTURE

THERMAL CONTROL

PROPULSION POWER/ENERGY SUPPLY

POWER CONDITIONNING & DISTRIBUTION

ORBIT & ATTITUDE CONTROL

DATA MANAGEMENT

HARNESS

EXPERIMENTS(scientific satellite)

COMMUNICATIONSMECHANISMSRECEIVERS/AMPLIFIERS/ANTENNAS

(telecoms satellite)

TELESCOPE/DETECTOR/ELECTRONICS(observation satellite)

Fully mission dependant

~ Contant for a class of spacecraft

10/25/2011

2

SPACECRAFT

ARE COMPLEX

ITEMS

TO BUILD

Man

pow

er (

desi

gn, p

rocu

rem

ent,

inte

grat

ion,

con

trol

, tes

t, m

anag

emen

t…)

THERMAL CONTROL

MAIN FUNCTIONS

PROVIDE, DURING ALL THE PHASES AND MODES,

THE SPECIFIED TEMPERATURE RANGES

TO ALL EQUIPMENTS

Deep Space

10/25/2011

3

THERMAL CONTROL

PENDING THE TEMPERATURE NEEDS, SEVERAL TECHNIQUES ARE POSSIBLE

HERSCHEL

PLANCK

Classicalspacecraft

THERMAL CONTROL

PASSIVE RADIATOR CONCEPT

RADIATIVE COUPLING WITH (cold) DEEP SPACE

INSOLATION FROM EXTERNAL HEATING SOURCES

SELECT ADEQUATE ε (emissivity) AND

α (absorptivity) ACCORDING THE NEEDS

Q (internal heat to dissipate)

T (~ specified temperature)

External Heating Fluxes(EHF)

(1-α) EHF Radiated Flux

= ε σ T 4 Thermal equilibrium :

α EHF + Q = ε σ T 4 S

T en Kelvin,

σ = Boltzman constant = 5.67 10-8 W/m2/K4

Surface S

αab

sorp

tivity

SELECTIVE

BLACK

SANDBLASTED

METALS

UN

PO

LIS

HE

D

ME

TA

LS

METALLIC

PAINTS

BLACK PAINTS

GREY

&

PASTEL

PAINTS

WHITE PAINTS

SURFACE MIRRORS

PO

LIS

HE

D M

ET

ALS

0 1

1

ε emissivity

FOR TYPICAL TEMPS (~ -10/+40 °OPERATIONAL MODE, ~ - 20 /+50 °STORAGE),

PASSIVE RADIATORS ARE USED

10/25/2011

4

THERMAL CONTROL

TECHNOLOGIES

AVOID COUPLING WITH EXTERNAL SPACE :

MULTI-LAYER INSULATION (w # 5 10-2 W/m2/K)

RADIATIVE COUPLING WITH COLD SPACE :

SECOND SURFACE MIRROR (ε # 0.84, α # 0.06)

PAINTS (mainly black or white)

ELECTRICAL HEATERS

STRUCTURE

MAIN FUNCTIONS

COPE WITH DESIGN AND QUALIF LAUNCHER REQUIREMENTS (loads, stiffness, interface)

DIMENSIONAL STABILITY DURING LAUNCH AND SPACE ENVIRONMENTS

PROVIDE SURFACES FOR MOUNTING OF EQUIPMENTS & RADIATIVE COOLING

ELECTRICAL & THERMAL CONDUCTIVITY

PROTECTION AGAINST RADIATIONS

10/25/2011

5

STRUCTURE

CONCEPT

TECHNOLOGIES

BOX WALLS :

ALUMINIUM OR HONEYCOMB SANDWICH

CENTRAL TUBE :

ALUMINIUM OR CARBON FIBER

GENERALY PREFERED CONCEPT: BOX SHAPE WITH INTERNAL CENTRAL TUBE

WHERE TANKS ARE ATTACHED, SHEAR WALLS, STRUSTS …

ATTITUDE & ORBIT CONTROL SUB-SYSTEM

MAIN FUNCTION (1)

TO FULFILL ITS MISSION, A SPACECRAFT HAS TO PERFORM THE POINTING OF ITS

PAYLOAD TOWARDS THE “TARGET” (earth, other planet, stars...),

IN POSITION (max allowed angular error) AS WELL AS SOMETIMES (when imaging

instruments) AS WELL AS OFTEN IN STABILITY (max error during a given time)

KEEP THE CORRECT ATTITUDE/POINTING(attitude : movement around the center of mass)

Time

Pointing error

Max angular changeallowable during the exposure time

Exposure time

Spec of stability : angular error / exposure time

10/25/2011

6

Typical pointing/stability needs

Earth ObservationTelecommunications Astronomy

Typical pointing: 0.01°

No stability requirement

Typical pointing: 0.1 to 0.01°

+ good stability (~ 10 - 3 °/s)

Typical pointing: < 1 arc’’

+ excellent stability (~ 10 - 4 °/s)

ATTITUDE & ORBIT CONTROL SUB-SYSTEM

MAIN FUNCTION (2)

INDEED, A SPACECRAFT IS FACING MANY PERTURBATIONS CHANGING, ON THE

MEDIUM AND LONG TERMS, THE CHARACTERISTICS OF ITS ORBIT:

- Flatness of the Earth

- Irregularities of the Earth density

- Solar flux

- Solar Gravity

- Moon gravity

- Aerobracking (below 1000 km)

KEEP THE CORRECT ORBIT (orbit : trajectory of the center of mass)

10/25/2011

7

ATTITUDE & ORBIT CONTROL SUB-SYSTEM

STABILISATION CONCEPTS

PASSIVE : GRAVITY GRADIENT

- stable for favorable mechanical configuration

- for Low Earth Orbit < ~ 1500 km

- low pointing performance > 1 deg

SEMI PASSIVE : SPIN STABILISATION

- required stable configuration (main inertia axis)

- mainly for GEosynchronous Orbit (N/S direction fixed)

- medium pointing precision ~ 0.1 to 1 deg

ACTIVE : 3 AXIS STABILISATION

- unstable configuration

- control by exchange of kinetic momentum with internal wheels

- high pointing precision < 0.1 deg

100 rpm

ATTITUDE & ORBIT CONTROL SUB-SYSTEM

ON BOARD ARCHITECTURE FOR SEMI PASSIVE OR ACTIVE ST ABLISATION

FLIGHT

CONTROL SWACTUATORS

ATTITUDE

SENSORS

DYNAMICSPACECRAFTBEHAVIOUR

ALLOWABLE ERRORS(stored in memory)

ONBOARD COMPUTER

EXTERNALPERTURBATIONS

ATTITUDE

COMPUTATION SW

EXTERNAL

REFERENCES

- Kinetic momentum (mean angular speed >> 0)

- Reaction wheels (mean angular speed ~0)

- Magneto-couplers

- Propulsion thrusters (see propulsion s/s)

- Sun sensor (coarse, fine)

- Earth sensor

- Star tracker

- Gyrometers (angular changes and speed)

10/25/2011

8

ATTITUDE & ORBIT CONTROL SUB-SYSTEM

TECHNOLOGIES

Startracker Earth sensor

GyrometerReaction wheel

Magnetotorquer

PROPULSION

MAIN FUNCTION DELIVERS FORCES (orbit control) AND TORQUES (attitude control)

CONCEPT PROPULSION BY REACTION THANKS TO EJECTED MASS

t0M0V0

t1M1 = M0 – dMV1 = V0+dV

dM, Vejection(relative velocity)

Thrust = dM/dt * Vejection M1 = M0 * exp (- dV/Vejection)

Conservation of the total quantity of movement:

M0*V0 = (M0-dM)*(V0+dV) + dM*(V0+dV-Ve) => M0*dV = - dM*Ve => dM/M0 = - dV/Ve

t1dM

V0+dV-Ve

Vejection / g = Specific Impulse (Isp)

10/25/2011

9

PROPULSION

TECHNOLOGIES THRUSTERS (1)

- COLD GAZ PROPULSION (Isp # 150 s)

- CHEMICAL PROPULSION

(solid, mono or bipropellant)

PROPULSION

TECHNOLOGIES THRUSTERS (2)

- ELECTRICAL PROPULSION

10/25/2011

10

PROPULSION

CONCEPT TANK

FREE FALL CONDITION EXCLUDES EMPTYING BY GRAVITY

SURFACE TENSION BECOMES DOMINANT

POWER/ENERGY SUPPLY

MAIN FUNCTIONS PROVIDE POWER/ENERGY DURING ALL PHASES AND MODES

CONCEPTS FOR POWER SUPPLY

PHOTOVOLTAIC EFFECT (η # 25 %)

Incoming solar flux

SEEBECK EFFECT (η # 5 %)

On board nuclear source (Pu238)

10/25/2011

11

POWER/ENERGY SUPPLY

TECHNOLOGIES FOR POWER SUPPLY

SOLAR ARRAY (100 W to 25 kW) Radio Isotopic Thermal Generator (~150 W)

POWER/ENERGY SUPPLY

CONCEPTS / TECHNOLOGIES FOR ENERGY SUPPLY

CHEMICAL REACTION

Li Ion SECONDARY CELLS (# 150 W.h/kg)

STACKED IN BATTERIES

(at 100 % depth of discharge)

10/25/2011

12

CONDITIONNING &

DISTRIBUTION

POWER/ENERGY CONDITIONNING & DISTRIBUTION

MAIN FUNCTIONS REGULATE THE POWER SUPPLIED AND DELIVER IT TO USERS

INSURE SYSTEM LEVEL ELECTRICAL PROTECTION

CONCEPT POWER IS DISTRIBUTED UNDER REGULATED (50 V)

OR SEMI REGULATED VOLTAGE (24/36 V), USING ELECTRONIC FUSES

(for avoiding failure propagation)

ENERGY

STORAGE

POWER

SOURCE

USERS

Power line (redunded)

Charge

Discharge

ON BOARD DATA HANDLING

MAIN FUNCTIONS COLLECT & PROCESS TELEMETRY DATA

PROCESS & DELIVER TELECOMMAND DATA

ON BOARD PROCESSING (reconfiguration, autonomy…)

DATA STORAGE

CONCEPT

User

Main

Computer

Group of Users

Data bus

Com

s/s TC decoder

TM coder

Direct TC for critical functions

ON BOARD DIGITAL DATA BUS WITH USERS

User User

10/25/2011

13

ON BOARD DATA HANDLING

TECHNOLOGY CORE IS THE PROCESSOR (current cap.: 16 bits, 20 MHz, 20 Mips)

AND THE SOFTWARE (often ADA) - STANDARD INTERFACES (OBDH)

COMMUNICATIONS

MAIN FUNCTIONS RECEIVE & DECODE TELECOMMANDS FROM THE EARTH

CODE & SEND TELEMETRY TO THE EARTH

SUPPORT SPACECRAFT LOCALISATION

CONCEPT

Receiver

Transmitter Modulator

Ultra StableOscillator

Demodulator

PHASE MODULATION OF A RADIOFREQUENCY CARRIER

High Gain Antenna(high focussing)

Operational mode

Low Gain Antenna(large coverage)

Emergency mode

On board data handling s/s

10/25/2011

14

COMMUNICATIONS

TECHNOLOGIES USED BANDS : S (2 GHz), C (4/6 GHz), X (7/8 GHz), Ku (12/14 GHz) ...

AMPLIFIER: SSPA (low frequency, low power), TWT (high power)

RECEIVER: LOW NOISE (FET)

ANTENNA: OPTIMIZED ACCORDING GAIN/COVERAGE

Traveling Wave Tube (S band, 200 W, η = 62 %, 1.8 kg) Antenna : focussing energy

Feedhorn

Low gain antenna

Main reflector

Sub reflector

COMMUNICATIONS : LINK BUDGET

Antenna axis

Antenna parameters

Aperture θ = 21/ F / D (F in GHz, D in m)

Gain in axis ~ 28,000 / θ2

(in dB 10 log G)

Simple link budget

The quality of a link is defined by the Carrier power to Noise

density ratio (C/No) given by the following relation (in dB):

C/No = EIRP + Fsl + G/T – kEIRP = Emitted Isotropic Radiated Power representing the

effective emitted power (in dBW, includes the amplifier output Pe,

internal emitting losses and the antenna gain Ge)

Fsl = Free space loss = 20 log (wavelength/(4 * π * path length))

G/T = figure of merit of the receiver (in dB/K), which includes the

receiving antenna gain and the temperature noise of the receiver

system (# 1300 K for receiving at spacecraft level)

k = Boltzmann constant = - 228,6 dBW/Hz/K

Emission : Pe Ge(EIRP)

Reception : G/T(figure of merit)Free space loss

Multiple link budget Link 1 Link 2

Internal

Global link

(No/C)g = (No/C)1 + (No/C)i + (No/C)2

10/25/2011

15

MECHANISMS

MAIN FUNCTIONS IN ORBIT DEPLOYMENT (single shot activation)

FINE POINTING (limited movment)

CONTINUOUS ACTIVATION (solar array pointing, wheels...)

CONFIGURATION CHANGE (filter wheel, shutter ...)

CONCEPT MOST IMPORTANT SOURCE OF FAILURE (difficult to test in

representative conditions, hard to have redundancy)

SIMPLICITY IS A MUST

CAREFULL CHOICE OF MATERIALS

HIGH DESIGN MARGIN (particularly torques)

A LOT OF VALIDATION/TESTS

SINGLE ACTUATION : SPRING, SHAPE MEMORY ALLOY, PYRO

MULTIPLE ACTUATION : ELECTROMAGNETIC MOTORS

MECHANISMS

TECHNOLOGIES

LUBRIFICATION: DRY (MoS2, soft metal, PTFE) FLUID (Perfluoropolyether PFPE)

TRANSMISSION: GEARS

HARMONIC DRIVES

10/25/2011

16

MECHANISMS

TECHNOLOGIES

MOTORS: STEPPER DC BRUSHLESS

GUIDANCE: CONTACT (rolling bearings) DISTANT (magnetic bearings)

=> Needs closed loop control

PYROTECHNICS

MAIN FUNCTION SINGLE USE ACTUATOR (valve opening, launch lock release...)

CONCEPT & TECHNOLOGIES SOLID POWDER BLOCK INITIATED ELECTRICALY

10/25/2011

17

HARNESS - WIRING

MAIN FUNCTIONS INTERCONNECT EQUIPMENTS FOR DATA EXCHANGE OR

POWER SUPPLY

CONNECTORS ARE PART OF THE HARNESS

CONCEPT & TECHNOLOGIES MATERIAL SELECTION (avoid outgassing)

CAREFULL ROUTING FOR:

- AVOIDING ELECTRO-MAGNETIC EFFECTS

(EMI/EMC, coupling with Earth magnetic field)

- EASE INTEGRATION AND TEST

FLIGHT HARNESS REALISED BY SPECIALIZED COMPANIES

HOW ASSESSING TECHNICAL MATURITY ?

Instruments and spacecraft sub-systems are classified according to a

"Technology Readiness Level" (TRL) on a scale of 1 to 9. Levels 1 to 4 relate to

creative, innovative technologies before or during mission assessment phase.

Levels 5 to 9 relate to existing technologies and to missions in definition phase.

10/25/2011

18

SYNTHESIS

THE DESIGN OF A SUB-SYSTEMS CANNOT BE INDEPENDANTLY FROM THE

OTHERS SINCE THERE IS A LOT OF INTERACTIONS

IN FACT, THE OPTIMUM AT SYSTEM/ARCHITECTURE LEVEL IS QUITE

OFTEN NOT THE SUM OF THE OPTIMAL SOLUTIONS AT SUBSYSTEM

LEVELS BUT MUCH MORE THE OPTIMAL SOLUTION IN TERM OF

INTERFACES

THIS IS WHY SYSTEM/ARCHITECTURE ENGINEERING IS ESSENTIAL

DEGREE OF MATURITY OF A TECHNOLOGY OR EQUIMENT IS MEASURED

BY TRL

Thanks for your attention

Questions ?