5. Spacecraft Environment MAE 342 2016

2/12/20

Spacecraft Environment Space System Design, MAE 342, Princeton University Robert Stengel

• Atmospheric characteristics • Loads on spacecraft • Near-earth and space environment • Spacecraft charging • Orbits and orbital decay

Launch Phases and Loading Issues-1

§ Liftoff § Reverberation from the ground § Random vibrations § Thrust transients § Winds and Transonic Aerodynamics § High-altitude jet stream § Buffeting § Staging § High sustained acceleration § Thrust transients

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Launch Phases and Loading Issues-2

§ Heat shield separation § Mechanical and pyrotechnic transients § Spin stabilization § Tangential and centripetal acceleration § Steady-state rotation § Separation § Pyrotechnic transients

Typical Acoustic and Shock Environment (Delta II) Sound Pressure (dB) Peak Acceleration (g)

Decibel (dB) ⎛ Measured Power ⎞ ⎛ Measured Amplitude⎞ 10log or 20log 10 ⎝⎜ Reference Power ⎠⎟ 10 ⎝⎜ Reference Amplitude⎠⎟

http://dangerousdecibels.org/education/information-center/decibel-exposure-time-guidelines/ 4

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Transient Loads at Thrusting Cutoff

5 Fortescue, et al, 2003

Properties of the Lower Atmosphere

• Air density and pressure decay exponentially with altitude • Air temperature and speed of sound are linear functions of altitude

US Standard Atmosphere, 1976

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Earth’s High-Altitude Explorer-9 Atmosphere

Temperature of the Density of the Atmosphere Atmosphere

Atmosphere not well-represented Altitude Molecules/cc Mean Free Path as a continuum at high altitude Sea Level 2 x 10^19 7 x 10^-6 cm 7 600 km 2 x 10^7 10 km

Lower Atmosphere Rotates With The Earth

• Zero wind at Earth’s surface = Inertially rotating air mass Jet Stream (typical) • Wind measured with respect to Earth’s rotating surface • Jet stream magnitude typically peaks at 10-15- km altitude

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Jet Stream Produces High Loads on Launch Vehicle • Launch vehicle must able to fly through strong wind profiles • Design profiles assume 95th-99th-percentile worst winds and wind shear

Aerodynamic Forces

⎡ ⎤ ⎡ Drag ⎤ CD ⎢ ⎥ ⎢ ⎥ 1 2 Side Force = ⎢ CY ⎥ ρV S ⎢ ⎥ 2 ⎢ ⎥ ⎢ C ⎥ ⎣ Lift ⎦ ⎣ L ⎦ • V = air-relative velocity = velocity w.r.t. air mass • Drag measured opposite to the air-relative velocity vector • Lift and side force are perpendicular to the velocity vector 10

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Aerodynamic Force Parameters ρ = air density, functionof height, h −βh = ρsealevele 3 ρsealevel = 1.225 kg / m ; β = 1/ 9,042 m

2 2 2 1/2 T 1/2 V = ⎣⎡vx + vy + vz ⎦⎤ = ⎣⎡v v⎦⎤ , m s 1 Dynamic pressure = q = ρV 2 , N m2 2 S = referencearea, m2 ⎡ C ⎤ ⎢ D ⎥ ⎢ CY ⎥ = non - dimensionalaerodynamiccoefficients ⎢ ⎥ CL ⎣ ⎦ 11

Aerodynamic Drag

1 Drag = C ρV 2S D 2

• Drag components sum to produce total drag – Skin friction – Base pressure differential – Forebody pressure differential (M > 1)

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Aerodynamic Moment

N’y(xs )

Lengthwise lift variation causes bending moment

N '(x) = normal force variation with length ≈ lift variation

xmax M x = N (x) x − x dx y ( ) ∫ y ( cm ) xmin

xmax xmax = N ' (x)dx x − x dx ∫ ∫ y ( cm ) xmin xmin 13

Typical Velocity Loss due to Drag During Launch

• Aerodynamic effects on Thrust-to- Velocity Loss, launch vehicle are most Weight Ratio m/s important below ~50-km 2 336 altitude 3 474 • Maintain angle of attack and 4 581 sideslip angle near zero to minimize side force and lift • Typical velocity loss due to drag for vertical launch – Constant thrust-to-weight ratio 2 – CDS/m = 0.0002 m /kg – Final altitude above 80 km 14

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Effects of Gravity and Drag on the Velocity Vector

Thrust/Weight = T/W = 2 ⎡ 1 2 ⎤ Thrust = 1960 Thrust − CDS ρ(h)V (t) + mg sinγ (t) ⎣⎢ 2 ⎦⎥ CD = 0.2 V!(t) = S = 0.1 m Mass = 100 γ!(t) = −gcosγ (t) /V(t)

Significant reduction in velocity magnitude Strong curvature of the flight path 15

Typical Properties of Launch Trajectories Thrust/Weight = 2

• Maximum dynamic pressure • Mach = 1 • maximum drag • maximum jet stream magnitude tend to occur at similar altitudes

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Gravity and Drag Effects during Single-Stage Thrust/Weight = T/W = 2 Orbital Launch

• Launch trajectory using flat-earth model • Red line signifies velocity due to rocket alone • Several km/s lost to gravity • With higher T/W and drag – Shorter time to orbit – Increased loss due to drag – Decreased loss due to gravity 17

Typical Ariane 4 Launch Profile

Fortescue, et al, 2003 18

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Ariane 5 Aerothermal Flux

Fortescue, et al, 2011 19

Orbital Lifetime of a Satellite • Aerodynamic drag causes orbit to decay dV C ρV 2S / 2 = − D ≡ −B* ρV 2S / 2 dt m

B* = CDS / m • Air density decreases exponentially with altitude

−h/hscale ρ = ρSLe

ρSL = air density at sea level

hscale = atmospheric scale height • Drag is highest at perigee – Air drag “circularizes” the orbit • Large change in apogee • Small change in perigee • Until orbit is ~circular • Final trajectory is a spiral 20

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Orbital Lifetime of a Satellite

• Aerodynamic drag causes energy loss, reducing semi-major axis, a da = − µaB* ρ e−(a−R)/hscale dt SL • Variation of a over time

a t e−(a−R)/hs da = − µB* ρ dt ∫ a SL ∫ a0 0

• Time, tdecay, to reach earth’s surface (a = R) from starting altitude, h0

hscale h0 /hscale tdecay = (e −1) µRB* ρSL 21

NRL Starshine 1 Orbital Decay (2003)

http://www.azinet.com/starshine/descript.htm 22

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Diurnal Variations in Earth’s Upper Atmosphere

Factor of 10 change in density

±20% change in temperature Large effect of solar activity

Explorer-9

Pisacane, 2005 23

Atmospheric Minimum solar activity Constituents

Explorer-17 Maximum solar activity

• Constituents at minimum and maximum solar activity • Different scale heights for different species

US Std. Atmos., 1976 24

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Atmospheric Ionization Profiles

Explorer-17

•Scale heights of electrons, ions, and neutrals vary greatly •Ionospheric electric field (set by heavy oxygen atoms) dominates gravity field for lighter ions, e.g., hydrogen and helium

US Std. Atmos., 1976 25

Mean Free Path

• At high altitude, the mean free path of molecules is greater than the dimensions of most spacecraft • Aerodynamic calculations should be based on free molecular flow • Heat exchange is solely due to radiation

Fortescue, et al, 2011 26

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Orbits About the Sun

Solar System Environment Low- and high-speed particles Heliospheric Current Sheet

• Solar wind • Plasma consisting of electrons, protons, and alpha particles • Variable temperature, density, and speed • 1.5-10 keV • Slow (400 km/s) and fast (750 km/s) charged particles • Geomagnetic storms 28

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Sunspots and Solar Flares

Sunspots Solar Flare

Coronal Loop

Fortescue, et al, 2011 29

Flux vs. Energy of Electrons and Protons

Deep Space Climate Observatory (DSCOVR) at L1

Fortescue, et al, 2011 30

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The Solar Spectrum

Fortescue, et al, 2011

Variability of Solar Radiation

Fortescue, et al, 2011

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Van Allen Belts

Magnetosphere and Van Allen Belts •Trapped Energetic Ions and Electrons •Light ions form the base population of the magnetosphere

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Earth’s Magnetosphere

Fortescue, et al, 2011 36

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Annual Dose of Ionizing Radiation

Si: Sieverts

Fortescue, et al, 2011 37

Spacecraft That Defined the Magnetosphere and Van Allen Belts

Explorer-1

Pioneer-3

• see Pisacane for discussion of Orbiting Solar Observatory mechanics and dynamics – plasma frequency – Debye length – spacecraft charging and ram-wake effects – motion of charged particles in a dipole field – trapped radiation 38

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“String of pearls” orbital configuration Lined up at apogee every 4 days Outer two spacecraft repurposed for ARTEMIS 39

Spacecraft Charging

Interaction of sunlight, space plasma, and spacecraft materials and electronics

Exterior Interior

NASA-HDBK-4002A, 2011

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Spacecraft Charging Damage Interaction of space plasma and spacecraft materials and electronics

SCATHA Satellite, 1979

NASA-HDBK-4002A, 2011

Spacecraft Charging Hazard Zones

NASA-HDBK-4002A, 2011 42

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Integral Flux Contours at Earth, Jupiter, and Saturn

NASA-HDBK-4002A, 2011

Space Debris

Ring of objects in geosynchronous orbit (GEO) altitudes Cloud of objects in low-Earth orbit (LEO) altitudes 44

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Micrometeoroids and Space Debris

• Nuts, bolts, and other fragments in orbit • July 2013 estimate • 170 million objects {< 1cm} • 670,000 objects {1 – 10 cm} • 29,000 objects {> 10 cm} • January 2007: Chinese anti-satellite test destroyed old satellite and added >1,335 remnants larger than a golf ball • U.S. shot down a failed spy satellite in 2008 -- more debris 45

Space Debris Density after 2009

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Satellites for Detecting Micrometeoroids and Space Debris Explorer-16 (“Beer can” Long-Duration Exposure Facility satellite), 1962 (LDEF), 1984

9 x 4 x 4 m Gravity-gradient stabilization 5.7 yr collecting data 2 x 0.6 x 0.6 m Returned to Earth by Space Shuttle Pressurized-cell penetration detectors, impact and other detectors, Scout launch vehicle 47

Growth Estimate of Low-Earth-Orbit Debris Population

ADR: Active Debris Removal

Fortescue, et al, 2011 48

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Mass Influx Rates of Micrometeoroids

49 Fortescue, et al, 2011

Space Debris/Micrometeoroid Damage to the Space Shuttle

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Distribution of Micrometeoroids and Space Debris (from LDEF)

Speed, Specific km/s Energy, km 45-caliber bullet 0.275 4 Space Junk 7.5 2867

Effect of Impact Angle on Relative Specific Energy

Impact Satellite Debris Relative Relative Angle, Velocity, Velocity, Velocity, Specific deg km/s km/s km/s Energy, km

180 7.5 7.5 0 0 45 7.5 7.5 10.6 5734 0 7.5 7.5 15 11468 52

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Atmospheric Composition of the Planets

Fortescue, et al, 2011 53

The Atmosphere of Mars

Martian Clouds

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The Atmospheres of Jupiter and Saturn

The Atmosphere and Surface of Venus

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Venus Landings

Venera 9

Proposed Venus Rover (NASA)

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