Final Project Discussionspacecraft.ssl.umd.edu/academics/697S11/697S11L22... · Topics to be Considered • Habitability • Access and space utilization ... • ECLIPSE ﬁnal report

Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Final Project Discussion• Final Report Discussion• Thermal Systems Design Overview

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© 2011 David L. Akin - All rights reservedhttp://spacecraft.ssl.umd.edu

http://spacecraft.ssl.umd.edu

http://spacecraft.ssl.umd.edu



Goals and Objectives• Goal: Create an opportunity to use the tools and

techniques discussed in ENAE 697 in the design of a realistic application

• Corollary Objectives:– Provide a means to assess your understanding of the

material for the purpose of grading– Expand the range of student involvement in the 2011 X-

Hab competition

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Groundrules• Must utilize existing HDU structural concept (5 m

diameter, vertical orientation cylinder with ellipsoidal endcaps, four docking ports

• Must maintain at least three active docking ports (two for rovers, one for airlock) although equipment can be temporarily positioned in front of port when rovers are not docked

• Must have an inflatable upper habitat with 5 meter diameter and ellipsoidal upper surface

• Crew of four 95% American males (worst case)

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Groundrules• Support crew for 90-day mission between resupply• Two crew EVA for 6 hours every day• Two 6-day rover sorties per day cycle• One 6-day rover sortie per night cycle• Solid stowage requirement 150 CTBs per resupply• Power must be budgeted, but is supplied

externally (i.e., somebody else’s problem)

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Topics to be Considered• Habitability• Access and space utilization• Personal space allocation• Life support design

– Air– Water– Food– Hygiene– Thermal

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More Topics• Growth options (e.g., different inflatables,

additional HDU modules)• Lighting• Power distribution• Ventilation• Windows• Stowage• Radiation protection• Power budget (max/nominal/quiescent)

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Final Project Contents• Interior layout of habitat (upper and lower levels)

– Looking for (reasonably) highly detailed CAD models!

• Selection and accommodation of life support systems, including support for EVA and rovers

• Trade studies that led to selection of specific systems used

• Budgets for installed mass, consumables, power• Analysis of all included topics (from previous

slides)

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Resources• ECLIPSE final report (particularly Chapter 7)• NASA Constellation life support assumptions

document• NASA advanced life support estimate document• All will be posted on spacecraft site TONIGHT• Don’t be afraid to do your own literature search!

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Thermal Systems Design• Fundamentals of heat transfer• Radiative equilibrium• Surface properties• Non-ideal effects

– Internal power generation– Environmental temperatures

• Conduction• Thermal system components

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Classical Methods of Heat Transfer• Convection

– Heat transferred to cooler surrounding gas, which creates currents to remove hot gas and supply new cool gas

– Don’t (in general) have surrounding gas or gravity for convective currents

• Conduction– Direct heat transfer between touching components– Primary heat flow mechanism internal to vehicle

• Radiation– Heat transferred by infrared radiation– Only mechanism for dumping heat external to vehicle

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Thermodynamic Equilibrium• First Law of Thermodynamics

! heat in -heat out = work done internally• Heat in = incident energy absorbed• Heat out = radiated energy• Work done internally = internal power used

(negative work in this sense - adds to total heat in the system)

€

Q −W =dUdt

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Radiative Equilibrium Temperature• Assume a spherical black body of radius r• Heat in due to intercepted solar flux

• Heat out due to radiation (from total surface area)

• For equilibrium, set equal

• 1 AU: Is=1394 W/m2; Teq=280°K

€

Qin = Isπ r2

€

Qout = 4π r 2σT 4

€

Isπ r2 = 4π r2σT 4 ⇒ Is = 4σT 4

€

Teq =Is4σ⎛

⎝ ⎜

⎞

⎠ ⎟

14

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Effect of Distance on Equilibrium Temp

Mercury

PlutoNeptuneUranus

SaturnJupiter

Mars

Earth

Venus

Asteroids

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Shape and Radiative Equilibrium• A shape absorbs energy only via illuminated faces• A shape radiates energy via all surface area• Basic assumption made is that black bodies are

intrinsically isothermal (perfect and instantaneous conduction of heat internally to all faces)

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Effect of Shape on Black Body Temps

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Incident Radiation on Non-Ideal Kirchkoff’s Law for total incident energy flux on solid

bodies:

! where– α =absorptance (or absorptivity)– ρ =reflectance (or reflectivity)– τ =transmittance (or transmissivity)

€

QIncident =Qabsorbed+Qreflected +Qtransmitted

€

Qabsorbed

QIncident

+Qreflected

QIncident

+Qtransmitted

QIncident

=1

€

α ≡Qabsorbed

QIncident

; ρ ≡Qreflected

QIncident

; τ ≡Qtransmitted

QIncident

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Non-Ideal Radiative Equilibrium • Assume a spherical black body of radius r• Heat in due to intercepted solar flux

• Heat out due to radiation (from total surface area)

• For equilibrium, set equal

€

Qin = Isαπ r2

€

Qout = 4π r 2εσT 4

€

Isαπ r2 = 4π r 2εσT4 ⇒ Is = 4 ε

ασT 4

€

Teq =αεIs4σ

⎛

⎝ ⎜

⎞

⎠ ⎟

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(ε = “emissivity” - efficiency of surface at radiating heat)

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Effect of Surface Coating on Temperature

ε = emissivity

α =

abs

orpt

ivit

y

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Non-Ideal Radiative Heat Transfer• Full form of the Stefan-Boltzmann equation

! where Tenv=environmental temperature (=4°K for space)

• Also take into account power used internally

€

Prad =εσA T 4 −Tenv4( )

€

Isα As + Pint =εσArad T4 − Tenv

4( )

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Example: AERCam/SPRINT• 30 cm diameter sphere• α=0.2; ε=0.8• Pint=200W• Tenv=280°K (cargo bay

below; Earth above)• Analysis cases:

– Free space w/o sun– Free space w/sun– Earth orbit w/o sun– Earth orbit w/sun

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AERCam/SPRINT Analysis (Free Space)• As=0.0707 m2; Arad=0.2827 m2

• Free space, no sun

€

Pint = εσAradT4 ⇒ T =

200W

0.8 5.67 ×10−8 Wm2°K 4

⎛

⎝ ⎜

⎞

⎠ ⎟ 0.2827m2( )

⎛

⎝

⎜ ⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟ ⎟

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= 354°K

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AERCam/SPRINT Analysis (Free Space)• As=0.0707 m2; Arad=0.2827 m2

• Free space with sun

€

Isα As + Pint = εσAradT4 ⇒ T =

Isα As + PintεσArad

⎛

⎝ ⎜

⎞

⎠ ⎟

14

= 362°K

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AERCam/SPRINT Analysis (LEO Cargo Bay)

• Tenv=280°K

• LEO cargo bay, no sun

• LEO cargo bay with sun

€

Pint =εσArad T4 − Tenv

4( )⇒ T =200W

0.8 5.67 ×10−8 Wm 2°K 4

⎛

⎝ ⎜

⎞

⎠ ⎟ 0.2827m2( )

+ (280°K)4

⎛

⎝

⎜ ⎜ ⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟ ⎟ ⎟

14

= 384°K

€

Isα As + Pint =εσArad T4 − Tenv

4( )⇒ T =Isα As + PintεσArad

+ Tenv4

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

14

= 391°K

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EVA Thermal Equilibrium• Human metabolic workload = 100 W• Suit electrical systems = 40 W• Total heat load = 140 W

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Q = �σAT 4 ⇒ A =Q

�σT 4

A =140

(0.8)(5.67× 10−8)(295)4= 0.41 m2



EVA Thermal Equilibrium with Sun• Human metabolic workload = 100 W• Suit electrical systems = 40 W• Total internal heat load = 140 W

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Q + αAIs = �σAT 4 ⇒ A =Q

�σT 4 − αIs

A =140

(0.8)(5.67× 10−8)(295)4 − 0.2(1394)= 2.2 m2



Sublimation• Water heat of sublimation = 46.7 kJ/mole• @ 18 gm/mole = 2594 W-sec/gm• Mass flow for 140 W = 0.54 gm/sec• per hour = 194 gm/hr• 8 hr total EVA time = 1.55 kg of water• @ 2 EVA/day and 180 days = 559 kg of water

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Sitting on a Planetary Surface

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IsTb

Th

Th



Radiative Insulation• Thin sheet (mylar/kapton with

surface coatings) used to isolate panel from solar flux

• Panel reaches equilibrium with radiation from sheet and from itself reflected from sheet

• Sheet reaches equilibrium with radiation from sun and panel, and from itself reflected off panel

Is

Tinsulation Twall

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Multi-Layer Insulation (MLI)• Multiple insulation

layers to cut down on radiative transfer

• Gets computationally intensive quickly

• Highly effective means of insulation

• Biggest problem is existence of conductive leak paths (physical connections to insulated components)

Is

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Emissivity Variation with MLI Layers

Ref: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 2002

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MLI Thermal Conductivity


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Effect of Ambient Pressure on MLI


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1D Conduction• Basic law of one-dimensional heat conduction

(Fourier 1822)

! whereK=thermal conductivity (W/m°K)A=areadT/dx=thermal gradient

€

Q = −KA dTdx

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3D ConductionGeneral differential equation for heat flow in a solid

! whereg(r,t)=internally generated heatρ=density (kg/m3)c=specific heat (J/kg°K)K/ρc=thermal diffusivity

€

∇ 2T r ,t( ) +g( r ,t)

K=ρcK∂T r ,t( )∂t

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Simple Analytical Conduction Model• Heat flowing from (i-1) into (i)

• Heat flowing from (i) into (i+1)

• Heat remaining in cell

TiTi-1 Ti+1

€

Qin = −KATi − Ti−1Δx

€

Qout = −KA Ti+1 −TiΔx

€

Qout −Qin =ρcK

Ti( j +1) − Ti( j)Δt

… …

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• Time-marching solution

where

• For solution stability,

Finite Difference Formulation

! =k

"Cv

= thermal di!usivityd =!!t

!x2

Tn+1i

= Tn

i + d(Tn

i+1 ! 2Tn

i + Tn

i!1)

!t <!x2

2!

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Heat Pipe Schematic

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Shuttle Thermal Control Components

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Shuttle Thermal Control System

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ISS Radiator Assembly

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Documents

Final Project Discussionspacecraft.ssl.umd.edu/academics/697S11/697S11L22... · Topics to be Considered • Habitability • Access and space utilization ... • ECLIPSE ﬁnal report