Thermal Hardware for Thermal Analysts

GSFC· 2015

Thermal Hardware for Thermal Analysts

David Steinfeld

NASA Goddard Space Flight Center Code 545, Thermal Engineering

Reason for This Course • There are 3 parts to Thermal Engineering:

1. Thermal Analysis 2. Thermal hardware installation 3. Thermal Vacuum Testing

• But many times Analysts are not involved in #2.

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Course Outline

• MLI Blanketing Theory 101 • MLI blanketing installation • Temperature Measurements • Heaters and Thermostats • Optical coatings (Paints and tapes) • Propulsion Systems (tanks, lines, and

thrusters)

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MLI Blanketing 101

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Thermal Analyst: “The actual MLI doesn’t look like what’s in my Thermal Model”

Blanket Tech: “David, can you help me out? The Thermal Analyst

can’t tell me what he wants”

Analyst vs. Hardware

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TSS Model of PLASTIC Actual MLI on PLASTIC

STEREO/PLASTIC as an example

Theoretical Blanket Effective Emissivity

-0.010

0.000

0.010

0.020

0.030

0.040

0.050

0 5 10 15 20 25 30

E-St

ar

Number of Layers

Kapton layers

VDA layers

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Actual MLI Blanket

0.000

0.010

0.020

0.030

0.040

0.050

0 5 10 15 20 25 30

E-St

ar

Number of Layers

VDA Effective Emissivity

Actual Blanket

Theoretical Blanket

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What affects MLI blanket ε*?

• Penetrations • Ground Straps • Crinkling • Stitching • Vents • Separator layers • Tightness • Cryogenic Temperatures • Atmospheric pressure

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What affects Optical Properties?

• Emissivity usually not effected. Solar Absorptance will be with age.

• Atomic oxygen effects outer layer – Silver Teflon needs to be 10 mil instead of 5 mil

thick in LEO

• Alpha increases with age (BOL vs. EOL)

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Touching Layers = Bad

• 1 ft2 blanket covering 30OC surface: – Good MLI blanket design = 1.2 watts lost – Smashed blanket = 38 watts lost

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Stitching Effects 1 ft wide blanket

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 1 2 3 4 5 6 7 8 9 10 11 12

E-St

ar

Distance (in)

SEAM SEAM

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Blankets Vent or Blow Up • Air Pressure on ground

– 14.7 psi – 2117 lbs per square foot. – But pressure in Space = 0 psi.

• Blankets usually go from Ground to Space (or inside T/V chamber)

– Air around MLI goes from 14.7 psi -> 0.

• MLI Blankets can only handle 0.1 psi (14.4 lbs per square foot). • Venting needed:

– Between MLI layers (or risk blowing up) – Between MLI and underlying metal (or risk blowing off surface) – Eliminate Gas conduction

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Generic Launch Pressure Inside Fairing

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

0 20 40 60 80 100 120 140 160 180 200

Pres

sure

(psi

)

Time (Sec)

Cryogenic Temperatures Affect MLI Blankets

0

0.002

0.004

0.006

0.008

0.01

0.012

-220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0

Effe

ctiv

e Em

issi

vity

Temperature (C)

Cold Temperatures effect MLI blanket efficiency

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Emissivity shifts to the far infrared at very cold temperatures.

Things Grow and Shrink

• Coefficient of Thermal Expansion – Things grow bigger when hot – Things shrink when cold – Aluminum shrinks/grows a lot compared to Kapton

• CTE = 0.000026 in/in OC • 72 inch piece, from -20 OC to +40 OC grows 1/8”

Metal

MLI Blanket Buttons

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Blanket Buttons, Etc…

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Top hat Blanket buttons

Velcro

ClickBonds (For heavier or thicker blankets)

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Bonding techniques • Buttons, Thermistors, Thermostats typically bonded with

Stycast 2850FT Cat 9 – Small bondline, so thermal resistance is low.

• Polymerics license required for bonding Flight hardware. • Surface preparation is key to a good bond:

– Clean surfaces – Abrade surfaces with sandpaper – Vacuum, then clean surface again – Hold down with Kapton until epoxy dries overnight.

• Think about how to handle vertical surfaces!

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Thermostats

• Typically bought from Honeywell. • Type 700 is typical thermostat style

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Style 701 (standard) Style 717 (Prop lines)

Heaters • Kapton Thermofoil Heaters • Applied with 3M Y966 Acrylic Adhesive

– Low outgassing – Y966 adhesive good to about +100OC

• Bond with Stycast Epoxy if hotter than +100OC, or watt density higher than 3.5 W/in2

– Overtaped with 3M 425 aluminum tape to help spread out heat.

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– Two thermostats wired in series • To prevent failed “on” condition

– Two heaters wired in parallel • To prevent failed “off” condition

– Heaters can be ordered with dual-elements • Cost is about the same as single element • Remember to order heaters with two color coded wires (to tell circuits apart)!

Heater-Thermostat Redundancy

-

thermostats

- Primary

Redundant

heater

heater thermostats

+

+

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Temperature Measuring • Thermocouple

– Cheap and easy. Voltage vs. Temperature • Remove after T/V testing or flyaway (snip and ground). • Type T or Type K. Make sure which one you are using! • Attach with 3M 425 Aluminum Tape

• Thermistor

– Non linear Ω vs. Temperature (negative slope) – Resistances 2252 Ω, 5K, 10K, etc…

• PRT

– Very linear Ω vs. Temperature (positive slope) – Usually used for high or low (cryogenic) temperature. – 4 wire variety enhances accuracy if needed (usually

cryogenic). Removes resistance of leads. – Resistances usually 100 Ω

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Thermistor

PRT

Thermal Enhancement • Nusil CV-2946

– 2-part material which needs to be mixed beforehand and degassed.

– Stored in a freezer or hardens in an hour

– Use Miller-Stephenson MS-143H as a release agent if needed. Teflon particles. Apply 3 layers.

• Arathane – mixed with 30-40% Boron Nitride also

good. – Cabasil makes it thick.

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Optical Coatings • Word of Advice: Never call an optical coating “Paint”!

• Things that effect Optical coatings:

1. Atomic Oxygen* 2. UV Radiation* 3. Proton-Electron particle Radiation 4. Contamination on the surface Note: * LEO orbits

• Example: Silver Telfon in LEO usually needs 10mil Teflon instead of 5 mil (AO erodes the Teflon)

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Optical Coatings, Page 2 • Thickness of the coating is key:

– Too thick makes the coating crack – Too thin effects the emissivity and solar absorptance

• Coating Selection – The Substrate: metal or composite? – Temperature range:

• Polyurethanes do not do well at hot temperatures. They turn brown. • Silicates work better when hot but have their own problems.

• Coat on flat side of the radiator, not on pocketed side if possible.

• Fillets and bolt patterns create 5-10X more time to coat. $$$$

• Talk to your Coatings Engineer before you get too far down the path.

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Propulsion Systems

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P P

Fuel Tank (MMH)

Oxidizer Tank (NTO)

P P

P

Helium HTK1 HTK2

F-H

FD-H3

CV-F

PV-BDN

CV-O PV-F1

FD-F1 FD-O1

FD-F2 FD-O2

F-O F-F

LV-FA LV-OA LV-FME1

LV-FME2

LV-OME1 LV-FB

LV-OME2

LV-OB

PV-FME PV-OME

ME

LV-R2 LV-R1

R1 R2

FD-H2

FD-H1

FD-HF FD-HO

R

R R

R

P

P P

P P

T-1A T-2A T-3A T-4A T-IB T-2B T-3B T-4B

PV-H1 PV-H2

PV-F2

PV-O1

PV-O2 FD-CVF FD-CVO

Helium

P-HTK

P-REG P-OTK P-FTK

P-FTA

P-FTB

P-OTB

P-OTA

P-FME P-OME

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Analyst vs. Hardware • Analyst:

1. SINDA model has heaters on all nodes of a prop line. 2. Use CALL HEATER subroutine for thermostat cycling. 3. Use e* of 0.05 for MLI

• Hardware: 1. Install Thermostats on Saddle Blocks. Pot terminals if necessary

Or buy 717 style Honeywell Thermostats.

2. Install thermostats/Saddle blocks on Prop Lines with Nusil and zip ties. 3. Wrap spiral Kapton heater around line 4. Hold down with 1 layer of 3M 425 Aluminum tape. 5. Apply 2nd layer of Aluminun tape 6. Add Thermocouple for T/V testing. 7. Wire everything up 8. Wrap MLI around pipe 9. Ground the MLI with its Ground Strap to structure

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Spiral Kapton Heaters for Prop Lines

Saddle Blocks w/ integral thermostats

Prop Line

Nusil Zip-tie

Prop Line Tstats on Saddle Blocks

Honeywell Model Style 717

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Propellant Liquids • Monoprop: Hydrazine • Bi-Prop (Fuel + Oxidizer)

– Monomethyl Hydrazine (MMH) is the fuel – Nitrogen Tetroxide (NTO) is the oxidizer

• The freezing point can be lowered if you add nitric oxide. • The resulting oxidizer Mixed Oxides of Nitrogen (MON). • NTO has a freezing point of about -9OC • MON-3 (3% nitric oxide) freezes at -15OC • MON-25 (25% nitric oxide) freezes at -55OC

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Propulsion Module Plumbing

Low Pressure Control Module

Pressurant Supply

Fuel and Oxidizer Control Module

Fuel Pressurant Line

Fill and Drain Valve Bracket

High Pressure Control Module

Fuel Tank Liquid Line

Oxidizer Pressurant Line

Fuel Tank

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Propulsion Tanks •Aluminum Tape •Thermostats •Thermistors •Heaters •MLI blanketing

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Page D-34

Propulsion Line Supports • Plumbing lines are supported by thermally

isolating brackets and standoffs – Machined Ultem 1000 Or Ultem 1200UC – Brackets are bonded or bolted to the primary

structure

• Lines can be held with compliant clamps – Tefzel Cable ties may be used for off module

plumbing runs – common for commercial satellites

Ultem isolator/ bracket

Triana Propulsion Module

Line Clamp

¼” Propellant Line

Saddle Clamp

“Racetrack” tube spacer and Tefzel

Cable Tie TFAWS 2015 – August 3-7, 2015

34

Page D-35

Fill and Drain Valve and Thruster Plumbing

ACS Thruster “A” Fuel Line

ACS Thruster “A” Oxidizer Line

ACS Thruster “B” Fuel Line

ACS Thruster “B” Oxidizer Line

ACS Thruster “A”

ACS Thruster “B”

Oxidizer F&D Valve (FD-O2) Fuel F&D Valve (FD-F2)

Pressurant Supply F&D Valve (FD-H1) Pressurant F&D downstream of PVs (FD-H2)

Oxidizer Tank Inlet (FD-O1)

Fuel Tank Inlet (FD-F1)

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Course Summary

• Learned about “real” vs. theoretical MLI • Learned about “Actual” thermal hardware instead of

“Thermal Model” Hardware. – Their bonding techniques and materials.

• Learned about the special case of Propulsion Thermal.

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