Characterization of a Radiometer Window for Mars Aftbody … · 2018-11-29 · 25-29 June, 2018...

AIAA Aviation Forum25-29 June, 2018

Ruth A. Miller, Stanford University

Chun Tang, Mark S. McGlaughlin, Todd R. White, NASA Ames Research Center

Thanh S. Ho, Megan MacDonald, Jacobs Technology at NASA Ames Research Center

Brett A. Cruden, AMA Inc. at NASA Ames Research Center

Characterization of a Radiometer Window for Mars Aftbody Heating

Including Ablation Product Deposition Using

a Miniature Arc Jet

https://ntrs.nasa.gov/search.jsp?R=20180007848 2020-03-05T04:01:01+00:00Z


Background

• Mars Entry Descent and Landing Instrumentation 2 (MEDLI2)

– Characterize aerodynamic, aerothermodynamic, and TPS performance

– Expands off MEDLI (Mars Science Laboratory, 2012)

– Pressure Transducers, Thermal Plugs, Heat Flux Sensors, Radiometer

2

Figure Credit: H. H. Hwang et al., 2016.

MEDLl2 (Mars 2020) Thermal Instrumentation

o PICA Aerothermal Plug • PICA Thermal Response Plug

Heatshield

. 0 SLA-56tV Aerothermal Plug • Heatflux Sensor

Radiometer Backshell

Pressure Instrumentation

o Supersonic Pressure • Hypersonic Pressure

Heatshield

O Backshell Pressure

Backshell


MEDLI2 Radiometer

3

• MEDLI2 radiometer consists of a

heat flux sensor behind a sapphire

window

• Measurement range: 0 - 15 W/cm2

Figure Credit: B. A. Cruden et al., 2015.

MEDLI2 Radiometer

• Spectral radiance for MSL entry from

Electric Arc Shock Tube (EAST)

experiments show peak radiance

around 2.7 μm and 4.3 μm due to CO2

• Expected backshell heating for

Mars 2020:

- Radiative: ~ 4.5 W/cm2

- Convective: ~ 1 W/cm2

3.5 - 63 sec

3 - 74 sec E - 85 sec ~ 2.5 I... - 96 sec (/)

I - 104sec N 2 E CJ

§: 1.5 -Q.) 1 CJ

C ctl

"'C 0.5 ctl 0::

0

-0.5 0 1 2 3 4 5

Wavelength (µm)


Radiometer Characterization

4

• Radiometer output

Sapphire

Window

Heat Flux Sensor

(Schmidt-Boelter

Gauge)

𝑇 λ

A λ

L λ

MEDLI2 Radiometer Cross-Section

L λ : Spectral radiance of source

(calibration or shock layer)

𝑇 λ : Spectral transmission of

window

A λ : Spectral absorbance of

heat flux sensor

𝑉𝑟𝑎𝑑 ∝ න𝑇 λ 𝐴 λ 𝐿 λ 𝑑λ

0.02 in

0.25 in

• Radiometer output is not

spectral, however

characterization will be done

spectrally

( ) ( ) ( ) ( )

1~ \ l ~ 7 •I

( ) II ' ( )

I c)\/ ( )+

( )

I


Transmission and Absorbance

5

Sapphire Window

• Transmission of ~88%

up to 5.5 µm

Heat Flux Sensor

• Absorbance of ~95%

100 12 100

~ --+

80 10 80 ---- ----~ 0 ~ 8 ~ ........ 0 0 ........ .._.. C 60 Q) 60 Q) 0

·u5 (.) (.)

C 6

C (/) !9 ro .E .0 (.) .... (/) 40 Q) 40 0 C ,.::: (/)

ro Q) 4 .0 .... a::: <( ~

20 2 20

0 0 0 0 2 4 6 8 0 2 4 6 8

Wavelength (µm} Wavelength (µm}


Measured Radiation

6

3.5 -~ 0

3 100 -Heat Flux Sensor Absorbance, A (1) Q) -E Radiometer W indow Transmission, T(l) <.)

~ C ::i. 2.5 ro I .c '- 80 en '-I - 63 sec 0

N 2 en E - 74 sec .c <.) 60 <(

~ 1.5 85 sec "'O C - - 96 sec ro

Q) 1 - 104sec C <.) 40 C 0

ro ·u5 "'O 0.5 -~ ro

20 E er en 0 C

ro '-

-0.5 0 I-

0 1 2 3 4 5 Wavelength (µm)


Measured Radiation

7

𝑆𝑙𝑜𝑠𝑠 = 1 −𝑇 λ 𝐴 λ 𝐿 λ 𝑑λ

𝑇𝑐𝑎𝑙𝐴𝑐𝑎𝑙 𝐿 λ 𝑑λ𝑥 100

Percent Signal Loss:

( _(_)_(_)_(_) _) ( )

3.5 --------------------

-E ::i. I 'en

I N

E (.)

~ ..__, a, (.)

C co

3

2.5

2

1.5

1

-c:, 0.5 co er

0

- 63 sec - 74 sec

85 sec - 96 sec - 104sec

-o.5-----------------o 0 1 2 3 4 5

Wavelength (µm)


Measured Radiation

8




Measured Radiance

Total Radiance

Measure of unaccounted for

radiation due to variation in

wavelength sensitivity

3.5 -~ 0


~ C ::i. 2.5 ro I .c '- 80

( en '-

I - 63 sec 0 N 2 en E - 74 sec .c <.) 60 <(

~ 1.5 85 sec "'O C - - 96 sec ro

Q) 1 - 104sec C <.) 40 C 0

ro ·u5 "'O 0.5 -~ ro

20 E er en 0 C

ro '-

-0.5 0 I-



Measured Radiation

9




Measured Radiance

Total Radiance

Measure of unaccounted for

radiation due to variation in

wavelength sensitivity

• Assuming radiometer calibration corrects for 1 - 2 µm 𝑇𝑐𝑎𝑙𝐴𝑐𝑎𝑙 = 85%

𝑆𝑙𝑜𝑠𝑠 = 1.8%!

3.5 -~ 0


~ C ::i. 2.5 ro I .c '- 80

( en '-

I - 63 sec 0 N 2 en E - 74 sec .c <.) 60 <(

~ 1.5 85 sec "'O C - - 96 sec ro

Q) 1 - 104sec C <.) 40 C 0

ro ·u5 "'O 0.5 -~ ro

20 E er en 0 C

ro '-

-0.5 0 I-



Thermal Protection System (TPS) Ablation

• Radiometer will be embedded in backshell TPS

• TPS ablation products from heatshield or backshell could be deposited on

the window

10

Image credit: NASA/JPL-Caltech

Backshell

SLA-561V(Silicone resin with

cork, phenolic

microballoon, silica

microballoon, and

refractory fiber fillers*)

Heatshield

PICA(Carbon Fiberform and

phenolic resin**)

*E. L. Strauss, 1967.

** H.K. Tran, et al., 1997.


Miniature Arc Jet (mARC) Facility

11

Pitot Probe

at 20 mm

from Nozzle

Gardon Gauge

at 2 mm

from Nozzle

mARC Flow• mARC previously

characterized in air*

• Heat fluxes > 1000 W/cm2

• Expected Mars 2020 heat

flux:

- Heatshield: ~ 150 W/cm2

- Backshell: ~ 5 W/cm2

• Characterize mARC in

Mars flight relevant

environment (90% CO2,

10% N2)

*A. Nawaz et al., 2016.

Flow

Direction


mARC Characterization Results

12

See paper for detailed mARC characterization results.

Flow rate of 0.25 g/s

Centerline heat flux: 550-700 W/cm2

Flow rate of 0.1 g/s

Centerline heat flux: 250-400 W/cm2

Test Conditions:

• 90% CO2, 10% N2 (by mass)

• Arc Current: 40 A

• Distance From Nozzle: 20 mm

400...--------------------,

N,.......,300 E

~ -;200 ::::,

u:::: .... ro ~ 100

(a) 0.1 g/s - Test8Run4 - Test 8 Run 4b - Test 8 Run 4c

0L--------~~~~=I 2.5 3 3.5

Radial Position (in)

aoo...--------------------.

N,.......,600 E

~ -; 400 ::::,

u:::: .... ro (l)

I 200

(b) 0.25 g/s - Test 7 Run 2k - Test 7 Run 21

Test 8 Run 2n

0L---------....::.:.:~a1::::===.....J 2.5 3 3.5

Radial Position (in)


Test Article and Expected Heat Rate

13

Computed surface heating rates for a wedge

at various inclination angles

Model inclination angle: 45°

• ~140 W/cm2 on TPS #1

• ~5 W/cm2 at the window

250

200 30 deg. 45 deg. 60 deg . 90 deg . Peak forebody ......

C\I 150 heat flux < E

~ ...... ~ 100 a

TPS#1 TPS#2 Window location

50

Peak aftbody heat flux

00 0.025 0.05 0.075 s [m]


Test Matrix

14

Test Conditions:

• 90% CO2, 10% N2 (by mass)

• Mass Flow Rate: 0.1 g/s

• Arc Current: 40 A

• Distance From Nozzle: 20 mm

• Model Inclination Angle: 45°

Run

Number

Window

Number

Duration

(sec)TPS #1/TPS #2

Copper

Slug?

1 1 55 PICA/PICA Yes

2 4 40 PICA/PICA No

3 3 30 PICA/SLA Yes

4 6 30 PICA/SLA No

5 2 30 SLA/SLA Yes

6 5 30 SLA/SLA No


Radiometer Windows

15

SLA/SLA, with Copper Slug, Window 2

PICA/PICA, with Copper Slug, Window 1

PICA/SLA, with Copper Slug, Window 3

)

PICA/PICA with Copper Slug

Window 1

PICA/PICA without Copper Slug

Window4

SLA/SLA with Copper Slug

Window2

SLA/SLA without Copper Slug

Windows

PICA/SLA with Copper Slug

Window3

PICA/SLA without Copper Slug

Window6

• ..

. .,,. -. •.;

0 •

.:-,.'. :

. ' . .. • . ~, ' ,-~~t~.,

"'


Radiometer Window Transmission Post-mARC Test

16

100 - Initial - PICNPICA Window 1

90 - PICNPICA Window 4 PICNSLA Window 3

80 - PICNSLA Window 6 - SLNSLA Window 2

70 - SLNSLA Window 5

--~ 0 ._. 60 C 0 Cl)

50 Cl)

E Cl) C 40 ro I,...

f-

30

20

10

0 0 1 2 3 4 5 6 7 8

Wavelength (µ m)


Radiometer Window Transmission Post-mARC Test

17

OH Str.

CH Str.

SiH

OH Str.

SiOH

CH Str.

OH Str.

SiOH

C6H6O

C6H6

C=C Str.

C6H6O

C6H6

C=C Str.C6H6O

C6H6

C=C Str.

SiH

PICA/PICA SLA/SLA PICA/SLA 100 100 100

80 80 80

~ ~

~ ~

~ ~

C 60 C 60 C 60 0 0 0 ·u; ·u; ·u; rJl rJl rJl .E .E .E rJl 40 rJl 40 rJl 40 C C C ro ro ro .... .... .... I- I- I-

20 20 20

0 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8

Wavelength (1.tm) Wavelength (µ,m) Wavelength (µ,m)

l --lnitial --Window1-withCu --Window41 ! --Initial --Window 2 - with Cu --Windows! ! --Initial --Window3 - with Cu --Window61


Comparison to EAST MSL Data

18

PICA/PICA • Window 1 SLA/SLA - Window 2 PICA/SLA • Window 3 3.5 3.5 3.5

~ -+ ~ -+ ~

3 100 3 100 ~ 3 Heat Flux Sensor Absorbance 100 ~

E Q)

E ~ E ~ u C: C: C: ::t 2.5 ro ::t 2.5 ro ::t 2.5 ro

,!_ 80 .0 ,!_ 80 .0 ,!_ 80 .0 <(l ... <ll ... <ll ...

Transmission - Post- 0 ' 2 0 ' 2 Window

0 N 2 (/) N (/) N <ll E mARC .o E .o E Transmission - .0 ~ 60 <( ~ 60 <( ~ 60 <(

~ 1.5 -0 ~ 1.5 -0

~ 1.5 Post-mARC -0 C: C: C:

Q) ro

Q) ro

Q) ro

u 40 C: u 40 C: u 40 C: C: 0 C: 0 C: 0 .!!! ' iii .!!! ' iii .!!! ' iii -0 0.5 Cl)

-0 0.5 Cl) -0 0.5 Cl)

ro .E ro .E ro .E Cl'.:: 20 Cl) Cl'.:: 20 Cl) Cl'.:: 20 Cl)

0 C: 0 C: 0 C: ro ro ro ... i= i= I-

-0.5 0 -0 .5 0 -0 .5 0 0 2 3 4 5 0 2 3 4 5 0 2 3 4 5

Wavelength (µ m) Waveleng1h (µ m) Waveleng1h (µ m)


Percent Signal Loss

19

Initial PICA/PICA PICA/PICA SLA/SLA SLA/SLA PICA/SLA PICA/SLA

Copper

Slug?--- Yes No Yes No Yes No

Window

Number--- 1 4 2 5 3 6

Max Sloss

(%)1.8 12.2 13.1 27.9 29.0 19.7 19.1

• Signal loss of 12 - 30% from ablation products coating the sapphire window in both

2.7 µm and 4.3 µm bands

• SLA/SLA likely an over-test

• PICA/SLA more representative with ~ 20% signal loss


Window 1

n PICA/PICA

without Copper Slug Window4


Window2

..__;;:I'


Window5


Window3

( PICA/SLA



Conclusions

20

• Initial

- Transmission of radiometer window ~ 88% up to 5.5 µm

- Absorbance of heat flux sensor ~ 95%

- Radiometer measures about 85% of total expected radiation, which is correctable

through calibration

- About 1.8% loss due to variation in wavelength sensitivity

• Post-mARC Testing

- Decreased radiometer window transmission at ~3 µm, ~4.5 µm, > 5.5 µm

- 12 - 30% of signal lost due TPS ablation products


Window1

PICA/PICA without Copper Slug

Window4


Window2


Windows


Window3

f PICA/SLA



Future Work

21

• How “flight-like” were the conditions in the mARC?

Flight Matched Conditions

Peak heatshield heat flux on TPS #1

Peak backshell heat flux at window location

Heat load

Not Flight Matched Conditions

Heat profile

Length scale

• Other questions:

- How does cold-soak during interplanetary transit impact window transmission and

ablation product deposition?

- How does window transmission degrade as a function of time during entry?

Repeat flight and mARC test CFD

Blowing boundary condition that matches the mass loss rate predicted by material

response models

Compare concentration of ablation products over the window

If the flight concentration is less than the mARC test, these results will be treated as an

over-test

AIAA Aviation Forum25-29 June, 2018 22

Thank you!Questions?


Appendix

23


XPS Results – Atomic % (Average)

24

PICA/PICA

Window 4

SLA/SLA

Window 2

PICA/SLA

Window 6

C 1s 59.8% 54.7% 52.1%

O 1s 29.1% 27.9% 30.2%

Si 2p 4.5% 12.5% 11.1%

N 1s 3.7% 3.9% 4.8%

Cu 2p3 3.0% 1.0% 1.9%

• Identified elements (carbon, oxygen, and silicon) support conclusions from FTIR

data

• Windows in PICA/PICA models contained the most carbon

• Windows in SLA/SLA models contained the most silicon

• Presence of silicon in PICA/PICA windows could be from RTV-560 used to

adhere the TPS to the bracket or from insulating tape used inside the chamber

• Copper is assumed to come from the mARC electrodes as the arc erodes them

Characterization of a Radiometer Window for Mars Aftbody … · 2018-11-29 · 25-29 June, 2018...

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