Progress in Manufacturing & Characterizing Domestic Lyocell PICA and Comparison to Heritage PICAMairead Stackpoole and Ethiraj Venkatapathy, NASA Ames Research Center, Moffett Field, CA 94035

Steve Violette, Fiber Materials Inc, Biddeford, ME 04005 Background – PICA and PICA Sustainability

State of the Art Low Density Carbon Phenolic Ablators

Summary• NASA ARC is working with SMD-PSD to address PICA rayon sustainability concerns

• Remaining Sniace heritage rayon has been procured by NASA and is being stored for

future SMD-PSD mission – enough heritage rayon available to support a single

mission (OSIRIS-REx scale)

• NASA is also evaluating a domestic rayon alternative (Lyocell) for qualifying a

replacement PICA thereby providing a sustainable domestic source that is more

certain for long-term availability• Demonstrated ability to cast lyocell derived fiberform that meets PICA spec

(demonstrated in both a near net shape cast unit and in billet form)

• Successfully infused lyocell PICA and achieved density targets for both near net shape

cast unit and billets. NDE completed to evaluate void content and fiberform alignment

• Limited thermal and mechanical property measurements in process

• High and medium condition arc-jet testing give confidence that PICA-D (domestic

lyocell based PICA) performance is comparable to heritage PICA (rayon based)

• Low condition arc jet test (NF relevant) scheduled for early Oct 2017

• Limited initial testing and property dataset indicate that Lyocell Derived PICA is a

potential drop in replacement for rayon derived PICA

• Proposers will have the final report detailing findings from this study by Dec 2017 to

make assessments.

Stardust SRC post flight with PICA forebody heat shield

(0.8m max. diameter)

• Phenolic Impregnated Carbon Ablator (PICA) is a low

density (~ 0.27g/cm3) ablator first used as the forebody

heatshield for the Stardust sample return capsule

where it was used as a single piece heatshield

• Since Stardust, PICA was used on the Mars Science

Lab (MSL) in a tiled configuration, on the OSIRIS-REx

sample return capsule as a single piece and slated for

Mars 2020 as a tiled configuration.

Securing Remaining Heritage (Sniace) Rayon

• NASA ARC funded by SMD has procured and graphitized all remaining heritage rayon

through FMI. FMI is retaining the carbonized fibers in bonded storage for future mission

use to be decided by SMD-PSD (in storage for up to 10 yrs)

• There is a sufficient quantity of heritage rayon available to support a single

mission (~ OSIRIS-Rex scale) thereby providing a flight unit, spare unit and

material for manufacturing process development

• The quantity of heritage rayon available is not sufficient to support fabrication of PICA

needed for larger ( >> 1 m) heat-shield or back-shell applications

Qualification of an Alternative Based FiberForm® PrecursorRole of Rayon/Lyocell in PICA

Manufacturing

Rayon or Lyocell

Conversion to carbon

FiberForm® billet preform

Single piece PICA heatshield (< 1.25m max diameter)Near net shape preform

AcknowledgementsPICA sustainability activities are funded by NASA’s Science Mission Directorate

Presented at OPAG, Sept 6-7 2017, La Jolla, CA

Net Casting, Billet Fabrication and Infusion• 7 billets of fiberform manufactured to optimize the process using lyocell fibers – billets

span the spec density range – fiberform target densities achieved

• Development and fabrication of 1 relevant scale, net-shaped FiberForm heatshield

blank (OSIRIS REx scale) completed – density targets in net cast achieved

• Process refinements and lessons learned have been documented

• Limited Non Destructive Evaluation (NDE) in progress on the lyocell near net shape

fiberform unit to ensure features such as internal voids or inclusions are in family with

rayon derived fiberform and fiber alignment is as expected.

Near net shape preforms

Trimmed prior to infusion Post-infusion

Arc Jet Characterization• 3 conditions targeted – testing currently in progress (completed in Oct 2017)• NF proposers provided guidance on test conditions

• OSIRIS Rex and Stardust tested at ~1500W/cm2 and 0.55 atm

Material Density Centerlinerecession

LyocellDerivedPICA

nominal 4.0mm

RayonDerivedPICA

nominal 4.2mm

Rayon DerivedPICA

Lyocell DerivedPICA

Post testPost test

Pre test Pre test

• NASA ARC recently learned that heritage rayon utilized in PICA has stopped production

leading to a flight-qualified PICA sustainability challenge.

• NASA ARC is now funded by SMD to address PICA rayon sustainability – two

approaches are being pursued:

• Secure the remaining heritage (Sniace) rayon.

• Develop and implement plans to certify a Lyocell based PICA

Plan to Demonstrate Feasibility of Sustainable Domestic Lyocell PICALyocell is being evaluated as a “rayon alternative” FiberForm® precursor – Lyocell is a

sustainable domestic source and previous work indicates Lyocell is a feasible alternative• FMI completed a limited study on FiberForm® made with Lyocell in 2005 and preliminary

mechanical and thermal properties were evaluated

• Study concluded that the ‘Lyocell derived’ FiberForm® was comparable to baseline

‘rayon derived’ FiberForm®

• Study did not complete infusion to make PICA, also, study did not address near-net-

shape casting with Lyocell derived heatshield units

SMD-PSD funded ARC to manufacture and perform limited property and aerothermal

characterization of Lyocell based PICA

• Fabrication of PICA billets & a near net shape heatshield using Lyocell based

FiberForm®. Activity supports tiled heatshield & smaller scale single piece heatshield

designs. Target drop-in replacement for heritage PICA

• Characterization includes thermal /mechanical properties and arc jet testing of

instrumented coupons - NASA ARC worked with NF proposing orgs to ensure arc jet

testing is at mission relevant conditions

Tiled PICA heat shield(> 1.25m max diam)

Post-gel

Trimmed X-ray (fiber alignment and FOD/void check

Cast unit density coupon cut plan

Arc Jet Test MatrixPost-test recession

(1550W/cm2)

Lyocell Derived PICARayon Derived PICA

Example in-depth T/C trace (1550W/cm2)

• Initial results indicate recession

and thermal response between a

lyocell-derived and a rayon-

derived PICA are comparable.