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Micrometeoroid/Orbital Debris MLI

MMOD-IMLI utilizes IMLI’s structural strength to support ballistic layers, providing both thermal insulation and micro-meteoroid and orbital debris protection. MMOD-IMLI has 24% of the mass of a multishock shield with equivalent stopping power, with heat transfer on the order of 0.1 W/m2.

In a MMOD-IMLI: Integrated Thermal Insulation and Micrometeoroid/Orbital Debris Protection Phase I project Quest built a 120-layer blanket/shield, conducted hypervelocity impacts and measured heat leak. MMOD-IMLI had a measured heat leak of 1.58W/m2 for an eight layer blanket, and the 8.0 kg/m2 blanket was able to completely stop a 5.4mm particle at 6.6km/s, which would provide a 95% probability of no penetration for the selected Orbital Fuel Depot mission.  With this measured performance, the team has successfully demonstrated critical function in a proof-of-concept, and demonstrated feasibility of MMOD-IMLI, moving the technology to TRL 3.

Micrometeoroid Orbital Debris-IMLI is a unique system that provides both thermal insulation and MMOD shielding.  MMOD-IMLI is an integrated system based on proprietary discrete spacer technology system developed by Quest Thermal Group and Ball Aerospace for Integrated MultiLayer Insulation (IMLI).  IMLI is a next generation thermal insulation system providing 30 – 40% lower heat leak per layer than conventional MLI, in a robust bonded up structure.  MMOD-IMLI combines the thermal radiation barriers of IMLI, the precise control of layer spacing with polymer spacers, and high strength ballistic Kevlar and Nextel layers.  MMOD-IMLI provides excellent thermal insulation, with measured results matching our latest TAK thermal modeling for heat leak from the active radiation barriers. Heat leak was measured through a full MMOD-IMLI blanket installed on a Quest tank via LN2 boil off calorimetry.  MMOD-IMLI test coupons with 120 layers (12 ballistic layers and 108 dual aluminized mylar layers) were fabricated and used for Hyper Velocity Impact (HVI) testing conducted at JSC/White Sands Test Facility. A preliminary model of the MMOD-IMLI shield was combined with a model for an Orbital Fuel Depot mission by Eric Christiansen and Dana Lear of JSC to develop preliminary Ballistic Limit Equations, and actual hypervelocity impact results indicated an MMOD stopping power of a 5.4mm diameter particle.

The team (NASA JSC, Ball and Quest) worked collaboratively to establish an Orbital Fuel Depot (OFD) mission profile, analyze the fluence and impact risk of that mission, and develop a finite element model in order to predict the Probability of No Penetration (PNP).   Inputs were established for an OFD based on an extended Centaur cryotank set in a selected orbit. MMOD fluence and impact risk analysis were performed by Dana Lear and Eric Christiansen of JSC, who developed an OFD Finite Element Model and used Bumper-II MMOD risk analysis code to estimate the risk performance of an MMOD-IMLI shield.  Preliminary assessment indicated a 120 layer MMOD-IMLI shield/thermal blanket might meet the goal of >95% PNP over a 15 year OFD mission.  Using Bumper code and starting from existing multishock shield bumper equations, a theoretical model was developed to take into account the number of ballistic layers, spacing and additional thermal layers.

Ballistic test coupons were constructed based on the mission and modeling assessments.  The MMOD-IMLI hypervelocity impact test coupons were comprised of six sets of Nextel and Dual Aluminized Mylar (DAM) as outer layers and six sets of Kevlar and DAM as inner layers. These twelve sets of layers formed 120 layers in total, with layer spacing controlled by polymer spacers, with a known areal mass in the layers, and with the blanket thickness predicted to prevent full penetration during hypervelocity impact.  Preventing full penetration was critical to assess the test results and compare to model predictions.  The mass of the ballistic coupons was 8.02kg/m2 as compared to a standard Whipple shield mass of 15 - 20 kg/m2 and a traditional four layer Nextel multishock shield mass of 10.8 kg/m2 (to stop a critical diameter particle of 6.3mm for the selected PNP). MMOD-IMLI coupons were subjected to hyper velocity impact testing at White Sands Test Facility (WSTF) where a 3.2mm projectile traveling at 7 km/s penetrated to the 7th ballistic layer. Model predictions were the particle would stop by the 6th layer.  A second shot was a 5.4mm projectile traveling at 6.63 km/s and was predicted to stop at the 12th ballistic layer, and was stopped within the MMOD-IMLI blanket at the 12th layer.

Micrometeoroid/Orbital Debris MLIA thin MMOD-IMLI blanket was designed, fabricated and installed on a test tank to measure thermal performance.  The MMOD-IMLI thermal blanket had a structure representative of the thick MMOD shield with one layer of Nextel, four layers DAM, one layer of Kevlar and four layers of DAM.  This blanket had 6 ½ “IMLI” layers (effective radiation barriers with low conductance spacers) plus two ballistic layers. An improved thermal model was developed in TAK2000 (Thermal Analysis Kit) that allows layer by layer detail to be modeled for the various layers in MMOD-IMLI.  This modeling indicates the high emissivity ballistic layers contribute little to thermal insulation.  Heat leak was measured at 1.58W/m2, for 6 ½ layers, which calculates to 1.01W/m2 for 10 full IMLI layers, and compares well to the measured heat leak of 0.95W/m2 for a regular 10-layer IMLI blanket. The apparent thermal conductivity for MMOD-IMLI is 0.117 mW/m-K, higher than the k value for IMLI (0.069mW/m-K), due to inclusion of thicker non-thermally performing ballistic layers and less control over layer touching with woven Nextel and Kevlar layers.

In this Phase I program the team was able to model an Orbital Fuel Depot mission for MMOD requirements, predict the MMOD shielding behavior of this novel MMOD-IMLI multilayer, widely spaced structure, build a 120-layer coupon, determine it could stop 5.4mm particles at 7km/s, build and install an eight layer MMOD-IMLI blanket on a tank and measure a thermal conductance of 1.58W/m2.  Feasibility of the MMOD-IMLI concept was successfully proven, a prototype was demonstrated in a laboratory environment for TRL3, and MMOD-IMLI continues to be a novel concept that could provide both thermal insulation and effective MMOD shielding in a single lightweight system.

 

Micrometeoroid/Orbital Debris MLI