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Load Bearing MLI

Improvements in cryogenic propellant storage are needed to achieve reduced or zero boil off of cryopropellants, critical for long duration missions. Techniques for reducing heat leak into cryotanks include using passive multi-layer insulation (MLI) and vapor cooled or actively cooled thermal shields.  Large scale shields cannot be supported by tank structural supports without heat leak through the supports. Traditional MLI also cannot support shield structural loads, and separate shield support mechanisms add significant heat leak. Quest Thermal Group and Ball Aerospace, with NASA SBIR support, have developed a novel Load Bearing multi-layer insulation (LBMLI) capable of self-supporting thermal shields and providing high thermal performance.  

Quest has continued development of LBMLI in a Phase III NASA multicenter test program, including design, modeling and analysis, structural testing via vibe and acoustic loading, calorimeter thermal testing, and Reduced Boil-Off (RBO) testing on NASA large scale cryotanks. Collaborators included Ball Aerospace, NASA Marshall Space Flight Center, NASA Ames Research Center, NASA Glenn Research Center, and NASA Kennedy Space Center.

LBMLI uses the strength of discrete polymer spacers to control interlayer spacing and support the external load of an actively cooled shield and external MLI. Structural testing at NASA Marshall was performed to beyond maximum launch profiles without failure.  LBMLI coupons were thermally tested on calorimeters, with superior performance to traditional MLI on a per layer basis. Thermal and structural tests were performed with LBMLI supporting an actively cooled shield, and comparisons are made to the performance of traditional MLI and thermal shield supports. LBMLI provided a 56% to 74% reduction in heat leak per layer over traditional MLI with tank standoffs, a 44% reduction in mass, and was advanced to TRL5. Active thermal control using LBMLI and a broad area cooled shield offers significant advantages in total system heat flux, mass and structural robustness for future Reduced Boil-Off and Zero Boil-Off cryogenic missions with durations over a few weeks.

Highlights

  • LBMLI structurally supported a Broad Area Cooled shield without tank standoffs
  • LBMLI with BAC shield survived simulated launch ascent environment
  • LBMLI reduced heat flux by 56 to 74% per layer over traditional MLI
  • LBMLI/BAC successfully demonstrated a tube-on-shield active cooling concept
  • LBMLI was matured with these ground tests to TRL5

 

Load Bearing MLI is a next generation MLI that uses discrete polymer spacers to maintain layer density, structurally support thermal shields and reduce heat leak through the insulation system. It has advantages over traditional netting MLI with improved thermal performance per layer, more predictable and repeatable performance, estimated lower fabrication and installation costs, and can be installed onto large cryotanks using modular panels.

LBMLI successfully met NASA’s program goals for key performance parameters.

NASA LBMLI key performance parameters
Load Bearing MLI

Specific results for LBMLI from this NASA test program include:

  • Quantitative data was obtained on the thermal and structural performance of LBMLI, an advanced insulation technology, with coupon and tank ground testing in simulated space thermal-vacuum environment and launch ascent environment.
  • LBMLI successfully structurally supported a 6kg BAC shield and 6kg outer MLI through launch ascent loads (acoustic loading, vibe loading and rapid depressurization).
  • LBMLI reduced heat load into the tank by 56% compared to traditional MLI on a per layer basis for operation from 20K (LH2 tank) to ca. 90K (BAC shield).
  • LBMLI reduced heat load into the tank by 74% compared to MLI on a per layer basis for operation between 77K (tank) and 160K (BAC shield).
  • LBMLI reduced mass over conventional MLI with tank supports by 44%.
  • LBMLI (and traditional MLI) heat flux at low temperatures (20K to 90K) was higher than modeled and requires additional study.
  • Benefits of LBMLI over conventional MLI were successfully demonstrated for both passive and active thermal control.
  • LBMLI was matured to TRL5.
  • LBMLI technology was recommended for infusion into future Cryogenic Propellant Storage and Transfer Technology Demonstration Missions.