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Wrapped MLI

New vehicles need improved cryogenic propellant storage and transfer capabilities for long duration missions. Multilayer insulation (MLI) for cryogenic propellant feedlines is much less effective than MLI tank insulation, with heat leak into spiral wrapped MLI on pipes 3 to 10X higher than conventional tank MLI. Better insulation for cryogenic feed lines is an important enabling technology that could help NASA reach cryogenic propellant storage and transfer requirements. Improved insulation for Ground Support Equipment could reduce cryogen losses during launch vehicle loading. Wrapped-MLI (WMLI) is a high performance multilayer insulation using innovative discrete spacer technology specifically designed for cryogenic piping to reduce heat flux.

The poor performance of MLI wrapped on feed lines is due to compression of the MLI layers, with increased interlayer contact and heat conduction. WMLI uses polymer spacers that maintain precise layer spacing, with a unique design to minimize contact area/length ratio and reduce solid heat conduction.

We report on the continued development of WMLI. Novel polymer spacers were designed, analyzed, fabricated and tested; different installation techniques were examined; and novel corner rapid prototype shell spacers to speed installation on real world piping were designed and tested.  Prototypes were installed on tubing set test fixtures and heat flux measured via calorimetry. WMLI offered superior performance to traditional MLI installed on cryogenic pipe, with 2.2W/m2 heat flux compared to 26.6W/m2 for traditional spiral wrapped MLI (5 layers, 77K to 295K). WMLI as inner insulation in Vacuum Jacketed Pipe can offer heat leaks as low as 0.09 W/m, compared to industry standard VJP with 0.31W/m. WMLI could enable improved spacecraft cryogenic feedlines and industrial hot/cold transfer piping.

Highlights

  • Novel discrete spacers for pipe insulation were designed, modeled, prototyped & tested
  • WMLI had good performance (2.2W/m2) with 12x lower heat leak than spiral wrapped MLI
  • Rapid prototype nested shells were developed for quick installation on complex tubing
  • WMLI offers robust, repeatable, high performance insulation for cryogenic feedlines
  • WMLI is a novel pipe insulation system for spacecraft & industrial transfer piping

 

Wrapped MLI Wrapped MLI

WMLI offered superior performance to traditional MLI installed on cryogenic pipe, with 2.2W/m2 heat flux compared to 5.5W/m2 for advanced clamshell netting MLI and 26.6W/m2 for traditional spiral wrapped MLI (5 layers, 77K to 295K). WMLI as inner insulation in Vacuum Jacketed Pipe provided heat flux as low as 0.09 W/m, compared to industry standard VJP with 0.31W/m.

Table: Wrapped MLI measured performance versus spiral wrapped & clamshell conventional netting MLI
Wrapped MLI

Table: Comparison of WMLI/VJP and industry standard Vacuum Jacketed Pipe
Wrapped MLI

In a NASA Phase II SBIR program, Quest achieved significant improvements in WMLI performance, accomplished all program technical objectives, and demonstrated that WMLI is a superior, next generation cryogenic pipe or vacuum jacketed pipe insulation, with up to 12-fold lower heat flux than current insulation.

WMLI is a high performance, next generation pipe insulation system, with applications for spacecraft cryogenic piping. WMLI exceeds current Vacuum Jacketed Pipe performance, and could offer improved VJP products for industrial hot/cold transfer piping.

Specific results for WMLI include:

  • A unique discrete spacer was designed for concentric feedline insulation with low Area/Length to control insulation layer spacing and reduce heat conduction.
  • New feedline insulation techniques were developed leading to high performance thermal systems with rapid installation.
  • WMLI thermal models were developed that provide fair accuracy in predicting heat fluxes of installed insulation.
  • WMLI provided substantially lower heat leak than traditional MLI on feedlines, and better performance than MLI in Vacuum Jacketed Pipe.