Launch Vehicle MLI

Launch Vehicle MLIThe product family includes Launch Vehicle MLI (LVMLI), which offers the insulating properties of IMLI with a robust structure and more durable outer layer to withstand aerodynamic launch loads. LVMLI includes more rigid layer separation than IMLI to operate in both the aerothermal launch environment and the ground environment on the pad. LVMLI supports an internal vacuum that increases its insulating capabilities over IMLI, and can enable longer on-orbit coast times for cryogenic upper stages. LVMLI has successfully completed thermal and structural testing, and is ready for additional aerodynamic testing.

Launch Vehicle–MLI (LV-MLI) is an innovative thermal insulation robust enough to survive launch on the outside of launch vehicles and provide high performance on-orbit heat leak reduction for launch vehicle cryopropellant tanks. During LV-MLI Phase I the team designed, built and tested a robust LV-MLI system that had a measured heat leak of 3.46W/m2 for a 2½ layer blanket (0.25kg/m2), and withstood aerodynamic shockwave and vibration Atlas/Delta launch ascent profiles.  The LV-MLI prototype had 68-fold lower heat leak than 0.75” SOFI tank insulation, and 31% of SOFI mass.  The feasibility of LV-MLI was successfully demonstrated with a component laboratory validation and performance close to that modeled, moving the technology from TRL2 to TRL4.

ULA indicated if LV-MLI can survive launch and reduce heat leak by half, it would be of benefit to Atlas/Delta capabilities. A program goal was therefore to have a heat leak <47W/m2 (half of 95W/m2 heat leak through SOFI plus white paint), and LV-MLI achieved a heat leak of 3.46W/m2.  LV-MLI reduced the heat leak through bare, unpainted SOFI foam (236W/m2) by 98.5%.

Launch Vehicle MLI

Another goal was to demonstrate the survivability of LV-MLI in the aerodynamic launch environment. A collaborative effort of NASA, ULA, Ball Aerospace and Quest established preliminary aerodynamic and thermal requirements for LV-MLI.  Atlas Centaur aerodynamic launch profiles were used to design an aerodynamic launch simulation test fixture that delivered 2.5psi air pressure over 10cm at 18Hz.  Static and dynamic Finite Element Analysis was performed, and predicted LV-MLI would maintain structural integrity during launch ascent. Three LV-IMLI configurations were fabricated and tested under aerodynamic loading, and survived with no damage to the structure, mylar or spacers. One coupon tested was LV-MLI bonded over SOFI, a likely initial flight configuration, with no degradation. Coupons underwent vibration testing at the GEVS 14.6Grms profile with no damage. Compressive and shear loads were applied to measure the strength of the spacers, and compared to modeled values.

Thermal performance was modeled via a new detailed one-dimensional layer by layer TAK2000 model that included conductive and radiative heat flows between layers, emissive heat losses from the spacers, and contact conductive heat losses from light contact base dual aluminized mylar layers.  The TAK model accurately predicted IMLI and LV-MLI thermal performance; IMLI 10-layer heat leak predicted was 0.95W/m2 in good agreement with the measured value of 0.95W/m2; and 2 ½ layer LV-MLI was predicted to have 3.56W/m2, in fair agreement with a measured 3.46W/m2. The TAK model allows accurate system performance prediction, and helps guide design. The thermal model predicts that a 1½ layer LV-IMLI system could provide a heat leak of 5.73 W/m2 (2.4% of the heat leak of SOFI), more than meeting ULA’s heat leak goal, with a mass of 0.076 kg/m2 (9.5% of the mass of SOFI).

LV-MLI uses proprietary discrete spacer technology in a rugged bonded up structure, could be bonded to the sidewalls of LOX/LH2 cryotanks in the Centaur/DCSS/ACES/iCPS, and withstand aerodynamic loading during launch ascent.  LV-MLI can significantly decrease heat leak into upper stage cryotanks and increase payload capacity for NASA, national security and commercial missions that require multi-hour coasts for MEO and GEO orbit insertion.

This Phase I program evaluated Launch Vehicle-MLI aerodynamic and thermal requirements, designed a LV-IMLI insulation system, designed and built an aerodynamic simulator, built and tested LV-IMLI prototypes for structural and thermal performance, compared performance to that predicted, and successfully determined feasibility of LV-MLI.

Performance Compared to SOFI

Launch Vehicle MLI

Cryogenic upper stages on launch vehicles have on-orbit coast times limited by propellant boil-off, and LVMLI provides an ideal insulation solution with superior performance. LVMLI has 144x lower heat transfer per thickness than SOFI. For a 200 m2 tank, the difference in propellant lost to boil-off is estimated as 3600kg in 10 hours on-orbit. LVMLI mass is estimated as 180kg, SOFI mass is 140kg. As a low-risk path to flight demonstration, LVMLI could be used in conjunction with SOFI to provide both ground hold and long on-orbit coast times.

Thermal performance can be even further improved, as demonstrated by Load Bearing MLI (LBMLI), in which vapor cooled shields are self supported by IMLI spacers, without requiring tank supports or standoffs.

Launch Vehicle MLI