Ryuta Hatakenaka

Thermal Performance and Practical Utility of a MLI Blanket using Plastic Pins for Space Use

A new type of non-machine-sewn (zero stitch) MLI blanket has been developed to achieve high thermal performance while maintaining workability of production and assembly equivalent to the conventional type. Tag-pins, which are widely used in commercial applications to hook price tags to products, are used to fix the films in place. The pin material is changed to polyetheretherketone (PEEK) for use in space. Thermal performance is measured using a boil-off calorimeter, in which a rectangular liquid nitrogen tank is used to evaluate the degradation at the bending corner and joint of the blanket. A test piece of zero-stich MLI shows significantly improved thermal performance (eff is smaller than 0.0050 at ordinary temperature) despite having the same fastener interface as traditional blankets, while the venting design and number of tag-pins are confirmed as appropriate in depressurization test.

Electrically insulated MLI and thermal anchor

The thermal shield of JT-60SA is kept at 80 K and will use the multilayer insulation (MLI) to reduce radiation heat load to the superconducting coils at 4.4 K from the cryostat at 300 K. Due to plasma pulse operation, the MLI is affected by eddy current in toroidal direction. The MLI is designed to suppress the current by electrically insulating every 20 degree in the toroidal direction by covering the MLI with polyimide films. In this paper, two kinds of designs for the MLI system are proposed, focusing on a way to overlap the layers. A boil-off calorimeter method and temperature measurement has been performed to determine the thermal performance of the MLI system. The design of the electrical insulated thermal anchor between the toroidal field (TF) coil and the thermal shield is also explained.

Inflation and Peel-off Characteristics of MLI Blanket under Depressurization Environment

The inflation and peel-off characteristics of a multilayer insulation (MLI) blanket under a depressurization environment have been evaluated for establishing a JAXA design standard. The venting conductance of gas flow from inside to the outside of MLI was evaluated in a steady state test, and was confirmed to take a value of the same level regardless of shape or size or pressure level when having the same perforation, spacer type, and attachment specification. In the depressurization test, MLI was observed as not inflating in a region of higher pressure even at higher depressurization speed, while inflating in a lower pressure region. The differential pressure between the inside and outside of MLI peaks when the level of pressure drops to about one kilo pascal or less. In addition, a simple mathmatical model of MLI inflation and venting is constructed and numerical simulations based on the model are conducted, which indicate that depressurization ratio (depressurization speed per the level of pressure) and volume of MLI are the dominant parameters.

Visualization of Internal Fluid Behavior in a Miniature Loop Heat Pipe using Neutron Radiography

Vapor-liquid distributions inside 100W-class loop heat pipes (LHPs) with and without a secondary wick have been observed using neutron radiography. Water is chosen as the working fluid in both cases to obtain pictures with good contrast. In the previous study (Okamoto et al., AIAA-2010-6031), a visualization result of a transient dry-out behavior in the primary wick is presented, whereas this paper has shown a result of detailed analysis on the liquid distribution in the evaporator in equilibrium state. Image processing has shown that the position of the vaporization area (vapor-liquid interface) in the fin-shaped portion of the primary wick shifts depending on the amount of heat load. The temperature trend indicates the fins are not totally dried, but in two-phase state even when the higher heat load is applied. In addition, the performance of secondary wick against gravity is also shown and the operation limit has been discussed based on a visual observation and a theoretical estimation.

Characteristics Variation of Reservoir Embedded Loop Heat Pipe under the Orbital Environment in Three Years

A deployable radiator (DPR) on the Engineering Test Satellite-VIII (ETS-VIII) was launched to a geo stationary orbit by the H-IIA rocket on 18 Dec. 2006. The DPR, an experimental apparatus on ETS- VIII; it has a Reservoir-Embedded Loop Heat Pipe (RELHP) for heat transfer from the experimental heat load to the DPR radiator. The RELHP reservoir is embedded in the evaporator for reliable function of the Loop Heat Pipe (LHP). This paper describes the characteristics of the DPR and the RELHP under an orbital environment over three years.