NASA Technical Reports Server (NTRS) 20130009431: Using Pre-Melted Phase Change Material to Keep Payloads in Space Warm for Hours without Power

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by  NASA Technical Reports Server (NTRS)

achieve maximum van der Waals forces. veloped at JPL to make this process sim- of the wedge leaning to the same side,
By maximizing the real area of contact pler, more reliable, and to allow new i.e., an actual overhang of the fibers,
that these fibers make and minimizing geometries not previously possible. which is more like the arrangement of a
the bending energy necessary to achieve These new geometries will make the ad- gecko foot’s fibers. A third critical differ-
that contact, the net amount of adhe- hesive and the reliability significantly ence is the use of a standard positive No-
sion has been improved dramatically. better, and will drive down cost and de- valac photoresist, which has a wide
The suspension structure consists of velopment time. process latitude.
millimeter-scale fibers that are bonded to The process involves using optical li- The new microfabrication process has
the contacting level through a wet assem- thography to make a master pattern, allowed the shape of the wedge-like
bly step. These millimeter-sized fibers and from this master pattern, making a fibers to be controlled. Prior to these
serve as a discretized way of both con- reusable master mold that is used to cast process improvements, only right-angle
forming to roughness on the surface and the adhesive strips. To create the master wedges had been fabricated. Now, the
distributing the overall climbing loads photoresist pattern that will be used to process not only allows for increased
down to the individual contacts. These make the master mold, a self-aligned control over the angle of these fibers,
structures have been tested on an experi- double exposure technique was used. but is also much more reliable, manufac-
mental testbed meant to determine the Two different angled UV exposures are turable, and cost-effective.
contact forces very exactly, and have also performed using a single opaque pat- This work was done by Aaron Parness and
been demonstrated by hanging weights tern on a transparent wafer. This simpli- Victor E. White of Caltech for NASA’s Jet
off of a patch adhering to a variety of walls fies fabrication considerably. Propulsion Laboratory. Further information
(glass, metal, wood, plastic, drywall, etc). A second advantage of this technique is contained in a TSP (see page 1). NPO-
This material is fabricated via a mold- is the ability to achieve right-angle 48156
ing process. A new process has been de- wedge-shaped structures with both sides
Using Pre-Melted Phase Change Material to Keep Payloads in
Space Warm for Hours Without Power
Goddard Space Flight Center, Greenbelt, Maryland
Adding phase change material from the radiator(s) to space. For the which is about 225 kJ/kg, and a range of
(PCM) to a mission payload can main- interplanetary Probe, PCM is melted by melting points. For example, C18H38 has
tain its temperature above the cold sur- heaters just prior to separation from a melting point of 28 °C, which is well
vival limit, without power, for several the orbiter when power is available within the payload temperature limits.
hours in space. For the International from the orbiter power system. After At the time of this reporting, paraffin
Space Station, PCM is melted by heaters the Probe separates from the orbiter, wax PCM had a TRL (technology readi-
just prior to the payload translation to the PCM releases its latent heat to make ness level) of 7.
the worksite when power is available. up the heat loss from the Probe exte- This work was done by Michael Choi of God-
When power is cut off during the six- rior to space. dard Space Flight Center. FFurther information
hour translation, the PCM releases its Paraffin wax is a good PCM candidate. is contained in a TSP (see page 1). GSC-
latent heat to make up the heat loss It has a high solid-to-liquid enthalpy, 16539-1
10 NASA Tech Briefs, January 2013