NASA Technical Reports Server (NTRS) 20120006574: Electrospray Collection of Lunar Dust

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by  NASA Technical Reports Server (NTRS)

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This work was done by Slava G. Turyshev, of charge deposited on particles by the
Corner-Cube Retroreflector William M. Folkner, Gary M. Gutt, James G. droplets. Removal rates of 95–99 per-
Instrument for Advanced Williams, Ruwan P. Somawardhana, and cent and greater are typically observed,
Lunar Laser Ranging Richard T. Baran of Caltech for NASA’s Jet even at moderate gas flow rates — all
A paper describes how, based on a Propulsion Laboratory. Further information is without the generation of ozone due to
structural-thermal-optical-performance contained in a TSP (see page 1). corona discharge.
analysis, it has been determined that a NPO-47489 This work was done by Joseph Bango and
single, large, hollow corner cube (170- Michael Dziekan of Connecticut Analytical
mm outer diameter) with custom dihe- Corp. for Glenn Research Center. Further in-
dral angles offers a return signal com- Electrospray Collection formation is contained in a TSP (see page 1).
parable to the Apollo 11 and 14 of Lunar Dust Inquiries concerning rights for the commer-
solid-corner-cube arrays (each consist- A report describes ElectroSpray Ion- cial use of this invention should be addressed
ing of 100 small, solid corner cubes), ization based Electrostatic Prec ip itation to NASA Glenn Research Center, Innovative
with negligible pulse spread and much (ESIEP) for collecting lunar dust parti- Partnerships Office, Attn: Steven Fedor,
lower mass. The design of the corner cles. While some HEPA filtration pro- Mail Stop 4–8, 21000 Brookpark Road,
cube, and its surrounding mounting cesses may remove a higher fraction Cleveland, Ohio 44135. Refer to LEW-
and casing, is driven by the thermal en- (>99.9 percent) of the particles, the high 18629-1.
vironment on the lunar surface, which efficiency may not be appropriate from
is subject to significant temperature an overall system standpoint, especially
variations (in the range between 70 in light of the relatively large power re- Fabrication of a Kilopixel
and 390 K). Therefore, the corner quirement that such systems demand. Array of Superconducting
cube is enclosed in an insulated con- The new electrospray particle capture Microcalorimeters With
tainer open at one end; a narrow-band- technology (inspired by the late Nobel Microstripline Wiring
pass solar filter is used to reduce the Laureate Dr. John B. Fenn) is described A document describes the fabrication
solar energy that enters the open end as a variant of electrostatic precipitation of a two-dimensional microcalorimeter
during the lunar day, achieving a that eliminates the current drawbacks of array that uses microstrip wiring and in-
nearly uniform temperature inside the electrostatic precipitation. The new ap- tegrated heat sinking to enable use of
container. Also, the materials and ad- proach replaces corona prone field with high-performance pixel designs at kilo-
hesive techniques that will be used for a mist of highly charged micro-droplets pixel scales (32×32). Each pixel is the
this corner-cube reflector must have generated by electrospray ionization high-resolution design employed in
appropriate thermal and mechanical (ESI) as the mechanism by which incom- small-array test devices, which consist of
characteristics (e.g., silica or beryllium ing particles are attracted and captured. a Mo/Au TES (transition edge sensor)
for the cube and aluminum for the cas- In electrospray, a miniscule flow rate on a silicon nitride membrane and an
ing) to further reduce the impact of (microliters/minute) of liquid (typically electroplated Bi/Au absorber. The pixel
the thermal environment on the instru- water and a small amount of salt to en- pitch within the array is 300 microns,
ment’s performance. hance conductivity) is fed from the tip where absorbers 290 microns on a side
The instrument would consist of a sin- of a needle held at a high voltage poten- are cantilevered over a silicon support
gle, open corner cube protected by a sep- tial relative to an opposite counter elec- grid with 100-micron-wide beams. The
arate solar filter, and mounted in a cylin- trode. At sufficient field strength, a high-density wiring and heat sinking are
drical or spherical case. A major goal in sharp liquid meniscus forms (known as a both carried by the silicon beams to the
the design of a new lunar ranging system so-called “Taylor Cone”), which emits a edge of the array. All pixels are wired out
is a measurement accuracy improvement jet of highly charged droplets that drift to the array edge.
to better than 1 mm by reducing the through the surrounding gas and are ECR (electron cyclotron resonance)
pulse spread due to orientation. While collected on the walls of a conductive oxide underlayer is deposited under-
achieving this goal, it was desired to keep tube. Particles in the gas have a high neath the sensor layer. The sensor (TES)
the intensity of the return beam at least probability of contact with the droplets layer consists of a superconducting un-
as bright as the Apollo 100-corner-cube either by adhering to the droplets or derlayer and a normal metal top layer. If
arrays. These goals are met in this design otherwise acquiring a high level of the sensor is deposited at high tempera-
by increasing the optical aperture of a charge, causing them to be captured on ture, the ECR oxide can be vacuum an-
single corner cube to approximately 170 the collecting electrode as well. The nealed to improve film smoothness and
mm outer diameter. This use of an spray acts as a filtration material that is etch characteristics.
“open” corner cube allows the selection continuously introduced and removed This process is designed to recover
of corner cube materials to be based pri- from the gas flow, and thus can never be- high-resolution, single-pixel x-ray
marily on thermal considerations, with come clogged. microcalorimeter performance within
no requirements on optical trans- Experiments determined that ESIEP arrays of arbitrarily large format. The
parency. Such a corner cube also allows can collect particles with efficiencies as critical current limiting parts of the cir-
for easier pointing requirements, be- high as or higher than traditional co- cuit are designed to have simple inter-
cause there is no dependence on total in- rona-based EP, owing to the higher faces that can be independently verified.
ternal reflection, which can fail off-axis. specificity of charging and higher levels The lead-to-TES interface is entirely de-
NASA Tech Briefs, January 2012 39