NASA Technical Reports Server (NTRS) 20100001345: Cryogenic Flow Sensor

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Technology Focus: Sensors

# Cryogenic Flow Sensor

Marshall Space Flight Center, Alabama

An acousto-optic cryogenic flow sen-
sor (CFS) determines mass flow of
cryogens for spacecraft propellant
management. The CFS operates unob-
trusively in a high-pressure, high-flow-
rate cryogenic environment to provide
measurements for fluid quality as well
as mass flow rate. Experimental hard-
ware uses an optical “plane-of-light”
(POL) to detect the onset of two-phase
flow, and the presence of particles in
the flow of water.

Acousto-optic devices are used in
laser equipment for electronic control
of the intensity and position of the laser
beam. Acousto-optic interaction occurs
in all optical media when an acoustic

wave and a laser beam are present.
When an acoustic wave is launched into
the optical medium, it generates a re-
fractive index wave that behaves like a si-
nusoidal grating. An incident laser
beam passing through this grating will
diffract the laser beam into several or-
ders. Its angular position is linearly pro-
portional to the acoustic frequency, so
that the higher the frequency, the larger
the diffracted angle.

If the acoustic wave is traveling in a
moving fluid, the fluid velocity will af-
fect the frequency of the traveling wave,
relative to a stationary sensor. This fre-
quency shift changes the angle of dif-
fraction, hence, fluid velocity can be de-

termined from the diffraction angle.
The CFS acoustic Bragg grating data
test indicates that it is capable of accu-
rately determining flow from 0 to 10
meters per second. The same sensor
can be used in flow velocities exceeding
100 m/s. The POL module has success-
fully determined the onset of two-phase
flow, and can distinguish vapor bubbles
from debris.

This work was done by John Justak of Ad-
vanced Technologies Group, Inc. for Marshall
Space Flight Center. For more
information, contact Sammy Nabors, MSFC
Commercialization Assistance Lead, at
sammy.a.nabors@nasa.gov. Refer to MFS-
32730 - 1 .

# Multi-Sensor Mud Detection

This technology is also applicable to terrain hazard assessment in terrestrial or planetary
situations.

NASA’s Jet Propulsion Laboratory, Pasadena, California

Robust mud detection is a critical per-
ception requirement for Unmanned
Ground Vehicle (UGV) autonomous off-
road navigation. A military UGV stuck in a

A General Dynamics Robotic Systems (GDRS) ex-
perimental unmanned vehicle (XUV) navigates
through a muddy grass field during a data col-
lection for the Daytime Mud Detection System.

mud body during a mission may have to be
sacrificed or rescued, both of which are un-
attractive options. There are several char-
acteristics of mud that may be detectable
with appropriate UGV-mounted sensors.
For example, mud only occurs on the
ground surface, is cooler than surround-
ing dry soil during the daytime under
nominal weather conditions, is generally
darker than surrounding dry soil in visible
imagery, and is highly polarized. However,
none of these cues are definitive on their
own. Dry soil also occurs on the ground
surface, shadows, snow, ice, and water can
also be cooler than surrounding dry soil,
shadows are also darker than surrounding
dry soil in visible imagery, and cars, water,
and some vegetation are also highly polar-
ized. Shadows, snow, ice, water, cars, and
vegetation can all be disambiguated from
mud by using a suite of sensors that span
multiple bands in the electromagnetic
spectrum. Because there are military oper-
ations when it is imperative for UGV’s to
operate without emitting strong, de-

tectable electromagnetic signals, passive
sensors are desirable.

JPL has developed a daytime mud de-
tection capability using multiple passive
imaging sensors. Cues for mud from
multiple passive imaging sensors are
fused into a single mud detection image
using a rule base, and the resultant mud
detection is localized in a terrain map
using range data generated from a stereo
pair of color cameras. Thus far at the
time of this reporting, JPL has:

1. Performed daytime data collections,
on wet and dry soil, with several candi-
date passive imaging sensors, including
multi-spectral (blue, green, red, and
near-infrared bands), short-wave in-
frared, mid-wave infrared, long-wave
infrared, polarization, and a stereo
pair of color cameras.

2. Characterized the advantages and dis-
advantages of each passive imaging
sensor to provide cues for mud.

3. Implemented a first-generation mud
detector that uses a stereo pair of color

NASA Tech Briefs, January 2010

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