Whipple Shield and Dust Flux Instrument
The purpose of the Whipple Shield is to protect the spacecraft from damage
from impacting dust particles. The Dust Flux Monitor Instrument (DFMI) is used
to monitor the dust particle impacts and transmit this information directly
back to Earth.
The Whipple shield is designed to shadow the spacecraft to protect it during
the high speed
encounter with particles in the cometary coma. Bumper shields are composite
panels which disrupt particles as they impact. Nextel blankets of ceramic
cloth further dissipate and spread the particle debris. Three blankets are
used in the main body shield, and two are used in the solar array shields.
The composite Catcher absorbs all of the debris for solid particles up
to 1 cm in diameter for the shield protecting the spacecraft main body.
Dust Flux Monitors
The Dust Flux Monitor Subsystem includes a dedicated, sophisticated
instrument, the DFMI for small particles, and two separate acoustic impact
sensors that monitor
for larger impact events by the relatively rare, but especially dangerous
The Dust Monitoring System has four basic goals:
To monitor the dust environment for spacecraft health and
interpretation of any spacecraft anomalies;
To provide real-time flux measurements for large impacting comet dust
particles for early determination of the potential hazard to the
spacecraft when the spacecraft begins to experience the coma environment;
To measure the spatial and temporal variations of particle flux and mass
distribution during the STARDUST flyby of Comet P/Wild-2. The DFMI
measurements will provide cumulative and differential fluxes over the particle
mass range 1 x 10-11g to 2 x 10-4g (particle diameter
range 2 mm to 518 mm), as
well as cumulative flux for particles with mass >2 x 10-4 g;
To provide the context for the collected dust samples.
Developed under the direction of Tony Tuzzalino at the University of Chicago,
the DFMI is a highly sensitive instrument
designed to detect particles as small as a few microns. It is based on a
very special polarized plastic (PVDF) that generates electrical pulses when
impacted or penetrated by small high speed particles.
The DFMI is derived from the flight heritage obtained from
earlier and current dust instruments and sensors. These
instruments make exclusive use of the polyvinylidene fluoride (PVDF) dust
sensor developed in the laboratory of Professor John Simpson
at the University of Chicago, which include:
- The Dust Counter and Mass Analyzer (DUCMA) instruments successfully flown
on the Vega missions to Comet Halley:
- The ERIS Observer instrument (developed by Lockheed) which utilized PVDF
dust sensors provided by the University of Chicago. Excellent data were
obtained but remain classified;
- The Space Dust (SPADUS) instrument for the Advanced Research and Global
Observation Satellite (ATGOS) to be launched December 1998 (Earth
- The High Rate Detector (HRD) on the Cassini mission to Saturn
(launched October 15, 1997).
The Dust Flux Monitor Instrument (DFMI) consists of a Sensor Unit (SU),
Electronics Box (EB), and the two acoustic sensors mounted to the STARDUST
spacecraft. The SU is mounted to the Whipple shield, and the EB is mounted
internally to the spacecraft enclosure.
The SU consists of two independent PVDF dust particle sensors (sensor 1 and
sensor 2) mounted in a frame. Each sensor will be connected to the EB by a
cable with a length of 1.4 meter. The combined eight mass thresholds of
sensor 1 and sensor 2 provide cumulative and differential particle fluxes over
the particle mass range.
The acoustic sensors are in two different locations.
Each device is a
quartz piezoelectric transducer that converts any vibrations in the
shield it is monitoring into electrical signals that are relayed to the
The first sensor is mounted to the first Whipple shield, the so-called
Bumper shield. The second is mounted to a special acoustic plate, consisting
of a thin, stiff graphite-fiber epoxy sheet sewn to the first Nextel blanket.
It has been shown, by testing in the laboratory of J.A.M. McDonnell
(University of Kent, Canterbury, England) that particles of about 1 mm
and larger will penetrate the bumper shield to produce a signal in this