PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "T. Farnham 2006-07-07"
RECORD_TYPE = STREAM
OBJECT = INSTRUMENT
INSTRUMENT_HOST_ID = "SDU"
INSTRUMENT_ID = "SRC"
OBJECT = INSTRUMENT_INFORMATION
INSTRUMENT_NAME = "SAMPLE RETURN CAPSULE"
INSTRUMENT_TYPE = "DUST SAMPLE COLLECTOR"
INSTRUMENT_DESC = "
The descriptions in this file were written by Tony Farnham using
information from the ``Stardust Mission Plan document'' (used by
permission from the Stardust project).
Instrument description
-----------------------
The Sample Return Capsule (SRC) was a system for non-destructively
collecting cometary and interstellar dust particles, then storing the
samples and returning them to the Earth for detailed analysis.
The Sample Return Capsule was about a meter in diameter, and opened
like a clamshell, allowing the collecting grid to be deployed into the
dust stream to collect samples. The SRC was mounted along the negative -x--axis
of the Stardust spacecraft. It consisted of four main components: the
sample collector, the aeroshell (backshell and heat shield), the
parachute system, and the avionics.
Sample CollectorCOllector
----------------
The sample collector was a passive system for collecting dust
grains. It consisted of an aluminum grid encasing multiple
microporous silica aerogel blocks that acted as the dust
collectors. The grid array was exposed to a stream of dust
particles, which were gradually slowed by the low-density aerogel.
The aerogel dissipated the kinetic energy of the particles so they
were not destroyed during the collection process. Graded density
media werewas used to give even lower density for the initial impact.
The aerogel collector grid allowed collection from both sides. One
side of the collector (facing the +x direction) was used to collect
samples during the comet encounter and the opposite side was used
for interstellar dust collection. Each side of the collector
contained a total of 1000 cm^2 of useful collecting area.
After the samples were obtained, the collector grid could fold up
into a compact configuration in the sample return capsule. Stowage
of the collector was achieved by first folding the collector grid
onto the boom via the wrist joint and then folding the boom/collector
into the SRC canister via the shoulder joint.
In addition to allowing the collector grid to fold up into the SRC,
where it was protected, this deployment mechanism was the key for
maximizing the amount of time available for the capture of
interstellar dust particles. The mechanism allowed the collector to
be steered via the wrist joint about the spacecraft y-axis toward
the negative -z--axis. The collector field-of-view remained unobstructed by
the SRC backshield for 51 degrees of this motion, half the grid was
in shadow at 63 degrees, and all of the grid was in shadow at 75
degrees. (Note that for the shadow definition, the interstellar particle (ISP) stream is
assumed to be incoming perpendicular to the aerogel grid.) It is
worth noting that the collector field-of-view would remain
completely unobstructed for 65 degrees of the motion should the
shoulder joint be used during interstellar dust particle
collection. However, usage of the shoulder joint with the
collector fully deployed was considered to be an unnecessary risk.
Aeroshell
---------
The aeroshell was used to protect the SRC during the cruise phases
and during re-entry into the Earth's atmosphere. During re-entry,
the aeroshell removed dissipated over 99 percent of the initial kinetic energy
of the vehicle and protected the sample canister against the extreme
aerodynamic heating of atmospheric entry. The heat shield was a 60
degree half angle blunt cone made of a graphite/epoxy composite
covered with a thermal protection system. Ablative material was
also applied to the backshell to protect the capsule from the
effects of recirculation flow.
Parachute System
----------------
During the entry and descent phases, a G-switch initiated timer with
What is a G-switch? A "gravity" switch?
backup pressure sensors provided the required parachute deployment
timing. The parachute system incorporated a drogue and main chute
into a single parachute canister. The parachute canister contained a
mortar tube that held the drogue chute. A gas cartridge was housed
outside the canister and was used to pressurize the mortar tube and
expel the drogue chute. The drogue chute was used to stabilize the
descending SRC through the transonic and subsonic atmospheric
regimes. The drogue was discarded using one of two redundant cutters,
extracting the main chute as it moves away from the SRC. Upon ground
impact, a cutter in the riser of the main chute was commanded by a
G-switch, separating the main chute from the SRC to prevent surface
winds from dragging the SRC across the ground.
Avionics
--------
The avionics design included a UHF locator beacon used as an SRC
location aid for the ground recovery team. The beacon was activated
upon main chute deployment. It was powered by a set of primary cell
lithium sulfur dioxide batteries, which had enough capacity to
operate the beacon for 40 hours. Additional SRC tracking was provided
by skin tracking from two C-band radar sites at the Utah Test and
Training Range (UTTR) landing site. A mylar target mounted on the main
chute provides an equivalent one square meter of radar cross section.
Earth Return Sequence
---------------------
On January 15, 2006, the Sample Return Capsule returned to the Earth.
Prior to separation, the spacecraft was placed at the separation
attitude and the SRC was spun up using a spin release mechanism. This
provided the spin stabilization that the SRC required for successful
atmospheric entry. After the SRC separated, the spacecraft executed a
divert maneuver, to put it into a heliocentric orbit.
The SRC entered the atmosphere at 09:57 UTC on January 15, 2006. The
SRC continued to free-fall to an altitude of about 3 km, at which
point the parachute deployed, allowing the SRC to safely land safely at the
Utah Test and Training Range. It was recovered and transported to a
staging area at UTTR for retrieval of the sample canister, which was
then be transported to the planetary materials curatorial facility at
Johnson Space Center.
"
END_OBJECT = INSTRUMENT_INFORMATION
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REFERENCE_KEY_ID = "N/A"
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END_OBJECT = INSTRUMENT
END