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 -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 COllector
   ----------------
 
   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 was 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 -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 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 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
   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 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.