The sample return capsule is a blunt-nosed cone with
a diameter of 152 centimeters (60 inches). It has five
major components: a heat shield, backshell, sample return
canister, parachute system and avionics.
The total mass of the capsule, including the parachute
system, is 205 kilograms (420 pounds).
A hinged clamshell mechanism opens and closes the capsule.
The science canister housing the solar wind collector
arrays and ion concentrator fits inside, with a central
rotating mechanism to extend the collector arrays. The
capsule is encased in a carbon impregnated material
known as carbon-carbon and an ablative material called
SLA- 561 to protect the samples stowed in its interior
from the heat of reentry. A parachute activated by a
mortar unit is carried inside the capsule and will be
used to slow its descent.
The heat shield is made of a graphite-epoxy composite
covered with a thermal protection system. The outermost
thermal protection layer is made of carbon-carbon. The
capsule heat shield remains attached to the capsule
throughout descent and serves as a protective cover
for the sample canister at touchdown. The heat shield
is designed to remove more than 99 percent of the initial
kinetic energy of the sample return capsule.
The backshell structure is also made of a graphite-epoxy
composite covered with a thermal protection system: a
cork-based material called SLA-561V that was developed
by Lockheed Martin for use on the Viking missions to Mars,
and have been used on several missions including Genesis,
Pathfinder, Stardust and the Mars Exploration Rover missions.
The backshell provides the attachment points for the parachute
system, and protects the capsule from the effects of recirculation
flow of heat around the capsule.
The science canister is an aluminum enclosure containing
the specialized collector arrays and ion concentrator.
On the inside of the lid of the science canister is
a bulk solar wind collector array. The specialized collector
arrays are rotated out from inside the science canister.
Underneath the stowed collector arrays, the ion concentrator
forms the bottom of the science canister. The canister
is inside the sample return capsule, which is mounted
to an equipment deck suspended between the backshell
and heat shield on a set of support struts.
The parachute system consists of a mortar-deployed
2.1-meter (6.8-foot) drogue chute to provide stability
at supersonic speeds, and a main chute 10.5 by 3.1 meters
(about 34.6 by 12.1 feet).
Inside the canister a gas cartridge will pressurize
a mortar tube and expel the drogue chute. The drogue
chute will be deployed at an altitude of approximately
33 kilometers (108,000 feet) to provide stability to
the capsule until the main chute is released. A gravity-switch
sensor and timer will initiate release of the drogue
chute. Based on information from timer and backup pressure
transducers, a small pyrotechnic device will cut the
drogue chute from the capsule at about 6.7 kilometers
altitude (22,000 feet). As the drogue chute moves away,
it will extract the main chute. At the time of capture,
the capsule will be traveling forward at approximately
12 meters per second (30 miles per hour) and descending
at approximately 4 meters per second (9 miles per hour).