Earth Return Sequence of
Events
Sample Earth Return
Phase Design
This phase of the STARDUST mission begins two weeks
before Earth re-entry and ends when the SRC is transferred
to its ground-handling team. The planned landing
site is the Utah Test and Training Range (UTTR).
Following touchdown, the SRC will be recovered by
helicopter or ground vehicles and transported to
a staging area at UTTR for retrieval of the sample
canister. The canister will then be transported
to a dedicated Stardust handling and curation laboratory
at Johnson Space Center. The Earth Return is divided
into four subphases:
- Earth Approach
- Entry
- Terminal Descent
- Recovery
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Earth Return Timeline
Time Event Description
E - 67 days Navigation cutoff for TCM at E-60d
E - 60 days TCM to remove accumulated flight errors
E - 37 days Navigation cutoff for TCM at E-30d
E - 30 days TCM to cleanup residual flight errors and set
up direction bias for next TCM
E - 19 days On Low Gain Antenna at similiar Sun-relative
attitude as required for SRC Release
E - 13 days Navigation cutoff for TCM at E-10d
E - 10 days TCM to perforum preliminary entry
E - 44 hours Navigation cutoff for TCM at E-1.5d
E - 36 hours TCM to perform final entry targeting
E - 7.5 hours Go/No-go Decision for SRC release
E - 4 hours SRC spin release (spin rate of 14 to 20 rpm)
E - 3.7 hours Spacecraft divert maneuver
(to prevent spacecraft entry)
Earth Approach
Earth Approach Subphase
Beginning with Earth Approach, the period of near-continuous DSN
tracking commences. During this
period two TCMs are involved nominally: at ER (Earth reentry)
-10 d, ER-36 hr. The SRC will be released at ER-4 hr
after the last TCM and will enter the atmosphere
at a nominal entry angle of -8.2°. The approach
velocity to Earth will be approximately 6.4 km/s
with a right ascension of 205.7°, a declination
of 11.1°, and velocity at entry (assumed to
be at an altitude of 125 km) of 12.8 km/s. The
entry corridor control accuracy attainable,
based on the Navigation Plan, is 0.08°.
The spacecraft will perform a divert maneuver
subsequent to the SRC release to avoid entering
the atmosphere.
Entry
Entry Subphase
Entry begins when the spacecraft reorients for
SRC release from the spacecraft bus and ends with
parachute deployment. The SRC will be released
from the spacecraft bus approximately 4 hours
before entry. Significant activities include verifying
spacecraft attitude, depassivating the batteries, initiating the SRC on-board
timer/sequencer, turning off spacecraft-bus-provided
heater power to the SRC, cutting the connecting cable and releasing the SRC.
The SRC will perform a direct entry at Earth.
After entry the SRC will continue to free-fall
until approximately 3 km, at which point the parachute
deployment sequence will initiate. Elapsed time
from entry to parachute deploy will be approximately
10 minutes.
Terminal Descent - SRC
with Parachute
Terminal Descent Subphase
Descent begins when the parachute deployment sequence
initiates and continues until the SRC/parachute
system has descended into the recovery zone, the
UTTR.
The velocity of the SRC must be reduced from the
initial entry velocity of 12.8 km/s to a level
that permits soft landing.
The aeroshell removes over 99% of the initial
kinetic energy of the vehicle to protect the sample
canister against the resultant extreme aerodynamic
heating. The heatshield is a 60° half-angle
blunt cone made of a graphite/epoxy composite
covered with a thermal protection system. Ablative
material on the backshell protects the lander
from the effects of recirculation flow around
the entry vehicle.
Taking into account SRC release and entry corridor
uncertainties, vehicle aerodynamics uncertainties
and atmospheric dispersions, the landing footprint
ellipse for the SRC has been determined to be
approximately 30 km by 84 km. The SRC will approach
the UTTR on a heading of approximately 122°
on a north-west to south-east trajectory. Local
time of landing will be approximately 3:00 am.
Landing Site
Ground Recovery
Recovery Subphase
Recovery begins a few hours before the SRC touches
down. Retrieval is via ground transportation or
helicopter. Given the small size and mass of the
SRC, it is not expected that its recovery and
transportation will require extraordinary handling
measures or hardware other than a specialized
handling fixture to cradle the capsule during
transport. A gas sample from the canister will
be taken for volatile monitoring. Transportation
of the SRC to a staging area at the UTTR for packing.
The sample return capsule then will be transported
to its final destination, the planetary material
curatorial facility at Johnson Space Center.
Appendix
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Acronyms
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