IEEE Geoscience and Remote Sensing Magazine - June 2013 - 66

systems teams to evaluate the science coverage of the
constellation as well as the dispersion of Observatories
through various mission phases. The mission operations
team will pick up the scenarios developed and maintain
and use these scenarios to support the mission operations Flight Dynamics tasks.
CYGNSS Flight Dynamics tasks are straight forward
and include assessing satellite locations in support of
ground station scheduling and working with the systems team to assess, plan, and execute drag maneuvers
as required to maintain constellation coverage and
positioning. STK is an industry recognized tool with a
mature tool set fully capable of supporting satellite constellation analysis.
8. deploYMent Module

minimized by averaging 4 push springs (Fig. 11) to reduce
microsat cg location criticality and minimize the effects
of spring tolerances. Screening the springs during DM
assembly further reduces tip off errors. Each Observatory
is secured to the DM by torquing the Qwknut actuator
into the microsat nadir baseplate, compressing the separation springs to achieve desired spring load for Observatory ejection. Tapered alignment pins, combined with
the Qwknut actuator, rigidly constrain each Observatory
to the DM for launch. Preliminary FEM quasi-static load
analysis of the fully integrated FS indicates that launch
loads have a 2.17 safety factor against ultimate loads.
The FEA also indicates the first natural frequency of the
structure is a radial mode (Lobar) at 47.6 Hz in the launch
configuration, avoiding harmonic coupling with the LV
during launch.

8.2. dePloyMenT Module aVionics
The DM uses a heritage electronic sequencer to release
the Observatories in a pre-determined sequence stored
within the sequencer memory. The sequence is initiated
via a standard LV discrete signal when the LV arrives
at the required orbit. The sequencer then performs the
deployment sequence by actuating the Qwknut actuators. Sequence timing incorporates constellation separation requirements and deployment actuation tolerances.
Hardware safety is ensured through the use of a 2-stage
command, single-fault tolerant actuator driver design
that includes a pre-flight Safe/Arm connector to fully disarm the system.
A 28 Vdc DC 140 W-hr Li-Ion battery is used to power
the DM avionics and activates the deployment Qwknut actuators. The battery is fully charged at launch with
<5% of capacity required to complete the orbit insertion
and deployment sequence.
In support of pre-launch operations, the DM avionics route Observatory battery trickle charge power
from the GSE to the Observatory via
separation connectors, with battery
temperature signals acquired by the
DM avionics and routed to the GSE
for monitoring. Pre-launch Observatory command and telemetry handling is also provided by the DM
avionics. The GSE command data
stream is routed to each Observatory command hardline interface
with only buffering provided by the
DM. Specific command targeting is
a function of S/C ID; the Observatory ignores the command if the S/C
ID is not applicable. The DM enables
Observatory pre-launch health and
status monitoring by multiplexing
fIGure 11. 2-tier deployment module provides balanced separation forces by using a
the Observatory hardline telemetry.
matched spring deployment mechanism.

8.1. dePloyMenT Module sTrucTure
The deployment module (DM) serves as the constellation carrier during launch and then deploys the
Observatories into their proper orbital configuration
once on orbit.
The DM consists of 2 AL cylindrical sections or tiers,
each with 4 mounting/separation assemblies (Fig. 10).
The tier design approach simplifies Observatory-DM
integration by enabling easy access of GSE while minimizing potential for damage inherent in a single core
structure. The mounting/separation assemblies are positioned 90° apart to release the Observatories in pairs
opposite each other, balancing deployment forces and
keeping disturbance torques well within LV capabilities.
Tier 2 is clocked 45° from Tier 1 to provide proper orbital
dispersal vectoring.
Deployment is initiated using flight-proven, high-reliability Qwknuts. Observatory separation tip-off errors are

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Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - June 2013