cold gas rcs for the nea scout cubesat aiaa space 2017 · flat plate optical model published in...
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Cold Gas RCS for the NEA Scout
CubeSat
AIAA SPACE 2017
1
Brandon Stiltner1 Andrew Heaton2
Chris Becker2 Ben Diedrich1
Juan Orphee2 Ivan Bertaska2
1Jacobs ESSSA Group / NASA MSFC 2NASA MSFC
https://ntrs.nasa.gov/search.jsp?R=20170012287 2020-05-29T10:17:34+00:00Z
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The Near Earth Asteroid Scout will
• Image/characterize a NEA during a slow flyby
• Demonstrate a low cost asteroid
reconnaissance capability
Key Spacecraft & Mission Parameters
• 6U cubesat
• ~86 m2 solar sail propulsion system
• Manifested for launch on the Space Launch
System (EM-1/2019)
• Up to 2.5 year mission duration
Target Reconnaissance with medium field imaging
Shape, spin, and local environment
Close Proximity ImagingLocal scale
morphology, terrain properties, landing site
survey
Near Earth Asteroid (NEA) Scout Overview
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NEA Scout is split into three major parts:
1. Avionics
2. Solar Sail and Deployer
3. RCS
3
116.2
mm
NEA Scout’s Mechanical Configuration
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NEA Scout’s Solar Sail
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Light reflects off of the Solar Sail,
providing a small but continuous amount
of thrust.
‘Fuel’ never runs out.
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NEAS Control System Overview
Star Tracker/
Drive Control
Electronics*
(BCT)
IMU
(Sensonor)
Sun Sensors*
(BCT)
5
4X RWA 15 mNms
(BCT)
Active Mass Translator
Cold gas RCS
Solar Sail
Subassembly
Science
Camera
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The AMT allows NEA Scout’s two halves to move relative to each
other.
The AMT shifts the CM to trim the solar sail torque.
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NEA Scout’s Active Mass Translator (AMT)
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The AMT shifts the CM relative to
the solar sail’s Center of Pressure
(CP).
The solar torque can be trimmed or
reversed (allowing for reaction
wheel desaturation).
NEA Scout’s Active Mass Translator (AMT)
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Occupies about 2U of volume on NEA Scout.
Holds 1.25kg of R236fa (refrigerant) propellant.
Two axial jets (Z-axis) for thrust maneuvers.
Four canted jets for attitude control.
Each Jet produces 0.025 N of thrust.
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NEA Scout’s Reaction Control System
Y
XZ
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RCS Forces and Jet Selection
Projection of CM
onto X-Y plane
RCS Jet Thrust
Jet #4Jet #1
Jet #3 Jet #2
45o
XY
Ax Jet #2 Ax Jet #1
Y
XZ
Body Axis Jet 1 Jet 2 Jet 3 Jet 4 Mx (N-mm) My (N-mm) Mz (N-mm)+X 1 0 0 1 3.534 0.007 -0.008-X 0 1 1 0 -3.159 0.007 0.008+Y 1 1 0 0 0.188 6.792 0.230-Y 0 0 1 1 0.188 -6.778 -0.230+Z 0 1 0 1 0.188 0.007 4.211-Z 1 0 1 0 0.188 0.007 -4.211
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RCS Control Logic – Phase-Plane
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RCS Control Performance - Detumble
Control engaged at t = 20s.
Nulls the rates within 1 minute.
Uses 3 grams of propellant.
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RCS Control Performance – Sun Pointing
After nulling the rates, the RCS’ second requirement is to point
toward the sun for charging.
This is an autonomous maneuver that uses sun-sensors to locate
the sun.
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RCS Control Performance - TCM
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RCS Control Performance – Sail Flex Avoidance
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RCS Control Performance – Mom. Management
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NEA Scout uses a cold gas RCS
system for propulsion.
The RCS has four canted jets for
attitude control and two axial jets
for thrust maneuvers.
The RCS utilizes a simple control
logic known as a phase-plane.
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Conclusions
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BACKUP
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NEA Scout Mechanical Layout (alt. view)
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NEA Scout Solar Sail Technology
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Light reflects off of the Solar Sail
Provides a small but steady amount of thrust
‘Fuel’ never runs out!
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1st Full Scale Solar Sail Ground Deployment
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Simulated NEA Scout Mission CONOPS
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Flight System Configuration – Stowed
116.2mm
366mm
239.4mm
NEAS Inside PSC
6U Dispenser
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Manifested on SLS EM-1; mounted in MSA and
housed within Planetary Systems Corp.
Cannisterized Satellite Dispenser (CSD)
Project interfaces with Secondary Payload Office
(SLS) and Launch Services Program (Dispenser)
Handover to GSDO installed in dispenser and
powered-off
After Orion separation, ICPS performs disposal
maneuver
Post-disposal, secondary payload sequencer
activated
Each payload dispensed at designated times via
signal from sequencer
Separation switches on payload activated upon
deployment, powering on spacecraft
SLS Interface
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Flat Plate optical model published in
Wright and cited by McInnes
Shows tangential and normal components
Tangential component important to torque
P = solar pressure
A = area
𝑟 = total reflectivity
s = fraction of reflection that is specular
𝛼 = sun incidence angle
Bf, Bb = front and back side non-Lambertian
coefficients
ef, eb = front and back side emissivities
Thrust Model: Underlying Physics
24
𝑓𝑛 = 𝑃𝐴 1 + 𝑟𝑠 cos2 𝛼 + 𝐵𝑓 1 − 𝑠 𝑟 cos 𝛼 + 1 − 𝑟𝜀𝑓𝐵𝑓 − 𝜀𝑏𝐵𝑏
𝜀𝑓 + 𝜀𝑏cos 𝛼
𝑓𝑡 = 𝑃𝐴 1 − 𝑟𝑠 cos 𝛼 sin 𝛼 𝑡
F_solarF_normal
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Flight System Overview
Star Tracker/
Drive Control
Electronics*
(BCT)
Iris 2.1 Transponder
and Electronics
NEA Imager
IMU
(Sensonor)
LGAs
6x 18650 Lithium Batteries
(Panasonic)
Sun Sensors*
(BCT)
25
4X RWA 15 mNms
(BCT)
Active Mass Translator
Cold gas RCS
MGAHAWK Solar Array
(MMA)
Solar Sail
Subassembly
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Mission ConOps
26*time not to scale
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Other Reaction-Jet Control System (RCS)
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Corner
displacements
Solar Sail Thrust Model and Analysis Flowchart
Integrated model
• Detailed model of booms
• One-element model of membrane
• Structural analysis with thermal
deformations
Membrane model
• Detailed (~5 cm) model of membrane
• No model of booms
Sail shape mesh
Thermal model
• Radiative and
conductive heat
transfer
Thrust
model
Attitude
control
model
Reduced/simplified
dynamic model
Shape
solution
Dynamic model
• Fixed-bus model
• Stiffness matrix includes the effects
of sail tensioning and thermal loading
• Reduced dynamic model is
integrated with the spacecraft bus for
attitude control studies
Fixed-Bus Sail System Bending Mode
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Summary
• Numerous challenges exist in implementing a Solar Sail mission,
particularly within a CubeSat form factor
• Extensive design, analysis, and testing has been performed to-date to
address these challenges
• Difficulty in validating analytical models and performing ground (1G)
demonstrations given gossamer nature of Solar Sails
• NEA Scout flight on SLS EM-1 flight opportunity (2018) will provide a
giant leap forward in clarifying our understanding of Solar Sail modeling
and performance
Project Status
• On track for August Design Review with significant flight procurements
to follow
• Flight System integration starts June 2017
• Manifested on SLS EM-1 for 2018 deep space flight opportunity
• NEA flyby anticipated in 2021
Summary & Project Status
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Solar Sail Subsystem Overview
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Single Sail Spool
Spacecraft Wire Channel
Boom Deployers
TRAC Booms
Deployment Motor
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Solar Sail Subsystem Overview
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Solar Sail Booms (@NeXolve)
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Disturbance Torques: Active Mass Translator (AMT)
3333
Trimmed StateNominal State
AMT
CP
CM
Thrust
Disturbance
Torque
KEY
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Transient Solar Sail Deployment – Shape Phases
Single sail membrane drives initial ‘bow tie’ effect: Booms are do not maintain 90deg relative
orientation (less predictable induced disturbance force) and direct sunlight on booms drive
significant thermal deflections
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NEA Scout Science
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JPL IntelliCam
(Updated OCO-3
Context Camera)
Target Detection and Approach:
50K km, Light source observation
SKGs: Ephemeris determination and
composition assessment (color)
Close Proximity Science
High-resolution imaging,
10 /px GSD over >30% surface
SKGs: Local morphology
Regolith properties
NEA Reconnaissance
<100 km distance at encounter
50 cm/px resolution over 80% surface
SKGs: volume, global shape, spin
properties, local environment
Reference
stars
Target