CubeSat Proximity Operations Demonstration (CPOD):
Enabling Technologies for Future Space Robotic Servicing Missions
Robert T. MacMillan,* Jason J. Westphal,* Christopher W. T. Roscoe,* Marco Villa,†
*Applied Defense Solutions, Columbia, Maryland
Mission Overview
Abstract
Rendezvous Demonstrator
Cygnus COTS
Dragon COTS
DART
Orbital Express
Mass >2000 kg
Power 3.5 kW
Fuel Hydrazine
Mass >4200 kg
Power 5 kW
Fuel NTO/MMH
Mass 360 kg
Power Batteries
Fuel Hydrazine
Mass 952 kg
Power 1.2 kW
Fuel Hydrazine
CPOD is Evolving Proximity Operations and Docking
to a Low Mass/Low Power CubeSat Platform
Navigation Sensors
NFOV Camera
Docking Camera
IR Cameras
ISL Ranging
GPS
Mass 5-6 kg
Power <50 W
Fuel R134a
2 x 3U
CubeSats
CPOD Spacecraft
Challenges
Processor Limitations
Distributed Architecture
Sensor and Range Agnostic
The CubeSat Proximity Operations Demonstration (CPOD) mission, currently
scheduled for launch in late 2015 or early 2016, will demonstrate rendezvous,
proximity operations, and docking with a pair of identical 3U CubeSats. This program
uses innovative hardware and software solutions to address several of the unique
challenges associated with using small, low-cost, low-power components to
accomplish complex mission objectives, previously demonstrated only by much larger
and more sophisticated spacecraft. This poster presents an overview of the CPOD
mission and spacecraft, key aspects of the software design and architecture, and
novel hardware and software design features, including an electromagnetic threefinger universal docking mechanism, a miniature cold-gas propulsion system, and
onboard autonomous GNC algorithms utilizing passive optical sensors, range capable
inter-satellite link radios, and limited computing resources. We postulate how small
autonomous spacecraft like CPOD will enable future space robotic servicing missions
at low cost with acceptable risk.
How can small autonomous spacecraft contribute as
components of future space robotic servicing architectures?
Solar Panel Arrays
with MPPTs
Thermal
Radiators
GPS
Patch
Inspection
Docking Mechanism
Maneuverability for diverse viewing
angles, distances, and fields of view using
a wide variety of sensor modalities …
S-Band
Patch
Thermal
Radiator
Separation
Devices
Star
Trackers
UHF
Antennas
GPS Receiver
Cold Gas
Thrusters (8)
Battery Module
Redundant capabilities available through
on-orbit spares or via replenishment ondemand enhance system availability …
Multiple diverse sensor modalities for
additional characterization of space
weather, vehicle status, or …
Logistics and Upgrade
How can small autonomous spacecraft contribute to your mission?
Inertial Reference
Module (IRM)
Battery Module
Guidance Solution
RPOD
Module
• Valid for circular, eccentric orbits, including J2
• Impulse times determined by primer vector history
• Optimization uses iterative solution, low computational
burden
• Solves n-impulse optimization but avoids implementing
nonlinear numerical solver
• Fuel cost is much lower than traditional 2- or 3-impulse
analytical methods
Endeavour Bus
Docking Mechanism –
Chaser
Docking Mechanism –
RSO
Chaser moves to 0.5m of RSO
+V-Bar
+
-
Relative Altitude (m)
RSO
Initial Misalignment
Chaser
Electro-magnets activate to bring vehicles together
+R-Bar
-0.1
-0.2
-0.3
-0.4
-0.5
Downrange Distance (m)
Locked Together
Self Aligning
200m
Rbar
Inject into Walking
Safety Ellipse
200x400x200m
400m
200m
100m
5.2
6
Reduce Size
Safety Ellipses &
NFOV checkout
100x200x100m
50x100x50m
B
Vbar
A
5.3
Stabilize into
Safety Ellipse
about CubeSatB
200x400x200m
-200m
4
NFOV Bearings & Ranging
Drift ~2km during checkout
( assumes mirrored Attitude )
ISL Ranging
Docking Bearings
Docking Ranging
IR1 B & R
IR2 B & R
Rbar
6.3 Reduce Size
Transfer to
V-bar @ 20m
Approach to 5m
7.5 & IR2 checkout
10m
7.3
15m
20m
7.2
Reduced Size NMC & IR1
checkout 10x20m
7.4
7.6
Approach & Dock
Approach to 10m
& IR1 checkout
Nominal trajectory – 4-burn sequence
Radial offset provides safety in case of abort
fuel cost: 0.14 m/s
50m
A
Vbar
fuel cost: 0.225 m/s
Safety Ellipse &
Docking Sensor
checkout
25x50x25m
25m
B
Example: Formation Reconfiguration
• Initial configuration: 400 x 200m Natural Motion
Circumnavigation
• Final configuration: 800 x 400m Natural Motion
Circumnavigation
• Analytical solution uses two radial burns at v-bar
crossings (top figure)
• Optimal solution results in three predominantly alongtrack burns at various locations (bottom figure)
Initiate Safety
5.1
Ellipse
200x400x200m
5m
Fuel-Optimal n-Impulse Maneuver Targeting
Propulsion
Module
NFOV Ranging
2 km
Replenishment of degraded functionality
or upgrade to new capabilities; potential
to raise TRL of experimental capabilities …
S-Band Transmitter
UHF Radio
∆GPS via ISL
ISL Ranging
NFOV Bearings
Anomaly Assessment
Segmented and distributed spacecraft architectures offer additional opportunities …
Resiliency
Concept of Operations
RENDEZVOUS
Large Mass – Mission Application
DOCKING
CPOD
†Tyvak Nano-Satellite Systems, Irvine, California
7.1
Transfer to In-Plane NMC
25x50m