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 †Tyvak Nano-Satellite Systems, Irvine, California

Mass 360 kg Power Batteries Fuel Hydrazine

Rendezvous Demonstrator

DART Orbital Express

Mass 952 kg Power 1.2 kW Fuel Hydrazine

Large Mass – Mission Application

Dragon COTS Cygnus COTS

Mass >2000 kg Power 3.5 kW Fuel Hydrazine

Mass >4200 kg Power 5 kW Fuel NTO/MMH

CPOD is Evolving Proximity Operations and Docking to a Low Mass/Low Power CubeSat Platform

2 x 3U CubeSats

Mass 5-6 kg Power <50 W Fuel R134a

Navigation Sensors NFOV Camera

Docking Camera IR Cameras ISL Ranging

GPS

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 three-finger 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.

Abstract CPOD Mission Overview

CPOD Spacecraft

ISL Ranging

∆GPS via ISL

ISL Ranging

NFOV Bearings

400m 200m

Vbar

Rbar

2 km

100m

NFOV Ranging

200m

-200m

Initiate Safety Ellipse 200x400x200m

5.1

4

Inject into Walking Safety Ellipse 200x400x200m

5.2

Stabilize into Safety Ellipse about CubeSatB 200x400x200m

5.3 A

B

Reduce Size Safety Ellipses & NFOV checkout 100x200x100m 50x100x50m

6

REN

DEZ

VO

US

DO

CK

ING

NFOV Bearings & Ranging

50m

Vbar

Rbar

B A

25m 5m 10m 15m

Docking Ranging

IR1 B & R

IR2 B & R

7.1

6.3

Reduced Size NMC & IR1 checkout 10x20m

Transfer to V-bar @ 20m

Approach to 10m & IR1 checkout

Reduce Size Safety Ellipse & Docking Sensor checkout 25x50x25m

20m

7.3 7.5

Docking Bearings

7.2

Approach & Dock

7.6

7.4

Approach to 5m & IR2 checkout

Drift ~2km during checkout ( assumes mirrored Attitude )

Transfer to In-Plane NMC 25x50m

Concept of Operations

Fuel-Optimal n-Impulse Maneuver Targeting • 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

Guidance Solution

Nominal trajectory – 4-burn sequence

Radial offset provides safety in case of abort

Battery Module

GPS Receiver

Inertial Reference

Module (IRM)

S-Band Transmitter

Cold Gas

Thrusters (8)

RPOD

Module

UHF Radio

Propulsion

Module

Endeavour Bus

Battery Module

Docking Mechanism

UHF

Antennas

Separation

Devices

S-Band

Patch

GPS

Patch

Thermal

Radiators

Solar Panel Arrays

with MPPTs

Thermal

Radiator

Star

Trackers

Initial Misalignment

Locked Together

Self Aligning

Docking Mechanism – Chaser

Docking Mechanism – RSO

Downrange Distance (m)

+V-Bar

-0.5 -0.4 +R-Bar

Re

lati

ve A

ltit

ud

e (

m)

Chaser

-0.3 -0.2 -0.1

+ -

Electro-magnets activate to bring vehicles together

RSO

Chaser moves to 0.5m of RSO

How can small autonomous spacecraft contribute as components of future space robotic servicing architectures?

Inspection Anomaly Assessment

Resiliency Logistics and Upgrade

Maneuverability for diverse viewing angles, distances, and fields of view using a wide variety of sensor modalities …

Multiple diverse sensor modalities for additional characterization of space weather, vehicle status, or …

Segmented and distributed spacecraft architectures offer additional opportunities …

Redundant capabilities available through on-orbit spares or via replenishment on-demand enhance system availability …

Replenishment of degraded functionality or upgrade to new capabilities; potential to raise TRL of experimental capabilities …

How can small autonomous spacecraft contribute to your mission?

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 along-track burns at various locations (bottom figure)

fuel cost: 0.225 m/s

fuel cost: 0.14 m/s