Astrodynamics Technologies

OPAG workshopFeb 21,2018

Ryan P. RussellThe University of Texas at Austin

ryan.russell@utexas.edu

OPAG workshopFeb 23,2018

Agenda• Introductions• Astrodynamics for Outer Planets

- Overview- Specifics to OPAG- Enabling successful past/current missions- Enabling/improving future missions- Recommendations: (consider treating Astrodynamics as

a “push technology” rather than “pull”)

Who is the Astrodynamics Community?

• I am attempting to represent a large community of researchers and practitioners

• NASA centers, FFRDCs, Universities, international space agencies

• Professional Societies- American Astronautically Society (AAS)

• Astrodynamics Specialist Meeting• Spaceflight Mechanics Meeting

- American Institute of Aeronautics and Astronautics (AIAA)• Astrodynamics Technical Committee (chair elect)• GNC Technical Communities

- International Symposium on Space Flight Dynamics (ISSFD)

Astrodynamics Defined…

• The study and application of the dynamics of spacecraft and celestial bodies

• Synonyms: celestial mechanics, orbit mechanics, and spaceflight mechanics

• Astrodynamics is an applied, cross-cutting discipline that includes - mathematics - optimization theory - estimation theory - statistics and probability - environment modeling- numerical/data analysis- computational engineering

Domains of Astrodynamics• Earth focused

- Military (assets, technologies to support DoD, GPS, space catalogue, space situational awareness)

- Commercial (design, launch, track commercial satellites, GEO/LEO)

- Science/Exploration (ISS, Earth remote sensing, weather etc.)

• Beyond Earth (~Science/Exploration)- Moon, cis-lunar- Inner planets- Small bodies (comets/asteroids)- Outer planets

(and planetary moon systems)

Outer Planets Astrodynamics

• Mission Destinations…- Gas Giant systems

• Jupiter• Saturn• Uranus• Neptune

- Kuiper belt bodies- Icy moons

• Titan/Enceladus• Europa/Ganymede/Callisto

Roles of Astrodynamics• Mission design

- Concept feasibility/early mission development- Proposal reference trajectory- Extended missions designs- Trajectory optimization/Path planning

• Flight operations/Technologies- Modeling/simulation- Tracking/Orbit determination- Automated maneuver planning - GNC (Guidance, Navigation, Control)

• Estimation theory• Autonomy/Robotics (e.g. OpNav, precision landing)

• Science recovery- Orbit determination (plus sought after parameters)- Remote sensing/Data analysis/Signal processing

Outer Planet Astrodynamics

• “It’s a solved problem” - doesn’t apply here…

• Outer planet missions are among the hardest missions to design

• Extraordinarily large design space• Difficult constraints

- Radiation- Lighting- Timing/Long seasons

• Strong non-Keplerian dynamics- third body- non-spherical gravity- Tether applications

• Outer planet missions stand to benefit the most from improved Astrodynamics methods/software

Success Stories• Voyager grand tour, Galileo tour, Cassini

- Mid-mission, development of new tour design tool (MTOUR), enabled extended missions, grand finale

• Celestial Mechanics & Dynamical Systems->Third body dynamics missions: Genesis, Spitzer, ICE, Lunar missions

• Dawn: low-thrust optimization software Mystic enabled its success (and lifeline preventing it from being canceled). Hayabusa another example

• Cassini• Europa Clipper/Europa Lander/Juice• Jupiter System Grand Tour (weak capture at all 4 Icy

moons for no ∆v)• MOSTLY EXECUTED AS “PULL TECHNOLOGY”

Outer Planet Astrodynamics

OBJECTIVE:

Mission Science Return

Mission Co

st ($

)

Conventionalmethods

State of the artmethods To be 

discovered methods? 

Maximize Science →Minimize Cost ↓

Flagship Class…

New Frontiers…

Discovery…

Exploring the Design Space

• Each dot is a point design• Single dots can be massive effort (say team of

engineers, working for weeks)• Need new automated methods to search full space

Metric 1

Metric

 2

Notional Design Spacewith 3 Performance Indices

radiation

want to minimize both objectives

Typical Mission Study/Proposal

• Rushed timeline, limited budget• Most elements of spacecraft system

require/hinge on a credible reference trajectory

• Basic mission design (necessarily) fixed at an early stage

• Common Result:- Best feasible point design is

chosen/fixed- design space not fully explored- Point of no return reached…

• With competition for discovery/new frontier proposals, the stakes are high

Reference trajectory

Science requirements

Spacecraft Systems Design

Iterative Design Cycle

Astrodynamics Tools

Astrodynamics Focus Areas (next decade)

• Multibody dynamics research- Orbit stability - Highly non-spherical gravity fields - Ballistic Capture- Planetary moon tours / Resonance hopping

• Numerical methods- Analytical solutions/Fast proxy models- High performance computing- Monte Carlos, high fidelity sims, long-term orbit prediction, body ephemerides- Planetary protection simulations,

• Optimization Theory- Global optimization- Combinatorial optimization- Low thrust optimization - Optimization of tethered/sail/non-propellant propulsion

• Small Satellite missions (i.e. low budget, low res sensors etc)• GNC technologies

- Aero braking/ EDL technologies (e.g. Titan) - Precision terrain relative navigation (e.g. Europa, Enceladus)- Autonomy/ AutoNav/ Optical navigation- Advanced Estimation Techniques- Autonomous approach, orbit insertion, and tour execution

vetted to zeroth order by many in the community

Suggestion forward• Maximize the impact of mission studies by investing in precursor

astrodynamics research programs (“Give it a Shot!”…)• Tap into the large community of Astrodynamicists

- NASA, FFRDCs, non-profits, universities, international • Open up competitive opportunities for solution methods (before mission

studies, lower TRL)• Solicit “push technologies” rather than “pull”• Help remove the stovepipes

- More opportunities for collaborations- Centers of Excellence, MURIs, etc.- Encourage cross-center collaborations

• Similar model to Science (competitions, annual mechanisms to propose new ideas etc)

• Advocate for astrodynamics language (specific to mission destinations) in steering documents, NASA HQ technology calls

• Low investment (mainly software/simulations) potential high payoff

Example Technologies

Low-Thrust Trajectory Design

• Why consider low-thrust systems ?- More efficient propulsion (high Isp, no fuel with solar sail)- Larger payload ratio (smaller launch vehicle)- Cheaper- Flexible mission design with extended launch windows

Deep Space 1Mission: Testing / FlybyBodies: Comet BorrellyIsp: 3100 s

1998‐2001

SMART‐1Mission:  OrbiterBodies:  MoonIsp: 1640 s

2003‐2006

HayabusaMission: Sample ReturnBodies: ItokawaIsp: 2900 s

2003‐2010

DawnMission: Flyby / OrbiterBodies: Mars‐Vesta‐CeresIsp: 3100 s

2007‐2015

Challenges of Low-Thrust• HUGE design space• Highly non-linear

Multi-body problems

Long thrusting periods

Multiple local

minima

Multi-revolution problems

Constraints

Low Energy Third-Body Dynamics

~Ballistic Capture

Quasi‐ballistic captureLoosely orbit for “free”

Primary

Multiple Flyby Trajectories

Titan Enceladus Cycler

Long Life Periodic Science OrbitsEnceladus Vesta

Europa

Ganymede 

Phobos

• Applications- Planetary protection- Collision probability- Navigation Monte

Carlos- Uncertainty

Quantification

• Fast proxy model• Make a non-Gaussian

distribution using a sum of Gaussians

• Split the distribution in multiple dimensions

Full distributionApproximate distribution

Gaussian Mixture Models

Fast Gravity Models

Mj

rjrcm

Point mascon model Interpolation model

Multi‐core models

Analytic Models (e.g. low-thrust, oblate planets, three-body)

• Orbit averaging• Perturbation theory• Choice of independent variables, coordinates

matter• Speed allows massive, rapid searches • New/improved methods

- Vinti model: Oblate bodies (large J2 like Earth all the gas giants)

- Control models (analytic low thrust models)- Series solutions (modern taylor series,

others) - STARK MODEL (from physics –charged

particles in homogeneous e field)

tNtN-1t2t1t0

u0uN-1

u1xN

xN-1

x2

x1

x0

Numerical propagation: SLOW

Analytic Models: FAST

Analytic propagation of Saturn insertion

Auto/Optical Navigation at Small bodies

• Autonomous• On‐board• Filtering 

(EKF/UKF/DDF)• Approach/

Descent• Pinpoint landing 

S.L.A.M.(simultaneous localization and mapping)• Body Spin State• S/C position• S/C attitude

BACKUPS

Introductions…My Research Interests

• Trajectory optimization• Multi-body dynamics• Perturbation methods• Numerical methods/ HPC• Planetary moon missions• Gravity modeling• Optimal control• Space Situational Awareness• Navigation/ Proximity Operations