XSS-11 Targeting Concept

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The ARES Mission to Mars The First Flight of an
Airplane on Another Planet Presented at the
Aerospace Control and Guidance Systems Committee
Meeting October 21, 2005 By Jeff Zinchuk and Lee
Norris Draper Laboratory - Cambridge, MA
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Topics

• Background and Program Overview
• Science
• Airplane deployment and ground track
• LaRC Planetary Airplane Risk Reduction Activities
• Draper Guidance and Navigation Algorithm
  Activities

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ARES Mars Proposal Complements and Extends the
Core Mars Program

• Exploration of Mars requires gathering scientific
  and engineering data over large areas of the
  planet
• Airplanes enable exploration of areas
  inaccessible to rovers with increased resolution
  over orbiters blends ground truth of rovers with
  global measurements of orbiters
• Simultaneous in-situ measurements of Mars
  atmosphere, surface, and interior
• Science themes
• Crustal Magnetic anomalies (where do we come
  from?)
• Regional atmospheric chemistry (follow the
  water) to determine climate history and ability
  to support past life
• Planetary airplanes are a new platform for
  planetary science and exploration

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Science Themes
Builds on Viking, Mars Global Surveyor, and
Odyssey discoveries, providing a window into the
evolution of Mars atmosphere, surface, and
interior

• Crustal Magnetism
• ARES extends MGS-discovered crustal magnetic data
  to high spatial resolution to understand its
  nature and origin
• An aeromagnetic survey is utilized to
  characterize the crustal magnetism source
  structure

• Near Surface Atmospheric
• Chemistry
• Follow the water, chemically-active gases and
  precise isotopic measurements
• Potential gases of biogenic volcanic origin and
  atmospheric state variables

• Underlying Geology Mineralogy
• Geologic understanding of the oldest known crust
  in the solar system
• Understanding mineralogy associated with the
  crustal magnetic anomalies

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Reference Science Payload
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Straightforward Mission Architecture Maximizes
Use of Proven Technologies and Existing
Infrastructure

• Short duration, scripted mission minimizes
  operations complexity
• Traverse and measurement techniques similar to
  those employed on earth
• Heritage carrier spacecraft (Genesis/Odyssey) and
  Entry System (MPF/MER)

Launch Oct-Nov 2011 Flight August 2012
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Airplane Deployment
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ARES Flight on Mars Entry Video
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Pre-Planned Controlled Scientific Survey
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Flight Path and Navigation Requirements
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ARES Flight on Mars Traverse Video
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ARES Status

• Draper supported NASAs Langley Research Center
  in 2002-3 for a Mars Scout Program Phase A Study
  Aerial Regional-Scale Environmental Survey
  (ARES) of Mars
• Scout Program run on 4-year cycles complements
  Mars Exploration Program
• ARES one of four proposals (25 submitted)
  selected for Phase A studies
• ARES not selected for implementation (Phases B,
  C, D) but LaRC will re-propose in 06
• Phoenix selected perceived to be low risk
• ARES science was rated Category 1
• Some perceived technology development risks
  (cost/schedule)
• ARES Team
• JPL - Program management, mission design and
  operations
• LaRC - Atmospheric science and aeronautic
• Lockheed - Heritage Genesis-design S/C
• Aurora - Airframe subsystems
• Draper - Autonomous GNC and sensors, integrated
  avionics subsystem (computer/flight software,
  hardware-in-the-loop simulation (HILSim)

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ARES transitions into PARR

• During Phase A study, a high altitude drop
  demonstration (HADD-1) was performed using
  half-scale model of airplane
• Although ARES established viability of
  airplane-based planetary exploration,
  implementation risk must be lowered to enable
  mission selection in 07
• PARR program objective is to reduce risk in high
  risk technology areas
• Program risk reduction strategy
• Use ARES design reference mission and entry
  system hardware as baseline designs
• Demonstrate perceived high risk technology in
  ground-based tests (HILSim and propulsion
  components)
• Show system-level readiness via additional
  HADDs (2, 3)

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PARR Program - Technology Focus
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FCS Risk Reduction Tasks for GNC

• Develop 6 DOF simulation using airplane
  performance and environmental models to support
  analysis and performance characterization of
  potential GNC implementations for an airplane
  flight on Mars
• Assess GNC sensor suites
• Assess trajectories
• Assess guidance algorithms
• Assess navigation algorithms
• Develop large Kalman filter for navigation
  options
• Develop guidance algorithms for two types of
  mission straight or parallel paths
• Incorporate LaRC-supplied control algorithms

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Draper Items to Consider

• How to improve initial state knowledge (or
  accommodate large velocity uncertainty)
• How to accommodate significant uncertainty in
  winds
• Strategies for altitude determination

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PARR Guidance, Navigation, And Control

• Mission Data
• Nominal Trajectory

• ADS Data
• Radar Altimeter Data
• IMU Data
• Initial Condition Data
• Other Sensor Data

• Position
• Velocity

• Heading Cmd
• Altitude Cmd

Control
Navigation
Guidance

• Aileron Cmd
• Rudder Cmd
• Elevator Cmd
• Engine Cmd

• Attitude
• Body Rates
• ADS Data

• Navigation determines the position/velocity/atti
  tude state of the aircraft at the current time
• Guidance determines the heading and altitude
  commands necessary to fly the desired path
• Control determines the lifting surface and
  engine commands needed to meet Guidance commands

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Aircraft Model And Control System

• Aircraft model and Control algorithms provided by
  NASA Langley
• Preliminary versions currently in use in Draper
  6DOF simulation
• Preliminary Navigation and Guidance algorithms
  are being designed based on this simulation
• Primary interfaces to Control are heading command
  and altitude command
• Heading rate command capability may be added at a
  later date

Control System Characteristics
Step Response
q
90 deg
60 deg
30 deg
t
Angular Rate
q dot
90 deg
60
30
t
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PARR Navigation
Baseline Instrumentation
Requirements
Inertial Measurement Unit (IMU) ? delta
velocity, delta angle

• Determine near optimal estimate of current
  position, velocity, and attitude state of the
  aircraft for Guidance by blending available
  sensor data
• Estimate the aircraft attitude states needed by
  Control
• Estimate the three components of wind velocity
  for use by Guidance in implementing the
  trajectory
• Locate previous path points (see below) which can
  be used in Guidance in implementing a parallel
  ground path trajectory

Radar Altimeter

• Air Data System (ADS)
• Angle Of Attack
• Angle Of Sideslip
• Airspeed
• Barometric Altitude

Optional Instrumentation

• Camera (Optical Flow)
• Sun Sensor
• Laser Altimeter
• Etc.

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PARR Navigation Filter
Filter Design
State Vector

• The Navigation filter blends information from a
  variety of sensors to form the best estimate of
  the current state of the aircraft
• The relative weightings of the sensor
  measurements are based on the (statistically
  expressed) expected qualities of the measurements
• A Kalman filter provides the minimum variance
  linear estimate of the state of the aircraft
  assuming Gaussian measurement error from the
  sensors
• The Kalman filter estimates not only the aircraft
  state but also system errors which affect the
  aircraft state

position (3 elements)
Rac
velocity (3 elements)
Vac
attitude (3 elements)
qac
Ab
accelerometer errors (9 elements)
Asfe
Amar
Gb
gyro errors (9 elements)
Gsfe
Gmar
gravity model error (3 elements)
GR
wind speed (3 elements)
Wned
previous path points (12 elements)
PPP
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Previous Path Points
1.)
2.)

• The desired trajectory is nominally oriented with
  legs 1, 3, and 5 aligned with North
• Legs 1, 3, and 5 should be parallel
• Legs 1, 3, and 5 are 100 km in length
• Legs 2 and 4 are less than 5 km in length

2

• The turns between legs provide observability of
  the wind
• Wind estimates on the first leg will not be
  precise
• As a result, leg 1 may be curved due to unknown
  wind

1
3
5
1
4
3.)
4.)

• Navigation will estimate the location of four
  points along the first leg
• In addition to estimating the current state of
  the aircraft, Navigation will continue to
  estimate the location of these four previous
  points throughout the mission
• This allows updating of the estimates when the
  wind values are better known

• The previous path points will be used by
  Guidance to construct legs 3 and 5 parallel to
  leg 1

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Navigation Results

• Relative Navigation error is better than absolute
  Navigation error
• Preliminary covariance analysis indicates
  relative error of 3 km 1 sigma

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PARR Guidance
Issues
Requirements

• Provide heading commands to implement an open
  loop (non-parallel path) trajectory
• Provide heading commands to implement a parallel
  ground path trajectory
• Compensate for the effects of winds along the
  path for all trajectories
• Provide altitude commands to implement the
  desired altitude profile

• The primary issue for Guidance is dealing with
  the effect of uncertain winds on the groundtrack
  of the aircraft
• The Mars atmosphere is unpredictable and
  unmodeled
• Navigation can accurately estimate a constant
  wind
• The issue is not the speed or direction of the
  wind, but the degree of variability
• If the components of the wind change
  significantly with time or distance, Guidance
  will find it more difficult to accurately hold
  the desired groundtrack

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Lateral Channel Guidance

• The trajectory will be defined by a series of
  points along the desired path
• These points may be adjusted during the flight to
  shape the second and third legs to match the
  shape of the first
• Guidance will develop heading commands to lead
  the aircraft onto the desired trajectory
• The heading commands will look ahead along the
  trajectory to anticipate turns
• The commanded heading will be adjusted to null
  the estimated wind so that the desired
  groundtrack is maintained

desired heading
d
heading command desired
heading f(d)
f(rate of change of desired
heading)
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Vertical Channel Guidance
Constant Altitude

• Three (or more) options exist for the altitude
  channel as indicated
• The requirements for the gravimeter are believed
  to be constant altitude above the ellipsoid
• The terrain following approach is most easily
  implemented using the radar altimeter
• The altitude requirements for other science
  missions are not yet specified
• The baseline approach for altitude is modified
  constant altitude, in which the aircraft flies at
  a constant altitude unless the distance to the
  local terrain (as measured by the radar
  altimeter) goes below a threshold, in which case
  the aircraft will climb to maintain the threshold

Terrain Following
Modified Constant Altitude
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Guidance Results (Without Wind)

• Plot shows a test trajectory used in evaluating
  Guidance algorithms
• Trajectory is the basic shape of the proposed
  groundtrack for magnetometer studies
• Tracking error is least during straight legs
• Improved performance is expected as further
  Guidance development occurs

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Guidance And Navigation Trade Studies
Alternate Sensors
Purpose

• At this point the science which drives the
  mission has not been firmly specified
• Several alternative combinations of instruments
  and trajectories will be evaluated such that when
  the science requirements are specified, a
  significant portion of the required design will
  have been done
• The goal is to provide a catalog of options
  which specify the instrumentation and
  trajectories necessary to meet a variety of
  objectives

• The baseline set of sensors have been evaluated
  using preliminary covariance analysis and appears
  to be satisfactory for a variety of missions
• Alternate sensors such as a camera with image
  processing may be required if the trajectory must
  pass over a specific landmark
• Additional sensors may also be required for
  increased accuracy or redundancy

Modified Trajectories
Alternate Trajectories

• Several non-parallel path trajectories will be
  assessed (maximum distance North, dogleg, etc.)
  to support atmospheric science missions
• At least one parallel path trajectory will be
  assessed to support magnetic field studies
• New trajectories may arise due to as yet
  unspecified science requirements

• Wind speed and direction are most observable when
  measurements are made in two orthogonal
  directions
• This implies that wind estimates are generally
  not accurate until the second leg of a parallel
  path trajectory
• Wind knowledge can be obtained earlier by doing a
  series of maneuvers prior to initiating leg 1

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Program Status

• Draper has 6 DOF deterministic simulation up and
  running
• Based on LaRC aerodynamic database and initial
  control laws
• Guidance and navigation algorithms are being
  integrated to assess navigation performance under
  various trajectories and sensor suites
• Airplane control laws are still being developed
  at LaRC to incorporate additional control modes
  for robust deployment and pull out
• Focus will be on analyzing absolute and relative
  navigation performance
• 6 month analysis to support science selection and
  proposal underway
• EM model of flight hardware has been procured and
  is running with first flight software build
• GNC code will be embedded in RAD750 flight
  processor and fly Hardware-in-the-Loop 6 DOF
  simulation
• Processor will be executing airplane flight
  control, and science data collection,
  compression, and telemetry