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• System Design Review
• Introduction
• December 9, 2008

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Agenda

• Project Background
• Mission Overview
• Mitigation, Payload, Telecom, and Instruments
• Trajectory, Propulsion, and ACS
• Structures, Thermal, and Power
• Budget and Scheduling
• Summary

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Apophis 99942 Background Information
Project Background

• Discovered on June 19th, 2004 by R. A. Tucker, D.
  J. Tholen and F. Bernardi at Kitt Peak
• Orbital models have identified several close
  Earth approaches, occurring roughly every 7
  years. When Apophis passes by in 2029 it could
  pass through a gravitational keyhole which would
  swing Apophis into a collision path with Earth in
  2036
• As an Aten class NEA, Apophis rated as high as 4
  on the Torino scale but has been downgraded to a
  0 as its probability of impact has been commonly
  accepted at 1/45,000

Source http//neo.jpl.nasa.gov/apophis
December 9, 2008
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APEP
Project Background

• Agencies from around the world, including
  NASA/JPL, Caltech, and Arecibo, have analyzed and
  identified Apophis orbital elements and physical
  properties with limited levels of accuracy
• Uncertainty in the effects from albedo and
  gravitational forces over time are again causing
  concern about a potential impact with Earth
• The Fall 07 426, Spring 08 401 and Fall 08 402
  classes started the design of the Apophis
  Preliminary Exploration Platform (APEP) mission.
  Objectives were
• Rendezvous with Apophis in 2013, act as a beacon
  to enable precise tracking,
• Measure physical characteristics most relevant to
  improved accuracy of orbit prediction.
• If Apophis is on a collision course with Earth
  and planning of a mitigation mission is started
  after APEP discovers this fact, changing the
  course of the asteroid may be impossible.

AAA System Design Review
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December 9, 2008
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Current Mission
Project Background

• The challenge facing this team is to develop a
  system that can sufficiently modify the
  trajectory of Apophis such that it will not
  impact the Earth in 2036.
• A subsidiary goal is to design the spacecraft
  such that it can be fabricated and tested in the
  AggieSat Laboratory.
• The class was originally split into four teams.
  Each team examined multiple methods of
  deflection, including but not limited to
• Gravity Tractor
• Solar Sublimation
• Kinetic Impactor
• Electric Propulsion Devices
• Albedo Modification Systems
• Nuclear Burst
• Each team then investigated one method in depth
  and presented the method to the rest of the
  class. The best design was chosen as the system
  that would be developed by the whole class as a
  unified team.
• The Gravity Tractor was chosen as the best design
  and therefore is the focus of this presentation.
• Albedo modification is being investigated as a
  secondary mitigation technique.

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December 9, 2008
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Apophis 99942 Physical Data
Project Background

• LL-chondrite composition
• Estimated rotational period of 30.57 h
• Keyhole Event - April 2029
• Results in resonant return and impact in April
  2036

Sources http//ssd.jpl.nasa.gov/sbdb.cgi?sstr999
42orb1cov0log0discovery
Chesley, Milani, Vokrouhlicky, Icarus 148,
118138 (2000)
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AAA System Design Review
December 9, 2008
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Rationale for Exploration and Mitigation Mission
Launch Dates
Project Background
2015
2010
2020
2025
2040
2035
2030
December 9, 2008
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• System Design Review
• Mission Overview
• December 9, 2008

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Deflect Apophis System(DAS) Mission Statement
Mission Overview

• The DAS mission is to intercept the near-Earth
  asteroid Apophis 99942 and perturb its orbit to
  prevent an Earth impact in 2036.

December 9, 2008
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Mission Requirements
Mission Overview

• Withstand launch environment associated with an
  Atlas V class launch vehicle and space
  environment associated with proposed mission
  profile
• Have a launch date and travel time to Apophis
  that permits mitigation to begin no later than
  2022
• Be capable of rendezvous with Apophis
• Carry enough consumables to complete the
  mitigation mission
• Be capable of communications with a ground
  station from post-deployment through
  end-of-mission
• Deflect Apophis by at least 3 Earth radii
• Comply with all US and International laws

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AAA System Design Review
December 9, 2008
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Mission Overview
Top-Level Mission Profile
Maintain 400 m standoff distance from Apophis
for 4 years
Deploy albedo altering experiment during
mitigation
Launch DAS mission by 2022
Rendezvous with Apophis after 5 month travel
time
Relay data to ground stations on Earth to
determine mitigation effectiveness
AAA System Design Review
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• System Design Review
• Mitigation, Payload, Telecom, and Instruments
• December 9, 2008

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Design Requirements
Mitigation, Payload, Telecom, and Instruments

• Mitigation
• Deflect the course of Apophis by a minimum of 3
  Earth Radii by 2036
• Telecommunications
• Establish and maintain communication with Earth
• Provide ability to track trajectory of Apophis
• Instruments
• Provide images of Apophis
• Provide ability to track trajectory of Apophis

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Design Assumptions
Mitigation, Payload, Telecom, and Instruments

• Mitigation
• Primary method is gravity tractor
• Mass of Apophis is 2.78?1010 kg
• Apophis diameter is 270 m
• Payload
• Deployment of the albedo change material takes
  place near end of primary mitigation
• Telecommunications
• Maximum distance from spacecraft to Earth is 2 AU

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Design Approach
Mitigation, Payload, Telecom, and Instruments

• Achieve a balance of reasonable standoff distance
  and system mass
• Limit the mitigation time period to the lifetime
  of the electrical propulsion system
• Use telecommunications equipment with deep space
  flight heritage
• Deploy an experimental albedo change package

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Gravity Tractor Concept
Mitigation, Payload, Telecom, and Instruments

• Use Newtons Law of Universal Gravitation
• Use a spacecraft to impart a gravitational force
  upon Apophis to gently move Apophis to a
  non-Earth impacting orbit
• Utilize the 2029 flyby to enhance mitigation
  efforts
• Small changes pre-flyby result in large changes
  in Apophis trajectory post-flyby

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Standoff Distance and Deflection Results
Mitigation, Payload, Telecom, and Instruments

• Nominal Thrusting Case
• 12 mN of thrust from each of 2 EP thrusters
• 38 canting angle for each thruster
• Total duration of mitigation 4 years
• Resulting nominal standoff distance 222 m from
  Apophis CG
• Resulting Deflection 60 Earth Radii

Standoff distance is too close to Apophis surface
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Standoff Distance and Deflection Results
Mitigation, Payload, Telecom, and Instruments
The selected standoff distance is shown here

• Upper Bounding Case for standoff distance
• 4 mN of thrust from each of 2 EP thrusters
  (minimum case)
• 38 canting angle for each thruster
• Total duration of mitigation 4 years
• Resulting maximum standoff distance 385 m from
  Apophis CG
• Resulting Deflection 25 Earth Radii

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Albedo Change
Mitigation, Payload, Telecom, and Instruments

• Any change in albedo alters solar pressure and
  the Yarkovsky effect
• Fmax 0.70 N from solar pressure and Yarkovsky
  effect
• Orbit Deviation (assuming 25 kg coating)
• By 2036, a 4 change in albedo (beginning in
  2018) will deflect Apophis between 17 and 45
  Earth radii
• Model based on comparison with results of Chesley
  paper

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Albedo Treatment Options
Mitigation, Payload, Telecom, and Instruments

• Paint
• Heavy
• Difficult to apply
• Freezing possible
• Chalk
• Lightweight
• May coat unevenly

• Reflective Sheet
• Very large
• Difficult to open and deploy onto surface
• Glass Beads
• Heavy
• May be covered by dusty surface
• Easy to carry and release

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Albedo Change Mechanism
Clam-shell release near the asteroid
Spring-Loaded cassette ejector
Pressurized clam-shell cassette containing a cake
of hydrolyzed Nano Titanium Dioxide Powder
(cosmetic powder)
Explosive decompression disburses powder and
ionizes the solid matrix
Electrostatic force attracts and binds the powder
to the asteroid surface
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AAA System Design Review
December 9, 2008
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Baseline Design
Mitigation, Payload, Telecom, and Instruments

• Telecom subsystem is a dual string design
• Support two-way X-Band plus Ka-Band downlink
• Equipment includes X/X/Ka SDST transponders, 17W
  X-Band SSPA, 3.5 W Ka-Band SSPA, 1 m HGA, 2
  X-Band LGAs, waveguide transfer switches, X-Band
  diplexers, filters, waveguide and coax cabling

Design Rationale

• Dual string design due to mission duration
• Ka-Band downlink added for improved navigational
  accuracy

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Tracking Apophis
Mitigation, Payload, Telecom, and Instruments

• The instruments in conjunction with the telecom
  subsystem need to be capable of tracking the
  deflected trajectory of Apophis
• Tracking will use the same method as APEP mission
• Uses 2 Laser Range Finders and an optical
  navigation imaging camera
• Uses telecom subsystem as either a transponder or
  a beacon with the DSN to relay position of Apophis

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Navigation Camera
Mitigation, Payload, Telecom, and Instruments

• The camera will serve as an imaging camera to
  collect science data
• The data will include high-resolution color
  images of the asteroid
• The nav camera will provide images taken through
  different filters
• These images will provide information on gas
  composition, gas and dust dynamics, and jet
  phenomena, if they exist.

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Mitigation, Payload, Telecom, and Instruments

• Laser Range Finder (LRF)
• The laser range finder will be used to measure
  the distance between the spacecraft and Apophis
  surface. It is also possible to use Doppler
  effect techniques to measure the relative
  velocity between the spacecraft and Apophis.
• In order to make a stereoscopic
• measurement of the asteroid surface
• to determine whether it's rigid or rubble
• pile, two LRFs will be used.

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Laser Range Finder
Mitigation, Payload, Telecom, and Instruments

• A conceptual design of the laser range finder is
  shown. It consists of
• A solid-state laser transmitter with optical
  diverger
• A reflective telescope that functions as an
  optical receiver
• An Analog/Digital conversion unit and digital
  processing unit

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• System Design Review
• Trajectory, Propulsion, and ACS
• December 9, 2008

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Requirements and Assumptions
Trajectory, Propulsion, and ACS

• Trajectory
• Launch to Earth escape
• Transfer orbit for rendezvous with Apophis
• Maintain tractor position at Apophis
• Propulsion
• Use chemical rocket for launch/transfer to
  Apophis
• Use electric engine for mitigation
  station-keeping
• Attitude Control System (ACS)
• Maintain desired orbital position and orientation
  relative to Apophis

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AAA System Design Review
December 9, 2008
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Lambert Problem Setup
Trajectory, Propulsion, and ACS
Source Dr. John Junkins
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Solution to Lambert Problem
Trajectory, Propulsion, and ACS
Depart Feb 19, 2022 Time of Flight 144 days
Minimum ?v Solution (4.276 km/s)
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December 9, 2008
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Launch Window
Trajectory, Propulsion, and ACS
Departure Date February 19, 2022 (/- 25
days) Time of Flight 144 Days
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Launch Vehicle
Trajectory, Propulsion, and ACS

• The launch vehicle will be an expendable launch
  vehicle from the Atlas V class
• The Atlas V 401 is a 2 stage rocket capable of
  launching up to 2400 kg to Earth escape.
• Notable payloads to Earth escape
• Mars Reconnaissance Orbiter
• New Horizons

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Transfer Orbit
Trajectory, Propulsion, and ACS

• Assume an Isp329 sec
• In order to arrive at Apophis with a 500 kg
  spacecraft, 1381 kg of chemical fuel is required
• Mass at launch (to Earth escape) is 1881 kg

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AAA System Design Review
December 9, 2008
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Engine Selection
Trajectory, Propulsion, and ACS

• Aerojet 445
• Chemical Rocket used for transfer to Apophis and
  rendezvous

• Busek BHT-200 (x2)
• Electric Engine used to perform gravity tractor
  operation
• Each engine is installed at a 38º canting angle
  to avoid exhaust impingement on Apophis

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Aerojet 445 Hi-PAT Specifications
Trajectory, Propulsion, and ACS

• Specific Impulse 329 s
• Thrust/Steady State 445 N
• Mass 5.44 kg
• Propellant Type Hydrazine/NTO
• Propellant Mass 1381 kg
• Flow Rate 141 g/s
• Currently in use

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Busek BHT-200 Specifications
Trajectory, Propulsion, and ACS

• Input Power 50W-300W, 200Wnominal
• Voltage 250V
• Current 800 mA
• Propellant Flowrate 0.94 mg/sec
• Xenon Propellant Mass 250 kg
• Thrust 4-17 mN, 12 mNnominal
• Specific Impulse 1390 sec
• Efficiency 43.5
• Successfully used by the TacSat-2 experimental
  satellite launched on December 16, 2006

Source http//www.busek.com/index.html
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Attitude Determination
Trajectory, Propulsion, and ACS

• 2 Star Trackers
• For improved accuracy and redundancy
• 8 Sun Sensors
• Adcole coarse 1-axis
• 1 Inertial Measurement Unit
• Northrop Grumman LN-200

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AAA System Design Review
December 9, 2008
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Attitude Control and Manuevering
Trajectory, Propulsion, and ACS

• 4 Reaction Wheels
• Teldix RSI 02 0.2-1.6 Nms momentum capacity
• For stability and slewing
• Pyramid formation
• Hydrazine Thrusters
• 8 MR-103C 1 N (0.2-lbf) by Aerojet
• Pointing and momentum dumping
• 4 MR-106E 22 N (5-lbf) by Aerojet
• Thrust vector control

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• System Design Review
• Structure, Thermal, and Power
• December 9, 2008

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Design Requirements
Structure, Thermal, and Power

• Structures
• Structure should withstand launch loads,
  frequencies, and pressures
• Satellite bus should provide support for all
  instruments
• Thermal
• Maintain all instruments and components within
  survivable temperatures
• Power
• Provide enough power to operate necessary systems
  through all phases of the mission

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Design Assumptions
Structure, Thermal, and Power

• Spacecraft mass at Apophis 500 kg
• Optimal angle of Hall thrusters 38
• Assume worst case hot and cold are at periapse
  and apoapse of Apophis orbit, respectively
• Spacecraft modeled as a conductive sphere for
  thermal analysis

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Conceptual Bus Design
Structure, Thermal, and Power

• Utilize body mounted solar arrays
• All fuel tanks and components housed internally
  for thermal control
• Material of main structure 6061T6 Al

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Thermal
Structure, Thermal, and Power
Approximate spacecraft as a sphere of equivalent
surface area.
Model does not identify hot/cold spots Internal
satellite configuration currently unknown
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Thermal
Structure, Thermal, and Power
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Power Requirements
Structure, Thermal, and Power

• Provide enough power and storage to operate the
  spacecraft in all modes throughout the mission
• Provide power switching and power regulation
• Redundancy as necessary
• Solar array is primary power source

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Power Assumptions
Structure, Thermal, and Power

• Battery Assumptions
• Rechargeable batteries will be used for secondary
  power
• Battery will provide high A-h per unit mass
• Bus voltage of at least 28 Volts
• Array Assumptions
• Array is large enough to charge the batteries
  while supplying power to spacecraft
• Array must provide 1100 Watts

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UTJ GaAs Solar Array
Structure, Thermal, and Power

• Array Rationale

• Gallium Arsenide has a high absorptivity
• Requires few microns of thickness to absorb
  sunlight
• GaAs cells are relatively insensitive to heat
• Gallium arsenide is very resistant to radiation
  damage

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Lithium Ion Battery
Structure, Thermal, and Power

• Battery Rationale

• Li-ion batteries are lighter than other
  equivalent batteries
• They have a higher energy density than most
  batteries
• They operate at higher voltages compared to most
  batteries
• They have a lower self discharge rate (Retain
  charge for long time)

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• System Design Review
• Budget and Scheduling
• December 9, 2008

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Timeline
Budget and Scheduling
2010 Finalize preliminary design
2022 Rendezvous complete. Begin mitigation
2011 Begin prelim. testing analysis
2027 Mission Ends
2022 LAUNCH
2012 Begin major testing analysis


2018 Make adjustments, Continue testing
2015 Prototypes assembled for testing
Albedo Mitigation Study
AAA System Design Review
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Work Breakdown Example
Budget and Scheduling
from Space Mission Analysis Design
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Key Funding Assumptions
Budget and Scheduling

• For the purposes of this study, it should be
  assumed that the total funding available for
  development of a 2022 Apophis deflection mission
  will be
• Between 100-200 million dollars
• Excluding Launch vehicle, mission operations
  system, technology development, flight validation
  demonstrations, mission operations

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Cost Estimation Method
Budget and Scheduling

• Parametric Estimating- Use math relations between
  design parameters and cost that are compiled from
  statistics of previous programs. These relations
  are called CERs (Cost Estimating
  Relationships).
• CERs only applicable to the range of historical
  data
• Parametric estimating unsatisfactory for items
  involving major technological advancements or
  fundamental paradigm shifts. The current mission
  does not fall into this category so this
  estimation method is sufficient.

Space Mission Analysis Design
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Terms
Budget and Scheduling
from Space Mission Analysis Design
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Breakdown of Small Satellite Costs
Budget and Scheduling
from Space Mission Analysis Design
43 contingency , then multiply by factor of 3
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Comm CDH Subsystems
Budget and Scheduling
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Sensors and Telecom
Budget and Scheduling
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ACS Subsystem
Budget and Scheduling
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Structures and Mechanisms
Budget and Scheduling
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Thermal Management Subsystem
Budget and Scheduling
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Power Subsystem
Budget and Scheduling
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Propulsion Subsystem
Budget and Scheduling
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Educational Outreach
Budget and Scheduling

• Target audience
• Educational institutions
• Classroom presentations
• Introduce students to
• space technology
• Design competition
• Opportunities for students to do research
• Development of creative solutions for the mission
• Opportunities for interested parties to
  participate in modification of albedo studies

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Trajectory, Propulsion
Structures, Thermal, Power

• Launch Window 1/28/22-3/16/22
• Flight Time 144 Days
• Total Delta V 4.28 km/s
• Launch Vehicle Atlas V class
• BUSEK BHT 200 4-17 mN
• Chemical transfer, EP for mitigation

• Dry Mass 250 kg
• Primary Material 6061-T6 Al
• Worst Case Hot 61 C
• Worst Case Cold -25 C
• Array GaAs to supply 1100 Watts, 4.8 m2
• Batteries Saft Li-Ion

Mitigation, Payload, Telecom
Budget and Scheduling

• Gravity Tractor Duration 4 Years (total)
• Standoff 385 m
• Albedo treatment experiment

• Overall Budget 100-200 million
• Initial Projected Cost - 80.2 million
• Preliminary Design Complete 2010
• Testing and Analysis 2010-2018
• Launch 2022

AAA System Design Review