OSIRIS-REx Status Report
(and What We’ve Learned
about Bennu)
Carl Hergenrother
Asteroid Astronomy Lead
SBAG – 2013 July 11
NASA Headquarters – April 30, 2013
1
Recent Accomplishments
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TAGSAM microgravity testing @ JSC
Mission “upgraded” to Category 1
2012 DA14 flyby and Chelyabinsk media events
OLA authorization received for Phase B2/C
Successful Mission Preliminary Design Review
‘Name That Asteroid’ winner announced – we are going to Bennu
NFPO directed Project to remove all “STEM education” activities and eliminate
E/PO element
APMC KDP-C Confirmation Review – Confirmed!
Start of Phase C – 6/3/2013
NASA Headquarters – April 30, 2013
OSIRIS-REx Science Team Meeting #4 – June 18-20, 2013
2
2
Asteroid (101955) 1999 RQ36 is now . . .
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Bennu
 Bennu is an Egyptian
mythological bird that
was born from the heart
of Osiris
 It is associated with the
Sun, creation, and
renewal
 The name was selected
in an international
contest run by the
Planetary Society
NASA Headquarters – April 30, 2013
Image credit:
http://www.touregypt.net
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INITIAL CHARACTERIZATION: 1999
Bennu
10
Discovery: Sept 11, 1999 by the LINEAR survey
Visual Magnitude
12
Follow-up: ~200 astrometric observations between
Sept 12 – 24, 1999
14
Radar: Arecibo and Goldstone observations from
Sept 21 – 25, 1999
16
18
Visible Spectroscopy: McDonald Observatory for 5 nights in
September 1999
LINEAR Detection limit
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22
24
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Date
NASA Headquarters – April 30, 2013
4
REACQUISITION AND PHYSICAL CHARACTERIZATION: 2005
10
Bennu
Reacquisition: 71 observations between Aug 8 – Sept 17, 2005
Visual Magnitude
12
Vis-IR Spectroscopy: NASA IRTF observations on Sept 4, 2005
14
Photometry: Lightcurve and ECAS colors on Sept 14 – 17, 2005
16
18
Radar: observations from
Sept 16 – Oct 2, 2005
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Catalina Sky Survey
Detection limit
(Mt. Lemmon)
22
24
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Date
NASA Headquarters – April 30, 2013
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FINAL CAMPAIGN: 2007 - 2012
Bennu
10
Thermal IR: Spitzer observations on May, 2007 and Aug., 2012
Visual Magnitude
12
14
16
18
Radar: Further Arecibo observations in Sept, 2011
Phase function: Photometric measurements through May, 2012
Light Curve: Hubble-WFC3
observations in Sept. and
Dec., 2012
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22
24
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Date
NASA Headquarters – April 30, 2013
6
A QUALITY ORBIT REQUIRES EXTENSIVE OBSERVATION
Uncertianty in Semi-major Axis (km)
1.E+08
Reacquisition
∆a = 4 km
1.E+07
1.E+06
Second Radar
∆a = 100 m
1.E+05
Obs. at opposition
∆a = 15 m
1.E+04
1.E+03
1.E+02
1.E+02
1.E+01
9/10/99
9/15/99
9/20/99
Discovery
∆a = 376,000 km
9/25/99
1.E+01
9/30/99 10/5/99
Date
Follow-up
∆a = 20,500 km
1.E-01
First Radar
∆a = 43 km
NASA Headquarters – April 30, 2013
1.E+00
1.E-02
1.E-03
Jun-05
Sep-05
Dec-05
Date
Mar-06
Jul-06
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RADAR AND PHOTOMETRY ARE POWERFUL SOURCES OF
INFORMATION ABOUT ASTEROID PHYSICAL PROPERTIES
Measurements of the distribution
of range and radial velocity
provided two-dimensional images
with spatial resolution of 7.5 m
 Images used to construct a
geologically detailed threedimensional model and define the
rotation state
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Size = 492-m (±20 m, mean diameter)
• Shape = spheroidal “spinning top”
• Rotation state = 4.29 hr period, 180º
obliquity
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Radar also probed the nearsurface bulk density (1.7 g cm-3)
and structural scales larger than a
few centimeters
NASA Headquarters – April 30, 2013
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FINDING THE RIGHT ASTEROID MEANS
KNOWING WHAT IT IS MADE OF
• OSIRIS-REx seeks to return samples from a
Carbonaceous Asteroid
• Visible, near-infrared spectroscopy and
ECAS photometry show that Bennu is a Btype asteroid
• Linear, featureless spectrum with
bluish to neutral slope
• Near-IR thermal emission starting at 2 µm
suggest an albedo of 3-5%
• The hydrated CI and CM carbonaceous
chondrite meteorites are the most likely
analogs
NASA Headquarters – April 30, 2013
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AN OSIRIS-REX FIRST: MEASURING A PLANETARY MASS
USING RADAR AND INFRARED ASTRONOMY
• The three precise series of radar ranging position measurements over two
synodic periods allows us to measure the Yarkovsky acceleration
• The asteroid has deviated from its gravity-ruled orbit by 160 kilometers in
just 12 years
• This result, when combined with the thermal inertia and the shape model,
constrains the mass to 6.278 (-0.942/+1.883) x 1010 kg
• Mass and shape constrain the bulk density to 0.980 ± 0.147 g/cm3
• Spitzer observations yield a very low albedo – 4.5 ± 1.5%
NASA Headquarters – April 30, 2013
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SURFACE PROPERTIES ARE CONSISTENT WITH ABUNDANT
LOOSE REGOLITH AVAILABLE FOR SAMPLING
• Radar polarization shows transition to a “rough” surface at a scale smaller
than the shortest (3.5-cm) wavelength
• The thermal inertia is substantially below the bedrock value – regolith grains
are significantly smaller than the scale of the skin depth (~1 cm)
• The asteroid’s shape, dynamic state, and geomorphology provide additional
evidence for the presence of loose particulate regolith
• There is one ~10–m boulder apparent on the surface
NASA Headquarters – April 30, 2013
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Backup Charts
NASA Headquarters – April 30, 2013
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THERMAL IR OBSERVATIONS PROVIDE CRITICAL
KNOWLEDGE FOR SPACECRAFT DESIGN
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Spitzer observations yield a very low albedo – 4.5 ± 1.5%
Combining the asteroid shape, rotation state, ephemeris, and albedo
yields a global temperature model
Thermal IR observations provide ground truth for this model
Direct input into the mission Environmental Requirements Document
NASA Headquarters – April 30, 2013
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MISSION DESIGN CONSTRAINTS 2: SIZE AND ROTATION
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OSIRIS-REx must be able match
the rotational rate of the target,
achieving a spacecraft attitude
where we “hover” over the
sampling site
This constraint translates into a
limit on the rotation period of the
asteroid
The majority of asteroids <200 m
are rapid rotators, with rotation
periods as short as one minute
•
•
 Lightcurve reveals a rotation
period of 4.297 0.002 hours
Rapid rotation greatly increase the
risk during proximity operations
Centrifugal forces have also likely
ejected most regolith particles from
the surface
NASA Headquarters – April 30, 2013
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OSIRIS‐REX IS DEVELOPING CRITICAL TECHNOLOGIES FOR
EXPLORING NEAR‐EARTH ASTEROIDS
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Astronomical characterization in
support of mission design
Measurement of asteroid global
characteristics
Detailed characterization of an
asteroid surface at sub-cm scales
Mission-critical data processing and
analysis on a tactical timeline
Accurate navigation in microgravity
Delivery to a specific location on the
asteroid surface
Successful contact and acquisition of
material from an asteroid surface
Safe return of the sample to Earth
NASA Headquarters – April 30, 2013
Without guidance
With guidance
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MISSION DESIGN CONSTRAINTS 1: ORBIT
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Use of solar power: aphelion < 1.6 AU
Thermal constraints: perihelion > 0.8 AU
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Mission propellant and sample return
capsule (SRC) performance
requirements: inclinations <10˚
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These two requirements constrain both
the semi-major axis and the orbital
eccentricity of the target
Objects on low-inclination orbits require
a minimum amount of delta-V for
rendezvous and provide low re-entry
velocities for the SRC
Quality of orbital knowledge: sufficiently
precise to allow us to design a trajectory
ensuring the spacecraft could
rendezvous with the target
The orbit of Bennu meets all of our
mission-target criteria
NASA Headquarters – April 30, 2013
Note: Bennu inclination = 6.03˚
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KNOWLEDGE OF ASTEROID MASS SUBSTANTIALLY
ENHANCES MISSION PLANNING
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NASA Headquarters – April 30, 2013
Mass and shape constrain the bulk
density to 0.980 ± 0.147 g/cm3
They are combined to produce a
global gravity-field model that
facilitates orbital stability analysis
Combining the gravity-field model
and rotation state yields global
surface-slope distributions and
accelerations
All this information is critical to
evaluating our ability to safely
deliver the spacecraft to the
asteroid surface and maintain
nominal attitude during sampling
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THE GREAT VALUE OF ASTEROID SAMPLES ARE IN THE
DETAILED KNOWLEDGE OF SAMPLE CONTEXT
• Dynamical studies characterize the
asteroid history and provide sample
context
• Combined dynamical and spectral
information to identify the most
likely main-belt origin
• Discovered the “Eulalia family” –
formed between 900–1500 Myr
ago from the breakup of a 100–160
km parent body
• Found compelling evidence for an
older and more widespread
primitive family in the same region
• Either one of these families could
be the source of 1999 RQ36 – need
sample return to discriminate
between the two
NASA Headquarters – April 30, 2013
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STUDY OF THIS POTENTIALLY HAZARDOUS ASTEROID IS
STRATEGICALLY IMPORTANT
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1999 RQ36 is classified as a potentially hazardous object
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Diameter larger than 150 meters
MOID of 0.0027 AU with the Earth
The Yarkovsky effect is the most significant non-gravitational
acceleration acting to alter the asteroid’s orbit
We can confidently predict eleven approaches to Earth closer than
0.05 AU over a span of 481 years
•
~10-3 probability of a 3000 MT impact late in 22nd century
NASA Headquarters – April 30, 2013
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THE ROTATION STATE IS WELL CONSTRAINED FROM
LIGHTCURVE MEASUREMENTS
• Achieved a frequency of
observations which resulted in a
lightcurve covering a full rotation
cycle each night for 4 nights of
observing
• Lightcurve reveals a rotation
period of 4.297 0.002 hours
• The low amplitude is consistent
with the rotation of a nearly
spherical body
NASA Headquarters – April 30, 2013
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TAGSAM – THE OSIRIS-REX SAMPLING STRATEGY IS
DESIGNED TO COLLECT ABUNDANT PRISTINE REGOLITH
NASA Headquarters – April 30, 2013
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Mission Timeline
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Selection: May 25, 2011
Preliminary Design Review (PDR): March, 2013
Critical Design Review (CDR): April, 2014
System Integration Review (ATLO): February, 2015
Launch: September, 2016
Earth Gravity Assist (EGA): September, 2017
Asteroid Arrival (AA): August, 2018
Asteroid Departure (Dep): March, 2021
Sample Return: September, 2023
End of Mission (Sample Analysis – SA): September, 2025
NASA Headquarters – April 30, 2013
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OUR SAMPLE IS COLLECTED DURING A FIVE-SECOND
TOUCH-AND-GO MANEUVER
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Approach surface within
vertical and horizontal
speed constraints
Surface contact is made
with sampler head
Compression of spring in
the Touch-and-Go Sample
Acquisition Mechanism
(TAGSAM) arm
Rebound from surface using
stored energy in spring
Fire thrusters to accelerate
away from RQ36
NASA Headquarters – April 30, 2013
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OUR PAYLOAD PERFORMS EXTENSIVE CHARACTERIZATION AT
GLOBAL AND SAMPLE-SITE-SPECIFIC SCALES
OCAMS
(UA)
SamCam images the sample site, documents sample acquisition, and images
TAGSAM to evaluate sampling success
MapCam provides landmark-tracking OpNav, performs filter
photometry, maps the surface, and images the sample site
PolyCam acquires 1999 RQ36 from >500K-km range, performs star-field OpNav,
and performs high-resolution imaging of the surface
OLA (CSA) provides ranging data out to 7 km and maps the asteroid shape
and surface topography
NASA Headquarters – April 30, 2013
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SPACECRAFT-BASED REMOTE SENSING PROVIDES GROUND
TRUTH FOR OUR ASTRONOMICAL DATA
OVIRS (GSFC) maps the reflectance albedo and spectral
properties from 0.4 – 4.3 µm
OTES (ASU) maps the thermal flux and spectral
properties from 4 – 50 µm
Radio Science (CU) reveals the mass, gravity field,
internal structure, and surface acceleration distribution
REXIS (MIT) maps the elemental abundances of the asteroid surface
NASA Headquarters – April 30, 2013
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OUR DESIGN REFERENCE MISSION PROVIDES
SUBSTANTIAL OPERATIONAL MARGIN
NASA Headquarters – April 30, 2013
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Phase Function for 1999 RQ36
NASA Headquarters – April 30, 2013
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Finding a Boulder in Space
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10-m Boulder Apparent Magnitude
Catalina Sky Survey
Detection limit
(Mt. Lemmon)
Visual Magnitude
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28
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32
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1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Date
NASA Headquarters – April 30, 2013
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Carbonaceous Boulder Statistics
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A carbonaceous asteroid with a diameter < 10 meters and albedo < 0.07 would
have an absolute magnitude > 28.5.
As of April 2013, 78 NEAs with H > 28.5 have been discovered.
72 of the 78 were discovered by surveys operated by the University of Arizona
(Catalina Sky Survey, Mount Lemmon Survey, Spacewatch)
NASA Headquarters – April 30, 2013
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Asteroid Boulder Orbits
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Of the 78 only 8 have been characterized in any way
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6 Rotation Periods (1991 VG, 2006 RH120, 2008 JL24, 2008 TC3, 2010 TD54, 2012 KT42)
3 Taxonomy (2008 TC3, 2010 TD54, 2012 KT42)
3 Radar Observations (2006 RH120, 2012 XB112, 2013 EC20)
Quality of Orbits
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The following plots were obtained from MPC orbit data for the 78 NEAs fainter than H of 28.5
Nearly 2/3rd were only observed for 2 days or less, nearly 1/3rd were followed for less than 1 day
Only 27 of the 78 have positional uncertainties less than ~1 million km.
Only 15 of the 78 have positional uncertainties less than ~1/4 of a million km
Only 3 have positional uncertainties less than ~14,000 km
NASA Headquarters – April 30, 2013
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Boulder Search Strategy
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The plot below compares the length of observations (in days) with the minimum delta-V for each
of the H > 28.5 objects
Note that the objects with the longest arcs of observations also have some of the lowest delta-Vs
• This is due to two reasons:
• One these objects were specifically observed because they have low delta-Vs
• Low delta-V objects spend a longer time in the vicinity of Earth due to their lower
relative velocity and, as a result, are observable for longer
• The take away …
• Instead of looking for every small
asteroid flying near cis-lunar
space, effort should be focused
on the low delta-V objects
• Search for temporary
captures
• Search for objects leading or
trailing Earth by a few
degrees
NASA Headquarters – April 30, 2013
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1999 RQ36 Semi-major Axis Drift Uncertainty
NASA Headquarters – April 30, 2013
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1999 RQ36 Semi-major Axis Uncertainty
NASA Headquarters – April 30, 2013
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