OSIRIS -REx Status Report (and What We’ve Learned about Bennu)

NASA Headquarters – April 30, 2013 1

OSIRIS-REx Status Report(and What We’ve Learned

about Bennu)

Carl HergenrotherAsteroid Astronomy LeadSBAG – 2013 July 11


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

OSIRIS-REx Science Team Meeting #4 – June 18-20, 2013 2

Recent Accomplishments


Asteroid (101955) 1999 RQ36 is now . . .

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

Image credit:http://www.touregypt.net


INITIAL CHARACTERIZATION: 1999

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

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Bennu

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LINEAR Detection limit

Discovery: Sept 11, 1999 by the LINEAR survey

Follow-up: ~200 astrometric observations between Sept 12 – 24, 1999

Radar: Arecibo and Goldstone observations from Sept 21 – 25, 1999

Visible Spectroscopy: McDonald Observatory for 5 nights in September 1999


REACQUISITION AND PHYSICAL CHARACTERIZATION: 2005

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

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Bennu

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Catalina Sky SurveyDetection limit(Mt. Lemmon)

Reacquisition: 71 observations between Aug 8 – Sept 17, 2005

Vis-IR Spectroscopy: NASA IRTF observations on Sept 4, 2005

Photometry: Lightcurve and ECAS colors on Sept 14 – 17, 2005

Radar: observations fromSept 16 – Oct 2, 2005


FINAL CAMPAIGN: 2007 - 2012

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

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Bennu

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Thermal IR: Spitzer observations on May, 2007 and Aug., 2012

Radar: Further Arecibo observations in Sept, 2011

Phase function: Photometric measurements through May, 2012

Light Curve: Hubble-WFC3observations in Sept. andDec., 2012


Jun-05Jul-0

5

Sep-05

Oct-05

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1E-03

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A QUALITY ORBIT REQUIRES EXTENSIVE OBSERVATION

Discovery∆a = 376,000 km

First Radar∆a = 43 km

9/10/99 9/15/99 9/20/99 9/25/99 9/30/99 10/5/991E+01

1E+02

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1E+08

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Unce

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km)

Follow-up∆a = 20,500 km

Reacquisition∆a = 4 km

Second Radar∆a = 100 m

Obs. at opposition∆a = 15 m


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 three-dimensional model and define the rotation state• Size = 492-m (±20 m, mean diameter) • Shape = spheroidal “spinning top” • Rotation state = 4.29 hr period, 180º

obliquity Radar also probed the near-

surface bulk density (1.7 g cm-3) and structural scales larger than a few centimeters


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 B-type 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


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%


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


Backup Charts


THERMAL IR OBSERVATIONS PROVIDE CRITICAL KNOWLEDGE FOR SPACECRAFT DESIGN

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


MISSION DESIGN CONSTRAINTS 2: SIZE AND ROTATION

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• Rapid rotation greatly increase the

risk during proximity operations • Centrifugal forces have also likely

ejected most regolith particles from the surface

Lightcurve reveals a rotation period of 4.297 0.002 hours


OSIRIS REX IS DEVELOPING CRITICAL ‐TECHNOLOGIES FOR EXPLORING NEAR EARTH ‐

ASTEROIDS

Without guidance With guidance

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


MISSION DESIGN CONSTRAINTS 1: ORBIT

Use of solar power: aphelion < 1.6 AU Thermal constraints: perihelion > 0.8 AU

These two requirements constrain both the semi-major axis and the orbital eccentricity of the target

Mission propellant and sample return capsule (SRC) performance requirements: inclinations <10˚ 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 Note: Bennu inclination = 6.03˚


KNOWLEDGE OF ASTEROID MASS SUBSTANTIALLY ENHANCES MISSION PLANNING

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


STUDY OF THIS POTENTIALLY HAZARDOUS ASTEROID IS STRATEGICALLY IMPORTANT

1999 RQ36 is classified as a potentially hazardous object• 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


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


TAGSAM – THE OSIRIS-REX SAMPLING STRATEGY IS DESIGNED TO COLLECT ABUNDANT PRISTINE

REGOLITH


Mission Timeline

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


OUR SAMPLE IS COLLECTED DURING A FIVE-SECOND TOUCH-AND-GO MANEUVER

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


OUR PAYLOAD PERFORMS EXTENSIVE CHARACTERIZATION AT GLOBAL AND SAMPLE-SITE-

SPECIFIC SCALES

PolyCam acquires 1999 RQ36 from >500K-km range, performs star-field OpNav, and performs high-resolution imaging of the surface

MapCam provides landmark-tracking OpNav, performs filter photometry, maps the surface, and images the sample site

OLA (CSA) provides ranging data out to 7 km and maps the asteroid shape and surface topography

SamCam images the sample site, documents sample acquisition, and images TAGSAM to evaluate sampling success

OCAMS (UA)


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


OUR DESIGN REFERENCE MISSION PROVIDES SUBSTANTIAL OPERATIONAL MARGIN


Phase Function for 1999 RQ36


Finding a Boulder in Space

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

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10-m Boulder Apparent Magnitude

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Catalina Sky SurveyDetection limit(Mt. Lemmon)


Carbonaceous Boulder Statistics

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)


Asteroid Boulder Orbits

Of the 78 only 8 have been characterized in any way 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 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


• 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

Boulder Search Strategy


1999 RQ36 Semi-major Axis Drift Uncertainty


1999 RQ36 Semi-major Axis Uncertainty

OSIRIS -REx Status Report (and What We’ve Learned about Bennu)

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