Upload
haven
View
56
Download
0
Tags:
Embed Size (px)
DESCRIPTION
OSIRIS -REx Status Report (and What We’ve Learned about Bennu). Carl Hergenrother Asteroid Astronomy Lead SBAG – 2013 July 11 . Recent Accomplishments. TAGSAM microgravity testing @ JSC Mission “upgraded” to Category 1 2012 DA14 flyby and Chelyabinsk media events - PowerPoint PPT Presentation
Citation preview
NASA Headquarters – April 30, 2013 1
OSIRIS-REx Status Report(and What We’ve Learned
about Bennu)
Carl HergenrotherAsteroid Astronomy LeadSBAG – 2013 July 11
NASA Headquarters – April 30, 2013 2
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
NASA Headquarters – April 30, 2013 3
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
NASA Headquarters – April 30, 2013 4
INITIAL CHARACTERIZATION: 1999
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
10
12
14
16
18
20
22
24
Bennu
Date
Visu
al M
agni
tude
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
NASA Headquarters – April 30, 2013 5
REACQUISITION AND PHYSICAL CHARACTERIZATION: 2005
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
10
12
14
16
18
20
22
24
Bennu
Date
Visu
al M
agni
tude
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
NASA Headquarters – April 30, 2013 6
FINAL CAMPAIGN: 2007 - 2012
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
10
12
14
16
18
20
22
24
Bennu
Date
Visu
al M
agni
tude
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
NASA Headquarters – April 30, 2013 7
Jun-05Jul-0
5
Sep-05
Oct-05
Dec-05
Feb-06
Mar-06
May-06
Jul-06
1E-03
1E-02
1E-01
1E+00
1E+01
1E+02
Date
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
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08
Date
Unce
rtian
ty in
Sem
i-maj
or A
xis (
km)
Follow-up∆a = 20,500 km
Reacquisition∆a = 4 km
Second Radar∆a = 100 m
Obs. at opposition∆a = 15 m
NASA Headquarters – April 30, 2013 8
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
NASA Headquarters – April 30, 2013 9
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
NASA Headquarters – April 30, 2013 10
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 11
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 12
Backup Charts
NASA Headquarters – April 30, 2013 13
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
NASA Headquarters – April 30, 2013 14
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
NASA Headquarters – April 30, 2013 15
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
NASA Headquarters – April 30, 2013 16
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˚
NASA Headquarters – April 30, 2013 17
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
17
NASA Headquarters – April 30, 2013 18
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 19
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
NASA Headquarters – April 30, 2013 20
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 21
TAGSAM – THE OSIRIS-REX SAMPLING STRATEGY IS DESIGNED TO COLLECT ABUNDANT PRISTINE
REGOLITH
NASA Headquarters – April 30, 2013 22
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
NASA Headquarters – April 30, 2013 23
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
NASA Headquarters – April 30, 2013 24
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)
NASA Headquarters – April 30, 2013 25
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 26
OUR DESIGN REFERENCE MISSION PROVIDES SUBSTANTIAL OPERATIONAL MARGIN
NASA Headquarters – April 30, 2013 27
Phase Function for 1999 RQ36
NASA Headquarters – April 30, 2013 28
Finding a Boulder in Space
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
20
22
24
26
28
30
32
34
10-m Boulder Apparent Magnitude
Date
Visu
al M
agni
tude
Catalina Sky SurveyDetection limit(Mt. Lemmon)
NASA Headquarters – April 30, 2013 29
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)
NASA Headquarters – April 30, 2013 30
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
NASA Headquarters – April 30, 2013 31
• 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
NASA Headquarters – April 30, 2013 32
1999 RQ36 Semi-major Axis Drift Uncertainty
NASA Headquarters – April 30, 2013 33
1999 RQ36 Semi-major Axis Uncertainty