Asteroid explorer, Hayabusa2,reporter briefing

June 11, 2020
JAXA Hayabusa2 ProjectTopics
Regarding Hayabusa2,
Current trajectory plan
Status of the second ion engine operation
Recent scientific paper publications

2020/6/11

Hayabusa2 reporter briefing

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Contents
0. Hayabusa2 and mission flow outline
1. Current status and overall schedule of the project
2. Current trajectory plan
3. Status of the 2nd ion engine operation
4. ONC photometric observations of Ryugu
5. Estimate of the thermophysical properties of Ryugu with the TIR
6. Future plans

2020/6/11

Hayabusa2 reporter briefing

3Overview of Hayabusa2
Objective
We will explore and sample the C-type asteroid Ryugu, which is a more primitive type than the S-type asteroid
Itokawa that Hayabusa explored, and elucidate interactions between minerals, water, and organic matter in theprimitive solar system. By doing so, we will learn about the origin and evolution of Earth, the oceans, and life, andmaintain and develop the technologies for deep-space return exploration (as demonstrated with Hayabusa), a fieldin which Japan leads the world.
Expected results and effects
By exploring a C-type asteroid, which is rich in water and organic materials, we will clarify interactions between
the building blocks of Earth and the evolution of its oceans and life, thereby developing solar system science.
 Japan will further its worldwide lead in this field by taking on the new challenge of obtaining samples from acrater produced by an impacting device.
We will establish stable technologies for return exploration of solar-system bodies.
Features:World’s first sample return mission to a C-type asteroid.
World’s first attempt at a rendezvous with an asteroid and performance of observation before and after projectile
impact from an impactor.
Comparison with results from Hayabusa will allow deeper understanding of the distribution, origins, andevolution of materials in the solar system.
International positioningJapan is a leader in the field of primitive body exploration, and visiting a type-C asteroid marks a newaccomplishment.
This mission builds on the originality and successes of the Hayabusa mission. In addition to developing planetaryscience and solar system exploration technologies in Japan, this mission develops new frontiers in exploration ofprimitive heavenly bodies.
NASA too is conducting an asteroid sample return mission, OSIRIS-REx (launch: 2016; asteroid arrival: 2018;
Earth return: 2023). We will exchange samples and otherwise promote scientific exchange, and expect furtherscientific findings through comparison and investigation of the results from both missions.

2020/6/11

Hayabusa2 reporter briefing

Hayabusa 2 primary specifications(Illustration: Akihiro Ikeshita)
MassApprox. 609 kg
Launch3 Dec 2014
MissionAsteroid returnArrival
27 June 2018
Earth return2020
Stay at asteroid Approx. 18 months
Target body
Near-Earth asteroid Ryugu
Primary instruments
Sampling mechanism, re-entry capsule, optical cameras, laser
range-finder, scientific observation equipment (near-infrared,thermal infrared), impactor, miniature rovers.

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Mission flow
LaunchDec 3, 2014

Earth swing-by
Dec 3, 2015

MINERVA-II-1 separation
Sep 21, 2018

Ryugu arrival
June 27, 2018

Target marker
separation
Oct 25, 2018

Ryugudeparture
Nov 13, 2019

Targetmarker
complete
End of 2020
MINERVA-II2 separation
separation
Sept. 17,
(image credit: illustrations including spacecraft
Oct. 3, 20192019
by Akihiro Ikeshita, others by JAXA)

Earth return

2020/2/20

MASCOT
separation
Oct 3, 2018

Secondtouchdown
July 11, 2019

Targetmarker
separation
May 30,2019

Hayabusa2 reporter briefing

Impactor (SCI)
5 April, 2019

First touchdown
Feb 22, 20195

1. Current project status & schedule overview
Current
status:– The 2nd ion engine operation began on May 12.
– Operations continue as planned, while precautions are in place to prevent the spread of
the new coronavirus infection.
– Discussions continue with Australia regarding capsule retrieval.
2015

Scheduleoverview

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2020/6/11

Hayabusa2 reporter briefing

6Earth equatorial plane
coordinate system

2. Current Trajectory Plan
Earth orbit
Ryugu departure2019/11/13)

1 ion engine
operation(deceleration)

Red arrow ion engine acceleration direction     

1.3 million km
2.1 million km(passing the alphelion during the return trip on May 9)

Ryugu distance
2.64 million km
Flight speed
23.0 km/s
Total flight distance 48.6 billion km
380 million km remaining
Return trip ion engine use 42% complete

6/11

st2020/6/11

Earth return2020/1112)

6/11 current orbit
Earth distanceSun distance

2nd ion engine
operation(acceleration)

Earth equatorial plane
coordinate system

The 1st ion engine operation was in the deceleration
direction for timing adjustments. In the 2nd operation,ions were injected in the acceleration direction for
final precision guidance.

Hayabusa2 reporter briefing

7Rad4iu smillion

2. Current Trajectory PlankmRad1
iu s.

4moilli

Rankdm1
iu smoilli

nkm

The plane containing
the Earth is used as a“target” to guide
Hayabusa2 to the Earth

Solid line: Hayabusa2 flight path
(Route when orbit is controlled)

2nd ion engine
operation period
Dotted line: Ballistic flight path(virtual path without orbit control)[Conceptual diagram of the return
trajectory control]     
2020/6/11

1st ion engine
operation period• The 1st ion engine operation changed to an orbit
where the closest approach to Earth was 1.4
million km, compared with the previous 4 millionkm.
• The 2nd ion engine operation plans to change theclosest distance from 1.4 million km → 10,000
km or less (orbit passes just beyond the edge ofthe Earth).
• 2nd ion engine plan: By the end of August, therequired injection amount will be exhausted andthe ion engine temporarily stopped. The precise
orbit will be measured, and precise orbit
adjustments with the ion engine will be performed
for about 1 week.
• All Hayabusa2 ion engine operations will becomplete by the end of September.

Hayabusa2 reporter briefing8

3. 2nd ion engine operation status••••

In the 1st ion engine operation for return phase, 881 hours of powered navigation and ⊿V=100m/s were achieved
from Nov. 20, 2019 – Feb. 20, 2020 over a total of 7396 hours of flight.
From May 12, 2020, the 2nd ion operation began.
Currently, 1 ion engine is operating with a trust of about 9.7 mN. From August, the operation will be increased to 2.
Between May – September, the total operating time will be 2014 hours with ⊿V=160m/s, and this is expected tocomplete the operation.
About 3.5kg of xenon propellent will be consumed. As of the end of September, about 35 kg –about 55%-- remains.

*IPPU=ion engine power supply
2020/6/11

    
Hayabusa2 reporter briefing94. ONC photometric observations of Ryugu“Global photometric properties of (162173) Ryugu”
Tatsumi et al. (2020) Astronomy & Astrophysics

••
•
•
•

Summary of the results from Ryugu photometric observations with the ONC over about half ayear between 2018/07-2019/01.
Comparing ground-based and ONC observations, the calibration accuracy of ONC was shown tobe high as the two observation sets agree within the error range.
The global reflectance map reveals the inhomogeneity in the reflectance of Ryugu.
Results suggest the average geometric albedo of Ryugu is 4.0±0.5%, the standard reflectance isa dark 1.87±0.14% and the carbon content is as high as >2wt.%.
A weak phase reddening (surface reddening with the increase of the phase angle) was confirmedwith Ryugu. This suggests fine particles are present on the surface. The same degree of phasereddening was also confirm with Bennu, suggesting surface conditions may be similar.

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Hayabusa2 reporter briefing10

4. ONC photometric observations of Ryugu
Ryugu

Phaseangle

Sun

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Earth• The photometric function and reflectance(albedo) were obtained from Ryugu
observations with the ONC for about half ayear between 2018/07-2019/01.
→ Reflectivity depended on illuminationand observation angle, so observations
under a wide range of angle conditions werenecessary.
• By changing the positional relationshipbetween the Sun and Earth, Ryugu could beobserved over a wide range of phase angles.
• This is clue to the asteroid surface
conditions.
Hayabusa2 reporter briefing11

4. ONC photometric observations of Ryugu
Ryugu photometric function

Reflectivity

Ryugu

Phaseangle

Sun

2020/6/11

EarthPhase angledegColorONC observationGreyground observation
Tatsumi et al. (2020)
Hayabusa2 reporter briefing12

4. ONC photometric observations of Ryugu•

Global standard reflectance (albedo) map of Ryugu created from ONC observations

Tatsumi et al. (2020)
2020/6/11

Hayabusa2 reporter briefing13

4. ONC photometric observations of Ryugu••

Comparison of ONC and groundobservations show agreement of the spectraof Ryugu within error range.
→ONC calibration accuracy guarantee
Geometric albedo*: 4.0±0.5%Standard reflectance**(REFF(30,0,30)):1.87±0.14%→Consistent with thermal metamorphic
carbonaceous meteorites, carbon content
expected to be >2wt.%*Reflectance value when light is applied from the front andreflectance measured from the front.
**Reflectance when light shines from a direction tilted at 30 deg
from the front and reflectance when brightness aimed fromthe front.

2020/6/11

Thermally modified carbonaceous meteorites sample

Darker indicatesmore
carbonRyugu
Carbon content (wt.%) powderchip
Cloutis et al. (2012)

Hayabusa2 reporter briefing

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4. ONC photometric observations of Ryugu• The surface of Ryugu is observed to becomeslightly redder as the phase angle increased
phase reddening).
– Suggests the existence of fine particle about
the size of that wavelength length.
– Shows multiple light scattering on thecelestial surface. However, this effect ismuch weaker than that on Itokawa.
– Phase reddening is similar to that on Bennu→ the surface reflection may have similar
characteristics.
2020/6/11

Hayabusa2 reporter briefing

Tatsumi et al. (2020)15

5. Thermophysical property estimates of Ryugu with the TIR“Thermophysical properties of the surface of asteroid 162173
Ryugu: Infrared observations and thermal inertia mapping”
Shimaki et al. (2020) Icarus 348, 113835

https://doi.org/10.1016/j.icarus.2020.113835 Posted2020/5/16• Distributions of thermal inertia and roughness of Ryugu were estimated using
TIR observations from 2018/8/1 and a thermal model calculation of the unevensurface.
• The thermal inertia of Ryugu was found to be uniformly low, and porous
boulders were scattered evenly across the entire surface.
• The surface of Ryugu was found to be as rough as ‘A‘ā lava.
• The obtained thermal inertia and unevenness have a significant influence on thecalculation of Ryugu’s orbital evolution.

ʻAʻā lava by Rina Nogouchi Ryugu is uneven on scales of several meters square, ʻAʻā lava is uneven over several tens of centimeters square.

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Hayabusa2 reporter briefing16

5. Thermophysical property estimates of Ryugu with the TIR
From the thermal images with TIR and the thermal model calculation of the unevensurface, the effect of the roughness on the surface temperature was demonstrated.

From this side, the
ground appears cool
(evening)
Unevensurface

Fromthis side,thegroundappears warm(noon)

S
undire ctio n•Warm(Sunfacing)
Cool(shadowed)

Roughness effect©JAXAChiba Institute of Technology

2020/6/11

Thermography of Ryugu on 2018/8/1
from Shimaki+, Icarus 2020

Hayabusa2 reporter briefing

a Temperature history without using the TIR and uneven
thermal model calculation TPM1b Temperature history
using the uneven thermal model calculationTPM2. Γ and σ
are thermal inertia and unevenness, respectively.
From Shimaki+, Icarus 2020

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5. Thermophysical property estimates of Ryugu with the TIR•••

Roughness effectpredicted from ground and flyby observations. With hovering observations & 2D imaging, high time and spatial
resolution (4.5m) achieved.
Global thermal inertia22545 J m-2 s-0.5 K-1 tiu 300100 tiu, Okada+, Nature 2020 → Porous boulders scattered evenly overthe surface. -- Dense rocks (basalt etc) >2000 tiu porous carbonaceous chondrites 600-1000 tiu
Global irregularity RMS surface slope 475, similar to ʻAʻā lavasmall at equatorial ridge → evidence suggests mass transfer
between equator and mid-latitude.  Ryugu is uneven on scales of several meters square, ʻAʻā lava is uneven over several tens of centimeters square

Left Ryugu thermal inertia map.  mark the main craters.Right Ryugu roughness map. modified from Shimaki+, Icarus 2020

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Hayabusa2 reporter briefing18

5. Thermophysical property estimates of Ryugu with the TIR
モモタロウ クレーター
キビダンゴ クレーター

キンタロウ クレーター• Large craterThermal inertia
similar to the global average→ No evidence of collisionejecta deposits or consolidation• Large boulderThermal inertia
can be lower than the globalaverage.
→ Suggests low-density,“rubble”-like structure.

熱慣性ONC 画像

ウラシマ クレーター. b2500. b1

凹凸度

00.5

Yarkovsky effect©JAXAChiba
Institute of Technology

0Large crater and boulder images with ONC, thermal inertia
and roughness. Shimaki+, Icarus 2020

2020/6/11

Hayabusa2 reporter briefing• Ripple effect The obtained
thermal inertia and roughness
influences the Yarkovsky effect(orbit change) and YORP effect(rotation speed change)→ significant impact on thecalculation for Ryugu’s orbitalevolution.

196. Future plans
Operation schedule
2020/5/12 2nd ion engine operation
Press & media briefings
2020/7TBD)
Press briefing TBD

2020/6/11

Hayabusa2 reporter briefing

20Reference material

2020/6/11

Hayabusa2 reporter briefing

21Return cruise operation plan
Return phase orbit map��������� ���������� �������� ��������������������������������������F����� ��������������������������������������������DF�������������������� ��������������� ���������E������������F    
2020/6/11

Hayabusa2 reporter briefing��� ��������������������E������������D ������������F
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Electric propulsion (ion engine)• Name: µ10• Converts xenon* into plasma (ions), which is accelerated by applying voltage.
• A microwave discharge system is used to generate ions.
• Four units are mounted, and simultaneous operation of three generates thrusts of up to 28 mN.
• Approximately 60 kg of loaded xenon fuel, allowing acceleration up to 2 km/s.
• It is used to alter trajectories when cruising from Earth to the asteroid and back.

Injection test  a flight model ina vacuum chamber*Why we use xenon• Xenon is a monoatomic molecule, so its ionization voltage is smaller than that of gasses
comprising two or more atoms. This increases the ratio of added energy that is used foracceleration.
• Reactivity is lower than that of other substances.
• Mass (atomic weight) is large, improving the efficiency of acceleration.
Hayabusa 2 ion engine

2020/6/11

Hayabusa2 reporter briefing(© JAXA)
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Referencehow the ion engines work

IPPU(ion engine power supply)
Fig: Schematic diagram of microwave discharge type ion engine  
2020/6/11

Fig: System diagram of microwave discharge type ion engine                   Hayabusa2 reporter briefing         

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1st ion engine operation results

Ion engine operation history after leaving Ryugu (2019.11.20 – 2020.2.20)

Average generated thrust (mN)

11/13
Good-bye Ryugu

2020/6/11

Commissioning
11/20~28

1st return phase
IES operation 12/3~2/3

3 engine operationCommissioning Orbit determination
2/4
trim operation

2 engine 

1 engineDecrease in number due to increase in solar distance

Hayabusa2 reporter briefing

25Optical navigation camera (ONC)               
ONC-W1ONC-W2

2D Si-CCD (1024 x 1024 px)

DetectorONC-T

Objective: Images fixed stars and the target asteroidfor spacecraft guidance and scientific measurements

Viewing direction

Down (telephoto)

Down(wide)

Viewing angle

6.35  6.35

65.24 65.24



Focal length

100m∞

1m∞"!

Side (wide)

Spatial resolution

1m/pix@alt. 10km
1cm/pix@alt. 100m

Observation
wavelength

color (390 480
550 700 860 950 monochromatic (485nm#655nm)
589.5nm Wide)

2020/6/11

10m/pix @alt.10km
1mm/pix @alt.1m

Hayabusa2 reporter briefing

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Thermal Infrared Imager6TIR

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#4 ")!#52 #4 ") #5#&')*'45Temperature [K]The surface temperature of the asteroid changes
over the day, rising in sunlight and decreasing atnight. Diurnal change in surface temperature islarge in fine soils like sand and highly porous rock,'and small in dense rock. We will examine thephysical state of the asteroid’s surface by 2D
imaging (thermography) of thermal radiation from $
the asteroid.
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