Current status of the asteroid explorer,Hayabusa2, leading up to arrival atasteroid Ryugu in 2018

June 7th, 2018
JAXA Hayabusa2 ProjectToday’s Topics
For the Hayabusa2 spacecraft:
・Completion of ion engine operation
・Optical navigation
・Future schedule2

Contents
０．Hayabusa2 mission overview
１．Current status and project schedule
２．Ion engine operation
３．Optical navigation
４．Mission schedule
５．Other topics
６．Future plans

3Overview of Hayabusa2
Objective
We will explore and sample the C-type asteroid Ryugu, which is a moreprimitive type than the S-type asteroid Itokawa that Hayabusa explored,and elucidate interactions between minerals, water, and organic matterin the primitive solar system. By doing so, we will learn about the origin
and evolution of Earth, the oceans, and life, and maintain and develop
the technologies for deep-space return exploration (as demonstratedwith Hayabusa), a field in 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 ofEarth 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 newchallenge of obtaining samples from a crater produced by an impacting
device.
・We will establish stable technologies for return exploration of solarsystem bodies.
Features:・World’s first sample return mission to a C-type asteroid.
・World’s first attempt at a rendezvous with an asteroid and performanceof observation before and after projectile impact from an impactor.
・Comparison with results from Hayabusa will allow deeper
understanding of the distribution, origins, and evolution of materials inthe solar system.

International positioning：
・Japan is a leader in the field of primitive body exploration, and visitinga type-C asteroid marks a new accomplishment.
・This mission builds on the originality and successes of the Hayabusa
mission. In addition to developing planetary science and solar system
exploration technologies in Japan, this mission develops new frontiersin exploration of primitive 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, andexpect further scientific findings through comparison and investigationof the results from both missions.

(Illustration: AkihiroIkeshita)
Hayabusa 2 primary specifications
MassLaunchMission
ArrivalEarth return
Stay at asteroid
Target body

Approx. 609 kg
3 Dec 2014
Asteroid return
2018
2020
Approx. 18 months
Near-Earth asteroid Ryugu

Primary instruments
Sampling mechanism, re-entry capsule, optical cameras, laser
altimeter, scientific observation equipment (near-infrared, thermalinfrared), impactor, small rovers

4Outline of mission flowLaunch
December 3rd, 2014

Asteroid arrival
June 27th, 2018 (planned)▲
Earth swing-by
December 3rd, 2015

Examination of asteroid via remote sensing
observations, followed by the release of
the small lander and rovers. Obtainsamples from the asteroid surface.
Return to Earth
End of 2020

Departure from the asteroid
November – December, 2019

Create artificial
craterSample analysis(Illustration: Akihiro

After confirming site safety,
touchdown to the crater tocollect subsurface material

Releaseimpactor
Create an artificial crater on
the asteroid surface using
an impact device.
5１. Current status andproject schedule
Current status：– The distance between Ryugu and the spacecraft is about 2100km as oftoday (June 7)– On June 3, ion engine operation was completed.
– Arrival at Ryugu is scheduled around June 27.
– Optical navigation is being used on the approach to Ryugu.
Schedule overview：
201512

Event3

Initialoperation2016
10 12

EDVEGA2017

2018

42019

2020

6 7approach
Journey to asteroid

swing-by12

12

Re-entry
Earth return

Asteroid proximity operations

launchEarth swing-by

Arrival at Ryugu

Departure from Ryugu

Capsule re-entry(Dec 3)(Dec 3)(Scheduled: June27)(Nov～Dec)(Late 2020)

ESA（MLG/WLH）
Southern hemisphere station
test operations
operations (CAN/MLG)(May 21- 22)
Oct
May

Ion engine operations ※Mar JunMarMay

Optical navigation
May Jul

NovAprJan

Jun

Interim period（Solar conjunction）
Dec Jan
TBD

TBD TBD

TBD

6

２．Ion engine operation• The third phase of ion engine operation began on January 10, 2018 and was completed onJune 3 at 14:59 JST. The velocity increase was 393 m/s.
• This completes the forward cruise ion engine operation.
• During the forward cruise, 24 kg of xenon propellant were consumed, leaving 42 kg remaining.
• Total increase in speed for the forward cruise is about 1015 m/s.
Thruster Hayabusa2 Hayabusa

History of thrust from the ion engine system (IES)Time averaged combined thrust (mN)

30

Cumulative
operation time(hours)

25

20

15

Total power
production(MN・s)

1050Jul
JanJulJan
Jul
JanJulJan
Jul
2014 2015 2015 2016 2016 2017 2017 2018 2018
MonthIncludes
operation test. Maximum thrust“IES” refers to (mN)
one or morethrusters

A6450

7B1112809

C5193

11989

D6418

14830

IES

6515

25590

Total

18073

39635

A

0.21740.0001B

0.00020.3221C

0.17350.2639D

0.2191

0.3613IES

0.6102

0.9474

A

10.03

7.42

B

7.61

8.36

C

10.08

8.30

D

10.16

7.95

IES

29.67

24.12

7

２．Ion engine operation• Experience from Hayabusa allowed the frequency of unplanned stops of ion
engine operation (from automatic safety procedures) to be greatly reduced andthe stable operation time improved via appropriate selection of the monitoring
settings.
– Hayabusa 68 times /25590 hours → average 376 hours– Hayabusa2 4 times /6515 hours→ average 1629 hours• Ground tracking time was reduced by 35% compared to Hayabusa, making
operation more efficient.
Ratio of ground tracking time to powered navigation time:– Hayabusa 5059 hours /25590 hours = 20%– Hayabusa2 850 hours / 6515 hours = 13%
A shortened “half-pass” for just four hours a day was frequently used while
operations 5 – 6 times a week were continued. This shortened time is due togood results from the spacecraft, including the ion engine operation andimprovements in the orbit determination technique from radio navigation.

8

２．Ion engine operation
Summary of forward cruise ion engine operation
Phase-3 ion engine
operations(2018.01.10–06.03)
Trajectory toRyugu
Hayabusa 2 orbit■Before swing-by
PeriodPhase-2 ion engine
operations(2016.11.22–2017.04.26）

SunEarthorbit■After swing-by

Δv
m/s

Timeh

IES operations test-−−

2015.03.03–21

IES Powered Navigation 1244409

2015.05.12–13

IES max. thrust test

3424

2015.06.02–06

IES Powered Navigation 2211102

2015.09.01–2

IES Powered Navigation 32

1. 3

12IES：ion engine system

Phase-1 ion engine operations(2016.03.22–05.21, incl. addedburns)

Earth swing-by(2015.12.03)

No. ofthrusters

Initial check

Launch(2014.12.03)

Arrive atRyugu(Jun–Jul2018)

Name

PeriodName

No. of thrusters

Δv
m/s

Time

2016/3/22〜2016/5/21

Phase 1: Ion engine operation

3（2 at times）

127798 h

2016/11/22〜
2017/4/26

Phase 2: ion engine

3（2 at times）

435

2558 2593

Phase 3: ion engine

2→3

393

2426 2475

Because there was adifferent between theinitially reported value
and the engineering
database stored value

2018/6/7
correction

9３．Optical navigation• Optical navigation (precisely “hybrid navigation using optical andradiometric observations”) is a method of approaching a target celestial
body using a camera (or similar device) mounted on a spacecraft.
• This technique is essential for Hayabusa2 to arrive at Ryugu.
• Radio navigation alone is not precise enough to arrive at the 1km
asteroid Ryugu at a distance of 300 million km from Earth.
Reason：The error in the Ryugu’s position was about 220km at thebeginning of May 2018. (Error of 3σ or 99.7％ probability.)
Note：The position of the spacecraft can be estimated within an errorof several km from a 300 million km distance by a techniquecalled DDOR (Delta Differential One-way Range).
※ DDOR technology was not used in the case of Hayabusa, so the error on thespacecraft position was big. However, radar observations of Itokawa were possible,
so the asteroid orbit was more accurately known. This meant that it was necessary
for us to use optical navigation for Hayabusa to arrive at Itokawa.
10

３．Optical navigation
Optical navigation using the STT (Star Tracker)•In May, ion engine operation
was ongoing, making it
impossible to point the Optical
Navigation Camera at Ryugu.
Instead, an image of Ryugu
was attempted with the StarTracker, which is usually used
to determine the orientation ofthe spacecraft.

•From the position of Ryugu
imaged, more accurate orbitsof the spacecraft and asteroid
were estimated.

•The distance from thespacecraft to Ryugu is about
70,000km and the asteroid
has the brightness of a 5th
magnitude star.
Photograph of Ryugu using the Star Tracker. From the right, the images were taken at around 01:00 on May 12,
02:00 on May 13 and 01:00 on May 14 (JST). These are taken from the spacecraft in the direction of Pisces.
("Psc" is an abbreviation of Pisces.) The field of view is 9°×7°. (Image credit: JAXA, Kyoto University, Japan
Spaceguard Association, Seoul National University.)
11

３．Optical navigation
Optical navigation using the ONC (Optical Navigation)
・From June 5, the ONC (T and W1)
photographed Ryugu to attempt
optical navigation.
・The picture on the right was taken
on June 6, around 04:15 JST in thedirection of Ryugu.
・The distance to Ryugu is about2600km.
・The brightness of Ryugu is about -5magnitudes.
・Because the exposure time was aslong as 178 seconds, Ryugu isbright and blurred (the purpose wasto image the background stars.)
Ryugu imaged by the ONC-T. The photograph was taken around 04:15 JST on June 6, 2018. The field of view is 6.3 degrees x 6.3 degrees.
Exposure time is 178 seconds. Ryugu is located in the constellation of Gemini （Gem).
Ground observation team: JAXA, Kyoto University, Japan Spaceguard Association, Seoul National University.
ONC team: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University,
University of Aizu, AIST

12３．Optical navigation
Optical navigation using the ONC (Optical Navigation)
・Image with an exposure time ofabout 0.09 seconds.
・Only asteroids appear as points.
・The image is about 3 pixels indiameter.
1 pixel = about 22 arc seconds= about 0.3 km@2600km
・The shape is still unknown.

Ryugu imaged by the ONC-T. The photograph was taken around 04:15 JST on June 6, 2018. The field of view is 6.3 degrees x 6.3 degrees.
Exposure time is approximately 0.09 seconds.
Ground observation team: JAXA, Kyoto University, Japan Spaceguard Association, Seoul National University.
ONC team: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University,
University of Aizu, AIST

13

４．Mission schedule
Most recent operations:• June 3: Start of asteroid approachContinue optical navigation until asteroid arrival
A detailed report will be available at the press briefing on June 14• Arrival at Ryugu is scheduled for around June 27 (this mayvary by several days, depending on actual operations).
Operations in the asteroid vicinity:• The exact schedule will be determined by observations
between June – August.
• The schedule at the present time is shown on the next slide.
14

４．Mission schedule
Provisional version
YearMonth, day

EventStatus

2018

January 10
June 3June 3June 27
End of July
AugustSept - Oct
Sept - Oct
Nov - Dec
January
FebruaryMar - Apr
Apr - MayJuly
Aug - Nov
Nov - Dec

Third stage of ion engine operation begins
Ion engine operation ends
Start of asteroid approach (distance: 3100km）
Arrival at asteroid Ryugu (altitude 20km）
Medium altitude observations #1（alt. 5km）
Decent to measure gravity （alt.1km）
Period for touchdown operation #1
Period for rover deployment #1
Solar conjunction (communication unavailable)
Medium altitude observations #2（alt. 5km）
Period for touchdown operation #2
Crater generation operation
Period for touchdown operation #3
Period for rover deployment #2
Remain near asteroid
Departure from asteroid

Complete
Complete
Complete
Planning
Planning
Planning
Planning
Planning
Planning
Planning
Planning
Planning
Planning
Planning
Planning
Planning

2019

This schedule may be changed for multiple factors after arrival at Ryugu. Please note
therefore, that the situation is not fixed, except where marked ‘Complete’.

15５．OtherOutreach & other activities■“Imagining Ryugu” contest• 18 domestic nodes, 7 from overseas• Number of submissions：
1819 domestic (unreported nodes: 1)
150 overseas (unreported nodes: 1)• Project members also created imaginary suggestions.
(In Japanese: http://www.hayabusa2.jaxa.jp/topics/20180605/)■Hayabusa2 “ask any question” box (Japan Planetary Society)• We am to collect as many possible questions and answers forthe project, so that as many people as possible can know
about Hayabsua2.
(In Japanese: http://planetary.jp/hayabusa2/FAQ/index.html)
16

６．Future plans
Media correspondence, information disclosure：• Next press conference is scheduled for the morning of June 14(@ the Tokyo Office).
• Arrival at 20km above Ryugu is scheduled for around June 27.
At this time, a press release will be posted and press briefing (@the Sagamihara campus) will be scheduled.
• We plan to hold regular press briefings after July.
• The spokespeople for the Hayabusa2 Project are Professor
Kobota and Associate Professor Yoshikawa, JAXA Institute ofSpace and Astronautical Sciences. They will accept interview
requests regarding Hayabusa2.

17

Reference material18Primary spacecraft components
Deployable camera(DCAM3)

X-bandhigh-gain
antenna

Solar array paddle

X-band lowgain antenna
X-band midgain antenna
Ka-band highgain antenna

Optical navigation
Lasercamera, ONC-T altimeter,
LIDAR

Near-infrared
spectrometer,
NIRS3

Thermalinfrared camera,
TIR

Scientific observation equipment
Star trackers

Ion engine

Near-infrared spectrometer(NIRS3)

RCS thrusters
Optical navigation
cameraONC-T, ONC-W1Re-entry capsule
Laser altimeter
Optical(LIDAR)
navigation
camera ONCSmall lander & rovers
W2Sampler horn

MASCOT

Minerva ２II-1A
Built by DLR andCNES

II1B

MASCOT lander

II-2

II-1: By the JAXA Minerva-II teamII-2: By Tohoku Univ. & the Minerva-II
Consortium

Minerva-II rovers

Thermal infrared
camera(TIR)
Small carry-on impactor (SCI)
Target markers × 5

Size： 1 ×1. 6×1. 25 m (main body)
Solar paddle deployed width 6m
Mass ： 609 kg (incl. fuel)19Electric propulsion (ion engine)• Name: μ10
Microwave discharge-type ion engine with 10cm
diameterThis was named after the ISAS mu rocket.
• Converts xenon* into plasma (ions), which isaccelerated by applying a voltage.
• A microwave discharge system is used to generateions.

• Four units are mounted, and simultaneous
operation of three generates thrusts of up to 30mN.

Injection test in a flight model
vacuum chamber• Approximately 66 kg of loaded xenon fuel, allowing
a velocity increase of up to 2 km/s.

• Usedalter
trajectories when cruising from Earth*Whywetouse
xenon
to the isasteroidand back.
• Xenona monoatomic
molecule, so its ionization

voltage is smaller than that of gas comprising of two
or more atoms. This increases the ratio of addedenergy that is used for acceleration.

• It is easy to fill the tank at high density (density 1.2– 1.5)
• Reactivity is lower than that of other substances.
• Mass (atomic weight) is large, improving theefficiency of acceleration.

Hayabusa2 ion engine
20

Reference: How ion engines work[[Translation onnext slide]]

Source: Dynamic Navigation withIon Engines (Space Engineering
Series 8), Corona Publishing (2006)
DC discharge
methodDifferent ion generation systems

Cathode forthermionic emission
Note: The ion engine developed in the U.S., the U.
K. and the former NASDA was a DC discharge
Kaufman-type ion engine or a Ring-Cusped ion

Microwave discharge
methodMicrowave generator
Note: The ion engine developed at the ISAS in Japanis a microwave discharge-type ion engine.

21

Electrostatic
acceleration

Ion
production

Neutralization

Propellant
PlasmaDischarge

Neutralizer
PlasmaThrust rate

Propellant
Discharge
Ion source

Screen grid

Acceleration
grid

DecelerationgridPotential22

Remote sensing equipment
Optical Navigation Camera (ONC）

ONC-T (telephoto)

Thermal Infrared Camera (TIR）

ONC-W1,W2 (wide-angle)

Imaging for scientific observation and navigation

Near-infrared Spectrometer (NIRS3）

Infrared spectra including the 3-μm band:
investigates mineral distributions on the asteroid
surface

8–12 μm imaging: Measures asteroid surface temperature

Laser Altimeter (LIDAR）

Measures distance between the asteroid and the spacecraft
in a range of 30 m–25 km23

Optical Navigation Camera (ONC）
ONC：Optical Navigation CameraObjective: Images fixed stars and thetarget asteroid for spacecraft guidanceand scientific measurements
Scientific measurements：• Form and motion of the asteroid:
Diameter, volume, direction of inertial
principal axis, nutation• Global observations of surface topography
Craters, structural topography, rubble,
regolith distribution• Global observations of spectroscopic properties
of surface materials
Hydrous mineral distribution, distribution oforganic matter, degree of space weathering• High-resolution imaging near the sampling point
Size, form, degree of bonding, andheterogeneity of surface particles;
observation of sampler projectiles and surface
markings• Elucidation of features of target
asteroid• Distribution of hydrous minerals
and organic matter, space
weathering, boulders• Sampling site selection• Basic information on where tocollect asteroid samples• Ascertaining sample state• High-resolution imaging ofsampling sites

W1
FoV
T
FoV

ONC-T

ONC-W1

ONC-W2

2D Si-CCD (1024 × 1024 px)

Detector
Viewing
direction

Downward (telephoto)

Viewingangle

6.35° × 6.35°

65.24° × 65.24°

100 m–∞

1 m–∞

Focal length

Downward (wideangle)

Sideward (wideangle)

Spatialresolution

1 m/px @ 10-km alt.
1 cm/px @100-m alt.

10 m/px @10-km alt.
1 mm/px @1-m alt.

Observation
wavelength

390, 480, 550, 700, 860,950, 589.5 nm, and wide

485–655 nm

24

Asteroid Ryugu
Orbit of Ryugu
Name: Ryugu

Permanent designation : 162173
Provisional designation : 1999 JU3Discovered: May 1999

Size

: Approx. 900 m

Shape: Nearly spherical

Rotation period: approx. 7 h 38 min

Rotation orientation: Ecliptic longitude λ= 310°–340°
Ecliptic latitude β= –40°±–15°

Reflectivity: 0.05 (blackish)Type: C type (assumed to comprisematerials containing water andorganics)

Orbital radius: Approx. 180,000,000 km

Orbital period: Approx. 1.3 yr

Density and mass

: Density is currently unknown, but
presumed to be 0.5–4.0 g/cm3: Mass is approx. 1.7 × 1011 kg –1.4×1012 kg.

Estimated shape(by T. Mueller）

25