Outline of the operation ofMINERVA-II2 (Rover 2) deployment
Sep. 24 (Tue) 2019

Prof. Kazuya Yoshida
Tohoku University(University Consortium for MINERVA-Ⅱ2 Development)

Micro-Rovers and Landers
Onboard Hayabusa-2

Deployed in Sep. 2018

This time©JAXA

Deployed in Oct. 2018

MASCOT

By DLR/CNES
By JAXA

By Univ. consortium2

Status of Rovers 2 and Purpose of thedeployment (update)⚫In the onboard function tests, the communication system
between Hayabusa 2 and Rover 2 can be established. However,the Rover 2 data processor cannot be booted normally. Thissituation is still the same since it was reported in November
2018.
⚫To obtain scientifically interesting/meaningful results from therover 2 deployment, the Hayabusa 2 team, the University ofColorado in US, Kyushu Institute of Technology, and Tohoku
University have discussed possible options.
⚫Instead of operating the rover 2 on the surface for the mobility
and imaging missions, the idea was developed to release therover at a higher altitude and put it into an orbit to go around
Ryugu. If the orbital motion of rover 2 is observed by the opticalcameras from Hayabusa 2, we will make a better understandingof the gravity field of Ryugu.
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Goal of the Updated Rover 2 Operation⚫ Acquire the scientific data that contributes toimproving the accuracy of Ryugu's gravity model.
⚫ Accumulate the engineering experience for orbital
maneuvering technology by orbiting a small artifact
such as a CubeSat around an asteroid.
Operation Plan
⚫ Separate Rover 2 at an altitude of about 1km fromthe surface of Ryugu.
⚫ Inject Rover 2 into an equatorial orbit toward thedirection of the Ryugu’s rotation.
⚫ Observe the motion/trajectory of Rover 2 opticallywith ONC-W1, W2, and ONC-T imagers.
4Prediction of Orbit
item

Predicted value

Type of orbit

Around equator

Orbital life

5 days（±few days）

No. of revolution

8 times（±few times）

Orbital period （1st rev.）

17 hours（±few hours）

Equator

Ryugu’s rotation axis andequator ©JAXA
Expected Rover 2 orbit in the HP coordinate ©JAXA

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Expected Behavior of Rover 2⚫ The touch-down speed of Rover 2 on the surface of Ryugu will
be about 0.5 m/s. This is the same level as dropping from aheight of about 1.5cm on the 1G ground, then it is unlikely thatthe rover will be damaged by the touch-down impact.
⚫ The following onboard instruments of Rover 2 will not befunctioned unless the data processing system is restored.
- Micro-hop movement with an eccentric motor (Tohoku Univ.)- Elastic-reaction movement using leaf springs (Osaka Univ.)- Impulsive movement using a permanent magnet (TokyoDenki University)- MICAM imager (Tokyo University of Science)⚫ The elastic-reaction mechanism using bimetal springs(developed by Yamagata University) will react to thetemperature changes due to the periodic sunlight and shade onRyugu, then produce some hopping motions of the rover.
However, it is difficult to observe the resulting movement.

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ROVER2 specification◼ size: Φ15 [cm] ×14.5 [cm] (h)◼ mass: 877 [g]◼ power: 2 [W] in average◼ mobility: multiple hopping modes◼ mission: surface imaging
MINERVA-II2 ©JAXA

ROVER2 onboard actuators

ROVER2 onboard sensors◼

Micro-hopping by vibration of cilia◼

Micro-Camera (2): close-up imaging◼

Hopping by permanent magnet action◼

Temperature sensors (6)◼

Hopping by bi-metal action due toambient temperature change◼

Accelerometers (2)：contact detection◼

Photodiode (6)：sun-angle detection forattitude determination◼

Hopping with Leaf-Spring action

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Bi-Metal

Eccentric Motor w/ Cilia◼ driven by temperature change◼ utilize bi-metal’s buckling◼ assembles 2-units -> Hop◼ driven by DCbrushed motor◼ utilize centrifugal force◼ utilize ex. cilia units-> Micro-Hop

27.5 g

Yamagata Univ.

Leaf-Spring

Tohoku Univ.

24.4 g

Permanent Magnet◼ driven by releasing compression
leaf springs (2 units)◼ driven by DC-brushedmotor◼ utilize spring’s elastic energy -> Hop◼ utilize magnetic force ofpermanent magnets-> Hop

7.0 g

Osaka Univ.

Tokyo Denki Univ.

29.2 g(developed byScience University of Tokyo)

Specifications◼ VGA/SXGA color images◼ COTS CMOS imager◼ Wide angle lens（H125.3° x V97.7°）◼ Focal length: 10cm, 1cm◼ Mass: 39g
マーチソン隕石

活性炭

砂利・岩石

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(Fact Sheet) History of MINERVA-II2 (Rover 2) development
1. Based on opinions from the external evaluation committee members in themission review of the Hayabusa 2 pre-project (2007-2010), a framework wasdiscussed to include university/non-JAXA members into the engineering
challenge for the surface exploration robots, such as MINERVA that waspreviously developed for Hayabusa 1.
2. A consortium for the surface rover development was formed by university
researchers who responded to a call sent to the Japan Society of MechanicalEngineers, Japanese robot researchers' mailing list, University SpaceEngineering Consortium (UNISEC), ISAS Engineering Committee Lunar
Planetary Surface Exploration Technology (STEPS) working group, etc. in April
2011.
3. In 2012, at the approval review for move to a full-project, it was decided thatMINERVA-II1 shall be developed by JAXA and MINERVA-II2 shall be developedby the University Consortium as an optional payload of Hayabusa 2.
4. In 2013, the substantial development of MINERVA-II2 (Rover 2) was started in
the Consortium under the leadership of Tohoku University.
5. September 1, 2014, JAXA and Tohoku University signed an "Agreement onMounting a Small Surface Exploration Robot (MINERVA-II2) on Hayabusa 2".
6. December 3, 2014, Hayabusa 2 was launched.

The Status of MINERVA-II2 (Rover 2)(The press conference on November 8, 2018)
1.

After the launch of Hayabusa 2, the onboard status checkprocedures were performed for MINERVA-II2 in December 2014,
June 2015, and October 2017, then the communication link wasconfirmed between Hayabusa 2 and Rover 2.

2.

However, the telemetry data (including HK data) on the internal
state of the rover 2 has not been obtained due to the booting
anomaly of the rover 2 data processing system. The same symptom
was observed in the pre-launch tests. Through the ground-based
testing and analysis using the non-flight Engineering Model, thepossibility of a fully functional rover operation is considered very
low.

3.

Under the collaboration with JAXA’s Hayabusa 2 team, theConsortium is currently studying an operation plan that will produce
meaningful results through the deployment of Rover 2 (which isscheduled around July 2019.)
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