Acta Astronautica 62 (2008) 639–647www.elsevier.com/locate/actaastro

Hayabusa—Its technology and science accomplishment summaryand Hayabusa-2

Jun’ichiro Kawaguchi∗, Akira Fujiwara, Tono UesugiInstitute of Space and Astronautical Science (ISAS), Japan Aerospace Agency (JAXA), 3-1-1 Yoshinodai, Sagamihara 229-8510, Japan

Received 22 December 2006; received in revised form 14 March 2007; accepted 15 January 2008Available online 15 April 2008

Abstract

Hayabusa performed five descents last November, among which two touching-down flights were included. Actually Hayabusamade three touching-downs and one long landing on the surface of Itokawa during those two flights. This paper summarizeshow series of descents were planned and operated. The contents focus their attention on the correction maneuvers planning aswell as what kind of terminals with what kind of software tools were actually built and used. The project team had distilledand accumulated their experiences through the rehearsal flights and accomplished this difficult mission. This paper presents theentire story about it.© 2008 Published by Elsevier Ltd.

1. Introduction

The Hayabusa spacecraft launched in May of 2003arrived at the target asteroid Itokawa in September 12thof 2005, having been propelled via its proprietary ionengines and through the Earth gravity assist in May of2004. After the arrival, the spacecraft jockeyed its po-sition from the Gate Position (around 20 km from theasteroid) to the Home Position (around 7 km from theasteroid) to perform the in situ scientific observationin September and October of 2005. This scientific ob-servation was highly successfully done and the resultswill be presented in LPSC meeting this March and alsoin the COSPAR meeting this July. This paper providesneither those remote sensing phase operation nor thescientific results, but the guidance and navigation oper-ation in the descents and touch-downs and landing for

∗ Corresponding author. Tel.: +81 42 759 8219;fax: +81 42 759 8458.

E-mail address: kawaguchi.junichiro@jaxa.jp (J. Kawaguchi).

0094-5765/$ - see front matter © 2008 Published by Elsevier Ltd.doi:10.1016/j.actaastro.2008.01.028

sample collection of the Itokawa. Those who are inter-ested in shall refer to the past papers on the guidanceand navigation and the papers on the science results thatappear in near future.

The major purpose of the paper is in how accuratelythe spacecraft was navigated and guided at the distanceof 2 AU from the Earth. The Itokawa surface exposedwas completely different from any surface condition ofthe asteroids that ever have been glimpsed. The sur-face is full of big boulders and there is little space forthe spacecraft to touch down and to land. Even withthe very small speed of 1 cm, the dispersion duringan hour exceeds the dispersion specification of 30 mthat is almost the similar size of the candidate area fortouching-down.

The Hayabusa project team devised and devel-oped its new and unique navigation way while theactual operation was conducted. This paper summa-rizes the contents of the operation and the relatedpapers at this meeting will describe the detailedstrategies.

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2. Practice descent (Rehearsal-1) on November4th, 2005

For the first rehearsal descent, Hayabusa commencedits descent at 19:17 GMT on November 3rd at the al-titude of about 3.5 km. It took an aim at calibrating itsproximity laser range finders, the visibility calibrationand the image processing of a target marker as well as atdeploying a hopping robot MINERVA. Down to about700 m in attitude, the onboard navigation computer de-tected an anomalous information (LIDAR reflection waslost), and the abort command was issued and sent at03:30 GMT on November 4th. Despite the interruption,the project team acquired a very important informationthrough this practice descent flight, and that this prac-tice does make the strategy stiffer. This means the Laserrange Finder (LRF) calibration and Nav&Guid experi-ence.

3. Navigation and guidance test on November 9th,2005

About the first rehearsal flight, through the investiga-tion, owing to a lot of spots identified on the successiveimage processing caused the onboard navigator at a losswhat the right descent path should be. And this prob-lem was found corrected by appropriate parameters setto the processor.

The spacecraft lost two reaction wheels aboard andit was found at this test that the persistent thrusting forattitude control gave fluctuated disturbance force andthe perturbation that amounted to a significant level forthe precise guidance to the landing site. A new supporttool on the ground was concluded required. In addi-tion, in view of the high resolution images taken aboard

Fig. 1. Close-up Image taken on November 9th. Opposition andHayabusa Shadow (up).

during the first rehearsal presented that the second land-ing site candidate ‘Woomera Desert’ area may not besuitable for the sampling site any more, since the areais covered with much more boulders than anticipated.At the Navigation and Guidance Test Descent, two de-scents were performed (left), and LRF measurementswere correctly obtained (right).

This test descent on November 9th aimed at veri-fying the items above and if those were appropriatelyfixed, verifying both its proximity LRF and the targetmarker tracking function with illumination via flashlamps aboard. Hayabusa lowered the altitude twicedown to 70 m and 500 m, respectively (Fig. 1).

4. The 2nd Rehearsal descent on November 12th,2005

As for the 2nd Rehearsal descent, on November 12th,at around 03:00 JST (GMT+9 h), Hayabusa started thedescent at the altitude of 1.4 km. This aimed at verify-ing the Nav&Guid skills and deploying the MINERVAlander on the Itokawa surface.

Descent operation took one hour more and the projectdecided to shift the closest approach to occur duringthe DSN pass switched from the JAXA’s UDSC an-tenna. The lowest altitude reached was about 55 m. TheMINERVA was released at the altitude of about 200 m.However, it failed to be placed on the surface with alittle ascent velocity of about 15 cm/s, which slightlyexceeded the escape velocity. The verification of LRFsensors was correctly performed successful.

At the second closest approach, Hayabusa separateda target marker to make sure if the separation, detec-tion, flash lamp function and the extraction of naviga-tion information all functioned properly. The test wassuccessful.

5. First touch-down attempt for sampling onNovember 20th

As a fourth descent, the Hayabusa performed thefirst touching-down attempt for sampling on November20th (JST). Hayabusa started descent at the distance ofabout 1 km from Itokawa, at 21:00 JST (12:00 UTC)on November 19th. Approaching, descending and theguidance and navigation were all performed in order asplanned. And having been directed from the ground at04:33 JST on November 20th (19:33 UTC on November19th) for the final vertical descent, Hayabusa succeededin making it descend precisely close to the intendedarea. Current analysis concluded the guidance accuracywas within 30 m in terms of the hovering point.

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Fig. 2. Doppler velocity history: descent velocity.

The landmark tracking/position estimation techniqueperformed and the ground support have less accuracywhile Hayabusa is in a distance. However, as this plotshows, the accuracy was well assured when the dis-tance becomes close within 1 km. What this plot showsis how precisely the approaching guidance and naviga-tion were accomplished in the approach phase. Whenthe final vertical descent commenced, the speed wasabout 12 cm/s. Hayabusa flight computer commandedthe target marker to be released at the altitude of 54 m at05:28 JST (20:28 UTC), followed by the spacecraft de-celeration of 9 cm/s at 40 m at 05:30 JST (20:30 UTC)forcing the marker depart from the spacecraft. It wasconfirmed that the marker was actually positioned andplaced properly through both the camera images and thetelemetry information, which indicate the descent speedof the spacecraft. (See Fig. 2) Latest estimation says themarker landed in South-West (upper right in the image)area of the MUSES-Sea. Hayabusa then switched theLaser altimeter to LRF mode at the altitude of about35 m and started hovering at the altitude of about 25 mby canceling the residual descent velocity.

The Doppler information obtained as in Fig. 2 showsevery delta-V applied autonomously and well agreedwith the plan commanded.

The Laser Altimeter (LIDAR) measurement obtainedtogether with the integrated Doppler measurement his-tory associated with this first touching-down flight wasobtained. Note once the terrain alignment started, theLIDAR information transmission terminated as sched-uled. And as the integrated Doppler information said,the spacecraft position moved even inside the equato-rial surface distance. This shows the spacecraft movedto the polar gained latitude toward the polar direction.As the subsequent paper describes, the Hayabusa space-

Fig. 3. Target marker (at 05:33 JST at 32 m).

craft was estimated to have moved to south, where thespacecraft started landing for half an hour.

The spacecraft succeeded in deploying the targetmarker with the 880,000 signatures onboard at the areaspecified. The target marker was photographed andthe images are shown in Fig. 3. This does show howaccurately the guidance and navigation were accom-plished as planned. As scheduled, the spacecraft madea free fall until it reached the 17 m altitude at 05:40JST (20:40 UTC), and the Terrain Alignment Controlmode commenced, when the telemetry transmissionwas terminated and it was taken over by the beacon-only radio configuration via a wide angle Low GainAntenna (LGA). Since then, neither instruments infor-mation nor house keeping information were obtainedin real time on the ground.

However, according to the data reproduced so far,Hayabusa-carried Fan Beam Sensor (FBS), an obstacledetector, seemed to have received the laser reflectionsignal from something around and an emergency ascentcommand was requested issued from the Data Handling

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Fig. 4. LRF data at touch-downs and landing (D-beam, m).

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Fig. 5. Attitude error angle (Y -axis, degree).

Unit (DHU), the primary flight computer aboard. Butat that instance, the attitude deviation was large and didnot meet the emergency ascent burn requirement andthe ascent was cancelled by the DHU. As a result, thespacecraft decided to continue the descent as long as nointerruption was directed from the ground. As a matterof fact, nothing was commanded from the ground, whilethe touching-down trigger including take-off sequencewas cancelled beyond it.

The height became almost zero at 06:10 JST (21:10UTC) as shown in Fig. 4. And then another bouncingwas observed later at 06:30 JST (21:30 UTC) also as inFig. 4. This resulted in very soft landing on the surfaceand the spacecraft continued to sit on the surface for halfan hour, before the emergency take-off command was

sent to the spacecraft at 07:14 JST (22:14 UTC). Duringthe period from 06:40 JST (21:40 UTC) to 07:10 JST(22:10), the same engines had been commanded firedat almost 100% duty, with the LRF read-out of almostzero.

Fig. 5 indicates the error angle (Y ) to the targetorientation that was specified at the terrain alignment.As the total magnitude of the error angle including X

and Z direction equals to the Itokawa’s rotation angu-lar velocity and this shows the angular motion of bothHayabusa and Itokawa was identical to each other. Be-sides the thruster firing accumulation monotonously in-creases with no corresponding angular motion. This in-dicates the attitude was fixed regardless of the thrusterfirings and the Hayabusa was caught in the Itokawa.

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This in turn indicates the Hayabusa kept sitting on thesurface until commanded to lift-off it.

The data reproduced said that Hayabusa made slowspeed bouncing (touching-downs) twice, followed bythe complete landing and staying still for 30 min long.This was confirmed by the LRF read-out and attitudehistory. The touching-down speed at both bouncing,was about 10 cm/s. As of today, no serious damage wasfound and reported as for the instruments.

Hayabusa continued this landing status stably beforethe emergency take-off was directed from the ground at06:58 JST (21:58 UTC). No projectile was shot, sincethe FBS detection disabled the triggering sequence asstated above. Landing attitude seems that sitting on thesampler horn sustained by two corners of the spacecraftbottom plate or by the tip-ends of the solar array panels.

Hayabusa now became the first spacecraft that hastaken off from the extra-terrestrial body’s surface. Thespacecraft after lift-off fell into the Safe-Hold Mode,since the ground based operation directed extraordinaryattitude maneuvers during a short period. It took a fewhours for the spacecraft to resume the communicationby directing the RF configuration resumed. It was foundthat the spacecraft functioned very normally.

6. The 2nd touching-down attempt

With the practices and first touching-down plus land-ing experience, the Hayabusa attempted to have anothertouching-down for sampling on November 25th (UTC).

Hayabusa started the descent at 22:00 JST on Novem-ber 25th. The descent path taken was almost same asthat at the 1st touching-down attempt, toward the westpart of the MUSES-Sea. Approach information with al-titude and descent rate are shown below. As already onetarget marker was in the MUSES-Sea, to avoid the con-fusion, the project decided not to release a new marker,this time. And also the obstacle detection sensor wasset not to be referred to, since it reported inappropriateor too-sensitive signal. The traps that the sequence ofevents should not pass are reduced this time. Once theterrain alignment sequence starts, the SOE was set sothat the lift off must be only if the sampler horn defor-mation is detected.

The touching-down operation was planned originallyduring the DSN pass preceded by the UDSC (JAXA)pass. However, based on the experience by that time,the project decided to switch antenna relatively, early sothat the sophisticated operation can be performed onlyduring the Goldstone pass, which is immediately passedto the UDSC pass after the touching-down.

7. Approach and descent path planning (2ndflight)

In Fig. 6, approach and descent trajectory are shown.The target trajectory is successively updated during thedescent and not vigorously identical to the planned path.The right figure shows the trajectory in Itokawa-fixedcoordinate. Both show the path was built correctly andguidance was successful. The landmark tracking navi-gation was not primarily assumed for the descent beforelaunch, since it does not seem to fit for the real-timeoperation. The primary guidance was assumed by theonboard software that detects the center of illuminationthat is assumed to coincide with the center of mass.

Fundamentally this assumption is true; however, evena small amount of inconsistency was found to causethe dispersion over the expected dispersion area. Dur-ing the flight data evaluation process, very efficient andquick landmark tracking method was exploited on theground (Fig. 7). And with the trajectory prediction wasfound useful with the attitude control derived acceler-ation compensated and also with the path predicted infeed-forward manner. Both, in other words, constitutesa real time extended Kalman filter plus feed-forwardcontrol scheme. The flight results obtained showed theguidance accuracy was almost within 5 mm/s before thefinal automated final vertical descent started. This sat-isfied the guidance and navigation requirements.

Fig. 8 shows the descent speed history measured atthe DSN station. Fig. 9 shows the altitude history in-tegrating Doppler measurement. It is observed that thehovering took place at the low altitude and started as-cent.

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Fig. 6. Planned and actual path in 2nd flight.

644 J. Kawaguchi et al. / Acta Astronautica 62 (2008) 639–647

Fig. 7. Navigation (semi-inertial coord).

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Fig. 8. Descent rate in 2nd touch-down.

8. Hovering and attitude behavior at touch-down

It is observed that the hovering, a part of terrain align-ment was performed at the altitude of 7 m in Fig. 10.

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Fig. 9. Distance/altitude in 2nd touch-down.

The attitude fluctuation was stable within well smallwidth until the touch-down at 0707 JST (2207 UTC),which shows no contact of the spacecraft with the sur-face took place before it.

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Fig. 10. LRF history (Unit: m) in 2nd touch-down.

Later, the data will show how the Reaction ControlSystem (RCS) jets were fired at the touching-down. Ev-erything was smoothly done and the project team wasconfident in having a safe touch-down to the surface.The lift-off occurred very normally and ascent directionwas due the Sun direction, which was expected assum-ing the touch-down area should be perpendicular to theSun direction. The spacecraft lifted off the surface with0.5 m/s.

The operation station was switched from the Gold-stone DSN site to the JAXA’s UDSC site as scheduled.No data gap occurred and the operation was almostcomplete, until the unexpected fuel leak took placeafter the three axis stabilization was reestablished. Thedetails will be described later in the paper.

Hayabusa is now the first spacecraft that could landfor sampling at the extra-terrestrial objects. In view ofthe robotic exploration, Hayabusa could demonstrate itsunique and new methodology in the planetary explo-ration. At the same time, this success made Japan tobe at the front position in deep space exploration. Theproject thinks this Hayabusa success does contribute tothe not only domestic but also the world-wide spaceactivities.

9. Status of Hayabusa after 2nd touching-down forsampling

Hayabusa finished its second touching-down for sam-ple collection and took off from the asteroid surface onNovember 26th. And it successfully decelerated its as-cent speed four hours later.

When the stop maneuver ended, thruster-2 temper-ature went down very quickly and it showed the leak

occurred there. Shutting-off commands were kept sentfor both A and B systems to stop the leak and thoseworked before the LOS from the UDSC.

On December 8th, Usuda station observed a sud-den shift of the range-rate measurement at 04:13 UTCwith the corresponding gradual decrease of signal in-tensity AGC (Automated Gain Controller) read. Butthe control capability of it was not enough strong forthe spacecraft to withstand the disturbance on Decem-ber 8th. Estimation says the spacecraft may be in alarge coning motion and that is why the spacecraft hasnot responded to the commands sent from the groundstation.

Hayabusa leaving 2007 to Earth in 20103 108

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Fig. 11. Return trajectory postponed to 2010.

646 J. Kawaguchi et al. / Acta Astronautica 62 (2008) 639–647

Point-A

Muses-SeaHayabusa’s Shadow

Release 051114 ISAS/JAXA

Point-A

Muses-SeaHayabusa’sShadow

Release 051114 ISAS/JAXA

Fig. 12. World’s best resolution asteroid image. This image clarifies the regolith transition area for the first time.

Hayabusa was recaptured on January 23rd of 2006,when the attitude was significantly drifted 70◦ offset.Since then the attitude control with Xe gas thrusterswere performed to resume the operation. Since March,the spacecraft has been operated normally.

And it is concluded that the commencement of thereturn cruise during December is found difficult. Theproject has determined that the return cruise should startfrom 2007 so that the spacecraft can return to the Earthin June of 2010, three years later than the original plan,as long as no immediate resumption takes place verysoon. New trajectory (red line) leaving Itokawa vicinityin spring of 2007, returning to Earth in June of 2010is shown here in Fig. 11. The Xenon gas consumptionmeets the current amount that remains. There will besome strategy needed and left for the operational dis-cussion on how the attitude is protected against unex-pected disturbance.

10. Concluding remarks

The summary of descents, touching-downs and land-ing of the Hayabusa to the Itokawa surface was pre-sented. Hayabusa is the first spacecraft that landed onthe surface and lifted off again. The major output interms of the guidance and navigation is in the fact thatthe spacecraft succeeded in the pin-point landing at anextra-terrestrial object. The guidance accuracy accom-plished was down to several millimeters per second andthe final dispersion well satisfied the expected conditionof within 30 m.

Fig. 12 is an image example taken for the sciencepurpose. A number of images were taken during theproximity period and they are presently under detailedanalysis and will be reported in the papers soon.

For all fuel leak accidents, the spacecraft was for-tunately restored and has been operated normally now.Every output from the Hayabusa will be highly uti-lized for the next mission such as ‘Hayabusa-2’ in nearfuture.

11. Hayabusa-2

Taking the advantage of the Hayabusa accomplish-ments, Japan Aerospace Exploration Agency (JAXA)has started the second attempt to collect sample of an as-teroid as quickly as possible. JAXA thinks major parts ofthe new technology were successfully verified throughthe Hayabusa mission and JAXA will pursue the realsample and return from an extra-terrestrial object forthe first time in the world, while the Hayabusa is con-ceived to have captured a small amount of particles atthe first touchdown to Itokawa surface and JAXA is try-ing their best effort to make it fly back home, Earth in2010. The Hayabusa-2’s target is currently under inten-sive discussion, but it will be a C-type near Earth aster-oid, to which launch windows are open in 2010 to 2011.JAXA will disclose the exploration scenario in severalmonths about the mission.

For Further Reading

[1] Proceedings of Asteroid Sample and Return Workshop, ISAS,June 29, 1985.

[2] J. Kawaguchi, Scientific Satellites Prospect, ISAS Report no.43, ISSN0285-2853, December, 1986.

[3] J. Kawaguchi, et al., Launch readiness of the MUSES-C, asample and return from an asteroid, IAC-02-Q.5.2.04, in: 53rdInternational Astronautical Congress, 10–19 October, Houston,TX, 2002.

J. Kawaguchi et al. / Acta Astronautica 62 (2008) 639–647 647

[4] M. Kaasalainen, CCD photometry and model of MUSES-C target(25143) 1998 SF36, A&A 405 (2003) L29–L32.

[5] J. Kawaguchi, MUSES-C launch and early operations report,in: AAS/AIAA Astrodynamics Specialists Conference, AAS-03-662, Big Sky Resort, Big Sky, Montana, August 3–7, 2003.

[6] J. Kawaguchi, et al., The Ion Engines Cruise Operation andthe Earth Swingby of ‘Hayabusa’ (MUSES-C), IAC-04-Q_5_02,October 4-8, 2004, Vancouver, Canada.

[7] J. Kawaguchi, et al., Hayabusa (MUSES-C)—rendezvous andproximity operation, IAC-05-A3.5.A.01, October 16–21, 2005,Fukuoka, Japan.

[8] J. Kawaguchi, et al., Guidance and navigation operation forrehearsals and touch-downs in Hayabusa, AAS-06-183, in:AAS/AIAA Space Flight Mechanics Meeting, Tampa, Florida.