Hayabusa2
Hayabusa2 is an asteroid sample-return mission operated by the Japanese space agency, JAXA. It follows on from the Hayabusa mission which returned asteroid samples in 2010. Hayabusa2 was launched on 3 December 2014 and rendezvoused with near-Earth asteroid 162173 Ryugu on 27 June 2018. It surveyed the asteroid for a year and a half and took samples. It left the asteroid in November 2019 and is expected to return to Earth on 6 December 2020.
Hayabusa2 carries multiple science payloads for remote sensing, sampling, and four small rovers that investigated the asteroid surface to inform the environmental and geological context of the samples collected.
Mission overview
Asteroid 162173 Ryugu is a primitive carbonaceous near-Earth asteroid. Carbonaceous asteroids are expected to preserve the most pristine materials in the Solar System, a mixture of minerals, ice, and organic compounds that interact with each other. Studying it is expected to provide additional knowledge on the origin and evolution of the inner planets and, in particular, the origin of water and organic compounds on Earth, all relevant to the origin of life on Earth.Initially, launch was planned for 30 November 2014, but was delayed to 3 December 2014 at 04:22 UTC on a H-IIA launch vehicle. Hayabusa2 launched together with PROCYON asteroid flyby space probe. PROCYON's mission was a failure. Hayabusa2 arrived at Ryugu on 27 June 2018, where it surveyed the asteroid for a year and a half and collected samples. It departed the asteroid in November 2019 to return the samples to Earth in late 2020.
Compared to the previous Hayabusa mission, the spacecraft features improved ion engines, guidance and navigation technology, antennas, and attitude control systems. A kinetic penetrator was shot into the asteroid to expose pristine sample material that was later sampled for return to Earth.
Funding and history
Following the partial success of Hayabusa, JAXA began studying a potential successor mission in 2007. In July 2009, Makoto Yoshikawa of JAXA presented a proposal titled "Hayabusa Follow-on Asteroid Sample Return Missions". In August 2010, JAXA obtained approval from the Japanese government to begin development of Hayabusa2. The cost of the project estimated in 2010 was 16.4 billion yen.Hayabusa2 was launched on 3 December 2014, arrived at asteroid Ryugu on 27 June 2018, and remained at a distance of about 20 km to study and map the asteroid. In the week of 16 July 2018, operations were begun to lower this hovering altitude.
On 21 September 2018, the Hayabusa2 spacecraft ejected the first two rovers, Rover-1A and Rover-1B, from about 55 metres altitude that fell independently to the surface of the asteroid. They functioned nominally and transmitted data. The MASCOT rover deployed successfully on 3 October 2018 and operated for about 16 hours as planned.
The first sample collection was scheduled to start in late October 2018, but the rovers encountered a landscape with large and small boulders but no regolith to sample, so the mission team decided to postpone the sample acquisition to 2019 and evaluated several options. Its first surface sample retrieval took place on 21 February 2019. On 5 April 2019, Hayabusa2 released an impactor and created an artificial crater on the asteroid surface. Hayabusa2 failed on 14 May 2019 to drop off reflective markers necessary for descent and sampling, but it successfully dropped one off from an altitude of 9 metres on 4 June 2019. The sub-surface sampling took place on 11 July 2019. The spacecraft departed the asteroid on 13 November 2019 and it is expected to deliver the samples to Earth in late 2020.
Spacecraft
| Hayabusa2 | Performance |
| Propulsion | μ10 ion thruster |
| Number of thrusters | 4 |
| Total thrust | 28 mN |
| Specific impulse | 3000 seconds |
| Acceleration | 49 μm/s2 |
| Power | 1250 W |
| Spacecraft wet mass | 610 kg |
| Ion engine system dry mass | 66 kg |
| Ion engine system wet mass | 155 kg |
| Solar array | 23 kg |
| Xenon propellant | 66 kg |
| Hydrazine/MON-3 propellant | 48 kg |
| Thrust | 20 N |
The design of Hayabusa2 is based on the first Hayabusa spacecraft, with some matured improvements. It has a mass of with fuel, and electric power is generated by bilateral solar arrays with an efficiency of 2.6 kW at 1 AU, and 1.4 kW at 1.4 AU. The power is stored in eleven inline-mounted 13.2 Ah lithium-ion batteries.
;Propulsion
The spacecraft features four solar-electric ion thrusters for propulsion called μ10, one of which is a backup. These engines use microwaves to convert xenon into plasma, which is accelerated by applying a voltage from the solar panels and ejected out the back of the engine. The simultaneous operation of three engines generates thrusts of up to 28 mN. Although this thrust is very small, the engines are also extremely efficient; the 66 kg of xenon reaction mass can change the speed of the spacecraft by up to.
The spacecraft has four redundant reaction wheels and a chemical reaction control system featuring twelve thrusters for attitude control and orbital control at the asteroid. The chemical thrusters use hydrazine and MON-3, with a total mass of 48 kg of chemical propellant.
;Communication
The primary contractor NEC built the spacecraft, its Ka-band communications system and a mid-infrared camera. The spacecraft has two high-gain directional antennas for X-band and Ka-band. Bit rates are 8 bit/s–32 kbit/s. The ground stations are the Usuda Deep Space Center, Uchinoura Space Center, NASA Deep Space Network and Malargüe Station.
;Navigation
The optical navigation camera telescope is a telescopic framing camera with seven colors to optically navigate the spacecraft. It works in synergy with the optical navigation camera wide-field and with two star trackers.
In order to descend to the asteroid surface for sampling, the spacecraft released one of five target markers in the selected landing zones as artificial landmark with highly reflective outer material that is recognized by a strobe light mounted on the spacecraft. The spacecraft also used its laser altimeter and ranging and other sensors during sampling.
Science payload
The Hayabusa2 payload incorporates multiple scientific instruments:- Remote sensing: Optical Navigation Camera, Near-Infrared Camera, Thermal-Infrared Camera, Light Detection And Ranging
- Sampling: Sampling device, Small Carry-on Impactor, Deployable Camera
- Four rovers: Mobile Asteroid Surface Scout, Rover-1A, Rover-1B, Rover-2.
Remote sensing
The Near-Infrared Spectrometer is a spectrograph operating at wavelengths 1.8–3.2 μm. NIRS3 was used for analysis of surface mineral composition.
The Thermal-Infrared Imager is a thermal infrared camera working at 8–12 μm, using a two-dimensional microbolometer array. Its spatial resolution is 20 m at 20 km distance or 5 cm at 50 m distance. It was used to determine surface temperatures in the range -40–150 °C.
The Light Detection And Ranging instrument measured the distance from spacecraft to the asteroid surface by measuring the time of flight of laser light reflection. It operated over the altitude range between 30 m–25 km.
When the spacecraft was closer to the surface than 30 m during the sampling operation, the Laser Range Finders were used to measure the distance and the attitude of the spacecraft relative to the terrain. The LRF-S2 monitored the sampling horn to trigger the sampling projectile.
LIDAR and ONC data are being combined to determine the detailed topography of the asteroid. Monitoring of a radio signal from Earth allowed measurement of the asteroid's gravitational field.
Rovers
Hayabusa2 carried four small rovers to investigate the asteroid surface in situ, and provide context information for the returned samples. Due to the minimal gravity of the asteroid, all four rovers were designed to move around by short hops instead of the normal wheels. They were deployed at different dates from about 60 m altitude and fell freely to the surface under the asteroid's weak gravity. The first two rovers, called HIBOU and OWL, landed on asteroid Ryugu on 21 September 2018. The third rover, called MASCOT, was deployed 3 October 2018. Its mission was successful. The fourth rover, known as Rover-2 or MINERVA-II-2, failed before release from the orbiter. It was released on 2 October 2019 to orbit the asteroid and perform gravitational measurements before impacting the asteroid a few days later.MINERVA-II
MINERVA-II is a successor to the MINERVA lander carried by Hayabusa. It consists of two containers with 3 rovers.MINERVA-II-1 is a container that deployed two rovers, Rover-1A and Rover-1B, on 21 September 2018. It was developed by JAXA and the University of Aizu. The rovers are identical with a cylindrical shape, diameter and tall, and a mass of each. They move by hopping in the low gravitational field, using a torque generated by rotating masses within the rovers. Their scientific payload is a stereo camera, wide-angle camera, and thermometers. Solar cells and double-layer capacitors provide the electrical power.
The MINERVA-II-1 rovers were successfully deployed 21 September 2018. Both rovers performed successful missions on the asteroid surface, providing images and even video from the surface. Rover-1A operated for 113 asteroid days returning 609 images from the surface, and Rover-1B operated for 10 asteroid days returning 39 images from the surface.
The MINERVA-II-2 container held the ROVER-2, developed by a consortium of universities led by Tohoku University in Japan. This was an octagonal prism shape, diameter and tall, with a mass of about. It had two cameras, a thermometer and an accelerometer. It had optical and ultraviolet LEDs for illumination to detect floating dust particles. ROVER-2 carried four mechanisms to relocate by short hops.
Rover-2 failed before deployment from the orbiter but was deployed on 2 October 2019 to orbit the asteroid and perform gravitational measurement before impacting the asteroid a few days later on 8 October 2019.
MASCOT
The Mobile Asteroid Surface Scout was developed by the German Aerospace Center in cooperation with the French space agency CNES. It measures 29.5 × 27.5 × 19.5 cm and has a mass of. MASCOT carries four instruments: an infrared spectrometer, a magnetometer, a radiometer, and a camera that imaged the small-scale structure, distribution and texture of the regolith. The rover is capable of tumbling once to reposition itself for further measurements. It collected data on the surface structure and mineralogical composition, the thermal behaviour and the magnetic properties of the asteroid. It has a non-rechargeable battery that allowed for operations for approximately 16 hours. The infrared radiometer on the InSight Mars lander, launched in 2018, is based on the MASCOT radiometer.MASCOT was deployed 3 October 2018. It had a successful landing and performed its surface mission successfully. Two papers were published describing the results from MASCOT in the scientific journals Nature Astronomy and Science. One result of the research was that C-type asteroids consist of more porous material than previously thought, explaining a deficit of this meteorite type. Meteorites of this type are too porous to survive the entry into the atmosphere of planet Earth. Another result was that Ryugu consists of two different almost black types of rock with little internal cohesion, but no dust was detected. A third paper describing results from MASCOT was published in the Journal of Geophysical Research and describes the magnetic properties of Ryugu, showing that Ryugu does not have a magnetic field on a boulder scale.
Objects deployed by ''Hayabusa2''
Sampling
The original plan was for the spacecraft to collect up to three samples:1) surface regolith that exhibits traits of hydrous minerals;
2) surface regolith with either unobservable or weak evidence of aqueous alterations;
3) excavated sub-surface material.
The first two surface samples were scheduled to start in late October 2018, but the rovers showed a scenery of large and small boulders and no regolith to sample, so the mission team decided to postpone sampling to 2019 and evaluate several options. The first surface sampling was completed on 22 February 2019 and obtained a substantial amount of regolith, so the second surface sampling was postponed and was eventually cancelled to decrease risk to the mission.
The second and final sample was of excavated material dislodged by a kinetic impactor shot from a distance. All samples are stored in separate sealed containers inside the sample return capsule.
Surface sample
Hayabusa2 sampling device is based on Hayabusa. Its first surface sample retrieval was conducted on 21 February 2019, which began with the spacecraft's descent, approaching the surface of the asteroid. When the sampler horn attached to Hayabusa2 underside touched the surface, a projectile was fired at 300 m/s into the surface. The resulting ejecta particles were collected by a catcher at the top of the horn, which the ejecta reached under their own momentum under microgravity conditions.Sub-surface sample
The sub-surface sample collection required an impactor to excavate a crater to eventually obtain material deeper from the sub-surface, which has not been subjected to space weathering. This required removing a large volume of surface material with a substantial impactor. For this purpose, Hayabusa2 deployed on 5 April a free-flying gun with one "bullet", called the Small Carry-on Impactor ; the system consists of a copper projectile shot to the surface by an explosive propellant charge. Following SCI deployment, Hayabusa2 also left behind a deployable camera to observe and map the precise location of the SCI impact, while the orbiter maneuvered to the far side of the asteroid in order to avoid debris from the impact.Approximately 40 minutes after separation, when the spacecraft was at a safe distance, the impactor was fired into the asteroid surface by the detonation of shaped charge of plasticized HMX for acceleration. The copper impactor was shot to the surface from an altitude of about 500 metres and it excavated a crater of about 10 metres in diameter, exposing pristine material. The next step was the deployment on 4 June 2019 of a reflective target marker in the area near the crater to assist with navigation and descent. The touchdown and sampling took place on 11 July 2019.
Sample-return
The spacecraft collected and stored the samples in separate sealed containers inside the sample-return capsule, which has a thermal insulation, 40 cm external diameter, 20 cm in height, and a mass of ~16 kg.At the end of the science phase in November 2019, Hayabusa2 used its ion engines for changing orbit and return to Earth. When Hayabusa2 flies past Earth in late 2020, it will release the capsule spinning at one revolution per three seconds. The capsule will re-enter the Earth's atmosphere at 12 km/s and it will deploy a radar-reflective parachute at an altitude of about 10 km, and eject its heat-shield, while transmitting a position beacon signal. The sample capsule is planned to land at the Woomera Test Range in Australia. The total flight distance would be 5,240,000,000 km.
Once on Earth, any volatile substance will be collected before the sealed containers are opened. The samples will be curated and analyzed at JAXA's Extraterrestrial Sample Curation Center, where international scientists can request a small portion of the samples.