Hayabusa

The asteroid exploration mission by the Institute of Space and Astronautical Science (ISAS) originated in 1986–1987 when the scientists investigated the feasibility of a sample return mission to Anteros and concluded that the technology was not yet developed.[14] Between 1987 and 1994, joint ISAS / NASA group studied several missions: an asteroid rendezvous mission later became NEAR, and a comet sample return mission later became Stardust.[15]

In 1995, ISAS selected asteroid sample return as an engineering demonstration mission, MUSES-C, and the MUSES-C project started in fiscal year 1996. Asteroid Nereus was the first choice of target, 1989 ML was the secondary choice. In early development phase, Nereus was considered out of reach and 1989 ML became the primary target.[16] A launch failure of M-V in July 2000 forced MUSES-C's launch to be delayed from July 2002 to November/December, putting both Nereus and 1989 ML out of reach. As a result, the target asteroid was changed to 1998 SF₃₆.[17] In 2002, launch was postponed from December 2002 to May 2003 to recheck O-rings of reaction control system since one of it was found using different material than specified.[12] On 9 May 2003 04:29:25 UTC, MUSES-C was launched by an M-V rocket, and the probe was named "Hayabusa".

Ion thruster checkout started on 27 May 2003. Full power operation started on 25 June.

Asteroids are named by their discoverer. ISAS asked LINEAR, the discoverer of 1998 SF₃₆, to offer the name after Hideo Itokawa, and on 6 August, Minor Planet Circular reported that the target asteroid 1998 SF₃₆ was named Itokawa.[18][19]

In October 2003, ISAS and two other national aerospace agencies in Japan were merged to form JAXA.

On 31 March 2004, ion thruster operation was stopped to prepare for the Earth swing-by.[20] Last maneuver operation before swing-by on 12 May.[21] On 19 May, Hayabusa performed Earth swing-by.[22][23][24][25][26][27][28] On 27 May, ion thruster operation was started again.[29]

On 18 February 2005, Hayabusa passed aphelion at 1.7 AU.[30] On 31 July, the X-axis reaction wheel failed. On 14 August, Hayabusa's first image of Itokawa was released. The picture was taken by the star tracker and shows a point of light, believed to be the asteroid, moving across the starfield.[31] Other images were taken from 22 to 24 August.[32] On 28 August, Hayabusa was switched over from the ion engines to the bi-propellant thrusters for orbital maneuvering. From 4 September, Hayabusa's cameras were able to confirm Itokawa's elongated shape.[33] From 11 September, individual hills were discerned on the asteroid.[34] On 12 September, Hayabusa was 20 km (12 mi) from Itokawa and JAXA scientists announced that Hayabusa had officially "arrived".[3]

On 15 September 2005, a 'color' image of the asteroid was released (which is, however, grey in coloring).[35] On 4 October, JAXA announced that the spacecraft had successfully moved to its 'Home Position' 7 km from Itokawa. Closeup pictures were released. It was also announced that the spacecraft's second reaction wheel, governing the Y-axis, had failed, and that the craft was now being pointed by its rotation thrusters.[36] On 3 November, Hayabusa took station 3.0 km from Itokawa. It then began its descent, planned to include delivery of a target marker, and release of the Minerva minilander. The descent went well initially, and navigation images with wide-angle cameras were obtained. However, at 01:50 UTC (10:50 am JST) on 4 November, it was announced that due to a detection of an anomalous signal at the Go/NoGo decision, the descent, including release of Minerva and the target marker had been canceled. The project manager, Junichiro Kawaguchi, explained that the optical navigation system was not tracking the asteroid very well, probably caused by the complex shape of Itokawa. A delay of a few days was required to evaluate the situation and reschedule.[37][38]

On 7 November, Hayabusa was 7.5 km from Itokawa. On 9 November, Hayabusa performed a descent to 70 m to test the landing navigation and the laser altimeter. After that, Hayabusa backed off to a higher position, then descended again to 500 m and released one of the target markers into space to test the craft's ability to track it (this was confirmed). From analysis of the closeup images, the Woomera Desert site (Point B) was found to be too rocky to be suitable for landing. The Muses Sea site (Point A) was selected as the landing site, for both first and, if possible, second landings.[39]

On 12 November, Hayabusa closed in to 55 m from the asteroid's surface. MINERVA was released but due to an error failed to reach the surface. On 19 November, Hayabusa landed on the asteroid. There was considerable confusion during and after the maneuver about precisely what had happened, because the high-gain antenna of the probe could not be used during final phase of touch-down, as well as the blackout during handover of ground station antenna from DSN to Usuda station. It was initially reported that Hayabusa had stopped at approximately 10 meters from the surface, hovering for 30 minutes for unknown reasons. Ground control sent a command to abort and ascend, and by the time the communication was regained, the probe had moved 100 km away from the asteroid. The probe had entered into a safe mode, slowly spinning to stabilize attitude control.[40][41] However, after regaining control and communication with the probe, the data from the landing attempt were downloaded and analyzed, and on 23 November, JAXA announced that the probe had indeed landed on the asteroid's surface.[42] Unfortunately, the sampling sequence was not triggered since a sensor detected an obstacle during descent; the probe tried to abort the landing, but since its orientation was not appropriate for ascent, it chose instead a safe descent mode. This mode did not permit a sample to be taken, but there is a high probability that some dust may have whirled up into the sampling horn when it touched the asteroid, so the sample canister attached to the sampling horn was sealed.

On 25 November, a second touchdown attempt was performed. It was initially thought that this time, the sampling device was activated;[43] however, later analysis decided that this was probably another failure and that no pellets were fired.[44] Due to a leak in the thruster system, the probe was put in a "safe hold mode".[45]

On 27 November, the probe experienced a power outage when trying to reorient the spacecraft, probably due to a fuel leakage. On 30 November, JAXA announced that control and communication with Hayabusa had been restored, but a problem remained with the craft's reaction control system, perhaps involving a frozen pipe. Mission control was working to resolve the problem before the craft's upcoming launch window for return to Earth.[46] On 2 December, an attitude (orientation) correction was attempted, but the thruster did not generate enough force. On 3 December, the probe's Z-axis was found to be 20 to 30 degrees from the Sun direction and increasing. On 4 December, as an emergency measure, xenon propellant from the ion engines was blown to correct the spin, and it was confirmed successful. On 5 December, attitude control was corrected enough to regain communication through the medium gain antenna. Telemetry was obtained and analyzed. As the result of telemetry analysis, it was found that there was a strong possibility that the sampler projectile had not penetrated when it landed on 25 November. Due to the power outage, the telemetry log data was faulty. On 6 December, Hayabusa was 550 km from Itokawa. JAXA held a press conference about the situation so far.[47][48]

On 8 December, a sudden orientation change was observed, and communication with Hayabusa was lost. It was thought likely that the turbulence was caused by evaporation of 8 or 10cc of leaked fuel. This forced a wait of a month or two for Hayabusa to stabilize by conversion of precession to pure rotation, after which the rotation axis needed to be directed toward the Sun and Earth within a specific angular range. The probability of achieving this was estimated at 60% by December 2006, 70% by spring 2007.[49][50]

Animation of Hayabusa's trajectory returning from Itokawa to Earth.
   Hayabusa   Itokawa ·   Earth ·   Sun

On 7 March 2006, JAXA announced[51][52] that communication with Hayabusa had been recovered in the following stages: On 23 January, the beacon signal from the probe was detected. On 26 January, the probe responded to commands from ground control by changing the beacon signal. On 6 February, an ejection of xenon propellant was commanded for attitude control to improve communication. The spin axis change rate was about two degrees per day. On 25 February, telemetry data was obtained through the low-gain antenna. On 4 March, telemetry data was obtained through the medium-gain antenna. On 6 March, Hayabusa's position was established at about 13,000 km ahead of Itokawa in its orbit with a relative speed of 3 m per second.

On 1 June, Hayabusa project manager Junichiro Kawaguchi reported[53] that they confirmed two out of four ion engines were working normally, which would have been sufficient for the return journey. On 30 January 2007, JAXA reported that 7 out of 11 batteries were working and the return capsule was sealed.[54] On 25 April, JAXA reported that Hayabusa started the return journey.[55][56] On 29 August, it was announced that Ion Engine C onboard Hayabusa, in addition to B and D, had been successfully re-ignited.[57] On 29 October, JAXA reported that the first phase of trajectory maneuver operation had finished and the spacecraft was now put in a spin-stabilized state.[58] On 4 February 2009, JAXA reported success in reignition of the ion engines and starting the second phase of the trajectory correction maneuver to return to Earth.[59] On 4 November 2009, the ion engine D automatically stopped working due to an anomaly from degradation.[60]

On 19 November 2009, JAXA announced that they managed to combine the ion generator of ion engine B and the neutralizer of ion engine A.[61] It was suboptimal but expected to be sufficient to generate the necessary delta-v. Out of 2,200 m/s delta-v necessary to return to the Earth, about 2,000 m/s had been performed already, and about 200 m/s were still necessary.[62] On 5 March 2010, Hayabusa was on a trajectory that would have passed within the lunar orbit. Ion engine operation was suspended to measure the precise trajectory in preparation to perform Trajectory Correction Maneuver 1 to the Earth-rim trajectory.[63][64] On 27 March, 06:17 UTC, Hayabusa was on a trajectory which would pass 20,000 km from Earth center, completing the orbit transfer operation from Itokawa to Earth.[65] By 6 April, the first stage of Trajectory Correction Maneuver (TCM-0) which led to a rough Earth rim trajectory was completed. It was planned to be 60 days until reentry.[66][67][68][69] By 4 May, the probe completed its TCM-1 maneuver to align precisely to the Earth rim trajectory.[70] On 22 May, TCM-2 started, continued for about 92.5 hours, and finished on 26 May.[71] It was followed by TCM-3 from 3 through 5 June to change the trajectory from the Earth rim to Woomera, South Australia,[72][73] TCM-4 was performed on 9 June for about 2.5 hours for a precision descent to Woomera Prohibited Area.[74]

The reentry capsule was released at 10:51 UTC on 13 June.

The glowing return capsule is seen forward of and below the parent Hayabusa probe bus as the latter breaks up.

The reentry capsule and the spacecraft reentered Earth's atmosphere on 13 June 2010 at 13:51 UTC (23:21 local).[75] The heat-shielded capsule made a parachute landing in the South Australian outback while the spacecraft broke up and incinerated in a large fireball.[76]

An international team of scientists observed the 12.2 km/s entry of the capsule from 11.9 km (39,000 ft) on board NASA's DC-8 airborne laboratory, using a wide array of imaging and spectrographic cameras to measure the physical conditions during atmospheric reentry in a mission led by NASA's Ames Research Center, with Peter Jenniskens of the SETI Institute as the project scientist.[77][78]

Since the reaction control system no longer functioned, the 510 kilograms (1,120 lb) space probe re-entered the Earth's atmosphere similar to the approach of an asteroid along with the sample re-entry capsule, and, as mission scientists expected, the majority of the spacecraft disintegrated upon entry.[79]

The re-entry seen from the Woomera Test Range

The return capsule was predicted to land in a 20 km by 200 km area in the Woomera Prohibited Area, South Australia. Four ground teams surrounded this area and located the re-entry capsule by optical observation and a radio beacon. Then a team on board a helicopter was dispatched. They located the capsule and recorded its position with GPS. The capsule was successfully retrieved at 07:08 UTC (16:38 local) of 14 June 2010.[80] The two parts of the heat shield, which were jettisoned during the descent, were also found.[81]

After confirming that the explosive devices used for parachute deployment were safe, the capsule was packed inside a double layer of plastic bags filled with pure nitrogen gas to reduce the risk of contamination. The soil at the landing site was also sampled for reference in case of contamination. Then the capsule was put inside a cargo container which had air suspension to keep the capsule below 1.5 G shock during transportation.[82] The capsule and its heat shield parts were transported to Japan by a chartered plane and arrived at the curation facility at the JAXA/ISAS Sagamihara Campus on 18 June.[83]

A Tokyo Metropolitan Government adviser and former lieutenant general, Toshiyuki Shikata, claimed that part of the rationale for the reentry and landing part of the mission was to demonstrate "that Japan's ballistic missile capability is credible."[84]

On 16 November 2010, JAXA confirmed that most of the particles found in one of two compartments inside the Hayabusa sample return capsule came from Itokawa.[86] Analysis with a scanning electron microscope identified about 1,500 grains of rocky particles, according to the JAXA press release.[87] After further studying the analysis results and comparison of mineral compositions, most of them were judged to be of extraterrestrial origin, and definitely from the asteroid Itokawa.[88]

According to Japanese scientists, the composition of Hayabusa's samples was more similar to meteorites than known rocks from Earth. Their size is mostly less than 10 micrometers.[89] The material matches chemical maps of Itokawa from Hayabusa's remote sensing instruments. The researchers found concentrations of olivine and pyroxene in the Hayabusa samples.

Further study of the samples had to wait until 2011 because researchers were still developing special handling procedures to avoid contaminating the particles during the next phase of research.

In 2013 JAXA announced that 1500 extraterrestrial grains had been recovered, comprising the minerals olivine, pyroxene, plagioclase and iron sulfide. The grains were about 10 micrometers in size.[90] JAXA performed detailed analyses of the samples by splitting particles and examining their crystal structure at SPring-8.[91]

The 26 August 2011 issue of Science devoted six articles to findings based on dust collected by Hayabusa.[92] Scientists' analysis of the dust from Itokawa suggested that it had probably originally been part of a larger asteroid. Dust collected from the asteroid surface was believed to have been exposed there for about eight million years.[92]

Dust from Itokawa was found to be "identical to material that makes up meteorites."[92] Itokawa is an S-type asteroid whose composition matches that of an LL chondrite.[93]