hayabusa

Hayabusa (はやぶさ - peregrine falcon) is an unmanned space mission led by the Japan Aerospace Exploration Agency to collect a sample of material from a small near-Earth asteroid named 25143 Itokawa (dimensions 540 meters by 270 meters by 210 meters) and return the sample to Earth for further analysis.

The Hayabusa spacecraft, formerly known as MUSES-C (ミューゼスＣ), was launched on 9 May 2003 and rendezvoused with Itokawa in mid-September 2005. Having arrived at Itokawa, Hayabusa is studying the asteroid's shape, spin, topography, color, composition, density, and history. In November 2005, it landed on the asteroid to collect samples, but failed to collect a sample. Nevertheless, there is a high probability that some dust swirled into the sampling chamber, so it was sealed, and the spacecraft is slated to return to Earth by June 2010.

The spacecraft also carried a detachable mini-lander but it failed to reach the surface (see Minerva mini-lander below).

Mission firsts

Other spacecraft, notably Galileo and NEAR Shoemaker, have visited asteroids before, but the Hayabusa mission, if successful, will mark the first time that an asteroid sample is returned to Earth for analysis.

In addition, Hayabusa is the first spacecraft designed to deliberately land on an asteroid and then take off again (NEAR Shoemaker made a controlled descent to the surface of 433 Eros in 2000, but it was not designed as a lander and was eventually deactivated after it arrived). Technically, Hayabusa is not designed to 'land': it simply touches the surface with its sample capturing device and then moves away. However, it is the first craft designed from the onset to make contact with the surface of an asteroid.

Despite its designer's intention, Hayabusa did land and sit on the asteroid surface for about 30 minutes (see the November 19 entry in the recent events section below).

Mission profile

The Hayabusa spacecraft was launched on 9 May 2003 at 04:29:25 UTC on an M-5 rocket from the Uchinoura Space Center (still called Kagoshima Space Center at that time). Following launch, the spacecraft's name was changed from the original MUSES-C to Hayabusa, the Japanese word for falcon. The spacecraft's xenon ion engines (two separate units, each with two exhausts), operating near-continuously for two years, slowly moved Hayabusa toward a September 2005 rendezvous with Itokawa. As it arrived, the spacecraft did not go into orbit around the asteroid, but remained in a station-keeping heliocentric orbit close by.

Hayabusa surveyed the asteroid surface from a distance of about 20 km, the "gate position". Afterwards, the spacecraft moved closer to the surface ("home position"), and then approached the asteroid for a series of soft landings and collection of samples at the safest site. Autonomous optical navigation was employed extensively during this period because the long communication delay prohibits Earth-based real-time commanding. At the second Hayabusa touchdown with its deployable collection horn, the spacecraft was programmed to fire tiny projectiles at the surface and then collect the resulting spray. Any samples that were collected are now held inside a separate re-entry capsule. However, it is currently uncertain whether the metal projectiles were fired during contact.

After a few months in proximity to the asteroid, the spacecraft was scheduled to fire its engines to begin its cruise back to Earth. This maneuver was delayed due to problems with attitude control and the thrusters of the craft. Once it is on its return trajectory, the re-entry capsule will be detached from the main spacecraft at a distance of about 300,000 to 400,000 km from the Earth, and the capsule will coast on a ballistic trajectory, re-entering the Earth's atmosphere. This is currently planned for June 2010. The capsule will experience peak deceleration of about 25 G and heating rates approximately 30 times those experienced by the Apollo spacecraft. It will land via parachute near Woomera, Australia.

MINERVA mini-lander

Hayabusa carried a tiny mini-spacecraft (weighing only 591 g, and approximately 10 cm tall by 12 cm in diameter) named MINERVA (short for MIcro/Nano Experimental Robot Vehicle for Asteroid). Unfortunately, an error during deployment resulted in the craft's failure..

This solar-powered vehicle was designed to take advantage of Itokawa's very low gravity by using an internal flywheel assembly to hop across the surface of the asteroid, relaying images from its cameras to Hayabusa whenever the two spacecraft were in sight of one another.[1]

MINERVA was deployed on November 12, 2005. The lander release command was sent from Earth, but before the command could arrive, Hayabusa's altimeter measured its distance from Itokawa to be 44m and thus started an automatic altitude keeping sequence. As a result, when the MINERVA release command arrived, MINERVA was released while the probe was ascending and at a higher altitude than intended, so that it escaped Itokawa's gravitational pull and tumbled into space. [2] [3] [4]

Had it been successful, MINERVA would have been the first "space hopper" to see action. Instead, it joins ranks with the hopper (PrOP-F) carried on the failed Phobos 2 mission, which also never saw use.

The United States space agency NASA had originally planned to build a miniature rover as part of the Hayabusa mission, but the project, developed by JPL and called Muses-CN, was cancelled in November, 2000, for budgeting reasons.

Scientific and engineering importance of the mission

Scientists' current understanding of asteroids depends greatly on meteorite samples, but it is very difficult to match up meteorite samples with the exact asteroids from which they came. Hayabusa will solve this problem by bringing back pristine samples from a specific, well-characterized asteroid. Accordingly, Hayabusa "will bridge the gap between ground observation data of asteroids and laboratory analysis of meteorite and cosmic dust collections," says mission scientist Hajime Yano. ¹ Also in comparing the data from the onboard instruments of the Hayabusa with the data from the Near Shoemaker mission will put the knowledge on a wider level.

The Hayabusa mission has a very deep engineering importance for JAXA, too. First it will help JAXA to further test its technologies in the fields of ion engines, autonomous and optical navigation, deep space communication, and close movement on objects with low gravity among others. Second, since it was the first-ever soft contact with the surface of an asteroid it has enormous influence on further asteroid missions.

Changes in mission plan

The Hayabusa mission profile has been modified several times, both before and after launch.

• The spacecraft was originally intended to launch in July 2002 to the asteroid 4660 Nereus (the asteroid (10302) 1989 ML was considered as an alternative target). However, a July 2000 failure of Japan's M-5 rocket forced a delay in the launch, putting both Nereus and 1989 ML out of reach. As a result, the target asteroid was changed to 1998 SF₃₆, which was soon thereafter named for Japanese rocket pioneer Hideo Itokawa. [5]
• Hayabusa was to deploy a small rover supplied by NASA, called Muses-CN, onto the surface of the asteroid, but the rover was cancelled by NASA in November 2000 due to budget constraints.
• In 2003, while Hayabusa was en-route to Itokawa, a large solar flare damaged the solar cells aboard the spacecraft. This reduction in electrical power reduced the efficiency of the ion engines, thus delaying the arrival at Itokawa from June to September 2005. Since orbital mechanics dictate that the spacecraft must still leave the asteroid by November, the amount of the time it was able to spend at Itokawa was greatly reduced and the number of landings on the asteroid were reduced from three to two.
• Two reaction wheels that govern the attitude movement of Hayabusa failed in 2005; the X-axis wheel failed on July 31, and the Y-axis on October 2. After the latter failure, the spacecraft is now being turned on the X and Y axes with its thrusters. JAXA claims that since global mapping of Itokawa has been completed, this is not a major problem, but the mission plan was altered.
• The November 4 'rehearsal' landing on Itokawa failed, and was rescheduled.
• The original decision to sample two different sites on the asteroid was changed when one of the sites, Woomera Desert, was found to be too rocky for a safe landing.
• The November 12 release of the MINERVA mini-probe ended in failure.

In-flight event log

• On July 31, 2005, the X-axis reaction wheel failed.
• On August 14, 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. [6] Other images were taken from August 22 to August 24. [7]
• On August 28, Hayabusa was switched over from the ion engines to the bi-propellant thrusters for orbital maneuvering.
• From September 4, Hayabusa's cameras were able to confirm Itokawa's elongated shape. [8]
• From September 11, individual hills were discerned on the asteroid. [9]
• On September 12, Hayabusa was 20 km from Itokawa and JAXA scientists announced that Hayabusa had officially 'arrived'. [10]
• On September 15, a 'colour' image of the asteroid was released (which is, however, grey in colouring) [11]
• On October 4, 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.[12]
• On November 3, 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 mini-lander. The descent went well initially, and navigation images with wide-angle cameras were obtained. However, at 1:50 am UTC (10:50 am JST) on November 4, 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, Jun-ichiro Kawaguchi, explained that the optical navigation system was not tracking the asteroid very well, probably caused by the complex shape of Itokawa. A few days delay was required to evaluate the situation and reschedule. [13] [14]
• On November 7, Hayabusa was 7.5 km from Itokawa.
• On November 9, Hayabusa performed a descent to 70m to test the landing navigation and the laser altimeter. After that, Hayabusa backed off to a higher position, then descended again to 500m 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.[15]
• On November 12, Hayabusa closed in to 55m from the asteroid's surface. MINERVA was released but due to an error failed to reach the surface.
• On November 19, Hayabusa landed on the asteroid. There was considerable confusion during and after the manoeuvre about precisely what had happened, due to the fact that the high-gain antenna of the probe cannot 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 altitude.[16] [17] However, after regaining control and communication with the probe, the data from the landing attempt were downloaded and analyzed, and on November 23, JAXA announced that the probe had indeed landed on the asteroid surface. [18] 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 attitude 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 currently attached to the sampling horn was sealed.
• On November 25, a second touchdown attempt was performed. It was initially thought that this time, the sampling device was activated [19]; However, later analysis decided that this was probably another failure and that no pellets were fired.[20]. Due to a leak in the thruster system, the probe was put in a safe hold mode. [21]
• On November 30, 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. [22]
• On December 6, Hayabusa was 550km from Itokawa. JAXA held a press conference about the situation so far. [23] [24] On November 27, the probe experienced a power outage when trying attitude correction, probably due to a fuel leakage. On December 2, an attitude correction was tried, but the thruster did not generate enough force. On December 3, the probe's Z-axis was found to be 20 to 30 degrees from the sun direction and increasing. On December 4, as an emergency measure, xenon propellant from the ion engines was blown to correct the spin, and it was confirmed successful. Attitude control was commanded using the xenon gas. On December 5, attitude 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 is a strong possibility of the projectile of sampler not penetrated when it landed on November 25. Due to the power outage, the telemetry log data was faulty.
• On December 8, a sudden altitude 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. [25] [26]
• On March 7, 2006, JAXA announced [27][28] that communication with Hayabusa had been recovered in the following stages:
  • On January 23, the beacon signal from the probe was detected.
  • On January 26, the probe responded to commands from ground control by changing beacon signal.
  • On February 6, an ejection of xenon propellant was commanded for attitude control to improve communication. The spin axis change rate was about 2 degrees per day.
  • On February 25, telemetry data was obtained through low-gain antenna.
  • On March 4, telemetry data was obtained through medium-gain antenna.
  • On March 6, Hayabusa's position was established at about 13000km ahead of Itokawa in its orbit with a relative speed of 3m per second.
• On June 1, Hayabusa project manager Jun-ichiro Kawaguchi reported [29] that they confirmed two out of four ion engines work normally, which will be sufficient for return journey.

Timeline of future events

• February 2007: Hayabusa will begin its return to Earth.
• June 2010: Hayabusa will release its samples to return to Earth in a re-entry capsule.

External links

Official sites

• JAXA page on Hayabusa mission overview
• ISAS/JAXA page on mission
• ISAS/JAXA Hayabusa mission movie
• ISAS Hayabusa mission overview, construction, launch (audio in Japanese)
• ISAS/JAXA Hayabusa Today (live updates of the craft's position)
• Hayabusa mission official page (partially broken)
• NASA page on mission
• JPL/NASA PDF document about cancelled Muses CN Rover
• Hayabusa's Scientific and Engineering Achievements during Proximity Operations around Itokawa (JAXA press release on November 2)
• The 37th Lunar and Planetary Science Conference has Special Session on Results of the Hayabusa Mission, and a poster session Results of the Hayabusa Mission
• Special issue: Hayabusa at Asteroid Itokawa, Science, Vol 312, Issue 5778, Pages 1273-1407, June 2, 2006
• Initial Scientific Results of Hayabusa’s Investigation on Itokawa ~Summary of the Special Issue of “Science”Magazine~ (ISAS/JAXA press release)

News sites

• MSNBC article, "The real promise of Japan's asteroid mission"
• Probe set for asteroid touch down
• MSNBC article, "Japan shoots for a piece of an asteroid"
• Ambitious mission hopes to return bits of asteroid Comprehensive article by Spaceflight Now
• Thruster problem latest hurdle for asteroid probe A second article by Spaceflight Now
• Fate of Japan's troubled asteroid probe still uncertain A third article by Spaceflight Now

Notes

• Note 1: Source: June 2005 issue of Sky and Telescope, pp. 34-37, "Japan's asteroid archaeologist"
• (2006). "Hayabusa at Asteroid Itokawa (Special Issue)". Science (5778): 1273-1373.