* Astronomy

Blobrana · L

RE: HAYABUSA (MUSES-C) mission

Blobrana · L

Image captured at 21:06 JST, 19 November, 2005.

Image captured at 0:22 JST, 20 November, 2005.

Blobrana · L

This is an image of the target marker released toward the "Muses Sea" sampling site on Itokawa by Hayabusa on November 10, 2005.

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Credit: ISAS / JAXA

-- Edited by Blobrana at 23:28, 2005-11-19

Blobrana · L

Minerva

Blobrana · L

RE: HAYABUSA (MUSES-C) mission

Blobrana · L

The loss of the Minerva robot was due to mission controllers do not fully understanding how to deal with the spacecraft's motion after the periodic thruster firings.

During a 40-minute transfer window, when the main data link with the spacecraft was being switched from an antenna in Japan to one in Australia, information about the spacecraft's vertical motion was unavailable to ground controllers.

Mission controllers sent the release command, failing to realise the spacecraft had just fired its thrusters to maintain a minimum height above the asteroid – an adjustment it performed every 10 minutes or so during the descent.
The officials simply did not account for all possible mission scenarios during the antenna changeover.
The command took about 16 minutes to travel from the Earth to the spacecraft, and when it arrived, the thruster firing had raised Hayabusa's altitude to about 200 metres. So Minerva was released while its mother ship was moving away from the asteroid at about 15 centimetres per second – faster than the space rock's 13 cm per second escape velocity – and the robot simply drifted into space.

"This is (our) responsibility. Our readiness was not so complete." - Jun'ichiro Kawaguchi, project manager.

Nonetheless, the mother ship's practice descent was a success. It approached the asteroid to within 55 m and its laser range-finder – which had never before been tested – successfully helped the craft maintain its orientation with respect to the asteroid's surface.

Blobrana · L

Japan's Hayabusa probe successfully performed a close approach to the surface of the asteroid Itokawa today, clearing the way for an attempt to land and retrieve soil samples next week.

"We performed the touchdown test with success," mission managers reported on the Web site of the Japan Aerospace Exploration Agency, or JAXA.

However, Japan's Kyodo news agency quoted space officials as saying that an attempt to send a mini-robot called MINERVA to the asteroid's surface met with failure.

Credit ISAS / JAXA
A picture taken by the Hayabusa probe during Saturday's close approach shows the tip of the asteroid Itokawa. Hayabusa's shadow can be seen near the asteroid's edge as an I-shaped mark.

The 591-gram MINERVA (MIcro/Nano Experimental Robot Vehicle for Asteroid), was designed to hop gently across Itokawa's surface. Three small TV cameras were supposed to take pictures, while temperature sensors would have provided insight into the texture of the soil.

The hopper robot was deployed at 3:24 p.m. Japan time, from a distance of about 55 metres. Hayabusa “was able to establish radio contact with the free-flying MINERVA,” according to the JAXA report. But at the later update, officials said the small probe was now expected to drift away from Itokawa and not fall to the surface as planned. Its batteries are expected to be exhausted in a day or two.

"regrettably, as for leaving MINERVA on Itokawa's surface, it seems that it is not possible." - JAXA.

Meanwhile, the Hayabusa mothership has safely returned to its home position, about 6.4 kilometres distant from the asteroid.
Preliminary indications pointed to a problem with the delicate manoeuvres behind MINERVA's deployment.
While awaiting the ground command to deploy MINERVA, the Hayabusa mothership was under autopilot control to maintain a set distance above the surface. As it drifted up or down to a range limit, Hayabusa fired small gas thrusters to stay within the designated interval.

According to Junichiro Kawaguchi, a JAXA scientist, the deployment command happened to arrive at Itokawa during a period when Hayabusa was drifting away from the surface. Since the escape velocity associated with the asteroid's faint gravitational pull is so small — about 20 centimetres per second — MINERVA was sent on a flight path that took it away from the asteroid.
Kyodo quoted Kawaguchi as saying the mission team tried to make sure that the deployment signal would arrive while Hayabusa was descending. For some reason, this did not work.

The asteroid is currently falling inward toward the sun and is crossing Earth’s orbital path, but on the far side of the sun. At that range (about 290 million kilometres), the travel time for a radio message is 16 minutes each way.

"It is very disappointing that it did not work out nicely. We found out various things about the asteroid, so we will study the data and hope it will lead to the successful landing of Hayabusa (on Nov. 19)." - Junichiro Kawaguchi.

Credit ISAS / JAXA
The MINERVA mini-robot is equipped with temperature sensors and three cameras. A pair of scissors is shown for a size comparison.

MINERVA is a small robot lander whose weight is 591g. Although it is a tiny lander, MINERVA was to investigate the surface of ITOKAWA using three small colour CCD cameras.
These cameras are installed at 5-cm height from its bottom. Two of the cameras make up a stereo pair that is capable of looking at distance from 10 to 50 cm. The pair could have observed the detailed surface conditions at the landing area of MINERVA. A camera that can see further away is installed on the other side. It was to observe more distant regions of the surface and can operate while hopping.
Using the onboard camera of HAYABUSA, the best image surface resolution of ITOKAWA was 30 m during the global mapping phase.

The cameras on MINERVA have a image resolution of less than 1 mm when they observe 10 cm distance objects and can observe minerals making up a rock. MINERVA was to have investigated the size of regolith grains covering the surface of ITOKAWA.
Among pins attached to the top and the bottom of MINERVA, six are thermal sensors which were to measure the surface temperature of ITOAKAWA. From temperature variation data, scientists could tell whether the surface of ITOKAWA is rich in sands or rocks.

Blobrana · L

Nov. 12: Rescheduled rehearsal for descending (Release the probing robot "Minerva")
Nov. 19: First sampling (Release the target marker with signatures)
Nov. 25: Second sampling

Blobrana · L

The Hayabusa spacecraft will attempt to sample the asteroid on November 19.

The Japan Aerospace Exploration Agency (JAXA) are now prepared to carry out a landing at the “Muses Sea” site, perform a sampling task, and then perform another touchdown on November 25

During a rescheduled descent test that verified the probe’s guidance and navigation functions on November 9, the craft came within 70 meters of the surface.
Engineers have managed to work out the problems that forced the cancellation of the November 4 landing test. The onboard navigation computer detected anomalous information during that practice run. The problem resulted in an abort command being transmitted to the probe by Earth controllers, thereby stopping the rehearsal. Consequently, the spacecraft fired its chemical engines and returned to the home position.

Images taken by the on board cameras have been used to target prospective touchdown locations on Itokawa. One newly released image shows the shadow of the spacecraft cast upon the asteroid’s surface.

Hayabusa is now ready for its historic attempt to gather and return asteroid specimens to Earth.

Blobrana · L

Engineers, scientists, and officials at the Japan Aerospace Exploration Agency (JAXA) spent the weekend pouring over data and regrouping after their asteroid chaser Hayabusa on Friday aborted the scheduled release of its lander to the surface of asteroid Itokawa. While the "abort" was a setback, it was by no means the end of the mission.

Hayabusa will still go for the two touch-and-go landings to collect samples of the asteroid's surface materials slated for November 12 and November 25, according to Junichiro Kawaguchi, the missions project manager, but those dates may now change. They hope to release the lander, named Minerva, short for MIcro/Nano Experimental Robot Vehicle for Asteroid, during one of those descents.

Hayabusa began its descent from a "hovering" position about 3 kilometres from the asteroid in the early morning hours Japan Standard Time (JST) on November 4. The spacecraft was to have descended to just about 30 meters above the asteroid to test several instruments, and then move in closer to about 15 meters to release a target marker and then Minerva.

Since it takes around 17 minutes for a signal to reach Hayabusa from Earth, Hayabusa had been equipped with an autonomous navigation system; hence was carrying out commands on its own. The spacecraft descended slowly and smoothly over a period of several hours. Then, when it got to 700 meters from the asteroid.
"The abort signal was issued," But Hayabusa "continued down a few hundreds meters when it actually diverted" - Junichiro Kawaguchi.

By Sunday, Hayabusa had flown up to an altitude of 9.6 kilometres from Itokawa and was then to travel back down its "home" position of about 7 kilometres . The spacecraft is currently around 290,689,380 kilometres from Earth.

The team has not yet figured out exactly why the spacecraft aborted at the time it did, but they have an idea it's got something to do with the navigation camera. Hayabusa's navigation, guidance, and control system utilizes an Optical Navigation Camera (ONC), a Light Detection And Ranging (LIDAR), a Laser Range Finder (LRF), and Fan Beam Sensors (FBS). It is able to autonomously decide each move on its own by measuring the distance to and the shapes of the asteroid surface using the ONC and LIDAR.
"How the spacecraft sees the terrain depends on where the camera is with respect to (the asteroid). This may have caused the spacecraft (to be) at a loss for what the target direction (was)" - Junichiro Kawaguchi.

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