Hayabusa: To 880,000 Little Princes and Princesses

November 21, 2005
Yasunori Matogawa
Director, Office of External Relations
ISAS

When we held the campaign –Let's Fly to Meet your 'Star Prince (Little Prince)' (World's First Attempt to Land Names on Asteroid)” prior to the launch of the Hayabusa (May 2003), we were pleasantly surprised when we received 880,000 applications from 149 countries. Those astonishing number of names were engraved on the Hayabusa target marker, which is only about the size of a softball.

First of all, I am very delighted that I can report to you that the target marker successfully arrived on the surface of the Itokawa. The marker was released from the Hayabusa as a guiding indicator for landing on Nov. 20, 2005 (Japan Standard Time, JST. All dates and times in this report are JST), the day of the first landing attempt on the Itokawa.

At around 9:00 p.m. on Nov. 19, the Hayabusa, which was at an altitude of about 1 kilometer, started descending in the sky over the Itokawa, some 300 million kilometers away from earth. The descent was amazingly smooth compared to the two rehearsals. Its speed was controlled to about 4 cm per second. This navigation and control method was the result of the efforts of the Hayabusa team who had been carefully studying how to overcome numerous difficulties, including the malfunctioning of two reaction wheels in the last few months.

First, we tried to combine the remaining healthy reaction wheel and the gas jet, but a minor error occurred in the orbit whenever we emitted the gas jet. When such errors accumulated, the orbit was deviated. Then, we came up with the jet method that could minimize such errors caused by the gas jet, studied it carefully by simulating it both on orbit and on earth, and tested it during the rehearsals. Our efforts were successful.

At 4:30 a.m. on the 20th, at an altitude of 450 meters, the speed of the Hayabusa was increased to about 10 cm per second to approach the Itokawa while the explorer was controlled to stay in the line connecting the center of the Earth and that of the Itokawa. For more than an hour, the Hayabusa approached the Itokawa under ultimate control in which an error in speed per second was just a few millimeters. The speed was about the same as that of an ant. During that time, just before 5:00 a.m., Project Manager Junichiro Kawaguchi made the –Go” decision based on progress up to that point.

At 5:46 a.m., at an altitude of 54 meters, a wire that connected the target marker to the bottom of the Hayabusa was disconnected by the cutter. The target marker with 800,000 names who wanted to meet the Le Petit Prince was detached. The Hayabusa continued to descend at 10 cm per second for 140 seconds before reducing its speed to 4 cm per second. The target maker that was set free dropped onto the surface of the Itokawa, which was lit up by a flash lamp from the Hayabusa. Although the marker separation itself had already been rehearsed, it was the first time for us to skillfully guide the Hayabusa to the direction of the falling maker to take images automatically. The people's names hoping to meet Le Petit Prince were delivered to the Itokawa through such careful guidance.

At 5:47 a.m., at an altitude of 35 meters the Hayabusa team's maneuvers entered into unknown territory, where we had never succeeded before. The explorer was descending using the Laser Range Finder (LRF). The Light Detection and Ranging (LIDAR), which had been guiding the Hayabusa, was no longer useful. Although we had carried out a measuring test on the LRF during the rehearsals, it was the first time to actually have the explorer descend under the control of the LRF. At an altitude of 25 meters, hovering by the LRF was performed. This was also a first experience for us.

At 5:55 a.m., the loud voice of –the altitude is 17 meters” echoed in the control room. At 6:00 a.m., the Hayabusa entered into autonomous mode to control its axis vertical to the surface of the Itokawa. Communications with the NASA Goldstone Station were switched to beacon mode (with only carrier waves) using the low gain antenna without modulation. The altitude was confirmed by Doppler data.

–Bravo! Landing!” Everybody there firmly believed the success.

The sampler horn of the Hayabusa is programmed to release a 5-gram bullet (10 mm in diameter) as soon as the horn receives a landing signal from the Hayabusa's sensor, then catch dust and particles blown up by the bullet hitting the surface of the Itokawa, and, in a second, return to ascending mode.

However, at the very end of the landing and sampling process, trouble loomed. Even though it was the time to ascend, Doppler data never indicated it happened. Moreover, data showed us that the explorer was still –descending” at 2 cm per second. Without knowing what was going on, 30 minutes passed eerily. Based on the limited available information, the Hayabusa seemed to drift at an altitude of 10 meters. If the explorer became too heated by the surface of the Itokawa, onboard equipment could be damaged. Project Manager Kawaguchi then decided to –send a Delta V”, meaning to send a command to emit a gas jet to have the Hayabusa ascend.

Unfortunately, the tracking period by the Goldstone station was about to end, thus we had to switch the operation to the Usuda station in Nagano, Japan. We did not want to lose the explorer during the switching, thus we sent a –safe-hold mode” command under the instruction of Project Manager Kawaguchi. The safe-hold mode is a control to spin the Hayabusa while making its solar array paddles always face the Sun. The above two decisions were very timely and appropriate.

However, probably due to surface heat from the Itokawa of over 100 degrees Celsius, the amplifier for the communication system did not work perfectly, thus the beacon mode continued with the Usuda station for a while. Time passed without knowing what was going on with the Hayabusa, but, finally, thanks to the efforts of the engineers at the Usuda Station, communications by the mid gain antenna (MGA) were restored. We then found that the Hayabusa had been successfully sifted to the safe-hold mode. Moreover, it seemed to move away from the Itokawa by some 60 to 70 kilometers.

Whether the Hayabusa landed on the Itokawa or not is still under discussion and that will be clarified by analyzing telemetry data. Before that, we need to restore the three-axis control from the safety mode within the tracking operation time of the Usuda station on the 21st. After completing this difficult task, we can easily receive precious data about the landing that is stored in the Hayabusa by using the high gain antenna (HGA). We shall calmly wait till then.

The first landing trial went like this. The target maker with 880,000 signatures from people who wanted to see the Le Petit Prince who lives on a very tiny asteroid in vast space fulfilled an important guiding role. It now stays on the asteroid Itokawa semi-permanently as a –name list of princes and princesses from the planet earth.”

For further developments, please regularly check the JAXA website.

The Hayabusa mission, which is one of the finest monumental achievements in the history of space exploration, is not complete. The team, led by Project Manager Kawaguchi whose motto is to –Never give up”, is working hard night and day to renew their determination to overcome the final hurdle of landing and sampling and will try again on the 25th or later. I would like to extend my congratulations and appreciation to all 880,000 little princes and princesses of Earth for a successful arrival at the Itokawa, while profoundly feeling happiness at being able to share this moving experience with young Japanese engineers who are becoming some of the best in the world at asteroid exploration.

Do your best, Hayabusa team!

November 30, 2005