Hayabusa will try again on the 26th
The space journalist Shin-ya Matsuura attended a press briefing by JAXA yesterday afternoon. This is a translation of his blog.
The briefing started 6pm. JAXA will try the second attempt of the touch down with Hayabusa around 7am on the 26th, provided they successfully position the spacecraft along the line between the Earth and Itokawa tonight (24th). Final GO decision will take place around tomorrow (25th) noon.
The project manager Kawaguchi came into the pressroom at 6pm.
Condition today: nominal. They will try the touch down on the evening of 25th to 26th morning. Spacecraft will be brought into the position tonight with NASA station.
The probe is scheduled to make the touch down just after 7am (in probe time) on the 26th. The communication will be switched to beacon mode just before, so they will not be in the real time contact. Even if everything goes smoothly, it will not be before 11am before they can say anything about the situation.
According to the telemetry the temperature rise was 60 to 70 deg C during the last landing. No damage to the spacecraft was observed. The sensors hanging outside the spacecraft suffered some effects. They will fix the problem tonight. No contaminations to the sensors that were attached to the ground were observed.
There are some instruments such as laser range finder which cannot be tested until the spacecraft closes in to the asteroid. They will be tested on the fly.
The software had 7 to 8 traps during the 19th to 20th landing. They will change some parameters to ensure the continuity of the sequence for the second touch down.
Questions and answers at Sagamihara:
Aviation Week: I understand there might be some dusts in the sampler capsule caused by the landing at 10cm/s. What would you do?
Kawaguchi: We will close the capsule tonight.
Kyodo: You have spent fair amount of propellant. How critical is it? If you abort before you release the target marker, would you try yet another chance?
Kawaguchi: As for the propellant, it all depends on how precisely we perform the attitude control. Communication speed depends on it. We have experienced 8 bps on the way to Itokawa. If we limit ourselves only an hour of operation per day, we would be able to preserve the propellant. As of now we limit our capabilities upon returning the spacecraft and concentrate on taking a sample. We are not optimistic though.
If we are to abort the touch down maneuver at the early stages of the descent, there would be less effect to the propellant. There would be much effect once the spacecraft goes into perpendicular descent. If the effect is small, we would like to take a challenge again.
Unknown: How did you feel when you know Hayabusa has been landed?
Kawaguchi: We were just very happy. The whole operation team, I mean. I myself regard more value on taking off than landing. In the past NASA spacecraft NEAR has landed on an asteroid. Hayabusa landed and took off and yet it is still functioning.
Microphone switched to Tokyo office:
Jiji: Don't you know what was the obstacle which triggered off the sensor?
Kawaguchi: We have no images near the spacecraft. We will examine the surface images near the target marker, to see whether there were any obstacles which would generates the reflected lights.
(According to other source, JAXA/ISAS believes the probe has landed near the upper left corner of the target marker picture, in the Muses Sea. There were no big obstacles there, so they are speculating whether the obstacle sensor was accidentally triggered by unexpected amount of light coming back from the surface of Itokawa. Opposition effect? May or may not be.)
Mainichi: We would like to know the quantitative amount of the propellant. Why the touch down sequence is scheduled one hour later then the previous attempt? You said you would try the downward acceleration in the last press briefing. Would you still be planning to do that?
Kawaguchi: We know the amount of propellant but I would not disclose it because the figures would spread out on its own. The sequence shifts one hour behind because of the rotation of Itokawa is not exactly 12 hours. In our last attempt we also accelerated the spacecraft downward by 2 cm/s then entered into the free fall. We might increase this number.
NHK: Could you tell which sensor has the problem? What do you mean by " to ensure the continuity of the sequence"? Do you try the condition of the touch down that would not allow the spacecraft to rest on the surface?
Kawaguchi: The sensor in question is one of the heaters. We believe the heater itself is okay. We have very advanced control of the heaters. We just configure it in a different way this time.
For example, we change the threshold of the obstacles sensor to ensure the continuity of the sequence.
There remains some possibilities that we might send commands from the Earth at the very last timing. So there remains some possibilities of landing still. Not everything is judged autonomously.
Tokyo: When would you know the outcome of the spacecraft maneuver tonight? What do you mean by the sensor to "configure it in a different way"?
Kawaguchi: As of now we plan to perform the maneuver around 1am tonight, from the NASA station. If things go smoothly we would like to start at 22:00. It could be lagged behind until 3am. About the sensor... (???)
Gekkan Tenmon: The spacecraft had been landed in the attempt on the 20th. Does this mean the error in the altitude was 10m? What is the error of the Doppler shift?
Kawaguchi: I myself had speculated it should have been very low. I was curious why it did not land because the spacecraft had a downward velocity. At that point we did not realize the touch down sequence was stopped. We were wondering why the spacecraft would not come back if it had been landed.
This was the background why we could not declare the landing in the last press briefing.
Doppler shift measures the rate of displacement. We obtain the amount of displacement by integrating the shift. This method accumulates an error. We adjust the displacement by occasionally measuring the distance from the surface to reduce the error. The accuracy is an order of a few ten meters.
From the Tokyo office:
Unknown: We would like to hear from you about the status of the maneuver tonight.
Kawaguchi: We would know the result in the communication from Usuda tomorrow. We will disclose it after 11am.
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