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Sanjay Limaye

Live from Sagamihara: Akatsuki Orbit Insertion Success!

Posted by Sanjay Limaye

07-12-2015 10:16 CST

Topics: mission status, Akatsuki (Planet-C), Venus

Sanjay Limaye continues his first-hand account of the Akatsuki orbit insertion, begun here.

December 7, 2015

3:50 am, outside ISAS

Akatsuki is speeding towards Venus at 3.28 km/sec, only 72,000 km away. The sky is partly cloudy so Venus should be visible. Time to go to find the telescopes being set up at ISAS for the public to see Venus.

More than 50 people showed up from as far away as Scuba as well as Sagamihara for the public viewing through telescopes set up in the ISAS compounds. Now the viewing is at the nearby museum which has a telescope. Quite a few people at the viewing session had seen my previous blog entry posted here! A few came up to me and inquired if I was writing and thanked me.

There is a live commentary going on in the Project area and engineers are checking off milestones. Akatsuki is moving at 4 km/sec and only 40,000 km from Venus....

8:00 am, inside ISAS

Takeshi Imamura walks into the work room for breakfast. He is guarded, cautiously optimistic and confident.

Akatsuki is moving at 6.34 km/sec, about 11,100 km away only.

Chikako Hirose, a young female engineer, leads the trajectory design. She will know from the Doppler shift how the burn went. Delta-V expected is ~ 100 m/s. Canberra, Usuda and another JAXA dish near Kagoshima are tracking.

Chikako Hirose (ISAS) who worked on the Akatsuki trajectory, pleased that her work paid off.


Chikako Hirose (ISAS) who worked on the Akatsuki trajectory, pleased that her work paid off.

8:13 am. We see the Usuda station signal in the control room

8:30 am. Akatsuki is behind the planet so we cannot see the signal from the high-gain antenna.

8:33 am. Received confirmation of the first command of the burn sequence has been executed. One-way light time is about 8.5 minutes.

Akatsuki Control Room during the orbit insertion process.


Akatsuki Control Room during the orbit insertion process.

8:37 am. Some of the team are peering through the glass window into the control room

8:38 am. One of the staff has made special labels for soy milk boxes - a pun on the Japanese word for orbit insertion. "Tounyu" is the name of soy milk and the orbit insertion term.

8:51 am. Maneuver has started.

9:01 am. Graph of expected Doppler shift is on the right screen. So far actual Doppler matches the maximum!

9:19 am. Takehiko tells me now that it has reached 90%. Akatsuki is in orbit it would seem!

9:21 pm. Thrust now is higher than 100%! Could be slight misalignment of thrust value than assumed?

9:23 am. Every one clapping! Masato declared we are in orbit!!

Akatsuki is in orbit!


Akatsuki is in orbit!
Masato Nakamura declares Akatsuki is in orbit around Venus.


Masato Nakamura declares Akatsuki is in orbit around Venus.

Compared to the exuberance at similar NASA mission events, it feels quite subdued! The Akatsuki team achieved something that no mission has done before – put a spacecraft into orbit around a planet using only the attitude control thrusters. An event that one could not even conceive or propose!

Takeshi Imamura comes out of the control room into the work/break room and looks greatly relieved. He still has work to do. In fact now that the spacecraft is in orbit, the attitude of the spacecraft has to be continuously updated. The commands will be generated manually and uploaded until the orbit is known better.

For the insertion burn, the high-gain antenna could not be used because the orientation of the spacecraft required to be such as to produce thrust counter to the direction of motion to reduce the speed. The medium-gain antenna was receiving signal from the ground station and transponding it back to provide the two-way Doppler, since the entire maneuver was visible from Earth. However, the signal received from the medium-gain antenna is quite weak. When the telemetry data from Akatsuki started to be received after the 8 minute 20 second one-way light time delay, a graph was flashed on the right screen showing the expected cumulative velocity change for maximum thrust from the four rockets and several other curves showing values for different fractions of the maximum thrust. We are all watching the data trickle in – the real delta-V points were falling on the maximum thrust curve! Exciting!! Trajectory calculations were done elsewhere using the data from Usuda (JAXA) and Canberra (NASA/JPL DSN). At one moment there is a break in the graph, a gasp is heard, but the graph resumes again as the data flow continues. The Usuda DSN had switched to a different orbit model, which caused a few seconds break.

12:00 PM JST Press Briefing

JAXA's press release on the successful arrival at Venus is posted on their website.

The conference hall at ISAS is full of media persons. Nakamura arrives and an ISAS Press Officer asks him some questions, a after a few words begins taking questions from the media. No handlers for the briefing, no senior officials from ISAS or JAXA – is the Program Manager’s show. I notice only a few persons from the Akatsuki team. Very different from a typical NASA briefing.

Masato is smiling answering questions – it is all in Japanese, so I cannot understand anything, except guess at the question and the answer from Nakamura when he uses the spacecraft model to illustrate. At one point there was laughter - Prof. Nakamura said that unfortunately he cannot give a refund for the express ticket to Venus, but glad that he took us to Venus.

In half an hour the briefing is over.

Venus in the ultraviolet from Akatsuki, December 1, 2015


Venus in the ultraviolet from Akatsuki, December 1, 2015
UV (365 nm) image from Akatsuki taken on when Akatsuki was 1.1 million km away from Venus, five days before orbit insertion.
Venus in the infrared from Akatsuki, December 1, 2015


Venus in the infrared from Akatsuki, December 1, 2015
Venus at 900 nm wavelength imaged from the IR1 camera when Akatsuki was 1.1 million kilometers away from Venus, five days before orbit insertion.

Following are translations of tweets from the press briefing by space journalist Shinya Torishima (@Kosmograd_info), translated by @5thstar.

See other posts from December 2015


Or read more blog entries about: mission status, Akatsuki (Planet-C), Venus


Atom: 12/07/2015 12:44 CST

This is a great day for both Dawn missions (Akatsuki=Dawn in Japanese). First the long delayed orbit insertation around Venus and Dawn's arrival at it's final mapping orbit (Low Altitude Mapping Orbit) around Ceres. Congradulations to both mission teams!

Mewo: 12/07/2015 01:49 CST

If I understand correctly, Akatsuki had to expend nearly every last puff of attitude control fuel to make orbit. How will it perform attitude control now?

Tomas: 12/07/2015 11:12 CST

No, the fuel was used the same as for the main thruster. It has common tank, the main thruster just used additional oxidizer to get higher efficiency(ISP).

Mewo: 12/08/2015 01:59 CST

Oh, OK. Thanks. :)

masanori: 12/08/2015 10:08 CST

Konbanwa Sanjay sensei!! It was so nice talking with you at Venus watching party at ISAS. Thanks for introducing your colleague Mr Kevin (Right? His name sounded to me like this). I'm so glad for Akatsuki behaved as commanded when VOI. Looking forward to tomorrow's confirmation with all ready for celebration. Dear Mewo. I would like to answer to your question, with hoping that my very bad English language works. I have heard about this for several occasions, including the press conference on 09 Nov 2015. The team has always thought about how to achieve original goal of the mission even in this situation. So when designing how to achieve it, their calculation on fuel has always included the ones to use for the changes of orientation and of orbit when orbiting Venus, too. So yes, they used most of the remaining fuel when on 7 Dec 2015. But they understand how much of fuel is remaining AND it's enough for doing science for next 2 years. PLUS, as Akatsuki behaved as commanded on VOI-R1, there was no need for additional thruster burn (VOI-R1c), so I think the largest amount possible of fuel is remaining now. Which is really a good news.

Mewo : 12/08/2015 11:23 CST

Dear masanori, thank you very much for the detailed explanation. The situation is clearer to me now. i'm looking forward to the excellent new data Akatsuki will bring and it is encouraging to know the spacecraft still has enough fuel for a lengthy mission. JAXA and all involved in recovering Akatsuki deserve congratulations for this success.

5thstar: 12/09/2015 03:11 CST

Hi! Thank you for quoting my translations! Nice article! I'm also very pleased with this success. You wrote "as far away as Scuba as well" but there's no place called Scuba in Japan. You might want to check with your colleague but I think it's Tsukuba. There's a JAXA space center called TKSC. It does sound like Scuba.

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