Akatsuki Venus Climate Orbiter Options

[Paolo]

I thought it was time to start a separate thread on this mission, launching soon
some good medium-resolution images of the spacecraft are available on JAXA digital archives
http://jda.jaxa.jp/jda/p3_e.php?time=N&...mp;mission=4066

[elakdawalla]

I just want to chime in a note of thanks to you for your work in translating these documents, pandaneko.

[pandaneko]

Page-30

Example 3: Clarifyinng mechanism for complex patterns (UVI+LIR)

(1st character set after above in yellow box):

In particular, complex abosrption patterns in dark area

(2nd character set):

Are solar light absorbing materials lifted from lower height?
Are they newly chemically produced at cloud tops?
Are they moved horizontally?
What kind of convection, pulsage, random flow currents are involved?

(3rd character set in yellow box):

Very clear boundary between dark and light regions

(4th character set):

In particular, complex absorption patterns in dark area
Is there a barrier of horizontal mixture of absorbing material and haze (translation unsure, P)?
Is new aerosol produced in a particular area?

(5th character set):

Clarify air mass transport and change (?) process at cloud top from observing distribution of absorption materials and haze (UVI),
cloud temp. variation with height (LIR), wind velocity disribution form cloud tracing

P

[pandaneko]

I have this nagging thought. In fact, I have had it for long time by now.

If Akatsuki was able to enter a kind of orbit around Venus with its smaller
engines, then why did they bother with the larger engine that failed?

They could have designed a craft with a few more of these smaller engines and
made Akatsuki go around in a proper circle? Tha wouod have been a lot cheaper?

P

[cndwrld]

I have this nagging thought. In fact, I have had it for long time by now.

If Akatsuki was able to enter a kind of orbit around Venus with its smaller
engines, then why did they bother with the larger engine that failed?

They could have designed a craft with a few more of these smaller engines and
made Akatsuki go around in a proper circle? Tha wouod have been a lot cheaper?

P

Hello-

You can get into orbit with big engines or with small engines. But if you
plan to use a big engine, and then only have small engines, things
get difficult.

Look at the Dawn mission at Ceres. They have an ion engine, which has very
small thrust. But the engine is designed to operate for a very long time.
This was in the design, and the approach to Ceres was designed for the
amount of thrust available.

The main Akatsuki engine seems to have burned for about 3 minutes out of
the planned 12 minutes. So the spacecraft did slow down significantly, but
not nearly enough. So it went past Venus pretty fast. Later, some burns
were performed, but I assume that the spacecraft was still moving fast
when it returned to Venus.

All they had available were the attitude thrusters. I do not now know anything
about the Akatsuki attitude thrusters, but in general they are quite small
compared to a main engine, say 1 to 5% as big. And they are not designed to
fire continuously for long periods of time. Attitude thrusters are designed
to give very short bursts that are very accurate. Akatsuki now had to use
thrusters designed for short bursts, for a very long continuous burn. I
suspect that the thrusters were never designed, let alone even tested, for
such a long continuous burn. If I had been the propulsion engineer on
Akatsuki, I would have been very afraid of a failure of one or more of
the thrusters.

So, the answer to your question is: you can use small engines or big engines.
But if your mission is designed for one or the other, it is very very
difficult to change the mission design because your hardware may not work.

I hope this may have been helpful. Sorry if it is not.

[pandaneko]

cndwrid

Gracias y mucho obligado. Le entiendo muy bien.

Thaks.

P

[pandaneko]

Page-11

(Page title):

Akatsuki's health

Akatsuki is currently flying along an orbit nearer to the sun than Venusian orbit. Consequently it is experiencing a harder thermal
environment than originally planned.

Therefore, we changed its attitude so that the most heat resistance face (+Z) will point to the sun.

Akatsuki passed the 9th (final) nearest Sun point on 30 August 2015. At each point of the space craft the temp. is drecreasing
as predicted, showing that Akatsuki is in good health (except the main engine).

(on the left hand graph, vertical scale is solar radiation strength in W/mxm, and the horizontal scale is date)

(Character sets on the graph from top to bottom are):

Akatsuki (green)
Solar orbit (just above green dotted lines)
Transition (or transfer?) orbit (just above red dotted lines)
Maximum solar radation on 17 April at 3665 W/mxm
Venus (red in middle)
VOI on 7 December with 2621 W/mxm
Earth (blue in middle)
Launch 21 May

P

[pandaneko]

Page-13

(Note that page-12 does not have characters)

Akatsuki- Venus exploration

We wish to understand the climate of Venus which is often said to be very similar to the earth, by 3-D type
remote sensing into the cloud layers from orbit.

・ Why Super Rotation?, the high speed atmospheric motion
・　How can the atmosphere move vertically and north-south?
・ How are all covering clouds formed?
・ Are there lightenings in the absence of ice crystals?
・ Are there active volcanoes?

Page-14

Mysterious wind - Super rotation

Atmosphere rotates much faster than the speed of self rotation in the same direction (360km/h)

P

[pandaneko]

Page-15

Atmospheric circulation on earth type planets

(with the earth in 4th quadrant and clockwise)

(at 21:00 direction): Hudley circulation
(at 22:00 direction): Ferrell circulation
(just before mid night): Polar circulation
(on the globe from above, Westerly and Trade wind)

(in the 3rd quadarnt is Mars. Character in the top box is Winter and that in the bottom box is Summer.
On the globe at top is Westerly and below it is Trade wind. Outside the globe, horizontally across is Hudley and above it is Ferrell)

(1st quadrant is Venus with super rotation)
(2nd quadrant is Titan with super rotation)

Page-16

Clouds are formed by atmospheric circulation

(graphic here)

Clouds are responsible for planetary refletion and surface temperatures

P