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