Akatsuki Venus Climate Orbiter Options

[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]

Page-5

Main events up to now
(right hand side strings, top to bottom)

・ Akatsuki was launched on 21 May 2010.

・ Insertion into Venus circular orbit was attempted on 7 December 2010. However, due to main engine failure firing was stopped
after 2 minutes and 38 seconds (planned firing was for 12 minutes) and Akatsuki is currentlyflying in an orbit around the sun.

・ With a view to the reunion with Venus in winter of 2015 three orbit corrections were made during November 2011. (DV1, DV2, DV3)

・ Further orbit corrections were made during July 2015. (DV4-1, DV4-2, DV4-3)

・ Akatsuki passed the last nearest Sun point in August 2015 (9th approach). Akatsuki is currently seen to be healthy
except for the main engine.

・ Re-insertion attempt is planned for 7 December 2015. (VOI-R1)

(left hand table, top to bottom)

21 May 2010 Launch by H2-A #17)

7 Dec 2015 VOI-1
1 Nov 2011 DV1
10 Nov 2011 DV2
21 Nov 2011 DV3
17 July 2015 DV4-1
24 July 2015 DV4-2
31 July 2015 DV4-3
30 Aug 2015 Nearest Sun (last and 9th)
Sept-Dec 2015 additionl corrections
6 Dec 2015 attitude change
7 Dec 2015 Re-insertion attempt VOI-R1

P

[pandaneko]

cndwrid

Gracias y mucho obligado. Le entiendo muy bien.

Thaks.

P

[gwiz]

You can get the same velocity change out of your propellant load using a long burn with a small engine or a short burn with a large engine. However, for orbital insertion it is much better to have the burn near the peri-apsis as a given velocity change there brings the apo-apsis altitude down fastest. A short burn is thus better, as a long burn is spread over a large altitude range and so ends up giving a higher apo-apsis.

[hendric]

Like in Akatsuki, sometimes the rockets for the attitude thrusters and the main thrusters use the same fuel system, with the attitude thrusters using the fuel as a monopropellant (one-part) (like in the Martian, where Watney drips the fuel on a catalyst) but the main thrusters using the fuel together with an oxidizer as a bipropellant (two-part), typically hypergolic (self-igniting when mixed). When used as a bipropellant, the reaction is much more energetic, and provides greater thrust. When used as a monopropellant, the reaction is less energetic, but only requires pumping one liquid. The simplicity of only having to pump one fluid matters when you have multiple attitude thrusters around a probe. The thrust bipropellant provides is worth the additional weight and complexity if the delta-V required is high enough, like orbit insertion.

[pandaneko]

Page-6

Schedule on 6 December 2015

6/Dec daytime attitude change
7/Dec 04:30 Usuda station visible starts
08:22 Akatsuki enter Venusian shadow
08:51- fire attitude control engines, data acquisition/confirmation
11:30
12:00 explanation to the presss re firing
afternoon transfer to Camberra station
afternoon attitude change

Note:

At time of press conference the only known fact will be the result of engine firing.
Whether or not the intended orbit insertion is a success can only be confirmed during 7-9 December.
About that confirmation a seperate press conference is scheduled for 18:00 on 9 December.

P

[pandaneko]

Page-7

Orbit diagram at time of orbit insertion attempt (helio centric)

(On this page there are 3 main components, orbit diagram on left, box above and box below. The box below is the blow up of
the small box on the orbit diagram. The character set at the lower left bottom = Helio centric orbit diagram)

(Box above):

1. Currently, Akatsuki is flying ahead of Venus
2. From around 1 December Akatsuki will be flying outside of Venusian orbit. For this reason Akatsuki's speed will be less
and as a result Venus will catch up with Akatsuki.(Distance between them will become less)
3. On 7 December Venus will ovetake Akatsuki and at that instant velocity reduction will be attempted for orbit insertion

(Box below):

Upper left character set: Red circle=Venus position, square=Akatsuki position every other day
Lower right character set: Expansion of insertion details, helio centric orbit

Character sets upper right to lower left along orbit are:
(Red line=Venus, green line=Akatsuki)

1 December 2015
Approach from outside
Attitude control:(A)+Z Sun attitude->(B)VOI+R1 attitude
7 December 2015
Venus orbit insertion

(On the orbit diagram itself):
Outermost is Earth, red circle is Venus, green circle is Akatsuki
Character sets with numbers are all dates, 12=December
Character set along 1AU = 8 minutes 19 seconds

P

[pandaneko]

Page-8

(page title):
Orbit at time of insertion attempt (Venus centred)

(Blue box at top right is the same as that on page-7, therefore not translated)

1: (about the largest box on lower right)

(Top left corner is ): at time of VOI-R1 and the red arrow pointing to the sun, and the blue to earth.

(At bottom right corner there are 3 lines of character sets. These are, from top down):

○ is every one hour.
Expansion of insertion sequence
Orbit with Venus at centre

(Along the orbit lines, character sets outside the orbits in clockwise direction are):

Akatsuki (near circled number 1)
Shadow
VOI-R1 firing
VOI-R1 firing as neccessary
In the case of no VOI-R1 firing

(Inside the orbit curvature):

Venus
Direction of Venus motion


2: (about the orbit diagram on left)


(There are two oblong boxes here):

(Box on left reads):
Furthest Venus height 480,000-500,000 km
Dec. 2015 - Mar. 2016

(Box on right):
Furthest Venus height 310,000-330,000 km
Around April 2016

(Character sets ouside the closed orbits clockwise):

Akatsuki's motion
In absence of VOI-R1 firing
(inside the smallest closed orbit): Venus motion

P

[pandaneko]

Page-9

(page title): Engines to be used

(inside red framed box): Attitude control engine/top side (23N), used for orbit insertion
(inside blue framed box): Attitude control engine/down side (23N)
(character set at very bottom):
In order to make the craft into VOI-R1 orientation (sun is in the jet direction) on one day before (6 December 2015) VOI-R1 firing
will be conducted using the top side (+Z) attitude control engine which can best tolerate the solar beam input.

Page-10

(page title): Attitude changes before and after VOI-R1

(on the left hand orbit diagram):

(A)+X Sun
( VOI-R1 attitude
© VOI-R1c attitude
(D) Venus observing attitude

(yellow stars indicate attitude change positions)

(upper left arrows): sun direction in red, earth direction in blue at time of VOI-R1 operation

(on the right hand 4 blocks):

(character set just above these 4 blocks): craft attitude as seen from earth

(4 blocks clockwise are):

Blk1: (A)+Z Sun attitude
Blk2: (B)VOI-R1 attitude
Blk3: (D) Venus observing attitude
Blk4: © VOI-R1c attitude

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

[pandaneko]

Page-17

Various hypotheses about super rotation

(just below this page title on the right is an ellipse with red dotted lines. In it the character reads "acceleration zone")

(on the very lefthand narrow vertical gap are, top down):

stratsphere, clouds, and convection zone

(There are three graphics on this page, each with two character sets, top down):

(left hand graphic): Waves and random flow, Hudley circulation
(graphic in middle): Thermal tidal waves, Thermal tidal waves (never heard of this, P)
(right hand graphic): Gravity waves, Kelvin waves

(with each of these graphics characters at bootm from left to right are):

South pole, Equator, North pole

(below all these)

It is commonly assumed that some kind of huge waves are driving the atmosphere. Akatsuki wants to find out what it is.

P

[pandaneko]

Page-18

How are sulfulic acid clouds formed on Venus?

(against pale blue background just below page title above):
North-South and vertical cross-sections of Venusian upper atmosphere

(and just left of above): Height

(on this page there are 9 boxes. They are, anti-clockwise, starting from the first box, B1, which contains):

B1: H2SO4 is photochemically formed from SO2、H2O、CO2

B2: Upward transport of SO2、H2O ?

B3: Condensation of H2SO4 in upward stream？

B4: SO2、H2O、CO circulation

B5: H2SO4 decomposing into SO2、H2O

(This box is sandwiched by Equator on its left and Poles on its right)

B6: H2SO4 gas formation？

B7: Evaporation of H2SO4

B8: Transport of cloud seeds and CO

B9: Super rotation

P

[pandaneko]

Page-19

(Top): Venusian activities and lightenings

(Bottom): Venusian terrain obtained by NASA Magellan radar exploration

Page-20

Instruments on board Akatsuki

(Three blocks of characters on left)

Block1:

・　There are 6 instruments.

1.1 : 5 cameras covering ulyra violet to mid infrared range (IR1, IR2, LIR, UVI, LAC)

1.2 : Reference frequency generator for radio wave occultaton (USO)

・　　Data from 4 cameras except LAC is all controlled, processed, and recorded by mission system consolidated processor (DE)

・　Against the craft total mass of approx. 500kg, the total mass of 6 cameras and DE is approx. 37kg.

(On the right hand graphic there are 8 purple character bloks. These are from top to bottom):

1. Consolidated processor for mission system (DE)
2. Lightening and atmospheric light camera (LAC)
3. Mid infrared camera (LIR)
4. Ultra violet imager (UVI)
5. 1 micron camera (IR1)
6. 2 micron camera (IR2)
7. Radio waves
8. Radi wave occultation (RS)

(On the same graphic there are 7 character blocks in white. These are from left to right, and then top down):

1. Sequence control and on board procesing
2. Lightening and atmospheric lights
3. Cloud top temp. and cloud top height
4. Sulfur dioxide and unknown chemical substances
5. Ground surface material, active volcanoes, and water vapour
6. Lower layer clouds, cloud top height, and carbon monoxide
7. Temp. distrbution with altitude and sulfulic acid vapour

(characters lower bottom are neglected as being plain)

P