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Akatsuki Venus Climate Orbiter
JRehling
post Jan 17 2018, 10:08 PM
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These are wonderful. A similar palette is being used by many amateurs making IR/UV images at much lower resolution.
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jccwrt
post Jan 18 2018, 03:00 AM
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A couple of attempts to merge the sunlit cloud deck imaged in near-UV and near-IR with nighttime thermal data taken at the 2.26 micron wavelength, which appear to be the least overexposed of the 2 micron camera images. The two sets of images were taken up to 2 hours apart, so the geolocation of these images probably isn't super accurate but should be fairly representative. I've also added a heat colormap to colorize the thermal infrared data - the scale doesn't correspond to specific temperatures or anything, it's just there to enhance some of the detail present in those images while also emphasizing that it's thermal data.





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JRehling
post Jan 18 2018, 04:43 PM
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Nice display of IR! It certainly gives the impression that we should not touch Venus without protective gloves.

It's hard to tell from just a couple of images, but I'd like to see a global average of limb darkening. There should be some limb darkening but in any single image, the regional variations are a bigger factor.
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scalbers
post Jan 18 2018, 08:39 PM
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I would guess the limb darkening has an interesting dependence on phase angle and location along the limb. A fun simulation project as well.


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scalbers
post Mar 8 2018, 06:04 PM
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I'm curious whether any of the recent data or images would show how much limb darkening Venus exhibits at a low phase angle (fully lit). Is it possible to assess this with an image using only visible wavelengths?


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JRehling
post Mar 9 2018, 08:54 AM
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QUOTE (scalbers @ Mar 8 2018, 11:04 AM) *
I'm curious whether any of the recent data or images would show how much limb darkening Venus exhibits at a low phase angle (fully lit). Is it possible to assess this with an image using only visible wavelengths?


That's an issue that I would love to see addressed. It certainly seems in all images that I've seen that this has at least some difference, though subtle, across the visible spectrum.

Venus Express imaged a glory on Venus, which implies that such a thing is perhaps in their data, unless the whole disk was not imaged. I haven't seen any such image that captures such a wide view.

Over the last few months I've been extremely eager to get a terrestrial photo of Venus at its fullest. I captured an image just four days ago with Venus at a phase angle of 18.5. (And immediately thereafter, an image of Mercury.) I wish it'd been less, and/or that the quality were higher, but weather has not been helping me out. I've seen few terrestrial images of a relatively "full" Venus in color. Perhaps what you are looking for can be approximated with this or a better terrestrial image.

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vikingmars
post Mar 9 2018, 12:04 PM
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QUOTE (jccwrt @ Jan 18 2018, 04:00 AM) *
A couple of attempts to merge the sunlit cloud deck imaged in near-UV and near-IR with nighttime thermal data taken at the 2.26 micron wavelength, which appear to be the least overexposed of the 2 micron camera images. The two sets of images were taken up to 2 hours apart, so the geolocation of these images probably isn't super accurate but should be fairly representative. I've also added a heat colormap to colorize the thermal infrared data - the scale doesn't correspond to specific temperatures or anything, it's just there to enhance some of the detail present in those images while also emphasizing that it's thermal data.


How nice ! Thanks very much jccwrt (and also to Ant103) : I'm feeling the heat too smile.gif
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scalbers
post Mar 9 2018, 04:34 PM
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Indeed now's a good time to get low phase angle images from Earth as JRehling did 2 posts up. I found this reasonably low phase angle view from MESSENGER (sorry this isn't Akatsuki) posted at The Planetary Society and processed by ugordan. Looks like there's some darkening even on the brighter limb. Interesting to see also how the subtle details look with the visually realistic processing.

http://www.planetary.org/multimedia/space-...01387b94_o.html


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pandaneko
post Jun 10 2018, 05:29 AM
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I have been thinking, ever since, and I may be going mad...?

If Akatsuki managed to enter whatever orbit it is in now with only chemical thrusters, then all future missions may benefit from not having
a large main engine. Instead, they can carry more instruments?

It will also be cheaper to make?

P
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Explorer1
post Jun 10 2018, 02:40 PM
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The main engine was most efficient, it was expressly designed to be good at Venus orbit insertion; the minor thrusters used much of the fuel and had to burn for much longer, to barely get into a much larger, less scientifically optimal orbit around the planet.
Ion thrusters so far have worked well for reaching small bodies (like Hayabusa 2, Dawn, etc.) New generations of ion engines might make them more usable at planets (see the Bepicolombo mission for an example).

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JRehling
post Jun 10 2018, 10:08 PM
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Compare the apoapses of various Venus orbiters:

Venera 15: 72,078 km
Pioneer Venus: 66,630 km
Venus Express: 63,000 km
Magellan: 7,762 km
Akatsuki (planned): 80,000 km
Akatsuki (actual): 330,000 km

All had relatively low periapses, so the Magellan orbit was somewhat circular, but the others were all highly elliptical, with Akatsuki's orbit being by far the most elliptical.

The greater the apoapsis distance, the more time that the orbiter spends far away from the planet, reducing resolution of imagery. That is why a closer orbit is more desirable. (Although an orbit that is too close would be unable to image large portions of the planet at a time.) The energy requirements for getting into a low-apoapsis orbit are much greater than for a high-apoapsis orbit.

For this reason, it is expensive to get into a low-apoapsis orbit, but it is still desirable, to increase the science return. Measuring the value of science, though, depends upon the goals. Akatsuki can still perform great observations, but it gets fewer of them in a given amount of time at high resolution because of the engine failure. Maybe for some science goals this is not that important, but generally, mission planners have valued the higher rate of return of the most detailed imagery.
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avisolo
post Aug 20 2018, 02:51 PM
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Venus, Earth and the Moon:
https://i.imgur.com/xiF7aZx.png

Source:
http://darts.isas.jaxa.jp/pub/pds3/staging...174_l2b_v10.fit
http://akatsuki.isas.jaxa.jp/en/topics/news/001085.html

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