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Venus Express
Phil Stooke
post Jan 13 2015, 02:55 PM
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I am hoping we will be able to say - roughly - where Venus Express burns up over the planet. I have tried to find this for Pioneer Venus Orbiter and Magellan was well, without success.

We should be able to figure it out, assuming the time of the atmospheric entry is know. For VE we might not know exactly which orbit is its last, but we could extrapolate. For PVO and Magellan the exact entry orbit is known. Since we will have the periapsis latitude, and the orientation in space of both the orbit and the planet at that time, the entry area should be identifiable within a few hundred km (I'd settle even for 1000 km). But I can't put those things together myself. If anyone can put the geometry together for the older missions I would be very pleased to see it, and I hope the VE case will be possible as well even with limited or no telemetry, if we can approximate the time of entry.

Phil



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Gerald
post Jan 13 2015, 04:10 PM
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I'd think, predicting uncontrolled re-entry is close to impossible.
A probe may enter the upper atmosphere, and leave it again.
During this aerobreaking the probe may disintegrate. Dependent of whether, when and to which degree the probe disintegrates, the drag coefficient, mass and area will change, all of which are relevant for the further fate. Density, temperature, wind, and composition of Venus' atmosphere are more variable parameters.
Assuming all parameters known, the resulting system of differential equations is called 'stiff', meaning it's numerically very unstable, and difficult to solve.

My expectation would be, that the probe will end up as several fragments settling at different locations almost along one or more (displaced by angle) circumferences.
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Phil Stooke
post Jan 13 2015, 04:55 PM
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Not really - it has to happen at periapsis so we know the latitude, and for near-polar orbits, if we know the plane of the orbit and the orientation of Venus we know the longitude. I don't see this like a 'skip entry' like Apollo or Chang'E 5 T1. And I only want an approximate position - just to say "over Alpha Regio" or "over Fortuna Tessera" would be quite sufficient. It should just be geometry - periapsis latitude plus or minus a bit and sub-surface longitude of that particular periapsis (plus or minus a couple of orbits if necessary, and for a slow-rotating planet that's not much difference). I just can't put it together myself.

I would actually expect the solution to be an ellipse a few hundred km wide and 1000 km long, approximately.

Phil


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Gerald
post Jan 13 2015, 05:51 PM
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Determining the nominal periapsis points should be possible.
(Candidates for break-up.)
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Gerald
post Jan 13 2015, 11:04 PM
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QUOTE (Phil Stooke @ Jan 13 2015, 05:55 PM) *
if we know the ... the orientation of Venus ...

This WGCCRE paper, you co-authored, provides a basis for the orientation of Venus (Table I, c).
(Edit: For January 31, 2015, 12 h, I get d = 5509, hence W = 160.20 − 1.4813688d = 160.20 − 1.4813688 * 5509 = -8000.66 = 279.34 (mod 360) degrees east of point Q, one of the two intersections of the ICRF equator with the Venus equator.)

I didn't yet find the pointing of the orbital plane of VEX. The periapsis latitude should be 82 N.
The break-up is expected to be near the end of January 2015.
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scalbers
post Jan 13 2015, 11:53 PM
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QUOTE (mcaplinger @ Mar 12 2014, 07:58 PM) *
I'm not an etymologist but "glory" is a well-accepted term that appears in popular scientific literature all the time (see, e.g., the references at the bottom of the wikipedia article), at least in the United States.

Perhaps there is some technical distinction between different effects, or perhaps it's called something different in other countries.

It's also a "glory" at this UK based site: http://www.atoptics.co.uk/droplets/gloab.htm. I think the other names are generally for other effects.

On the Wikipedia page Philip Laven's link is another one with a lot of explanation.


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cndwrld
post Jan 14 2015, 09:29 AM
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For anyone interested, here is an image from the Venus Express planning tool which shows the planned orbits from 04 January through 31-Jan-2015, DOY 031. If you want to take a whack at figuring out the final minutes of the mission, maybe this will help.

The pericentre height today was predicted to be at an altitude of 130 km.

Some explanations of the image:
*The planet position is that of the last orbit (orbit 3223).

*The centre of the image where the orbits cross is the north pole. The
right side is in darkness; the left side is lit. Atmosphere not
shown.

*The orbit track is from top to bottom.

*The purple triangles near the centre are the pericentre points. They are at Position [lat, long]: [73.6133799 (N), 159.509745 (E)] (degrees)

*The orbit track in yellow shows it is in sunlight; the orbit track in cyan
means it was in the dark. For example, the last orbit starts on the upper
left, goes past pericentre and over the pole. The image of the planet is
for the last orbit, so the orbit track changes to cyan as it crosses
the terminator.


First orbit: 3194 (04-Jan-2015, DOY004)
Final orbit: 3223 (31-Jan-2015, DOY031)

Attached Image


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cndwrld
post Jan 16 2015, 08:38 AM
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The latest press release on VEX status is here.


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cndwrld
post Jan 28 2015, 10:55 AM
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This is probably our last view of Venus Express.
ESA Rocket Science blog here.


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ZLD
post Jun 19 2015, 04:27 AM
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I suppose this fits here.

'Hot Lava Flows Discovered on Venus' - VEX/ESA

Finally able to another peg in a long mystery, and (likely) another active planet in the solar system.


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Paolo
post Jun 19 2015, 06:26 AM
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unfortunately the paper by Shalygin et al. is beyond the paywall
http://sci.esa.int/venus-express/56053-sha...ev-et-al-2015/#
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xflare
post Jun 19 2015, 07:13 AM
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We need to go back to Venus, it's been neglected for too long now.
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ZLD
post Jun 19 2015, 07:30 AM
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QUOTE (xflare @ Jun 19 2015, 02:13 AM) *
We need to go back to Venus, it's been neglected for too long now.


A whole 6 months? laugh.gif

By December, there may be another chance to reaffirm these findings with Akatsuki, granted in a somewhat limited capability. But yeah, a couple Discovery class orbiters flown in parallel for some interferometric SAR or simultaneous left and right looking SAR, along with a multispectral imager with thermal for comparison to ground data. Would be a good update to what we have.


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cndwrld
post Jun 19 2015, 07:33 AM
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I don't see us going back to Venus any time soon, sadly. On the other hand, there are many year's worth of data in the VEX archive that has hardly been looked at yet. With the small size of the Venus science community, I think there are a lot of discoveries waiting in the PSA archive.

This would be a great time, if you're a grad student, to decide to focus on Venus. There's a ton of essentially new data available, and not a lot of competition to look at it. And if you master this stuff now, then you'll be solidly in the community when another spacecraft finally does get to Venus.


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ZLD
post Jun 19 2015, 01:44 PM
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From several of the same associates including the primary author in 2012, 'Search for ongoing volcanic activity on Venus: Case study of Maat Mons, Sapas Mons and Ozza Mons volcanoes'. Seems likely that this is a similar process to what they were using in this new article.


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