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Venus Express
cndwrld
post Nov 24 2014, 09:31 AM
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Due to solar effects, Venus Express must do regular burns to raise the pericentre of the orbit. These used to be done in a single burn. But because the fuel is so low, there is concern about how fast the fuel can collect on the fuel tank sponge. The burns are now broken into multiple small burns, to avoid burping.

And one day, there just won't be any fuel. We are currently well within the error bars of the measurements, so every burn (even a daily momentum dump of a few milligrams of fuel) could be the last one and therefore be the last day of the mission. But one of the bigger burns for pericentre raising is probably where we'll run out of fuel.

Sunday we started our most recent pericentre raising burn sequence. The first two burns, on Sunday and Monday, went well. Tomorrow, Tuesday, will be orbit 3151 (25-Nov-2014, DOY329). The plot attached shows our projected pericentre altitude for this 28 day medium term planning period, and our slowly increasing pericentre altitude as we do the sequence of nine burns.

Every day, we're hoping the burn worked. Either it works, or we're done. So it is a bit nerve wracking.

We know this might be the last mission to Venus for 20 years, so we are concious of trying to wring out every last bit of science data that we can.

Attached Image


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nprev
post Nov 24 2014, 05:35 PM
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Wow. Thanks for the update, cndwrld; a bittersweet situation for the program to be sure, but quite interesting in terms of fuel consumption modeling.


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Paolo
post Dec 5 2014, 08:31 AM
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contact with VEx was lost last 28 November
http://blogs.esa.int/rocketscience/2014/12...xpress-anomaly/

EDIT: some telemetry packets have been received afterwards confirming the probe to be spinning
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Ron Hobbs
post Dec 16 2014, 11:03 PM
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Well, it is now officially over.

Venus Express goes gently into the night

Thank you, Venus Express!
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Explorer1
post Dec 17 2014, 12:46 AM
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And farewell to Venus too, at least until whenever the next visitor shows up...
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cndwrld
post Dec 17 2014, 09:18 AM
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Yes, we're done. We have a few months of clean-up to do, to ensure everything gets documented and archived. Then we're off to other things.

The data archive will survive, and be used for a very long time. Especially since there may not be another serious mission for a very long time (although let's hope Akatsuki makes it into orbit in Nov 2015). The Planetary Science Archive at ESA is a great resource.

We can't be sure of the VEX pericentre altitude. But it is likely that it will burn up in late January 2015. There will be no way to know for sure exactly when it burns up, but there is no doubt that it will unless aliens refuel it. The spacecraft was in Sun hold mode, with its panels pointed to the Sun. We happen to have just come out of Superior Conjunction, so the spacecraft, when pointing at the Sun, put the Earth into a side lobe of the high gain antenna. This allowed us to get an unreliable but occasional downlink/uplink. The spacecraft, for the moment, can probably stay on the Sun using its thrusters and just pushing out gas. But the gas pressure is not enough to get you slewed around to direct Earth pointing and hold it, so each time the spacecraft tried that it panicked and stayed on Sun pointing. As it stays pointing at the Sun, the Sun-Venus-Earth angle grows every day, taking us out of the side lobe of the antenna. The angle was such that we finally lost even minimal contact, and we know it isn't ever going to improve.

Best guess is that the spacecraft stays Sun pointing until it gets a very slight nudge from the upper atmosphere. With only the gas pressure in the thrusters (if even that is left), the spacecraft will tumble and continue dropping about 3 km lower every day. Tumbling means that power is irregular from the panels, if they generate any at all. Eventually, the pericentre altitude will get low enough that the dynamic pressure of the atmosphere tears the MLI thermal insulation, when the electronics will fail due to loss of thermal control. At that point, it's brain dead. And eventually, the inert body will get trapped by the atmosphere and do its final plunge. Nothing is expected to survive down to the surface.

Astrium built a heck of a spacecraft. Its brother, Mars Express, continues to carry the flag at Mars. And Venus Express data will generate Ph.d's for decades, and be the basis for any future missions (as Venera and Pioneer Venus et al were for VEX). Every mission stands on the shoulders of the ones before.

On 31 January, I'll hoist a few drinks to Venus Express. After a decade, it will be weird to work on something else.





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Paolo
post Dec 17 2014, 09:31 AM
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thank you for the update. just a quick question: is sporadic contact still maintained or was it lost for good? do we know the time of the last contact?
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cndwrld
post Dec 17 2014, 11:32 AM
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As far as I know, there won't be any more attempts at contact. They tried for a long time, but the geometry means that it is over.


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MahFL
post Dec 17 2014, 12:40 PM
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Farewell VEX smile.gif .
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J.J.
post Dec 21 2014, 02:04 AM
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Can only add my own belated thanks to the VEX team for a job well done.


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Tom Tamlyn
post Dec 21 2014, 06:39 AM
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A hearty thank you to cndwrld for your final detailed report, and for all the other reports you've given us over the years.

Please let us know about your next project. I assume it will be on topic rolleyes.gif, but you should tell us (briefly) even if it isn't.
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tedstryk
post Dec 21 2014, 12:52 PM
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What an amazing mission. A big thank-you to all who worked on it.


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cndwrld
post Dec 27 2014, 04:46 PM
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QUOTE (Tom Tamlyn @ Dec 21 2014, 07:39 AM) *
A hearty thank you to cndwrld for your final detailed report, and for all the other reports you've given us over the years.

Please let us know about your next project. I assume it will be on topic rolleyes.gif, but you should tell us (briefly) even if it isn't.


I've got funding for about six months to finalize the stuff at the VEX Science Operations Centre. Then I expect to be moving over to Mars Express science operations. There's not a lot of fuel left on MEX either, but it needs very, very little to maintain orbit. So we hope it will keep working as well as it has so far, for some years to come. For me, that's great. I love looking a pictures of rocks. And living in Spain.


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cndwrld
post Jan 9 2015, 11:34 AM
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Venus Express is no longer functional, but it isn't dead yet. The ground station time was already booked and not suitable for other missions, so they look for VEX once a day. And we continue to see little bits of the carrier signal. There are too many variables to use the carrier signal for any kind of status information, but at least we know that our old friend is still alive at the moment.

ESA blog post here.


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nprev
post Jan 9 2015, 09:51 PM
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That's gotta be...more than a little heartbreaking. She's sure not gong down without a fight, though.


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