Venus Express Options

[cndwrld]

The Venus Express Mission Operations Report 257, for our 89th monthly planning cycle, is now on-line.

It includes an overview of our simultaneous seasons of solar eclipses and Earth occultations, targets for the surface mapping campaign, and an explanation of how we manage orbit correction maneuvers as fuel and oxidizer tanks approach low liquid levels in zero gravity.

VEX Mission Operations Report 257 (Planning Cycle 089))

[cndwrld]

The Venus Express mission operations summaries now go up to the end of April 2013. Reports 258 and 259 are available.

These two reports cover the entry into, and exit from, the superior conjunction shutdown, automation of spacecraft passes at the Mission Operations Centre and thermal fuel gauging tests.

The status report archive is here.

[Doug M.]

It includes an overview of our simultaneous seasons of solar eclipses and Earth occultations, targets for the surface mapping campaign, and an explanation of how we manage orbit correction maneuvers as fuel and oxidizer tanks approach low liquid levels in zero gravity.

I understand that measuring remaining levels of fuel in a spacecraft is something of a black art. That said, do we have an idea approximately how much fuel remains, and how long it's likely to last?

By the way, these are great -- thank you for posting them, and please do continue.


Doug M.

[cndwrld]

I understand that measuring remaining levels of fuel in a spacecraft is something of a black art. That said, do we have an idea approximately how much fuel remains, and how long it's likely to last?

By the way, these are great -- thank you for posting them, and please do continue.


Doug M.

We typically get zero feedback for the public outreach stuff, so thanks for the note.

The fuel/ox level measurement is quite the black art. What we have right now is the numbers from the archaic but still prevalent method on all spacecraft: bookkeeping. Those numbers tell us that we can make it to at least December 2014 and probably a bit later. But there's enormous uncertainty in those numbers after 7 years of daily burns. The numbers from the new method are still being evaluated. And there's only been one advanced test, so we'll have one data point from that. Maybe next year we'll get more tests, and numbers. For now, that's all we've got.

[Doug M.]

We typically get zero feedback for the public outreach stuff, so thanks for the note.

You're very welcome! Seriously, I check in every couple of months and skim a bunch of these. Read like that, they're really interesting. A bit dry, but that's to be expected. They give a good picture of what it's like to actually run a spacecraft over time.

The fuel/ox level measurement is quite the black art. What we have right now is the numbers from the archaic but still prevalent method on all spacecraft: bookkeeping. Those numbers tell us that we can make it to at least December 2014 and probably a bit later. But there's enormous uncertainty in those numbers after 7 years of daily burns. The numbers from the new method are still being evaluated. And there's only been one advanced test, so we'll have one data point from that. Maybe next year we'll get more tests, and numbers. For now, that's all we've got.

I assume that fuel is the limiting factor? If you had enough fuel to go to, say, 2016, there'd be nothing else that would stop you from continuing the mission?

Also, according to the mission FAQ online the plan is to decommission VE with a terminal burn into the atmosphere. Is that still the plan -- and if so, wouldn't you want a reserve of fuel for that final burn?


Doug M.

[Explorer1]

Well, the orbit would decay sooner or later, given the sun's influence. It's only a matter of how soon it will happened.

[Doug M.]

Well, the orbit would decay sooner or later, given the sun's influence. It's only a matter of how soon it will happened.

Right, but IIUC once they run out of fuel, they won't be able to stabilize the orbiter, and they'll lose contact with Earth. Whereas, if they keep a bit of fuel, they can get some science from that terminal orbit -- observations at a much lower altitude than they would otherwise have dared. At least, that's the plan with Cassini and with MESSENGER. Don't know about Venus Express.


Doug M.

[cndwrld]

Right, but IIUC once they run out of fuel, they won't be able to stabilize the orbiter, and they'll lose contact with Earth. Whereas, if they keep a bit of fuel, they can get some science from that terminal orbit -- observations at a much lower altitude than they would otherwise have dared. At least, that's the plan with Cassini and with MESSENGER. Don't know about Venus Express.


Doug M.

The VEX spacecraft is in great shape. I'm continuously surprised by how robust it has been. All the usual consumables (batteries, wheels, solar panels, star trackers) are in great shape. Kudos to Astrium. We're just running out of gas.

The plan for the final day is, as you say, a controlled burn into the atmosphere. At Venus, we all get a Viking funeral. And the 'control' part is the hard part. But once the fuel is gone, there's always something left. We say 'fuel' and sort of mean three things: fuel, oxidizer (in our case, a dual system) and pressurant. When the fuel or ox runs dry, there's still impulse to be gained just by pushing out the other fluid. And even when both the fuel and ox are gone, you can still blow the helium out. Neither of the latter two options give you much, but we won't need much. Our apocentre is very high; just blowing helium out for a while would probably be enough to tip our pericentre low enough so that in a few orbits we'd be toast.

I'm sorry the status reports are so dry. Sigh. There's nothing I can do. The alternative is to have nothing at all.

[Doug M.]

The VEX spacecraft is in great shape. I'm continuously surprised by how robust it has been. All the usual consumables (batteries, wheels, solar panels, star trackers) are in great shape. Kudos to Astrium. We're just running out of gas.

It's the same with Mars Odyssey, Cassini, and MESSENGER. It really is striking how many long-lived spacecraft we have out there now. Even putting aside the Voyagers, I know of well over a dozen space probes and comsats that are over 10 years old and still in good repair and active. (And I'm sure there are plenty more that I don't know of.) It's particularly impressive for a probe like VEX that is in a challenging thermal and radiation environment.

The plan for the final day is, as you say, a controlled burn into the atmosphere. At Venus, we all get a Viking funeral. And the 'control' part is the hard part. But once the fuel is gone, there's always something left. We say 'fuel' and sort of mean three things: fuel, oxidizer (in our case, a dual system) and pressurant. When the fuel or ox runs dry, there's still impulse to be gained just by pushing out the other fluid. And even when both the fuel and ox are gone, you can still blow the helium out. Neither of the latter two options give you much, but we won't need much. Our apocentre is very high; just blowing helium out for a while would probably be enough to tip our pericentre low enough so that in a few orbits we'd be toast.

So, basically you could alter your orbit by mechanical rather than chemical means! Very cool.

cheers,


Doug M.

[stevesliva]

Gravity Probe B spent a lot of time blowing out helium...

[cndwrld]

Got another status report through the system. I hope another couple will get through and get posted soon. The archive is HERE.

No. 260 - Automation of spacecraft passes, thermal fuel gauging tests, start of the twenty-fourth solar eclipse season and the fifteenth Earth occultation season
Report for the period 28 April to 25 May 2013.

This reporting period covers four weeks of Venus Express operations. It includes the automation of spacecraft passes at the Mission Operations Centre, thermal fuel gauging tests, start of the twenty-fourth eclipse season and the fifteenth Earth occultation season.

[cndwrld]

Yay! We got another status report out. It is here in the VEX Status Report Archive, and covers 26 May to 22 June 2013.

It includes continuation of the twenty-fourth eclipse season and the fifteenth Earth occultation season, implementation of the automation of spacecraft passes at the Mission Operations Centre, thermal fuel gauging tests, and handling of a spacecraft event time anomaly.

[cndwrld]

The press release on the gravity waves on Venus was finally posted.

Yes, gravity waves exist on Venus. And no, these are not waves in gravity, but waves in clouds which happen to be called 'gravity waves' and which are common on Earth when calm stratified air passes over a high physical obstacle.

The information is on this ESA Venus Express page.

[Doug M.]

Really interesting stuff!

Two things caught my eye. One, Venus Express' elliptical orbit is placing tight constraints on observation -- they can only get good information periodically. As is often the case with Venus, we're left thinking "if we just had another mission..." No disrespect to Venus Express, which has been doing amazing work for seven years now! But, man, it would be nice to get a fresh set of eyes there, and a close-up look at that crazy atmosphere.

The other thing was "We don't yet fully understand how such topographic forcing can extend to high levels". The "ripples over a submerged boulder" analogy is useful, but we're talking about waves that are ~10x higher than the obstacle that's creating them, propagating up to a level where the atmosphere is a small fraction as dense. The physics of that have got to be interesting.


Doug M.

[Paolo]

It's more or less what Akatsuki was supposed to do. observe Venus'atmosphere continuously for up to 20 hours at a time.