I'm used to reading excellent articles by Emily, but this one I found to be of truly extraordinary interest:

http://www.planetary.org/blog/article/00002070/

Yes. And the funny thing is, my mind was being all boggled by the implications of the mission, and then I got to the bit about 15kg of solid hydrogen. Holy cow!

I wonder why they chose solid hydrogen instead of liquid helium for the coolant. My best guess would be that the mass of the helium tank would be too great for the WISE mass budget (the Herschel spacecraft seems to be basically a giant liquid helium tank with attached optics and electronics), plus liquid helium might be slightly overkill for the wavelengths it will study.

Bill

Is it harder to control the torques from Liquid Helium? Does it slosh a little more an fight gyros?

A handy free article on solid hydrogen:

http://www.tvu.com/PEngPropsSH2Web.htm

"macroscopic crystals characterized by different nuclear spin states"

Whoa! This takes Pasteur separating chiral crystals to a whole new level. That is just plain bizarre!

Sounds like you're right, and there's one other advantage. From Bill Irace: "Our detectors do not require He temp (1.5 K) and solid Hydrogen (6.5 K) has about 7X the specific heat as liquid He: ergo lower weight system."

--Emily

Huh. I'd always thought that hydrogen needed to be highly pressurized to freeze; guess I was confusing that with what's needed to achieve its 'metallic' phase. Pretty ingenious, and as you said in your blog, Emily, this looks to be an exciting mission!

I know it's really premature to begin talking about what to do after WISE sublimates all it's solid hydrogen before it's even launched. Nonetheless, I imagine there must be some contingency planning for a WISE warm mission analogous to that of Spitzer. See the discussion of Spitzer beginning at this link.

Among the things NASA mentions is the detection of asteroids during the Spitzer warm mission. WISE warm might be able to continue its asteroid survey.

Steve M

Wide-field Infrared Survey Explorer
WISE preparation for launch from Vandenberg Air Force Base ;
http://mediaarchive.ksc.nasa.gov/search.cfm?cat=216
Launch scheduled 7th December 2009

The latest Sky and Telescope has a nice article on this - I was astonished that they gave even odds to finding a brown dwarf CLOSER than Alpha Centauri.

Given that smaller stars are more numerous than larger ones, I'd have thought it almost a certainty they'd find a number of brown dwarves closer than Alpha Centuri. What I'm wondering is whether a brown dwarf inside the Oort Cloud might be responsible for otherwise-difficult-to-explain things like the orbit of Sedna.

--Greg

I'm somewhere between evens and 'almost a certainty' but I agree that their statement of the odds is probably on the cautious side of what they are actually thinking. I say this because they will be able to detect objects below the small end of what we normally think of as brown dwarfs.

I too wouldn't be surprised if there were one or more brown dwarfs closer than the Alpha Centauri system. However, I'm also pretty confident that orbital anomalies in the extreme outer Solar System could just as easily be explained by the nearby passage (within 1 light-year) of stars and/or brown dwarfs, which has doubtless happened more than once over geological time.

Would definitely be interesting if we do have a very nearby neighbor, though. Might take decades of observation to determine whether such an object was just passing by or actually associated with the Sun.

I suppose I should say that, after LCROSS and the mystery of the incredible plume, I'm all in favor of NASA making conservative predictions but being prepared to record spectacular results.

It's funny; there's not a lot of buzz about WISE, but between brown dwarves and optically-dim Earth-crossing asteroids, it promises to deliver an incredible wealth of information.

If they manage the extended mission, they'll have two shots of each object, six months apart. Since their resolution is 2.75 seconds of arc per pixel, that ought to give them a good clue as to which objects at least MIGHT be associated with the sun. Too much or too little change in position would mean it's either going to fast or located too far away.

--Greg

Greg, the onboard frozen Hydrogen is expected to last 10 months, allowing WISE to map most of the sky a second time in order to see what has changed. So only a partial 2nd survey should be possible...
Launch is now set to 9th December

I guess I'm counting on even that number having some safety factor in it. :-)

Something else I've thought about recently is that two observations six months apart aren't enough to characterize an orbit. Even if it finds thousands of new asteroids, the fact that we can't observe them from the ground seems to limit the immediate usefulness of the data. Or perhaps it's hoped it could justify a followup mission a few years later? Or maybe just offer good initial targets for Pan-STARRS.

My personal hope is still that it finds a brown-dwarf companion to the sun that offers some explanation for things like the orbit of Sedna and the abrupt edge of the Kuiper belt -- not to mention a REALLY great flagship mission target. And even if not, WISE ought to be able to absolutely rule out the possibility of such a thing.

We're probably still a good year away from any results, I guess. Unless they really DO find that brown dwarf.

--Greg

When is a brown dwarf a black dwarf? When it no longer emits any visible light at all? If they find any of those nearby I think Herschel will be on the case.

I always thought that a black dwarf was a completely burned-out star, normally a former white dwarf...considerably more massive than a brown dwarf.

Probably right. I just wanted to make the point that WISE could discover objects close to room temperature. Would it really be appropriate to call them brown dwarfs? If the term 'black dwarf' is to be confined to cooled white dwarfs then we need a new name for cooled brown dwarfs and other objects that were never even hot enough to be brown for any length of time but could still turn up in IR surveys.

Existing and future narrow angle instruments should be able to follow up on them. You'd never get Herschel, Keck or VLT time for a large area survey, but they are definitely candidates for followup.

It isn't just two obsevations six months apart;
There’ll be sufficient overlap, so that each position in the sky gets eight or more independent exposures on successive orbits.

Thing is, what if we have a companion brown dwarf about a 0.5 LY out with an orbital period of 100,000 years or so? Finding such a thing should be easy with WISE, but it may take a decade or more to confirm that it's probably in orbit around the Sun, even longer to derive a decent ephemeris. The problem isn't frequency of observation, it's very low orbital velocities for distant objects.

New Horizons is still trying to work out ephemeris uncertainties for Pluto because it hasn't been observed for even half an orbit since its discovery.

Proxima Centauri is 0.21 ly from the Alpha A/B barycenter, and even after 100 years, we're still not QUITE sure it's actually orbiting the other two.

http://en.wikipedia.org/wiki/Proxima_Centauri

I'd hope we'd do a BIT better with an object nominally orbiting our own sun, but it'd still take a while. Even with the overlapping observations, I think the trouble with the WISE data will be that it spans just one year. Of course, something that barely moves after one year (like a remote brown dwarf) probably won't get lost easily, but an Earth-crossing asteroid might well be hard to find again.

As for black dwarfs, the Universe probably isn't old enough for any to exist yet:

http://en.wikipedia.org/wiki/Black_dwarf

There are already known brown dwarfs with estimated temperatures as low as 500K:

http://en.wikipedia.org/wiki/Brown_dwarf#D...gh_mass_planets

It seems plausible that smaller, cooler ones exist and even might be more plentiful than regular stars, given the mass/frequency curve we seem to see everywhere else in the universe. WISE could well find LOTS of brown dwarfs closer to the sun than (say) 4 light years.

I guess we'll know in eighteen months or so!

--Greg

If the IR broadband signature for brown dwarfs really is distinctive enough, candidates can be followed up with large ground-based telescopes once WISE points them out. That would give much higher angular resolution as well as time baseline. One of the bumper-sticker descriptions of WISE (back when it was NGSS, which someone thought would be too confusing compared to NGST which is now JWST) was that it should discover both the most luminous galaxies and our nearest stellar neighbors; practically something for everybody.

I can't wait to begin the exoplanet surveys for all of those local brown dwarfs!

David

Launch postponed: The WISE launch is currently scheduled for no earlier than Saturday, December 12th, at 6:09:33 am pacific, from Vandenberg Air Force Base in CA...

...and even that doesn't look likely at this point.

We might want to lower our expectations just a bit for finding brown dwarfs closer than Proxima. There is a distinct possibility for finding none at all.

At least not until after it launches anyway. Which is now set for Sunday the 13th. I'll miss that one, but if it gets bumped over to Monday or Tuesday I might be able to make it again.

If there actually is a close brown dwarf, that would be so interesting...

Launch now set for 1409-1423 GMT on the 14th (0609-0623 PST.)

Yep Monday now. It looks like I might get a tour of the actual launch pad Sunday night. Stay tuned. I might also be blogging it on well-respected site. Although it is still raining like crazy down in Southern Cal where I am now.

Do tell, now! MOST cool; looking forward to some on-site reporting!

These postponements worry me because they've already packed the solid hydrogen, so every day of delay is probably costing us a least a day (maybe more) of mission time.

--Greg

I was thinking that, too, but logically there has to be some sort of cooling in place till just before launch; certainly the possiblity (even probability) of a delay on the pad had to be considered even during early planning. That stuff wouldn't last long at all even in a Dewar vessel in terrestrial ambient conditions.

If I recall correctly from my conversation with them, they re-run the chilling routine every other day. So every other day you reset the clock on the frozen hydrogen. Which means that if you're the science team you really want the spacecraft to launch on that first rather than second day. I would imagine that with the weekend's delay, Monday will be "day 1" of that cycle.

Also, I just remembered that the chilling routine involves a team of poor guys whose sole job is to run those tanks of liquid helium up the tower to the top of the rocket, where the spacecraft is, remove the old tank, hook up the new tank, run the old tank down to the bottom of the tower, and repeat.

Thanks, Emily. Figured there had to be something; didn't think that it'd be pretty!

I think those kinds of details are funny. It's amazing all the weird, different ad-hoc solutions it takes to get each unique spacecraft launched. I smirk every time I see the enormous backshell for MSL, because it has a monster hatch (big enough for Buzz Aldrin to fit through) that had to be cut into it so they can install the RTG on to the rover's butt at the very last opportunity before launch, while the spacecraft is stacked on top of the rocket on the launch pad. And they have to have three redundant air conditioning systems in the assembly tower because if things fail, that RTG will heat everything up in a hurry. Every mission has weird stuff like this. It's not like sticking your laptop on top of a firecracker and booting it up after it's safely in orbit -- each spacecraft has to have something difficult even before you launch it.

Ooooh, yeah. Space systems engineering itself is a black art, really. Each & every SV is really a creation unique unto itself with at least one quirky little piece of impromptu ingenuity that turns out to be vital to making the whole mission succeed. Gotta love these people!

Not to mention it's requirements like that - late/specific access to the payload and custom mods to the vehicle/pad that drive launch costs up. Not that they're not already significant...

It's been raining like crazy for the last couple days, and still is, but it looks like tomorrow morning is going to be clear out on the coast. I think we're pretty much GO for 6:09 am Monday Pacific Time. Crossing my fingers on getting out of here in time today to make it over there.

Weather in L.A. was spectacular this morning. Bright clear blue sky and sun. Rain? What rain? Go WISE!

Here's a photo of solid hydrogen floating on liquid helium...

http://www.grc.nasa.gov/WWW/RT/RT2002/5000...laszewski2.html

Here's an interesting blog on the subject: No Turkeys in the Cleanroom
"...our valiant Utah cryo crew worked right through Thanksgiving. Our project managers brought Thanksgiving dinner and all the trimmings up to the crew at Vandenberg. Of course, they weren’t allowed to bring pumpkin pie into the cleanroom on top of the tower with WISE and the rocket, but they got to have a little bit of holiday cheer. Thanks, cryo crew!"


Hopefully they'll be home for Christmas!

Something similar happened with ESA's ISO far-IR observatory (pardon the redundancy with the acronym). A team had to head out to check something on the Ariane 4 booster well after the area would normally be cleared, and one of the payload teams took the opportunity to head out at the same time and top off its liquid helium dewar. With the boiloff from external conditions in French Guyana, scuttlebutt was that this added a few months to the cryogenic mission lifetime (something like 27 months of an expected 24 and required 18).

Wise has been succesfully deployed in orbit

Yes indeed. And I missed the launch

Can't wait for the science results to start coming in.

Here's a general "mission/science expectations" summary post, since I was curious, and I had to dig around a bit to get it:

Emily says, "There's a one-month commissioning phase before science starts. ... The main imaging instrument gets turned on in five days. Sixteen days after launch, the cryostat cover will be blown off. Then there are two weeks of checkouts of instruments and systems, followed by a nine-month nominal mission. That nine months will allow them to perform 1.5 complete sky surveys."

There's one sky survey in six months because it's in a sun-synchronous orbit and thus WISE hits both sides of the sky in its orbit (obviously), and it scans the skies by waiting for Earth to orbit the Sun.

Space.com adds that "WISE will capture about 5,700 pictures a day of the infrared sky. The mission management team says it will release the first science data within one month of launch."

And one of the project scientists said in the press conference that they'll be announcing interesting objects as they spot them. But the bulk of the data will be released in two big chunks at the very end of the mission - first release, April 2011, second, March 2012, according to this.

In case it's not obvious: I think this mission is very exciting. Congrats to NASA on a successful launch!

For those who like observing things in orbit:

I've pasted the entire post here.

Seeing WISE
"WISE is now in the Heavens Above orbit database. It will be favorably placed over Los Angeles on the morning of Dec 24, and I will try to observe it. You can get predictions for you own location from Heavens Above and try to spot it. If you try leave a comment describing your observation." -- Ned Wright, WISE PI