Out to Launch (#2)

Here we go again…  The webcam is here or here.

2:00 am:  We arrived earlier this evening (morning?) to change caps on our LN2 dewar–we’re trying to keep the detectors colder before they get to the flight line by pumping on the LN2 as long as possible.  Word is the weather forecast hasn’t changed.  The primary worry at this point that the low-level winds increase.

2:20 am:  The CSBF electronics crew is finishing some checks; the crane is waiting outside to pick us up.

2:22 am:  Rollout time!

2:45 am:  We’re hanging from the crane and the SIP rollbars are on.  CSBF is attaching the ballast and doing more checks of the communications.

2:46 am:  These reflective safety vests we’re wearing make me think of the Beastie Boys song Intergalactic.

3:05 am:  Okay, everything’s ready to go–we’re just waiting for the scheduled time to move to the flight line.

3:15 am:  Just watched the weather man launch a couple of pibals (“pilot balloons”) to measure the low-level winds.  They definitely blew sideways more than on a perfectly calm day, but he’ll let us know if we’re within the acceptable range.  Still, it’s important for the winds to have a definite direction for balloon layout and launch.  With their blinking tracking lights and loopy trajectories, the pibals look somewhat like crazed fireflies…

3:35 am:  With a little Arcade Fire for mood, it’s go time.

5:30 am:  Back in from flight line.  It’s a nerve-wracking part of the preparations:  checking that everything is working, but not being able to fix much.  The worry is always that there will be a new problem that causes a launch scrub.  Thankfully, we’re ready for flight.

However, indications are that the low-level winds are higher than forecast.  Sounds like we’ll be watching for the next hour before a final decision is made to launch or not.

6:00 am:  Low-level winds are too high right now for launch (14-18 knots at the top of the balloon).  We’ll wait until 6:30 to see if they come down, but then we’ll have to scrub.

6:45 am:  Scrub-a-dub-dub.  Winds are too high to launch safely, so we’ve got to roll back in and start the process over…

3:30 pm:  Update from the weather briefing:  a frontal system is moving in which will keep us from launching for at least a couple of days.  Hopefully we’ll have better luck later this week.

4/27, 3:30 pm:  Update from the weather briefing: we’re showing again tomorrow, usual time.  Low level winds are forecast to be on the high side again, but we just need one day…

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Show Time, Second Time

The float winds have slowed nicely since last week (down to the mid-30 knots, from a high of 60!).  Those winds give a pretty solid flight forecast for the next few days, as much as 30 hours at float.  Tomorrow morning’s surface and low-level winds are forecast to be acceptable, so we’ll show for a launch attempt.  The gondola will be loaded onto the gondola at 2:30 am and roll out to the flight line an hour later.  If all goes well, launch will be in the 7-8 am range.  We’re well-rested and ready to go–here’s hoping!

Ranging Westward

With no launch opportunity available until Monday, today we spend a good Friday driving westward to see the MacDonnell Ranges.  As in the East MacDonnell Ranges, the gaps, pools, and chasms were stunning.  The additional height of the ranges to the west made our stops even more incredible.

What We Came For

The news at today’s weather briefing was expected, but unwelcome:  The winds at float altitude continue to be as high as 55 knots (nautical miles per hour).  Those high winds will push us east rapidly, forcing us to cut down after less than 20 hours at float to avoid crossing a mountain range.  That’s not enough time make our observations, so: we wait.  The current forecast suggests lower float winds starting next Monday, so we might have a window then.[1]

Still, now seems like an appropriate time to discuss what exactly we’re trying to observe down here in Australia.  Why isn’t twenty hours enough?  What is it we’re looking for?  To my mind, the answer is both simple and complex.  We have specific targets we expect to detect at certain significance, but this individual balloon campaign is situated in a larger context of scientific exploration.

First, the specific targets.  The center of the Milky Way Galaxy is home to two specific sources of gamma-ray emission.  The first is a cloud of antimatter positrons, produced perhaps by black hole binary systems.  When these positrons encounter electrons (their oppositely-charged matter counterpart), they annihilate and produce gamma-rays of very specific energy, 511 keV.  The shape and intensity of the emission produced by this cloud should provide clues to its origin, and satellite experiments have made progress in this direction already.

INTEGRAL 511 keV map (Weidenspointner et al. 2008)

The second major source of diffuse gamma-ray line emission near the Galactic Center and in the Galactic Plane is due to an unstable form of aluminum.  Like all heavy elements (including all those found around us on Earth!), it is produced by massive stars.  Since the aluminum decays away fairly quickly after it is produced, mapping it can tell us about the life cycles of stars and the formation of elements (known as “nucleosynthesis.”)

COMPTEL 26Al map

With its fine energy resolution and broad field of view, NCT is designed to make  maps like these.  Still, one of the great parts of high-energy astrophysics is the wide range of exotic sources, and we hope to do interesting science with some of the other sources we see along the way.  These include supernova remnants and faraway active galaxies driven by accretion disks around supermassive black holes.

One of the most interesting possibilities is to extend our New Mexico observations of the Crab Pulsar (a rapidly rotating neutron star).  As a Compton telescope, NCT is capable of measuring gamma-ray polarization.  This is a technique I am particularly interested in and which is just starting to come into its own.  Polarization measurements of pulsars should help distinguish between models of the source of their gamma-ray emission.

Of course, the sky in gamma-rays is hardly stagnant, and so there’s also room for serendipity:  transients like gamma-ray bursts (my speciality), the more rare soft gamma-repeaters, and large solar flares would all provide great discovery potential if they were to occur while we were flying.

Let’s be clear, though.  Particularly with the forecast of an abbreviated flight–well below our hopes for this campaign–it is unlikely that NCT will make “best-ever” measurements of any source we’re targeting during this flight.  Why do it, then?  First, we hope to fly NCT again in the years to come, maybe even on an around-the-world flight.  The data we obtain now can be combined with that taken later for increased exposure, and we’ll learn more about the analysis methods in the process.  Additionally, our measurements will provide important verification of results obtained by other instruments, particularly those employing different technologies and imaging techniques.  These cross-checks are crucial to the scientific process.  Finally, our efforts help lay the groundwork for future satellite missions, whose higher cost and longer timelines require proven technologies.

The gamma-ray sky is full of fun, interesting things we’d like to learn more about–now if we can just convince the winds to let us take a look!

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Out to Launch (#1)

Today’s our first launch attempt in Alice Springs!  You can follow along on the webcam here or here.

2:15 am:  My, it’s early!  The gondola is all buttoned up and ready to roll out.  CSBF just put our rotor on the crane, and the electronics crew is doing final checks of the SIP.

Getting set up on the crane.

3:15 am:  We’re on the crane and all buttoned up.  CSBF is finishing final checks of the communications links.

Ready to go.

3:45 am:  The crane is rolling out to the flight line, and we’re following it out!

NCT on the flight line.

5:30 am:  Flight line checks complete, back to the hangar to warm up.  A couple of hiccups there slowed us down, but we’re comfortable with how things sit at the moment.  Word is the winds are looking kind of marginal for launch, so we’ll see.

6:25 am:  Launch scrubbed–low level winds were too high.  We’ll have another weather briefing this afternoon, seems likely we’ll show tomorrow again.

Someone went ballooning--it just wasn't us.

3:30 pm:  No show tomorrow.  The winds at float are too high–50 knots!–to give us even 24 hours at float at extremely poor (i.e., low) altitudes.  That short of a flight would keep us from getting even one full observation of the source we came down to observe, the Galactic Center.  Also, the surface winds tomorrow morning look pretty tough for launching.

The forecast for the next couple of days is similar, so we’ll see how it develops.  We may have a day that gets above our minimums.  The good news is after Sunday the float winds should slow a bit and potentially allow for a longer flight.

NCT Launch Opportunity Tomorrow

The low-level winds tomorrow (4/20, Alice Springs) look quite favorable, so NCT will show tomorrow morning for a potential launch opportunity.  We’ll roll out of the hangar around 2:30 am; if everything goes well, launch will be in the 7-8 am range.  You can follow along on the webcam here or here, and I’ll update live when I can get to my computer.

Unfortunately, the winds at float altitude are forecast to increase substantially relative to those during TIGRE’s ~54 hour flight just a few days ago.  We’re likely to get more like a single day, as we’ll be blown more rapidly out of the area we can safely fly over.  Still, you never know–we’ve been lucky before.

My immediate priority: get some rest!  I’ve got to get up again in four hours!

Flying TIGRE

TIGRE’s launch this morning was great fun to watch.  From our distant vantage point outside the airport fence, the CSBF crew made it look smooth and easy.

ABC had a nice article about the launch, including a great video from the airport.

Here are some of my pictures, in a nice gallery format!