I am a part of all that I have met;
Yet all experience is an arch wherethro’
Gleams that untravell’d world, whose margin fades
For ever and for ever when I move.
–Tennyson, “Ulysses“

With the completion of the NASA report on the balloon launch mishap, the last chapters of our Australian saga have been completed.  The report has a hugely detailed accounting of all that happened that day, but I can at last share the missing piece of this blog’s narrative.  The immediate cause of the mishap was a mechanical failure in the launch crane’s release mechanism, which prevented the balloon and our instrument from lifting off of the crane at the proper time.  As the crew positioned to abort, the balloon pulled our instrument off of the crane.  The whole world saw the consequences.

After extensive review, NASA has resumed regular balloon operations with a re-engineered release mechanism and improved launch procedures; two scientific payloads were successfully launched in Antarctica in December.  The HERO team will return to Alice Springs early this year to complete their delayed campaign.

As for NCT, upon its return to the U.S. we were pleased to find that despite the extensive damage to the gondola, the instrument’s key components were remarkably unscathed.  The detectors, electronics, and shields all appear operable.  We hope to rebuild, using our experience to make improvements where possible, and to fly again someday soon.  For now, though, NCT’s future remains uncertain.

I won’t be part of that campaign, though.  I’m finishing up my PhD this spring and looking towards new opportunities.  Still, I will always be grateful for the experiences I had—and the people I shared them with—while I was gone ballooning.

Obviously this was not the outcome I–we–were working so hard towards.  Nevertheless, I believe the NCT team has reason to be very proud of our efforts.  It was a huge challenge to turn around and fly again on a new continent less than a year after our New Mexico campaign.  Ingenuity, perseverance, and effective teamwork were all crucial in overcoming the obstacles we encountered.  On the way, we had help from many people who proved uniformly capable, friendly, and supportive.  The instrument we rolled out to the launch pad two weeks ago was fully prepared to do excellent science.

I am saddened, though, by the reach of the media coverage of our launch failure.  Videos of accidents have a huge visceral impact, so these images will be more viewed and remembered than those from the many successful launches CSBF conducts in the USA, Sweden, Australia, and Antarctica each year.  The impression created–that NASA ballooning is unsafe or wasteful–could not be more false.  For many types of astronomy, stratospheric balloons provide the lowest-cost, most efficient access to space, costing ten or a hundred times less than satellites which can take a decade longer to prepare.  Balloon scientists build affordable telescopes which do cutting-edge science, enriching our understanding of the universe we live in.  The CSBF personnel perform inherently challenging balloon launches with extraordinary capability, exquisite professionalism, and remarkable good humor.

I started this blog two years ago as a way to share what I was learning about stratospheric ballooning with my friends and family.  After the roller coaster of emotions these campaigns have brought, I continue to be convinced of the compelling story presented by this remarkable scientific enterprise.  It has been a privilege to share its drama, excitement, and culture with a broader audience.

We’ve packed everything up, provisionally.  Most everyone from our team has left now.  I took a few days away up in muggy Darwin.  It was a pleasant diversion to see some colors other than red!  Some pictures below.

Given the media attention this incident has brought, I’m inclined not to discuss the crash in too much detail.  Obviously there will be a full investigation into what went wrong today, so it doesn’t seem helpful to add premature speculation.  I have a tremendous amount of respect for the CSBF personnel, and I’d like to avoid complicating the process for them.  In short, NCT came off the launch vehicle badly and hit the ground several times as the abort completed.  The aftermath you can see below.

NCT’s core components appear to have come through remarkably unscathed.  The cradle landed upright, and the detectors and shields appear undamaged.  The card cages were scattered about, but their exteriors show only minor damage.  The electronics bay was destroyed, though, and all of the systems in it suffered some degree of damage.  Virtually all of the cabling snapped.  Many of these systems have been tested and used for decades.  They have become so familiar that their loss feels oddly personal.

We’ve cleaned everything up and brought it back to the hangar.  Sincere thanks are due to the HERO team for their calm and capable help with the gondola recovery.

Tomorrow we’ll–it’s so hard to say–start packing up for home.

1:50 am:  Well, it’s extremely calm on the surface this morning–a nice change since yesterday.  Hopefully the low-level winds are low as well?  The full moon is shining brightly on this clear, chilly morning.

2:10 am:  Looks like we’ll roll out today, at least.

2:30 am:  Winds are lower than forecast, for a change.  Sounds like we’ll be doing a final go/no-go near sunrise again.

2:35 am:  Holding for a small repair on the CSBF SIP (the communications package).

2:50 am:  Okay, about to roll out.

3:15 am:  Button up is proceeding nicely.  There’s a camera crew here from the ABC science program Catalyst, which is pretty cool.

3:30 am:  Heading out to the flight line.  Winds look a bit iffy at the moment, but what else is new?

5:15 am:  In from the flight line–it’s cold out there!  Our flight line checks were the smoothest yet, although there’s some weirdness with the clock on one cardcage we’re trying to sort out.  The good news is that right now we’ve got winds low enough to launch.  There’s a small air current that they want to drop a bit, so at the moment CSBF is aiming for an 8 am launch.

6:00 am:  We’re waiting a final launch decision, but word is the winds are still acceptable.

6:10 am:  Just got word that CSBF is laying the balloon out!  Launch looks extremely likely.  It’s only a sure thing once inflation starts, though.

6:50 am:  Winds came up a little bit on the last pibal, but we’re go for launch.

6:55 am:  Inflation is starting now–no turning back!  Launch should be in about an hour. We’re heading out to the pad to watch–more updates, post-launch!

9:00 am:  It’s hard to find words to describe what just happened.  We had a complete launch failure and abort, and much of the gondola and its systems were destroyed.  Thankfully no one was hurt.  A full accounting will have to wait–for now we’re just trying to pick up the pieces.

1:45 am:  The blustery winds we felt on the way in wouldn’t seem to bode too well for our chances today…

2:15 am:  Well, that was easy–no flight today.  With winds above 20 knots and clouds preventing an inversion layer, there was no chance.  Forecast is good for the next three days, so we’ll be showing again tomorrow morning barring any drastic shifts.

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…

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!

[Back] (A note on winds:  There are three types of wind relevant to scientific balloons.  The first, surface winds, are what we feel on the ground and hear about in the weather forecast.  Above the surface to a few hundred meters are the “low-level” winds, which may have substantially different speed and direction than the surface winds.  The interplay of surface and low-level winds is crucial in determining whether a balloon can be launched.  Upon inflation, the balloon is at its most vulnerable and most dangerous–winds at different levels can push the balloon while the gondola is still attached to the crane.  A successful launch requires low-level and surface winds which are light and consistently directed.

The winds at float altitudes (around 40 km) are the largest factor in determining the length of the flight, as they tend to push the balloon towards the boundaries of the allowed flight area.  Typically, float winds have different intensities at different altitudes, so some rudimentary steering is possible by letting the balloon droop to lower altitudes at night or by dropping ballast to raise it.

CSBF has a dedicated meteorologist on staff who provides custom forecasts for the balloon flights.  He makes detailed predictions of the surface and float winds each day, simulates expected flight trajectories, and on launch days monitors the winds and determines the balloon layout direction.)