Dr. Kimberly Ennico Smith, SOFIA Project Scientist
SOFIA, the world’s only flying observatory, is in Christchurch, New Zealand for the next few weeks, to enable unique infrared observations from the Southern Hemisphere. From here, we can study our galaxy’s center and nearby galaxies, the Magellanic Clouds, which will feature prominently in our observations in the weeks to come.
I flew onboard SOFIA on the journey south from its home base at NASA’s Armstrong Flight Research Center, in southern California. We stopped in Honolulu, Hawaii, to refuel and change crews on the way to New Zealand.
During the flight, I got a chance to hang out in the cockpit and spend time with the flight engineer. He explained what all the dials and buttons do — some monitor the temperature of the engines and control the engine heaters, others monitor the airplane’s elevation.
The rest of my fellow passengers were a mixture of mechanics, software engineers, telescope operators, and avionics technicians. We got to chatting about all sorts of avionics systems and swapped stories. They know the world of aircraft inside and out and it was truly a pleasure to pick their brains over the two long flights down south.
We are ready to observe the solar system and beyond from the National Science Foundation’s Antarctic Program Facility at Christchurch Airport!
There are 60 busy scientists and support specialists in Christchurch, New Zealand, but everyone paused on Monday evening, June 29. That’s when the mission briefing room was packed to capacity with everyone anticipating the night’s flight. There was a buzz in the air; as the briefing went on, more and more people were caught up in it.
The night’s mission was to observe Pluto as it passed in front of a star. The event, known as an occultation, would cast Pluto’s faint shadow across the Earth’s surface, and the center of that shadow would pass somewhere off the southern coast of New Zealand. Many ground-based observatories and research teams would be observing the occultation as well, but SOFIA, NASA’s largest airborne observatory, would attempt to fly exactly in the center of the shadow to observe the occultation from the ideal vantage point.
Should SOFIA capture the occultation, the research teams would be able to determine the detailed pressure and temperature profile of Pluto’s atmosphere, and verify if there are aerosol particles or dust in the dwarf planet’s atmosphere. If SOFIA were to hit the shadow in the exact mid-point, researchers could even determine whether there are winds in Pluto’s atmosphere and learn how they behave.
As the briefing went on, Mission Director Nancy McKown reminded everyone that this was only one of 14 science missions planned during the deployment, which includes observations of more than 40 celestial objects, each just as important as the next. Her attempt at calming the excitement in the room lasted for a few short minutes as people reflected on SOFIA’s overall mission, but the excitement was soon back in full force.
Research Scientist Michael Person from the Massachusetts Institute of Technology (MIT) also spoke about the night’s mission. Person’s area of research focuses on the techniques needed to observe stellar occultations, eclipses, and transits. He has a special interest in Triton, Pluto, and a number of objects that reside in the Kuiper Belt that stretches from Neptune out past Pluto. As Principal Investigator for this flight’s Pluto occultation observations, Person would be responsible for coordinating the work of all of the instrument teams on board.
A Little Bit of Back Story
An entire room full of science specialists, led by Jeff VanCleve and Ken Bower, had been working on where to fly SOFIA for the night’s observations. They looked at the weather forecast and developed a number of flight plans for a variety of possibilities, depending upon where the shadow would fall. Some predictions called for the center of Pluto’s shadow to fall north of Wellington, New Zealand, while others put it between the island nation and Antarctica. Working with observers at the U.S. Naval Observatory and Lowell Observatory’s Discovery Channel Telescope, both in Flagstaff, Arizona, with additional support from telescopes in Australia and Chile, Pluto observations were made and the data was provided to astronomers at MIT. They in turn made calculations to generate predictions for Pluto’s path that were provided to the SOFIA team, who generated a flight plan that would put the observatory in the shadow’s track.
Once the science flight plan was generated, it was turned over to SOFIA’s navigator for the flight, Jeff Wilson, who then converted it for use by air traffic controllers.
The observations would be made at 39,000 feet, an altitude that did not require maximum thrust from SOFIA’s four 50,000 pound thrust JT-9D-7J engines. The air at 39,000 feet was predicted to be very clear of infrared-blocking water vapor, and flying at the lower observation altitude provided more reserve power to the pilots in case they needed to make up a minute or two on the flight plan to intercept the shadow at the precise point.
Below the cockpit, on SOFIA’s main science deck, teams coordinated by Instrument Scientist Maureen Savage would monitor the three instruments used together to capture the occultation:
The First Light Infrared TEst CAMera (FLITECAM), an infrared camera collecting data between wavelengths of 1 and 5.5 microns.
The High Speed Imaging Photometer for Occultations, HIPO – Principal Investigator Ted Dunham, a visible light camera that was co-mounted with FLITECAM.
Fun fact: When FLITECAM and HIPO are mounted together, they are known as “FLIPO.”
The third instrument in use was the Focal Plane Imager-Plus (FPI+), a highly sensitive tracking camera on board SOFIA that can also be used as a photometer collecting data at visible and near-infrared wavelengths between 0.36 and 1.1 microns. FPI+ is managed by a team from the German SOFIA Institute at the University of Stuttgart, with Principal Investigator Jürgen Wolf heading the team.
All three-instrument teams would work together on this flight to ensure the success of their observations both individually and as a group.
The SOFIA team’s Pluto fever was being fed by the anticipated success as well as a keen awareness of NASA’s New Horizons spacecraft, which will pass by the distant celestial body on July 14. Data from SOFIA’s observations will be an important part of a decades-long study of Pluto’s atmosphere that provides a baseline and context for New Horizon’s fly-by observations. Studying a target with as wide a variety of sensors as possible results in the most complete understanding of an object. That’s why NASA will often observe a celestial object with sensors that cover the entire electromagnetic spectrum. In Pluto’s case, New Horizons provides ultraviolet, radio, and visible wavelength coverage while SOFIA collects data in both the visible and infrared bands.
SOFIA is a GO!
As the mission briefing continued, each of the responsible team leads presented the status of their part of the mission.
The command pilot for the flight would be Clayton “Ace” Beale. Ace briefed the weather, fuel load, alternate landing fields, in case Christchurch’s notorious fog rolled in, and discussed flight timing for the mission.
Navigator Jeff Wilson, call sign “Elvis,” presented the night’s flight plan with the caveat that it might change depending upon the information received during the flight on Pluto’s estimated track. In flight, Wilson would collaborate with Jeff VanCleve and co-Mission Director Karina Leppik as updated Pluto shadow position forecasts were received from MIT.
Aircraft Operations Engineer Andrew Fischer said, “All aircraft systems are ready.” Fischer’s words captured the work of Aircraft Crew Chiefs Jerry Dobbins and Sal Ramirez and their crew of more than 20 technicians and engineers who worked in often cold and wet conditions to prepare the aircraft and its airborne systems for the flight.
Oliver Ziele, representing the telescope team from the German SOFIA Institute, reported: “The telescope is balanced and the telescope bearing temperature is within limits.”
Matt Enga, whose group is responsible for all of the mission communication systems on board the observatory – computers that interface between the telescope to the instruments – reported all systems were ready for the night’s mission.
Shawn Granen from SOFIA’s information technology group talked about computer protocols on the flight and then announced: “The celestial map overlays have been uploaded.”
SOFIA is a GO!
With all systems reporting as ready for the flight, Mission Director McKown reviewed the mission timing – when the crew had to board, when the door would close, taxi and takeoff times. With that, the excited crew grabbed their gear and headed for the plane.
Once on board, last minute details were attended to and the main cabin door was closed. On-board, in-flight safety technicians Mike Moore and Steve Laney gave the safety briefing and everyone took their seats. The engines were brought to life, and with clearance from the tower SOFIA headed out to the runway.
Having received permission from the control tower to take the runway and take off, Ace Beale positioned SOFIA facing south on Christchurch International Airport’s Runway 20. Beale, co-pilot Dean Neeley, and flight engineer Tom Speer completed their checklists and with the brakes holding SOFIA back, all four engine throttles were pushed forward as the flying observatory began to shake, building up thrust. At 10:07 p.m., local time, SOFIA thundered down the runway lifting off into the cold New Zealand night sky.
SOFIA flew to the south to set-up and test all systems. There were a couple of rough patches as systems were synchronized, but nothing the experienced group on board could not handle.
As the instrument teams were watching Pluto’s movements across the night sky, an updated prediction of the shadow’s path was received on board. Jeff Van Cleve’s pencil was processing the data and converting the prediction into a flight path. He then went upstairs to the cockpit to confirm his numbers, calling MIT on the aircraft’s satellite phone.
Having replanned the flight with navigator Wilson to intercept the shadow everything was set. Then another further updated position prediction came in. This one required the aircraft to be positioned 227 km (141 miles) north of the current flight path.
The race was on. SOFIA was trying to reposition itself before the Pluto’s shadow passed in front of it.
On the screen, everyone on board could see Pluto begin to approach the occulting star. Then it got closer. Then closer. The excitement was building on the science deck.
At a point approximately -44.8 latitude by 171.0 longitude SOFIA’s instruments captured Pluto’s shadow. As SOFIA reached the precise center of Pluto’s shadow, viewing Pluto exactly centered in front of the star, the star’s light brightened, which was reflected on the light curve as an obvious spike in the center. That momentary “central flash” held a wealth of data about Pluto’s atmosphere. As Pluto completed its pass in front of the star, there was loud shouting, clapping, handshaking, and congratulating all around!
“In this single flight we were able to obtain observations covering four different wavelengths as close to the predicted center of the occultation as possible, which shows the power and flexibility of SOFIA to go wherever is required for events like these,” said Ryan Hamilton of SOFIA’s FLITECAM team. “We faced challenges at every point and overcame them all, and we’re all excited as can be for the next part of these observations: the science and interpretation!”
Shortly after the mission, occultation principal investigator Michael Person said, “All of the instrument teams worked together very well to get us the best possible result. The HIPO team, based at Lowell Observatory, the UCLA-based FLITECAM team, and the German FPI team all came together to help each other overcome challenges during the mission, resulting in successful observations of the event from all cameras. I couldn’t be more pleased with the cooperation from the instrument teams, the aircraft, and observatory personnel with our efforts to observe this historic occultation.
Two reporters, Nadia Drake and Govert Schilling were on board this flight and documented the experience. Their articles can be found below.
Many thanks to the telescope operators for helping us through these complicated observations. The instrument for tonight’s and tomorrow night’s flights is the Cornell University developed Faint Object infrared CAmera for the SOFIA Telescope (FORCAST), a dual-channel mid-infrared camera and spectrograph sensitive from 5 to 40 microns.. SOFIA flies above 99% of the water vapor in Earth’s atmosphere that blocks infrared radiation from reaching the ground. The super dry atmosphere over the southern ocean was exceptionally good for the duration of the flight, which enabled the team to get better results.
During the first science leg we observed V1309 Scorpii. At first this object was thought to be a “classical nova,” where a white dwarf star accretes material onto its surface from a companion star until the material ignites, causing a surface explosion. But it was later determined to be an explosion resulting from the merger of a binary star system, where the two stars spiral in toward one another until they finally collide. This is a very faint source that proved to be exceptionally challenging to get set up to observe. Once the observations were under way, however, the data looked to be acceptable. Luckily most of the effort was front-loaded, since soon after we began observing in earnest, the flight crew notified us that we could see the aurora outside. And it was just stunning, brighter and more active than anyone on the main deck had ever seen.
The following science leg included observations of Eta Carinae, a system of two stars that are five million times brighter than our Sun. Eta Carinae can only be seen from the Southern Hemisphere, and this observation was the focus of our guest investigator, Pat Morris, from the California Institute of Technology, who was on board to assist with data collection. These observations proved to be challenging. The goal was to observe the faint emission surrounding Eta Carinae that originated in an earlier period of mass loss. To see this emission, we had to very carefully position the observation field next to Eta Carinae itself, the brightest IR stellar source in the sky. Unfortunately, besides the difficult setup, there were some technical issues on this leg that resulted in some lost observing time. Nevertheless, the data obtained looked very good. We are well positioned to optimize our observations of Eta Carinae on upcoming flights.
The last object we observed this evening was Westerlund 1 – one of the most massive star clusters in the Milky Way Galaxy. These observations were straightforward and rewarded us with some beautiful images of the most densely populated field observed by the FORCAST team to date.
These pages will bring news and information about our science observations during our mission’s six-week deployment to observe the southern skies.
SOFIA arrived in Christchurch, New Zealand, on June 14 (New Zealand date) to begin the observatory’s second Southern Hemisphere deployment. The team’s first visit to Christchurch was in 2013, and that deployment was an outstanding success. The quality of the science data obtained from our previous flights out of Christchurch was excellent, and we’re expecting similar results again this year.
As you read this, our staff is conducting mission operations from the National Science Foundation’s U.S. Antarctic Program (USAP) facility on Christchurch International Airport. Our mission is grateful to the National Science Foundation for making this facility available to us. The USAP facility is not in use during New Zealand’s winter, which is the reverse season to the Northern Hemisphere, so this is an ideal opportunity to make use of an otherwise idle base.
In 2013, SOFIA flew with one instrument, the German REceiver for Astronomy at Terahertz Frequencies, GREAT. This year our scientific productivity will be greatly increased, as we will make observations with four instruments (Faint Object InfraRed CAmera for the SOFIA Telescope – FORCAST, First Light Infrared Test Experiment CAMera – FLITECAM, GREAT, and High-speed Imaging Photometer for Occultations – HIPO).
With a four-fold increase in science instrument capability, we will perform science observations on parts of the universe that are not accessible from the Northern Hemisphere. Additionally, we will incorporate a special observation which we call a “target of opportunity,” to observe a Pluto occultation as it passes in front of a star. The Pluto observation has the potential to provide cross-mission science data to the New Horizons mission, further demonstrating SOFIA’s scientific productivity. SOFIA’s observation of Pluto will occur on June 29th, just a couple of weeks before the New Horizons’ spacecraft fly-by of Pluto on July 14th.
I am really excited about the science plan for this year’s Southern Hemisphere campaign, and I have no doubt that there will be obstacles and challenges during deployment operations. The science we obtain will be worth all of the long hours and the days away from home.
I look forward to everyone’s safe return home and to another SOFIA team success!