Instrument Prep and ATom’s First Test FlightJuly 22nd, 2016 by Christina Williamson
I’m Christina Williamson, a postdoctoral scientist at CIRES CU-Boulder/NOAA-ESRL interested in Atmospheric Aerosols, the small particles in the air that cause haze, and on which clouds are formed.
I’m working with a few colleagues from NOAA to take a suite of instruments on NASA’s ATom mission that will measure the number and size of particles in the air as we fly around the world. We’re interested in this because aerosols in the atmosphere affect how much of the energy from the sun is absorbed and how much is reflected back to space by clouds and by the aerosols themselves.
Over the past few weeks we’ve brought our instruments down from NOAA’s Earth-Science Research Laboratory in Boulder, Colorado to NASA Armstrong in California, integrated them onto the plane and tested how they perform while the plane is flying. We’re running five instruments, measuring aerosols in different size ranges, which, after modifying to optimize performance for ATom conditions, and testing in the lab, we put together in a flight rack. Everything we fly is secured in the rack with aircraft grade hardware so that it cannot shake loose or be propelled out during flight, and the rack is then screwed to the seat tracks of the plane.
We sample aerosols in flight by pulling air in through an inlet tube that is mounted on a plate where the window would normally be. We plumbed this to our instruments taking care to route the flow to minimize the number of aerosol particles that get lost by sticking to the walls of the tubing on their way from outside to the instruments.
On the plane we tested the instrument set-up while it was still in the hangar, checking for leaks and that particles were being transmitted well, as well as other things like electrical connections and communications. I ran some calibrations to check that nothing had shifted in the instrument performance in the move from the lab. We also spend a good deal of time neatly tying down all of the cabling and plumbing, securing it to the rack and the body of the plane and making sure everything in the rack will hold fast during even the most turbulent of flights.
All this involved many days working on the plane in the hangar. Palmdale, where the Armstrong base is located, can get above 40C (104F) this time of year. The air-conditioning from the plane’s ground unit cannot quite compete with combination of heat from outside and from electrical scientific equipment operating inside (not to mention a lot of busy scientists and crew), so it gets pretty hot. We’re working often in the cramped spaces between two instruments, or a rack and the wall, or laying cabling and plumbing along the floor, so it’s hot, awkward and dirty work, but the excitement of working on the plane and seeing everything come together for the flights more than compensates for that.
The crew conducted a shakedown flight without scientists just to check that everything was integrated safely, and then we went up for out first test flight on July 12. This was my first time flying in a research plane. Some more experienced scientists delighted in telling me horror-stories of maneuvers and low-flying turbulence making people ill before we took off. I was nervous, mainly about how my instruments would perform, as there are controls for things like pressure and flow that I can’t test on the ground, and also because I didn’t want to embarrass myself by getting ill on the test flight.
We flew from the base out over the Pacific, then back inland over the LA-Basin and back to base. The ATom mission flights will be constantly profiling between about 0.2 and 12km (650 feet to 7 miles) altitude, so we did a lot of ascending and descending to check that the instruments can cope with it and to look at the fuel performance of the plane with this payload. To really test every instrument, the pilots did some really fast ascents and descents (for example, flow into the inlets is affected by the incline). I had to be up out of my seat testing some things on the instrument during part of this: the crew really weren’t joking when they said to hang on.
Our instruments behaved well, needing just one or two quick software fixes that I was able to implement as we flew, and I started to relax and enjoy the flight. We can stream video from cameras in the cockpit and one looking directly down below the plane, which is great. We also have a window by my seat, so I can look out.
Once over the Pacific and out of the LA-area high air traffic we dropped seriously low — had there been a whale breaching below I would have easily seen it. We also did some very low flying over the Central Valley, which produced interesting data and interesting views (although also a reasonable amount of turbulence).
During the flight we had to do some maneuvers. These are used to calibrate instruments measuring wind-speed. The crew advised us to sit down for these, and I’m glad I did, as some of them had my body weight almost out of the seat and pulling on the seatbelt. If you throw a small object in the air during one of the maneuvers you can watch it appear to hover as it falls under gravity but then you and the plane also move down away from it. It felt a bit like being in a roller coaster, and by the end of all the maneuvers I was glad to return to more normal flight. It can make you a little queasy, but just eating something or walking about the cabin afterwards really helps.
The aircraft is noisy in flight, partly because there is less insulation on it than on a normal passenger plane, and partly because of all the pumps and fans etc. on our instruments. We therefore all wear headsets, which cancel background noise and enable us to communicate with other scientists and the crew. We get some bleed-over from the channel the pilots are on, which is quite fun.
I was quite surprised when we arrived back already, four hours of flight goes by so quickly when you’re operating instruments and concentrating on the science behind what you’re seeing compared to a passenger flight. It was a good feeling to have a successful flight under the belt, to see that the instruments worked as expected and that my body coped fine with the flying conditions. We have one more test-flight just before we take off for the mission-proper. I’m looking forward to it!