Alan Nelson's Daily Commentary for 6 September 1999

Kwajalein Island, Republic of Marshall Islands

Turns out that the translation from raw data files to summary data files is not a simple translation. Apparently the raw data files are storing everything that is coming back from the sonde and the up to 30 calibration values that are unique to each sonde. Rather than trying to figure out what the equations are, I will simply use the software to do the summarizing for me. I've got about half of the Kwajalein sondes done today.

Yesterday was really "Black Sunday" for a couple projects. The tethersonde winch broke in such a way that it can't be fixed before the end of the project. It had to be pulled down by hand from 400 meters! Those who participated in that pull-down appreciate what the winch used to do! The breakdown of the winch corresponded to a day when three radiosondes got released from Meck. The project had been looking forward to getting data from both the tethersonde and the radiosondes at the same time. There isn't nearly as much of that duplicate collection as we would like to have.

The Convair also had engine problems again and though they "feathered" (see next paragraph) the engine as quickly as they could, there are metal filings in the engine from the breakdown. The Convair will also not be fixable before the end of KWAJEX. That also puts several sensor teams out of business because their sensors were flying on the Convair. That puts an unfortunate hole in data collection for the next week.

Back to "feathering" an engine: Simple aircraft engines have a "fixed-pitch propeller". That means that all the propeller can do is spin. That's really all most of us expect propellers to do! But more sophisticated propellers, in addition to spinning, can also be twisted so that the propeller can take a shallower or deeper bite out of the air. It turns out that a small bite gives the airplane more power, and a bigger bite gives an airplane more speed. In that respect, a "variable-pictch propeller" gives exactly the same advantage as gears on a bike or a car. A low gear is like taking a smaller bite: more power but you really have to pedal fast to get anywhere. A high gear lets you go really fast, but you can't get a bike started in a high gear. All this leads up to feathering. When an aircraft propeller is feathered, it is turned so that the edge is pointing straight forward. That means it isn't taking any bite out of the air. Engines are only feathered just before they are turned off. By feathering an engine in flight, it makes sure that the propeller won't spin as it gets dragged through the air by the other engine. The hope is that by stopping the rotation, you won't do any further damage to the engine.

There is another "mission" over tonight--the kind of mission that means a missile is coming our way from California. One very special piece of equipment is here for that launch. This is the first Boeing 767 ever built! After it went through all its tests to be checked out as a commercial airliner, it was turned into a research platform. That module that looks like an upside-down canoe on the top of the airplane is 84 feet long. It houses an infrared sensor that is capable of detecting the heat of a human body against the background of space at a distance of 1,000 miles. With that sort of sensitivity, there doesn't need to be an engine burning or a missile heating up during re-entry. Instead, this instrument is capable of detecting a missile during the middle "cold" period of its trajectory.

One problem with infrared rays, is that they don't go through glass. That's how greenhouses work and why a car heats up when left in the sun: light comes through the window and warms up the interior. The heat that would be radiated back out of the car would be in the form of heat waves--but that's what infrared rays are. So light comes into the car, is transformed into infrared (or heat) and those rays are blocked by the glass window and the heat stays in. For the Boeing 767's infrared sensors, that means they really want to be looking out an open window. They accomplish that by blowing a stream of smooth air out the front edge of the openings on top of the plane. The module and openings have been shaped very carefully in a wind tunnel so that the smooth air forced out the front edge joins with air flowing around the plane. That eliminates the turbulent air that we get when we open a car window when going along a highway. So the 767 is truly looking out through an air window!

We were given a tour of the plane. It is quite a bit bigger inside than the DC-8. But I couldn't take any pictures inside. Take my word for it--the 767 is a lot bigger than a bus!

Alan Nelson