Instrumentation

The ALTAIR optical balloon payload, shown in the component diagram below, contains four monochromatic visible light sources, at 440 nm (blue), 532 nm (green), 635 nm (red), and 690 nm (also red) wavelengths.  Each source is approximately 25 mW in power, similar in brightness to a 10th magnitude star when the payload is at its observing altitude of approximately 20 km.  The light from each of the sources is directed, via optical fibers, into an integrating sphere.  The total amount of light from each source input into the integrating sphere, and projected toward the ground, is continuously monitored via two photodiodes, each of which are calibrated to a precision of better than 0.1% at each wavelength, at any given viewing angle.  The payload is flown via helium weather balloon to an altitude of approximately 20 km (65000 ft), i.e. in the lower stratosphere (above approximately 99.5% of the Earth's atmosphere by mass), above observatories, for example Pan-STARRS in Hawaii. The GPS position and attitude of the payload are continuously monitored at intervals of 0.05 seconds.  Following telescopic observation, the payload is released from the balloon, and returns to Earth via parachute, ready for its next flight.  A typical flight trajectory is shown at right.