NASA engineers are developing a precision attitude sensor or star tracker that would be able to locate stars during daylight hours. The team at NASA's Wallops Flight Facility (WFF), located on Virginia's Eastern Shore, is working on a low-cost, off-the-shelf solution to overcome the challenges of collecting data in daylight, the US space agency said in a statement.
The star tracker is being developed specifically for the Wallops Arc Second Pointer (WASP) which would use the star tracker's data to point a balloon-borne scientific payload with incredible accuracy and stability.
Currently, WASP usually employs the commonly used ST5000 star tracker. However, this device cannot take images in the daytime even at 120,000 feet where scientific balloons operate. Though relatively dark at those altitudes, the scattering of sunlight off the atmosphere can overwhelm the starlight in most star cameras.
"A precision attitude sensor capable of working in the daylight would extend science operations through the day which would significantly increase the amount of science collected," explained engineer Scott Heatwole. Currently, the only precision attitude sensor available in daytime is a sun sensor. "This is not ideal because it provides only two axes of attitude and is not precise over a range of targets across the sky," he noted.
According to Heatwole, his daytime star tracker consists of a commercial firewire camera attached to a lens and baffle that help filter out visible light, allowing it to sense points of reference in the near-infrared wavelength bands.
In 2014, a prototype of the device flew on two WASP missions. The first, the flight of the HyperSpectral Imager for Climate Science (HySICS) collected radiance data as WASP pointed the instrument toward the Earth, the sun, and the Moon. The goal was to see what the star tracker saw at 120,000 feet.
The second WASP mission, launched a couple months later in October, carried the Observatory for Planetary Investigations from the Stratosphere (OPIS). Its mission was to gather time measurements of Jupiter's atmospheric structure - a challenge for the new star tracker because the gas giant is a bright object.
In the coming months, the team plans to fine-tune the algorithms to eliminate the extra light experienced during the OPIS mission and then retest the technology during a sounding rocket flight this summer and additional WASP missions in 2016 and 2017.