NASA Space Shuttle Atlantis is carrying two iPhone 4s to the ISS (International Space Station) for experimentation.

The phones, which have been tagged “space certified,” are loaded with a specifically developed app, SpaceLab for iOS that can be downloaded from the Apple App Store. The app will allow astronauts to conduct various experiments via the app’s features such as Limb Tracker, State Acquisition, LFI (Lifecycle Flight Instrument and Sensor Calibration).

The Limb Tracker will allow the astronauts to take photos of Earth that will match the arc to the horizon through manipulation of an overlay. This is equivalent to a “manual” horizon sensor. It will find out an estimate of altitude and “off axis” angle, a measurement of the angle of the image with respect to the Earth's center.

The State Acquisition will conduct a navigational experiment that will use a series of photographs with reference to an image of the Earth. The statistics will combine information from the three-axis gyro and accelerometer that will estimate the position of the spacecraft as per its latitude and longitude. The estimated position is then generated by manipulating and matching a wireframe overlay of the Earth's coastlines to the acquired Earth image(s).

LFI’s experiment will exemplify the effects of radiation on the device by monitoring certain areas of memory for Single Bit Upsets that sometimes is harmed by exposure to radiation.

The Sensor Calibration experiment will use a series of photos of a referred image that will be combined with the transmitted information using three-axis gyro and accelerometer measurements for calibrating the gyros and the accelerometers (i.e. bias and scale coefficients). This will improve the knowledge and accuracy of subsequent measurements.

The smartphones will be later returned to Earth via the Russian Soyuz as soon as the experiments are conducted. Flight data will be collected, examined, and then shared via the application.

Atlantis is on a 12-day mission and is scheduled to dock with the ISS at 11:06AM EDT on Sunday, MacRumors reported.