Public Release: 

NASA honors researchers behind film from space

Technical University of Denmark

A group DTU Space researchers has received special recognition from NASA for their short film of the Moon's orbit around Earth as seen from space. The film has attracted international attention and gained widespread media coverage, featuring on the BBC, Discovery and in the Guardian.

Professor John Leif Jørgensen received the NASA Group Achievement Award in the USA on behalf of the team in recognition of their outstanding achievement, contributing significantly to NASA's mission. NASA also presented Professor John Leif Jørgensen with the Exceptional Public Achievement Medal.

The time lapse movie consists of a series of images captured by the two star cameras developed and hand-built by the research group at the Measurement and Instrumentation division at DTU Space. The cameras are mounted on NASA's probe Juno, launched from Earth in 2011. Juno's final destination is Jupiter, but to reach that deep into space, Juno was initially sent on a return trip beyond Mars, passing Earth on its way back in October 2013 to exploit Earth's gravitational field for acceleration purposes. The unique images were captured on the probe's way back from Mars to Earth, ensuring the first ever footage of Earth-Moon system from space.

The cameras primarily function as stellar compasses, enabling the researchers to establish the exact orientation of the probe at all times. But Professor John Leif Jørgensen and his team also saw this as a unique opportunity to use the camera as more than just stellar compasses. However, it required a great deal of persuasion and an animated visualization of the film to get NASA to agree to the idea of using the star cameras to create the unique footage.

The cameras started shooting every five minutes when Juno was four million kilometres away from Earth. The film starts at a distance of tree million kilometres, and the shooting lasted for four days. The images required major editing to create a coherent film, and this process was headed up by PhD students at DTU Space, David Pedersen and Andreas Jørgensen.

The photo shows the unedited images, and how the interlaced video technology of the sensor ensures that the objects are photographed twice, in each image. The probe is rotating about its axis once per minute, so with a time between images of 5min, the space probe cannot manage to place the objects in the same place in two consecutive frames. Further, the stellar compass on the Juno probe has been designed to photograph stars and faint objects, such as Jupiter and its moons. The sunlight on Earth and the Moon is 25 times stronger than on Jupiter, resulting in saturation of the sensor's video amplifier. This effect is seen as vertical lines in the images. To produce the film, the researchers removed the lines and compensated for the movement of Earth and the Moon in each frame by using measurements provided by the other three star cameras.

In the film from DTU Space, the researchers have added three figures to illustrate the actual distance between Juno and Earth, and the speed at which Juno travels relative to Earth and the Moon. The figures show how Earth's gravitational field is used to increase the speed of the probe relative to the Sun, whereas the speed relative to Earth is the same before and after the encounter. This increase is crucial for Juno to reach Jupiter. The impact of this flyby is actually similar to the acceleration delivered by the booster rocket launching Juno.

When the probe reaches Jupiter in 2016, it will remain in orbit for a year or so. In orbit around Jupiter,he space probe will complete 33 orbits while measuring the magnetic and gravitational fields, investigating the weather systems, and determining the water content in the atmosphere. All this data will enhance our understanding of the origins and early development of the solar system.

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