Science

Star Trek or science? Interplanetary laser ranging

A dissertation completed by TU Delft PhD candidate Dominic Dirkx, from the Aerospace Engineering faculty, shows how using Interplanetary Laser Ranging (ILR) to measure the distance between earth and other bodies in the solar system can yield more accurate results than the current technology.

A relatively new field, this also has the potential to advance our knowledge of the origin of life on our own planet, as well as elsewhere in the solar system.

Published October 22, 2015, the dissertation is titled ‘Interplanetary Laser Ranging (ILR): analysis for implementation in planetary science missions’. While this sounds like something from Star Trek, the paper aims to look at how using ILR to measure the distance between earth and other bodies can increase the science return of interplanetary missions. Currently these distances are measured using radio waves, which are accurate up to one metre. Dirkx claims that his dissertation shows how using ILR can reduce this margin of error to 5 mm.

ILR is derived from a technology currently used to measure the distance between earth and satellites, by bouncing a laser off the mirrors on earth-orbiting satellites, and using the time before the beam returns to work out the distance. Unfortunately, as the distance to other planetsis too large to use mirrors, ILR necessitates putting a laser in space as well as on earth and shooting laser pulses between these. This is very similar to what they do now with radio systems Dirkx explained. “My research has shown that this laser ranging definitely has a great potential to improve these kinds of measurements.”

Measuring this distance more accurately is useful as it also provides us with more detailed information about other aspects of celestial bodies. By measuring the distance between Earth and Mars at two different times, the example Dirkx gave Delta, you are looking at how these planets have moved in this time. “When you look at motion in the solar system you are inferring something about the gravity field, and gravity is generated by mass.” As such, this allows us to learn more about the mass and internal structure of the body, for example whether its mass is found mainly at the centre or in the outer layer, whether it has a mantle or ocean under the surface.

This knowledge, in turn, would have implications for what we know about how the solar system was created, potentially allowing us to expand our knowledge of how water and life came to our own planet, and even about whether there are suitable conditions for life elsewhere in the universe.

With his thesis and PhD defence completed, Dirkx states that he is happy with his results, and although some expressed scepticism about using this new technology when the current method works, the reception has overall been positive.

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