ESA title
Artist's impression of SMART-1
Science & Exploration

SMART-1's lunar encounter

01/09/2004 1717 views 0 likes
ESA / Science & Exploration / Space Science

Since its launch on 27 September 2003, SMART-1 has been slowly travelling to the Moon.

It has spiralled away from Earth, getting slightly further away from its home planet on each orbit.

On 17 November 2004, it will be captured by the Moon’s gravity and will start to spiral in towards the Moon on each orbit.

On 19 August 2004, SMART-1 had its first encounter with the Moon's gravitational field. The spacecraft was approximately 197 000 kilometres from the Moon and 230 000 kilometres from Earth. Despite the fact that it was closer to the Moon, SMART-1 was still within Earth's ‘sphere of influence’, due to the much larger mass of Earth. However, the gravitational influence of the Moon on SMART-1's orbit has been enough to change it significantly.

Once SMART-1 has been captured by the Moon's gravity, it begins to work its way closer to the lunar surface
Once SMART-1 has been captured by the Moon's gravity, it begins to work its way closer to the lunar surface

SMART-1 is nearing the point between Earth and the Moon where there is a gravitational equilibrium. In one direction from this position, Earth's gravity will be dominant and in the opposite direction, the Moon's pull will be stronger.

While the precise point of equilibrium is stable, objects near this region will 'wobble'. Predicting how they 'wobble' involves a branch of mathematics called ‘multi-body dynamics’, a subject still a matter for theoretical research.

The ESA flight dynamics team, located at ESOC, used powerful computing techniques to analyse the low-intensity gravitational disturbance to SMART-1's orbit. They ensured the desired changes in SMART-1’s course were made correctly. The spacecraft will pass the point of gravitational equilibrium on 17 November.

The Moon's orbit around Earth is virtually fixed – it orbits every 27.4 days. SMART-1’s Earth orbit, after the 19 August course change, was altered to encounter the Moon every 27.4 days. The SMART-1 orbit is, therefore, now in ‘resonance’ with that of the Moon.

The next lunar resonances will occur on 15 September and 12 October, with lunar capture on 17 November. SMART-1 will arrive in its operational orbit around the Moon in January 2005.