content 20-March-2018 10:27:20

Lunar Capture

On 11 November 2004 at 10:30 UTC, close to the 331st Earth apogee, SMART-1 was at the first Lagrange point of the Earth-Moon system, where the orbit is neither Earth, nor Moon bound. SMART-1 then crossed over to the region where the Moon's gravitational pull on the spacecraft is stronger than that of the Earth and was on its way to lunar capture.

Spiralling down to operational orbit

In its 332nd orbit around the Earth, after three weeks of unpowered flight, the electric propulsion (EP) drive was fired on 15 November at 05:24 UT, to bring the spacecraft into lunar orbit. Roughly 12 hours later, at 17:48 UT, SMART-1 had its first perilune passage.

This first burn in a series of EP firings, lasted 108 hours and ended on 19 November 2004 at 17:48 UTC. Over the next three months, periodic firing of the EP resulted in the continuous reduction of the orbit's semi-major axis, allowing SMART-1 to reach its operational orbit around the Moon.

Copyright ESA

SMART-1 and Moon orbit for the period 2-20 November 2004, during which the spacecraft crossed the first Lagrange point of the Earth-Moon system. (Click image for hi-res version)

The following table lists the dates of the first 12 perilune passages as well as the period between two sequencial passages. It shows the steady decrease in orbital period caused by the lowering of SMART-1's orbit.

Event Day and Time (UTC) Period (h)
Perilune Passage 1

15-11-2004 @ 17:47:38.762Z

Perilune Passage 2 19-11-2004 @ 11:01:02.127Z 75
Perilune Passage 3 22-11-2004 @ 14:29:38.449Z 69
Perilune Passage 4 25-11-2004 @ 11:36:11.520Z 59
Perilune Passage 5 27-11-2004 @ 22:42:28.011Z 59
Perilune Passage 6 30-11-2004 @ 01:59:00.054Z 51
Perilune Passage 7 01-12-2004 @ 23:25:21.011Z 46
Perilune Passage 8 03-12-2004 @ 16:05:27.002Z 41
Perilune Passage 9 05-12-2004 @ 05:08:18.135Z 37
Perilune Passage 10 06-12-2004 @ 15:08:27.116Z 34
Perilune Passage 11 07-12-2004 @ 22:40:07.437Z 31
Perilune Passage 12 09-12-2004 @ 04:08:57.443Z 29

Between 10 and 18 January 2005 the EP operations were temporarily interrupted to estimate the remaining fuel and plan accurately for a mission extension. After this period, the periodic firing of the EP resumed and SMART-1 reached its operational orbit on 27 February, some three and a half months after lunar capture.

Status Reports Coverage

The period from lunar capture up to reaching the operational orbit is covered in the status reports no. 31 to no. 35

Last Update: 03 August 2006

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See Also