SMART-1 completes its first orbit around the Moon

Status Report From: European Space Agency
Posted: Sunday, November 21, 2004


Today, 19 November 2004, at 10:58 UTC, SMART-1 passed its second perilune and successfully completed its first orbit around the Moon. The first orbit started on 15 November at 17:47 UTC when SMART-1 passed its first perilune.

The next perilunae will occur with increasingly shorter intervals as the orbital period of the spacecraft continuously decreases. This isdue to the thrust provided by the electric propulsion system, which is used to reduce the semi-major axis of the orbit.

The first firing of the electric propulsionengine started on 15 November at 05:23 UTC and the engine has performedflawlessly since.It will remain on until 17:48 UTC today, providinga total thrust timeof 108 hours.

Upcoming events

Perilune passages

Event Day and Time (UTC) Period (h)
Perilune Passage 1 15-11-2004 @ 17:47:38.825Z 89
Perilune Passage 2 19-11-2004 @ 10:58:46.976Z 75
Perilune Passage 3 22-11-2004 @ 14:09:38.299Z 69
Perilune Passage 4 25-11-2004 @ 11:11:06.898Z 59

Electric propulsion burns

Event Day and Time (UTC) Duration (s)
EPP Start 15-11-2004 @ 05:23:53 390 299
EPP End 19-11-2004 @ 17:48:52 0
EPP Start 20-11-2004 @ 19:09:52 39 095
EPP End 21-11-2004 @ 06:01:27 0
EPP Start 21-11-2004 @ 22:54:03 27 651
EPP End 22-11-2004 @ 06:34:54 0
EPP Start 22-11-2004 @ 13:15:54 26 268
EPP End 22-11-2004 @ 20:33:42 0
EPP Start 23-11-2004 @ 19:11:49 33 388
EPP End 24-11-2004 @ 04:28:17 0
EPP Start 24-11-2004 @ 18:30:12 87 455

Eclipse period

Another important event in the near future is a fairly long eclipse caused by the satellite crossing the Moon's umbra for 1 hour and 50 minutes on 22 November starting at 08:52 UTC. The spacecraft has proved, during the transfer orbit, to be able to withstand even longer eclipses. However, since the batteries have not been discharged for that longsince many months, the ESOC flight control team and the ESTEC and industry specialists will closely follow the event.

Orbital/Trajectory information

The following osculating orbital elements of the first orbit have been determined by a tracking campaign:

EPOCH (UTC) 2004/11/15 17:47:38.7

Elements WRTMoonand its equator of date
Pericentre Distance (km)

6 704.286533

Apocentre Distance (km)

53 207.630341

Semi Major Axis (km)

29 955.958437



Inclination (deg)


Asc. Node (deg)


Arg. of Pericentre (deg)


True Anomaly (deg)


Osc. Orbital Period (h)


SMART-1 first lunar orbit, both predicted (green line) and measured (blue line)

These elementsare extremely close to the calculated elements of the planned orbit (see Status Report No. 31). This accurate prediction isevidence of both the good performance of the electric propulsion engine (about 1% above nominal) and the accuracy of the trajectory calculation by the flight dynamics team. In the diagramthe predicted and measured osculatingfirst lunar orbits are plotted. The accuracy is so good that the two lines coincide (the difference is smaller than the thickness of the lines).

One interesting point to note is that although the osculating orbital period is129 hours, the actual orbit was only 89 hours. This illustrates the significant impact that theengine burns have on the orbit and marks the meaning ofthe osculating orbit, which is the orbit that would be travelled by the spacecraft if at that instant all perturbations, including EP thrust, would cease.

// end //

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