|status reports||24-June-2019 18:10:32|
No. 24 - Cruising beyond 100 000 km from Earth
11 June 2004The spacecraft is now flying its 302nd orbit, in good status and with all functions performing nominally. The current thrusting strategy, adopted end of May (see Status Reports #20 and #21), is progressing with thrust arcs around perigee for about one third of every revolution. The thrust arcs duration is for about 18 hours out of an orbital period of 55 hours. The thrust duration will progressively increase to almost 40 hours in orbit 321 in mid-August, by which point the orbital period will exceed 5 days.
The Electric Propulsion power has been throttled down again according the predictions of the solar array output power, from 1338 W to 1311 W. We are now approaching the minimum power (on early July) due to the Earth-Sun distance approaching maximum for the year.
The thruster change of state, caused by the varying amplitude of the anode current oscillation (see last report for more explanation) is now seen once every four pulses, where the last third of the pulse exhibits higher thrust and lower current oscillations. The thrust stays, for the most part, at around -1%, with +1.2% measured after the state change. No Optocoupler Single Event Transients, causing the flame-out, have been observed during this period.
Up to 6 June 2004, the electric propulsion system had cumulated a total ON time of about 2414 hours, consumed about 38 kg of Xenon (46% of the total propellant on board) and imparted to the spacecraft a velocity increment of about 1760 ms-1.
The Attitude and Orbit Control System (AOCS) has also performed nominally. A short double blinding, by the Earth and the Moon, of the Star Tracker camera heads occurred on 25 May and lasted for around 3 minutes.
The hydrazine consumption from the beginning of the mission until date, 6 June 2004, has been just 0.14 kg, leaving 7.95 kg. These numbers are the average obtained from the two independent hydrazine bookkeeping techniques used by the Flight Dynamics team.
The last Reaction Wheel offloading happened on 21 April, proving how well the Electric Propulsion gimbals control mechanism is keeping the spacecraft total momentum build-up at extremely low level.
We have recently detected a possible degradation of performance on one of the two transponders. A parameter measured on board seems to indicate a reduction of radiated power transmitted by the radio system presently in use. A test will be performed as soon as possible comparing the affected transmitter with the redundant one, measuring the power received at the ground station.
Several cruise observations have been performed with the instruments:
The AMIE team had a meeting in Neufchatel, coinciding with taking the first SMART-1 images of the full Moon just before the lunar eclipse on 4 May.
The osculating orbital elements are periodically computed by the ESOC specialists. These elements define the so called "osculating orbit" which would be travelled by the spacecraft if at that instant all perturbations, including EP thrust, would cease. So it is an image of the situation at that epoch. In reality the path travelled by the spacecraft is a continuous spiral leading from one orbit to another. The most recent osculating elements are as follows:
In this diagram the osculating orbits at launch (GTO) and at different times are plotted. Clearly visible are the large effects that the operations of the electric propulsion have had on the orbit expansion. The height of the apogee, in particular, has dramatically increased and now exceeds 100 000 km.
Since the start of the mission, the electric propulsion system has changed the orbital parameters as follows:
Bernard H. Foing
Last Update: 15 July 2004For further information please contact: SciTech.firstname.lastname@example.org
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