[meteorite-list] SMART-1 Update - April 19, 2006

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Apr 24 20:45:16 2006
Message-ID: <200604241732.KAA07766_at_zagami.jpl.nasa.gov>

http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=39073

Small Drop in Solar Array Power
European Space Agency
SMART-1
April 19, 2006

Report for period 20 February to 19 March 2006

SMART-1 operations have been nominal during this period. It has been
found that after an eclipse occurred on 28 October, there was a drop in
the solar array +Y current of about 1.1 Amps (~52 Watts). The Swedish
Space Corporation (SSC), SMART-1's industrial prime contractor, has
suggested that the most probable cause is the loss of one subsection of
the solar array at the +Y panel. The small reduction in power is not
causing any problem for the spacecraft's day-to-day operation.

The payload operations have also run as planned and D-CIXS successfully
uploaded a software patch.

SMART-1 is aiming at being the first ESA mission to command spacecraft
operations automatically. The Ground Operations Automation Review (GOAR)
took place on 16 March 2006. The board assigned some actions and called
for a delta review to be done on 31 March.
      
End-of-Mission Planning

All information relevant to the impact of SMART-1 is being consolidated
at the moment:

    * Flight Dynamics (FD) has completed the analysis of the
      end-of-mission planning
    * The FD analysis will be complemented with a technical note being
      produced by the SSC and a thermal simulation being done at ESTEC
    * The SMART-1 Principal Investigator, Bernard Foing is also
      coordinating the Moon Smart Impact, predictions and observation
      campaign

Without any changes to its orbit, SMART-1 would impact the Moon around
17 August 2006. However, science requirements have asked for pushing
back this date to 3 September. To achieve this extension, the perilune
distance will be increased by a series of perilune raising manoeuvres
from the end of June through early July. The perilune raising manoeuvre
strategy details are as yet to be finalised.

The accuracies of the planned delta-V generation using RWOL doesn't
allow phasing control. Consequently, the time of the selected impact
perilune may shift during the perilune raising manoeuvres. If the shift
exceeds a certain amount, a new perilune can be selected. To support
this selection the project scientist defines a slot of 5.5 hours for the
impact. This slot will always contain one and usually only one perilune.

The initial state prior to perilune raising manoeuvres, on 18 May 2006:

    * Radius of perilune = 2124 km (Moon radius = 1738 km)
    * Radius of apolune = 4714 km
    * Coordinate system = Z-axis towards Moon north pole of date, X-axis
      towards descending node of Earth equator of epoch 2000 w.r.t. Moon
      equator of date
    * Inclination = 90.6??
    * Right ascension of ascending node = 239.3??
    * Argument of perilune = 232.2??
    * Xenon left = 0.260 kg (0.060 kg usable with special operations)
    * Hydrazine left = 6.3 kg

The current plan for the perilune raising manoeuvre comprises:

    * 63 revolutions with about 3 hours of intermittent thrust centred
      around apolune
    * Thrust direction along the velocity with some in-plane tilt when
      away from apolune
    * Total delta-V = 12.032 m s-1
    * Total hydrazine usage = 2.6 kg
    * Total perilune raising = 90 km
    * Total duration = 14 days + 3 days (halt for orbit determination
      and delta-V calibration)
    * Start date = 21 June 2006 (end of push broom operations)
    * End date = 8 July 2006
    * Slots for trim = 26-27 July 2006 and 30-31 August 2006
    * Current impact time prediction = 3 September 2006, 02:00 UTC

Around impact, the perilune reduces 1.2 km per revolution. Clementine
data provided by the Science and Technology Operations Centre (STOC) are
used for the Moon topography. The accuracy of this model is still to be
determined and should be provided by the STOC. To guarantee impact at
the selected perilune, trims of the perilune altitude have to be
introduced. These correct for propagation uncertainty in the perilune
altitude which may be up to 1.0 km per month, caused by for example
uncertainties in the Moon gravity field. Without these trims, impact may
occur 1 revolution earlier or later.

Expected evolution of the perilune radius from 18 May to 3 September.
Note the increase at the start of July due to the perilune raising
manoeuvres.

Height above lunar surface for the nominal impact orbit on 3 September
2006, 6 minutes around the perilune.

Position of the perilune on the lunar surface for the nominal impact
orbit (central green line), plus 2 additional orbits on either side of
the impact orbit. The successive perilune points are indicated by the 5
squares (from right to left). The blue lines indicate surface levels.

Future Activities

The future activities are focused on:

    * Finalising the end of mission impact on the Moon analysis
    * Tone ranging test on SMART-1 with Chinese CLTC Kashi station and
      with ISRO
    * Start using the SMART-1 Ground Operations Automation System (S1 GOAS)
    * Preparation of papers for Spaceops and IAA in Valencia

Spacecraft Status

The spacecraft status is good with all functions working nominally.

AOCS
The AOC subsystem has done well in the period covered by this report.
Most noticeable during this period were four double blindings between 3
and 5 March 2006, and a suspected glitch in the startracker software.
This internal startracker problem caused an autonomous reboot of the
startracker on 5 March 2006 at 01:06:39, leaving the spacecraft without
startracker data for only a couple of seconds and causing no harm.

The startracker has had no problems with temperature during the
reporting period. The below figure shows the startracker CCD
temperatures for the period covered by this report. The table below
lists the temperature statistics for this period. Note that the
startracker starts having problems when the temperature is higher than 19??.

Temperature (??C) of the startracker CCDs for the reporting period: CHU1
(blue) and CHU2 (red).

The following table lists the temperature statistics for this period.

Camera Head Unit Min. T (??C) Max. T (??C) Average (??C)
CHU1 -12.36 +11.66 -6.6
CHU2 -2.27 +16.24 +11.92

TT&C
The performance of the TTC subsystem has been nominal during this period.

EP, Power and Thermal
The performance of the Power and Thermal Subsystems during the reporting
period was very good. The small drop in power, possibly indicating a
loss of one subsection of the solar array at +Y panel, is no problem for
the daily operations.

Orbital Information

SMART-1 OD415, Close to Apolune 2093
Epoch (UTC) 2006/03/20 08:29:41.4

Elements WRT Moon and its equator of date

Pericentre Distance (km) 2299.558770
Apocentre Distance (km) 4537.902013
Semi Major Axis (km) 3418.730391
Eccentricity 0.327365
Inclination (??) 90.678149
Ascending Node (??) 238.986563
Argument of Pericentre (??) 244.990510
True Anomaly (??) 179.999998
Osculating Orbital Period (h) 4.982560

The changes since apolune 2059 are as follows:

    * semi-major axis -0.3 km
    * perilune height -18.2 km
    * apolune height +17.5 km
    * orbital period -0.0 min
Received on Mon 24 Apr 2006 01:32:38 PM PDT