SOHO Status Report - February 2004
03 Feb 2004 10:51
The spacecraft status is nominal, with the High Gain Antenna (HGA) Z-axis in a fixed position.
With the HGA Z-axis parked, SOHO continues to experience "keyhole" periods every three months. Manoeuvres (including a 180° roll) are now executed during keyholes. With station keeping manoeuvres every three months, the burns are very small. The last two manoeuvres were held on 7 October (¿V of 0.14 ms-1) and 30 December (¿V of 0.075 ms-1).
On 2 September a test showed that the 26m DSN stations can acquire low rate telemetry through the Low Gain Antenna (LGA) by tweaking the receiver parameters. SOHO no longer relies on 34m stations for recovery from, for example, Emergency Sun Reacquisition mode.
The big proton event on 28 October was uneventful for the platform. The star tracker experienced only a single star swap. The solar arrays degraded by 1.2%.
Operations and Archiving
All instruments are nominal and SOHO science operations are progressing smoothly.
The winter keyhole saw significant data losses due to competition for 34m and 70m ground stations from the Mars missions and Stardust. VIRGO calibrations were secured by carefully planned use of the on-board recording capacity. Some MDI magnetograms were secured by diverting them to the medium rate telemetry. Keyhole operations went very smooth.
Links to the SOHO archives (including mirrors) are accessible at http://soho.estec.esa.nl/data/.
Over two weeks in October/November, the Sun featured three unusually large sunspot groups (including the largest one of this solar cycle), 11 X-class flares (including the strongest ever recorded), numerous halo coronal mass ejections (two with near-record speeds) and two significant proton storms. Satellites, power grids, radio communication and navigation systems were significantly affected. The events, among the best observed ever, with data from multiple spacecraft and ground based observatories, will be the subject of analysis for years to come.
The events caused unprecedented attention from the media and the public. Images from SOHO and quotes from SOHO scientists appeared in nearly every major news outlet. The attention wiped out all existing SOHO web traffic records (requests/data volume): Monthly (31 million/4.3 TB), weekly (16 million/2.6 TB), daily (4.8 million/0.7 TB), and hourly (0.4 million/33 GB). The daily and hourly volumes were bandwidth limited.
The analysis of high-resolution spectroscopic observations of comet C/2002 X5 (Kudo-Fujikawa) from UVCS has revealed a quasi-spherical cloud of neutral hydrogen and a variable tail of ionized carbon (C+ and C2+) that disconnected from the comet and subsequently regenerated. The high abundance of C2+ and C+ relative to water (24%) found is unexplainable by photodissociation of carbon monoxide but instead attributed to the evaporation and subsequent photoionization of atomic carbon from organic refractory compounds present in the cometary dust grains.
The 13th SOHO Workshop, "Waves, oscillations and small-scale transient events in the solar atmosphere: A joint view of SOHO and TRACE" was held at Palma de Mallorca, Balearic Islands, Spain, on 29 September - 2 October 2003. Nearly 100 participants presented and discussed over 110 papers and posters. The proceedings will be published by ESA (SP-547).