Express zur Venus

Die ESA-Sonde Venus Express wird in den nächsten fünf Monaten eine 350 Millionen Kilometer lange Reise durch das innere Sonnensystem machen. Technology Review wird dieses Abenteuer mit einem Online-Missionstagebuch begleiten: Experten der ESA stellen uns hierfür ihre Analysen und Informationen ungeschnitten zur Verfügung.

Nach der Überprüfung, ob ihre Ausrüstung und ihre Nutzlast korrekt funktionieren, wird die Sonde "abgeschaltet" und tritt nur noch einmal am Tag mit der Erde in Kontakt. Erforderlichenfalls wird im Januar eine Kurskorrektur auf halbem Wege vorgenommen.

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Gelungener Zieleinlauf: Seit gestern früh herrscht im ESA-Kontrollzentrum in Darmstadt fieberhafte Aktivität. Im Schichtbetrieb haben die Spezialisten der Flugkontrolle die Venus-Express-Sonde für den kritischen Endspurt bereit gemacht: Den Einschuss in den Venus-Orbit.

Damit die Sonde, sollte während dieses kritischen Manövers ein Parameter einen kritischen Bereich verlassen, nicht in den "Safe Mode" fällt und sich automatisch zur Erde orientiert, sind während der vergangenen 24 Stunden zunächst alle Sicherheitsmechanismen heruntergefahren worden, erklärt der stellvertretende Flugleiter Peter Schmitz. "Morgen wechseln wir dann die Antenne, weil die zugehörige kryogenische Fläche jetzt in die Sonne kommt", sagt Schmitz. "Auch das wird noch einmal ein kritische Phase". Bis zum 13. April werden nach dem erfolgreichen Eintritt in den Orbit nun die Sicherheitssysteme wieder hochgefahren und die Prozeduren für den eigentlichen Messbetrieb auf die Sonde hochgeladen.

Venus Express Enters Orbit

10 Apr 2006

Venus Express has arrived at Venus after a 50 minute burn of the main engine and entered orbit around the planet.

10 to 11 April 2006: Final preparations for the manoeuvre 24 hours to 12 hours before VOI, spacecraft controllers will command Venus Express into its final configuration for the burn.

11 April 2006, 06:03 (UT): Venus Express slew manoeuvre This manoeuvre lasts about half an hour and rotates Venus Express so that the main engine faces the direction of motion.

11 April 2006 07:07 (UT): start of Venus Express Orbit Insertion Activities

12 to 13 April 2006: Spacecraft full reactivation starts During the 24 hours following the orbital capture, time will be dedicated to reactivate all spacecraft functions, including all internal monitoring capacity.

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Final Venus Approach Phase

21 Mar 2006 09:31 Report for period 10 March to 16 March 2006

The reporting period has marked the start of the final Venus approach phase. All activites will now focus on the navigation and preparation for the Venus Orbit Insertion operations.

DDOR measurements with ESA and DSN ground stations are continuously conducted.

At the end of the last Cebreros pass in the reporting period (DOY 075 13:00) Venus Express was 83 million km from the Earth, 105.4 million km from the Sun, and 10.1 million km from Venus. The one-way signal travel time was 278 seconds. Payload Activities

ASPERA The instrument is off.

MAG The instrument is off.

PFS The instrument is off.

In December 2005, during the first planned activation of the instruments, various calibration activities showed that the instrument sensor is working perfectly, but revealed that the instrument scanner is stuck in its closed position, inside the instrument box.

Several attempts to move it were made at the time, but the instrument did not respond. Experts then initiated a number of ground tests with a spare model of the scanner, and suspected a thermal problem by which low temperatures were blocking the rotation of the mechanism.

Another attempt to move the scanner was made on 16 March 2006, in warmer flight conditions. Unfortunately, the scanner remains stuck.

The next opportunity to perform another test on the spacecraft will be end of April, after the Venus Orbit Insertion. In the mean time, PFS will remain switched off with the scanner in a safe closed position.

SPICAV The instrument is off.

VeRA The USO is kept powered but muted.

VIRTIS The instrument is off.

VMC The instrument is off. Future Milestones

The spacecraft is now configured for the Venus approach phase and activities will focus only on this.

The intense navigation campaign is currently at a period of maximum activity in order to have an extremely precise assessment of the spacecraft trajectory versus its target point at the planet.

During the next reporting period the spacecraft will reach its perihelion (which is inside the Venus orbit around the Sun). The trajectory will then cross the orbital path of Venus on 11 April - when the orbit insertion manoeuvre will take place.

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Main Engine Calibration Test

17 Feb 2006 13:41 Report for Period 10 February to 16 February 2006

The reporting period has been dedicated to the Main Engine calibration activity, which was successfully conducted in the night between the 16 and 17 February. According to the first telemetry data the burn (3 seconds duration) was nominal and detailed calibration data will now be analysed by the engineers to assess the exact performance of the main engine.

Main Engine calibration burn has shown a working Main Engine thus giving the green light for the last mandatory sub-system to be used for the Venus Orbit Insertion. By coincidence the Main Engine calibration burn took place on mission day 100.

During the reporting period operations have been moved back to the Cebreros station and this will be used as prime station from now onwards.

Main Engine Calibration

At the end of the last New Norcia pass in the reporting period (DOY 048, 05:00) Venus Express was 46.6 million km from the Earth, 112.2 million km from the Sun, and 16.45 million km from Venus. The one-way signal travel time was 155 seconds. Spacecraft Status

AOCS The Main Engine calibration burn took place starting on DoY 048 (17 February 2006) at 00:17 with the Boost Initialisation Phase and then the Liquid Settling Phase. The Main Engine fired for circa 3 seconds between 00:27:08 and 00:27:11; the AOCS measured a delta-V of 2.838 m/s versus an expected value of 2.6. Telemetry and radiometric data will now be analysed by the mission teams to give a detailed assessment of the performance. At the exit of this mode the AOCS also successfully went through the first Sun re-acquisition since separation from the launch vehicle.

Payload Activities:

ASPERA The instrument is off.

MAG The instrument was on producing science and it has been switched off on DoY 44. It will be switched on again after the end of main engine calibration activities.

PFS The instrument is off.

SPICAV The instrument is off.

VeRA The USO is kept powered but muted.

VIRTIS The instrument is off.

VMC The instrument is off. Future Milestones

Activities in the next weeks will be focused to put the spacecraft on its final trajectory to the target point for the Venus Orbit Insertion and to complete outstanding PL check-out and SW update activities. These will include:

• VIRTIS EEPROM parameters update
• SPICAV check-out
• ASPERA calibration
• MAG last science acquisitions
• VMC SW update

Additional spacecraft activities will allow characterisation of the Sun sensors and of the outgassing from the –X face in preparation of the VOI phase.

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No. 14 - Continued Spacecraft Testing

13 Feb 2006 10:29 Report for Period 03 February to 09 February 2006

Operations during the reporting period have been moved again over the New Norcia station and spacecraft activities has focused on further TTC tests, characterisation of STRs acquisition performance, and Radio Science activities.

SC Monitoring and ASPERA calibration

At the end of the last New Norcia pass in the reporting period (DOY 040, 06:00) Venus Express was 38.2 million km from the Earth, 115.6 million km from the Sun, and 16.9 million km from Venus. The one-way signal travel time was 127 seconds. Payload Activities

ASPERA The instrument is off and it has been activated on DoY 036 and 039 for calibration activities.

MAG The instrument is ON producing science. It will be temporarily switched OFF during the Main Engine calibration activities.

PFS The instrument is off.

SPICAV The instrument is off.

VeRA The USO is kept powered but muted.

VIRTIS The instrument is off.

VMC The instrument is off. Future Milestones

During next week the Main Engine pressurisation and calibration will take place therefore all activities will be focused around this operation.

Operations will be moved back to Cebreros but the Main Engine burn itself will be executed during a New Norcia visibility slot in order to be able to monitor S-band 2-ways Doppler during the manoeuvre.

After this manoeuvre, and an eventual correction to be done one week later, the SC will be on the trajectory leading to the target point for the Venus Orbit Insertion to take place on the 11 April.

Two more weeks will be dedicated to outstanding payload check-out and SW upload activities, after this all spacecraft operations will be focused only to VOI preparation.

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Passive Cruise Phase Begins Report for Period 16 December 2005 - 05 January 2006

During the reporting period the spacecraft has been configured for a passive cruise phase and the only activities conducted on top of the routine ones are the DDOR tests with ESA (NNOCEB) and DSN (GDS-CAN) stations. Date: 09 Jan 2006

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No. 8 - End of Near Earth Commissioning Phase Report for Period 09 December to 15 December 2005

During the reporting period the last activities of the Near Earth Commissioning have been completed according to the plan. Two slots with the New Norcia ground station have been dedicated to test the performance of the TTC subsystem and of the Ultra Stable Oscillator (USO) for the radio science experiment (VeRA). In both occasions problems in operating the ground station equipment have affected the test. Date: 20 Dec 2005

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No. 7 - Ongoing NEC Activities Report for Period 02 December to 08 December 2005

During the reporting period all the activities for the Near Earth Commissioning of the instruments have been conducted according to the plan. The multi-instrument pointing scenario activities have been successfully concluded and the PFS instrument has been switched on for the first time. Date: 12 Dec 2005

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No. 6 - Payload Commissioning Continues Report for Period 25 November to 01 December 2005

During the reporting period all the activities for the Near Earth Commissioning of the instruments have been conducted according to plan. The SPICAV instrument has been successfully switched ON for the first time. Date: 05 Dec 2005

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No. 5 - Instrument First Light Report for period 18 November to 24 November 2005

During the reporting period all the activities for the Near Earth Commissioning of the instruments have been conducted according to plan. The MAG, VMC and VIRTIS instruments have all been activated for the first time. Date: 28 Nov 2005

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No. 4 - Platform Completes near Earth Commissioning; Payload Commissioning Underway

Report for period 11 November 2005 to 17 November 2005

During the reporting period all the activities foreseen for the Near Earth Commissioning of the platform have been conducted according to plan. The remaining testing activities on the platform side will take place in January (thermal characterization) and in February (main engine calibration). Date: 23 Nov 2005

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The Venus Express Launch and Early Orbit Phase (LEOP) activities again continued to run very smoothly. All foreseen activities were completed and it was also possible to bring forward some platform commissioning activities, which were planned for the coming week-end. A pinnacle in the reporting period was the first command send to Venus Express in X-Band via the new ESA 35m Deep Space Ground Station at Cebreros (Avila, Spain). Furthermore, the Trajectory Correction Manoeuvre (TCM-1) was successfully performed, which now brings Venus Express on the exact trajectory finally required for Venus Orbit Insertion.

The pass 4 LEOP operations included successful switching from the Low Gain Antenna (LGA) to the High Gain Antenna (HGA2), a test with the second S-Band transponder (S-Tx2), change in radio frequency band from S-Band to X-Band, and increase of the telemetry downlink bit rate to 91.4 kbps. At 17:10z the uplink carrier was established at Cebreros and the first command was transmitted from Cebreros to the Venus Express spacecraft at 17:21z in X-Band. This marked the successful achievement of a major milestone for the new ESA 35m ground station. Congratulations to the Cebreros station staff.

The first dump of the Solid State Mass Memory (SSMM) data was done at 19:47z, the first On-Board Control Procedure (OBCP) executed at 19:52z, and the first Reaction Wheel off-loading was performed (18:25z-00:19z).

Bonus activities in pass 4 encompassed Thermal Control System (TCS) heater switching, and successful commissioning of the Data Management System (DMS). It is to be noted that both the power and the thermal behaviour of the spacecraft are very close to pre-launch flight predictions.

Pass 5 activities started with the preparation for the Trajectory Correction Manoeuvre (TCM-1). The manoeuvre was again performed in the direction of Earth in order to be fuel optimal. The slew was started 05:39z and was completed 06:09z. Subsequently, TCM-1 started at 06:14:33z, had a manoeuvre duration of 209 sec and a magnitude of 3.43 m/sec. Post manoeuvre assessment based on Doppler data indicated that manoeuvre accuracy was within 0.034%. At 07:29z the spacecraft had been slewed back to the starting attitude. Thereafter, the Solid State Mass Memory (SSMM) data were dumped, the Ultra Stable Oscillator (USO) was switched-on and the Telemetry mode was changed. This completed the foreseen activities for pass 5. As a bonus, the Star Tracker commissioning was done.

With the end of the LEOP, the ground station support has now been significantly reduced and stations have been released. The mission will now be supported primarily by one pass per day from Cebreros. The support given by the ESA stations in Kourou, New Norcia/Perth and Cebreros, and by the NASA DSN stations of Canberra and Goldstone has been excellent.

The LEOP activities were completed on 11-Nov-05 (DOY 315) at 08:48z at Mission Elapse Time (MET) 53:15 hrs and the Venus Express spacecraft was 634,000 km away from Earth on route to Venus.

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Both the Venus Express spacecraft and ground segment continued to perform excellently. The highlight of this period was the successful planning and testing of the Trajectory Correction Manoeuvre (TCM-0).

The Venus Express Launch and Early Orbit (LEOP) operations continue to run very smoothly. Pass 2 activities encompassed loading of the On-Board Control Procedures (OBCPs), loading of the Service 12 and the dump of the Safe Guard Memory (SGM). The planned Reaction Wheels off-loading was not required. All foreseen Pass 2 activities were already completed about two hours after hand-over from Team A to Team B. The remainder pass activities were quiescent, in view of a well performing spacecraft and ground segment. It was considered to bring some activities forward, but after iteration with the project support team found to be not viable.

Pass 3 activities started with the preparation for testing the Trajectory Correction Manoeuvre (TCM-0). Given the slight over-performance from Soyuz/Fregat, it was decided to do the TCM-0 in direction of Earth in order to be fuel optimal. The slew was enabled at 05:20z, started 05:43z and was completed 06:13z. Subsequently, TCM-0 started at 06:38:52z, had a manoeuvre duration of 48 sec and a magnitude of 0.5 m/sec. Post manoeuvre assessment based on Doppler data indicated that the manoeuvre duration was about 1 sec less than commanded and revealed a negligible error in performance. At 07:33z the spacecraft had been slewed back to the starting attitude. This completed the foreseen activities for pass 3.

It is planned to advance some of the planned Data Management System (DMS) commissioning to be done in pass 4.

The support from the ESA and NASA DSN ground stations has been very good throughout the LEOP.

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Soyuz/Fregat lifted off right on-schedule at 03:33:34,454 UTC on November 9th, 2005 carrying with it the Venus Express spacecraft on the start of its 5 months journey to our sister planet Venus. The solid boosters separated as expected at 1:58 min into flight, shortly later (L+4:14 min) followed by the fairing, and the third stage separation occurred at 8:48 minutes after lift-off. The Fregat upper stage first burn (L+09:49 min) brought Fregat and Venus Express into a coast phase and the second Fregat burn (L+1:22 hrs) injected the composite into the required escape trajectory. Starsem announced the separation of Venus Express had occurred nominally (L+1:36:30 hrs).

When the ESA ground station in New Norcia (Western Australia) acquired the telemetry signal from Venus Express about two hours after launch at 05:30:42 UTC, the spacecraft status was as expected and the automatic separation sequence was seen to be in progress having already completed the pressurization of the propulsion system and the configuration of the thermal control.

The initial rate reduction and first Sun acquisition phase proceeded very smoothly, and this was followed by the deployment of the two solar array panels, which was completed at 05:49z. Following second Sun acquisition the automatic separation sequence was completed 06:11z.

After determination of the spacecraft phasing and communication link maintenance the first telecommands were up-linked from the New Norcia station at 06:09:29z. Initial spacecraft configuration was achieved as expected and the spacecraft entered SHM (Safe Hold Mode) at 08:44z.

Activities of the LEOP continued as planned. The first star tracker was switched on at 07:45z. The reaction wheels were switched on at 08:57z and the spacecraft was commanded into Normal Mode at 10:00z. The second Star tracker was switched on at 10:07z.

Thereafter LEOP software patches were removed/replaced and the spacecraft was fully configured for flight in Normal Mode at 11:15z

This completed a very successful first phase of the LEOP. The spacecraft has behaved very much as expected.

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