Bulletin 127 - August 2006 39 Accomazzo 8/8/06 1:42 PM Page 38

Accomazzo 8/8/06 1:42 PM Page 38

Venus Express

Andrea Accomazzo, Peter Schmitz & Ignacio Tanco Mission Operations Department, Directorate of From Earth to Venus Operations and Infrastructure, ESOC, Darmstadt, Germany

n the early morning of 9 November 2005, Venus Express left Earth aboard a Soyuz Ilaunch vehicle and headed for Venus. After several months of interplanetary cruise, a perfect capture burn on 11 April 2006 placed the spacecraft in orbit around our neighbouring planet. Only 48 hours later, the first astonishing images of the south pole were received on Earth. A few weeks later, after orbital manoeuvres, Venus Express achieved its operational science orbit ready to begin several years of observations.

Travel Planning Preparations for the Venus Express mission began in early 2003 at ESOC with the build-up of the Flight Control Team and the definition of the systems required to test, control and monitor the new spacecraft for its flight to and around Venus. Major reuse of the systems developed for Rosetta and Mars Express allowed the ground teams to focus on the required modifications and Reaching our improvements. The preparation phase went smoothly even though the mission posed new challenges for the operations Sister Planet team, mainly through the thermal

esa bulletin 127 - august 2006 39 Accomazzo 8/8/06 1:42 PM Page 38

Venus Express

Andrea Accomazzo, Peter Schmitz & Ignacio Tanco Mission Operations Department, Directorate of From Earth to Venus Operations and Infrastructure, ESOC, Darmstadt, Germany

esa bulletin 127 - august 2006 39 Accomazzo 8/8/06 1:42 PM Page 40

Operations & Infrastructure Venus Express

The Cebreros ground station The mission control team anxiously await confirmation of orbit capture, ESOC Main Control Room, 11 April 2006

for commissioning. Critical activities and VeRA instruments were then included switching communications to commissioned. X-band (for a high data rate) using the Once all the instruments were checked spacecraft’s second high-gain antenna out separately, a dedicated interference (HGA2) on the second day, and a small test concluded the NECP on course correction of 3.43 m/s 12 hours 15 December. Several instruments were later. In total, it took less than 53 hours operated simultaneously in various to complete all these activities, ready for modes to look at potential interferences the Near-Earth Commissioning Phase between them and with the spacecraft to being immediately afterwards. systems.

Near-Earth Commissioning Phase (NECP) Interplanetary Cruise Phase (ICP) During NECP, the spacecraft systems After NECP, the ICP lasted formally and payloads were checked out for the until 4 April 2006, a week before the first time in space; this took from Venus Orbit Insertion (VOI). ICP was 12 November to 15 December. Venus heater lines and heater switches were On 22 November, after the initial initially considered as a quiet period Express was still close to Earth, so the working properly. instrument health check of VMC and operationally speaking, with only a few brief travel time for the signals allowed As part of the Attitude and Orbital VIRTIS, the two cameras were pointed spacecraft activities to be carried out in very careful near-realtime commanding. Control System (AOCS) checkout, a towards Earth and imaged the Earth- preparation for VOI. However, it soon Critical checkout operations were startracker health check was performed Moon system from 3.5 million km out. turned into a very busy period during conducted during the 7 hours per day of together with calibration of the align- A minor modification to the VMC which many important spacecraft and ground station contact using the new ment. The Reaction Control System software was then installed to prepare it payload operations were scheduled. antenna at Cebreros. thrusters were fired to test their for the upcoming pointing and NECP was split in two parts. The first performance; a ‘disturbance torque interference campaign. Following this, Payload operations during cruise problems created by the roasting hot which had peeled off and was dispersed week was dedicated to a checkout of the characterisation’ assessed the forces SPICAV was commissioned. While only a 1-week payload checkout environment. In parallel, ESA built a by the air circulation system inside the spacecraft subsystems, while the from solar radiation on the spacecraft in To accommodate requests from the was originally planned, in mid-January new 35 m-diameter deep-space dish fairing. For safety, it was decided to remaining 4 weeks were used to test all various attitudes. Finally, the redundant science community for instrument 2006, payload operations in reality had antenna in Cebreros (E) to cope with the return the entire vehicle to the assembly the scientific instruments. Solar Array Drive Mechanism was calibrations with special spacecraft to be scheduled throughout the entire workload from the four interplanetary building and refurbish the Fregat. After tested by rotating the wings a few pointing, a dedicated pointing campaign cruise phase. Following the second missions operated by ESOC: Rosetta, frantic repair work, all was well for Subsystem checkout degrees. was prepared by the Venus Express payload pointing campaign in January, Mars Express, SMART-1 and Venus launch in the early hours of During the spacecraft checkout, all the For the data-handling subsystem, Science Operations Centre (VSOC) for almost all of the instruments were Express. 9 November. This time, everything went units of the radio-frequency (RF) several memory areas of the computers 27 November to 3 December. It was also operated several times for various System validation tests were according to plan: the Soyuz vehicle and subsystem (transmitters, receivers and were dumped to serve as a reference used to validate further the ground reasons. While the magnetometer was conducted during the summer of 2005, its upper stage operated flawlessly, antennas) were tested and the HGA-2 ground image of the onboard software. segment interfaces between VSOC at kept on for most of the time, to measure before the simulation campaign of delivering Venus Express into the radiation pattern was calibrated. For the In addition, the redundant Transfer ESTEC in The Netherlands and the interplanetary magnetic fields, ASPERA July–October. It was only at the end of targeted escape trajectory with near- thermal system, several heater configur- Frame Generator, responsible for the Mission Operations Centre (MOC) at was activated periodically to prepare for this successful campaign that the ground perfect precision. ations were tested to prove that the telemetry composition and modulation ESOC in Germany. The PFS, ASPERA the routine mission. The Radio Science segment was declared ‘green’ for launch. The early orbit phase went smoothly. on the RF signal, was tested. In the first contact after launch, the Launch and Early Orbit Phase (LEOP) signal was acquired from the craft’s Payload checkout The first launch attempt was scheduled S-band omnidirectional antennas. The During the payload commissioning all for 26 October 2005. However, routine solar wings were deployed automatically the scientific instruments were switched inspection of the assembled launch following separation from the upper on, tested and calibrated to check the vehicle revealed tiny pieces of insulation stage, and the reaction wheels were spun interfaces with spacecraft power, data- deposited on various surfaces of the up and put into service by the control handling, telemetry and telecommand spacecraft and the Fregat upper stage. team. Over the next few ground station systems, and to verify that the overall Their origin was uncertain, so the contacts, Venus Express was configured performance was satisfactory. launch was postponed to study the unexpected problem. It was quickly Andrea Accomazzo, Spacecraft Operations Manager, in ESOC’s ESA Director General Jean-Jacques Dordain congratulates Flight determined that hydrazine propellant Mission Control Room during the launch of Venus Express on Director Manfred Warhaut upon receiving confirmation thatVenus had damaged Fregat’s engine insulation, 9 November 2005 Express had successfully entered orbit, 11 April 2006

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Operations & Infrastructure Venus Express

The Cebreros ground station The mission control team anxiously await confirmation of orbit capture, ESOC Main Control Room, 11 April 2006

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Operations & Infrastructure Venus Express

team performed several frequency-drift the first firing of the main 400 N engine. Throughout the cruise, about 50 ground How Venus Express Reached Operational Orbit tests on the onboard Ultra Stable In preparation for this important event, station passes in addition to the normal Oscillator to characterise the frequency the thermal system was configured to Cebreros communication passes were Date (UT) 400/10 N? Burn Type Speed Change (m/s) Duration (s) Venus Orbit stability over time. The PFS, SPICAV, warm the helium tank, the data- scheduled with NASA stations to get 10 Nov 05 10 N test 0.500 50 – VMC and VIRTIS instrument teams handling system was switched to a Doppler and ranging measurements 11 Nov 05 10 N launch correction 3.430 211 – took the opportunity to retest, fine-tune special telemetry mode that provided from an independent (non-ESA) source and improve their onboard software. more frequent subsystem data, and the for orbit determination. In addition to 17 Feb 06 400 N main engine calibration 2.840 154 – RF system transmitted an S-band the conventional Doppler and ranging 24 Feb 06 10 N main engine calibration 0.137 14 – Spacecraft operations during cruise carrier signal throughout the engine methods, the new ‘Delta Differential comparison During the cruise phase, the experiment burn to simulate the operation planned One-way Range’ technique was used for 30 Mar 06 10 N trajectory correction 0.130 14 – teams were not alone in using the time for VOI. On 17 February, the engine navigation. With two ground stations 11 Apr 06 400 N capture 1251.590 3163 330 685 x 662 km, 9 d to prepare for the routine mission – the firing went perfectly – to the relief of the simultaneously measuring the signals 15 Apr 06 10 N pericentre control #1 5.806 504 330 685 x 257 km, 9 d Flight Control Team had to get the whole project team! A week later, a from Venus Express and an extragalactic 20 Apr 06 400 N apocentre lowering #1 200.300 529 99 108 x 259, 40 h spacecraft ready for Venus arrival. At small adjustment was made using the source (a quasar), navigators could 23 Apr 06 400 N apocentre lowering #2 105.320 343 70 463 x 268 km, 26 h the start of ICP on 16 December, the 10 N thrusters, tweaking the trajectory determine the position of the spacecraft batteries were discharged to 50% for a change from by the main engine test. very accurately. 26 Apr 06 10 N apocentre lowering #3 9.165 670 68 000 x 268 km, 25 h month to save battery life for the routine The next milestone was then a 30 Apr 06 10 N apocentre lowering #4 8.035 603 67 000 x 268 km, 24.2 h mission. During the rest of the month, rehearsal on 6 March of the VOI Venus Orbit Insertion 3 May 06 10 N apocentre lowering #5 1.952 233 66 582 x 268 km, 24.02 h several navigation tests were performed operations, performed using the 70 m VOI lasted from one week before the 6 May 06 10 N pericentre control #2 3.101 301 66 582 x 249 km, 24.0 h using NASA’s Deep Space Network DSN antenna in Madrid. To train the capture burn to 26 days afterwards, (DSN) stations and, for the first time, Flight Control Team and ground station when the last of a series of seven orbit- Cebreros combined with the New operators from ESA and DSN, and to control manoeuvres placed Venus trajectory-correction manoeuvres (13, 6 increase robustness included turning off About half an hour into the burn, the Norcia station in Australia. Those tests rehearse the communications aspects of Express in its operational orbit. The and 2 days before the burn), to correct monitoring of the power system. Most spacecraft swung behind Venus, cutting prepared for the intense navigation and VOI, Venus Express was turned to main strategy during this phase relied on for minor targeting errors as the AOCS and data-management system off its signal. It was reacquired on tracking campaign later during cruise. simulate the same low-gain antenna an early upload of the minimum set of spacecraft approached Venus. A ‘last monitoring was either disabled or schedule at 07:55 UT, confirming that Following the payload pointing geometry with Earth. Acquiring the commands necessary to perform the chance’ emergency manoeuvre slot was allowed only at local level; only low-level the capture trajectory was nominal campaign, an intense thermal character- S-band uplink was practised and one- insertion burn (done 4 days before the reserved at 6 hours before the burn. This reconfiguration possible. Rebooting the (again, to the relief of controllers). The isation campaign started on 23 January way and two-way Doppler data were burn). This set of commands included upload opportunity was to be used only Processor Module was forbidden and burn lasted about 50 minutes, and 2006 to correlate the thermal model monitored. Even the occultation by the slews to and from the burn attitude, if a trajectory estimation anomaly was the Mass Memory was also switched off. slowed the spacecraft by around with flight data. Venus Express was Venus expected during VOI was the X-band transmitter switched to identified in the final hours before This last point meant that no 1250 m/s. Venus Express was now in a pointed so that the Sun illuminated the simulated by temporarily switching off ‘OFF’ and ‘ON’ (as the transmitter was passage through pericentre (the closest telemetry could be stored during the highly elliptical, 10-day orbit around heat-critical faces +Y, –Y, –Z and –X at the onboard S-band transmitter. kept off during the burn), and related approach to Venus). In that case, an burn; in the event of problems, the Venus. an angle of 5º each for 24 hours, From the beginning of March until attitude control mode transitions. emergency pericentre-raising burn could Flight Control Team would have had The burn was performed close to followed by an equivalent cooling VOI on 11 April, the navigation and In the final days before insertion, be commanded if the path was too low very limited information on the possible quadrature – the Sun and Earth were 90º period. This exercise confirmed the tracking campaign was very intense. additional slots were reserved for (which would plough the craft into causes. The last command was sent up apart as seen from the spacecraft. Given thermal tolerances were acceptable for Venus), or conversely a longer insertion to Venus Express 12 hours before the the spacecraft design, controllers operations. It was noted that the burn if it was too high. Fortunately, only burn. wanted to avoid direct Sun illumination reaction wheel temperatures were higher the first of these slots, 13 days before On 11 April 2006, the spacecraft of the craft’s cold faces in order to than predicted after the Sun had been arrival, had to be used to perform a tiny ignited its main engine at 07:10 UT (at prevent overheating. This meant shining at 5º on the –X face. It was soon correction. the time, the signal took about 7 minutes swapping high-gain antenna usage from found that this contributed to some During this phase, Venus Express was to reach Earth). During the burn, ‘outgassing events’ that disappeared gradually commanded into a special, contact with the ground via the high- later on. fault-tolerant configuration in which gain antenna was not possible owing to In preparation for Venus arrival, the most of the autonomous ‘Failure its orientation, but the front low-gain startrackers were checked on 7 and Detection, Isolation and Recovery’ antenna was configured with the 8 February by pointing them at the same functions were disabled, thus transferring redundant transmitter to emit an regions of sky as they would see in the some monitoring functions to the Flight S-band carrier. The 70 m DSN antenna days just before VOI. Control Team. This minimised the at Madrid picked up this signal, which From 9 February, all activities focused chances of an automatic spacecraft was relayed in real-time to ESOC to on the mission’s next major milestone: reconfiguration being triggered close to monitor the spacecraft during most of or during the insertion burn, which the manoeuvre. would have resulted in a missed The Doppler signal from Venus Express during the capture burn, insertion and no possibility of trying VMC’s first image of the planet’s south pole. (ESA/MPS, displayed using Jet Propulsion Laboratory/DSN software installed Katlenburg-Lindau, Germany) at ESOC specifically for VOI again. The various measures taken to

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Operations & Infrastructure Venus Express

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Operations & Infrastructure

VIRTIS first image of the south pole. (ESA/INAF-IASE, Rome, Italy/Observatoire de The Venus Express mission Paris, France

HGA-2 to HGA-1. Awkwardly, this had Outlook Acronyms to be done during the insertion phase. It Venus Express is now orbiting the planet was decided that the safest strategy (in in its routine science operations phase, AOCS: Attitude and Orbit Correction order to avoid blinding the startrackers to end in October 2007 after two System with sunlight reflected from Venus) was Venusian sidereal days (486 Earth days). ASPERA: Analyser of Space Plasmas and to remain on HGA-2 until after capture, The spacecraft is operated by the MOC Energetic Neutral Atoms DSN: Deep Space Network and make the swap 24 hours later. at ESOC with inputs for science HGA: High-Gain Antenna With the spacecraft safely orbiting activities from the VSOC at ESTEC. ICP: Interplanetary Cruise Phase Venus, the Flight Control Team went Daily contacts with the spacecraft are MOC: Mission Operations Centre ahead with the first batch of science established through Cebreros. Science NECP: Near-Earth Commissioning Phase observations of the planet, which were data collection has just started and will PFS: Planetary Fourier Spectrometer RF: Radio Frequency produced and downloaded to the proceed in the coming months with SPICAV: Spectrometer for Analysis of the ground only 2 days after having additional types of observations Venus Atmosphere successfully performed the capture burn. possible only when the spacecraft is in VeRA: Venus Radio Science Experiment The team then commanded a series of an Earth-occultation season (July– VSOC: Venus Express Science Operations manoeuvres to bring the spacecraft August 2006) or a solar-conjunction Centre VIRTIS: Visible Infrared Thermal Imaging down to a 24-hour polar orbit suitable phase (October–November 2006). Spectrometer for science operations. To do this, five After the superior solar conjunction VMC: Venus Monitoring Camera manoeuvres were made at the pericentre in October, when the Sun is between the VOI: Venus Orbit Insertion of the transfer orbit, and two more at spacecraft and Earth, the Earth distance VSOC: Venus Express Science Operations the apocentre. Two firings were executed will start decreasing again. This will Centre with the 400 N main engine, first allow higher data rates for the science slowing Venus Express by 200 m/s and downlink. Spacecraft resources have then by 105 m/s. The others used the been designed so that an extension of 10 N thrusters, which will also be called two Venusian days is possible, to on from now on to maintain the orbit. January 2009. With the current Detailed information on Venus Express and its mission Finally, on 7 May, the operational orbit condition of Venus Express and the can be found in Bulletin 124 (November 2005), was reached and the commissioning of propellant margin, it is perfectly feasible pages 8–32. The Venus Express website provides the scientific payloads could be and might stretch even further. e up-to-date information at www.esa.int/venus completed on schedule.

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