The Flight Control Team

Chris Watson

The Flight Control Team operates from a Dedicated Control Room located at ESOC. The team is led by Spacecraft Operations Manager Chris Watson, who works closely with his colleague Micha Schmidt, the SOM for Herschel.

Chris was responsible for gathering the Flight Control Team (FCT) at ESOC and has overseen their training and preparation for launch since 2007. The team shares expertise with the Herschel FCT, as the two missions are closely inter-related for launch and operations.

Like all missions controlled from ESOC, the Planck FCT relies on a wide range of experts from other ESOC teams to ensure operations success, including Flight Dynamics, Ground Facilities, Navigation and Mission Data Systems.

Mission operations overview

Herschel & Planck launch configuration inside an Ariane-5

Together with Herschel, Planck was carried into space from ESA's Spaceport at the Guiana Space Centre, Kourou, French Guiana, on 14 May 2009, 13:12 CEST, by an Ariane 5 EC launcher.

Launch and Early Orbit Phase

The two vehicles separated some 26 minutes after launch, Herschel first, and then proceeded independently on different trajectories to the second Lagrange point of the Earth-Sun system (L2).

Prior to Planck's separation, the 'Sylda' support module burned several small thrusters, which were just sufficient to start Planck rotating at 1 rpm, which motion will continue during the satellite's operational life.

The Ariane-5 launcher burned its solid boosters for slightly less than 2½ minutes and its main and upper stage engines for about 25 minutes to inject Herschel and then Planck into transfer trajectories bound for L2.

Transfer and Commissioning Phase

On 3 July 2009, Planck was injected into a Lissajous orbit around the L2 point at a distance of around 1.5 million km from Earth. During the journey, Planck performed a number of manoeuvres:

Planck's cruise to L2

At L2, Planck performed a major manoeuvre to enter a small Lissajous orbit about the Lagrange point, with the Sun-spacecraft-Earth angle limited to fifteen degrees.

Lissajous orbits are the natural motion of a satellite around a collinear libration point in a two-body system and require less momentum change to be expended for station keeping than halo orbits, where the satellite follows a simple circular or elliptical path about the libration point.

Orbits about L2 are dynamically unstable; small departures from equilibrium grow exponentially with a time constant of about 23 days. Like Herschel, Planck will use its propulsion system to perform periodic orbit maintenance manoeuvres.

While complex, this orbit provides an ideal environment for a space observatory: far from the Earth and its magnetic field (that traps the solar wind) and with both the Sun and Earth orientated away from the sensitive payload-side of the spacecraft, which must be kept very cold. Emitted or reflected light from either the Earth or the Sun can damage sensitive instruments or disturb the cold environment necessary for them to function correctly.

The ground station - New Norcia - DSA 1

New Norcia: ESA's first 35m deep-space station

ESA's New Norcia station, DSA 1 (Deep Space Antenna 1), hosts a 35-metre deep-space antenna with transmission and reception in both S- and X-band and is located 140 km north of Perth, Western Australia, close to the town of New Norcia.

DSA 1 is designed for deep-space satellite missions and provides daily support to Mars Express, Rosetta and Venus Express for routine operations.

The ESA ground stations at Kourou and Maspalomas and Cebreros, Spain, also provided communications support during the Launch and Early Operations Phase (LEOP). In this period, operations will run in real time, nearly 24 hr/day. During the commissioning phase, Kourou and New Norcia will provide coverage 10 hr/day (shared between Planck and Herschel).

For Planck, the Earth-to-spacecraft distance will vary between approximately 1.2 to 1.8 million km.

Ground segment & mission control system

This mission uses SCOS-2000

Planck uses the SCOS-2000 mission control system.

The Planck ground segment comprises the HF and LI Data Processing Centres (DP Cs) and Instrument Operations Teams (IOTs), the Planck Science Office (PSO), and their links to the Mission Operations Control Centre (MOC).

It enables scientific survey operations including planning and monitoring, instrument commanding and operations, downlink and distribution of spacecraft and science telemetry, processing of scientific data, and generation and delivery of final data and products to the scientific community.

As the hub of the ground segment, the MOC conducts mission operations, including planning, execution and data return, and serves as the interface between the spacecraft and the the scientific community.

Planck's routine phase is planned to last approximately 15 months, or the time to make two full-sky surveys (overall mission life will be limited to the life of the on-board cryogenic cooling system).

Diagram of the Planck ground segment

In this phase, engineers anticipate that the instruments will operate continuously during each sky survey. The exact path that is followed by the spin axis (which is always kept approximately pointed at the Sun) is decided in principle before the beginning of each survey, and updated as required on a roughly fortnightly basis.

Orbit maintenance operations will be required at roughly monthly intervals. They will not require interruption of instrument operation.

Even though it is operated as an independent mission, Planck will benefit from many commonalities with Herschel. The off-line nature of the operations allows a common approach to the spacecraft control and the interface with the science ground segments. The major difference between the two systems, from an operations point of view, lies in the mission planning process and the supporting flight dynamics services.

The platform and payload

Planck spinning in space

The Planck spacecraft comprises a service module, which houses systems for power generation and conditioning, attitude control, data handling and communications, together with the warm parts of the scientific instruments, and a payload module. The payload module consists of the telescope, the optical bench, with the parts of the instruments that need to be cooled - the sensitive detector units - and the cooling systems.

Planck spins at 1 revolution per minute, with its spin axis oriented to the Sun. Its telescope is offset from the spin axis, which therefore sweeps out a large circle on the sky, which continuously moves as the Earth (and Planck) travel around the Sun.

The payload

Planck will carry a telescope with a 1.5-metre primary mirror. The telescope will focus radiation from the sky onto the payload, two highly sensitive detectors called the Low Frequency Instrument (LI) and the High Frequency Instrument (HF).

• Low Frequency Instrument (LI): An array of 22 tuned radio receivers that will be operated at –253°C. These receivers will work grouped in four frequency channels, centred between 30 and 70 GHz. They are based on devices called 'HEMTs' (High Electron Mobility Transistors), and work just like transistor radios. The transistors amplify the signal collected by the antenna (the telescope), and the amplified signal is then converted to a voltage.
• High Frequency Instrument (HF): An array of 52 bolometric detectors, which work by converting radiation to heat. The amount of heat is then measured by a tiny electrical thermometer, the signal from which is converted to a temperature by a computer. The HF detectors will work in six frequency channels centred between 100 and 857 GHz. They are operated at –273°C (only one tenth of one degree above absolute zero).

The Planck telescope and instruments are placed on top of an octagonal service module. A baffle surrounds the telescope and instruments protect them from stray light. Additionally a series of three 'V-grooves' between the service module and the telescope structure are used to prevent thermal radiation from the comparatively warm service module from heating the payload.

Image showing the optical path through Planck

The baffle and V-grooves are also used to effectively radiate to cold space some of the heat present on the payload module. This passive cooling is used to achieve a cold and stable background environment of about -223ºC (or 50ºK).The instrument coolers use this as a starting point for their further refrigeration of the payload.

Inside the service module are the computers and subsystems that allow the spacecraft to function, and to compress the raw data signals from the instrument detectors. At the base of the service module sits a flat, round solar panel for generating electricity from sunlight to power the spacecraft, and to protect the whole spacecraft from direct solar radiation.