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Cryosat System

Guy Ratier, Richard Francis & Constantin Mavrocordatos CryoSat Project, ESA Directorate of Earth TheThe CryoSatCryoSat SystemSystem Observation, ESTEC, Noordwijk, The Netherlands

Reinhold Zobl –– TheThe satellitesatellite andand itsits radarradar altimeteraltimeter Head of Earth Observation Programmes Department, ESA Directorate of Earth Observation, ESTEC, Noordwijk, The Netherlands

n the preceding article Prof. Duncan Wingham has outlined the genesis of ICryoSat, its scientific objectives and its programmatic constraints. The mission objectives are characterised by the determination of small height-related changes over a three-year period. This imposes requirements on the type of measurements to be made, the physical stability of the system, control of the measurement configuration, and consistency in the data-processing system. The programmatic constraints, on the other hand, may be simply characterised as the need for a relatively short development cycle with a stringent cost ceiling.

CryoSat is a fully integrated system in which all of the elements have been developed together within the programme to ensure the control needed to satisfy the mission objectives. However, in the interests of readability, the system’s description has been split over two articles: this one describing the elements that are to be launched into space, and the following one those parts that will remain on Earth.

Precision Measurements from Space The CryoSat is the part of the system that makes the measurements. The fundamental measure is the distance from the satellite to the Earth’s surface below, and for this a radar altimeter is used. Given the enormous success of the ERS radar altimeters over icy surfaces, this was a natural choice. CryoSat’s radar altimeter is called SIRAL, a contraction of SAR (Synthetic Artist’s impression of CryoSat at the moment of separation from the ’s upper stage Aperture Radar) and Interferometric Radar

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Earth Observation Cryosat System

Artist’s impression of CryoSat in orbit, flying almost towards the Exploded view of the CryoSat spacecraft viewer. The prominent features visible are the arrays, giving a roof-like appearance, and the three star trackers which are mounted on the rigid structure supporting the SIRAL antennas. The structure forming the ‘nose’ at the very front of the satellite is a thermal radiator for the heat generated by the SIRAL instrument CryoSat geometry was arranged such that every orbit has enough sunlight on one or SIRAL interferometer measurement. both of the solar panels to maintain a SIRAL measures the angle of arrival of the positive energy balance onboard. echo in its own reference frame, i.e. with This assumes, of course, that the solar respect to the line joining the centres of the panels have the intrinsic capability to two antennas, the ‘baseline’. Before that generate enough power in the first place, if information can be used to identify the the Sun were shining directly on them. The exact position on the Earth, we must know requirement to fit CryoSat inside the the orientation of that baseline, and in fairing of a ‘small’ launcher put absolute order to meet the mission objectives this constraints on the size of the panels, thus measure must also be precise to within removing one of the key degrees of 30 arcseconds. This is the angle subtended freedom in this equation. That only left one by a football at a distance of 2 km. parameter to ensure sufficient power The scientific mission objectives not generation – the efficiency of the solar only defined the type and accuracy of the cells themselves. Thus CryoSat, as a low- Altimeter, and this indicates where may talk loosely of height above sea level, measurements that had to be made (which cost mission, has ended up pioneering the improvements have been made in the but in this demandingly precise application led to the payload selection), but also their use of new, high-efficiency solar cells in instrument concept. As well as a we refer to height above a ‘reference location and timing. As Prof. Wingham . More about this later, but conventional mode, which offers ellipsoid’ – an exactly defined, almost explains in the previous article, this ‘where we can say right now that this choice was continuity with earlier missions, SIRAL spherical surface that closely approximates and when’ is encapsulated in the definition Kiruna in Sweden was selected. As well as played by heritage from the CHAMP and still cheaper than introducing fold-out can also operate in so-called ‘synthetic- to the shape of the Earth. To determine the of a specific orbit for CryoSat. The orbital enabling the sharing of resources with other GRACE , which were designed solar panels. aperture mode’. This increases the along- satellite’s position, and thus its height inclination is 92° (and therefore on-going ESA missions, this choice against similar orbital and programmatic The two SIRAL antennas are track resolution, enabling it to more readily above this reference ellipsoid, retrograde), with a mean altitude of about resulted in manageable requirements in constraints. accommodated side-by-side near the front distinguish the narrow ‘leads’ of open measurements from some further payload 720 km, the exact altitude being defined by terms of handling the 3 to 4 consecutive So instead of a rather ponderous of the satellite. They are slightly elliptical water between sea-ice floes. Over the items are needed. the required track-repeat characteristics. orbits per day during which contact with deduction of CryoSat’s design from the in outline in order to fit within the rough terrain at the edges of the major ice CryoSat includes a DORIS Receiver, a This orbit is not one of the class known as the ground station is not possible. mission’s requirements and constraints, launcher’s fairing – which slightly sheets, this increased along-track special radio receiver that picks up signals ‘Sun-synchronous’, for which the orbital The design of the CryoSat satellite was here we will take a ‘reverse engineering’ complicates the scientific data processing, resolution is further augmented by across- from a network of more than 50 plane maintains a fixed orientation with determined, as is always the case, by a look at CryoSat to show how it responds to but has no impact on performance. We track interferometry using the second transmitting stations evenly spread around respect to the Sun, because, as we shall see number of key factors. From the mission- these drivers. We will start with the most have already indicated that both the antenna and receive channel. The derived the Earth. By measuring the Doppler shifts later, this would have impacted on the science objectives came the payload obvious feature, its shape. So why does structural stability and knowledge of this angle of arrival of the radar echoes allows of these signals, the range-rate to each one satellite’s design. complement and its requirements, the orbit CryoSat look like dog kennel? assembly is vital to the mission more precise identification of the point can be determined. The accuracy of the and the minimum lifetime. Programmatic As mentioned earlier, the required orbit performance, and the design has a number from which the echo came. orbit that may be computed from such a Designing the System constraints included the need to operate is not Sun-synchronous. Every day the of special features to ensure this. In the SIRAL makes measurements of the dataset obviously depends on several The full CryoSat system has several parts, from a single ground station, launch on a orbital plane shifts to be almost 3 minutes calm environment of space, the principal range to the surface that are very precise: factors, not least the precision and and although will not describe here those ‘small’ and therefore low-cost launcher, earlier with respect to the Sun; in enemy of stability is heat, which causes each has an uncertainty of just a few tens accuracy of the Doppler-shift that will remain on the ground, we will extensive onboard autonomy, a low-cost 8 months, therefore, it drifts through all expansion. The first line of defence against of centimetres. The averaging of many measurements. In this DORIS excels, and outline the overall architecture as this has design and a decision to forego the normal local times. This means that the direction that is to use materials that are least such measurements brings the system for over a decade the system has been the an impact on the design of all of the approach of building precursor, ‘proof-of- from which sunlight falls on the satellite is susceptible to it. We have mainly used performance to the level needed to satisfy foremost means of making routine, high- elements. Programmatic constraints were concept’ models of the satellite (structural constantly changing. The operation of the Carbon-Fibre Reinforced Plastic (CFRP), the mission objectives. However, the precision orbit determinations. The dominant in this part of the system model, engineering model, etc.). SIRAL instrument demands that its which has a coefficient of thermal precise measurement of range alone is DORIS receiver is augmented by a passive definition and led to the minimum While it is not the case that these driving antennas point towards the Earth’s surface expansion close to zero. It is used for the insufficient. The exact position of the laser retro-reflector, which allows precise configuration required to satisfy the factors led inevitably to the CryoSat design to within a few tenths of a degree, and antennas themselves and also for the satellite at the time of each measurement is range measurements to be made by mission objectives. The key feature is that a (indeed during the competitive feasibility- furthermore that the two antennas are side- substantial ‘bench’ on which they are needed to convert this simple measure of ground-based laser-ranging stations. single ground station is used for CryoSat, study phase, another entirely different by-side as the satellite flies. This means mounted, and for the mounts for the star range into something scientifically The final item in this collection of high- both for command and control and for concept was developed), it is true that the that rotating the satellite to face the Sun is trackers fitted to this bench. We have also meaningful, which is the height of the precision payload equipment is a set of star downlinking, processing and distribution of main features of CryoSat can be traced out of the question. Mechanisms on used invar, a low-expansion metal surface above some known reference. We trackers, needed to complement the the science data. The ESA ground station at back to these drivers. A major role was also satellites are very costly and so the originally used for the pendulums of

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Earth Observation Cryosat System

The SIRAL electronic equipment mounted in the nose of the satellite Parameter LRM SAR SARIn

Receive chain left left left and right Centre frequency 13.575 GHz Bandwidth 350 MHz Transmit power 25 W makes it possible to accurately determine Noise figure 1.9 dB at duplexer output the arrival direction of the echoes both Antenna gain 42 dB along and across the satellite track, by Antenna 3 dB beamwidth (along-track) 1.0766° comparing the phase of one receive Antenna 3 dB beamwidth (across-track) 1.2016° channel with the other. In this mode, both Interferometer baseline – – 1.172 m receive channels are active and the Samples per echo 128 128 512 corresponding echoes are stored in the Sample interval 0.47 m time domain. The data rate is about twice Range window 60 m 60 m 240 m as high as for the normal SAR mode. In PRF 1970 Hz 17.8 kHz 17.8 KHz order to cope with abrupt height variations, Transmit pulse length 49 µs the range-tracking concept for this mode Useful echo length 44.8 µs has to be particularly robust. In SIRAL, Burst length – 3.6 ms 3.6 ms this is ensured by using narrow-band Pulses per burst – 64 64 tracking pulses, transmitted between Burst repetition interval – 11.7 ms 46.7 ms successive wideband measurement bursts. Azimuth looks (46.7 ms) 91 240 60 introduction of some special means of ocean. CryoSat’s DORIS receiver is part of an Tracking pulse bandwidth 350 MHz 350 MHz 40 MHz calibrating phase performance in flight. In the SAR mode, which also uses a overall system that is able to provide orbit Samples per tracking echo 128 The antenna subsystem has not been single receive channel, the along-track tracking measurements and time-transfer. Tracking sample interval 0.47 m 0.47 m 3.75 m immune to this. It was developed as a horizontal resolution of the altimeter is The DORIS system consists of a network Size of tracking window 60 m 60 m 480 m discrete item consisting of two Cassegrain improved during the on-ground processing of more than 50 ground beacons, receivers Averaged tracking pulses (46.7 ms) 92 32 24 antennas mounted side-by-side on the rigid by exploiting the Doppler properties of the on several satellites in orbit, and ground- Data rate 51 kbps 11.3 Mbps 2 x 11.3 Mbps antenna bench. The two antennas are echoes. The result is equivalent to segment facilities. It is part of the Power consumption 95.5 W 127.5 W 123.5 W identical, but one is used both to transmit decomposing the main antenna beam into a International DORIS Service (IDS), which Mass 62 kg and receive, whereas the other is used only set of 64 narrower synthetic beams along- also offers the possibility of precise to receive echoes. The Cassegrain design track. The footprints of the different sub- location of user-beacons. offers particular advantages for the SIRAL beams over a flat surface are adjacent Each beacon in the ground network as the resulting waveguide lengths are rectangular areas ~250m wide along-track, broadcasts two ultra-stable frequencies (at Key characteristics of the SIRAL much shorter than those required for the and as large as the antenna footprint 2036.25 and 401.25 MHz). The use of two more common, front-fed design. The entire across-track (up to 15 km). Consequently, frequencies allows the ionospheric effects clocks. existing equipment, in this case a large unit houses all the digital electronics, assembly went through a measurement a larger number of independent to be compensated for. Every 10 seconds, However, the majority of the satellite is conventional pulse-width-limited altimeter and the remaining boxes contain radio- campaign that challenged the capabilities measurements are available over a given the onboard receiver measures the Doppler made of aluminium, and so another vital called Poseidon-2, which is currently frequency circuitry and the transmitter’s of the test facility due to the exacting area, and this property is used to enhance shift of these signals using an ultra-stable part of the defence is isolation. The flying on the US-French Jason mission. power supply. Several innovations were phase-measurement requirements. the accuracy of the measurements over sea oscillator as a reference; this essentially sensitive antenna bench is attached to the SIRAL is a single-frequency Ku-band necessary compared to the Poseidon-2 We have already mentioned SIRAL’s ice. To ensure coherence between the enables the line-of-sight velocity to be rest of the satellite by a three-point quasi- radar, featuring some new design equipment, most notably due to the need ability to operate in different modes. The echoes from successive pulses, the pulse determined. The set of radial velocities isostatic suspension, which minimises the characteristics that enable it to provide data for significantly increased transmitter low-resolution mode operates in the same repetition frequency is about 10 times from the dense network of precisely transfer of thermal distortions and heat that can be more elaborately processed on power, which led to the development of a way as a conventional pulse-width-limited higher than for the low-resolution mode. located beacons forms a rich set of variations. The theme of isolation is the ground (a high pulse-repetition complete new transmitter section, and in altimeter and uses a single receive channel. The instrument operates in bursts, with a tracking data. The full set of DORIS carried further by the wrapping the bench frequency and pulse-to-pulse phase the provision of the second receive path. The rate at which the radar pulses are group of 64 pulses transmitted together, Doppler measurements goes through a and all its attachments with multi-layer coherence are needed for the along-track A less obvious but far more pervasive transmitted is low, relatively speaking, at followed by a pause during which the lengthy quality-control and checking insulation; even the antenna apertures are SAR processing). The across-track change was the new need for phase 1970 per second, and the echoes are echoes arrive. The echoes are then stored process within the ground segment (at protected from the hot Sun by an exotic interferometry needs a second complete stability, introduced by both the SAR and transformed from the time domain to the onboard in the time domain, without any CNES, as explained in the following single-layer insulation coated with receiver chain, including the second interferometric functions. Phase had never spectral domain and averaged onboard. averaging. Therefore, the data rate is article) before a final, high-precision orbit germanium. antenna. These features make this been an issue with previous altimeters, but The data rate at which science data are significantly higher, at 11.3 Mbps. determination is performed: this is the instrument unique. for SIRAL it is critical. Consequently, the generated in this mode is therefore low, at The SAR-Interferometric mode (SARIn) stable reference needed to extract the most The Payload: Re-use and innovation The electronics of the radar are divided SIRAL development effort has seen much 51 kbps. This mode will be used over ice- is used mainly over the ice-sheet margins, subtle signals from the SIRAL Like all of CryoSat’s equipment, the into a number of separate units, principally analysis, measurement, characterisation, sheet interiors, where the surface slopes where the surface slopes are high. The measurements. SIRAL radar altimeter is derived from for ease of manufacture and testing. One optimisation and tuning, as well as the are small. It will also be used over the combination of SAR and interferometry The DORIS system includes the

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possibility of encoding information on the The final element of the payload is the example of re-use. The star tracker uplinked signals, and two privileged laser retro-reflector, a passive optical provides real-time measurements of the CryoSat in a Nutshell master beacons, at Toulouse and Kourou, device for ground-based measurement of satellite’s orientation with respect to the Power provide such uplink services. Data the satellite’s orbit by laser-ranging stars, which together with the DORIS time CryoSat Mission • 2x GaAs body-mounted solar arrays, with 800 W each at uplinked from these stations (which is stations. Such reflectors are used on all and orbit information allows the onboard To determine fluctuations in the mass of the Earth's major normal solar incidence. updated weekly and used by all DORIS radar-altimeter satellites, and several other software to calculate the satellite’s land and marine ice fields. • 60 Ah Li-ion battery. instruments in orbit) include the spacecraft also. The device on CryoSat is orientation with respect to the Earth. coordinates of the stations, Earth-rotation based on an existing design that has been Measurement is half of the problem: it Mission Duration Propulsion parameters, etc. The uplinked data also flown on many Russian and other is also necessary to produce torques that Six months of commissioning followed by a three-year • 2 x 40 mN cold-gas thrusters. include time signals that allow satellites. will turn the satellite as needed to keep it operational mission. • Gaseous-nitrogen propellant (36 kg at 250 bar). synchronisation of the DORIS internal Earth-pointing within the required time reference using the International What Makes it Tick? tolerance. CryoSat’s main means of Mission Orbit Spacecraft Attitude Atomic Time (TAI) system. All of the data generated by CryoSat’s generating such torques is to use Type: LEO, non-Sun-synchronous • Three-axis-stabilised local-normal pointing, yaw-steering, These data are needed onboard because scientific payload have to be recorded electromagnets interacting with the Earth’s Repeat cycle: 369 days (30 day sub-cycle) with 6° nose-down attitude. DORIS is able to make real-time orbit onboard as the satellite is only in contact magnetic field. The devices themselves, Mean altitude: 717.212 km • Star trackers, magetometers, magetotorquers and 10 mN calculations from the data it collects, with its single ground station for brief called ‘magnetotorquers’, are simply Inclination: 92° cold-gas thrusters. though with significantly less accuracy periods. Typically there are 10 passes of multiple turns of wire wrapped around a Nodal regression: 0.25° per day • < 0.1° pointing error; < 0.001°/s stability. than the final precise orbit determination. 5 to 10 minutes duration each day, ferrite core, powered by a controllable However, this real-time orbit knowledge occurring on consecutive orbits. These electric current from the main computer. Command and Control has expected errors of less than a metre contacts are followed by a gap of 3 or 4 Magnetotorquers cannot produce torque Payload Integrated data-handling and AOCS and is used onboard by the central flight ‘blind orbits’. To handle the large data around the direction of the Earth’s field SIRAL (SAR/Interferometric Radar Altimeter): computer; communication by 1553 bus and software to control the satellite’s pointing volume, a 256 Gbit data recorder is itself, and this direction constantly changes serial links. (more on this later). Associated with installed. Following the modern trend, this with respect to the satellite. So a • Low-Resolution Mode provides conventional pulse-width- position, DORIS also computes time, is realised as solid-state memory with ‘backstop’ control in the form of a set of limited altimetry over central ice caps and oceans. accurate to about 10 microseconds, which literally thousands of RAM chips. The unit small cold-gas thrusters guards against • SAR Mode improves along-track resolution (~250 m) over On-board Storage is also used onboard as the master clock. is derived from similar equipment on excessive pointing errors. These are very sea ice through a significantly increased pulse-repetition • 1 Solid-State Recorder, capacity 256 Gbits. A final onboard service offered by ESA’s spacecraft and, small indeed, with a thrust of 10 mN – frequency and complex ground processing. • Data generated onboard: 320 Gbit/day. DORIS is the provision of the reference of course, comprehensive memory- about the same as the weight of 1 cc of • SAR Interferometric Mode adds a second receive chain to • Full mission operation with a single ground station at frequency to the SIRAL instrument, which management and data-handling functions water. Simulation has shown that these will measure the cross-track angle of arrival of the echo over Kiruna. does not have its own ultra-stable are built in. It can continue recording data need to fire for a total of about 3 seconds topographic surfaces at the margins of ice caps. oscillator. The frequency of the DORIS as it replays its memory into the data link per orbit. Although this is not long, it will, RF Links oscillator is continuously monitored as to the ground station. together with the gas used by the two Star Trackers (3) measure the interferometric baseline • X-band data downlink: 100 Mbps at 8.100 GHz. part of the precise-orbit-determination This downlink is a potential bottleneck 40 mN thrusters to maintain the orbit in the orientation, as well as driving satellite attitude control. • S-band TTC link: 2 kbps uplink, 8 kbps downlink. service, and this measurement is taken into because the total contact time is relatively face of air-drag, eventually consume the account in processing the SIRAL data. short. To overcome this, the downlink data 35 kg of pressurised nitrogen onboard. DORIS enables precise orbit determination, as well as Launch Vehicle CryoSat includes a set of three identical rate is especially high; at 100 Mbps, it is The attitude-control system has other providing in-orbit position to the AOCS. Rockot (converted SS-19), launch from Plesetsk. star trackers, which are the only means of more than 12 times as fast as the best ADSL sensors too, which are used during the determining the orientation of the SIRAL Internet access available in The Netherlands. initial stabilisation after separation from Laser enables tracking by ground-based lasers. Flight Operations interferometric baseline. They are also the Again this approach is built on heritage, this the launcher, and in emergencies. These • Mission control from ESOC via Kiruna ground station. principal three-axis attitude measurement time from ESA’s MetOp mission, with the are a set of magnetometers and an Configuration • Onboard measurements automatically planned according sensor in the nominal operating mode. They frequency and bandwidth reused from an ingenious sensor, the combined Earth-Sun • Simplified rigid structure with no moving parts. to a geographically defined mask. are lightweight, low-power-consuming, allocation originally given to . sensor, which measures the temperature • All electronics mounted on nadir radiator. fully autonomous devices. They are CryoSat is an unusual satellite in that it difference between a black and a mirrored Payload Data Processing accommodated such that the Sun and Moon has virtually no moving parts, the only surface on each face of the satellite. A • SIRAL electronics mounted close to antennas. • Data-processing facility at Kiruna ground station. can each blind only one head at any time; exceptions being a couple of valves in the clever piece of software then calculates the • SIRAL antennas on isostatically mounted plate with Star • Local archiving of data with precision processing after this makes the whole sensor system single- propulsion system. This has led to savings direction to both the Sun and the Earth. Trackers. one month following delivery of precision orbits from failure tolerant. The star-tracker algorithm is in cost as well as testing. One area where optimised to use rather faint stars, of around this lack of moving parts is particularly Putting it Together Dimensions DORIS ground segment. magnitude 5. Barely visible to the naked eye noticeable is in the attitude and orbit One of the key means by which the 4.60 m x 2.34 m x 2.20 m • Possibility of quick-look data. except at dark sites, they are far more control subsystem, where gyroscopes and CryoSat programme has been able to • User Services coordinated via ESRIN with dissemination numerous than the brighter stars and reaction wheels are usually commonplace. compress schedule and cost has been Mass of data from Kiruna. provide many more triangulation Attitude control for CryoSat is through a bold early programmatic 670 kg (including 36 kg of fuel). possibilities for the pattern-matching innovative since it principally exploits two decision. The idea was that by embracing process in all directions of the sky. of the payload equipment items, another existing equipment designs and building-

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shaken to simulate the effects of launch. Thereafter, it has been put into a sealed chamber and bombarded with all manner of electromagnetic signals to test its resistance to interference from the space environment, the launcher, and even from itself. Next it will be exposed to vacuum, simulating the extremes of solar ‘cooking’ and the chill of deep eclipse. The final test will see CryoSat placed in an acoustic chamber in which large horns will generate a sound field so intense that it would instantly deafen any engineer present – this simulates the extreme sound pressures experienced inside a launcher’s fairing during flight. In between times, CryoSat is constantly being probed and measured, both as diagnostics and status checking, and to verify that the Mission Control Centre is able to flawlessly monitor and control it.

Getting it Up There FULL PAGE ADVERT At the end of the test campaign, and after CryoSat in the EMC chamber at ESTEC in Noordwijk the Flight Acceptance Review, it will be time to ship the satellite to Russia for the in conservative margins, it would be launch. The launch vehicle, called ‘Rockot’, possible to directly build a proto-flight is a converted SS-19 inter-continental satellite; no test articles would be built. ballistic missile, with a versatile, re- The savings inherent in such an startable upper stage known as Breeze-KM. approach were very persuasive, in terms of The launch will take place from Plesetsk, both time and equipment. However, it was some 800 km north of Moscow. This very obvious that the benefit of test models, large facility has been used for Russian particularly the ‘engineering model’, goes launches for many years, although is beyond merely testing the hardware; they relatively new for European customers. allow unglamorous but essential work, The launch will be towards the north, CryoSat on the shaker at ESTEC for vibration testing such as test-procedure debugging, to be and the upper stage will shut down while done away from the critical path. So for over the Arctic. Then the composite of blind, as the only communication with the CryoSat we decided to build a ‘virtual CryoSat attached to the upper stage will launcher is from ground stations in Russia. satellite’ in software. This has been so coast through about half an orbit before the The separation of CryoSat from the useful for various aspects of testing that it Breeze-KM fires again, over South Africa. Breeze-KM after the final orbit-injection has already been cloned several times, a This final orbit-injection burn will put the burn is therefore delayed until the rather difficult feat to perform with a composite into the correct orbit, and again composite comes within range both of the hardware version! it will coast until reaching Europe. Russian stations and slightly thereafter the Nevertheless, by mid-2004 the proto- The launch time has been selected such CryoSat ground station at Kiruna. Then, flight CryoSat was ready for final testing. that the orbital plane is at right angles to the after almost a complete revolution, the This is an inescapable ordeal and involves a direction to the Sun, so that the composite final separation marking the start of long programme of ‘torture’ for the flies around the line marking dawn and CryoSat’s autonomous life in orbit will satellite. CryoSat had its mass properties dusk. This means that CryoSat is in sunlight occur somewhere over Romania. r (centre of gravity, moments of inertia, etc.) all the time and can receive power from the measured before it was attached to the solar arrays. A series of small burns by launcher-separation system and shocked, as Breeze-KM keep CryoSat close to its the explosive separation bolts fired. It was nominal Earth-pointing attitude. then clamped to a large table and severely All of these activities are performed

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