- Email: [email protected]
PROBA-3: Precise formation flying demonstration mission
Acta Astronautica 82 (2013) 38–46
Contents lists available at SciVerse ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
PROBA-3: Precise formation flying demonstration mission J.S. Llorente a,n, A. Agenjo a, C. Carrascosa b, C. de Negueruela b, A. Mestreau-Garreau c, A. Cropp c, A. Santovincenzo c a b c
SENER Ingenierı´a y Sistemas, Severo Ochoa, 4. E-28760 Tres Cantos, Madrid, Spain GMV Aerospace and Defence, Isaac Newton, 11, E-28760 Tres Cantos, Madrid, Spain ESA, Noordwijk, PO Box 299-2200 AG Noordwijk, The Netherlands
a r t i c l e in f o
abstract
Article history: Received 14 January 2012 Received in revised form 16 May 2012 Accepted 22 May 2012 Available online 25 June 2012
Formation Flying (FF) has generated a strong interest in many space applications, most of them involving a significant complexity for building for example on-board large ‘‘virtual structures or distributed observatories’’. The implementation of these complex formation flying missions with critical dependency on this new, advanced and critical formation technology requires a thorough verification of the system behaviour in order to provide enough guarantees for the target mission success. A significant number of conceptual or preliminary designs, analyses, simulations, and HW on-ground testing have been performed during the last years, but still the limitations of the ground verification determine that enough confidence of the behaviour of the formation flying mission will only be possible by demonstration in flight of the concept and the associated technologies. PROBA-3 is the mission under development at ESA for in-flight formation flying demonstration, dedicated to obtain that confidence and the necessary flight maturity level in the formation flying technologies for those future target missions. PROBA-3 will demonstrate technologies such as formation metrology sensors (from very coarse to highest accuracy), formation control and GNC, system operability, safety, etc. During the last years, PROBA-3 has evolved from the initial CDF study at ESA, to two parallel phase A studies, followed by a change in the industrial configuration for the Bridging step between A and B phases. Currently the SRR consolidation has been completed, and the project is in the middle of the phase B. After the phase A study SENER and GMV were responsible for the Formation Flying System, within a mission core team completed by OHB-Sweden, QinetiQ Space and CASA Espacio. In this paper an overview of the PROBA-3 mission is provided, with a more detailed description of the formation flying preliminary design and results. & 2012 Elsevier Ltd. All rights reserved.
Keywords: PROBA Formation flying GNC Coronagraph
n
Corresponding author. Tel.: þ 34 918 077 225; fax: þ34 918 077 208. E-mail addresses: [email protected] (J.S. Llorente), [email protected] (A. Agenjo), [email protected] (C. Carrascosa), [email protected] (C. de Negueruela), [email protected] (A. Mestreau-Garreau), [email protected] (A. Cropp), [email protected] (A. Santovincenzo). 0094-5765/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actaastro.2012.05.029
1. Introduction 1.1. PROBA-3 objectives The PROBA-3 Mission is the third of the PROBA missions dedicated to in orbit technologies demonstration. The main objective of PROBA-3 is to demonstrate precise
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
formation flying key technologies [1] for its application to future missions including:
Formation Flying concepts for several types of formation flying missions.
Formation Flying Guidance, Navigation and Control Algorithms.
Formation Flying metrology units, accuracy levels and transitions between them.
Formation Flying Autonomy. Formation Flying development, verification and validation tools.
Formation Flying Ground Segment and Operations required support.
The orbit trade-off has concluded with the selection of a highly eccentric orbit (HEO), with orbital period in the order of one day. The selected high apogee HEO orbit will provide around apogee a representative environment for the demonstrations to be performed, while requiring reduced launch capabilities compared with lower perturbation orbits such as L2. The reduced gravity gradient environment present during the high apogee region will allow representative high precision formation environments, while the perigee region, and the perigee passage, will exercise formation management and control through a wide range of gravity gradient disturbances, down to LEO-type of high gravity gradient. As complement to the end-to-end validation of the formation flying technologies, a scientific instrument, a Coronagraph, has been selected to provide advances in solar physics and in particular, deeper understanding of the Sun and its corona. The Coronagraph System can also be regarded as an independent verification of the attitude and position control systems of PROBA 3, as deviations in relative position or attitudes will be observable on the images produced by the coronagraph. The system is distributed over the two satellites; one carrying the detector and the second one carrying the Sun Occulter disc. Both spacecrafts are flying in precise formation during the science acquisition periods to generate the required ‘‘virtual’’ instrument. Finally, the mission will be complemented by some additional experiments. In particular several types of rendezvous strategies and different types of control in highly eccentric orbit will be verified.
1.2. The PROBA-3 mission The PROBA-3 mission consists of two small satellites to be injected by a single launch into a highly eccentric Earth orbit. Once separated from the launcher, the two spacecraft remain rigidly attached together in a stacked configuration. The bottom satellite will include propulsion capability to raise the stack orbit apogee from the injected one to the final nominal orbit of about 20 h period. Once into the target orbit, the two satellites are separated and the formation flying operations will start.
39
Immediately after separation, the satellites are autonomously acquiring the sun and subsequently they are placed into a safe relative trajectory, where collision is guaranteed to be not possible while also evaporation will not happen within a comfortable timeframe. For this mission, evaporation is defined as a separation between spacecrafts such that formation recovery is not possible within the available resources. Once the safe and stable configuration is achieved the in orbit commissioning starts. The Ground Segment and the various Space Segment Subsystems, Software, FDIR, formation-flying metrologies will be gradually commissioned and the Coronagraph System checkout performed. This gradual validation will be initially under control from ground, and will be completed when completely autonomous execution of the operations pre-planned for at least 7 day is performed, with staggered transitions until full autonomy is acquired. At the end of the commissioning phase the Ground and Flight segments will start nominal operation, and the formation flying capabilities of the System will be exploited. The demonstration will exercise generic formation configurations valid for multiple types of target missions, including a wide range of formation acquisitions, formation reconfigurations, manoeuvres, accuracies, information and commands exchanged between the satellites, etc. The Coronagraph science acquisition will be performed with one specific configuration of the formation flying, and will be performed regularly during the whole mission duration, interleaved with the rest of demonstrations, and experiments. At the end of the operational lifetime, the PROBA-3 satellites are de-orbited according to the international regulations and recommendations. Both satellites will be under control of the Mission Control Centre supported by the involved Ground Station(s) including ESA Redu as the main Ground Station and operations centre.
2. PROBA-3 formation flying demonstrations The PROBA-3 formation flying demonstrations will be organised around a set of general formation technology aspects, without the need to particularise for one specific formation flying mission. PROBA-3 intends to verify the techniques and technology which could be needed for as many future Formation Flying missions as possible, under the constrains and limitation of a low-cost demonstration mission. For practical reasons, PROBA-3 is being designed with focus on verification of the requirements coming from the XEUS studies, a potential formation-flying X-ray astronomy mission, such that future XEUS-like missions can reuse high-TRL technologies. Also the science payload (Coronagraph) determines some formation flying requirements and design decisions. PROBA-3 requirements are derived mainly from four sources [2].
40
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
(1) Generic formation flying capabilities and the associated technology development tools, techniques and facilities, compiled from previous initiatives and expectations. (2) Sun-coronagraphy payload capabilities (Fig. 1). (3) XEUS like mission requirements on FF and GNC. (4) Additional experiments like ISL-in-the-loop Experiment: commands to the actuators are transferred from the Coronagraph spacecraft (CSC) to the Occulter spacecraft (OSC). Collision Avoidance Experiment, by forcing the triggering of these manoeuvres under several conditions. Rendezvous in highly elliptical orbit, derived from the needs of Mars Sample Return. From these sources of requirements, the PROBA-3 formation flying mission will include the following capabilities:
Generic formation flying: maintain relative position
Formation Retargeting: the target direction vector will
These capabilities will be achieved in PROBA-3 including the following additional features:
Many different inertially-oriented formations to be
and attitude in any inertial direction.
Perigee pass reconfigurations: the formation flying
system will have to break formation, perform perigee pass and perform formation reacquisition after perigee. Safety management and Collision Avoidance: the Formation Flying System will detect risk for the mission (i.e. collision), and will activate the corresponding Collision avoidance, until leaving the system in a safe and stable formation. Formation Coarse Acquisition that will acquire the stable formation configuration with the coarse metrology. Formation Fine Acquisition: After Formation Coarse acquire, it will initiate the High accuracy metrology acquisition and use it to acquire highest performance. Formation Station Keeping Test: intended to maintain the formation in a stable and fixed configuration, with highest performance. Formation Resize Close and Far: reduction and/or increase of the nominal Inter-Satellite Distance (ISD) to minimum and maximum distance (range from 25 m to 250 m).
Fig. 1. Artistic view of PROBA-relative configuration analysed during the Bridging Step phase (esa/P.Carril).
be slowly rotated, up to a specified final angle from the original (maximum rotation of 301). Formation Resize and Retarget: combination of Formation Resize and retargeting. Coronagraph Observation formation: The Coronagraph satellite will be maintained in formation with the Occulter at a nominal distance from 147 m to 153 m, and highly accurate longitudinal and lateral positioning (Fig. 2).
tested during these operations, with nominal distances ranging from 25 to 250 m, and rotation/retargeting up to 301. Formation manoeuvres to be performed in rigid mode (maintaining formation during manoeuvre) and loose mode (no need to maintain formation properties during the manoeuvre). Precise formation to be acquired and maintained for predefined duration after every configuration acquisition. Precision formation flying to be performed at several different ISDs, with several levels of accuracy until arriving to the highest requirements in accuracy. Metrology validation from the coarse level accuracy to the highest level of accuracy. Formation and GNC Sensors and Actuators will be characterised in the different ranges of application (distance, FOV, velocities etc.). Formation and GNC System end to end testing in several types of configurations, including centralisation with inter-satellite link in the control loop. Stable tandem/parking orbits to be exploited as the default formation configurations to be used while in stand-by for instance after a safety conditions is recovered.
All these functions and capabilities have been incorporated into the formation flying and GNC configuration and design. The following sections provide a description of the current design solutions.
Fig. 2. Satellites relative configuration after the phase B1.
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
41
3. Formation flying configuration and design
tion flying activities.
3.1. General
(1) The apogee region includes a region of around 6 h around apogee, and is used for the precise formation demonstrations, using the low gravity gradient in that area. (2) The perigee region, where the satellites perform freeflight operation. (3) The perigee pass manoeuvre areas. Including the perigee/apogee entry/exit regions and the Mid Course Manoeuvres (MCM) region. In these regions control manoeuvres are computed and executed in order to
From the selected HEO orbital configuration, the system design evolution has determined the selection of a high inclination that improves orbit stability, and reduces the radiation dose. The selected orbit is 60524 800 km, with 591 inclination and Argument of Perigee of 1881. During nominal operation, every orbit is decomposed in three main regions in relation with the type of forma-
Fig. 3. PROBA-3 orbit activities schematic.
Fig. 4. Main architecture of the FFS.
42
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
arrive in free-flight to the apogee region entry with the best conditions and once there, perform the apogee formation reacquisition. Perigee pass manoeuvres will also be used for obtaining the desired formation configuration change between experiments (Fig. 3).
Formation Flying Management (FFM): plans the FF, and
The Formation Flying System has been defined in PROBA3 as ‘‘The On-Board System that includes all equipments (HW) and functions (SW) in charge of scheduling, acquiring, maintaining and modifying the absolute and relative position and attitude of the ensemble of SCs in the Formation in a controlled and stable manner’’. With this scope in mind the Formation Flying System covers all the functions and components required for organising the formation configuration status, changes and interactions, controlling and maintaining the satellites in the desired position and attitude and include the following components:
Formation Flying System level functions: on top of the different elements of the FFS, the overall System will form an entity that encompasses coordinates and integrates the elements of the system.
allocates the different types of commands and actions to the remaining elements in the System. It will include the Timeline for the Formation in terms of Experiments and Demonstrations. Formation Flying GNC (FF-GNC): controls the relative state (position and attitude) GNC. The FF-GNC will process the measurements obtained from the SC-GNC (see after), directly or via the Inter-Satellite Link (ISL), for the determination of the relative position and attitude, and it will determine the actions required for acquiring the trajectories as determined by the guidance as a function of the requests of the FFM. SC control (SC-GNC): at SC level performs the GNC activities for controlling the SC absolute state (attitude and delta-V). The SC-GNC actions will be driven by the control commands coming from the FF-GNC, typically by high level commands to autonomous SC-GNC modes. It will also include capabilities for control centralisation at FF-GNC in which case only low level commands will be executed at SC-GNC (functions are quite similar to the classical AOCS).
Fig. 5. Formation and SC modes.
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
FF-FDIR functions: a centralised FFS FDIR module will coordinate the detection and flags processing coming from the different elements of the FFS (FFM, FF-GNC, SC-GNC). FF-FDIR includes activation of Collision and Evaporation Avoidance Manoeuvres (CEAM). Additionally the FFS will have a tight coupling with the SC-Manager for taking decisions and executing them at SC configuration level as derived from the raised flags and commands generated by the FFS elements. The previous functional organisation is presented graphically in Fig. 4. The actions determined by the FF-GNC will be transmitted to the SC-GNC that will execute them at SC level.
43
3.2. Formation flying modes The overall architecture of modes reflects the three levels in the structure of the system corresponding to the Stack (CSC and OSC rigidly attached), SC level and Formation, which will allow the different configurations of SCs and formations during the mission. It will also allow the implementation of different types of configuration by reallocation of functions between modes. Fig. 5 shows a schematic of the SC-GNC modes in parallel with the FF-GNC. The full control (also the relative attitude) during the formation is performed by the FF-GNC. It also includes the possible SC configurations as a Formation, as individual SCs, or in stacked configuration.
Table 1 Modes configuration and acronyms. FF-GNC Stack
No FF
Individual SCs (OSC or CSC)
No FF
SC-GNC
Description
SAM/Safe IAM OCM SAM/Safe IAM/OCM
Sun Acquisition Mode. After separation, to acquire sun pointing attitude. Inertial Attitude Pointing. Orbit Control Mode (OCM) for DV thrusters actuation capability. Sun Acquisition Mode. Acquire and maintain sun pointing attitude. Inertial attitude pointing. Acquire and maintain inertial attitude and OCM submode to use the mN thrusters for small DV acquisition. Orbit Control Mode in CSC: Execute DV manoeuvres with 1N thrusters. Target Pointing Mode. The SC will use the formation sensors measurements for obtaining target pointing attitude. Thruster Based Inertial Mode: similar to IAM/OCM, but intended to exercise pure thrusters base control (including attitude). SC in FF. SC-GNC Mode dedicated to centralised attitude control, will only process the control commands generated by the FF-GNC. Formation Stand-By: The formation left in stable configuration and the FF-GNC control is inhibited or minimised. Tandem Maintenance: will correct small deviations from the stable Tandem configuration. Tandem Acquisition: The FFS performs acquisition of a tandem formation (stable and safe orbit). In safety cases, the TAQ is triggered with predefined orbit manoeuvres. In general TAQ can executed with parametric arguments. Formation Coarse Mode. Formation acquisition and coarse control. SC control can be in IAM, TPM or SCFF. Formation Reconfiguration. Performs formation resizing and re-pointing and other types of formation manoeuvres. Formation Fine Mode. Precise metrology for longitudinal and lateral position. Perigee Pass Mode. Implements the Perigee Manoeuvres and the perigee coasting.
CSC-OCM TPM TBIM SCFF Formation Flying Modes
FSB
SAM/IAM
TMN TAQ
IAM/OCM IAM/OCM
FCM
IAM/TPM/ SCFF IAM/TPM
FRM FFM PPM EXP CEAM
IAM/SCFF IAM/OCM/ TPM IAM/TPM/ SCFF FF/SAM
EXPeriment Mode. Special Mode devoted for implementation of ancillary experiments. Collision and Evaporation Avoidance Manoeuvres are executed to bring the formation in FSB.
Table 2 Summary of sensors configuration. Sensors
CSC
RF
1 Triplet þ 3 antennas þ Switches for all antennas. Redundant receiver/transmitter electronics. Sensor camera and emitter Sensor head Sensor emitter and receiver 3 STR. pyramidal config. With LOS 601 away from anti-Sun Full coverage with distributed cosine Sun Sensors.(6 2) 1 redundant receiver at each SC 2 3 axis systems at each SC 4 photodiodes, part of Coronagraph instrument Coronagraph sensor
CLS VBS HAM Star tracker Sun Sensor GPS Rate sensors SPS (shadow position sensor) OPS(Occulter position sensor)
OSC
Corner Cube LEDs Corner Cube
– 2 sets of 4 LEDs
44
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
Modes configurations and acronyms are included in Table 1.
Coarse relative navigation: optical sensors. Two types
3.3. FF and GNC equipments A wide range of sensors and actuators have been evaluated in previous phases, in first instance for the relative positioning, but also for absolute position and attitude determination and control. The formation position control (both absolute and relative) will include three levels/stages of accuracy which are obtained with three different types of technologies
Acquisition and coarse formation: radiofrequency type of positioning sensors (RF). This will include dedicated RF formation sensors, as well as the usage of absolute and relative GPS (RGPS). RGPS is intended especially for the perigee pass manoeuvres, and will not be used in the formation demonstrations.
of sensors are intended J CLS: Coarse Lateral Sensors. J VBS; intended mainly for one of the rendezvous experiments, and as alternative to the nominal set of sensors. High Accuracy Metrology (HAM) that provides high accuracy longitudinal measurements, and also lateral (TBC). It will be based on laser metrology.
Table 4 Performance definitions [4]. AA AAE AAME AAS LOS
Absolute Attitude AA Error AA Measurment Error AA Stability Line Of Sight
RD RDE RDME RDMS ALOS
Relative Displacement RD Error RD Measurment Error RD Measurement Stability Around Line Of Sight
Fig. 6. Formation pulses size at different epochs.
Table 3 Summary of the actuators configuration. Function
CSC
OSC
Orbit Injection/Perigee Man./Mission End
2 4 1 N Monopropellant 4DOF:1 linear þ3 attitude 2 8 10 mN cold gas (6DOF) 4 RWL (1 Nms) at each SC
–
Formation control/Perigee Man./CEAM/RW unloading/Acquisition and safe mode Attitude
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
45
Table 5 Most relevant attitude and position budgets with HAM (arcsec/mm) (at SRR).
AAE CSC AAME CSC AAS CSC AAE OSC AAME OSC AAS OSC
LOS (1r)
ALOS(1r)
2.8 0.42 0.83 64.6 16.8 2.88
19.4 18.48 2.1 65.11 17.3 3.38
In terms of attitude determination the main precision sensors to be used are precise STR mounted in special configuration to improve the attitude determination performance at the target line direction. The selected configuration guarantees that 2 STR heads are always active. Additionally the sun sensors (SS) and the rate sensors will be mainly used during the initial attitude acquisition and safe modes. The full list of selected sensors is shown in Table 2. For the control, three types of actuators are mounted in the SC
Reaction wheels (RWL), that will decouple the attitude
control from the relative position, and allow precise control without spending the limited resources of the SCs. Orbital control thrusters, based on monopropellant, will include control capability in 4 DOF (one DV and the 3 axis of the attitude) to the CSC and the stack configuration. Precise cold-gas milli-Newton thrusters, with 6 decoupled DOF control capability (2 sets of 8 10 mN) In this configuration Minimum Impulse Bit and authority for formation control, perigee passes and formation manoeuvres have been checked and a systematic evaluation of the required pulse sizes has been evaluated (Fig. 6 is an example). The full list of selected actuators is shown in Table 3.
4. System performance Specification and analysis of relative position performance require the extension of the concepts and terminology usually applied from the ESA Pointing Error Handbook [3]. These concepts have been extended to relative position and attitude, and they have been used for the specification and analysis of the PROBA-3 mission performance. The definition of the terms in used for the formation flying performance is incldued in Table 4. Table 5 shows preliminary budgets evaluation in pointing (left) and relative position (right). In order to achieve these performances a critical issue is the calibration of the formation sensors. For doing this calibration a process has been defined and analysed using several types of available sensors from the science payload and STR sensors: Calibration will be performed by comparison of stars detection results þ OPS both
RDE 35 m RDE 150 m RDME 35 m RDME 150 m RDMS 35 m(4 h) RDMS 150 m(4 h)
Long (1r)
Lat (1r)
0.36 0.36 0.21 0.21 0.082 0.026
1.82 2.17 0.99 1.01 0.83 0.84
(per (per (per (per (per (per
axis) axis) axis) axis) axis) axis)
detected at the coronagraph camera, and its comparison with the measurements being obtained by the CLS and HAM. The process will include (1) Observation with the Coronagraph camera of stars in its FOV. (2) Comparison of Coronagraph and STR attitude. (3) Observation with the Coronagraph camera of the OPS. (4) Comparison of FF sensor measurement and OPS measurement. (5) Combine all previous measurements to obtain calibration at the obtained distance. (6) Repeat the process at a different ISD. (7) Determine the components related with linear and angular calibration biases, by comparison of the calibration measurements at two different distances. The calibration process is described in [5] in mathematical form for determination of the achievable accuracy at calibration, that is obtained under certain assumptions.
5. Conclusion The PROBA-3 mission is intended to demonstrate in flight critical technologies required for the implementation of formation flying missions. The mission has been during the last year subject of several evolutions and analysis and is currently in the preliminary design phase. Within this paper a review of the mission and the associated formation flying demonstrations was performed, with some more detailed information on the formation flying organisation, basic design and selected equipments configuration. Finally it provides a brief presentation of the expected performance based on budget models and assumptions, and introduces the in flight precise calibration approach. The presented design that has been verified for feasibility and the preliminary results show good agreement with the expected results. References [1] PROBA-3 Mission Requirements Document, P3-EST-RS-1006, issue 2.3, July 2010. [2] PROBA-3 System Requirements Document, P3-EST-RS-1001, issue 2.3, July 2010. [3] E.S.A. Pointing Error Handbook ESA-NCR-502, issue 1, 19 February 1993.
46
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
[4] Error Budgets for Formation Flying Missions, NPD/5022/TD/TR/001, issue 1.0, 09 November 2007. [5] F.F.S. Pointing and Positioning Budgets, P3-SG-TN-3003, 2.1, March 2010. J. Salvador Llorente obtained MSc in Aeronautical Engineering at Universidad Polite´cnica de Madrid and MBA from ICADE (Madrid). He was responsible for development of the CLUSTER Attitude Determination and Dynamics Monitoring Flight Dynamics at ESA-ESOC (Darmstadt in Germany). He was associate professor at the Universidad Polite´cnica de Madrid for some years. Joined SENER on 1997, where he has been project manager for the AOCS of the Herschel–Planck missions, and later for the PROBA-3 mission, initially for the Formation Flying System and later for the overall mission. He also lead the AOCS group and the System Engineering initiatives at SENER. Alfredo Agenjo obtained MSc in Aeronautical Engineering at Universidad Polite´cnica de Madrid. Joined SENER as Systems Engineer on 2002, where he is especially dedicated to the area of GNC and AOCS for spacecrafts and other aerial vehicles. He has played a main role in the ACMS subsystem for the Planck spacecraft for ESA, starting in the phase B GNC algorithms design, up to the in-flight GNC commissioning in 2009. Alfredo Agenjo is currently responsible of the coordination of the design and validation of the Formation Flying System and GNC activities at SENER for the ESA PROBA-3 mission. Carmelo Carrascosa Sanz received a Masters in Aeronautical Engineering from the Polytechnic University of Madrid, Spain, in 1995. Since 1997 is working in GMV in different space missions. He has been involved in different technical areas; mission analysis, system engineering, flight dynamics, guidance, navigation algorithms based on GPS and spacecraft simulation tools. During 2005–2011 period, he was responsible for the Space Engineering Division of GMV. Recently, he is programme and business development executive in GMV, responsible for; business development and proposal elaboration, support to the different on-going programmes and promoting synergies of activities and technologies. Cristina de Negueruela Alema´n holds a Masters in Telecommunications Engineering by the University of Las Palmas de Gran Canaria and an MSc in Space Studies by the International Space University. She has worked at INTA, NASA and ESA in the fields of telecommunications, remote sensing, spacecraft systems engineering and mission analysis. She joined GMV in 2007 and was lead systems engineer and deputy project manager of PROBA-3 activities for over three years. She has since joined the Engineering and Studies division, where she is currently a project manager in the areas of mission analysis and simulators for Earth Observation missions.
Agnes Mestreau-Garreau is working at ESA/ ESTEC. After her engineering graduation, she joined ESA in 1992 and was involved in the development of the ENVISAT optical instruments. In 1994, she continues her professional experience in industry at EADSSODERN where she worked as optical engineer, head of optical section and finally as project manager of equipments. In 2004, she returned to ESA as team leader of assessment studies of future instruments and missions in the Concurrent Design Facility (CDF) team. Since 2009, she is the ESA Project Manager of the PROBA 3 mission. Alexander Cropp completed his undergraduate degree in electrical engineering at Imperial College, London in 1997, followed by a PhD in satellite engineering at the University of Surrey in 2001. He spent 7 years working for Surrey Satellite technology ltd (SSTL) as an AOCS engineer on a variety of projects including RapidEye, a 5-satelitte Earth observation constellation, and GIOVEA, the first Galileo in-orbit validation experiment satellite. He was also the AOCS team leader for 2 years, before joining ESA ESTEC in 2007. He is currently the ESA GNC lead on the PROBA3 project. Andrea Santovincenzo is presently Proba 3 System Engineer at ESA. Andrea Santovincenzo graduated in Aeronautics in 1990 at University of Rome (Italy). He started working as Propulsion and Thermal Engineer at Avio and moved after five years to ESTEC, the ESA technology centre in The Netherlands. He supported as Thermal specialist several ESA projects before becoming System Engineer at the Concurrent Design Facility (CDF) where he has been team leader of mission feasibility studies. He has also been System Engineer of the ESA projects Mars Sample Return, ExoMars, Mars Next and Iris in their early phases.
Contents lists available at SciVerse ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
PROBA-3: Precise formation flying demonstration mission J.S. Llorente a,n, A. Agenjo a, C. Carrascosa b, C. de Negueruela b, A. Mestreau-Garreau c, A. Cropp c, A. Santovincenzo c a b c
SENER Ingenierı´a y Sistemas, Severo Ochoa, 4. E-28760 Tres Cantos, Madrid, Spain GMV Aerospace and Defence, Isaac Newton, 11, E-28760 Tres Cantos, Madrid, Spain ESA, Noordwijk, PO Box 299-2200 AG Noordwijk, The Netherlands
a r t i c l e in f o
abstract
Article history: Received 14 January 2012 Received in revised form 16 May 2012 Accepted 22 May 2012 Available online 25 June 2012
Formation Flying (FF) has generated a strong interest in many space applications, most of them involving a significant complexity for building for example on-board large ‘‘virtual structures or distributed observatories’’. The implementation of these complex formation flying missions with critical dependency on this new, advanced and critical formation technology requires a thorough verification of the system behaviour in order to provide enough guarantees for the target mission success. A significant number of conceptual or preliminary designs, analyses, simulations, and HW on-ground testing have been performed during the last years, but still the limitations of the ground verification determine that enough confidence of the behaviour of the formation flying mission will only be possible by demonstration in flight of the concept and the associated technologies. PROBA-3 is the mission under development at ESA for in-flight formation flying demonstration, dedicated to obtain that confidence and the necessary flight maturity level in the formation flying technologies for those future target missions. PROBA-3 will demonstrate technologies such as formation metrology sensors (from very coarse to highest accuracy), formation control and GNC, system operability, safety, etc. During the last years, PROBA-3 has evolved from the initial CDF study at ESA, to two parallel phase A studies, followed by a change in the industrial configuration for the Bridging step between A and B phases. Currently the SRR consolidation has been completed, and the project is in the middle of the phase B. After the phase A study SENER and GMV were responsible for the Formation Flying System, within a mission core team completed by OHB-Sweden, QinetiQ Space and CASA Espacio. In this paper an overview of the PROBA-3 mission is provided, with a more detailed description of the formation flying preliminary design and results. & 2012 Elsevier Ltd. All rights reserved.
Keywords: PROBA Formation flying GNC Coronagraph
n
Corresponding author. Tel.: þ 34 918 077 225; fax: þ34 918 077 208. E-mail addresses: [email protected] (J.S. Llorente), [email protected] (A. Agenjo), [email protected] (C. Carrascosa), [email protected] (C. de Negueruela), [email protected] (A. Mestreau-Garreau), [email protected] (A. Cropp), [email protected] (A. Santovincenzo). 0094-5765/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actaastro.2012.05.029
1. Introduction 1.1. PROBA-3 objectives The PROBA-3 Mission is the third of the PROBA missions dedicated to in orbit technologies demonstration. The main objective of PROBA-3 is to demonstrate precise
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
formation flying key technologies [1] for its application to future missions including:
Formation Flying concepts for several types of formation flying missions.
Formation Flying Guidance, Navigation and Control Algorithms.
Formation Flying metrology units, accuracy levels and transitions between them.
Formation Flying Autonomy. Formation Flying development, verification and validation tools.
Formation Flying Ground Segment and Operations required support.
The orbit trade-off has concluded with the selection of a highly eccentric orbit (HEO), with orbital period in the order of one day. The selected high apogee HEO orbit will provide around apogee a representative environment for the demonstrations to be performed, while requiring reduced launch capabilities compared with lower perturbation orbits such as L2. The reduced gravity gradient environment present during the high apogee region will allow representative high precision formation environments, while the perigee region, and the perigee passage, will exercise formation management and control through a wide range of gravity gradient disturbances, down to LEO-type of high gravity gradient. As complement to the end-to-end validation of the formation flying technologies, a scientific instrument, a Coronagraph, has been selected to provide advances in solar physics and in particular, deeper understanding of the Sun and its corona. The Coronagraph System can also be regarded as an independent verification of the attitude and position control systems of PROBA 3, as deviations in relative position or attitudes will be observable on the images produced by the coronagraph. The system is distributed over the two satellites; one carrying the detector and the second one carrying the Sun Occulter disc. Both spacecrafts are flying in precise formation during the science acquisition periods to generate the required ‘‘virtual’’ instrument. Finally, the mission will be complemented by some additional experiments. In particular several types of rendezvous strategies and different types of control in highly eccentric orbit will be verified.
1.2. The PROBA-3 mission The PROBA-3 mission consists of two small satellites to be injected by a single launch into a highly eccentric Earth orbit. Once separated from the launcher, the two spacecraft remain rigidly attached together in a stacked configuration. The bottom satellite will include propulsion capability to raise the stack orbit apogee from the injected one to the final nominal orbit of about 20 h period. Once into the target orbit, the two satellites are separated and the formation flying operations will start.
39
Immediately after separation, the satellites are autonomously acquiring the sun and subsequently they are placed into a safe relative trajectory, where collision is guaranteed to be not possible while also evaporation will not happen within a comfortable timeframe. For this mission, evaporation is defined as a separation between spacecrafts such that formation recovery is not possible within the available resources. Once the safe and stable configuration is achieved the in orbit commissioning starts. The Ground Segment and the various Space Segment Subsystems, Software, FDIR, formation-flying metrologies will be gradually commissioned and the Coronagraph System checkout performed. This gradual validation will be initially under control from ground, and will be completed when completely autonomous execution of the operations pre-planned for at least 7 day is performed, with staggered transitions until full autonomy is acquired. At the end of the commissioning phase the Ground and Flight segments will start nominal operation, and the formation flying capabilities of the System will be exploited. The demonstration will exercise generic formation configurations valid for multiple types of target missions, including a wide range of formation acquisitions, formation reconfigurations, manoeuvres, accuracies, information and commands exchanged between the satellites, etc. The Coronagraph science acquisition will be performed with one specific configuration of the formation flying, and will be performed regularly during the whole mission duration, interleaved with the rest of demonstrations, and experiments. At the end of the operational lifetime, the PROBA-3 satellites are de-orbited according to the international regulations and recommendations. Both satellites will be under control of the Mission Control Centre supported by the involved Ground Station(s) including ESA Redu as the main Ground Station and operations centre.
2. PROBA-3 formation flying demonstrations The PROBA-3 formation flying demonstrations will be organised around a set of general formation technology aspects, without the need to particularise for one specific formation flying mission. PROBA-3 intends to verify the techniques and technology which could be needed for as many future Formation Flying missions as possible, under the constrains and limitation of a low-cost demonstration mission. For practical reasons, PROBA-3 is being designed with focus on verification of the requirements coming from the XEUS studies, a potential formation-flying X-ray astronomy mission, such that future XEUS-like missions can reuse high-TRL technologies. Also the science payload (Coronagraph) determines some formation flying requirements and design decisions. PROBA-3 requirements are derived mainly from four sources [2].
40
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
(1) Generic formation flying capabilities and the associated technology development tools, techniques and facilities, compiled from previous initiatives and expectations. (2) Sun-coronagraphy payload capabilities (Fig. 1). (3) XEUS like mission requirements on FF and GNC. (4) Additional experiments like ISL-in-the-loop Experiment: commands to the actuators are transferred from the Coronagraph spacecraft (CSC) to the Occulter spacecraft (OSC). Collision Avoidance Experiment, by forcing the triggering of these manoeuvres under several conditions. Rendezvous in highly elliptical orbit, derived from the needs of Mars Sample Return. From these sources of requirements, the PROBA-3 formation flying mission will include the following capabilities:
Generic formation flying: maintain relative position
Formation Retargeting: the target direction vector will
These capabilities will be achieved in PROBA-3 including the following additional features:
Many different inertially-oriented formations to be
and attitude in any inertial direction.
Perigee pass reconfigurations: the formation flying
system will have to break formation, perform perigee pass and perform formation reacquisition after perigee. Safety management and Collision Avoidance: the Formation Flying System will detect risk for the mission (i.e. collision), and will activate the corresponding Collision avoidance, until leaving the system in a safe and stable formation. Formation Coarse Acquisition that will acquire the stable formation configuration with the coarse metrology. Formation Fine Acquisition: After Formation Coarse acquire, it will initiate the High accuracy metrology acquisition and use it to acquire highest performance. Formation Station Keeping Test: intended to maintain the formation in a stable and fixed configuration, with highest performance. Formation Resize Close and Far: reduction and/or increase of the nominal Inter-Satellite Distance (ISD) to minimum and maximum distance (range from 25 m to 250 m).
Fig. 1. Artistic view of PROBA-relative configuration analysed during the Bridging Step phase (esa/P.Carril).
be slowly rotated, up to a specified final angle from the original (maximum rotation of 301). Formation Resize and Retarget: combination of Formation Resize and retargeting. Coronagraph Observation formation: The Coronagraph satellite will be maintained in formation with the Occulter at a nominal distance from 147 m to 153 m, and highly accurate longitudinal and lateral positioning (Fig. 2).
tested during these operations, with nominal distances ranging from 25 to 250 m, and rotation/retargeting up to 301. Formation manoeuvres to be performed in rigid mode (maintaining formation during manoeuvre) and loose mode (no need to maintain formation properties during the manoeuvre). Precise formation to be acquired and maintained for predefined duration after every configuration acquisition. Precision formation flying to be performed at several different ISDs, with several levels of accuracy until arriving to the highest requirements in accuracy. Metrology validation from the coarse level accuracy to the highest level of accuracy. Formation and GNC Sensors and Actuators will be characterised in the different ranges of application (distance, FOV, velocities etc.). Formation and GNC System end to end testing in several types of configurations, including centralisation with inter-satellite link in the control loop. Stable tandem/parking orbits to be exploited as the default formation configurations to be used while in stand-by for instance after a safety conditions is recovered.
All these functions and capabilities have been incorporated into the formation flying and GNC configuration and design. The following sections provide a description of the current design solutions.
Fig. 2. Satellites relative configuration after the phase B1.
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
41
3. Formation flying configuration and design
tion flying activities.
3.1. General
(1) The apogee region includes a region of around 6 h around apogee, and is used for the precise formation demonstrations, using the low gravity gradient in that area. (2) The perigee region, where the satellites perform freeflight operation. (3) The perigee pass manoeuvre areas. Including the perigee/apogee entry/exit regions and the Mid Course Manoeuvres (MCM) region. In these regions control manoeuvres are computed and executed in order to
From the selected HEO orbital configuration, the system design evolution has determined the selection of a high inclination that improves orbit stability, and reduces the radiation dose. The selected orbit is 60524 800 km, with 591 inclination and Argument of Perigee of 1881. During nominal operation, every orbit is decomposed in three main regions in relation with the type of forma-
Fig. 3. PROBA-3 orbit activities schematic.
Fig. 4. Main architecture of the FFS.
42
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
arrive in free-flight to the apogee region entry with the best conditions and once there, perform the apogee formation reacquisition. Perigee pass manoeuvres will also be used for obtaining the desired formation configuration change between experiments (Fig. 3).
Formation Flying Management (FFM): plans the FF, and
The Formation Flying System has been defined in PROBA3 as ‘‘The On-Board System that includes all equipments (HW) and functions (SW) in charge of scheduling, acquiring, maintaining and modifying the absolute and relative position and attitude of the ensemble of SCs in the Formation in a controlled and stable manner’’. With this scope in mind the Formation Flying System covers all the functions and components required for organising the formation configuration status, changes and interactions, controlling and maintaining the satellites in the desired position and attitude and include the following components:
Formation Flying System level functions: on top of the different elements of the FFS, the overall System will form an entity that encompasses coordinates and integrates the elements of the system.
allocates the different types of commands and actions to the remaining elements in the System. It will include the Timeline for the Formation in terms of Experiments and Demonstrations. Formation Flying GNC (FF-GNC): controls the relative state (position and attitude) GNC. The FF-GNC will process the measurements obtained from the SC-GNC (see after), directly or via the Inter-Satellite Link (ISL), for the determination of the relative position and attitude, and it will determine the actions required for acquiring the trajectories as determined by the guidance as a function of the requests of the FFM. SC control (SC-GNC): at SC level performs the GNC activities for controlling the SC absolute state (attitude and delta-V). The SC-GNC actions will be driven by the control commands coming from the FF-GNC, typically by high level commands to autonomous SC-GNC modes. It will also include capabilities for control centralisation at FF-GNC in which case only low level commands will be executed at SC-GNC (functions are quite similar to the classical AOCS).
Fig. 5. Formation and SC modes.
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
FF-FDIR functions: a centralised FFS FDIR module will coordinate the detection and flags processing coming from the different elements of the FFS (FFM, FF-GNC, SC-GNC). FF-FDIR includes activation of Collision and Evaporation Avoidance Manoeuvres (CEAM). Additionally the FFS will have a tight coupling with the SC-Manager for taking decisions and executing them at SC configuration level as derived from the raised flags and commands generated by the FFS elements. The previous functional organisation is presented graphically in Fig. 4. The actions determined by the FF-GNC will be transmitted to the SC-GNC that will execute them at SC level.
43
3.2. Formation flying modes The overall architecture of modes reflects the three levels in the structure of the system corresponding to the Stack (CSC and OSC rigidly attached), SC level and Formation, which will allow the different configurations of SCs and formations during the mission. It will also allow the implementation of different types of configuration by reallocation of functions between modes. Fig. 5 shows a schematic of the SC-GNC modes in parallel with the FF-GNC. The full control (also the relative attitude) during the formation is performed by the FF-GNC. It also includes the possible SC configurations as a Formation, as individual SCs, or in stacked configuration.
Table 1 Modes configuration and acronyms. FF-GNC Stack
No FF
Individual SCs (OSC or CSC)
No FF
SC-GNC
Description
SAM/Safe IAM OCM SAM/Safe IAM/OCM
Sun Acquisition Mode. After separation, to acquire sun pointing attitude. Inertial Attitude Pointing. Orbit Control Mode (OCM) for DV thrusters actuation capability. Sun Acquisition Mode. Acquire and maintain sun pointing attitude. Inertial attitude pointing. Acquire and maintain inertial attitude and OCM submode to use the mN thrusters for small DV acquisition. Orbit Control Mode in CSC: Execute DV manoeuvres with 1N thrusters. Target Pointing Mode. The SC will use the formation sensors measurements for obtaining target pointing attitude. Thruster Based Inertial Mode: similar to IAM/OCM, but intended to exercise pure thrusters base control (including attitude). SC in FF. SC-GNC Mode dedicated to centralised attitude control, will only process the control commands generated by the FF-GNC. Formation Stand-By: The formation left in stable configuration and the FF-GNC control is inhibited or minimised. Tandem Maintenance: will correct small deviations from the stable Tandem configuration. Tandem Acquisition: The FFS performs acquisition of a tandem formation (stable and safe orbit). In safety cases, the TAQ is triggered with predefined orbit manoeuvres. In general TAQ can executed with parametric arguments. Formation Coarse Mode. Formation acquisition and coarse control. SC control can be in IAM, TPM or SCFF. Formation Reconfiguration. Performs formation resizing and re-pointing and other types of formation manoeuvres. Formation Fine Mode. Precise metrology for longitudinal and lateral position. Perigee Pass Mode. Implements the Perigee Manoeuvres and the perigee coasting.
CSC-OCM TPM TBIM SCFF Formation Flying Modes
FSB
SAM/IAM
TMN TAQ
IAM/OCM IAM/OCM
FCM
IAM/TPM/ SCFF IAM/TPM
FRM FFM PPM EXP CEAM
IAM/SCFF IAM/OCM/ TPM IAM/TPM/ SCFF FF/SAM
EXPeriment Mode. Special Mode devoted for implementation of ancillary experiments. Collision and Evaporation Avoidance Manoeuvres are executed to bring the formation in FSB.
Table 2 Summary of sensors configuration. Sensors
CSC
RF
1 Triplet þ 3 antennas þ Switches for all antennas. Redundant receiver/transmitter electronics. Sensor camera and emitter Sensor head Sensor emitter and receiver 3 STR. pyramidal config. With LOS 601 away from anti-Sun Full coverage with distributed cosine Sun Sensors.(6 2) 1 redundant receiver at each SC 2 3 axis systems at each SC 4 photodiodes, part of Coronagraph instrument Coronagraph sensor
CLS VBS HAM Star tracker Sun Sensor GPS Rate sensors SPS (shadow position sensor) OPS(Occulter position sensor)
OSC
Corner Cube LEDs Corner Cube
– 2 sets of 4 LEDs
44
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
Modes configurations and acronyms are included in Table 1.
Coarse relative navigation: optical sensors. Two types
3.3. FF and GNC equipments A wide range of sensors and actuators have been evaluated in previous phases, in first instance for the relative positioning, but also for absolute position and attitude determination and control. The formation position control (both absolute and relative) will include three levels/stages of accuracy which are obtained with three different types of technologies
Acquisition and coarse formation: radiofrequency type of positioning sensors (RF). This will include dedicated RF formation sensors, as well as the usage of absolute and relative GPS (RGPS). RGPS is intended especially for the perigee pass manoeuvres, and will not be used in the formation demonstrations.
of sensors are intended J CLS: Coarse Lateral Sensors. J VBS; intended mainly for one of the rendezvous experiments, and as alternative to the nominal set of sensors. High Accuracy Metrology (HAM) that provides high accuracy longitudinal measurements, and also lateral (TBC). It will be based on laser metrology.
Table 4 Performance definitions [4]. AA AAE AAME AAS LOS
Absolute Attitude AA Error AA Measurment Error AA Stability Line Of Sight
RD RDE RDME RDMS ALOS
Relative Displacement RD Error RD Measurment Error RD Measurement Stability Around Line Of Sight
Fig. 6. Formation pulses size at different epochs.
Table 3 Summary of the actuators configuration. Function
CSC
OSC
Orbit Injection/Perigee Man./Mission End
2 4 1 N Monopropellant 4DOF:1 linear þ3 attitude 2 8 10 mN cold gas (6DOF) 4 RWL (1 Nms) at each SC
–
Formation control/Perigee Man./CEAM/RW unloading/Acquisition and safe mode Attitude
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
45
Table 5 Most relevant attitude and position budgets with HAM (arcsec/mm) (at SRR).
AAE CSC AAME CSC AAS CSC AAE OSC AAME OSC AAS OSC
LOS (1r)
ALOS(1r)
2.8 0.42 0.83 64.6 16.8 2.88
19.4 18.48 2.1 65.11 17.3 3.38
In terms of attitude determination the main precision sensors to be used are precise STR mounted in special configuration to improve the attitude determination performance at the target line direction. The selected configuration guarantees that 2 STR heads are always active. Additionally the sun sensors (SS) and the rate sensors will be mainly used during the initial attitude acquisition and safe modes. The full list of selected sensors is shown in Table 2. For the control, three types of actuators are mounted in the SC
Reaction wheels (RWL), that will decouple the attitude
control from the relative position, and allow precise control without spending the limited resources of the SCs. Orbital control thrusters, based on monopropellant, will include control capability in 4 DOF (one DV and the 3 axis of the attitude) to the CSC and the stack configuration. Precise cold-gas milli-Newton thrusters, with 6 decoupled DOF control capability (2 sets of 8 10 mN) In this configuration Minimum Impulse Bit and authority for formation control, perigee passes and formation manoeuvres have been checked and a systematic evaluation of the required pulse sizes has been evaluated (Fig. 6 is an example). The full list of selected actuators is shown in Table 3.
4. System performance Specification and analysis of relative position performance require the extension of the concepts and terminology usually applied from the ESA Pointing Error Handbook [3]. These concepts have been extended to relative position and attitude, and they have been used for the specification and analysis of the PROBA-3 mission performance. The definition of the terms in used for the formation flying performance is incldued in Table 4. Table 5 shows preliminary budgets evaluation in pointing (left) and relative position (right). In order to achieve these performances a critical issue is the calibration of the formation sensors. For doing this calibration a process has been defined and analysed using several types of available sensors from the science payload and STR sensors: Calibration will be performed by comparison of stars detection results þ OPS both
RDE 35 m RDE 150 m RDME 35 m RDME 150 m RDMS 35 m(4 h) RDMS 150 m(4 h)
Long (1r)
Lat (1r)
0.36 0.36 0.21 0.21 0.082 0.026
1.82 2.17 0.99 1.01 0.83 0.84
(per (per (per (per (per (per
axis) axis) axis) axis) axis) axis)
detected at the coronagraph camera, and its comparison with the measurements being obtained by the CLS and HAM. The process will include (1) Observation with the Coronagraph camera of stars in its FOV. (2) Comparison of Coronagraph and STR attitude. (3) Observation with the Coronagraph camera of the OPS. (4) Comparison of FF sensor measurement and OPS measurement. (5) Combine all previous measurements to obtain calibration at the obtained distance. (6) Repeat the process at a different ISD. (7) Determine the components related with linear and angular calibration biases, by comparison of the calibration measurements at two different distances. The calibration process is described in [5] in mathematical form for determination of the achievable accuracy at calibration, that is obtained under certain assumptions.
5. Conclusion The PROBA-3 mission is intended to demonstrate in flight critical technologies required for the implementation of formation flying missions. The mission has been during the last year subject of several evolutions and analysis and is currently in the preliminary design phase. Within this paper a review of the mission and the associated formation flying demonstrations was performed, with some more detailed information on the formation flying organisation, basic design and selected equipments configuration. Finally it provides a brief presentation of the expected performance based on budget models and assumptions, and introduces the in flight precise calibration approach. The presented design that has been verified for feasibility and the preliminary results show good agreement with the expected results. References [1] PROBA-3 Mission Requirements Document, P3-EST-RS-1006, issue 2.3, July 2010. [2] PROBA-3 System Requirements Document, P3-EST-RS-1001, issue 2.3, July 2010. [3] E.S.A. Pointing Error Handbook ESA-NCR-502, issue 1, 19 February 1993.
46
J.S. Llorente et al. / Acta Astronautica 82 (2013) 38–46
[4] Error Budgets for Formation Flying Missions, NPD/5022/TD/TR/001, issue 1.0, 09 November 2007. [5] F.F.S. Pointing and Positioning Budgets, P3-SG-TN-3003, 2.1, March 2010. J. Salvador Llorente obtained MSc in Aeronautical Engineering at Universidad Polite´cnica de Madrid and MBA from ICADE (Madrid). He was responsible for development of the CLUSTER Attitude Determination and Dynamics Monitoring Flight Dynamics at ESA-ESOC (Darmstadt in Germany). He was associate professor at the Universidad Polite´cnica de Madrid for some years. Joined SENER on 1997, where he has been project manager for the AOCS of the Herschel–Planck missions, and later for the PROBA-3 mission, initially for the Formation Flying System and later for the overall mission. He also lead the AOCS group and the System Engineering initiatives at SENER. Alfredo Agenjo obtained MSc in Aeronautical Engineering at Universidad Polite´cnica de Madrid. Joined SENER as Systems Engineer on 2002, where he is especially dedicated to the area of GNC and AOCS for spacecrafts and other aerial vehicles. He has played a main role in the ACMS subsystem for the Planck spacecraft for ESA, starting in the phase B GNC algorithms design, up to the in-flight GNC commissioning in 2009. Alfredo Agenjo is currently responsible of the coordination of the design and validation of the Formation Flying System and GNC activities at SENER for the ESA PROBA-3 mission. Carmelo Carrascosa Sanz received a Masters in Aeronautical Engineering from the Polytechnic University of Madrid, Spain, in 1995. Since 1997 is working in GMV in different space missions. He has been involved in different technical areas; mission analysis, system engineering, flight dynamics, guidance, navigation algorithms based on GPS and spacecraft simulation tools. During 2005–2011 period, he was responsible for the Space Engineering Division of GMV. Recently, he is programme and business development executive in GMV, responsible for; business development and proposal elaboration, support to the different on-going programmes and promoting synergies of activities and technologies. Cristina de Negueruela Alema´n holds a Masters in Telecommunications Engineering by the University of Las Palmas de Gran Canaria and an MSc in Space Studies by the International Space University. She has worked at INTA, NASA and ESA in the fields of telecommunications, remote sensing, spacecraft systems engineering and mission analysis. She joined GMV in 2007 and was lead systems engineer and deputy project manager of PROBA-3 activities for over three years. She has since joined the Engineering and Studies division, where she is currently a project manager in the areas of mission analysis and simulators for Earth Observation missions.
Agnes Mestreau-Garreau is working at ESA/ ESTEC. After her engineering graduation, she joined ESA in 1992 and was involved in the development of the ENVISAT optical instruments. In 1994, she continues her professional experience in industry at EADSSODERN where she worked as optical engineer, head of optical section and finally as project manager of equipments. In 2004, she returned to ESA as team leader of assessment studies of future instruments and missions in the Concurrent Design Facility (CDF) team. Since 2009, she is the ESA Project Manager of the PROBA 3 mission. Alexander Cropp completed his undergraduate degree in electrical engineering at Imperial College, London in 1997, followed by a PhD in satellite engineering at the University of Surrey in 2001. He spent 7 years working for Surrey Satellite technology ltd (SSTL) as an AOCS engineer on a variety of projects including RapidEye, a 5-satelitte Earth observation constellation, and GIOVEA, the first Galileo in-orbit validation experiment satellite. He was also the AOCS team leader for 2 years, before joining ESA ESTEC in 2007. He is currently the ESA GNC lead on the PROBA3 project. Andrea Santovincenzo is presently Proba 3 System Engineer at ESA. Andrea Santovincenzo graduated in Aeronautics in 1990 at University of Rome (Italy). He started working as Propulsion and Thermal Engineer at Avio and moved after five years to ESTEC, the ESA technology centre in The Netherlands. He supported as Thermal specialist several ESA projects before becoming System Engineer at the Concurrent Design Facility (CDF) where he has been team leader of mission feasibility studies. He has also been System Engineer of the ESA projects Mars Sample Return, ExoMars, Mars Next and Iris in their early phases.