Showing papers by "European Space Operations Centre published in 2013"

Relay support for the Mars Science Laboratory mission

Abstract: The Mars Science Laboratory (MSL) mission landed the Curiosity Rover on the surface of Mars on August 6, 2012, beginning a one-Martian-year primary science mission. An international network of Mars relay orbiters, including NASA's 2001 Mars Odyssey Orbiter (ODY) and Mars Reconnaissance Orbiter (MRO), and ESA's Mars Express Orbiter (MEX), were positioned to provide critical event coverage of MSL's Entry, Descent, and Landing (EDL). The EDL communication plan took advantage of unique and complementary capabilities of each orbiter to provide robust information capture during this critical event while also providing low-latency information during the landing. Once on the surface, ODY and MRO have provided effectively all of Curiosity's data return from the Martian surface. The link from Curiosity to MRO incorporates a number of new features enabled by the Electra and Electra-Lite software-defined radios on MRO and Curiosity, respectively. Specifically, the Curiosity-MRO link has for the first time on Mars relay links utilized frequency-agile operations, data rates up to 2.048 Mb/s, suppressed carrier modulation, and a new Adaptive Data Rate algorithm in which the return link data rate is optimally varied throughout the relay pass based on the actual observed link channel characteristics. In addition to the baseline surface relay support by ODY and MRO, the MEX relay service has been verified in several successful surface relay passes, and MEX now stands ready to provide backup relay support should NASA's orbiters become unavailable for some period of time.

End-of-life disposal trajectories for libration point and highly elliptical orbit missions

Abstract: Libration Point Orbits (LPOs) and Highly EllipticalOrbits (HEOs) are often selected for astrophysics and solar terrestrial missions as they offer vantage points for the observation of the Earth, the Sun and the Universe. Orbits around L1and L2 are relatively inexpensive to be reached from the Earth and ensure a nearly constant geometry for observation and telecoms, in addition to advantages for thermal system design. On the other hand, HEOs about the Earth guarantee long dwelling times at an altitude outside the Earth’s radiation belt; therefore, long periods of uninterrupted scientific observation are possible with nearly no background noise from radiations. No guidelines currently exist for LPO and HEO missions’ end-of-life; however, as current and future missions are planned to be placed on these orbits, it is a critical aspect to clear these regions at the end of operations. Orbits about the Libration point or Earth-centred orbits with very high apogee lie in a highly perturbed environment due to the chaotic behaviour of the multi-body dynamics1; moreover, due to their challenging mission requirements, they are characterised by large-size spacecraft. Therefore, the uncontrolled s/c on manifold trajectories could re-enter to Earth or cross the protected regions. Finally, the end-of-life phase can enhance the science return of the mission and the operational knowledge base. In this paper, a detailed analysis of possible disposal strategies for LPO and HEO missions is presented as a result of an ESA/GSP study. End-of-life disposal options are proposed, which exploit the multi-body dynamics in the Earth environment and in the Sun–Earth system perturbed by the effects of solar radiation, the Earth potential and atmospheric drag. The options analysed are Earth re-entry, or injection into a graveyard orbit for HEOs, while spacecraft on LPOs can be disposed through an Earth re-entry, or can be injected onto trajectories towards a Moon impact, or towards the inner or the outer solar system, by means of delta-v manoeuvres or the enhancement of solar radiation pressure with some deployable light reflective surfaces. On the base of the operational cost, complexity and demanding delta-v manoeuvres, some disposal options were preliminary analysed and later discarded such as the HEO disposal through transfer to a LPO or disposal through Moon capture 2. The paper presents the dynamical models considered for each disposal design: in the case of HEOs the long term variation of the orbit is propagated through semi-analytical techniques 2, considering the interaction of the luni/solar perturbations with the zonal harmonics of the Earth’s gravity field. In the case of LPOs the Circular Restricted Three Body Problem 4 (CR3BP) or the full-body dynamics is employed for the Earth re-entry option and the transfer towards the inner or the outer solar system, while the coupled restricted three-body problem 5 is used for the Moon disposal option. The approach to design the transfer trajectories is presented. In order to perform a parametric study, different starting dates and conditions for the disposal are considered, while the manoeuvre is optimised considering the constraints on the available fuel at the end-of-life. Five ESA missions are selected as scenarios: Herschel, GAIA, SOHO as LPOs, and INTEGRAL and XMM-Newton as HEOs. For each mission the disposal strategies are analysed, in terms of optimal window for the disposal manoeuvre, manoeuvre sequences, time of flight and disposal characteristics, such as re-entry conditions or the hyperbolic excess velocity at arrival in case of a Moon impact. In a second step, a high accuracy approach is used for validating the optimised trajectories. Finally, a trade-off is made considering technical feasibility (in terms of the available on-board resources and ∆vrequirements), as well as the sustainability context and the collision probability in the protected regions. General recommendations will be drawn in terms of system requirements and mission planning.

Knowing More about Knowledge Management at ESA.

Abstract: During the last years, ESA has gathered an extensive experience in Knowledge Management (KM). As a knowledge intensive organization, ESA pursues the efficient management of its expertise and know-how. In particular, it was decided to start a corporate KM project consisting of several pilot projects. The selected approach was built on pillars summarized in these four keywords: “integrated” (interconnection of its parts), “pragmatic” (concrete solutions compatible with the corporate culture), “business” (linked to the core business) and “open” (input and best practices gathered inside and outside the Agency). This paper presents the activities carried out within the set of pilots and the relations among them. These pilot projects are: iKnow Portal, Competency Management Tool, Expertise Directory, Knowledge Capture and Handover, KM Officer and Lessons Learned Harmonization. The future of KM in ESA is a challenge aiming at proposing integrated solutions in an environment with different cultures and several existing individual solutions. The achievement of it will certainly provide a better leverage for the institutional KM.

Manoeuvring considerations for quasi-periodic trajectories

Abstract: The lunar vicinity attracts attention in particular for long-duration human exploration enabling complex missions to multiple destinations. A variety of orbits exist near the Lagrangian points L1 and L2 that can serve as nominal orbit for such mission scenarios. One type so-called quasi-periodic orbits are studied in this paper for this purpose. Those orbits are associated with frequencies, phases, and amplitudes. The existence and main characteristics of quasi-periodic orbits around the far-side Lagrangian point in the Earth-Moon system are studied. Stability directions and corresponding stable and unstable manifold branches are determined and compared. A parametric set in angular phase space is introduced for the orbits and their hyperbolic invariant manifolds. Solutions are identified to transfer spacecraft between quasi-periodic orbits and to compensate phase differences between spacecraft bringing together the parametric orbit and manifold representation. The proposed technique utilise the stable manifold allowing for single manoeuvre transfers. The transfers are classified and characterised. Two transfer scenarios within the orbit families are discussed with respect to future missions that have to cope with regular vehicle traffic, rendezvous and docking activities. In the first case, two spacecraft are separated from a halo orbit and distributed on a quasi-periodic orbit. In the second case, a given phase difference between two spacecraft is compensated and a target orbit is defined in which the spacecraft finally rendezvous. Parameter studies show the existence of those transfers and their strong dependence on the time when the manoeuvre is performed.

Optimal manoeuvring between quasi-periodic orbits

Abstract: In the past halo orbits were used for most of the spacecraft missions going to the Lagrange point regions. However, other natural motions exist near these points presenting some advantages compared to halos. Quasi-periodic motions on invariant tori are associated with frequencies and amplitudes and surround the halo and vertical Lyapunov orbits. In this paper main characteristics of quasi-periodic orbits around the far-side Lagrange point in the Earth-Moon system are discussed. Optimal manoeuvres are identified to vary properties (phases, amplitudes) of an orbit. The proposed techniques utilise the stable manifold allowing for single manoeuvre transfers. The separation of spacecraft from a periodic orbit and a rendezvous scenario are discussed with respect to future missions, that have to cope with regular vehicle traffic, rendezvous and docking activities. Fuel-optimal transfers from a halo to a quasi-periodic orbit are identified in order to separate spacecraft. A second scenario assumes two spacecraft with a given phase separation on a quasi-periodic orbit. A target orbit is defined in which the spacecraft rendezvous. Parameter studies show that phase and amplitude changes strongly depend on the time when the manoeuvre is performed.