We present results of several years of research and data processing aimed at modelling the Mars gravity field and its longest wavelength time variations. The new solution includes tracking data from Mars Global Surveyor (MGS) from 1998 to 2006 (end of mission) and from Mars Odyssey from 2002 to the spring of 2008; this is the longest analyzed data set from these two orbiter missions as compared to previous works. The new model has been obtained by a team working in Europe, independently from the works of groups at NASA Jet Propulsion Laboratory (JPL) and Goddard Space Flight Center (GSFC), also with totally independent software. Observations consist in two and three-way Doppler measurements (also one way for MGS), and range tracking data collected by the Deep Space Network and have been processed in 4 day arcs, taking into account all disturbing forces of gravitational and non-gravitational origins; for each arc the state vector, drag and solar pressure model multiplying factors, and angular momentum dump parameters are adjusted. The static field (MGGM08A) is represented in spherical harmonics up to degree and order 95 and is very close to previously published models (in terms of spectral components and also over specific features); correlations with the global Mars topography are established and apparent depths of compensation by degree are derived. Lumped zonal harmonics of degree two and three are solved for every 10 days, exhibiting variations in line with previous results (including authors' ones); the work also shows the difficulty of finding clean signatures (annual and semi-annual) for the zonal coefficient of second degree. The k2 Love number is also derived from the ensemble of data, as well as from subsets of them; values between 0.110 and 0.130 are found, which are consistent with the existence of a Martian fluid core of significant radius.

The front steering (FS) launcher is one of two concepts that have been considered for the ITER electron cyclotron heating upper launcher by the European Union. During the development of a detailed conceptual design, the team involved with the FS launcher project listed all of the critical issues associated with installing an FS launcher in the ITER upper port, and then work was concentrated on providing a solution to each of the critical design issues. A similar procedure was Performed for the alternative launcher option (remote steering launcher). These actions helped the ITER International Team evaluate the two systems and then choose a final optimum launcher. This evaluation occurred at the end of 2005, with both systems having equivalent reliability, but the FS offered significant enhancement in the physics performance. These differences led ITER-IT to select the FS launcher as the reference design. The goal of this paper is to provide a generalized review of the critical design issues and their solutions as they pertain to the FS launcher. In addition, the overall design and performance of the FS launcher is given along with a brief description of an extended performance launcher design that relaxes the engineering constraints, while increasing the physics capabilities.

The ITER electron cyclotron (EC) upper port antenna (or launcher) is nearing completion of the detailed design stage and the final build-to-print design stage will soon start. The main objective of this launcher is to drive current locally to stabilize the neoclassical tearing modes (NTMs) (depositing ECCD inside of the island that forms on either the q = 3/2 or 2 rational magnetic flux surfaces) and control the sawtooth instability (deposit ECCD near the q = 1 surface). The launcher should be capable of steering the focused beam deposition location to the resonant flux surface over the range in which the q = 1, 3/2 and 2 surfaces are expected to be found for various plasma equilibria susceptible to the onset of NTMs and sawteeth. The aim of this paper is to provide the design status of the principal components that make up the launcher: port plug, mm-wave system and shield block components. The port plug represents the chamber that provides a rigid support structure that houses the mm-wave and shield blocks. The mm-wave system comprises the components used to guide the RF beams through the port plug structure and refocus the beams far into the plasma. The shield block components are used to attenuate the nuclear radiation from the burning plasma, protecting the fragile in-port components and reducing the neutron streaming through the port assembly. The design of these three subsystems is described; in addition, the relevant thermo-mechanical and electro-magnetic analyses are reviewed for critical design issues.

The purpose of the ITER ECRH upper port antenna (or launcher) will be to drive current locally to stabilise the NTMs (depositing ECCD inside of the island that forms on either the q=3/2 or 2 rational magnetic flux surfaces) and control the sawtooth instability (deposit ECCD near the q=1 surface). The launcher should be capable of steering the focused beam deposition location to the resonant flux surface over the range in which the q=1, 3/2 and 2 surfaces are expected to be found, for the various plasma equilibria susceptible to the onset of NTMs and sawteeth. ITER’s present reference design uses a front steering (FS) concept, with the moveable mirror close to the plasma. Two separate mirrors are used to decouple the focussing and steering aspects resulting in an optimised optical configuration providing a well focused beam over a large steering range. The launcher is capable of steering eight 2MW beams in all of the four allocated upper port plugs. Details of the FS launcher design relating to physics performance, mm-wave optical design and steering mechanism design are discussed in this paper. Introduction ITER is planned to have 24MW of installed EC power, which will be launched into the plasma via either the equatorial (EL) or upper (UL) launchers [1,2]. A remote controllable switch deviates the power to either launcher depending on the physics requirements as defined in the ITER Project Integration Document [3]. Initially, the four ports of the UL were dedicated to the single application of stabilising the neoclassical tearing modes [4] that could occur on either the q=3/2 or 2 flux surfaces in the relevant scenarios 2, 3a and 5. This translates into a steering range accessing 0.52 ≤ ρtor ≤ 0.85, where ρtor being the square root of the normalized toroidal flux. This steering range provided an adequate coverage to accommodate the uncertainties of the flux surfaces that will one day be realised in ITER. The single port of the EL was dedicated to all other physics applications (sawtooth control, central heating and current drive) as illustrated in figure 1a. This partitioning of applications had several shortcomings, mainly because the single port EL was given the majority of the physics applications, while the four port UL was dedicated to the single task of NTM stabilistation. The EL required a relatively large steering range accessing from on axis to ρtor ~ 0.55. Due to geometrical limitations the EL could not deposit the full power over the entire steering range and resulted in less than 100% full pass absorption in the outer 20% of its steering range [5] (see red band regions of figure 1a) FIGURE 1. (a) The capabilities of the EC system based on the PID (<2007) and (b) that offered with the launcher synergy. Note that the vertical axis corresponds to ρpol (square root of the poloidal flux) and not ρtor. A revision of the physics objectives was proposed in Ref. [6] that partitioned the applications of each launcher based on the need for either a narrow current deposition (control of sawtooth [7] and NTMs) as provided by the UL or bulk current drive and central heating as provided by the EL. To achieve this, the UL had to have an increased steering range to access the q=1 surfaces, or into ρtor ~ 0.3. This alleviates the EL of the required large steering range required (to access the q=1) and permits the launcher to be modified for better central coverage and the potential for counter ECCD and pure heating capabilities as outlined in Ref. [6] and illustrated in figure 1b. Note that the counter ECCD is useful for control of the q-profile in advanced (scenario 3a) and reverse shear (scenario 4) scenarios [8] as well as combining with co-ECCD to provide pure heating with no net current drive as has been demonstrated on ASDEX-Upgrade [9]. Note that the EC system is the only heating and current drive source on ITER that can provide either co-ECCD, counter-ECCD or pure heating, simultaneously with the capability to vary the deposition location and all via external actuators. These functions provide minor modifications to the EL, while increasing the flexibility of the EC systems to be applicable to a greater number of plasma scenarios. The key issue in achieving the full capabilities of the EC system 8Ass illustrated in figure 1b) is to increase the steering range of the UL, which has been achieved in the enhanced performance launcher (EPL) design [2]. The two steering mirrors of the UL are directed to two overlapping regions in the plasma cross section, 0.3 ≤ ρtor ≤ 0.8 for the upper steering mirror (USM) and 0.55 ≤ ρtor ≤ 0.85 for the lower steering mirror (LSM) as illustrated in figure 2. The overall steering range of each mechanism is actually decreased to reduce the induced stresses and prolong the steering mechanism longevity prior to the onset of cyclic fatigue. Note this design was prompted by ITER-IT request that the front steering launcher design use four upper ports (even though only three ports are required for steering the 24 beams) with the fourth port used to increase the launchers functionality and reduce the engineering constraints, both of which have been achieved at the cost of an additional fourth port to the European parties procurement package. The enhanced performance offered by the revision of the UL has now been incorporated in the revised PID [10]. FIGURE 2. The EPL has the range of the two steering mirrors (USM and LSM) scanning two different regions such that a larger region in the plasma is accessible. Each steering mirror can inject up to 13.3MW, the full 20MW can be deposited in the overlap region. Enhanced Performance UL design A simplified view of the current FS launcher design is shown in Figure 3. Eight circular HE11 waveguides (φWG=63.5mm, similar to the waveguide used in the transmission line) enter the port plug entrance on the right (note that there are four waveguides superimposed in this poloidal cut). Prior to the closure plate a diamond window and an in-line isolation valve is placed to provide the primary tritium barrier. The waveguide continue after the closure plate to a set of miter bends in a ‘dog-leg’ configuration used to angle the 8 beams (both in toroidal and poloidal directions) to two focusing mirrors with the incident beams partially overlapping in both toroidal and poloidal directions. The reflected beams are then directed downward to two flat steering mirrors, which redirect the beams into the plasma with a toroidal injection angle of β≈20o. FIGURE 3. The layout of the principle mm-wave components of the upper launcher. The deposition region of the two UL steering mirrors are displaced so that the upper steering mirror (USM) access further inward providing access to the inner NTMs and q=1 surfaces covering a range of ~0.3≤ρtor≤~0.8, while the lower steering mirror (LSM) access the outer NTMs covering a range of ~0.55≤ ρtor ≤0.85. An additional switching system is used prior to the port entrance that can deviate the beams coming from the 24 gyrotrons to either the 16 entrances associated with the USM or the 16 entrances with the LSM depending on the physics requirements. The optical design is optimized [11] so that the beam from the USM projects a slightly larger beam waist (29mm) further into the plasma to compensate for the longer path length as compared to the LSM with a waist of 21mm. This process was performed with dedicated beam tracing scans system [5,12] to insure a narrow and peaked jCD profile over the entire steering range. Note that four beams are incident on a single focusing and steering mirror, the overlapping of the beams permit the largest beam for a finite focusing mirror size within the confined space of the blanket shield module (BSM). The space in the BSM is shared between the mm-wave components and shield blocks to protect the components and port plug from the neutron flux. Nuclear analysis of the EPL has demonstrated that there is adequate shielding to protect both the critical components of the launcher and neighboring components [13]. Alternative configurations are under investigation to either improve the physics performance of the launcher, reduce complexity and/or to enhance maintenance access. For example, relocating the valves and windows located several meters from the closure plate alleviates the congestion at the port plug entrance and enhances the maintenance access to these components. Also replacing the mitre bends with free space mirrors improves the focusing of the beams for improved NTM stabilization efficiencies, while reducing the overall cost and complexity of the optical systems. These design modifications are under consideration for the next optical design of the launcher, which is expected for the end of 2007. Steering Mechanism design

Several modern solutions of the Mars gravity field have already been obtained from the Mars Gobal Surveyor (MGS) mission, by different NASA teams working at GSFC and at JPL, which also have shown that degree two and three lumped zonal coefficients exhibit time variations related to the seasonal cycle of carbon dioxide exchange between the planet surface and its atmosphere. A new solution of these time variations has been obtained by a third team working in Europe with a totally independent software. Five years of one and two way Doppler, and range tracking data collected by the Deep Space Network have been processed in three day arcs, taking into account all disturbing forces of gravitational and non gravitational origins; for each arc the state vector, drag and solar pressure model multiplying factors, and angular momentum dump parameters are adjusted. The zonal harmonics up to degree five and the k2 Love number are solved for. The zonals are estimated every ten days, or every thirty days in some variants, with a priori uncertainties either on their values or on their changes. The lumped C20 and C30 coefficients show similar patterns as in the anterior US solutions, also in accordance with the variations estimated from the output of a Global Circulation Model and from the HEND instrument on board Mars Odyssey. Annual and semiannual terms have been derived for comparisons and future evaluation in terms of global constraints put on such planetary mass transfer. Finally the values found for k2 (in the range 0.10 - 0.15 depending on the solution strategy) are discussed.

The ITER ECH heating and current drive system delivers 24MW (170GHZ), which can be directed to either the equatorial (EL) or upper (UL) port launching antennas depending on the desired physics application. The UL design uses two front steering (FS) mirrors that sweep eight beams in a poloidal plane providing co-ECCD over the outer half of the plasma cross section. A novel frictionless, backlash-free steering mechanism has been developed for an increased reliability and providing a steering mirror rotation of up to +/- 7 degrees ( +/- 14 degrees for RF beam). The principle aim of the UL is to stabilize the neoclassical tearing modes (NTM) and (by extending the steering range) access the q=1 flux surface for control of the sawtooth oscillation. Increasing the range of the UL can relax the EL steering range, and optimize the EL for enhanced performance with an optimized central deposition and potential for counter ECCD. This paper will summarize the present UL design status along with the proposed design modifications to the UL for enhanced performance and increased reliability.

In the absence of a network of geophysical observatories on Mars, experiments in Martian geodesy have to be conducted by analyzing radio science data from space probes. The orbit of a spacecraft is usually determined from a radio link with the Earth but can be improved to a much higher precision from the radio link with a lander on the Martian surface. A radio science package is included in the future Martian lander GEP (Geophysical Experiment Package), which might take part in the future ExoMars mission. A mission to Mars with an orbiter and a lander will thus provide us with radio science data of very high quality, which can be applied to geophysics in several ways. On the one hand radio science tracking data can be applied to the study of the gravity field of Mars, especially the time-variable gravity, which yields insight into the deep interior and the atmosphere dynamics. Tracking more than one orbiter simultaneously can serve to improve the determination of the lowest-degree time-variable zonal coefficients of the gravity field (J2, J3, J4, and J5) and the tidal response of Mars (the tidal Love number k2). Spacecrafts around Mars have been mostly in high inclination orbits (Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter are at inclination I=93 degree, Mars Express at I=87 degree), limiting the ability to properly separate the contribution of each coefficient Ji. A new mission with a low orbital eccentricity and a favorable orbital inclination would allow decorrelating J2 and J3 from the higher-degree harmonic coefficients of the gravity field. Such an orbit will therefore better extract time-variable gravity and improve our knowledge of the atmosphere and interior of Mars. Furthermore, an orbiter reaching a low altitude at pericenter (below 200 km) will improve our knowledge of the local structure of the crust and lithosphere, by way of the study of static gravity anomalies. On the other hand the orbiter can be used to determine the rotation variations of Mars. The combination orbiter-lander offers a more interesting geometry with three radio links (lander-Earth, lander-orbiter, orbiter-Earth) than with an orbiter (or lander) alone, so that more accurate values of the Martian rotation parameters can be obtained. Since rotation parameters (precession, nutation, polar motion, and length-of-day variations) are directly linked to the state and dynamics of the core and deep mantle, radio science with an orbiter and a lander offers a wonderful opportunity to elucidate unresolved questions about the deep interior of Mars as well as its atmosphere. The combined analysis of radio science data from the orbiter and from the lander will allow us to go

The seasonal carbon dioxide (CO2) cycle on Mars results in a time‐variable global redistribution of mass. These large‐scale variations are associated with changes in the gravity field, mainly in the two zonal gravity coefficients and , which have been recently evaluated from Doppler tracking data of the Mars Global Surveyor (MGS) spacecraft. In the present study, we calculated these variations from the mass redistribution obtained from outputs of two general circulation models (GCM) as well as from CO2 thickness measurements by the High Energy Neutron Detector (HEND) instrument on board the Mars Odyssey spacecraft and compared them to the observations. Tracking observations provide one of the most direct measures of the global‐scale atmospheric mass cycle. However, the associated uncertainties are relatively large, partly because the low‐degree zonals obtained from a single orbiter tracking analysis are contaminated by higher‐degree harmonics which are shown to have nonnegligible seasonal variations. Thus we investigated possibilities to improve the determination of the time‐variable gravity field by means of simulated geodesy experiments. Additional radio tracking of a second spacecraft with suitable orbital characteristics was shown to be able to separate the higher‐degree geodetic signatures. Radio links between landers on the Martian surface and a near‐polar orbiter can further better estimate especially the even zonals.

The objectives of a geodesy experiment performed on the basis of a network of landers, such as NEIGE (Netlander Ionosphere and Geodesy Experiment) are to measure variations of Mars' orientation and rotation in space with a precision of a few centimeters over annual and sub-annual periods. The lander positions are not well known upon landing, depending on the technical solution chosen for the entry-descent-landing phase, and thus need to be accurately determined to achieve the scientific objectives of a geodetic experiment. We performed numerical simulations of the NEIGE experiment to evaluate our ability to recover the lander positions from Doppler shifts measurements between an orbiter around Mars and those landers, with a precision of a few centimeters.

The Martian global‐scale CO2 seasonal cycle implies temporal variations in both the zonal gravity coefficients, such as 20, and in the rotation rate. To estimate the ability to detect simultaneously these two main geodetic signatures, a new approach based on a Network Science Experiment is investigated. We have numerically simulated the two types of Doppler signals involved, accurate orbiter tracking from the Earth and Martian lander tracking from the orbiter, by using a model of both the rotation variations and the seasonal variations of 20. Then, through a least square process, we have jointly adjusted the rotation and 20 parameters from an a priori knowledge. Our results show that it is possible to decorrelate 20 from all rotation parameters. We obtain an accurate adjustment of the 20 variations and a precision at the level of a few milliarcseconds for the estimation of the rotation rate variations.