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Performance-based funding provides powerful incentives to scale up the fight against HIV, TB, and malaria, argues a team of authors from the Global Fund.

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This analysis addresses the problem of constructing uncertainties in initial and final satellite orbital state vectors that are dynamically consistent in Lambert's boundary-value problem, given uncertainties in the initial and final position vectors. The structure of the general nonlinear problem is discussed in terms of transformations of the probability density functions of the given positions. For the linear (first-order) variational version of the problem, the covariance matrices of the state variations are presented in explicit terms of the covariance matrix of the given position variations and partitions of the state transition matrix of the nominal orbit. Equivalence is demonstrated between the linear variational results, which involve no iteration, and a weighted batch least-squares differential-correction solution of the orbit determination problem. To illustrate the utility of the working formulas in the linear variational problem, two approaches are taken: 1) an analytic approach to solve directly for the covariance terms, based on linearized dynamics, and 2) a numerical Monte Carlo-based approach that generates a sample covariance. The numerical results for state covariance from the analytic approach agree with results obtained by batch least-squares differential correction, and both agree with results from the Monte Carlo approach to within differences explainable by the limitations of sampling.

An experiment is described in which the performance of the Naval Space Command Fence Receiver Suite is evaluated using satellite laser ranging. Fence measurement accuracy and precision is presently assessed based on cataloged orbits, which are not suf ciently accurate for rigorous calibration and trend identi cation. Satellite laser ranging is a well-known high-precision data type, which can provide submeter reference positions routinely. Two methods of sensor evaluation are investigated. One is an ephemeris-based approach, where a truth reference orbit is determined from laser ranging data from a number of different satellites at different altitudes. Fence-based residuals are then computed from this truth. The second is a geometric method, which computes satellite positions directly using ranging data and angle data from the telescope. A mathematical treatment of the geometric dilution of precision for both methods is included in the discussion. The overall experiment showed that the fence sensor suite is operating to within 14-17 times its noise oor of 10 ¹rad at zenith. We believe that this is the most extensive measurement of the fence performance utilizing an external and independent data type, and due to the precision of the data type, its overall response and error trends are identi ed.

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