Trajectory Design and Optimization for LEO Satellites in Formation to Observe GEO Satellites’ Beams

This paper presents the methods and results for the trajectory design and optimization for the low earth orbit (LEO) satellites in formation to observe the geostationary orbit (GEO) satellites’ beams. The background of the trajectory design mission is the 9th China Trajectory Optimization Competition (CTOC9). The formation is designed according to the observation demands. The flying sequence is determined by a reference satellite using a proposed improved ephemeris matching method (IEMM). The formation is changed, maintained and transferred following the reference satellite employing a multi-impulse control method (MICM). Then the total observation value is computed by propagating the orbits of the satellites according to the sequence and transfer strategies. Based on the above methods, we have obtained a fourth prize in the CTOC9. The proposed methods are not only fit for this competition, but can also be used to fulfill the trajectory design missions for similar multi-object explorations.

Orbit determination and time synchronization for BDS-3 satellites with raw inter-satellite link ranging observations

To provide competitive global positioning and timing services under the condition that monitoring stations are confined to Chinese territory,inter-satellite link(ISL)technology is used by the third-generation BeiDou Navigation Satellite System(BDS-3).The ISL,together with the dual one-way links between satellites and anchor stations,may enable autonomous navigation for BDS-3.In this paper,we propose a general observation model for orbit determination(OD)and time synchronization(TS)directly using non-simultaneous observations,such as raw ISL pseudoranges.With the proposed model,satellite orbits,clocks,and hardware delay biases of ISL equipment can be determined simultaneously by jointly processing inter-satellite one-way pseudorange data and observation data from ground monitoring stations.Moreover,autonomous OD and TS are also achievable with one-way pseudorange data from anchor stations and satellites.Data from eight BDS-3 satellites,two anchor stations,and seven monitoring stations located in China were collected to validate the proposed method.It is shown that by jointly processing data from the ISL and seven monitoring stations,the RMS of overlap orbit differences in radial direction is 0.019 m,the overlap clock difference(95%)is 0.185 ns,and the stability of the estimated hardware delay biases for each satellite is greater than 0.5 ns.Compared with the results obtained with the seven stations,the improvements of orbits in radial direction and clocks are 95.7%and 90.5%,respectively.When the hardware delay biases are fixed to predetermined values,the accuracies of orbits and clocks are further improved.By jointly processing pseudoranges from the satellites and the two anchor stations,the RMS of overlap orbit differences is 0.017 m in the radial direction,and the overlap clock difference(95%)is 0.037 ns.It has also been demonstrated that under the condition of one-way ranging links,the accuracies of orbits and clocks obtained by the above two modes are still significantly better than those obtained by using the data from the monitoring stations alone.

Investigation of Mesoscale Available Potential Energy Spectra in a Simulated Tropical Cyclone

We investigated the moist mesoscale available potential energy(APE)spectra and corresponding spectral budgets of an idealized tropical cyclone(TC).The APE is defined with respect to a dry air mass using a modified potential temperature.For wavelengths below 500 km,the mesoscale APE spectra show a consistent quasi-linear shape and a–5/3 spectral slope in the troposphere and lower stratosphere during the mature period of the TC.The spectral APE budget in the troposphere is dominated by diabatic and energy conversion processes.The mesoscale APE is forcefully injected by the diabatic effect and immediately partially converted to other forms of energy by the buoyancy effect.The diabatic effect contains a positive contribution from the heating effect and a negative contribution from the dehumidifying effect,which weakens the heating effect by about 16%.The energy conversion tends toward the horizontal kinetic energy at larger scales and toward the gravitational potential energy of the total moist species at smaller scales.In the lower stratosphere,the mesoscale APE is primarily deposited by the three-dimensional divergent effect and removed by nonlinear interactions;however,the effect of the energy conversion is noisy.The lower troposphere and lower stratosphere are governed by clear downscale and upscale APE cascades,respectively,whereas the mid-and upper tropospheric mesoscale APE spectra undergo more complex cascade processes.