TerraSAR-X / TanDEM-X formation control - first results from commissioning and routine operations

Kahle, Ralph; Schlepp, Benjamin; Kirschner, Michael

doi:10.7446/jaesa.0302.02

Cited by 11 publications

(5 citation statements)

References 4 publications

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“…The achieved relative control accuracy is 5-10 m (RMS) in the cross-track (2D) direction and the along-track control accuracy is <30 m (RMS). The control requirements of 28/200 m (RMS) in the cross-track/along-track directions are clearly overachieved paving the way for the acquisition and processing of a global digital elevation model within the upcoming years of TDX-TSX formation flight [14].…”

Section: Formation Reconfigurationmentioning

confidence: 99%

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The TerraSAR-X/TanDEM-X Formation Acquisition–from Planning to Realization

et al. 2012

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On June 21, 2010 the TanDEM-X satellite (TDX) was injected into orbit at 15,700 km distance from its twin satellite TerraSAR-X (TSX), which has been in orbit since 2007. Already one month later TDX acquired a formation with TSX in order to build up the first single-pass radar interferometer in space. Within three years of close formation flying with flexible baselines ranging from 150 m to a few kilometers the twin satellites will collect interferometric radar measurements for the generation of a global digital elevation model with unprecedented accuracy. This paper elaborates on the TDX pre-launch analysis performed in the fields of collision assessment during orbit injection and target formation acquisition. To avoid a critical close approach shortly after TDX separation, the risk of collision between the already flying TSX satellite and the newly injected elements (DNEPR upper-stage, gas dynamic shield, and TDX satellite) had to be carefully analyzed. Further, the paper discusses a fuel-saving formation acquisition strategy, for which the maneuver budget is analyzed as a function of launch day and launch injection accuracy. Finally, flight results are presented to illustrate the successful formation acquisition realized in July 2010 and the formation reconfiguration process from the 20 km wide formation into the 300-400 m close formation performed in October 2010. This reconfiguration marked the start of the bi-static TDX/TSX instrument operation.

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Section: Formation Reconfigurationmentioning

confidence: 99%

“…Regarding the nominal separation performance a Δe 0 amounts to about 8 km, demanding for a total maneuver size of approximately 4.4 m/s based on Eq. (14). Considering the combined SMA/eccentricity correction, the total velocity change required in the in-plane direction is then…”

Section: Coarse Maneuver Budgetmentioning

confidence: 99%

The TerraSAR-X/TanDEM-X Formation Acquisition–from Planning to Realization

et al. 2012

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“…Here, a small inclination offset in the TDX orbit is installed, causing different RAAN drifts to build up larger horizontal baselines over time without the need for expensive RAAN adjustment maneuvers. 8 The relative eccentricity vector, on the other hand, reflects the secular perigee variation of the individual satellites. It performs a rotation about the origin of the relative eccentricity vector plane with a period of roughly 100 days.…”

Section: B Orbit and Formation Control Conceptsmentioning

confidence: 99%

“…In along-track direction the navigation accuracy is on the 1 m level where 200 m control accuracy is required. 8 In order to process the DEM data-takes with highest accuracy, the TDX-TSX relative position has to be known with an accuracy of 1 mm (1D, RMS). The vector between the SAR antenna reference points of the two satellites, the so-called baseline, is determined with the FRNS software (Filter for Relative Navigation of Spacecraft) developed at DLR/GSOC in cooperation with the TU Delft.…”

Section: Relative Navigationmentioning

confidence: 99%

Flight Dynamics Operations of the Tandem-X Formation

Kahle¹,

Schlepp²,

Aida³

et al. 2012

SpaceOps 2012 Conference

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Since end of 2010 the German TerraSAR-X and TanDEM-X satellites are routinely operated as the first configurable single-pass Synthetic Aperture Radar interferometer in space. The two 1340 kg satellites fly in a 514 km sun-synchronous orbit. In order to collect sufficient measurements for the generation of a global digital elevation model and to demonstrate new interferometric SAR techniques and applications, more than three years of formation flying are foreseen with flexible baselines ranging from 150 m to few kilometers. As a prerequisite for the close formation flight an extensive flight dynamics system was established at DLR/GSOC, which comprises of GPS-based absolute and relative navigation and impulsive orbit and formation control. Daily formation maintenance maneuvers are performed by TanDEM-X to counterbalance natural and artificial disturbances. The paper elaborates on the routine flight dynamics operations and its interactions with mission planning and ground-station network. The navigation and formation control concepts and the achieved control accuracy are briefly outlined. Furthermore, the paper addresses nonroutine operations experienced during formation acquisition, frequent formation reconfiguration, formation maintenance problems and space debris collision avoidance, which is even more challenging than for single-satellite operations. In particular two close approaches of debris are presented, which were experienced in March 2011 and April 2012. Finally, a formation break-up procedure is discussed which could be executed in case of severe onboard failures.

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“…In-space testing and demonstration of the performance of autonomous rendezvous, formation flight, and docking strategies were conducted on the mission's engineering test satellite VII (ETS-VII) [18], experimental satellite systems (XSS) 10 and 11 [19,20], Orbital Express [21], TerraSAR-X add-on for digital elevation measurement (TanDEM-X) [22], and prototype research instruments and space mission technology advancement (PRISMA) [23]. NASA's demonstration for autonomous rendezvous technology (DART) showed how errors in the programming of the guidance, navigation, and control system can lead to a collision between the chaser and target, the depletion of propellant reserves, and subsequent mission failure [24].…”

Section: Introductionmentioning

confidence: 99%

Experimental Characterization of Inverse Dynamics Guidance in Docking with a Rotating Target

Wilde

Ciarcià

Grompone

et al. 2016

Journal of Guidance, Control, and Dynamics

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The performance of an inverse dynamics guidance and control strategy is experimentally evaluated for the planar maneuver of a "chaser" spacecraft docking with a rotating "target." The experiments were conducted on an airbearing proximity maneuver testbed. The chaser spacecraft simulator consists of a three-degree-of-freedom autonomous vehicle floating via air pads on a granite table and actuated by thrusters. The target consists of a docking interface mounted on a rotational stage with the rotation axis perpendicular to the plane of motion. Given a preassigned trajectory, the guidance and control strategy computes the required maneuver control forces and torque via an inverse dynamics operation. The recorded data of 150 experimental test runs were analyzed using two-way analysis of variance and post hoc Tukey tests. The metrics were maneuver success, vehicle mass change, maneuver duration, thruster duty cycle, and maneuver work. The results showed that the guidance and control algorithm provided robust performance over a range of target rotation rates from 1 to 4 deg ∕s. = maximum available torque, N · m T z = chaser torque about z axis of laboratory coordinate system, N · m t = maneuver time, s t D = total duration of docking maneuver, s t DA = duration of final docking approach, s t FF = duration of free-flight phase, s t f = final maneuver time, s W = maneuver work, J x C ; y C T = planar position vector of chaser center of mass in laboratory coordinate system, m x T ; y T T = planar position vector of the target center of rotation in laboratory coordinate system, m x; y; z = Cartesian coordinate system fixed in laboratory x 0 ; y 0 ; z 0 = Cartesian coordinate system fixed to chaser spacecraft simulator x 0 0 ; y 0 0 ; z 0 0 = Cartesian coordinate system fixed to target object γ = auxiliary maneuver targeting angle, rad Δm = chaser mass change, kg Δr = positioning tolerance for completion of docking maneuver, m Δt DA = extended maneuver time beyond nominal maneuver time, s Δt G = time step of the guidance algorithm, s ζ = auxiliary maneuver targeting angle, rad θ C = chaser orientation angle in relation to laboratory coordinate system, rad θ T = target orientation angle in relation to laboratory coordinate system, rad χ ij = thruster activity for thruster j at time step ∈ 0; 1, s ω T = target object angular rate, rad∕s

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TerraSAR-X / TanDEM-X formation control - first results from commissioning and routine operations

Cited by 11 publications

References 4 publications

The TerraSAR-X/TanDEM-X Formation Acquisition–from Planning to Realization

The TerraSAR-X/TanDEM-X Formation Acquisition–from Planning to Realization

Flight Dynamics Operations of the Tandem-X Formation

Experimental Characterization of Inverse Dynamics Guidance in Docking with a Rotating Target

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