Markus Markgraf

GPS for Microsatellites – Status and Perspectives

GPS receivers nowadays provide a well established system for tracking of spacecraft in low-Earth orbit (LEO). In addition, GPS receivers serve as instruments for geodetic and atmospheric research on an ever growing number of science missions. The paper provides an overview of existing GPS receivers for LEO satellites, covering both fully space qualified as well as commercial-off-the-shelf (COTS) systems. The needs of pure navigation receivers and advanced science instruments are independently discussed and directions for future systems are identified. Potential benefits of the new Galileo constellation are addressed and recommendations for future receiver developments are given.

GPS based prediction of the instantaneous impact point for sounding rockets

As part of the range safety operations during a sounding rocket launch, a real-time prediction of the instantaneous impact point (IIP) is performed to monitor the expected touch down point in case of a boost termination. Supplementary to traditional radar tracking, the IIP prediction is nowadays based on GPS navigation data, which offer an inherently higher accuracy and reduced data noise. To comply with the increased tracking performance, a consistent set of equations suitable for real-time computation of the approximate IIP is established. Aside from a consideration of gravitational forces, reference frame rotation and Earth curvature, the model can also account for drag during the ascent trajectory provided that a priori information on the ballistic properties of the launch vehicle is available. The algorithm is tested for a representative set of mission profiles and applied to GPS flight data of an Improved Orion rocket and a Maxus rocket launched at Esrange, Kiruna.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved. Zusammenfassung

GPS Based Attitude Determination for the Flying Laptop Satellite

This paper introduces the GPS based attitude determination system (GENIUS) onboard the university small satellite Flying Laptop. The attitude determination algorithm which is based on a Kalman Filter and processes single differences of the C/A-code and carrier phase measurements is shortly described. The algorithm uses the LAMBDA-method to resolve the integer ambiguities of the double differences of the carrier phase measurements. These resolved ambiguities are then used to fix the single difference ambiguities in the filter. The results of ground based tests and numerical simulations are introduced and the accuracy of the attitude determination algorithm is assessed.

Global Positioning System Sensor with Instantaneous-Impact-Point Prediction for Sounding Rockets

The development and verification of a dedicated global positioning system (GPS) sensor for sounding rocket missions is described. It is based on the hardware design of a terrestrial low-cost, single-frequency coarse/acquisition (C/A) code receiver but operates an enhanced software that has been specifically adapted for high dynamics applications. Besides the navigation and timing function provided by traditional GPS receivers, the prediction of the instantaneous impact point (IIP) has for the first time been integrated into the receiver software. Making use of a newly developed perturbed-parabolic trajectory model, the receiver can directly perform real-time IIP predictions with an accuracy that is compatible with operational ground software and is only limited by atmospheric forces. It is expected that the availability of onboard IIP prediction will both simplify existing range safety systems and contribute to a future increase of the onboard autonomy of sounding rocket missions. The overall receiver performance is demonstrated with hardware-in-the-loop simulations and actual flight data for representative mission profiles.

Autonomous and Precise Navigation of the PROBA-2 Spacecraft

PROBA-2 is the second technology demonstration mission within the project for onboard autonomy of the European Space Agency (ESA). Besides other instruments and sensors, the micro-satellite will be equipped with two new types of global positioning system (GPS) receivers. These will support the spacecraft operations and demonstrate recent advances in the field of autonomous real-time navigation and offline orbit determination for micro-satellites. The paper provides an overview of the key PROBA-2 navigation elements and discusses their scope and capabilities. Special attention is given to the Phoenix-XNS miniature GPS receiver and its embedded navigation function which are presented along with a discussion of the employed filtering and processing algorithms. The impact of PROBA-2 attitude changes on the GPS tracking is analyzed and the employed strategies for minimizing possible outages are presented. Hardware-in-the loop simulations in a signal simulator testbed are used to demonstrate the feasibility of 1 m level real-time navigation using a single-frequency GPS receiver and to demonstrate the overall robustness of the PROBA-2 onboard navigation.

GPS Orbit Determination for Micro-Satellites – The PROBA-2 Flight Experience

The PROBA-2 microsatellite of the European Space Agency (ESA) is equipped with a novel single frequency global positioning system (GPS) receiver, which combines low resource requirements with a high navigation performance. Aside from supporting the spacecraft and mission operations, the Phoenix GPS receiver on PROBA-2 is used to study realtime and offline navigation using single-frequency GPS measurements. A 1 m accuracy is targeted for both applications which has so far been the domain of dual-frequency receivers. Following a mission overview, the achievable performance for ground-based orbit determination and real-time onboard navigation is discussed for different processing concepts based on flight data collected during the first half year of mission operations. It is shown that a 1 m or better accuracy can be achieved in either case, despite sub-optimal GPS tracking conditions induced by the mission specific attitude profile. Besides self-consistency checks and comparisons with independent GPS based orbit determination solutions, the accuracy is evaluated using satellite laser ranging (SLR) measurements as an external reference. The results show that single-frequency GPS tracking is sufficient to meet the navigation requirements of even advanced remote sensing missions in low Earth orbit, if their accuracy potential is properly exploited.

A GPS TRACKING SYSTEM WITH ONBOARD IIP PREDICTION FOR SOUNDING ROCKETS

The development and verification of a dedicated GPS sensor for sounding rocket missions is described. It is based on the hardware design of a terrestrial low cost L1 C/A code receiver but operates an enhanced software that has been specifically adapted for high dynamics applications. Besides the navigation and timing function provided by traditional Global Positioning System receivers, the prediction of the instantaneous impact point (IIP) has for the first time been integrated into the receiver software. Making use of a newly developed perturbed-parabolic trajectory model the receiver can directly perform real-time IIP predictions with an accuracy that is compatible with operational ground software and is only limited by atmospheric forces. It is expected that the availability of onboard IIP prediction will both simplify existing range safety systems and contribute to a future increase of the onboard autonomy of sounding rocket missions. The overall receiver performance is demonstrated with hardware-in-theloop simulations and actual flight data for representative mission profiles.

Radiation testing of commercial-off-the-shelf GPS technology for use on low earth orbit satellites

To assess the use of four types of commercial-of-the-shelf (COTS) GPS receivers under space radiation environment, Total Ionizing Dose (TID) radiation tests have been performed with a 60Co gamma-ray source.

Results of the GNSS receiver experiment OCAM-G on Ariane-5 flight VA 219

The fifth Automated Transfer Vehicle was launched on 29 July 2014 with Ariane-5 flight VA 219 into orbit from Kourou, French Guiana. For the first time, the ascent of an Ariane rocket was independently tracked with a Global Navigation Satellite System (GNSS) receiver on this flight. The GNSS receiver experiment OCAM-G was mounted on the upper stage of the rocket. Its receivers tracked the trajectory of the Ariane-5 from lift-off until after the separation of the Automated Transfer Vehicle. This article introduces the design of the experiment and presents an analysis of the data gathered during the flight with respect to the GNSS tracking status, availability of navigation solution, and navigation accuracy.

GSOC's Scatterometry GNSS receiver for ocean remote sensing: Design and initial results

The department of Space Flight Technology at the DLRs German Space Operations Center (GSOC) is currently developing a new Reflectometry/Scatterometry GNSS receiver for ocean remote sensing. This new instrument is being designed to be used in several conditions ranging from terrestrial applications to spaceborne GNSS experiments. One of its key features is the ability to compute at different scales a Delay Doppler Map (through time multiplexing the doppler space) on one reflection event at a time using a 3×3 fully digitally steerable antenna array. Another feature is to perform digital beamforming of the incoming downconverted digitized GPS signal after IF carrier and C/A demodulation. This significantly reduces the technical requirements and costs of the analog RF front-end chain and the computation bandwidth at the FPGA respectively. A prototype version of this Scatterometry GNSSR receiver is being developed as a proof of concept, using the Namuru II board as development platform.