In-orbit Operation Research Articles

PASSIVITY BASED ON ENERGY TANK FOR CARTESIAN IMPEDANCE CONTROL OF DLR SPACE ROBOTS WITH FLOATING BASE AND ELASTIC JOINTS

This paper presents a control structure for orbital servicing mission of CEASAR robotic arm developed by German Aerospace Center (DLR). In order to reduce mass the CEASAR arm is equipped with Harmonic-Drives with high ratio which unfortunately lead to high joint elasticity and high motor friction and have to be considered in controller design for successful manipulator in-orbit operations. Therefore, in this control structure, for high tracking control a cascaded position controller based on state feedback control structure with observer-based friction compensation and for safe interaction control with the environment a Cartesian impedance controller is used. The proposed control methods are very efficient and practicable. Furthermore, they are very robust with dynamic parameter uncertainties, coupling dynamics, and can simultaneously provide good results in term of the position accuracy and dynamic behavior. Simulation results validate practical efficiency of the controllers.

In-orbit operation of an atomic clock based on laser-cooled 87Rb atoms

Atomic clocks based on laser-cooled atoms are widely used as primary frequency standards. Deploying such cold atom clocks (CACs) in space is foreseen to have many applications. Here we present tests of a CAC operating in space. In orbital microgravity, the atoms are cooled, trapped, launched, and finally detected after being interrogated by a microwave field using the Ramsey method. Perturbing influences from the orbital environment on the atoms such as varying magnetic fields and the passage of the spacecraft through Earth’s radiation belt are also controlled and mitigated. With appropriate parameters settings, closed-loop locking of the CAC is realized in orbit and an estimated short-term frequency stability close to 3.0 × 10−13τ−1/2 has been attained. The demonstration of the long-term operation of cold atom clock in orbit opens possibility on the applications of space-based cold atom sensors.

In-orbit verification of microwave humidity sounder spectral channels coregistration using the moon

In-orbit verification of the coregistration of channels in a scanning microwave or infrared radiometer can in principle be done during normal in-orbit operation, using the regular events of lunar intrusion in the instrument cold space calibration view. A technique of data analysis based on best fit of data across lunar intrusions has been used to check the mutual alignment of the spectral channels of the microwave humidity sounder (MHS) instrument. MHS is a cross-track scanning radiometer in the millimeter-wave range flying on EUMETSAT and NOAA polar satellites, used operationally for the retrieval of atmospheric parameters in numerical weather prediction and nowcasting. This technique does not require any special operation or maneuver and only relies on the analysis of data from the nominal scanning operation. The coalignment of sounding channels and window channels can be evaluated by this technique, which would not be possible using Earth landmarks, due to the absorption effect of the atmosphere. The analysis reported shows an achievable accuracy below 0.5 mrad against a beam width at 3 dB and spatial sampling interval of about 20 mrad. In-orbit results for the MHS instrument on Metop-B are also compared with the prelaunch instrument characterization, showing a good correlation.

Using Geostationary Ocean Color Imager to Map the Diurnal Dynamics of Suspended Sediment Concentration in Estuary Area

ABSTRACT Kang, Y.Y.; Ding, X.R., and Ge, X.P., 2018. Using Geostationary Ocean Color Imager to map the diurnal dynamics of suspended sediment concentration in estuary area. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 101–105. Coconut Creek (Florida), ISSN 0749-0208. Geostationary ocean color imager (GOCI), the first in-orbit operation of the geostationary satellite ocean color sensor, provides hourly observations of the covered area. Quick atmospheric correction (QUAC) algorithm was used for GOCI data to remove the atmospheric effects and an artificial neural network (ANN) inversion model (multi-layer feed forward neural network) was proposed to derive suspended sediment concentration (SSC) via GOCI in coastal waters of Yongjiang estuary, China. This model has three parts those are the input layer with eight nodes, two hidden layers with seventeen nodes in...

Validation results of NmF2 and hmF2 derived from ionospheric density profiles of GNOS on FY-3C satellite

The first Global Navigation Satellite System Occultation Sounder (GNOS) which is compatible of both BeiDou System (BDS) and Global Positioning System (GPS) was successfully launched into orbit onboard the FengYun 3 C satellite (FY-3C) on September 23, 2013, and it has already gathered a large amount of ionosphere radio occultation (RO) data so far. However, the detailed analysis and validation of GPS ionosphere RO data have not been done up to now. Therefore, this paper discusses the configuration of the FY-3C GNOS, the methods and results of GPS ionosphere occultation processment, the quality analysis of the GPS ionosphere RO products, and the precision consistency between the GNOS GPS ionosphere RO product and ionosonde data. The peak electron density (NmF2) correlation coefficient is 0.97, the corresponding standard deviation is 16.08%. The peak value altitude (hmF2) correlation coefficient is 0.89, and the corresponding standard deviation is 23.79 km. The in-orbit operation of GNOS provides a basis data set for the monitoring, forecasting and research of ionosphere’s space weather.

Discussions on attitude determination and control system for micro/nano/pico-satellites considering survivability based on Hodoyoshi-3 and 4 experiences

The recent advancement of micro/nano/pico-satellites technologies encourages many universities to develop three axis stabilized satellites. As three axis stabilization is high level technology requiring the proper functioning of various sensors, actuators and control software, many early satellites failed in their initial operation phase because of shortage of solar power generation or inability to realize the initial step of missions because of unexpected attitude control system performance. These results come from failure to design the satellite attitude determination and control system (ADCS) appropriately and not considering “satellite survivability.” ADCS should be designed such that even if some sensors or actuators cannot work as expected, the satellite can survive and carry out some of its missions, even if not full. This paper discusses how to realize ADCS while taking satellite survivability into account, based on our experiences of design and in-orbit operations of Hodoyoshi-3 and 4 satellites launched in 2014, which suffered from various component anomalies but could complete their missions.

Design, fabrication and space suitability tests of wide field of view, ultra-compact, and high resolution telescope for space application.

We report on the design, manufacture, and testing of an ultra-compact telescope for 16 unit (16U) CubeSats for Earth and space observation. This telescope provides 1 arcsec resolution at a 2.9 degree field of view. Dimensions are optimized to 230 × 230 × 330mm3 with a mass of less than 6kg including support structure. Our catadioptric 5-element design consists of a full-aperture corrector, a Mangin primary mirror (PM), a secondary mirror (SM), and a 2-lens field corrector. The focal length is 745mm, and squared-circular aperture has an equivalent diameter of 241mm. The designed modulation transfer function (MTF) is 0.275 for the entire unit including baffles at a Nyquist frequency of 161 cycles/mm for the 450-800nm band. As one of the distinguishing features of our state-of-the-art design, all optical surfaces are spherical to simplify adjustment. For the best thermal stability, all optical elements are produced from fused silica. We describe the details of design, adjustment, and laboratory performance tests for space environments in accordance with the requirements for in-orbit operation onboard Earth-observation micro-satellites to be launched in 2018.

Review of Geostationary Interferometric Infrared Sounder

To measure the global atmospheric three-dimensional distribution and change of temperature and humidity is one of the key areas in atmospheric remote sensing detection; it is also a new research and development direction in the field of meteorological satellite application. As a main element of China second generation of geostationary meteorological satellite Fengyun 4 (FY-4), which was launched on Dec. 11, 2016, the Geostationary Interferometric Infrared Sounder (GIIRS) is the first interferometric infrared sounder working on geostationary orbit internationally. It is used for vertical atmospheric sounding and gains atmospheric temperature, humidity, and disturbances. The combination of Fourier transform spectrometer technology and infrared detectors makes GIIRS have high spectral resolution and large coverage over spatial areas. With this kind of instrument, meteorological satellites can improve the capabilities for severe weather event monitoring and numerical weather prediction. Here a concise review of the GIIRS development project, including its history, missions and functions, technical design, key technologies, system integration, calibration and in-orbit operation status, etc., is presented.

Long-term test of a stacked CdTe mini-HXI setup

This work presents a long-term operation of two stacked CdTe double sided strip detectors that are comparable with the CdTe detectors onboard Hitomi’s HXI. The goal of this test is to study the evolution of the spectroscopic performance of the detectors during a one year operation cycle which resembles the in-orbit operation cycle of Hitomi HXI. Crystal defects inside CdTe cause a degradation of the spectroscopic performance (polarization effect) of the crystal which is becoming worse during detector operation. In order to prevent crystal polarization, the detectors are reset (switch-off of the depletion voltage) once a day. Our main investigation was to study if a long-term degradation can occur as a result of incomplete depolarization during the reset. We present the hardware setup and the analytical steps that were used to investigate the detector stability during each day and over the whole testing period. For the anode signals our results show at 60 keV: a daily line drift of (−2.8±0.7) eV/ks while the long-term drift is (−1.5±1.2) eV/day. The degradation of the energy resolution is measured to be (+2.4±0.3) eV/ks FWHM and the loss of efficiency is (−0.29±0.02) %/ks.

In-orbit operation of the soft x-ray spectrometer onboard the Hitomi satellite

We summarize all of the in-orbit operations of the soft x-ray spectrometer (SXS) onboard the ASTRO-H (Hitomi) satellite. The satellite was launched on February 17, 2016, and the communication with the satellite ceased on March 26, 2016. The SXS was still in the commissioning phase, in which the set-ups were progressively changed. This paper is intended to serve as a concise reference of the events in orbit in order to properly interpret the SXS data taken during its short lifetime and as a test case for planning the in-orbit operation for future microcalorimeter missions.

An in-orbit Thermal Design of Optical Window in Space Solar Telescope

A complex space environment will influence a space solar telescope during its in-orbit operation, and the temperature change of the optical window will affect directly the imaging quality of the optical system behind it. The purpose of the thermal design is to ensure that all the parts of the optical window keep their temperature in a normal range, more importantly, to ensure that the window can rapidly return to its working state as soon as the Earth shadowing is ended, and to complete the operation in a whole period. In order to obtain the temperature distribution and the temperature variation of the window under the space thermal load in the whole period, we have made the steady-state simulation analysis and transient-state simulation analysis of the window with and without heating during the Earth-shadow time. A good thermal control result is obtained by comparing the two kinds of transient state simulation results of the temperature distribution, and by accordingly taking the appropriate thermal control measures on the window.

Spiral coning manoeuvre for in-orbit low thrust characterisation in CubeSats

The ability to accurately measure the level of thrust during in-orbit operations is fundamental to the characterisation of emerging propulsion systems for nanosatellites. Many new CubeSat missions use propulsion systems with thrust levels in the order of few micro-Newtons. Whilst laboratory sensing resources are able to resolve such low thrust values, in complementary in-orbit characterisation are limited and in the main not compatible with the standard CubeSat mission. Additionally, typical in-orbit assessment of micro-thrust is generally carried out through body angular speed changes, the effectiveness of which is drastically reduced when external perturbations and sensor noise approach or exceed the thruster action on the CubeSat. This investigation sets out to improve in-orbit micro-thrust characterisation via changes in body angular velocity periodicity due to off-centred thrust action in nearly axisymmetric CubeSats. Unlike traditional methods that rely on determining angular acceleration this method employs a frequency analysis of the transversal component of the angular velocity signal with the aim of reducing measurement error. Numerical simulations support the feasibility and adequacy of the proposed low-thrust gauging method, particularly for weak and noisy sensor signals. The robustness of the method allows for interchangeable analysed signal and enables the use of simple commercial-off-the-shelf rate sensors in fine micro-thrust characterisation.

Dynamic performance fluctuation of solid-lubricated rotating mechanism for intermittent operation caused by launch vibration load

Space mechanism is the key to success of long-term space missions. The service life of solid-lubricated space mechanisms is affected by various mechanical loads before in-orbit operation, among which the load caused by the launch vibration is the most severe one. Dynamic performance is an indication of the operating state of solid-lubricated mechanisms. The fluctuation of dynamic performances caused by the load of launch vibration is an unanswered but important question. In this paper, the fluctuation of dynamic performances of solid-lubricated rotating mechanisms for intermittent operation was studied by means of experiments and theoretical analyses. One group of rotating mechanisms for intermittent operation with solid-lubricated ball bearings were subjected to sine sweep tests and random vibration tests, followed by continuous operation test. The dynamic performance of mechanisms was obtained throughout all tests. The other group of mechanisms were studied with continuous operation test only for comparing the effects of vibration on the dynamic performance of mechanisms. At the same time, the sample moments of the dynamic performance of mechanisms were calculated and analyzed. The contact stress in the vibration tests was calculated by the Hertz theory. The fluctuation of the dynamic performances of solid-lubricated rotating mechanisms for intermittent operation caused by the load of launch vibration was then concluded with further discussion.

TheGaiamission

Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page at http://www.cosmos.esa.int/gaia.

Generation and Analysis of Correlated Pairs of Photons aboard a Nanosatellite

Satellites carrying sources of entangled photons could establish a global quantum network, enabling private encryption keys between any two points on Earth. Despite numerous proposals, demonstration of space-based quantum systems has been limited due to the cost of traditional satellites. We are using very small spacecraft to accelerate progress. We report the in-orbit operation of a photon pair source aboard a 1.65 kg nanosatellite and demonstrate pair generation and polarization correlation under space conditions. The in-orbit photon correlations exhibit a contrast of 97+/-2%, matching ground-based tests. This pathfinding mission overcomes the challenge of demonstrating in-orbit performance for the components of future entangled photon experiments. Ongoing operation establishes the in-orbit lifetime of these critical components. More generally, this demonstrates the ability for nanosatellites to enable faster progress in space-based research.

Note: Digital laser frequency auto-locking for inter-satellite laser ranging.

We present a prototype of a laser frequency auto-locking and re-locking control system designed for laser frequency stabilization in inter-satellite laser ranging system. The controller has been implemented on field programmable gate arrays and programmed with LabVIEW software. The controller allows initial frequency calibrating and lock-in of a free-running laser to a Fabry-Pérot cavity. Since it allows automatic recovery from unlocked conditions, benefit derives to automated in-orbit operations. Program design and experimental results are demonstrated.

Uncertainty-based Optimization Algorithms in Designing Fractionated Spacecraft.

A fractionated spacecraft is an innovative application of a distributive space system. To fully understand the impact of various uncertainties on its development, launch and in-orbit operation, we use the stochastic missioncycle cost to comprehensively evaluate the survivability, flexibility, reliability and economy of the ways of dividing the various modules of the different configurations of fractionated spacecraft. We systematically describe its concept and then analyze its evaluation and optimal design method that exists during recent years and propose the stochastic missioncycle cost for comprehensive evaluation. We also establish the models of the costs such as module development, launch and deployment and the impacts of their uncertainties respectively. Finally, we carry out the Monte Carlo simulation of the complete missioncycle costs of various configurations of the fractionated spacecraft under various uncertainties and give and compare the probability density distribution and statistical characteristics of its stochastic missioncycle cost, using the two strategies of timing module replacement and non-timing module replacement. The simulation results verify the effectiveness of the comprehensive evaluation method and show that our evaluation method can comprehensively evaluate the adaptability of the fractionated spacecraft under different technical and mission conditions.

Fault Diagnosis and Fault-Tolerant Control of Micro-Satellite Propulsion Mode Attitude Control

Micro-satellite has long-term in-orbit work in the harsh environment of space, the components such as actuators and sensors in the attitude control system continue to perform in-orbit control operations, therefore are prone to faults. In practical mission, such as formation flying, orbital transfer, de-tumbing and attitude control need to use thruster to control. As the thrust control is fail, the entire mission fails. In the paper, the two-stage unscented kalman filter is used to obtain the effectiveness factor value and system estimated states are obtained. Meanwhile, a robust thruster controller is designed with the estimated results to accomplish the joint design of Fault Detection and Diagnosis and Fault-Tolerant Control.

Autonomous star sensor ASTRO APS: flight experience on Alphasat

Jena-Optronik GmbH, located in Jena/Germany, has profound experience in designing and manufacturing star trackers since the early 80s. Today the company has a worldwide leading position in supplying geo-stationary and Earth observation satellites with robust and reliable star tracker systems. In the first decade of the new century Jena-Optronik received a development contract (17317/2003/F/WE) from the European Space Agency to establish the technologically challenging elements for which advanced star tracker technologies as CMOS Active Pixel Sensors were being introduced or were considered strategic. This activity was performed in the frame of the Alphabus large platform pre-development lead by ESA and the industrial Joint Project Team consisting of Astrium (now Airbus Defence and Space), Thales Alenia Space and CNES (Centre national d’etudes spatiales). The new autonomous star tracker, ASTRO APS (Active Pixel Sensor), extends the Jena-Optronik Astro-series CCD-based star tracker products taken the full benefit of the CMOS APS technology. ASTRO APS is a fully autonomous compact star tracker carrying either the space-qualified radiation hard STAR1000 or the HAS2 APS detectors. The star tracker is one of four Technology Demonstration Payloads (TDP6) carried by Alphasat as hosted payload in the frame of a successful Private Public Partnership between ESA and Inmarsat who owns and operates the satellite as part of its geo-stationary communication satellites fleet. TDP6 supports also directly TDP1, a Laser Communication Terminal, for fine pointing tasks. Alphasat was flawlessly brought in orbit at the end of July 2013 by a European Ariane 5 launcher. Only a few hours after launch the star tracker received its switch ON command and acquired nominally within 6 s the inertial 3-axes attitude. In the following days of the early in-orbit operations of Alphasat the TDP6 unit tracked reliably all the spacecraft maneuvers including the 0.1 and 0.2°/s spin stabilization for Sun pointing, all of the apogee engine thrusts, Moon field of view transits and recovered to stable tracking after several Earth and Sun blindings before the spacecraft entered a preliminary Earth pointing in a nominal geo-stationary attitude. The Jena-Optronik TDP6 operation center received daily the star tracker status and attitude data. The huge amount of acquired raw data has been evaluated to characterize the ASTRO APS (STAR1000) star tracker in-orbit performance. The paper will present in detail these data processing activities and will show the extraordinary good results. Due to the diverse transfer orbit satellite operations the key performance star tracker data like attitude random noise, single star noise, star brightness measurement, baffle Sun exclusion angle, temperature control, etc., could be derived and have been compared to the ground based laboratory and field measurements. The ultimate performance parameters achieved and verified as well as the lessons learned from the comparison to the ground test data are summarized in the conclusion of the paper.

Design and development of Shack–Hartmann wavefront sensor-based testing of high-resolution optical system for earth observation

The deformation of the optical surfaces of a large aperture high-resolution space-borne optical system induced by earth’s gravity on the ground, which is not present during in-orbit operations, necessitates the evaluation of its performance in terms of wavefront error at various stages of development of the earth observation system. A direct method of evaluation for an optical system at an integrated electro-optical module based on a Shack–Hartmann wavefront sensor (SH WFS) is proposed. Design and analysis of the wavefront sensor that are tailored to meet the requirements of the high-resolution optical system are described. We show that the procedure followed for the development of the SH WFS not only addresses the parameters of the wavefront sensor that are critical to its performance, but also aides in the wavefront sensor alignment and calibration. The performance of the developed SH WFS is demonstrated by testing a simulated telescope which is <italic<in situ</italic< verified in a test configuration using a standard Fizeau interferometer; a close match of the coefficients of Zernike modes between them is established.