Gravity Gradient Boom Research Articles

Design and testing of inflatable gravity-gradient booms in space

Inflatable space structures have many advantages such as small size, high reliability, and low cost. Aiming at a gravity-gradient boom for an XY-1 satellite, New Technology Verifying Satellite-1, a slender inflatable boom with low magnetic is presented. First of all, an inflatable boom with six self-supporting thin shells made of carbon and Vectran fiber composite materials on the inner wall was designed for eliminating a magnetic dipole moment and increasing structural stiffness. A precise stowage was designed for a tip mass surrounded by a pair of lightweight honeycomb blocks added on the top of the boom. The stowed boom was tested by sine sweep vibrations with three directions on the ground to verify the reasonable design. The XY-1 satellite which carried the inflatable boom was launched into low orbit. After being stowed state in space for at least 6 months, the inflatable boom orderly unfolded a 2.0 kg tip mass to 3.0 m away in May, 2013. The inflatable boom was successfully deployed from a series of photographs received on the satellite. The results show that this kind of lightweight inflatable boom with self-supporting thin shells can orderly unfold and fulfil the function of gravity-gradient in space for a long time.

Magnetic attitude control for Earth-pointing satellites in the presence of gravity gradient

A sliding mode control law is applicable to a variety of nonlinear problems and can adapt itself to disturbance torques and parameter uncertainties in real time. In this work, an adaptive sliding mode control law for purely magnetic actuated Earth-pointing satellite with a gravity gradient boom is presented. This control law has been developed for the BUAA-SAT microsatellite, which is designed and manufactured by Beihang University, Beijing. The new control law is a modification of the general sliding mode strategy that enables the satellite to achieve an Earth-pointing attitude and deal with the uncertainty of the principal moment of inertia, which is caused by the incomplete deployment of the gravity gradient boom. In addition, a B-dot algorithm is employed for the detumbling before the boom is deployed. The performance and applicability of the proposed methods have been analyzed and demonstrated by implementing the control law in the BUAA-SAT mission simulator and compared with the proportional derivative-like controller. Presented results show good performance in terms of acquisition and stability of the satellite rotation rate and Earth-pointing attitude.

Deployable dynamic analysis and on-orbit experiment for inflatable gravity-gradient boom

Inflatable structures have numerous advantages, such as small folding size, high deployable reliability, and low cost. This paper accomplishes several tasks with a focus on the gravity-gradient boom of microsatellite. An inflatable boom model balanced by inflatable deployment and delaminating resistance is presented. A system is established to simulate agravic deployment. The inflatable deployment of a tip mass has been tested with the aid of a 3.0m rolled deployable boom. The perturbation moment during the inflatable deployment is analyzed. Three inflatable booms are tested in a thermal vacuum chamber further. Based on the tests and analyses, the microsatellite which carried an inflatable gravity-gradient boom was launched into orbit successfully in November 2012. After being stored on-orbit for 6months, the inflatable method was applied to the inflatable boom to unfold the 2.0kg tip mass steadily at a distance 3.0m away from the microsatellite in May 2013. This work completes the test of inflatable on-orbit deployment on the base of microsatellite for the first time internationally.

수동형 자세제어 안정화 방식을 적용한 큐브위성의 열적 특성분석

히스테리시스 댐퍼를 조합한 영구자석과 중력붐을 적용한 수동형 자세제어 안정화 방식은 시스템의 단순화가 가능하여 임무목적에 따라 큐브위성의 자세제어에 용이하게 적용되고 있다. 상기의 자세제어 안정화 방식을 적용한 경우, 큐브위성의 자세 프로파일은 상이하며, 본 논문에서는 각각의 자세제어 방식 적용에 따른 큐브위성의 열적 특성을 궤도 열해석을 통해 분석하였다. 또한, 통신용 안테나 장착 등의 목적으로 태양전지셀이 장착되지 않는 판넬 표면의 상이한 열코팅 적용에 따른 큐브위성의 열적 영향을 분석하였다. Passive attitude stabilization methods using the permanent magnet combined with hysteresis damper and the gravity gradient boom have been widely used for the attitude determination and control of cube satellite, due to its advantage of system simplicity. In this paper, on-orbit thermal characteristics of the cube satellite considering the attitude profiles obtained from the above passive attitude stabilization methods have been investigated through on-orbit thermal analysis. In addition, the effectiveness of the various thermal coatings on the panel for the communication antenna installation has been verified.

Impact of the orbital eccentricity on the attitude performance before and after the deorbiting phase for Alsat-1

Due to the presence of periodic forcing terms in the gravity gradient torque, orbit eccentricity may produce large response for the roll, yaw and pitch angles. This paper investigates the influence of the orbit eccentricity on the performance of the attitude determination and control subsystem (ADCS) pointing of passive Low Earth Orbit (LEO) satellites stabilized by a gravity gradient boom or having long appendages before and after the deorbiting operation. The contribution of this work is twofold. First, the satellite attitude dynamics and kinematics are modeled by introducing the orbit eccentricity in the equations of motion of a LEO satellite in order to provide the best scenario in which satellite operators can keep the nominal functionality of LEO satellites with a gravity gradient boom after the deorbiting operation. Second, a Quaternion-based Extended Kalman Filter (EKF) is analyzed when the orbit eccentricity is considered in order to determine the influence of this disturbance on the convergence and stability of the filter. The simulations in this work are based on the true parameters of Alsat-1 which is a typical LEO satellite stabilized by a gravity gradient boom. The results show that the orbit eccentricity has a big influence on the pointing system accuracy causing micro-vibrations that affect the geocentric pointing particularly after the deorbiting phase. In this case, satellites have no orbital correction option. The Quaternion-based Extended Kalman Filter analyzed in this paper, achieved satisfactory results for eccentricity values less than 0.4 with respect to pointing system accuracy. However, singularities were observed for eccentricity values greater than 0.4.

3-Axis magnetic control: flight results of the TANGO satellite in the PRISMA mission

PRISMA implements guidance, navigation and control strategies for advanced formation flying and rendezvous experiments. The project is funded by the Swedish National Space Board and run by OHB-Sweden in close cooperation with DLR, CNES and the Danish Technical University. The PRISMA test bed consists of a fully manoeuvrable MANGO satellite as well as a 3-axis controlled TANGO satellite without any ΔV capability. PRISMA was launched on the 15th of June 2010 on board DNEPR. The TANGO spacecraft is the reference satellite for the experiments performed by MANGO, either with a “cooperative” or “non-cooperative” behaviour. Small, light and low-cost were the keywords for the TANGO design. The attitude determination is based on Sun sensors and magnetometers, and the active attitude control uses magnetic torque rods only. In order to perform the attitude manoeuvres required to fulfil the mission objectives, using any additional gravity gradient boom to passively stabilize the spacecraft was not allowed. After a two-month commissioning phase, TANGO separated from MANGO on the 11th of August 2010. All operational modes have been successfully tested, and the pointing performance in flight is in accordance with expectations. The robust Sun Acquisition mode reduced the initial tip-off rate and placed TANGO into a safe attitude in <30 min. The Manual Pointing mode was commissioned, and the spacecraft demonstrated the capability to follow or maintain different sets of attitudes. In Sun/Zenith Pointing mode, TANGO points its GPS antenna towards zenith with sufficient accuracy to track as many GPS satellites as MANGO. At the same time, it points its solar panel towards the Sun, and all payload equipments can be switched on without any restriction. This paper gives an overview of the TANGO Attitude Control System design. It then presents the flight results in the different operating modes. Finally, it highlights the key elements at the origin of the successful 3-axis magnetic control strategy on the TANGO satellite.

Three-axis active control system for gravity gradient stabilised microsatellite

In this paper, the control system of the first Algerian microsatellite in orbit Alsat-1 is presented. Alsat-1 is a 3-axis stabilised microsatellite, using a pitch momentum wheel and yaw reaction wheel, with dual redundant 3-axis magnetorquers. A gravity gradient boom is employed to provide a high degree of platform stability. Two vector magnetometers and four dual sun sensors are carried in order to determine the attitude. This paper examines the low Earth orbit (LEO) control system requirements and design in the context of a real system, the Surrey Satellite Technology Limited (SSTL) advanced microsatellite platform and puts forward designs for the control system to match the advanced capability of the enhanced microsatellite platform. Numerical results show the effectiveness of the implementation. Comparison with in orbit results is presented to evaluate the performance of the control system during accurate Nadir pointing control.

Satellite electricity on orbital time scales

The theory of electricity on gravity gradient gyrostats is generalized from a static and average charge with the Lorentz torque of previous efforts to the instantaneous and dynamic one here with the introduction of the Faraday torque due to a current along the metallic gravity gradient boom. There are then two sources for roll torque driven by orthogonal components of the geomagnetic field. The mass properties and wheel angular momentum lead to gyroscopic resonances near three times per orbit which greatly enhances the response to tiny charges and currents. The roll and yaw data streams are converted to charge and current by use of the solutions of the forced gyroscopic equations. Data from gyrostats at the (3, 2) and (3, 0) resonances are analyzed in detail to determine the time scales for the electrical flow. Onboard electrical activity with five minute and daily time scales must be due to relays and telemetry. Thus, it is the practice of the gounding of boxes to the bus which is the cause of the librations seen here. The spacecraft current loop is closed by the ambient photo-electric plasma, and it is the slow dissipation of this charge to the environment that limits the librations.

Citizen Explorer-I: an Earth observer with new small satellite technology

Citizen Explorer-I (CX-I), designed and built by students at Colorado Space Grant Consortium in Boulder to provide global ozone monitoring, employs a unique mission architecture and several innovative technologies during its mission. The mission design allows K-12 schools around the world to be involved as ground stations available to receive science data and telemetry from CX-I. Another important technology allows the spacecraft to be less reliant on ground operators using mission-specific software packages. Within the communications system of CX-I, Internet protocols are the main method for communicating with the satellite. As Internet protocols have not been widely used in satellite communication, CX-I provides an opportunity to study the effectiveness of using Internet protocols over radio links. The attitude determination and control system (ADCS) on CX-I uses a unique gravity gradient boom design constructed of tape measure material. These new technologies’ effectiveness will be tested for use on future small satellite projects within the space satellite industry.

Dynamics of a System of Bodies with Program-Variable Configuration

The dynamics of a system of rigid bodies with program-variable configuration is analyzed. A mathematical model is constructed using methods of analytical mechanics. The behavior of a microsatellite with a deployable gravity-gradient boom is analyzed as a numerical example

重力傾度ブームによる姿勢精度低下

Gravity gradient stabilization is applied to from small satellites to large space structures because energy is not necessary for attitude control and actuator is not either. The stability and accuracy of attitude depend on the mass property of satellite. Large moment of inertia is selected for suppression of the attitude error due to external disturbance torque. ‘Gravity gradient boom’ is often attached on the main body of satellite for this purpose. This paper discusses on the relation between mass property of gravity gradient boom and attitude accuracy using transfer functions from the disturbance forces to the attitude angles. The results show that gravity gradient boom does not always improve the attitude accuracy. For satellites with a long or heavy gravity gradient boom, the second orbital mode of roll and yaw angles are excited by solar radiation pressure torque when the orbit of satellite goes through the shadow of the earth.

The science and engineering payloads and experiments on sunsat

This paper describes the science payloads and experiments of the SUNSAT microsatellite which is to be launched in 1998. A very modular satellite mechanical structure has enabled the addition of additional experiments at a late stage of the program. The design and performance measurements of the engineering and technology payloads (a 10m resolution imager, an accurate ADCS system, a DSP processor board, gravity gradient boom and the solar panels) are reported. The science payloads —including a precision GPS receiver, laser retro-reflectors, magnetometer, and various school experiments — are described, indicating that a very complex microsatellite was developed as the first venture into space by a South African university.

A very low cost ground system for a micro-satellite mission

This paper describes the ground system currently being developed for what is thought to be a unique mission being flown in 1998. The main mission in question is called BADR-B (Urdu for Full Moon) and is a Pakistan mini-satellite designed to test out certain technologies and scientific instruments. BADR-B is a gravity-gradient stabilised spacecraft, and as such it incorporates a gravity-gradient boom for attitude control. The unique feature of this mission, however, is that the normal gravity-gradient tip mass at the end of the boom has been replaced by an autonomous micro-satellite. This consists of two scientific instruments (one for measurement of atomic oxygen, one for detection of small particulated debris) with completely self-contained power supply and data transmission. To transmit its data to the ground, the micro-satellite forwards its data remotely by an optical/rf link to the mini-satellite, and thereafter it is downlinked to one of two ground stations, these being at Lahore, Pakistan and at the Rutherford Appleton Laboratory (RAL), Chilton, England. In order to keep costs to an absolute minimum, the ground system at RAL for the micro-satellite is being designed with autonomy in mind, and the re-use of much existing hardware and software. The cost-efficient development of the hardware, software and operations is described in this paper.

Satellite attitude control using a torqued, 2-axis-gimbaled boom as the actuator.

Heretofore, satellites requiring precision attitude control have been equipped with momentum wheels and gas jets. This combination can be replaced by a commandable gravitygradient boom and considerably smaller wheels. Each of the two boom gimbal axes is equipped with a torquer and a shaft encoder. Satellite attitude control is maintained using an active attitude reference and torquing against the inertia of the boom. Gravity-gradient torques keep the boom anchored in the gravity field and small momentum wheels damp the boom librations. Yaw axis momentum control utilizes the orbital coupling of the roll/ yaw axes. Results of linear analyses, computer simulations, and some hardware tests exemplify the performance of this Commandable Gravity-Gradient System (COGGS) and demonstrate its feasibility. The system can be expected to statically point to any spot on the earth to within dbO.l0 and to track low-altitude satellites to within ±0.5°.

Gravity-gradient stabilization for a spinning satellite with despun line of sight

A spin-stabilized cylindrical satellite is suspended either magnetically or electrostatically from a gravity-gradient-stabilized reflector that directs a pencil beam of radiation emanating axially from the satellite toward the earth. Solutions for the motion of a gravity-gradient boom with reference to the local vertical are obtained. The dynamics of the satellite combining spin stabilization with gravity-gradient stabilization result in a stable system with a fixed nutation frequency that can be made high by design. Vibrations in the roll and yaw axes are easily damped by a nutation damper in the spinning cylinder. Damping of the pitch vibration of the reflector can be obtained with a single, cold-gas, pulsed jet that also can be used to prevent angular velocity decay of the spinning cylinder and to control the orbital period for station-keeping. The system described is basically passive as far as the control torques are concerned; however, active means are used to damp pitch vibrations of the nonspinning reflector. Thus, this system can achieve high accuracy of stabilization, in addition to the advantages of high reliability.