Drag-Based Formation Control of Millennium Space Systems Satellites

Aside from gravity, aerodynamic drag is typically the strongest environmental force acting on a spacecraft in low Earth orbit. While often treated as a disturbance whose perturbative effects on the orbit must be mitigated through periodic thruster burns, drag can potentially be harnessed for on-orbit maneuvering. This paper discusses a practical algorithm for achieving and maintaining a desired separation between two satellites using differential aerodynamic drag. By increasing the drag and thereby reducing the mean semi-major axis of “lead” vehicle, the separation between the satellites is increased. Conversely, by increasing the relative drag on the “chase” vehicle, inter-satellite separation is decreased. With this control concept, the derived algorithms compute how long each satellite should stay in either a minimum or maximum drag configuration and when the drag configurations should be changed. Flight results are presented for two propellant-free vehicles operated by Millennium Space Systems where this drag control strategy was successfully applied to achieve a desired inter-satellite separation. Using open loop commands, ephemeris knowledge from freely available TLEs, and the ability to orient the primary solar arrays differently while in eclipse, mission operators were able to achieve a vehicle separation within the required tolerance with minimal drift over time

Drag De-Orbit Device: A New Standard Re-Entry Actuator for CubeSats

With the advent of CubeSats, research in Low Earth Orbit (LEO) becomes possible for universities and small research groups. Only a handful of launch sites can be used, due to geographical and political restrictions. As a result, common orbits in LEO are becoming crowded due to the additional launches made possible by low-cost access to space. CubeSat design principles require a maximum of a 25-year orbital lifetime in an effort to reduce the total number of spacecraft in orbit at any time. Additionally, since debris may survive re-entry, it is ideal to de-orbit spacecraft over unpopulated areas to prevent casualties. The Drag Deorbit Device (D3) is a self-contained targeted re-entry subsystem intended for CubeSats. By varying the cross-wind area, the atmospheric drag can be varied in such a way as to produce desired maneuvers. The D3 is intended to be used to remove spacecraft from orbit to reach a desired target interface point. Additionally, attitude stabilization is performed by the D3 prior to deployment and can replace a traditional ADACS on many missions.This paper presents the hardware used in the D3 and operation details. Four stepper-driven, repeatedly retractable booms are used to modify the cross-wind area of the D3 and attached spacecraft. Five magnetorquers (solenoids) over three axes are used to damp rotational velocity. This system is expected to be used to improve mission flexibility and allow additional launches by reducing the orbital lifetime of spacecraft.The D3 can be used to effect a re-entry to any target interface point, with the orbital inclination limiting the maximum latitude. In the chance that the main spacecraft fails, a timer will automatically deploy the booms fully, ensuring the spacecraft will at the minimum reenter the atmosphere in the minimum possible time, although not necessarily at the desired target interface point. Although this does not reduce the risk of casualties, the 25-year lifetime limit is still respected, allowing a reduction of the risk associated with a hardware failure

Antibacterial activity of Malaysian produced stingless-bee honey on wound pathogens

The antibacterial activity of Malaysian stingless bee honey was tested on six common wound pathogens using agar well diffusion. All pathogens showed varying degrees of susceptibility to undiluted and diluted honeys produced by Geniotrigona thoracica of multifloral source (GTM) and Melastoma malabathricum L (Senduduk). Multifloral honey from Heterotrigona itama (HTM) failed to inhibit the growth of all pathogens, except for methicillin-resistant Staphylococcus aureus (MRSA) which has demonstrated moderate susceptibility to undiluted honey. It was found that the antibacterial activity of GTM and Senduduk honeys were concentration dependent. The minimum inhibitory concentration (MIC) assay showed that a lower value (3.13% v/v) was observed with GTM honey for all pathogens and Senduduk honey for Streptococcus pyogenes, MRSA, Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Interestingly, HTM honey showed MIC between 6.25 to 12.5% (v/v) in microdilution method. The minimum bactericidal concentration (MBC) of GTM honey ranged between 6.25 to 12.5% (v/v), whereas Senduduk and HTM honeys showed MBC of 25% (v/v). The lower MIC and MBC values exhibited by GTM honey indicate s potent antibacterial activity as seen in this honey. This study revealed that the Malaysian stingless bee honeys have promising antibacterial activity against wound pathogens, and this type of honey could be used as an alternative in treating infected wounds

PAssive Thermal Coating Observatory Operating in Low Earth Orbit (PATCOOL)

The PATCOOL is a NASA sponsored, University of Florida developed 3U CubeSat meant to investigate the feasibility of using a cryogenic selective surface coating as a new, more efficient way of passively cooling components in space. Initial tests on the ground demonstrate that this coating should provide a much higher reflectance of the Sun's irradiant power than any existing coating, while still providing far-infrared power emission. The ultimate validation of this technology requires on-orbit testing. PATCOOL hosts a 4-sample housing, with the samples shaped as thin cylinders (coin-like). Two samples are coated with state-of-the-art material, while the other pair uses the new coating to be evaluated. The temperatures of all samples during the mission (minimum 72 hours of data collection) are measured via thermistors. The samples are connected via thin Kevlar strings to the housing, to minimize heat transfer. The housing is designed to shield the samples from Earth's thermal radiation, and the CubeSat is attitude stabilized and controlled via a gravity gradient boom, magnetorquers and a reaction wheel set. Thermal Desktop simulations show PATCOOL's ability to thermally isolate the samples from heat exchanges other than with Sun and deep space, thanks to its thermal design and the chosen attitude profil

Passive Thermal Coating Observatory Operating in Low-Earth Orbit (PATCOOL) Cubesat Design to Test Passive Thermal Coatings in Space

The PATCOOL is a NASA sponsored, University of Florida developed 3U Cu-beSat meant to investigate the feasibility of using a cryogenic selective surface coating as a new, more efficient way of passively cooling components in space. Initial tests on the ground demonstrate that this coating should provide a much higher reflectance of the Suns irradiant power than any existing coating, while still providing far-infrared power emission. The ultimate validation of this tech-nology requires on-orbit testing. PATCOOL hosts a 4-sample housing, with the samples shaped as thin cylinders (coin-like). Two samples are coated with state-of-the-art material, while the other pair uses the new coating to be evaluated. The temperatures of all samples during the mission (minimum 72 hours of data col-lection) are measured via thermistors. The samples are connected via thin Kevlar strings to the housing, to minimize heat transfer. The housing is designed to shield the samples from Earths thermal radiation, and the CubeSat is attitude stabilized and controlled via a gravity gradient boom, magnetorquers and a reaction wheel set. Thermal Desktop simulations show PATCOOLs ability to thermally isolate the samples from heat exchanges other than with Sun and deep space, thanks to its thermal design and the chosen attitude profile

Effect of thawing conditions and corresponding frying temperature profiles on the formation of acrylamide in French fries

This study attempted to determine the effects of thawing conditions and corresponding frying temperature profiles on the formation of acrylamide in French fries. Frozen par-fried potato strips were thawed under three different conditions, at room temperature, using a chiller, and using a microwave. Unthawed par-fried potato strips were used as the control samples. Thawed (or unthawed) par-fried potato strips were deep-fat fried in palm oil at 180 ± 5 °C for 3.5 min. The temperature drop was monitored every 15 s for a total of 6 min; 3.5 min of frying time plus an additional 2.5 min until the oil temperature returned to 180 °C. The acrylamide content, oil content and colour of the French fries were measured. The frying temperature dropped substantially (more than 30 °C) from the initial temperature in the first 45 s of frying for all thawing conditions. After 90 s of frying, the smallest temperature drops were observed for French fries thawed using a microwave (20%), and the largest temperature drop prior to recovery was seen with the control sample (24%). At the end of the frying period (after 210 s), French fries thawed using a microwave had reached the highest final temperature (154 °C), and the control sample had reached the lowest final temperature (145 °C). The acrylamide contents of the French fries were found to be in the range of 77.4–106 ng/g, whereas the oil contents ranged from 16.4 to 20.5%. The lowest lightness, highest redness and highest yellowness were found for French fries thawed using a microwave. Although the thawing conditions did not significantly affect the formation of acrylamide, microwave thawing was found to be the best thawing method due to the resulting (relatively) low acrylamide and oil contents of the French fries and their desirable colour attributes. The results of this study can be used to recommend that the manufacturers of frozen par-fried potato strips specify the use of a microwave for thawing as part of the frying instruction on the packaging

Modulated Exo-Brake Flight Testing - Modeling and Test Results - Successes with Exo-Brake Development and Targeting for Future Sample Return Capability: TES-6,7,8 Flight Experiments

No abstract availabl

Using Differential Aerodynamic Forces for CubeSat Orbit Control

This paper focuses on the use of aerodynamic forces for CubeSat orbit control. This would enable fleets of CubeSats to fly in formation without the need for thrusters. To gain a better understanding of the behavior of satellites in orbit, a mathematical analysis of satellites in circular orbits with different altitudes was conducted first. This analysis shows that very small altitude differences could result in comparatively large changes in satellite separation over a reasonable time interval. A numerical-integrator based software simulation was developed to provide a more accurate orbit model and a control algorithm for changing satellite separation. Simulation results indicate that aerodynamic forces in low earth orbit would be strong enough for orbit control, but weak enough that any orbital maneuver would take days to weeks to complete (simulations at 600km altitude). This would allow satellite operators to determine satellite positions using NORAD data and Doppler shift measurements and control satellite configurations as needed from the ground

An Inverse Dynamics Satellite Attitude Determination and Control System with Autonomous Calibration

Attitude determination and control systems (ADACS) are responsible for establishing desired satellite orientations. Proper satellite orientation is necessary for many science instruments and communication systems. Popular sensors include magnetometers, sun sensors, and rate gyros, and popular actuators include reaction wheels and magnetorquers. This paper investigates an ADACS design using these sensors and actuators that could feasibly be implemented on a CubeSat. The B-Dot law is used for satellite de-tumbling, and a linear inverse dynamics PD controller is utilized for steady state pointing, allowing for the analytical estimation of optimal controller gains. The inverse dynamics controller calculates desired satellite angular accelerations and then calculates the torques required to achieve these angular accelerations. This makes controller performance independent of initial conditions or system inertia properties. This system uses the magnetorquers to dump reaction wheel momentum and analyzes the satellite’s kinematic response to applied torques in order to calibrate the rate gyros and estimate system moments of inertia. Simulation results corresponded well to the analytical predictions. Often, an oscillating equilibrium would occur when controller gains were low, but this oscillation could be mitigated by selecting large controller gains such that the system was heavily overdamped and scaling down large commanded angular acceleration values to within system capabilities

Precise re-entry and landing of propellantless spacecraft

Spacecraft returning scientific samples or humans from space must be capable of surviving re-entry and landing in a desired location. Traditionally, this has been accomplished via a propulsive de-orbit burn. However, it is not always possible to mount a propulsion system on board a satellite or a capsule. In the case of small satellites deployed from the International Space Station, for example, on-board propulsion systems are forbidden for safety reasons. Our work proposes a new technological solution for re-entering and landing a spacecraft in a desired location from a low Earth orbit using exclusively aerodynamic drag and eliminating the need for chemical propulsion. First, an iterative procedure is utilized to compute the desired state at the re-entry interface (100 km) such that a propagation of the vehicle dynamics in the nominal re-entry drag configuration from this initial state leads to a landing at a desired latitude and longitude on the surface of the Earth. Next, a re-entry point targeting algorithm is utilized to determine the on-orbit ballistic coefficient profile necessary to target the desired re-entry point. Finally, the ballistic coefficient profile during the final hours of the trajectory before the re-entry interface is iteratively modified to correct any remaining along-track error in the landing location. The proposed solution is applied to a small satellite system that is jettisoned from the ISS and is equipped with a deployable heat shield that also serves as a drag device