CubeSat constellations for disaster management in remote areas

In recent years, CubeSats have considerably extended their range of possible applications, from a low cost means to train students and young researchers in space related activities up to possible complementary solutions to larger missions. Increasingly popular, whereas CubeSats are still not a solution for all types of missions, they offer the possibility of performing ambitious scientific experiments. Especially worth considering is the possibility of performing Distributed Space Missions, in which CubeSat systems can be used to increase observation sampling rates and resolutions, as well as to perform tasks that a single satellite is unable to handle. The cost of access to space for traditional Earth Observation (EO) missions is still quite high. Efficient architecture design would allow reducing mission costs by employing CubeSat systems, while maintaining a level of performance that, for some applications, could be close to that provided by larger platforms, and decreasing the time needed to design and deploy a fully functional constellation. For these reasons many countries, including developing nations, agencies and organizations are looking to CubeSat platforms to access space cheaply with, potentially, tens of remote sensing satellites. During disaster management, real-time, fast and continuous information broadcast is a fundamental requirement. In this sense, a constellation of small satellites can considerably decrease the revisit time (defined as the time elapsed between two consecutive observations of the same point on Earth by a satellite) over remote areas, by increasing the number of spacecraft properly distributed in orbit. This allows collecting as much data as possible for the use by Disaster Management Centers. This paper describes the characteristics of a constellation of CubeSats built to enable access over the most remote regions of Brazil, supporting an integrated system for mitigating environmental disasters in an attempt to prevent the catastrophic effects of natural events such as heavy rains that cause flooding. In particular, the paper defines the number of CubeSats and the orbital planes required to minimize the revisit time, depending on the application that is the mission objective. Each CubeSat is equipped with the suitable payloads and possesses the autonomy and pointing capabilities needed to meet the mission requirements. Thanks to the orbital features of the constellation, this service could be exploited by other tropical countries. Coverage of other areas of the Earth might be provided by adjusting the number and in-orbit distribution of the spacecraft

Smallsat high-energy missions using ablative pulsed plasma thrusters

Faculdade UnB Gama (FGA

Measurement of the thrust generated by a hollow cathode with noble gases

Hollow cathodes (HCs) have been used for decades in various electric propulsion applications.  In spite of this, understanding and modelling of the HC discharge physical mechanisms is still far from satisfactory.  Further investigations are therefore necessary.  In particular, the thrust generated by a HC has actually been measured only in one instance, with a device quite different from the one investigated in this thesis.  A thrust measurement system has therefore been developed, in order to evaluate for what discharge conditions the highest values of specific impulse and in general the best performance are attained.  The system consists of a Cantilever beam Target (CBT) and of a Laser Optical Level (LOL).  Extensive thrust measurements with several noble gases as propellants are presented and discussed.  They show that several mN of thrust can be produced, at values of specific impulse exceeding, in some cases, 500s.  Such values confirm that the device is not just heating the gas, like a resistojet, but is operating in a fashion more similar to that of an arcjet, with the heavy particle average temperature sensibly higher than the wall value.  These encouraging results were obtained just by varying the discharge parameters, with very little attempt at optimising the electrode configuration. The use of different electrode configurations, like for instance and enclosed keeper, and the investigation of other propellants, could lead to the development of a viable HC microthruster, competitive with already existing devices.</p

Measurement of the thrust generated by a hollow cathode with noble gases

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Ablative Pulsed Plasma Thruster System Optimization for Microsatellites * **

The Ablative Pulsed Plasma Thruster (APPT) can operate nominally at the very low power levels typical for microsatellites. In this paper we briefly discuss the operating characteristics of an APPT and review the existing data together with the state of the art of the various system parts. In order to characterize the behavior of an APPT and design the propulsion system optimized for a particular mission, it is necessary to have relations connecting the various parameters. Semi-empirical correlations are obtained by interpolating experimental data, available in the literature, regarding thrusters actually used on satellites, flight-qualified or merely laboratory-tested. Their validity and significance is discussed by comparing them with theoretical considerations, similar results and experimental analyses by various authors. Together with expressions for the masses of the various components of the APPT system, they constitute the basis of our model. The model is then applied to the optimization of an APPT system for given satellite mass and mission requirements. Nomenclature Acronyms APPT Ablative pulsed plasma thruster MPD Magnetoplasmadynamic PFN Pulse forming networ

The thrust generated by a T6 ion engine hollow cathode

The thrust produced by a T6 ion engine main discharge hollow cathode was characterized using different propellants with a target-based measurement system, for discharge current values of 5–25 A and a wide range of mass flow rates. The calculated values of specific impulse are far in excess of those that could be attributed to the heating of a gas tothermal equilibrium with the walls, as in a resistojet. This would suggest an operation mechanism more similar to that of an arcjet. The main scaling parameter for the specific impulse appears to be the discharge power per unit mass flow rate (specific power)

Hollow cathode thrust measurement using a target: system calibration and development

The presence of high-energy ions, observed in hollow-cathode plumes, suggests that these devices might be converted into simple micro-ion thrusters. In order to investigate the ion emission, a target system for the measurement of thrust and ion current has been developed by the Astronautics Research Group at the University of Southampton. The cantilever beam target deflection is measured with a laser opticallever, also developed for this purpose. A direct calibration of the target has been performed, confirming that the predictions of the theory of slender beams are verified. This has been accomplished by applying known forces, in the form of weights, to target beams with the same shape but different thickness. An initial version of the measurement system has been set up and two different versions of the T6 ion thruster hollow-cathode are ready to be investigated in a vacuum rig

Development of electrostrictive force-feeding sub-system for liquid pulsed plasma thrusters

An electrostatically driven pressure valve has been successfully developed based on the electrostrictive force, delivering propellant to the discharge chamber via an open-end conduit, free of any moving parts. The proof-of-concept unit has been built and demonstrated stable operation. It was shown that the conventional theory of electrostriction in liquid dielectrics is applicable for the device. The electrostatic pump has been designed for a coaxial liquid-fed micro pulsed plasma thruster prototype operating in the 1 - 2 J energy range. Active mass dosage capability is proven as a function of applied voltage and pump operational time, introducing a new class of electronically controlled feeding systems. Experimental measurements demonstrate a minimum achievable mass bit ranging from 77 to 164 ug using the voltage-controlled operation. Moreover, the pump is able to deliver up to 1 mg of propellant for a single shot. In addition to the active control, the mass flow rate can be passively adjusted by changing the capillary dimensions (radius and length), conduit material and the propellant dielectric properties

Hydrogen Bonding and Solvation of a Proline-Based Peptide Model in Salt Solutions

The hydrogen bonding of water and water/salt mixtures around the proline-based tripeptide model glycyl-l-prolyl-glycinamide center dot HCl (GPG-NH2) is investigated here by multi-wavelength UV resonance Raman spectroscopy (UVRR) to clarify the role of ion-peptide interactions in affecting the conformational stability of this peptide. The unique sensitivity and selectivity of the UVRR technique allow us to efficiently probe the hydrogen bond interaction between water molecules and proline residues in different solvation conditions, along with its influence on trans to cis isomerism in the hydrated tripeptide. The spectroscopic data suggest a relevant role played by the cations in altering the solvation shell at the carbonyl site of proline(.), while the fluoride and chloride anions were found to promote the establishment of the strongest interactions on the C = O site of proline. This latter effect is reflected in the greater stabilization of the trans conformers of the tripeptide in the presence of these specific ions. The molecular view provided by UVRR experiments was complemented by the results of circular dichroism (CD) measurements that show a strong structural stabilizing effect on the beta-turn motif of GPG-NH2 observed in the presence of KF as a co-solute