1,721,157 research outputs found
A MAC Contest between LPL (the Champion) and Reins-MAC (the Challenger, an Anarchic TDMA Scheduler Providing QoS) Demonstration
No full textLPL [5], or BoX-MAC in its TinyOS implementation, is
arguably the most common MAC protocol for WSNs. Its
extensive use in real world deployments is justified by a simple
implementation, available online, that meets the requirements
of a vast majority of monitoring applications. Despite
the plethora of competitors, it still remains the reference in
the MAC scheduling world. However, its random nature inherently
hampers its possibility to support effectively any application
driven Quality of Service requirement.
To provide these guarantees, we offer REINS-MAC, a
TDMA-based MAC. While common TDMA solutions require
each node to rigidly follow an agreed upon communication
schedule, in REINS-MAC each individual defines its
own slot inside the overall frame. Despite the common belief
that such dynamic communication scheduling is infeasible
[3], REINS-MAC both adapts to the current network
topology, and allows each node to change the size and position
of its slot. REINS-MAC achieves the aforementioned
flexibility and anarchy by removing one fundamental parameter
of TDMA: the network-wide slot size constant.
This demo establishes a contest between REINS-MAC
and BoX-MAC under a variety of network conditions and
different parameter settings of a multi-hop monitoring application.
The audience is challenged to tune the BoX-MAC
parameters such as the sleep interval and modify the network
topology to create conditions that favor the CSMA solution.
For each setup, the behavior of the two protocols will be
scored on throughput, overhead, etc
Analytical low-jerk reorientation maneuvers for multi-body spacecraft structures
Full text linkA low-jerk attitude guidance method is developed, based on an analytical smoothing of a bang-off-bang maneuver. A set of closed-form equations are derived and used to plan constrained low-jerk maneuvers, with prescribed boundary conditions, inertia, time and maximum control torque. The guidance law is first developed for one-dimensional and then three-dimensional rotations using two different approaches: (i) by designing a rotation about the Euler axis and (ii) by using the inverse kinematics equations. A generic model of the torque induced by a multi-body appendage is derived using the lumped-parameter method. This method can also be used to approximate the dynamic behavior of flexible appendages. The simulations results show that the smoothing techniques reduce the excitation of multi-body and flexible structures during a slew maneuver
Trajectory optimization for the Hevelius-lunar microsatellite mission
No full textIn this paper trajectory optimisation for the Hevelius mission is presented. The Hevelius-Lunar Microsatellite Mission - is a multilander mission to the dark side of the Moon, supported by a relay microsatellite, orbiting on a Halo orbit around L2. Three landers, with miniaturized payloads, are transported by a carrier from a LEO to the surface of the Moon, where they perform a semi-hard landing with an airbag system. This paper will present the trajectory optimisation process, focusing, in particular, on the approach employed for Δv manoeuvre optimization. An introduction to the existing methods for trajectory optimization will be presented, subsequently it will be described how these methods have been exploited and originally combined in the Hevelius mission analysis and design
Halo orbit determination in the mission analysis of the Hevelius-lunar microsatellite mission
No full textThis paper introduces the mission analysis and design of the Hevelius - Lunar Microsatellite Mission. The objective of the mission is to place at least three landers on the dark side of the Moon, to perform some scientific experiments. A microsatellite orbiter is required to support the net lander as data-relay to the Earth. Moreover, another spacecraft, a carrier, has been designed in order to bring landers to the surface of the Moon, to map the landing site and to measure the gravitational field. The Hevelius mission analysis has been driven by the need to design lowcost and low-mass space missions. Since the relay satellite must continuously see the dark side of the Moon, an operative Halo orbit around the second Lagrangian point has been designed. Three different ways have been followed to determine the optimal Halo orbit. Optimal low-cost transfers to the Halo have been designed exploiting the invariant manifolds of the Earth-Moon L1 point while a Belbruno's WSB transfer to a frozen orbit around the Moon has been chosen for the carrier. The mission analysis process has been completed with a perturbations and eclipses analysis of the final operative orbits
Mission analysis of Hevelius-lunar microsatellite mission
No full textThis paper describes the mission analysis and design of the 'Hevelius - Lunar Microsatellite Mission'. The main goal of the overall mission is to place a net-lander on the far side of the Moon to perform some scientific experiments. Two different satellites have been designed to achieve this objective: a microsatellite orbiter to support the net-lander and a carrier spacecraft to transport the net-lander. An L2 Halo orbit has been selected for the orbiter in order to have a constant communication link between the landers and the Earth. The invariant manifolds of the Earth-Moon system have been used to design a low cost transfer trajectory to the L2 Halo orbit. Prior to the beginning of landing operations the carrier is parked into a frozen orbit after a WSB transfer. Finally the descent and landing phases have been designed in order to accomplish the final goals. The whole mission analysis and design process has been driven by the need for a low cost and low risk mission
An optimal steering law for sailing with solar and planetary radiation pressure
Full text linkAn optimal steering law for sails that exploit both solar and infrared planetary radiation pressure is presented in this paper. The optimal steering law maximises the orbit raise over one revolution of the sail around the planet. An indirect analytical approach, that uses Pontryagin Minimum Principle, is used to develop specialised steering laws for the sunlit and eclipse cases in a planar motion scenario. The law for the sunlit case uses both the solar and infrared radiation emitted from the planet, while the law for the eclipse case finds the optimal sail attitude that maximises the raise of the orbit using only the planetary radiation. Numerical results show that these laws lead to better performance in terms of orbit raising against other sub-optimal and optimal strategies exploiting the solar radiation pressure only. A numerical study is also carried out to show the effects of the reflectivity coefficient in the infrared band on the orbital motion of the sail
Sailing with Solar and Planetary Radiation Pressure
Full text linkLiterature on solar sailing has thus far mostly considered solar radiation pressure (SRP) as the only contribution to sail
force. However, considering a planetary sail, a new contribution can be added. Since the planet itself emits radiation,
this generates a radial planetary radiation pressure (PRP) that is also exerted on the sail. Hence, this work studied the
combined effects of both SRP and PRP on a sail for two case studies, i.e. Earth and Venus. In proximity of the Earth,
the effect of PRP can be significant under specific conditions. Around Venus, instead, PRP is by far the dominating
contribution. These combined effects have been studied for single- and double-side reflective coating and including
eclipse. Results show potential increase in the net acceleration and a change in the optimal attitude to maximise the
acceleration in a given direction. Moreover, an increasing semi-major axis manoeuvre is shown with and without PRP,
to quantify the difference on a real-case scenario
Preliminary mission analysis for the ESMO mission
No full textThe European Student Moon Orbiter, currently at preliminary phase A, is the first lunar spacecraft entirely designed by students, projected for launch in 2011 and to reach a stable lunar orbit around the Moon. This paper presents the trajectory analysis and design performed to accomplish the primary and secondary objectives of the mission. The requirements affecting the mission analysis are listed, including their effects on the target lunar orbit. The Outreach mission would send a spacecraft into a polar orbit around the Moon, the only payload on board being a Narrow Angle Camera. The Science mission will inject a nano satellite in a low, circular, polar orbit around the Moon. Two different transfer options were studied, making use of chemical and solar electric propulsion. Particular emphasis is put on the launch window analysis. In fact, being the spacecraft an auxiliary payload, the trajectory design must be compliant with any launch opportunity inside a three year launch window. Finally corollary studies, such as eclipse durations and ground station visibilities will be covered
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