LISA pathfinder micronewton cold gas thrusters: in-flight characterization

The LISA Pathfinder (LPF) mission has demonstrated the ability to limit and measure the fluctuations in acceleration between two free falling test masses down to sub-femto-g levels. One of the key elements to achieve such a level of residual acceleration is the drag free control. In this scheme the spacecraft is used as a shield against any external disturbances by adjusting its relative position to a reference test mass. The actuators used to move the spacecraft are cold gas micropropulsion thrusters. In this paper, we report in-flight characterization of these thrusters in term of noise and artefacts during science operations using all the metrology capabilities of LISA Pathfinder. Using the LISA Pathfinder test masses as an inertial reference frame, an average thruster noise of ~0.17¿¿µN/Hz is observed and decomposed into a common (coherent) and an uncorrelated component. The very low noise and stability of the onboard metrology system associated with the quietness of the space environment allowed the measurement of the thruster noise down to ~20¿¿µHz, more than an order of magnitude below any ground measurement. Spectral lines were observed around ~1.5¿¿mHz and its harmonics and around 55 and 70 mHz. They are associated with the cold gas system itself and possibly to a clock synchronization issue. The thruster noise-floor exhibits an excess of ~70% compared to characterization that have been made on ground on a single unit and without the feeding system. However this small excess has no impact on the LPF mission performance and is compatible with the noise budget for the upcoming LISA gravitational wave observatory. Over the whole mission, nominal, and extension, the thrusters showed remarkable stability for both the science operations and the different maneuvers necessary to maintain LPF on its orbit around L1. It is therefore concluded that a similar cold gas system would be a viable propulsion system for the future LISA mission.Peer ReviewedPostprint (author's final draft

Lost conversations: finding new ways for black and white Australians to lead together

It\u27s time for a game-changer in how black and white Australians relate.   The difficulties we have in coming together—to talk, to work, to lead change—are core to our challenge to reconcile, as a country. But if we want to shift the status quo, if we want to lead change on entrenched Indigenous disadvantage, we don\u27t need another program, initiative or money to try and \u27fix\u27 the problem. We need to start having a different conversation.  The result of two years experience working together as part of a Social Leadership Australia initiative, Lost Conversations brings together the diverse perspectives and personal stories of five Aboriginal and four non-Indigenous authors, all with first-hand knowledge of what happens when black and white Australians come together to try and work on change.  Lost Conversations asks the questions and starts the conversations that we daren\u27t have in Australia ... until now:  What is \u27black\u27 power? What is \u27white\u27 power?  What qualifies someone to lead in this cross-cultural space?  Why is this so hard to talk about?  Can we start to name these things and try to shift the status quo?  Can we change?  Should we?  &nbsp

Apollo 17: At Taurus Littrow

A summation, with color illustrations, is presented on the Apollo 17 mission. The height, weight, and thrust specifications are given on the launch vehicle. Presentations are given on: the night launch; earth to moon ascent; separation and descent; EVA, the sixth lunar surface expedition; ascent from Taurus-Littrow; the America to Challenger rendezvous; return, reentry, and recovery; the scientific results of the mission; background information on the astronauts; and the future projects

Dark Matter Candidates: What Cold, ..and What's Not

In this brief review of recent theoretical developments associated with the search for dark matter I describe the following: why baryons are now ruled out as dark matter candidates; SUSY WIMPS and signatures in the MSSM and NMSSM why claimed indirect signatures are probably not WIMP related, why axions may be of new interest, how WIMP detection might tell us about the galactic halo, and how theorists are preparing to avoid the next generation of experimental constraints.Comment: 6 pages, Invited Review talk, Neutrino 2006. To appear in Proceeding

D2D-Based Grouped Random Access to Mitigate Mobile Access Congestion in 5G Sensor Networks

The Fifth Generation (5G) wireless service of sensor networks involves significant challenges when dealing with the coordination of ever-increasing number of devices accessing shared resources. This has drawn major interest from the research community as many existing works focus on the radio access network congestion control to efficiently manage resources in the context of device-to-device (D2D) interaction in huge sensor networks. In this context, this paper pioneers a study on the impact of D2D link reliability in group-assisted random access protocols, by shedding the light on beneficial performance and potential limitations of approaches of this kind against tunable parameters such as group size, number of sensors and reliability of D2D links. Additionally, we leverage on the association with a Geolocation Database (GDB) capability to assist the grouping decisions by drawing parallels with recent regulatory-driven initiatives around GDBs and arguing benefits of the suggested proposal. Finally, the proposed method is approved to significantly reduce the delay over random access channels, by means of an exhaustive simulation campaign.Comment: First submission to IEEE Communications Magazine on Oct.28.2017. Accepted on Aug.18.2019. This is the camera-ready versio

Off the edge

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University London.Work which takes from elsewhere forms an important thread in European art music. There is a long tradition of music which variously borrows, thieves, pastiches, plagiarises, ironically ‘retakes’, hoaxes, impersonates and appropriates. The music I have written for Off the edge, while seeking to honour and add to this thread, also attempts to zoom in upon and make explicit the idea of an ultimate and irreversible composerly self-annihilation, a kind of one-way exit-gate from the world of authored musical works itself made of pieces of music, which so much of this tradition, I feel, points towards. (Of my nine pieces, it is perhaps Time to go—only, with its ‘à la suicide note’ texts and its music that seems to slide in from far beyond the frame that is ‘composer Luke Stoneham’, which manages to get closest to this.) I have chosen the title Off the edge, because all of my music tries to capture a sense of nocturnal peripheral vision: be content with catching glimpses of the composer Luke Stoneham, because as soon as you turn to look at him face-on, he disappears