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

Novel methods to measure the gravitational constant in space

We present two novel methods, tested by LISA Pathfinder, to measure the gravitational constant G for the first time in space. Experiment 1 uses electrostatic suspension forces to measure a change in acceleration of a test mass due to a displaced source mass. Experiment 2 measures a change in relative acceleration between two test masses due to a slowly varying fuel tank mass. Experiment 1 gave a value of G=6.71±0.42(×10-11)¿¿m3¿s-2¿kg-1 and experiment 2 gave 6.15±0.35(×10-11)¿¿m3¿s-2¿kg-1, both consistent with each other to 1s and with the CODATA 2014 recommended value of 6.67408±0.00031(×10-11)¿¿m3¿s-2¿kg-1 to 2s. We outline several ideas to improve the results for a future experiment, and we suggest that a measurement in space would isolate many terrestrial issues that could be responsible for the inconsistencies between recent measurements.Peer ReviewedPostprint (published version

Temperature stability in the sub-milliHertz band with LISA Pathfinder

This article has been accepted for publication in "Monthly notices of the royal astronomical society" published by Oxford University Press.LISA Pathfinder (LPF) was a technology pioneering mission designed to test key technologies required for gravitational wave detection in space. In the low frequency regime (milliHertz and below), where space-based gravitational wave observatories will operate, temperature fluctuations play a crucial role since they can couple into the interferometric measurement and the test masses’ free-fall accuracy in many ways. A dedicated temperature measurement subsystem, with noise levels in 10¿µK¿Hz-1/2 down to 1¿mHz was part of the diagnostics unit onboard LPF. In this paper we report on the temperature measurements throughout mission operations, characterize the thermal environment, estimate transfer functions between different locations, and report temperature stability (and its time evolution) at frequencies as low as 10¿µHz, where typically values around 1¿K¿Hz-1/2 were measured.Peer ReviewedPreprin

Luminescent Tetrahedral and Octahedral Manganese(II) Complexes with [O=P]-Donor Ligands

Luminescent Mn(II) complexes are of potential interest for lighting applications, for instance as replacement of expensive rare earths-based phosphors in fluorescent lamps [1]. The emission is related to the 4T1(G)→6A1(6S) transition and is strongly dependent upon the coordination geometry: tetrahedral complexes are normally green emitters, while octahedral species emit in the red range. However, the luminescent properties can be enhanced by the presence of rigid structures and light harvesting fragments, able to reduce the non-radiative decay and improve the absorption in the UV region [2]. On the basis of recent outcomes on dihalide derivatives with phosphine oxides, our research group exploited phosphoramides, arylphosphonic diamides, amidophosphates and phosphonates as ligands for the preparation of tetrahedral Mn(II) complexes having general formula [MnX2L2] (X = Cl, Br, I). The complexes were isolated from the reaction between the proper anhydrous MnX2 salt and L under mild conditions. The structure of the derivatives was ascertained by single-crystal X-ray diffraction. The species revealed to be appreciably luminescent in the green region upon excitation with UV-light, with emission maxima centered between 510 and 535 nm. The luminescence lifetimes are in the hundreds of μs range, strongly influenced by the choice of the coordinated halide. In general, the lifetime decreases passing from the chloro- to the bromo- and the iodo- derivative as a consequence of the increased spin-orbit coupling effect [3-5]. Instead, when 2-naphthyl or carbazolyl fragments were introduced in the skeleton of the [O=P]-donor ligands the corresponding tetrahedral Mn(II) complexes were characterized by dual emissions, with a band in the green region attributable to the metal center and another one, centered in the red region, ascribed to triplet states of the aromatic substituents [6-7]. Similar results were achieved with [O=P]-ligands based on P(III) such as dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) and 9,10-dihydro-9-oxa-10phosphaphenantrene-10-oxide (DOPO) [8]. On the other hand, the coordination of Mn(II) to phosphonates containing the (R/S)-BINOL fragment determined an almost pure 3LC emission with complete disappearance of the green band. Bidentate ligands prepared from DOPO allowed the isolation of the corresponding octahedral Mn(II) complexes characterized by intense emissions centered at 611 nm. Differently from tetrahedral derivatives the luminescent lifetimes are in tens of ms range for octahedral derivatives as the 4T1(G)→6A1(6S) transition is both parity and spin forbidden

Genomic landscape characterization of large granular lymphocyte leukemia with a systems genetics approach

Non peer reviewe

Possibilities for Measurement and Compensation of Stray DC Electric Fields Acting on Drag-Free Test Masses

DC electric fields can combine with test mass charging and thermal dielectric voltage noise to create significant force noise acting on the drag-free test masses in the LISA (Laser Interferometer Space Antenna) gravitational wave mission. This paper proposes a simple technique to measure and compensate average stray DC potentials at the mV level, yielding substantial reduction in this source of force noise. We discuss the attainable resolution for both flight and ground based experiments.Comment: To be published in Advances in Space Research, COSPAR 2002 conference proceedings (6 pages, 3 figures

(E,E)-Methyl 2-[(3-nitrobenzylidene)­aminomethyl]-3-phenylpropenoate

The mol­ecule of the title compound, C18H16N2O4, adopts a T-shaped conformation with E stereochemistry for the imine double bond. The (3-nitro­benzyl­idene)amino fragment is almost planar, the mean planes of phenyl ring and nitro group forming a dihedral angle of 8.9 (3)°. In the 3-phenyl­acryloyl unit, the acrylic ester fragment is also almost planar, with the phenyl ring twisted by 41.44 (7)°. In the crystal, the mol­ecules are linked by C—H⋯O hydrogen-bond inter­actions into chains running parallel to [01]

Measuring random force noise for LISA aboard the LISA Pathfinder mission

The LTP (LISA Testflight Package), to be flown aboard the ESA / NASA LISA Pathfinder mission, aims to demonstrate drag-free control for LISA test masses with acceleration noise below 30 fm/s^2/Hz^1/2 from 1-30 mHz. This paper describes the LTP measurement of random, position independent forces acting on the test masses. In addition to putting an overall upper limit for all source of random force noise, LTP will measure the conversion of several key disturbances into acceleration noise and thus allow a more detailed characterization of the drag-free performance to be expected for LISA.Comment: 7 pages, 3 figures. To be published in Classical and Quantum Gravity with the proceedings of the 2003 Amaldi Meetin

Synthesis of α-alkylidene cyclic carbonatesviaCO2fixation under ambient conditions promoted by an easily available silver carbamate

The simple and cost-effective compound [Ag(O2CNEt2)], in combination with PPh3, works as an effective catalytic precursor in the carboxylation of propargyl alcohols at ambient temperature and atmospheric CO2pressure, and in most cases under solventless conditions. The silver carbamate revealed a better performance than commercial silver oxide, Ag2O, and allowed to obtain a series of α-alkylidene cyclic carbonates in high yields