D. Bortoluzzi

The LTP experiment on the LISA Pathfinder mission

We report on the development of the LISA Technology Package (LTP) experiment that will fly onboard the LISA Pathfinder mission of the European Space Agency in 2008. We first summarize the science rationale of the experiment aimed at showing the operational feasibility of the so-called transverse–traceless coordinate frame within the accuracy needed for LISA. We then show briefly the basic features of the instrument and we finally discuss its projected sensitivity and the extrapolation of its results to LISA.

LISA Pathfinder: the experiment and the route to LISA

LISA Pathfinder (LPF) is a science and technology demonstrator planned by the European Space Agency in view of the LISA mission. As a scientific payload, the LISA Technology Package on board LPF will be the most precise geodesics explorer flown as of today, both in terms of displacement and acceleration sensitivity. The challenges embodied by LPF make it a unique mission, paving the way towards the space-borne detection of gravitational waves with LISA. This paper summarizes the basics of LPF, and the progress made in preparing its effective implementation in flight. We hereby give an overview of the experiment philosophy and assumptions to carry on the measurement. We report on the mission plan and hardware design advances and on the progress on detailing measurements and operations. Some light will be shed on the related data processing algorithms. In particular, we show how to single out the acceleration noise from the spacecraft motion perturbations, how to account for dynamical deformation parameters distorting the measurement reference and how to decouple the actuation noise via parabolic free flight.

Gravitational sensor for LISA and its technology demonstration mission

We describe the current design of the European gravitational sensor (GS) for the LISA Technology Package (LTP) that, on board the mission SMART-2, aims to demonstrate geodetic motion within one order of magnitude of the anticipated LISA performance. We report also the development of a noise model used in assessing the performance and determining the feasibility of achieving the overall noise goals for the GS. This analysis includes environmental effects that will be present in the sensor. Finally, we discuss open questions regarding the GS for LTP and LISA, ground testing, and verification issues.

LISA Pathfinder: mission and status

LISA Pathfinder, the second of the European Space Agencys Small Missions for Advanced Research in Technology (SMART), is a dedicated technology demonstrator for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission. The technologies required for LISA are many and extremely challenging. This coupled with the fact that some flight hardware cannot be fully tested on ground due to Earth-induced noise led to the implementation of the LISA Pathfinder mission to test the critical LISA technologies in a flight environment. LISA Pathfinder essentially mimics one arm of the LISA constellation by shrinking the 5 million kilometre armlength down to a few tens of centimetres, giving up the sensitivity to gravitational waves, but keeping the measurement technology: the distance between the two test masses is measured using a laser interferometric technique similar to one aspect of the LISA interferometry system. The scientific objective of the LISA Pathfinder mission consists then of the first in-flight test of low frequency gravitational wave detection metrology. LISA Pathfinder is due to be launched in 2013 on-board a dedicated small launch vehicle (VEGA). After a series of apogee raising manoeuvres using an expendable propulsion module, LISA Pathfinder will enter a transfer orbit towards the first Sun?Earth Lagrange point (L1). After separation from the propulsion module, the LPF spacecraft will be stabilized using the micro-Newton thrusters, entering a 500?000 km by 800?000 km Lissajous orbit around L1. Science results will be available approximately 2 months after launch.

LISA Pathfinder drag-free control and system implications

The top-level requirement of the LISA Pathfinder mission is the verification of pure relative free fall between two test masses with an accuracy of about 3 × 10 -14 m s -2 Hz -1/2 in a measurement bandwidth between 1 mHz and 30 mHz. The drag-free control system is one of the key technology elements that shall be verified. Its design is strongly connected to the overall system and experimental design, in particular, via the following issues: the differential test mass motion and thus the science measurements depend on the control system; design constraints, such as negative stiffness of test masses and electrostatic actuation cross-talk, have an impact on science and control system performance; derived requirements for control system components, in particular, the micro-propulsion system, must be within reasonable and feasible limits. In this paper, the control design approach is outlined and the system-related issues are addressed.

The LISA Pathfinder Mission

In this paper, we describe the current status of the LISA Pathfinder mission, a precursor mission aimed at demonstrating key technologies for future space-based gravitational wave detectors, like LISA. Since much of the flight hardware has already been constructed and tested, we will show that performance measurements and analysis of these flight components lead to an expected performance of the LISA Pathfinder which is a significant improvement over the mission requirements, and which actually reaches the LISA requirements over the entire LISA Pathfinder measurement band.

Experimental Study of Motorcycle Transfer Functions for Evaluating Handling

Summary The transfer functions of a motorcycle, especially that between roll angle and steering torque, qualify input-output characteristics - that is, motion produced as a function of steering torque - and are closely related to ease of use and handling. This paper describes the measurement of the transfer functions of a typical sports motorcycle, resulting from data collected in slalom tests. These functions are then compared to analytical transfer functions derived from known models in the literature. The comparison shows fair to good agreement. Lastly, the formation of steering torque is analysed and the observed transfer functions are interpreted in this framework. It is shown that gyroscopic effects are mostly responsible for the lag between steering torque and roll angle, and that there is a velocity for which the various terms that combine to form steering torque cancel each other out, yielding a ‘maximum gain condition’ for torque to roll transfer function which drivers rated ‘good handling’.

Testing LISA drag-free control with the LISA technology package flight experiment

The LISA test masses must be kept fre eo fs tray acceleration noise to within 3 × 10 −15 ms −2 Hz −1/2 in order to obtain the low-frequency gravitational wave sensitivity goal. The LISA technology package (LTP) is a dedicated ESA flight experiment for testing the drag-free control technology that must ensure purity of free fall in the LISA mission. We present here a brief description of the LTP experimental configuration, specific measurements to be performed and the requirements that must be met in order to demonstrate the LTP stray acceleration upper limit goal of 3 × 10 −14 ms −2 Hz −1/2 at 1 mHz.

Data analysis for the LISA Technology Package

The LISA Technology Package (LTP) on board the LISA Pathfinder mission aims to demonstrate some key concepts for LISA which cannot be tested on ground. The mission consists of a series of preplanned experimental runs. The data analysis for each experiment must be designed in advance of the mission. During the mission, the analysis must be carried out promptly so that the results can be fed forward into subsequent experiments. As such a robust and flexible data analysis environment needs to be put in place. Since this software is used during mission operations and effects the mission timeline, it must be very robust and tested to a high degree. This paper presents the requirements, design and implementation of the data analysis environment (LTPDA) that will be used for analysing the data from LTP. The use of the analysis software to perform mock data challenges (MDC) is also discussed, and some highlights from the first MDC are presented.

Measurement of the momentum transferred between contacting bodies during the LISA test-mass release phase?uncertainty estimation

The requirements for the Laser Interferometer Space Antenna (LISA) test-mass (TM) release phase are analysed in view of the building up of a testing facility aimed at on-Earth qualification of the release mechanism. Accordingly, the release of the TM to free-fall must provide a linear momentum transferred to the TM not exceeding 10−5 kg m s−1. In order to test this requirement, a double pendulum system has been developed. The mock-ups of the TM and the release-dedicated plunger are brought into contact and then the latter is quickly retracted. During and after release, the TM motion is measured by a laser interferometer. The transferred momentum is estimated from the free oscillations following the plunger retraction by means of a Wiener–Kolmogorov optimal filter. This work is aimed at modelling the measurement chain, taking into account procedure, instruments, mechanisms and data elaboration in order to estimate the uncertainty associated with the transferred momentum measurement by means of Monte Carlo simulation.