We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(exp -2)/square root of Hz, or (0.54 +/- 0.01) x 10(exp -15) g/square root of Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm square root of Hz, about 2 orders of magnitude better than requirements. At f less than or equal to 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(exp -2)/square root of Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.

/pdf/sub-femto-g-free-fall-for-space-based-gravitational-wave-1b27ej2js9.pdf

Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results

In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 
20
 
 
μ
Hz
. The Letter presents the measured differential acceleration noise figure, which is at 
(
1.74
±
0.01
)
 
 
fm
 
s
−
2
/
√
Hz
 above 2 mHz and 
(
6
±
1
)
×
10
 
 
fm
 
s
−
2
/
√
Hz
 at 
20
 
 
μ
Hz
, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency.

Beyond the Required LISA Free-Fall Performance: New LISA Pathfinder Results down to 20 μHz.

The existence of gravitational waves is the most prominent of Einstein's predictions that has not yet been directly verified. The space project LISA shares its goal and principle of operation with the ground-based interferometers currently under construction: the detection and measurement of gravitational waves by laser interferometry. Only in space, detection of signals below, say, 1 Hz is possible. LISA, a joint project of ESA and NASA, is a mission that will measure these low-frequency waves. LISA consists of three spacecraft in heliocentric orbits, forming a triangle with 5 million km sides. Launch for LISA is scheduled for 2011, following a technology demonstrator LTP in 2006.

/pdf/lisa-technology-concept-status-prospects-2jruba6h9n.pdf

LISA technology - concept, status, prospects

Space-based optical systems must be made from lightweight materials which can withstand significant acceleration and temperature changes Materials such as ZERODUR®, ULE® (Ultra Low Expansion material) and silica are all potentially suitable Depending on the specific requirements of the optical system and the transmissive or reflective nature of the optical layout these materials can be used by themselves or together to fabricate optical benches The geometrical layouts of these optical systems are often very complicated and the requirements for mechanical stability very stringent, thus jointing components presents a challenge In this paper we present developments of a novel chemical bonding process, originally invented at Stanford University for bonding silica components for the optical telescope for the Gravity Probe B mission Colloquially called silicate bonding, this process utilizes hydroxide catalysis to join optical components to optical mounts to obtain high stability whilst accommodating the requirement for precise alignment procedures

/pdf/hydroxide-catalysis-bonding-for-stable-optical-systems-for-4mc7knd1lv.pdf

Hydroxide-catalysis bonding for stable optical systems for space

The LISA Technology Package (LTP), to be launched by ESA in 2006/2007, is a technology demonstration mission in preparation for the LISA space-borne gravitational wave detector. A central part of the LTP is the optical metrology package (heterodyne interferometer with phasemeter) which monitors the distance between two test masses with a noise level of 10 pm Hz−1/2 between 3 mHz and 30 mHz. It has a dynamic range of >100 µm without any actuators for the pathlength. In addition to the longitudinal measurements, it provides alignment measurements with an expected noise level of <10 nrad Hz−1/2. While the basic design has been described previously by Heinzel et al (2003 Class. Quantum Grav. 20 S153–61), this paper gives new details on the laser stabilization, the phasemeter and recent prototype results.

/pdf/the-ltp-interferometer-and-phasemeter-41j2r87juz.pdf

The LTP interferometer and phasemeter

The interferometer of the LISA technology package (LTP) on SMART-2 is needed to verify the performance of the gravitational sensors by monitoring the distance between two test masses with a noise level of 10 pm Hz −1/2 between 3 mHz and 30 mHz. It must continuously track the motion of the test mass distance while that distance changes by many µ mw ith a speed of up to 20 µ ms −1 ,w ithout losing track of the sign of the motion and without exerting any influence on the test masses that might lead to a motion above that level. As a result of a detailed comparison study, a heterodyne Mach– Zehnder interferometer was selected as the baseline for the SMART-2 mission. Its design and expected performance are described in this paper.

/pdf/interferometry-for-the-lisa-technology-package-ltp-aboard-3mp7zkl4v3.pdf

Interferometry for the LISA technology package (LTP) aboard SMART-2

The LISA Technology Package (LTP), to be launched by ESA in 2008, is a technology demonstration mission in preparation for the LISA space-borne gravitational wave detector. A central part of the LTP is the optical metrology package (heterodyne interferometer with phasemeter) that measures the distance between two test masses with a noise level of 10 pm Hz−1/2 between 3 mHz and 30 mHz and also the test mass alignment with a noise level of <10 nrad Hz−1/2. An engineering model of the interferometer has been built and environmentally tested. Extensive functionality and performance tests were conducted. This paper reports on the successful test results.

/pdf/successful-testing-of-the-lisa-technology-package-ltp-pm2ykg6c0y.pdf

Successful testing of the LISA Technology Package (LTP) interferometer engineering model

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.

/pdf/testing-lisa-drag-free-control-with-the-lisa-technology-ab8njglm9e.pdf

M te Plate

Papers

Interferometry for the LISA technology package (LTP) aboard SMART-2

Successful testing of the LISA Technology Package (LTP) interferometer engineering model

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