ESA/ESTEC - Random Positioning Machine (RPM)

Random Positioning Machine

With the Random Positioning Machine (RPM), also referred to as “3-D clinostat”, hosted and operated at the Life and physical sciences Instrumentation and life Support (LIS) Laboratory of ESTEC, ESA’s technical centre located in the Netherlands, in collaboration with the Dutch Experiment Support Centre (DESC ), scientists are made available a tool able to simulate microgravity conditions on the ground.

The RPM is an affordable means to perform gravitropism-related experiments and it has demonstrated its value for stand-alone research studies as for preparing flight experiments.The RPM is relevant for fundamental biological research on animals or plants and single cells.

Short description of the RPM

The Random Positioning Machine is an instrument which was designed to provide an experiment with continuous random orientation changes in 3-dimensional space relatively to Earth’s gravity vector. The RPM is able to recreate on the ground effects close to those of a real microgravity environment. The principle of the RPM relies on “gravity-vector averaging” (i.e. there is no dominant orientation during the performance of an experiment) and on the fact that random changes in direction of the platform are faster than the response time to the gravitational stimulus of the studied system.

RPM functional architecture

The design of the RPM consists of two cardanic frames and the platform accommodating the experiment. The movements of the frames are generated via belts and two electro-motors. Both motors are controlled on the basis of feedback signals generated by encoders, mounted on the motor-axes, and by ‘null position’ sensors on the frames. The RPM is controlled by a computer hosting dedicated software.

Optional RPM features

Rotation rate ω and geometrical distance from the centre of rotation (R) enable the definition of “g-contours” through the following formula:

g = ω2.R.g0-1 (where g0= 9.81 m.s-2).

These parameters provide guidelines for the design and lay-out of experiment packages and for the interpretation of the experimental results. This means for instance that samples to be studied should be accommodated as close as possible to the centre of the RPM, as depicted by the residual accelerations diagram.

Optional RPM features

RPM and incubator based at the LIS Laboratory of ESTEC

For most of biological experiments which are candidates for the RPM, temperature, CO2 and humidity are important parameters to be controlled. The RPM was therefore designed to be operated inside an incubator for control of temperature (from 4◦C up to 40◦C), %CO2, (0-10%) and passive relative humidity control.

Technical Specifications

An additional optional feature is the provision of an accelerometer which can be mounted under the experiment platform in order to measure accelerations in the 3 dimension axes. Measurements data can be displayed on the user interface of the RPM. The average g level is calculated from the sensor output and indicates the symmetry in gravity nullification during the run of the experiment.

Technical Specifications

(According to the manufacturer’s specification: Dutch Space, The Netherlands)

Instrument size < 100 x 100 x 100 cm3
Experiment volume (max) 45 x 45 x 30 cm3
Functional experiment accommodation surface (when centred) 460 × 460 mm2
Experiment mass < 15 kg (max)
Slip-ring tracks to the experiment platform (e.g. for power, communication, video) 12
Utilisation scenarios Clinostat and hypo-g centrifuge modes: ω < 85 deg.s-1, hypo-g level 0.06g at 250 mm from the centre of rotation
Rotational speeds Random (0.1-2 rad.s-1)
Centrifuge (0.1-20 rpm)
Clinostat (0.1-20 rpm)
Experiment interfaces Switchable 12/15 Volt power line
RS232 (422) data bus (optical)

Scientific Applications

The RPM can be used to carry out scientific experiments in different research domains, mainly in biology, plant and animal physiology and microbiology. Dedicated experiments involving e.g. soft matter or material sciences could also considered.

Additional reading

[1] Van Loon, J.J.W.A. Some history and use of the Random Positioning Machine, RPM, in gravity related research. Adv. Space Res, 39: 1161-1165, 2007. DOI:10.1016/j.asr.2007.02.016

[2] A. G. Borst, J.J.W. A. van Loon. Technology and Developments for the Random Positioning Machine, RPM. Microgravity Sci. Technol., 21(4), 287-92, 2009. DOI 10.1007/s12217-008-9043-2

For questions or further detailed information please contact:

Robert Lindner
Head of Life and Physical Sciences Instrumentation and Life Support Section
European Space Agency, European Space Research and Technology Centre (ESTEC)
Noordwijk, The Netherlands
Tel. +31 71 56 54 678

Jack J.W.A. van Loon
Dutch Experiment Support Centre (
ACTA, VU-University Amsterdam, NL
Tel. +31 6 53 70 09 44

Last update: 23 January 2012

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