1.

INTRODUCTION

Following its important cryogenics heritage for the European Space industry for both ARIANE launcher program and Orbital Systems (180K high speed turbobrayton MELFI on-board the ISS since July 2006, 100mK dilution cooler for PLANCK High Frequency Instrument and HERSCHEL helium tanks and thermal links), AL/DTA is proposing a complete cryocooler system based on a pulse tube cryocoolers range and a dedicated CDE for earth Observations missions.

The cryocoolers are all featuring a splited coaxial pulse tube cold finger connected to a dual opposed pistons flexure bearing compressor with moving magnet type linear motors.

2.

MINIATURE PULSE TUBE COOLER - MPTC

The coaxial version of the Miniature Pulse Tube Cooler (Fig. 1) has been developed during the last two years^(1),(2). A batch of 3 cold fingers has been manufactured with a high quality level based on Air Liquide Standard Flight Procedures. Today, one MPTC unit is currently running in lifetime test at constant input power since August 2007. The amount of accumulated running hours as per July 2008 is 8050 hours without any degradation of the cold tip temperature. Engineering Model optimization and performance tests have been done to answer request for quote for the ESA Sentinel-3 mission (one of Low Earth Orbiting elements of Global Monitoring for Environment and Security) which responds to the requirements for operational and near-real-time monitoring of ocean, land and ice surfaces over a period of 15 to 20 years.

Fig. 1

EQM MPTC cold finger and compressor

This cryocooler has been optimized for 50W input power to the compressor motors. The cryogenic performances of the advanced MPTC are reported bellow:

The advanced MPTC performance mapping for various input powers and cold tip temperatures for 288K heat sinking conditions is presented in Fig. 2 hereafter. Cooler self-induced vibrations characterization of the MPTC EQM cooler is reported in the Fig. 3. As shown, the cold head self-induced vibrations have been measured bellow 70mN in all axes and in all directions. The RMS value is far bellow 0.1 N all along the bandwidth required in this program (0-300Hz).

Fig. 2

EQM MPTC cold finger and compressor

Fig. 3

EQM MPTC self induced forces at compressor interface - 50Wac input - 80K

An example of two MPTCs thermo-mechanical units in cold redundancy is attached in the Fig. 4, both cold fingers equipped with their thermal flexible link.

Fig. 4

MPTC redundant architecture integration

3.

LARGE PULSE TUBE COOLER - LPTC

The successful development of the Miniature Pulse Tube Cooler MPTC was driven by the need to cool detectors arrays at 80 K. In the meantime, there is a need for Earth Observation to cool Thermal Infrared detectors below 60K. At these temperatures, the cooling power of the MPTC, or the space qualified 50-80K Stirling cooler from EADS-Astrium UK Ltd, is marginal or not sufficient. In order to provide European coolers for the temperature range of 40-60 K, a large heat lift Pulse Tube Cooler LPTC is required in addition to the MPTC. An Engineering Model (EM) of the LPTC has been designed, manufactured and tested in partnership with AL/DTA, CEA/SBT and THALES Cryogenics BV in the framework of ESA/ESTEC contract 18433/04/NL/AR⁽³⁾. The EM (S/N001) performances were 2,3W cooling power lifted at 50K with 160W electrical input power to the compressor and 283K temperature rejection⁽³⁾. The EM was successfully tested to thermal and mechanical loads at qualification and duration levels.

Both LPTC and MPTC products are qualified against mechanical load profiles attached in the Fig. 6 (sinus load) and Fig. 7 (random load) for all axes. Beside that, the LPTC have been also submitted to stringent shock profile as par spectra attached in the Fig. 8 below.

Fig. 5

EM S/N001 installed on the shaker

Fig. 6

sinus load qualification profile

Fig. 7

random load qualification profile

Fig. 8

shock load qualification profile

Currently, four Engineering Qualification Models (EQM) are under production for various projects and an illustration of the EQM S/N002 is attached in the Fig. 10 together with its integration on a cryostat mock-up at Thales Alenia Space premises (Fig. 11).

Fig. 9

LPTC S/N001 during shock test.

Fig. 10

EQM LPTC S/N002 during curing/filling process

Fig. 11

EQM LPTC S/N002 integrated on a cryostat mock-up (courtesy of ThalesAlenia Space)

Beside cryogenic performance tests, the output forces of the LPTC EQM S/N002 have been measured on a dedicated test bench placed on a seismic block. The output forces at the compressor and cold finger warm end interfaces are measured separately on 3 axis over 1 kHz bandwidth in cryogenic operation and with controlled temperature interfaces (chilled water). The output force profile measured on the compressor piston axis (driving axis) is reported in the Fig. 12 for 80W ac input power applied on each of the compressor coil (160W total compressor).

Fig. 12

EQM LPTC S/N002 self induced forces at compressor interface – 160 Wac input – 50K

At the fundamental driving frequency, the output force is measured at less than 0.6N and all other harmonic levels are measured below 0.25N up to 1 kHz. The Fig. 12 illustrates also the Cooler Drive electronic (CDE) capability to reduce the output force levels once activated. The two coils of the compressor are then supplied separately (Master & Slave) with input voltage controlled over the fundamental and 7 harmonics. As shown, the output force level is drastically reduced over the controlled frequency bandwidth. For the fundamental, the level is reduced down to 25 mN. Notice that for frequency above 400 Hz, the level is not changed with and without active vibration control because the limited frequency harmonics contained in the control signal.

4.

COOLER DRIVE ELECTRONIC - CDE

The architecture of the CDE developed by Air Liquide in partnership with CAEN Aerospace is composed of three separated boards that implement the following functions:

4.2.

power board

This board (Fig. 13) houses two identical and independent Class-D amplifiers that are used to drive respectively Master coil and Slave coil (used for vibration reduction). Two couples of temperature monitors are sent to satellite TM in order to switch off the unit in case of failure that generates an increasing of power dissipation. Each amplifier provides one output voltage monitor that is an attenuated replica of the output voltage and one current monitor providing the replica of the output current. An additional thermistor for each amplifier, together with output voltage and current monitors, are sent to an analog protection circuit that switch-off both amplifiers in case over current, over voltage, over temperature, or output current mismatch between master and slave failure conditions. A flag with the relevant fault condition is sent to the control board in order to communicate the type of failure that has occurred to the instrument.

Fig. 13

EM power board of the CDE

5.

CONCLUSIONS

Air Liquide’s MPTC and LPTC Pulse Tube Coolers, including their CDE with vibration cancellation, are now available for Earth Observation applications. These two products represent clearly a technology enhancement and integration advantages compared to the former Stirling technology used in the past mainly in Europe.

A third cooler product is under development in partnership with CEA/SBT to provide 15–20 K pulse tube pre-cooling stage in alternative to two stage Stirling coolers.