Solar Orbiter Takes a Battering

| Environmental Testing

Vibration testing takes place in the launch configuration
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The European Space Agency’s Solar Orbiter undergoes intense environmental testing in preparation for its launch in 2020.

As if missions to space weren’t hostile enough, a launch planned for 2020 takes environmental extremes to new levels by sending the Solar Orbiter craft on a seven year mission to observe the sun, including its polar regions, from an elliptical orbit that takes the space craft inside Mercury’s orbit at its closest approach.

Built in the UK by Airbus Defence & Space, the European Space Agency’s (ESA) Solar Orbiter is currently undergoing intense environmental testing at the IABG test facility in Ottobrunn in Germany.

The Solar Orbiter Mission

Solar Orbiter was designed to perform unprecedented close-up observations of the Sun. To do so, it carries 10 instruments to observe the turbulent, sometimes violent, surface of the Sun and study the changes that take place in the solar wind that flows outward at high speed from it.

Its orbit will allow scientists to study the sun and its corona in much more detail than previously possible and to observe specific features for longer periods than can ever be reached by any spacecraft circling the Earth. In addition, it will measure the solar wind close to the Sun and provide high-resolution images of the Sun’s uncharted polar regions.

Thermal Vacuum Testing

The first phase of Solar Orbiter’s environmental testing campaign was conducted in IABG’s thermal-vacuum chamber last December. Inside the chamber, powerful lamps are used to produce a ‘solar beam’ that simulates the Sun’s radiation to demonstrate that the spacecraft can sustain the extreme temperatures it will encounter in the Sun’s vicinity.

During this test, the solar beam was used at its maximum flux of about 1800 W/m2, reaching temperatures up to 107.6ºC. An additional thermal-vacuum test was conducted on the heat shield that protects the entire platform from direct solar radiation: during this test, which used infrared plates to simulate the Sun’s heat, the heat shield reached higher temperatures, up to 520ºC, similar to what it will experience during operations.

Vibration Test Preparation

After the thermal vacuum testing, the orbiter remained at Ottobrun for the next phase of testing for assuring its mechanical integrity.

The spacecraft was placed in a stowed configuration as it will be within the shroud of the Atlas V launch vehicle and two solar arrays were fitted.

The instrument boom, fitted with its full suite of scientific instruments, was also integrated to the spacecraft’s platform and reference alignment measurements were carried out to compare against post-testing results.

In its full flight configuration with all deployable elements stowed, the spacecraft went through a number of pre-vibration manual deployment tests. These will be used as a reference for comparison with the final ‘live-fire’ deployment tests that will be conducted after the vibration test campaign.

Since the various appendages are not designed for deployment under Earth’s gravity, the procedure required a series of specially designed off-load rigs. These allow near frictionless deployment of the suspended parts, while simulating the weightlessness of space.

To enable each off-load rig to protect the deployable hardware, the spacecraft had to be orientated during each test so that the plane of the deployment was parallel to the ground.

Once the tests were completed, all of the deployed items were re-stowed and small hold-down-and-release devices were attached to them, ready to be fired after completion of the vibration test campaign.

Vibration Testing

The two-part mechanical vibration test phase has started and will continue during the summer of 2019. It is designed to verify the suitability of the spacecraft to survive the lift-off and journey to reach its operational orbits around the Sun.

The first part involves a sine vibration test on an electro-mechanical shaker, replicating the powerful thrust of the Atlas V launcher, sudden engine cut-offs and lateral wind shear events throughout the launch and ascent.

The sine vibrations are applied separately up to a frequency of 100 Hz in three axes with a series of low-level signature runs to determine whether the structural integrity changes. This stage has been successfully completed and was followed by acoustic tests, which covered the frequency spectrum from just below 100 Hz to 8 kHz. The largest excitations in the acoustic chamber existed in the approximate range of 100 to 500 Hz.

A number of tests were undertaken as the acoustic noise pressure was steadily increased toward the final required qualification levels.

Now, all the deployable appendages on the spacecraft are being deployed again, using the off-load rigs. This time, however, the various hold-down devices are all being fired to simulate post-launch deployment of both antennas, the solar arrays and the instrument boom. The boom has two phases of deployment, but only the first can be effectively deployed on the ground.

These deployed structures will then be returned to their stowed configuration and the hold-down release mechanisms will be re-commissioned, ready for flight.

A Drop in the Ocean

Extreme solar and vibration testing are not the only environmental ordeals that space vehicles are subjected to. Re-usable equipment also needs to be tested to ensure its re-usability once it has plummeted back down to earth.

One such test was recently carried out by the El Arenosillo Experimentation Centre in Spain on the Miura 5 orbital microlauncher. Miura 5 is designed to launch small satellites of up to 300kg to low Earth orbit and weighs 14 tonnes at liftoff.

For the test, a Chinook CH-47 helicopter lifted the 15m long Miura 5 demonstration first stage section to an altitude of 5km then dropped it over a controlled area of the Atlantic Ocean, 6km off the coast of Huelva in southern Spain.

During the descent, electronic systems inside the demonstrator controlled a carefully timed release of three parachutes to slow it down until its splashdown at a speed of about 10 m/s.

A team of divers recovered the demonstrator and hoisted it onto a tugboat, which returned to the port of Mazagón. The demonstrator appeared intact and is now at PLD Space in Elche, where it is undergoing inspection and further analysis.

PLD Space is also using its experience of such testing on the ESA’s Future Launchers Preparatory Programme.

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