Space: the final frontier for stepper motors

Paul Boughton

Alexander Hatzold explains why a new stepper motor standard for space is hitting the spot.

Within the past 10 years there has been a continuous shift within the space market. The big space agencies refocused their strategic orientation and gave up the lead in specific fields due to budget adjustments by the governments involved – for example, NASA giving up the space shuttle after 30 years in 2011 and now ESA is shutting down the ATV project in 2014 after just six years. This major shift opened up a market for new engineering companies with more competitive concepts and products. 

Creating an historic opportunity for a wide range of new applications, the market for application design became not only more innovative, but also more competitive and therefore price sensitive. 

Aside from the highly individual designs for very specific projects, there is a competition-driven, rising demand for reliable, out of the box space-suitable solutions. This puts suppliers in a challenging situation – the cost per piece has to be reduced while quality standards must be maintained. 

On the other hand, this increase in cost efficiency, along with an expanding variety of new space-related companies and applications, creates a higher demand in total and makes this market a growing one. Especially when it comes to the technical core of applications: from moving parts, mechanisms and actuators, to high precision adjustments of antennas, lenses and filters - creating the perfect fit to integrate space-specific needs with a standardised framework is quite a challenge. 

Space standards

Suppliers such as Phytron must expand their portfolio to be part of this new market. With 20 years of space heritage, more than 300 customised motors in space (including Cassini-Huygens, STERO, ROSETTA, CURIOSITY), and experience of serial production for special applications, Phytron has put a lot into the design of a new stepper motors series for the space market. 

To create a platform that provides highly reliable solutions with ECSS-qualified materials for a very competitive price without sacrificing space standards, a modular approach was taken. Despite the variety of applications, a specific set of challenges and matching features binds most of these projects together. This set defines the core of the new phySPACE series.

Because of the weight-related costs, the structural design of the motors needs to present an optimum of lightweight, stiffness and protection. Shock and vibration loads of a rocket launch can predamage the motor and drastically shorten the lifetime. A duplex bearing assembly and weight-optimised front flange dissipate the vibration loads safely into the housing structure.

Environmental challenges include a wide temperature range, ultra-high vacuum, radiation from 103J/kg up to 106J/kg and lack of thermal dissipation. With an operational temperature in between -40°C and 160°C, all materials selected for the motors can withstand a short-term temperature of up to 180°C. 

The design is radiation-hardened, and the structural elements such as housings, flanges and shafts are made of stainless steel or titanium.

For most applications, the cleanliness of the actuator itself is crucial. While representing an optimum of strength, ductility and high thermal resistance, adhesives and insulation materials also have to provide low outgassing rates at operational temperature compliant with European and US Space Standards.

Preconditioned at up to 200°C in vacuum chambers, the outgassing materials cannot deposit in the ball bearings or inside the motor. This way, the motors provide a minimum molecular contamination of the surrounding system so that they can also operate close to optical systems. The device also comes with a temperature sensor to guarantee the safe operation at all times – even inside a vacuum. Phytron has created a rock solid, proven and future-oriented series that optimises costs, yet remains highly reliable in the most arduous of conditions.

Integrating all of these aspects into a modular framework in combination with optional upgrades and modular test packages, engineers can now can now choose a pre-qualified Phytron motor. based on their particular application’s needs – from low-cost approaches up to ESA- and NASA-compliant projects. 

The approach of standardising space components will increase the market, help new applications to meet their economic restrictions and, at the same time, provide a very high level of reliability and functionality. 

Application designers that manage to shift towards standardised components will supersede their competition in the long run by creating more cost-efficient designs and projects within a shorter time.l

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Alexander Hatzold is head of Product Strategy and Marketing, at Phytron, in Gröbenzell, Germany.