Spacecraft – plus their accompanying ground segment on Earth – are among the most complex machines ever conceived. Putting them together involves amalgamating numerous, highly complicated subsystems in their own right, everything from the power control distribution units that keep electricity flowing through spacecraft to the onboard computers that run them; the receivers and transmitters that keep them linked to Earth to the star trackers that let them fix precisely where they are in space.
“All these items come accompanied by documentation of course, stating precisely how they are to be used,” explains software engineer Jorge Lopez Trescastro of ESA’s Flight Software Systems section.
“These details might include their electrical connections and their data interfaces, governing how they receive and send data – including their adoption of defined data standards such as Canbus, Milbus or SpaceWire. Of course such items must be used in the correct way, otherwise they might be damaged or malfunction, so it is vital that they are thoroughly and understandably documented.”
The snag for space engineers? Every company has their own way of detailing such equipment documentation, depending on natural or company-set semi-formal language that can often end up overcomplicated. Or even when that is not the case, the translation process between two different company-custom formats can lead to mistakes in interpretation or implementation.
“This is a problem across many sectors, including the automotive and electronics industries, but it is especially challenging in the space arena,” adds ESA software engineer Marek Prochazka. “These specifications for avionics units represents one of the biggest – and perhaps the most dangerous – source of human error during spacecraft design and integration.
“So we are working on standardising a formalized description of the product information and interfaces, to be stored not in natural language but structured in a digital way – through a commonly recognised standard of Electronic Data Sheets (EDS). The first step is to come up with a practical standard, but the real challenge will come afterwards: to build up a consensus across European industry to encourage its use, then put in place the training needed to integrate this new standard into existing processes.”
This effort involves two parallel approaches. One track is to reuse and strengthen an existing digital format, in the scope of the Spacecraft Onboard Interface Services architecture, SOIS. This was created initially through the Consultative Committee for Space Data Systems (CCSDS), a multinational forum for the development of communications and data systems standards for spaceflight. The SOIS EDS standard for communications and data handling is already available.
The other track involves the use of the ESA-led Space Avionics Open Interface Architecture, SAVOIR, federating the development of European space systems through common specifications and interfaces.
In a research activity, a SAVOIR working group aims to create a common European EDS format for multiple domains that would also contain additional space-specific data, such as electrical, thermal and mechanical information.
“All the information is well structured to form a computer-readable information tree,” adds ESA software engineer David Perillo.
“And one of the research activities we’re running is to create compiler applications that can actually read these EDS, then automatically generate associated engineering artefacts. This would be a huge benefit, to create and automatically update flight software source code or simulation models for evaluation and testing – not only written documentation.
“On this basis, the EDS would become living documents that can be nimbly employed and modified as needed across the entire mission life cycle, slashing the time needed to perform actions like validations and interface compatibility checks.
“In the end it’s going to be a matter of convincing the prime contractors in particular, but standard electronic data sheets will be a powerful way of increasing quality while reducing cost. It is going to be hugely valuable to get companies everywhere speaking the same technical language.”
The next step will be to consolidate the outcome of these activities, and make them ready for actual use in space programmes. NASA and ESA are using the SOIS EDS for the data model of the Lunar Gateway, an international outpost around the Moon planned for later this decade.