Portsmouth, United Kingdom

4 Links
Milton Keynes, United Kingdom

For decades, space exploration remained exclusive to large-scale international agencies, such as NASA and ESA. In more recent years, though, things have changed considerably. Now numerous commercial enterprises and academic institutions are entering this sector, which has led to the 'New Space' phenomenon.

Among the fundamental dynamics driving this has been access to more affordable technology and the emergence of open-source reference designs. These have helped lower the engineering barriers to entry, making it possible for smaller players to place the equipment they have designed and created into orbit.

Based in Buckinghamshire, 4Links plays an essential role in 'New Space' development. The company, founded in 2000, provides the engineering know-how and consultancy services SMEs need to complete their space projects.

The Loki development platform with the subsystem interfacing area shown on the right. (Photo: 4Links)

A recent focus for the 4Links team has been to produce a platform for both software and hardware that would make space-bound systems quick, easy, and cost-effective to develop. Named Loki, after the Norse god, who was known for being disruptive, the platform encourages design re-use without starting each new venture from scratch.

The objective of Loki is to provide space customers with a fully configurable processing platform onto which they can build their on-board computers. It is designed for satellites using the increasingly popular SpaceWire network infrastructure methodology. Based on programmable logic and modular construction, Loki reduces the engineering effort involved, leading to faster completion times and lower associated overhead costs.

Loki consists of an Eurocard format carrier board with a mezzanine board attached. The mezzanine board is responsible for all the fixed functionality aspects, including processing, memory, system management. At the mezzanine's centre is a high-performance Xilinx Kintex UltraScale FPGA device. It can be reprogrammed before launch or even updated once in flight. An I/O carrier board manages all the interfacing. Acting as a gateway, it covers communication with the different satellite subsystems and the input for powering the FPGA mezzanine.

The ability to put the mezzanine onto carrier boards with different I/O configurations makes it much easier to modify the setup as needed. The other key advantage of Loki is that the board is only required to be qualified once and can then be used for multiple configurations. As a result, everything can be ready for launch in a dramatically shorter time frame.

“The carrier/mezzanine approach makes this platform very appealing to our customers. It is much more agile, resulting in development progressing at an accelerated pace,” said As Spencer Saunders, Engineering Director at 4Links. “Another benefit for users is that they can initially get one board qualified and then reconfigure others. This qualification avoids the need for costly re-certification for each new project that they embark upon,” he added.

Engineering Considerations

As Loki is intended for use in satellites and other orbiting hardware, the overall weight of the hardware had to be kept to an absolute minimum. In addition, the cost-sensitive nature of most 'New Space' projects had to be recognized, which means that using MIL-SPEC custom-built components in the design would not be feasible. Highly resilient commercial-off-the-shelf alternatives had to be used instead. On top of this, the parts had to be resistant to damage. All the components selected needed to function for prolonged periods despite exposure to extreme temperatures, mechanical shocks, and vibrations.

How the carrier board would interface with each of the subsystems presented the 4Links development team with several additional design challenges to overcome. Moreover, conforming to all the requirements previously outlined, there would be very little room in which the necessary connectors could be fit. A high pin density configuration needed to be specified.

Harwin's compact, lightweight Gecko-SL connectors have already proved very popular in a multitude of space ventures. (Photo: Harwin)

Finding an Effective Interconnect Solution

Conventional connector solutions, like Micro-D format, would have too large dimensions for this type of implementation. As a result, the PCB would take up valuable room. Also, such connectors are heavier due to metal housings, so another option was needed.

Harwin and 4Links started discussions about Loki a little over a year ago. After extensive testing on samples, the decision was taken that the Gecko-SL connectors would be an excellent choice for the I/O carrier board and all its subsystem interfacing capabilities.

Harwin’s 1.25-pitch Gecko-SL connectors have clear advantages over specifying standard Micro-D components, being significantly lighter and compact. As with all parts of the Gecko family, they offer the extremely high reliability needed for mission-critical systems. The screw locking mechanism allows retention even when subject to intense torsion forces. The 4-finger Beryllium Copper contact design ensures that interconnection is maintained regardless of heavy shocks (50G/100G) and vibrations (20G). Gecko-SL connectors have a temperature range from -65 °C to +150 °C. In addition, they also exhibit impressive outgassing properties.

Gecko-SL connectors come in a wide variety of pin count options. It was also significant for the Loki platform, giving 4Links' technical staff greater flexibility in connection combinations they could successfully fit into the available area on the carrier board. As a result, very little space would be occupied by unused pins.

“Harwin's Gecko-SL offered the high pin density we needed, in a far better way than we could get from competing solutions, with only minimal board area needing to be allocated,” said Saunders. “Also, the greater pin count versatility, through all the different versions available, was appreciated. It has meant that we do not have to over-specify, as connectors with the required number of pins can be assigned to each function, without pins being left unused and space being taken up unnecessarily.”

According to Sanders, the quality of the products and the technical backup received from Harwin, have been pivotal in getting the Loki platform to market. The platform is already forming the basis of the on-board computing systems of numerous low earth orbit (LEO) satellite missions used in weather monitoring, Earth observation, and space debris removal.

This article was contributed by Andy Brayford, Business Development Manager Northern Europe, Harwin (Portsmouth, UK). For more info visit here .