This article provides insights into how hot zones are managed and mitigated in small satellite hardware.
It features the High Performance Radiators (HiPeR) Flexlinks product, designed and developed by Airbus Defence and Space Netherlands, which has the primary application of ensuring the transfer of heat from an initial to a final point in a space system. It also discusses how engineers can select the right configuration of thermal management system to suit their mission requirements.
The article was developed in collaboration with Airbus Defence and Space Netherlands B.V (Airbus DS NL), a paying participant in the satsearch membership program.
In the current age of NewSpace applications, the use of compact satellite components and the demand for high-power systems are both rising. One of the results of these trends is the generation of heat during operations, at higher intensities than have been produced by lower power systems and in smaller physical spaces.
A variety of more advanced payloads, attitude control subsystems, and data processing equipment are also increasingly being used in tighter envelopes. Alongside the greater power requirements these bring, they can also be highly sensitive to thermal variations.
Currently, more than 50% of the power generated in a satellite is converted into heat and this is pushing the industry to rethink, revise, and develop innovative new solutions for thermal system management. To meet this rising demand in the space industry, Airbus DS NL has developed high performance, customizable thermal straps called HiPeR Flexlinks.
The space industry has traditionally relied on large satellites, which are composed of numerous hardware components, for several application areas such as communication, Earth Observation (EO), and navigation.
With the introduction of NewSpace technologies, where small satellites are more widely used, satellite size can be reduced from several tonnes to just a few kilograms. And as component size is shrinking, this has also led to greater innovation in the software segment; ultimately uplifting demand for software-defined satellites.
In this transformation cycle, the heat generated by high-end components can be significant and therefore, thermal management products will be of crucial importance for serving the needs of a variety of space missions.
Thermal conductive links
Space systems consist of a complex nexus of electronics and high-power components which continuously, or intermittently, release heat during the operation of spacecraft. This heat, particularly if concentrated at a single location, can interrupt or cause severe damage to some components, ultimately disrupting the overall operation of the spacecraft.
HiPeR Flexlinks are a unique form of thermal strap that provides a medium to transfer the heat from the source of the application to a heat sink, which further transfers the heat to a radiator or heat pipe line.
The HiPeR Flexlink provides thermal coupling while introducing minimal mechanical coupling between two interface points within the system.
It consists of thin Pyrolytic Graphite (PG) sheets, stacked onto one another, operating as a flexible medium to transfer heat from one point to another. The PG consists of multiple layers of graphitic mono-crystal and its thermal conductivity is 3.5 times higher than copper, as well as 6-10 times higher than aluminum. This makes PG one of the most preferred materials for thermal management of space applications.
In HiPeR Flexlinks stacks of PG sheets include metal plates, allowing the product to also act as a thermal interface with other spacecraft structures. The product is then fitted with two aluminium blocks on the end of the straps to help it attach within the spacecraft. As graphite sheds particles, the product also consists of a layer of cleansleeve which prevents particulate contamination
HiPeR Flexlinks is at TRL9 for GEO, LEO and interplanetary missions, which makes it a market-ready product that can be deployed in a mission with a short throughput time, as per customer requirements.
It also has a wide range of applications which can be used in several space missions such as EO, navigation satellites, science missions, communication satellites, and more. This versatility is very important in today’s industry, as discussed in the next section.
The importance of flexibility
While linking a hot and cold spot, it is important not to introduce extra stiffness between the two interfaces. This is crucial for systems where high pointing accuracies are needed.
In HiPeR Flexlinks the thermal straps’ low stiffness feature prevents the transfer of mechanical loads between hot and cold spots due to displacements at those areas.
Physical flexibility leads to system setup flexibility; the ability to place thermal strap endpoints in a variety of different locations provides satellite designers with a greater number of options to fit systems together.
This in turn leads to operational flexibility. When satellite designers are confident that hot spots can be mitigated, wherever they occur, adaptable hardware and software architectures can be developed that meet a variety of application requirements.
Thermal straps should also be able to be integrated into complex satellite hardware setups in many different ways in order to provide the versatility needed to effectively manage heat during development and operation. The key to this is the level of configuration available, discussed in the next section.
How to choose the right conductive link for your needs
In all space procurement, engineers need to thoroughly research and analyze their mission needs before placing an order for a specific component, or choosing to have a custom solution created if a suitable standard product is unavailable.
With HiPeR Flexlinks customers can select from standard product ranges, but can also choose a specific configuration and further customize per their mission needs. The different integration options available are determined by the endfitting type and orientation of the product. For example, HiPeR Flexlinks are typically integrated in the following ways:
- Parallel – parallel
- Perpendicular – perpendicular
- Parallel – perpendicular
Each of these end fittings have key advantages. Based on the interface area and volume, the end fitting will vary in providing high thermal performance.
Considering the current trend of small satellites, such configuration needs may vary and customers have to create an actionable trade-off between the interface area and volume in order to choose the most suitable end fitting for their mission requirements.
Available configurations also take into account the flexibility stack length, mass, and the operating temperature capability. The stack length varies from 60 to 160 mm, while mass varies from 120 to 420 grams. Considering the thermal performance, the qualified temperature configuration is available between -150 to 70 degree celsius.
These are the key variables that engineers need to consider when assessing the right thermal management components for their system. If needed, a custom solution can be developed to fit the satellite or spacecraft’s particular thermal loads and mechanical interfaces.
It is also important to use all relevant specification and modeling information during design and integration. Building out a flatsat or engineering model of the system with the precise thermal strap arrangement intended for flight will help you to determine how to mitigate any hotspots in order to avoid major hardware, software, or operational changes.
This process relies on access to good documentation. For example, Airbus DS NL provides the following for HiPeR Flexlinks products:
- Certificate of Conformance (COC)
- CAD model (STP-file)
- Parts, Materials and Processes list (PMP list)
- User Manual (UM)
- Product Qualification Status List
- End Item Data Pack (EIDP) including statements about:
- Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)
- Log Sheets (Quality Control inspections)
- As-Built information
This documentation also provides confidence that the expected thermal performance levels can be reached.
Ultimately, however, the choice of how to manage thermal transfers in a satellite will come down to the overall application, and there are emerging areas in the industry where the process can be very important to ensure mission success.
One of the main reasons that thermal management is important in space applications is instrument precision, as mentioned above. In highly sensitive equipment minute errors or discrepancies in thermal management can create build-ups of heat that can lead to complete mission failure.
This is particularly important in the private sector where mission failure has immediate financial impacts. Given the tight funding landscape, commercial players need to carefully procure components to ensure the long-term success of their business.
Therefore, products such as HiPeR Flexlinks, which offer a wide range of configurations and robust operation in the space environment, are essential for the next generation of space missions.
Advancements in the upstream Earth Observation market, such as more powerful onboard image processing capabilities utilizing artificial intelligence (AI), might potentially increase the chances of more heat being generated in the system.
Similarly, use of optical communications equipment, an area where HiPeR Flexlinks are commonly used by several customers, can also result in an increased power budget for satellite-satellite and satellite-ground communication. And more power means more heat.
Alongside such processes, hotspots can be created in various innovative products and devices – wherever power is high, space is restricted, and/or precision is required.
Current and upcoming missions
Some of the missions and projects where HiPeR Flexlinks has been accepted for use include:
- Mega constellation; for the delivery of 900 thermal straps in just a few months, an in-house industrialized production line was prepared with a maximum manufacturing output of 26 thermal straps per day. These straps are currently flying.
- The thermal straps are also currently flying on a mission to the Sun, where high performance requirements are applicable.
- Soon to be launched onboard an Earth observation satellite, these Thermal straps were produced for cooling an optical instrument, which has very low operating temperatures (-150°C).
- Thermal straps were delivered for the RF instrument onboard a deep space mission, which is to be launched soon.
- Several missions for institutional and commercial customers are upcoming.
As can be seen, effective thermal management is important in a wide range of contexts and equipment as hotspots can occur in all sorts of systems and processes. Managing hotspots can be critical for ensuring mission success, particularly in cases where highly sensitive or power-hungry hardware is used.
The HiPeR Flexlinks portfolio has been developed by Airbus DS NL to provide a complete package of high performance thermal management systems; designed not only to help transport heat but also to bring robustness to missions and enable longer lifetime operations.
The Dutch team has developed the solution based on decades of experience in complex engineering systems and niche research capabilities, in order to try and eliminate even the most minor errors.