The Ins and Outs of Spaceflight Passive Components and Assemblies

By: Paul Kovacich, Engineering Manager, API Technologies

RF and microwave components deployed in space flight applications can experience hundreds of degrees

of temperature variation, massive amounts of radiation, and can be expected to operate at an elevated level

for sometimes decades. The demands of operating in a space environment bring many unique challenges

and unforgiving reliability requirements; therefore, designing passive components to meet these rigorous

operation criteria necessitates a high level of design expertise, qualifications/certifications, and testing

capability.

Advancements in telecommunications technology and an increased demand for connectivity to high speed

data services is leading to an increase in space deployments of telecommunications platforms. These

platforms offer services ranging from surveillance and military intelligence to GPS and commercial high-

speed data for home internet. Many remote industrial services also rely on satellite communications for

control and monitoring. However, deploying the sensitive RF/microwave equipment necessary to support

these critical data links—hundreds of miles from the surface of the earth—brings in a host of challenges

not seen on earth’s surface.

Though operation on land, air, and sea pose many extreme design challenges for RF/microwave passive

components, typically these platforms experience limited terrestrial exposure to temperatures, radiation, g-

forces, and pressures. In the bleakness of space, there are much greater extremes and environmental

instabilities to contend with. Couple these factors with the inability to provide maintenance service, and

these high performing space technologies must operate, reliably, for up to 15 years. The rigorous

operational requirements, in turn, demand stringent design and manufacturing practices for space qualified

components that must be taken into consideration throughout the design, fabrication, and delivery of space-

grade, or space flight, RF passive components and assemblies.

What Is The Big Difference Between Space Environments And Terrestrial Environments?

Though many of the electrical and RF performance criteria may be similar between space flight and

terrestrial passive RF components and assemblies, there are additional environmental considerations and

design requirements based on the physical geometry constraints of the components. For example, the

temperature range of operation for space-grade components in the US are required to meet the military

required temperature range, -55 ℃ to +125 ℃. Nevertheless, space qualified components are required to

operate in the extremes of these temperature ranges for 15 years without service, and potentially within a

hard vacuum.

The vacuum of space is unlike any terrestrial environment, as there is no dielectric atmosphere to insulate

between component elements or regulate temperature fluctuations. Specifically for high power and highly

sensitive assemblies, the lack of atmosphere may require the component or assembly to be hermetically

sealed. If not, effects such as multipaction and outgassing, can occur.

There are strict limits on materials that can be used in space, as outgassing, radiation-based material

degradation, and adverse material interactions can lead to catastrophic cascaded failures. Additionally,

materials such as cadmium and zinc will disintegrate in low pressures, and other metals, such as tin, will

develop metallic whiskers—called dendrites—that could bridge electrical connections and induce

component and assembly failures. Also, as there is no surface corrosion in space, when dissimilar and

similar metals touch, a metallic welding may occur, a process known as cold welding, and this may change

the RF and electrical behavior of metallic contacts.

Some insulators will also be reduced to dust when exposed to high cosmic radiation levels. For example,

Teflon materials may suffer derated electrical characteristics when exposed to radiation levels above 5

Megarads. Other materials may face the generation of hotspots when exposed to gamma, or other cosmic

radiation, and deteriorate. In space structures that also contain optics, for example, an outgassing material

or one that creates debris could deposit material or generate a haze that reduces the satellites optical

performance. Hence, every material that is used for space qualified devices must be an approved material,

or a nonstandard materials part request must be submitted in order to approve and validate the material

choice.

Another key difference with space flight hardware, is that the components and assemblies must be

completely shielded in a faraday cage. This cage is commonly composed of aluminum for low-weight

purposes, and must be of a necessary thickness to withstand radiation specifications delivered by the

organization deploying the hardware.

Design Considerations For Space Qualified, Or Space-Grade, RF Passive Components And

Assemblies

With these factors in mind, the size, weight, and specific shape of the component and assembly must be

kept to the minimal and most efficient format possible. Each kilogram of mass launched into space costs

thousands of dollars. Certain passive component topologies and technologies may not be viable for space,

as these methods cannot meet the weight or size restrictions. Ultimately, there is no opportunity for tune-

ups, service, or maintenance in space, so any component in space must be designed to survive within the

harsh environmental parameters for at least 15 years. This includes under high temperature and power

conditions for extended periods of time.

Moreover, the clever use of components can also lead to reduced circuit complexity and size, which may

involve much more detailed design resources invested upfront and may give designers with prior space

experience a significant advantage. For instance, as stability is a high priority requirement for space flight

components, in order to reduce size and circuit complexity, instead of adding frequency equalizer

components, negative and positive coefficient of thermal expansion materials can be used in conjunction to

reduce thermal variance in device performance (as you could in a resonator or filter tuning element).

As mentioned previously, in a hard vacuum, multipactor breakdown can take place when there are

significant voltage gradients between conductive elements of a component or assembly, mainly in high

power filters. For example, in a resonator cavity of a RF filter stage, the impedance changes within the

filter could lead to much higher voltage gradients than the input and output port impedances are specified

for. These internal potentials could cause ionization and eventually multipactor breakdown—cascading

electrons from one conductive surface to another. As using large gaps may not be an option, certain filter

topologies or materials may be unacceptable in space environments. Specialized simulation technology and

design experience are required to tackle obscure effects, such as multipactor breakdown.