Making it in Space
By Lynda Nolen, Bishop & Associates Inc.

10, 9, 8, 7, 6, 5, 4, 3, 2, 1 – Blast Off! With almost 3,000 satellites orbiting the earth daily and 20 more scheduled by the end of the year, designing electronic components that can operate properly, safely, and efficiently in space applications is a unique challenge to the electronic connector manufacturer. Although each country operates under the guidelines of a different space agency, consortium, or organization with their own set of standards and criteria for connectors used in space, most, if not all of these standards are similar in context and design. Having the capabilities to meet these standards and criteria, though, is what sets the connector manufacturer of space-grade connectors miles above their competition.

Similar to other harsh environment applications, connectors specified for use in space must meet a variety of unique and challenging criteria. In addition to being able to perform under extreme vibration, shock, and extended temperature ranges, connectors used in space applications must also meet out-gassing requirements (NASA SP-R-0022), exhibit low residual magnetism, and be able to withstand the highly corrosive atmosphere of space. Also, as would be expected, connectors used in space applications must be as small and lightweight as possible.

Based on exact function, connectors used in space are generally divided into three reliability levels or grades. Products procured to a reliability level 1 have the highest level of manufacturing control and testing per military specifications. Level 1 products are typically specified when the duration of the program is anticipated to be five years or greater. Level 3 products are considered to have little to no guaranteed reliability controls in the manufacturing process and no standardized testing requirements. Connectors procured to level 3 specifications are used in applications where the risk of failure is understood to be high, or is unknown. Level 3 products are typically used in programs where the mission duration is expected to be between one and two years. In addition to reliability levels, NASA also has a guidance tool for manufacturers and suppliers to determine specific testing requirements which define a number of specific space environments, including habitable pressurized modules, low earth orbit, geosynchronous earth orbit, transatmospheric vehicle, lunar surface, and Martian surface.

One of the most crucial requirements of connectors destined for space is the ability to meet the necessary out-gassing requirements. Out-gassing, which occurs in vacuum environments, is the result of gaseous molecules in the form of condensation developing on cooler surfaces when non-reactive additives, contaminants, absorbed gasses, or moisture evaporate from the material. This condensation or evaporated gas, which can be reduced in a number of ways, can degrade the performance of instruments and, in particular, optical surfaces.

The first and most prevalent way is to select materials, recognized and approved for their low out-gassing properties. An online searchable database of materials recommended for space applications is maintained by Goddard Space Flight Center (NASA). A second way is to “bake out” the material. Although various space agencies (NASA, ESA, and ESTEC) have agency-specific testing methods, the customary method of testing and comparing is described in standard ASTM-E595, developed by the space community. According to these standards, in the case of a bake out, an individual component, a completed connector, or even a complete connector assembly is placed in a vacuum oven for approximately 24 hours at 125°C and a minimum of 10^-6 Torr. Upon completion of the baking cycle, the initial mass of the material is compared to the mass after bake out. Products, especially nonmetallic materials approved for space applications, must not exhibit a Total Mass Loss (TML) of greater than one percent, nor during the test can the amount of material (condensation) collected on the cooled collector plate, located within close proximity of the specimen and referred to as Collected Volatile Condensable Material (CVCM), exceed 0.1 percent of the original total mass. It is interesting to note that out-gassing not only covers obvious things like insulator materials, epoxies, molding and potting compounds, but also marking materials and ink.

To ensure that connectors exhibit low residual magnetism, thus preventing distortion that can be created by radio frequency (RF) and magnetic interference, materials used in connectors specified for space applications must demonstrate low permeability. In most metal shell connectors, this means the base material must be some type of machined aluminum alloy or corrosion-resistant steel or brass, and the connector finish should be electroless nickel. For D-subminiatures, the preferred finish is gold-over-copper flash, and for coaxial connectors, passivated stainless steel or gold is required. Contacts, regardless of connector type, are required to be plated with 50 micro inches of gold. Finishes prohibited for use in space applications include cadmium, zinc, silver, and pure tin.

A variety of connector types are used in space applications, including: rectangular I/O, printed circuit board connectors, circular connectors, coaxial connectors, fiber optic, and application-specific connectors, like umbilical interface connectors and filter connectors.

Rectangular Connectors
Rectangular connectors used in space applications include D-subminiatures, rack and panel connectors, microminiature connectors, and nano-miniature connectors. Although each of these connectors can be unique in their particular application, they must all be able to operate effectively within the confines of a space environment. A major supplier of space-grade rectangular connectors, in particular microminature and nano-miniature connectors, is Omnetics. With 20 years experience in supplying space grade interconnects, Omnetics products have been used on a number of space programs, including:

• Cassini: Launched in 1997, the Cassini successfully completed its original four-year planned tour of Saturn and is now in extended mission operations. The first extension expires September 2010, but an additional extension has been issued, allowing Cassini to continue supplying information through May 2017.

• Mars Rover: Now in its seventh year of exploration, the rovers are used to explore the geological characteristics of Mars.

• Iridium Satellites: The world’s largest commercial satellite system, composed of 66 satellites and spares.

• Space Shuttle Program and COSTAR (Corrective Optics Space Telescope Axial Replacement)

Operating effectively within the confines of a space environment often means manufacturing products that require additional testing or manufacturing steps. “Although we primarily use materials and ink that already meet NASA’s out-gassing requirements, we also allow customers to specify any added out-gassing processing they may require. We essentially allow a customer to specify the specific level of space-level screening they require, ranging from Level 1 (Mission Critical) to Level 3 (Standard Reliability),” explained Greg Jones, North American sales manager for Omnetics. “While all of our products include a C of C (Certificate of Compliance), we frequently receive orders that are built to our customer’s Source Control Drawings (SCD). Depending upon the requirements identified in the SCD, we have the ability to screen, inspect, and test to whatever level they require.” If requested, Omnetics can also package connectors designated for space in alternative packaging, although Jones does comment that typical packaging includes bags, cases, trays, and tape and reel.

In addition to individual connectors, Omnetics also supplies the space community with micro and nano-miniature connectors fabricated with wire. “Our experience suggests both micro and nano connectors are commonly specified for orbital and deep space applications. Specifically, nano- connectors with wires are 100-percent tested at 100 DC for insulation resistance. The minimum resistance requirement is 5,000 megaohms. Common configurations found inside the box include wired, through hole, surface mount, and cable assemblies,” explains Jones.


Circular Connectors
Historically known for their ability to operate in extremely harsh environments, circular connectors are used extensively in space applications. Generally specified by a mil-spec call-out, ESCC (European Space Components Coordination) number, or GFSC (Goddard Space Flight Center) number, circular connectors are used to transfer both power and signal.

The most prevalent type of circular connector is based on the Mil-DTL-38999 series. Products procured using this military call-out are specified to class G, for non-hermetic connectors, or class H, for hermetic connectors. In order to meet out-gassing requirements, class G connectors are generally baked out after assembly.

Other variations of Mil-DTL-38999 connectors have also been developed to satisfy particular applications. For instance, the International Space Station has developed NASA space station program (SSP) and NASA space station quality (SSQ) drawing 21635, utilizing a Mil-DTL-38999 series IIl-type connector, for use in a manned spacecraft. This Zero-G, Lever Lock Connector, is designed for extravehicular activities (EVA), and offers a handle lock mechanism for use by a gloved astronaut.

Although not as prevalent, hermetic versions of Mil-DTL-5015 and Mil-DTL-26482 Series II connectors, as well as a variety of application-specific circulars, are also used in space applications.


PCB Connectors
In applications that require the use of mother and daughter board PCB connectors, one of the premier suppliers of space-grade connectors is Hypertronics, a division of Smiths Connectors. Similar to Omnetics, Hypertronics connectors have been used on a number of space programs, including:

• Mars Science Laboratory (MSL): Originally scheduled to launch in 2009, but postponed until 2011, this next-generation rover will provide additional capabilities over the current Mars rovers, including greater distance capabilities and increased payload (more instruments).

• Solar Dynamics Observatory (SDO): Launched in February 2010, the SDO is designed to understand the sun’s variability and influence on the earth.

• Lunar Reconnaissance Observatory (LRO): Launched in June 2009, the LRO is designed to gather necessary information for future long-duration lunar expeditions.

• Ares Rocket and the Orion Crew Vehicle

Utilizing their patented Hypertac® wire basket military socket contact, Hypertronics’ 2mm cPCI solved the requirements for a rugged, reliable connector to replace the CompactPCI® connectors, traditionally specified by designers of space flight hardware. Although the traditional CompactPCI connector has proven to be an invaluable connector for manufacturing equipment designated for the telecommunications and data-communications industries, the connector was not designed nor suited for applications where the ability to withstand high levels of shock and vibration played a crucial role in the application. Also, unlike connectors specified for space applications, CompactPCI connectors used in telecommunication or data communication applications generally were able to be upgraded or replaced with little to no effect on the equipment.

Understanding the limitations of the CompactPCI connector, particularly in the contact design, Hypertronics teamed up with NASA engineers to create a more ruggedized connector. Unlike traditional CompactPCI contacts, which are designed with stamped, blade-shaped contacts on the backplane connector and bifurcated socket tines on the daughter connector for two points of contact, Hypertronics’ Hypertac wire basket socket contact provides multiple linear contact paths, five in the case of the 2mm cPCI connector. “These numerous points of contact along its axis provide 360-degree coverage, making it nearly impervious to shock and vibration fretting,” said James R. Demers, international sales, Smiths Connectors North America. Currently the only approved source to GSFCs SFC S-311-P-822 drawing, Hypertronics’ 2mm cPCI connectors are used in all phases of space travel and exploration, from lift off to descend.

Hypertronics’ Hypertac contact system is not the only connector contact system designed to withstand the rigors of space travel; others include Omnetics thick-beam, flex contact and Positronic’s PosiBand® contact system. Omnetics’ thick-beam, flex-pin contact, similar to Hyperronics’, offers additional points of contact. “Both our micro and nano mil-spec complaint pins are made from beryllium copper (BeCu) for its spring member characteristics, and then plated according to these same specifications. Our design provides for four points of contact when engaged with Mil-DTL-83513 (micro) or Mil-DTL-32139 (nano) sockets. These four points of contact are proven to easily withstand the shock and vibration associated with space applications.”

Positronic’s PosiBand closed-entry contact system for standard and high-density D-subminiatures utilizes a two-piece contact design, rather than split-tine design. The main body of the contact provides the mechanical platform for the contact system, while the PosiBand spring clip provides normal force on the male contact. Unlike split-tine designs, which can be pried open during the mating process and in harsh environments, the PosiBand spring clip is more robust and less susceptible to damage. The PosiBand contact system has lower average insertion force, greater surface area at the male and female contact interface, and does not require annealing of the crimp barrels. All of this results in a more mechanically robust contact and more consistent electrical performance.

Fiber Optic Connectors
A relative new comer to the space community, fiber optic connectors have increasingly found a place in space applications during the last 10 years. Used in a number of space programs, including the International Space Station, Mars Science Laboratory, Lunar Reconnaissance Orbiter, and the James Webb Space Telescope, fiber optic connectors offer small physical size and weight, immunity to EMI and RFI, wide transmission bandwidth, the ability to transmit both analog and digital, as well as the low attenuation of light power over long distances. Although a number of fiber optic termini have been developed for space applications, currently the only space-qualified optical fiber connector is manufactured by Diamond SA. Referred to as the AVIM connector, Diamond’s connector is compatible with a wide variety of optical fibers, including single-mode, multi-mode, and polarization maintenance, and offers a miniaturized MIL-style ratchet system for high vibration and shock resistance.

Conclusion
Making it in space is no easy task. With no room for error and virtually no easy way to replace a defective connection, connectors used in all space applications must exhibit zero-defect characteristics. Special consideration much be taken to manage all raw materials and components that go into the connector or connector assembly. Manufacturers must maintain complete traceability of raw materials and components, and all completed products must be 100 percent visually inspected for proper markings and general workmanship. Connectors fabricated with wire into harnesses must be tested prior to installation in flight equipment, and must meet all applicable requirements of NASA-STD-8739.4 for workmanship.