Maintain Interconnect Integrity at Cryogenic Extremes with Deep Space Connectors

Technical Overview: Space and other cryogenic systems require connectors that maintain sealing and electrical continuity through extreme temperature cycling, vibration, mechanical shock, and vacuum conditions. Conventional MIL-DTL-38999 connector elastomers can crack below their -65°C lower operating limit, compromising environmental seals. Amphenol Aerospace Deep Space D38999 connectors apply upgraded elastomers and associated material changes for cryogenic service while retaining compatibility with corresponding MIL-DTL-38999 connectors. This article examines the cryogenic modification, independent environmental testing, and available configurations. It also compares featured insert arrangements spanning high-density signal connections and power distribution, with current ratings from 5 to 23 amperes per contact. (Overview courtesy of ChatGPT)

Space systems endure extreme temperature swings throughout their lifecycles. This makes connector selection particularly challenging for designers, as they must go beyond offerings typically suitable for harsh environments. For example, space can expose connectors to cryogenic temperatures below -153°C, but the elastomeric seals of standard MIL-DTL-38999 circular connectors typically crack below -65°C, risking electrical shorts. In addition, launch vibration, mechanical shock, and thermal cycling can damage interconnects and further compromise seals, while hard vacuum introduces material-outgassing concerns.

Designers need connectors that preserve sealing and connectivity in the harsh conditions of space and other cryogenic applications, including quantum computing.

This article briefly reviews the challenges to interconnect integrity in space and other cryogenic applications. It then shows how space-grade connectors from Amphenol Aerospace Operations help address these challenges while remaining compatible with standard 38999 caps and accessories.

Why cryogenic extremes defeat standard connector sealing

Space missions expose hardware systems to some of the most extreme thermal environments, from the intense thermal cycling between sunlit and orbital eclipse phases in low Earth orbit (LEO) to the extended cryogenic nights on the lunar surface and sustained deep cold in interplanetary transit. A connector that seals properly during integration and launch must maintain interconnect integrity through protracted thermal excursions or risk mission failure.

Connector failure threatens critical applications that rely on power and signal interconnects operating in cryogenic environments. Cracked seals or elastomeric components can cause costly downtime and lost data wherever deep cold is part of normal operation. Along with space travel, this includes applications ranging from the superconducting magnets of magnetic resonance imaging (MRI) systems to the quantum processors in some quantum computing systems.

Standard MIL-DTL-38999 circular connectors depend on elastomeric components to maintain their grommet-to-wire and contact-to-contact seals. At temperatures below -65°C, those elastomers typically crack (Figure 1), losing environmental sealing and, in the worst case, causing electrical shorts.

Figure 1: When subjected to cryogenic temperatures, standard MIL-DTL-38999 component seals exhibit noticeable fine cracks or fractures radiating from the pin contacts. (Image source: Amphenol Aerospace)

Intense cold is not the only factor affecting space systems. Launch and orbital maneuvers subject every interconnect to severe vibration and mechanical shock, which can worsen damage initiated by thermal cycling, while vacuum-sensitive systems must also account for material outgassing. Cracks opened by extreme cold can widen into failures that compromise the connector's environmental sealing.

Select a space-grade extension of a familiar platform

Amphenol Aerospace's Deep Space D38999 connectors address cryogenic challenges while remaining compatible with the familiar MIL-DTL-38999 interconnect standard series. Each Deep Space connector applies the (750) cryogenic modification to a commercially coded 38999 configuration. The modification upgrades the elastomers and other necessary components while preserving the corresponding connector’s mechanical interface. Deep Space D38999 connectors share the same high-temperature ratings as the 38999 parts, up to +200°C, depending on the model.

Because the configuration carries over unchanged, Deep Space connectors mate with standard counterparts and work with standard 38999 caps and accessories already qualified in existing designs. Engineers can work within a familiar design framework, specifying the Deep Space version of a known 38999 part number. Variants are available across the 38999 Series I, Series II, and Series III, as well as the Scoop-proof Junior Tri-Lock (SJT) series.

The (750) modification upgrades the elastomers to a silicone blend capable of operation at -195°C and includes other component and material upgrades that support operation at that extreme temperature. At the same time, the upgraded seals resist compression set, avoiding the performance degradation associated with permanent deformation from stretching and compression during normal connector operation. Note that the -195°C figure describes the upgraded elastomer rather than serving as a blanket rating for the complete connector, and not all connector styles attain that capability because of other component limitations. Consequently, designers should confirm the specifications for a specific style.

Surviving the rigors of launch and deep space operations

Deep Space connectors are designed to maintain their grommet-to-wire and contact-to-contact seals through the extreme thermal excursions that degrade standard elastomeric components. Amphenol's Deep Space D38999 performance has been confirmed through a series of environmental stress tests conducted by an independent laboratory on representative family members. In these tests, mated pairs of the TVPS00RF-15-35P(750) wall-mount receptacle and the TVS06RF-15-35S(750) straight plug were subjected to thermal cycling between -190°C and +175°C for five cycles, with a minimum dwell time of one hour (hr). The +175°C limit is a cycling condition applied to these +200°C-class parts, not a rating of the parts themselves. The samples completed the test sequence with no failures.

Amphenol Aerospace’s Deep Space 38999 Thermal Cycling video further demonstrates resilience under repeated temperature swings, with Deep Space D38999 connectors remaining fully engaged and their terminations and insulated leads intact after cryogenic thermal cycling (Figure 2).

Figure 2: A mated Deep Space D38999 receptacle and plug pair rests with its wiring harness after chamber exposure in Amphenol's thermal cycling demonstration. (Image source: Amphenol Aerospace)

The same testing program also subjected the mated pairs to random vibration of 43.92 g RMS for eight hours (hrs) per axis across two axes, while liquid nitrogen spray held the samples near -190°C. Electrical discontinuities were monitored at a 50 hertz (Hz) sampling rate throughout the test.

Electrical measurements taken at -190°C recorded insulation resistance above 10 gigaohms (GΩ) on every sampled contact and leakage current well below 1 mA during dielectric withstand voltage testing at 1,300 V_AC. In extended 100 hr static testing, the Deep Space D38999 elastomers maintained integrity under conditions that cause benchmark parts to crack and fail.

Meeting diverse demands for signal and power interconnect in cryogenic applications

Like their standard 38999 counterparts, Deep Space parts are available in multiple ratings to meet specific signal and power requirements. Among other configurations, the Deep Space series offers mating pairs comprising wall-mount receptacles with crimp pin contacts and straight plugs with crimp socket contacts. Each receptacle has a matching plug with the same numeric shell size and insert-arrangement combinations. For example, one such matching pair is the TVPS00RF-15-35P(750) receptacle and the TVS06RF-15-35S(750) plug used in the stress-testing program.

The modification code includes configuration options beyond the cryogenic elastomer. A (750) code indicates the upgraded elastomer and other associated components; a (750P) suffix replaces the twinax and coax with power contacts; and a (750H) replaces the contacts with high-current pins. Any of these can be ordered with outgassing treatment by adding an S, yielding the (750S), (750PS), and (750HS) variants for vacuum-sensitive payloads where material outgassing is a concern.

Within each mating-pair class, the insert arrangement defines the contact count and contact complement, which in turn determine the applicable current and voltage ratings.

The high-density signal class, identified by the standard “35” insert arrangement pattern number, offers the most positions and has the lowest per-contact rating of 5 A. It has voltage ratings of 400 V_AC and 500 V_DC. This class includes four configurations:

• The 6-position 9-35 with a size 9 shell, represented by the TVPS00RF-9-35P(750)
• The 13-position 11-35 with a size 11 shell, represented by the TVPS00RF-11-35P(750)
• The 37-position 15-35 with a size 15 shell, represented by the TVPS00RF-15-35P(750) and TVS06RF-15-35S(750) pair that was used in the stress tests
• The 55-position 17-35, represented by the high-density TVS06RF-17-35S(750) (Figure 3)

Figure 3: The Deep Space D38999 TVS06RF-17-35S(750) straight plug illustrates the high-density insert configuration for the signal class. (Image source: Amphenol Aerospace)

A mid-current class raises the per-contact rating to 7.5 A and provides voltage ratings of 600 V_AC and 850 V_DC in two configurations:

• The 19-position 15-19 with a size 15 shell and insert arrangement 19, represented by the TVPS00RF-15-19P(750)
• The 32-position 19-32 with a size 19 shell and insert arrangement 32, represented by the TVPS00RF-19-32P(750) receptacle and TVS06RF-19-32S(750) plug (Figure 4) pair

Figure 4: The TVS06RF-19-32S(750) straight plug, with its 32-position insert arrangement, offers a mid-current class rating of 7.5 A per contact. (Image source: Amphenol Aerospace)

A single 4-position arrangement forms the 13 A class at the same 600 V_AC and 850 V_DC ratings, pairing the TVPS00RF-13-4P(750) receptacle with the TVS06RF-13-4S(750) plug (Figure 5) in a compact size 13 shell with an insert area that provides four large contacts.

Figure 5: The 4-position TVS06RF-13-4S(750) straight plug pairs a compact size 13 shell with four large crimp contacts rated at 13 A. (Image source: Amphenol Aerospace)

At the top of the current range, the 23 A class operates at the same 600 V_AC and 850 V_DC ratings and includes:

• The 6-position 17-6 with a size 17 shell and insert arrangement 6, represented by the TVPS00RF-17-6P(750)
• The 11-position 21-11 with a size 21 shell and insert arrangement 11, with the TVPS00RF-21-11P(750) receptacle and the TVS06RF-21-11S(750) plug (Figure 6) occupying the largest size 21 shells in the stocked set

Figure 6: The 11-position TVS06RF-21-11S(750) straight plug in the size 21 shell has the highest current rating of 23 A per contact. (Image source: Amphenol Aerospace)

Shell size alone does not determine the class. For example, the size 17 shell appears in both the 55-position signal arrangement and the 6-position 23 A arrangement. Designers should therefore select the required insert arrangement and contact configuration, then confirm the complete specifications for the individual part number.

Conclusion

Conventional elastomeric seals in standard MIL-DTL-38999 connectors crack and fail under extreme cold, risking mission failure in space vehicles and other applications that expose systems to cryogenic temperatures. Amphenol Aerospace’s Deep Space D38999 connectors are engineered for cryogenic environments while remaining compatible with standard 38999 connectors. This allows designers to build on a familiar connector platform while selecting and qualifying the specific Deep Space configuration for their application.