Space-based Design—Challenges, Use Case, and Choosing the Right Connectors

As the realm of space is moving more and more toward commercial applications, there is an increasing need for components that can reliably handle the rigorous environment (see Figure 1's example of a Mars rover)—and electrical connectors are among them. Like any other component intended for use in a space environment, engineers must ensure that the connectors they select comply with the appropriate material and performance standards. Early in the design phase, they must also account for those issues that are highly specific to the space environment. 

 

Figure 1. Space exploration systems face extreme environments. Image used courtesy of Bel Fuse

 

There are several inherent limitations of space applications that severely limit where and how designers integrate connectors into their systems. There is limited volume available for parts used in any space application, making the size of every element in the design highly constrained. Minimizing mass is also critical for keeping launch costs down. 

The failure of a part, even in a ground application, can be highly problematic, leading to increased downtime, direct repair costs, lead time, and the time needed to complete the repair. For space applications, all of these problems can quickly become prohibitively expensive. Unsurprisingly, the resources required to commit human labor or remote-controlled robotics for maintenance can be exorbitant. 

Therefore, highly reliable, easy-to-maintain solutions with small volume and mass are desirable for space applications.

This article discusses several concerns to consider when selecting components for space applications, while also touching on relevant standards and key problem areas. It also provides an in-depth example—low earth orbit (LEO) satellites—before discussing some specific connectors suitable for space applications with these challenges in mind.

 

Problems Related to Space Applications

In developing any equipment intended for a space environment, specific issues must be accounted for by the engineers responsible for the design. These include:

• Outgassing
• Radiation
• Vibration
• Space allowance
• Costs related to failure/repair
• Power required for launch

 

The Vacuum of Space and Outgassing

Outgassing refers to the release of gasses when a non-metallic material is subject to heat or a vacuum. The chemical compounds released during outgassing can be volatile, and the vapors can collect on the surface of critical components. As these vapors collect on surfaces, they can lead to short-circuits between components, connectors, or leads. Because of the issues surrounding outgassing, the materials used in connectors for space applications must be carefully selected. See below for the LEO example use case for relevant outgassing standards.

 

Cosmic and Thermal Radiation

Both cosmic and thermal radiation pose issues for space application designs, with the sun being the primary radiation source. There is no atmosphere to protect components from UV radiation, which can change the chemical structure of polymers and lead either to hardening or weakening of the material.

Radiation can also cause the failure of the electronic and electrical systems in space vehicles or satellites. Charged particle radiation, primarily from galactic cosmic rays, solar proton events, or merely trapped in radiation belts, is another problem that must be addressed during the design phase.

One common solution to radiation issues is using insulators to protect critical components or the use of plating materials (such as gold) that can reflect a broad spectrum of electromagnetic radiation, are immune to absorbed radiation, and serve as excellent conductors.

 

Vibration at Launch

Vibration, shock, and impact loads at launch are extremely powerful. In particular, it is critical that the integrity of electrical connections is not compromised during launch. A loose connection can be particularly dangerous at launch, but even a non-life-threatening loose connection later during the flight can be prohibitively expensive to fix later. For satellites, it can lead to a loss of control and data transfer capabilities. For missions that involve human life, a loose connector can be fatal.

 

Example: Low Earth Orbit Satellite (LEOs)

With some of the key design challenges of space applications summarized, let’s take a look at an example of how NASA has developed component categories specific to one use case: LEO satellites (see Figure 2).

 

Figure 2. An example of a LEO satellite in space. Image used courtesy of Cinch Connectivity Solutions

 

LEO satellites orbit within a radius of 3 x the earth's radius (~2,000 km) and have an orbit period of about 128 minutes. Even though they are not operating in deep space, they are still subject to extremely harsh conditions. Their design involves all the issues discussed above, including outgassing, radiation, vibration, and SWaP (size, weight, and power).

The Defense Logistic Agency's (DLA) qualified product database (QPD) records the outgassing characteristics of many different materials. The outgassing characteristics are quantified by the total mass loss (TML %) and collected volatile condensable materials (CVCM %) as measured according to ASTM standards E1559 and E595. 

In addition, NASA issued the space station external contamination requirement SSP 30426. This requirement defines the limits for molecular deposition and the release of particulates for compliance: TML of 1.0% and CVCM of 0.1% or less.

The materials most prone to outgassing are chemically derived, with composite materials being most common. Fortunately, connectors are available that comply with NASA requirements for outgassing.

When engineering LEO satellites, radiation and its effect on electronics remains a severe issue. NASA has developed several component categories specific to LEOs:

• Commercial
• Radiation toleration
• Radiation-hardened (rad-hard)
• Latch-up 

The least rigorous is commercial (in which the customer assumes all risk) with a radiation hardness of 2 to 10 krad. The most stringent is rad-hard, which can handle between 200 krad to 1 Mrad. 

To meet NASA requirements, connectors must meet vibration requirements as evaluated per EIA-364-28 or MIL-STD-1344 Method 2005 Random Condition VI. The specific testing conditions primarily depend on the type of coupling, and the test standards involved are EIA-364-42 (impact) and EIA-364-27 (mechanical shock).

SWaP is a significant factor in space applications, primarily because of the impact of weight on fuel requirements for LEOs and both volume and weight with regard to shipping/storage costs. Therefore, the more compact and lightweight an electrical connector solution is, the better.

 

Connector Solutions for Space

Bel/Cinch offers several products suitable for use in the harsh environment of space, starting with Duracon MIL-DTL-83513 Micro-D Connectors, as seen in Figure 3. The D-shaped micro-miniature rectangular connectors are qualified and listed on the DLA QPD. And in addition to their excellent reliability, they are densely compacted, 0.050” (1.27 mm) pitch interconnects.

 

Figure 3. Dura-Con MIL-DTL-83513 connectors and assemblies for space applications. Image used courtesy of Bel

 

Another solution for space environments is the Bel/Cinch qualified parts for space (QPS) attenuator (Figure 4). This standard line of QPS attenuators is manufactured from materials that meet or exceed 1% TML and 0.1% CVCM outgassing requirements. 

 

Figure 4. QPS attenuators qualified using testing guided by MIL-DTL-3933 level T qualification. Image used courtesy of Bel

 

The Trompeter Twinax/Triax Solutions (Figure 5) are commonly used in MIL-STD-1553B applications and fully support video, broadcast, telecommunications, and instrumentation need with off-the-shelf and custom solutions.

 

Figure 5. The Trompeter Twinax/Triax Solutions. Image used courtesy of Bel

 

Solutions for Space Connectors and Cabling

Designing products destined for space, whether a small LEO satellite or a flight capsule with passengers onboard, can be exceptionally challenging. In addition to the usual specifications involved with interconnect solutions, there are also national and international standards for performance and material selection as well as issues such as the effects of radiation, extreme operating environments, and SWaP constraints.

Fortunately, companies like Bel/Cinch have rugged, reliable, compliant solutions for connectors and cabling. This includes connectors made from approved material in the DLA QPD, classified according to NASA radiation component categories specific to LEOs, and tested according to EIA-364-28 or MIL-STD-1344 vibration standards.

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