Since 1995 Adherent Technologies, Inc. (ATI) has performed cutting edge materials science research for NASA applications. Programs included development of light curing resins for space inflatables, resulting in the Rigidization on Command® technologies, structural repair tape, electrically conductive thermal control coatings culminating in the ECOTHEC material, and a variety of specialty foam applications ranging from self-deploying wheels and antennas to foam-in-space technology for large structures and sample return containers. We are also actively supporting NASA efforts for lunar exploration by developing dust mitigation and in-situ resource utilization technology for regolith use.
Rigidization on Command® (ROC)
Much of ATI’s work on fast-curing light-initiated resins has resulted from the development of the Rigidization on Command® concept, which is specifically directed toward the fabrication of lightweight structures for space applications. By combining a rigidizing resin system with a supporting fiber system, we can produce a self-supporting structure that does not collapse upon pressure loss. The potential of the ROC® concept has been demonstrated in previous programs that included development and testing of resin chemistry, thermal analysis, structural analysis, and fabrication of demonstration hardware tubes and toroids. The ROC® concept originally used composites fabricated with photocurable epoxy matrix resins using cationic cure chemistry that offers the following advantages:
- High cure strength
- Low outgassing (solvent/water free, unlike gels)
- No temperature dependence (-20°C cure)
- “Living polymer” (guaranteed cure/extra margin)
- Predictable behavior
- Low shrinkage (unlike gelatins)
- No complex elastomer/fabric interactions
- Indefinite storage life.
The concept has also recently been extended to rigidizing inflatable wings for unmanned aerial vehicles. These systems consisted of fast-curing acrylate resin systems combined with a woven glass fabric that was then used to form subscale prototype wings.
Inflatable structures constructed with ROC® resin systems require only sufficient inflation gas for deployment and are rigidized only when desired with the use of internal light sources. By integrating carbon and glass fiber reinforcements, it is possible to add structural stability to the membrane with minimal weight penalty.
The light-cured prototype strut (pictured at right) exhibited mechanical properties equivalent to those of thermally cured struts of the same construction, being able to support a 30 kg weight on a 100 g/m beam.
As with all composites, the physical properties of greatest interest (strength, modulus, thermal expansion, and dimensional stability) are all fiber-dominated. The ROC® resin systems are compatible with most fiber types and provide excellent fabrication flexibility and mechanical stiffness in the cured structures. Cure has been obtained at temperatures as low as -20°C. A review of the literature suggests that this approach may be one of the most significant developments in inflatable spacecraft technology in several decades.
This system is easily applicable to components of large inflatable space structures such as long tubes or struts. The low shrinkage and predictable mechanics, however, suggests that the ROC® chemistry may also be ideal for inflatable components such as sunshields, parabolic antennas, and telescope reflectors where the dimensional accuracy is critical.
For many space applications minimizing launch weight is only one part of the equation. Making large parts compatible with the limited storage volume available is an equally difficult task. The failure of the main antenna unfolding mechanism nearly terminated the Galileo mission early on, and data flow was critically reduced for the duration. ATI suggested self-deploying compressed foams as an alternative to mechanical systems, and NASA supported the research in three different programs. By using open-cell urethane foams, it is possible to manufacture parts which are mechanically rigid at room temperature but can be softened by warming. In the soft state the part can be compressed for packing. Upon cooling, the part then stays compressed with a volume reduction of up to 20:1. For deployment, all that is needed is warming above the softening point, and the foam returns to its original shape. This has been successfully demonstrated for both wheel shapes for rovers and for antennas of up to 1 meter in diameter. Metallization of the foam surface using flame-spray techniques produced a working RF antenna.
Future interplanetary space mission concepts require very large antennas to be deployed in deep space to act as permanent relay stations for continuous communication between spacecraft and Earth independent of planetary alignment. For these football field size structures, even highly compressed foam parts become too large to be launched directly. To construct these reflectors, ATI envisioned inflatable structures stabilized by a foam backing deployed in situ. Using the gases generated during foam expansion to temporarily pressurize a thin membrane mold, it is possible to fill large structures with an open-celled foam that will provide mechanical and thermal dampening to an inflatable reflector. This current program, in cooperation with ILC Dover and Applied EM, aims at developing a Ka band reflector.
Regolith is a dust-like material covering large areas of the lunar surface. Generated by eons of meteorite impacts and unchanged by erosion, these very fine particles are extremely abrasive and a health hazard to astronauts. On the other hand, the regolith is also the most abundant and easiest resource to access for in-situ fabrication on the moon. ATI’s programs aim at two different applications, manufacture of building materials from regolith using a polymeric binder to produce a concrete-like material, and dust mitigation coatings for both high traffic areas and as thin coatings for gas-flow exposed surfaces, for example around landing fields.
ATI has a long history of studying the properties of polysilylene polymers. These materials, industrially only used as photoresist resins, are characterized by an all-silicon main chain, giving it tailorable electrical properties. These properties have been used at ATI in the design of fast scintillators, in coatings for solar sails, and in specialty coatings for space and defense applications.
Electrically Conductive Thermal Control Coating (ECOTHEC)
ECOTHEC is a polysilylene binder-based thermal control coating for satellite use, combining excellent solar absorption and emissivity properties with the ability to conduct charges away from the surface and into the main structure of the spacecraft. This prevents charge build-up and eliminates static discharges that can damage the satellite electronics. In addition to these primary properties the material shows excellent adhesion to substrates (4.5 to 5 according to ASTM D3359-B) and durability, especially during ground handling.
The coating is resistant to impact, and, when damaged, does not peel or crack in the surrounding areas. It is solvent resistant and does not absorb water, though we do not recommend pressure washing above 60 psi.
Custom formulations with selected pigments are available for testing purposes; commercial quantities require a three month lead time.