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Tiny probes take the heat

Tiny probes take the heat

Sometimes to find the best solution to a big problem, you have to start small. So NASA is sending soccer ball-sized probes into space to test new materials.
A team of NASA engineers has been working on a new type of thermal protection system (TPS) for spacecraft that would improve on what’s available now. Having seen success in the laboratory with these new materials, the next step is to test in space.
The Conformal Ablative Thermal Protection System, or CA-TPS, will be installed on a small probe flight article provided by Terminal Velocity Aerospace (TVA) and launched on Orbital ATK’s seventh contracted commercial resupply services mission for NASA to the International Space Station.
TVA’s RED Data2 probe, only slightly larger than a soccer ball, is an unmanned exploratory spacecraft designed to transmit information about its environment.
“The purpose of the flight test is to gather supply vehicle break up data and at the same time demonstrate performance of the conformal ablative thermal protection system as the probe – encapsulated with TPS – enters Earth’s atmosphere,” explains Ethiraj Venkatapathy, project manager for Thermal Protection System Materials with NASA’s Space Technology Mission Directorate’s (STMD) Game Changing Development (GCD) program. “Thermal protection is a vital element that safeguards a spacecraft from burning up during entry.
“Data obtained from flight tests like this one with TVA and NASA, combined with testing at different atmospheric compositions, allows us to build design tools with higher confidence for entry into other planetary atmospheres such as Venus, Mars or Titan,” he adds. “Partnering with a small business to get flight data for a developmental material is a very inexpensive way of achieving multiple goals.”
The TPS Venkatapathy and his team are designing uses newly emerging materials called conformal PICA (C-PICA) and conformal SIRCA (C-SIRCA), short for Phenolic Impregnated Carbon Ablator and Silicone Impregnated Reusable Ceramic Ablator, respectively.
The probe is essentially a hard aeroshell covered with the TPS and outfitted with sensors called thermocouples. To measure temperature during atmospheric entry, the thermocouples are embedded within the heat shield’s C-PICA and the back shell’s C-SIRCA to capture data for understanding how the materials behave in an actual entry environment.
After Orbital ATK’s resupply services launch arrives at the ISS, the probes will remain on the cargo ship awaiting their opportunity to go to work. Projected to be released from the ISS in June, once the cargo ship re-enters Earth’s atmosphere and breaks up, the probes will deploy and then begin capturing data through the thermocouples embedded in the TPS.
“The probes are designed to be released from the metallic shell and once they are released, they start to get heated. The thermal response data are collected from the various locations where thermocouples are embedded within the TPS,” explains Robin Beck, technical lead for the conformal TPS development. “The probe includes an antenna that allows it to communicate with an Iridium satellite. As the probe descends into the atmosphere and slows to the speed of sound, the data are collected and stored, then transmitted to the Iridium satellite above, which in turn transmits the data to researchers on the ground.”
Once the flight test’s data are collected, TVA’s probe is allowed to fall into the ocean and is not recovered; however, these tiny spacecraft will contribute in a very big way to ensure the predictive models developed based on testing in ground facilities are valid and applicable in space.
“There are known and unknown risks, but both NASA and TVA are motivated to be successful as the benefits also translate to the larger community that wants to have on-demand access to space,” says Venkatapathy. “This technology has the potential to lower the cost of access to space for small payloads while making it attractive for universities and the non-aerospace community who may be novices to flight testing – a challenge in and of itself and not risk free.”
Because there is no backup for a spacecraft’s TPS, it is critical to understand and develop prediction capabilities that allow safe, robust entry system design. A successful flight test at this scale will increase confidence in the conformal ablator and allow mission planners to consider C-PICA and C-SIRCA for use in future programs such as New Frontiers or Orion.
Picture: The entry probe and their metal outer shell. The metal shell allows the probe to be connected with the supply ship and also facilitates the probe to be released during break-up of the supply spacecraft during re-entry.