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This picture shows the entry probe and the 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 reentry. Credit: NASA

Sometimes to find the best solution to a big problem, you have to start small.

A team of NASA engineers has been working on a new type of Thermal Protection System (TPS) for spacecraft that would improve upon the status quo.

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 on April 18.

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," explained 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."

The three probes shown in the above picture will reentry during the supply spacecraft break-up and collect data. The probe on the left has conformal TPS, the probe in the middle is Orion’s Avcoat TPS and the probe on the right is made of Shuttle Tile. Credit: NASA

"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 continued. "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.

With funding through STMD/GCD, NASA's Ames Research Center led the work providing conformal ablative materials and TPS instrumentation installed on Terminal Velocity's probes. Terminal Velocity is also working with NASA's Johnson Space Center with funding from STMD's Small Business Innovation Research program for miniaturizing and improving the data acquisition and transmission system as well as providing support for ISS flight certification.

Through the ISS Exploration Flight Project Initiative, Johnson certified three TVA probes for flight. One probe uses the conformal ablative materials, another has the Orion heat-shield material and the third probe uses shuttle tile material for reference. TVA delivered the assembled probes to the Cargo Mission Contract group for this flight.

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 reenters 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.

 

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