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CUBESAT EXO-BRAKE DEVICE READIES FOR MILESTONE EARTH LANDING

The return and recovery of payloads from space has long been a trial for aerospace engineers due to the complex combination of technology and cost required for success. Today, a new generation of CubeSats, or miniaturized spacecraft, built with largely Commercial-Off-The-Shelf (COTS) equipment is on a clear flight path to solve this decades-old challenge.

From soil deposits to space-based experiments, payloads provide extraordinary knowledge about our universe and often vital insight into improving our lives on Earth. The study of rock and soil samples from the Moon has helped scientists better understand the formation of the Moon and the Earth. Now, what if there was a way to easily collect and quickly return samples from space or even planets like Mars, without massive investment?

As part of the Technology Educational Satellite Series (TechEdSat) program, advanced university students and NASA Ames Research Center investigators are developing the hardware and operations infrastructure necessary for the on-demand return of small payloads.

A key aim for the program is to build and test a low-cost propulsion-free re-entry system, called the Exo-Brake. An Exo-Brake-enabled CubeSat relies on Commercial-Off-The-Shelf (COTS) navigation and radio frequency communication links to guide the satellite from space to a specified location on Earth while keeping the payload in tact.

The Exo-Brake system has completed a series of tests, laying the foundation for future autonomous de-orbit and target capabilities. Upcoming 2018 TechEdSat launches will build on and push those boundaries even further with the anticipated landing of the first fully recoverable payload from space by a nanosatellite.

Mission Focused

TechEdSat is a collaborative platform for testing planetary mission concepts and developing state-of-the-art technology. Part of the TechEdSat program is the development and launch of a series of CubeSat satellites that test technologies to support re-entry, descent and landing capabilities.

Marcus S. Murbach, principal investigator for the TechEdSat program at NASA Ames Research Center, noted, “TechEdSat is a rapid incremental skunkworks-style development approach where we gradually test and improve flight dynamics, positioning and communications until we get a working solution.”

As part of the TechEdSat program, six CubeSat satellites have been developed, launched and tested thus far. Each nanosatellite has tested various components, all working towards developing successful entry, descent and landing capabilities.

The First Missions

The TES-1 mission deployed October 4, 2012 from the International Space Station (ISS) was a one-unit cube (10 cm x 10 cm x 10 cm). This mission successfully demonstrated the use of a robotic arm to maneuver and deploy the TES-1 payload from the ISS into space. TES-1 functioned for seven months until burning up upon re-entering Earth’s atmosphere.

TES-2, launched on August 21, 2013, successfully demonstrating the use of a satellite network service to transmit short data messages (maximum 1960 bytes) between Earth and the satellite.

With a communication approach and operational robotic arm, tested on TES-1 and TES-2, the TechEdSat team moved on to developing the components that would facilitate on-demand entry, descent and landing of small payloads from space on TES-3. Enter the Exo-Brake, a device that relies on drag—instead of propulsion—to accurately de-orbit small objects from the ISS.

Murbach adds, “With the help of high-fidelity simulations, our goal is to demonstrate a low-cost, propellant-free method of returning small payloads quickly, and to fairly precise locations for retrieval.”

The Exo-Brake

The Exo-Brake is a braking device with avionics capabilities and a parachute-like system. The Exo-Brake deploys from the back of the nanosatellite and is used to slow and control the satellite’s descent into the Earth’s atmosphere.

Murbach explains, “Essentially, we want the satellite to follow a soft trajectory, like a badminton birdie instead of a bowling ball, from space to Earth. Hence the need for an effective GNSS (receiver) to provide regular position data as we manage the flight.”

The device was first flown and tested in a fixed configuration on TES-3 and 4, both of which consisted mostly of COTS components allowing for easily reproducible, cost effective future flight variations.

Navigating Descent

TES-3, deployed from the ISS on November 20, 2013, was a three-unit (10 cm x 10 cm x 30 cm) volume craft. It incorporated a GNSS/Iridium dual-patch antenna and the lightweight, easily integrated a NovAtel®, part of Hexagon's Positioning Intelligence division, OEM615™ multi-frequency GNSS receiver. At just 4.6 cm x 7.1 cm x 1.1 cm in volume and a weight of just 24 g, the receiver is ideal for space-constrained applications.

The GNSS receiver is essential for providing accurate positioning data of satellites while in orbit, and in future missions will provide data during descent as well. The OEM615 was selected because it was relatively inexpensive and had been used on previous NASA sub-orbital projects. Murbach notes, “We knew the receiver worked well in the space environment for relatively short missions and we’ve gotten good technical support when needed.”

TES-4, also a three-unit configuration, had a similar avionics configuration and further developed the capability of the Exo-Brake de-orbiting system. TES-4’s demonstration of a satellite-to-satellite communications system allowed for more frequent communication with the satellite, leading to more accurate satellite altitude and position predictions, which are important for optimal operation of the Exo-Brake.

TES-5, launched December 9, 2016, where it further demonstrated re-entry and landing technologies in addition to the Exo-Brake. For instance, the craft included multiple wireless sensors to transmit real-time data and a Wi-Fi communication link to send data back to Earth.

The Milestone Mission

TES-6, the sixth mission of the TechEdSat Series, was the first live test of the Exo-Brake prior to testing its de-orbiting capabilities, self-powered wireless sensors and radio frequency communications links.

The 3.5-unit (10 cm x 10 cm x 40 cm) volume with a mass of 3.51 kg was fabricated from a basic aluminum (T-6060) extrusion with a 400 mm length compatible with the NanoRacks CubeSat Deployer. For onboard navigation, GNSS/Iridium dual-patch antennas facilitate GNSS/Iridium reception/locking (just like in the previous TES-3, 4 and 5 missions). A second Iridium antenna is side-mounted on the satellite and used during the terminal re-entry phase.

TES-6 was launched November 12, 2017 on the Orbital ATK-8 spacecraft supply mission from the NASA Wallops Flight Facility in Virginia. Once launched, TES-6 began orbit at about 440 km above the Earth. After tracking the satellite for many orbits, the NASA team estimated a drag setting that would force the satellite along a re-entry trajectory to the boundary of Earth’s atmosphere and space, or the Karman line (altitude of 100 km above sea level).

Murbach explains, “We targeted a point above the atmosphere at 100-120 km. Then, with the GNSS receiver position data as our guide, we used a joystick to synchronize the satellite’s descent and hit the target area. If the target is high, we’ll increase the drag, etc. The TES-6 mission was extraordinarily successful in that we were able to gather the GNSS positions via Iridium and adjust as needed to reach our target position.”

While the Exo-Brake system for TES-6 was not designed to survive re-entry into the atmosphere, future missions planned for 2018 will be outfitted with a recoverable braking device.

A Drag-Modulated De-Orbit

Scheduled to launch in late 2018, TES-7 is a two-unit CubeSat. It will test the High Packing Density Exo-Brake, an upgraded braking system from TES-6 that includes a novel strut design without modulation capabilities while also demonstrating a CubeSat Identity Tag (CUBIT) RF-ID system for identifying functioning and non-functioning nanosatellites. It will fly with the NovAtel OEM615 multi-frequency GNSS receiver.

Following TES-7, the NASA Ames team will launch TES-8, a six-unit CubeSat that features a semi-autonomous control system to automate the position, communication and target adjustments, the NovAtel OEM617 receiver and the highly anticipated first fully recoverable payload from space by a nanosatellite with the next generation Hot Exo-Brake. The Hot Exo-Brake system includes a high temperature strut design from TES-7 and modulation functionality, thus allowing controlled entry into the atmosphere, and the possibility to survive re-entry.

The program goal is to develop passive Exo- Brake systems that can be used for small-sat disposal as well as the development of technologies to support on-demand sample return from low Earth orbit scientific or manufacturing platforms such as the ISS.

While the goal of returning samples from the space station or other orbiting platforms is integral to the project, NASA hopes the TechEdSat program also provides the building blocks for larger scale systems that might enable future small or nanosatellite missions to reach the surface of Mars and other planetary bodies in our solar system.

The Exo-Brake project is funded by the Entry Systems Modeling project within NASA’s Space Technology Mission Directorate’s Game Changing Development program, Ames Research Center and the NASA Engineering and Safety Center.