NASA Astrobee Robotic Free Flyer: International Space Station, Here We Come!
NASA Ames Intelligent Robotics Group picks the Inforce 6501™ Micro SOM for both the middle-level processor (MLP) and the high-level processor (HLP) platforms due to its strict SWaP and high-performance requirements.
The NASA Ames Intelligent Robotics Group (IRG) [Mountain View, Calif.] conducts applied research in computer vision, geospatial data systems, human-robot interaction, planetary mapping, and robot software . The IRG is currently tasked with developing new robots for the International Space Station (ISS) to extend and enhance human exploration missions. One of their ongoing projects is developing the Astrobee, a cube-shaped autonomous robotic free flyer to replace the ageing Smart Synchronized Position Hold, Engage, Reorient, Experimental Satellite (SPHERES) free-ﬂying robots, which have operated on the ISS since 2006. The Astrobee is expected to join the ISS via a launch during the latter part of 2017, when it will serve as a robotic assistant to offload routine, repetitive, but long-duration tasks. These may include doing environment surveys, sensor measurements, performing routine maintenance, and assist ISS crews with their science experiments . The Astrobee can be remotely operated by astronauts in space or by mission controllers right here on earth.
Why replace something that’s been a research workhorse for so many years on the ISS?
SPHERES can operate within one ISS module and has a restrictive operating space of just 2 x 2 x 2 cubic meters due to its beacon-based localization. Secondly, SPHERES is based on a stand-alone digital signal processor (DSP) which is quite limited in compute power and is not upgradable to the latest available processing technologies. Today’s science experiments in microgravity or “zero gee” that rely on these robots, have gotten quite complex and require a lot more computational power. Thirdly, several tasks require manual intervention (such as setup, teardown, changing battery packs on the robot, etc.), wasting valuable astronaut time on the ISS. Moreover, SPHERES requires crew supervision at all times.
The Astrobee buzzes in….
NASA Astrobee free-flyer element consists of subsystems for structure, propulsion, power, guidance, navigation and control (GN&C), command and data handling (C&DH), thermal control, communications, docking mechanism, and a perching arm .
The NASA Astrobee is designed to be a free-flowing autonomous robot that can move throughout the ISS without relying on navigation beacons. A visual navigation system (based on edge-detection computer vision algorithms) on-board helps avoid obstacles. It is designed to host science equipment and run compute-intensive software. It will dock to a charging station automatically to recharge its batteries. The NASA Astrobee has a perching arm to grip handrails on the ISS to conserve power while running research experiments [avoids using propulsion systems and navigation]. One can imagine several intra-vehicular-activity (IVA) use-cases:
- As a free-flying camera to assist crew and mission control monitor payloads, or to record crew activity.
- Perform environmental monitoring [air quality/noise] via onboard sensors anywhere on the ISS.
- For automated inventory control (the ISS has hundreds of objects that can be RFID tagged, making it easier to keep track of)
Technical challenges in building the NASA Astrobee avionics
As seen in the block diagram below , the avionics provides computation and communication resources for the NASA Astrobee. The three compute platforms are the low- [LLP], mid- [MLP], and high-level-processor [HLP], which are configured to perform specific functions. These processor boards communicate with each other via an Ethernet backbone (switch) and a USB (hub) to augment connections with peripheral devices/sensors and science payloads. The docking interface via the Ethernet switch allows data transfer between the NASA Astrobee and the ISS when it’s docked.
- The LLP (micro-controller based) provides a closed-loop control between the propulsion subsystem and the inertial measurement unit (IMU). Its flight software will receive additional validation for added reliability. This processor also ensures the safety of the system should other processors fail. 
- The MLP is the main processor for the NASA Astrobee free-flyer platform. It commands the LLP and the perching arm. It will host most of the flight software, including the vision-based navigation system. It will also act as a sensor hub, aggregating data from multiple sensors. The MLP primarily communicates via WiFi with the external world and via a wired connection when docked. It is also interfaced with the fisheye camera, depth sensor, and perching arm.
- The HLP drives the touch-screen display for providing status updates. It will access NASA Astrobee functionality through network calls to the mid-level processor. It is also a dedicated processor module to run guest science software in isolation from the flight software and has the ability to add multiple payloads.
Criteria for choosing the right compute platforms for the NASA AstrobeeAstrobee’s LLP, MLP, and HLP
The folks at the NASA Ames IRG did an exhaustive study that compared commercial compute platforms (System-on-modules [SOM] and single-board-computers [SBC]) from several vendors before narrowing down their choices for the LLP, MLP, and HLP. Choosing an appropriate compute platform is the most critical part of designing the avionics for the NASA Astrobee and the team at NASA Ames IRG used multiple attributes and accorded importance/weight based on the processor module type (LLP/MLP/HLP) being used. The stringent criteria included :
- Computing power: The MLP runs vision-based mapping and navigation algorithms, which requires high-end processing power.
- Software development cost: The MLP runs the Robot Operating System (ROS) package on a Linux OS and hence compute modules that support this requirement along with appropriate device drivers is critical
- Hardware development cost: Processor platforms that can be easily mounted to the backplane get better scores.
- Modularity: Crews on the ISS should be able to swap these boards effortlessly should a failure occur or an upgrade is required. SOMs with edge connectors get a higher score since no wires and nuts/bolts need to be operated.
- Connectivity: Ethernet, I2C, SPI, USB 2.0, and WiFi are basic requirements for the MLP to communicate with the LLP, HLP, and external devices.
- Power consumption: Depending on use-cases, the NASA Astrobee should be able to run on batteries upwards of 9 hours. Lower the power consumption, higher the score.
Inforce 6501 Micro SOM is the chosen platform for both the MLP and HLP
Four of Inforce Computing’s platforms figured in a study of nine products from six independent vendors. Of these, the Inforce 6501 Micro SOM got the highest overall score of 3.14 (see the trade study results in Table-1 below), beating some well-known names and vendors out there. The Inforce 6501 Micro SOM scored high marks for computing power, modularity, software development cost, and communications. Given that it is a SOM, a custom carrier board design is required (like all SOMs do), which adds an incremental cost. Nevertheless, a full-fledged Inforce 6501 development kit allows independent software development and testing that requires no additional hardware design costs.
Other factors that weigh heavily in favor of the Inforce 6501 Micro SOM are:
- Qualcomm Snapdragon 805 processor (APQ8084) based, providing quad-core 2.7GHz CPU processing, with heterogeneous compute that includes Hexagon DSP, Adreno GPU and dual ISPs enabling streaming of 1080p HD and H.264 encoded video to the ground
- Support for Linux (Ubuntu) and being able to run ROS on it–this is the first known port of ROS on the Qualcomm Snapdragon 805 processor (APQ 8084).
- Readily available camera (4K HD capable ACC-1H30) and display (4” ACC-1H10) accessories and associated device drivers to run on an Android OS (for the HLP).
- Design assistance services for custom carrier board design (inclusive of technical support and reference schematics).
- Cross-compatibility with a common carrier board design, making it easily swappable and upgradeable in the future
- Weighs under 3oz and measures just 28mm x 50mm, making it a nice fit for the NASA Astrobee’s enclosure dimensions
Prototypes working and making great progress towards launch in 2017
In a series of NASA YouTube videos, the progress of the NASA Astrobee project can be seen, demonstrating the perching arm and other capabilities:
Inforce’s products are no strangers to space (or shall we say near-space)—recall the Inforce 6410 classic SBC was launched on a weather balloon to operate at near space (100K feet, 1% atmosphere, and extremely cold conditions). The Astrobee will be a strong demonstrator of Inforce’s contemporary mobile technology based SOMs being put to great use in exciting embedded applications.
All photos courtesy of NASA Ames Research Center publications—see below.
 NASA Astrobee—a free flying robot
 Astrobee: Developing a Free Flying Robot for the International Space Station— a paper published for the American Association of Aeronautics and Astronautics