The ever-increasing demand for more powerful computing platforms with mission-critical capabilities for future space exploration is a recurring theme for many recently started space programs. And the effort to meet these demands is worldwide. Over the past two years, NASA has made significant progress in formulating future space systems to enable further human exploration throughout the universe. This not only includes the moon and the familiar destinations currently explored by the International Space Station (ISS), but also brings us closer to a new frontier of previously unexplored regions, with Mars first on the list.
Efforts Span the Globe
Four new NASA vehicles specifically developed for human exploration include the Orion crew exploration vehicle (CEV) (Figure 1) for human transport as well as ARES first stage, ARES I and ARES V launch vehicles. NASA’s unique solution in the development of these vehicles combined the traditional approach of selecting prime contractors to build and demonstrate these four systems, coupled with the funding of two private companies under the Commercial Orbital Transportation Systems program. The combination proved a cost-effective space transport alternative for both humans and cargos to the ISS. When the Space Shuttle retires in the early 2010s, the systems derived from this program are expected to continue to sustain the ISS for years to come.
Meanwhile, the European Space Agency (ESA) is also planning to launch the new Autonomous Transfer Vehicle (ATV) to provide similar transport capabilities in support of the ESA Columbus module as part of the ISS operations. Other countries such as China, Russia and Japan are also pursuing next-generation space transport development.
Computing Advances Lead to Progress
Additional new space or near-space programs are requiring reliable high-performance computing. One of the most recent successes is the Orbital Express program. For the first time in human history, this program demonstrates that two satellites (ASTRO and NextSat) can dock with each other in full autonomy, with no human involvement or intervention during the process. The onboard computers provide real-time processing of thousands of sensor inputs that allows immediate decision-making, enabling the independent spacecraft to dock with each other from a distance of over four miles (seven kilometers).
Other examples include hypersonic vehicle programs like the FALCON program, space-borne weapons such as the Kinetic Energy Interceptor, next-generation GPS, commercial tourism including the SpaceShip Two, responsive space platforms such as TacSat, and Internet in space with software-defined radios from the NASA CONNECT program.
Even though the choice of embedded computing products with higher performance is greater today than a few years ago, the challenge to operate a high-performance and reliable computer system in space requires a unique combination of design techniques.
Other Space Mission Successes
The twin NASA rovers, Spirit and Opportunity, represent some groundbreaking developments in recent space missions. Both rovers have been working around the clock for months to provide invaluable information to ground-based teams studying the geology on Mars in preparation for future human exploration. Another new plan for the intermediate lunar exploration is to deploy multiple mini-rovers on the lunar surface to investigate and map out resources available around the potential landing sites before human arrival. All these ideas are becoming reality via advanced robotics controlled by high-performance computer systems.
Some of the recent demanding space operations demonstrated in robotics include:
• Docking between two space-borne objects, such as a transfer vehicle or capsule and another space platform like the ISS. (Docking is one of the primary robotic capabilities needed for various exploration tasks.)
• Autonomous maneuvering of multiple spacecraft and rovers with LIDAR instruments.
• Precision pointing or tracking of space-borne laser communication systems.
• Teaming of multiple spacecraft, as in the Orbital Express mission.
• Remote servicing of one spacecraft by another spacecraft, as in the Hubble Robotic Service mission (demonstrated in a simulated space environment).
Successful execution of these tasks depends upon unique software and hardware capabilities designed to accommodate the demands of specific functions (Table 1).
Functional Hardware Elements
Meeting the performance elements noted in Table 1 requires specific hardware capabilities in a uniform, integrated design. To achieve the cost, compatibility and lead-time advantages of an off-the-shelf approach, these capabilities must be contained within industry-standard form-factors. For example, to provide superior performance under demanding conditions while surviving a hostile space environment, a system designed with one or more processors and a set of I/O cards in a conduction-cooled 3U CompactPCI (cPCI) form-factor might include some or all of the features outlined in Table 2.
Modular System Design
The ability to use a common set of space electronics modules in a common enclosure for various space system applications creates the foundation for a modular and plug-and-play architecture. Multiple subsystems can also operate concurrently to offer capabilities that are more complex as well as redundant or coordinated mission operations. To achieve rapid and cost-effective space system integration with the “plug-and-play” methodology, there are three key elements to consider: a widely accepted open bus architecture (such as CompactPCI), a radiation-tolerant FPGA implementation of bus interface and the use of a common enclosure design.
A mature and well-defined open architecture, a primary element in achieving a modular, flexible space system, allows the modules to seamlessly operate together with a common protocol and a physical bus interface. In contemporary spacecraft design, some popular open architectures include VMEbus and CompactPCI (cPCI). In particular, CompactPCI has recently gained significant notoriety due to the small, rugged form-factor of modules, plenty of available user-defined backplane I/O pins and the extensive knowledge base across various industries such as telecom, military and space applications.
The use of open architecture also permits various parties to develop modules that can work together properly in a single bus interface within the same enclosure. A customer typically procures most of the modules required for a specific spacecraft avionics solution, then develops one or two custom I/O cards with the same bus interface to provide unique or proprietary capabilities not offered otherwise. Open architecture helps minimize this time-consuming and costly effort.
Other benefits include using space-proven hardware, further reducing costs associated with continually re-inventing and re-architecting the spacecraft mission computer. Time-to-market and the pressures of platform qualification prior to launch decrease. Typical features in a cPCI system solution could include:
• A PowerPC processor module as the system controller;
• Redundant processor modules or additional modules for increasing performance and reliability;
• Coordinated reset signals on a cPCI backplane;
• A backplane with no wire harness, increasing reliability in launch conditions or hypersonic cruising environments;
• A custom reset to allow each individual processor module to reset itself or the whole cPCI backplane bus and;
• Local and cPCI bridges on processor modules to separate high-speed traffic and increase overall system throughput.
FPGA Implementation
To enable a flexible architecture for space applications, the common bus interface must be implemented in a radiation-tolerant silicon solution. In the case of cPCI, radiation-hardened FPGAs can be used for this implementation on each module to communicate across a cPCI bus. In addition to offering a bus interface, the same FPGA can also control operations for onboard interfaces to minimize real-time interactions or relax timing constraints from software to complete specific tasks.
An example of such a design is an analog I/O card. As shown in Figure 2, the front-end of the FPGA implemented on the card is a cPCI interface. The back-end of the FPGA provides full control of the analog-to-digital conversion sequence, the digital-to-analog outputs and the in-flight loop-back, built-in testing capability. This configuration limits software interaction command relays that start or stop conversion, initiate a test or designate a specific digital output value for analog conversion. Also, the cPCI bus provides four independent interrupts for the FPGA to define four unique events, resulting in more flexible software coordination.
Common Enclosure Design
One of the most time-consuming activities when creating a spacecraft avionics subsystem is the development of a unique I/O harness that offers the front-panel I/O through various connectors. Also, unique test setups—test cables, test equipment and test procedures—required for each new application tend to add complexity.
A reconfigurable backplane used in a 3U small form-factor cPCI bus architecture could be implemented through multiple space-qualified switching circuits that allow any specific card slot to be configured to host a unique I/O card. This feature is crucial for future exploration to outer planets, where each mission has only a limited weight allocation for spare components onboard the spacecraft.
A common enclosure and modular card design can help reduce the number of card and enclosure types needed to maintain high levels of capabilities for any unforeseen situation by allowing shared resources. Figure 3 depicts this reconfigurable backplane that eliminates the I/O harness between the backplane bus interface and the enclosure’s front-panel connectors for modules or cards. As many satellite and spacecraft programs have determined in the past, wire harnesses do not hold up well in harsh, rugged environments. In fact, they can significantly impact the launch vehicle system’s reliability. Several of the newer Microsat programs have mandated the use of “wireless” harnesses to increase system reliability during launch, docking and orbit insertion, all of which are associated with severe shock and vibration.
Space exploration is continuing to evolve, paving the way for a deeper understanding of the universe around us. Within these newer space vehicles lie powerful computing systems that continue to clear the path for each subsequent mission. The road has been long, but the advancing technologies incorporated into off-the-shelf components, combined with the flexibility afforded by these components, have proven to be a worthwhile pairing that is leading us toward new discoveries. Next stop, the Red Planet.
Aitech Defense Systems
Chatsworth, CA.
(888) 248-3248.
[www.rugged.com].
