Linux Out of the Real World

Debian Linux has taken flight aboard the Space Shuttle Columbia.
Communications: Some Software Design Thoughts

Two pairs of processes want to communicate between the orbiting experiment and the ground side support computer. The main control process in the experiment communicates with a recorder/data display/remote control program on the support computer, using several different types of data (events-log, sensor readings, and control-parameter settings going down; control and meta-control commands going up). Another pair of processes mirror directories from the payload to ground side, in order to send data that was buffered before communications were established. Images from the frame grabber are sent using this method.

In this situation, it is natural to want a packet-switching, multiplexing communication system with an interface available to many processes. Since the channel is unreliable, you want some type of validation of received data. The usual networking code is not usable, since there are no packet-drivers for the interfaces NASA presents. In the interest of simplicity and code reusability, we chose to implement a modular user-space communication system.

We wanted the communications interface presented to our communicating processes to be identical on both machines (experiment and ground side support computer). Since these two machines need to talk to different hardware and software interfaces, we abstracted the NASA interfaces from the multiplexer. Between the multiplexer and NASA sits a process that performs the packetizing and unpacketizing they want us to do (possibly fragmenting and defragmenting multiplexer packets) and relays the data. The end result is that the payload and the ground side support computer can communicate in a UDP-like fashion. Multiplexer packets sent are guaranteed to arrive intact and correct or not at all. It's a miniature networking stack in user land.

When the old DOS version of the payload flew in 1996, we rented space in SpaceHab. SpaceHab is a privately owned company that rents a large volume in the Shuttle payload bay and some services (power, communications, etc.) from NASA, and then turns around and rents smaller quantities of volume and services to experimenters. The economic relationship between the three parties (NASA, SpaceHab, experimenter) in this situation defy comprehension by the author. Anyway, SpaceHab provides a significantly more functional communications interface, called the Serial Converter Unit (SCU). Sure, it's still a 9600 bps serial line, but the SCU has (angels sing) flow control.

Sebastian Kuzminsky is an undergraduate in Computer Science and Applied Mathematics at the University at Colorado at Boulder. If space flight work were not so fun and time consuming, he would have been a graduate by now. Questions about PGBA and other Bioserve payloads are welcome. He can be reached via e-mail at


White Paper
Linux Management with Red Hat Satellite: Measuring Business Impact and ROI

Linux has become a key foundation for supporting today's rapidly growing IT environments. Linux is being used to deploy business applications and databases, trading on its reputation as a low-cost operating environment. For many IT organizations, Linux is a mainstay for deploying Web servers and has evolved from handling basic file, print, and utility workloads to running mission-critical applications and databases, physically, virtually, and in the cloud. As Linux grows in importance in terms of value to the business, managing Linux environments to high standards of service quality — availability, security, and performance — becomes an essential requirement for business success.

Learn More

Sponsored by Red Hat

White Paper
Private PaaS for the Agile Enterprise

If you already use virtualized infrastructure, you are well on your way to leveraging the power of the cloud. Virtualization offers the promise of limitless resources, but how do you manage that scalability when your DevOps team doesn’t scale? In today’s hypercompetitive markets, fast results can make a difference between leading the pack vs. obsolescence. Organizations need more benefits from cloud computing than just raw resources. They need agility, flexibility, convenience, ROI, and control.

Stackato private Platform-as-a-Service technology from ActiveState extends your private cloud infrastructure by creating a private PaaS to provide on-demand availability, flexibility, control, and ultimately, faster time-to-market for your enterprise.

Learn More

Sponsored by ActiveState