Shuttle System

Lisa Loiselle

Data Processing System (DPS) Engineer

Which console do you man in the Firing Room?

C12

What system(s) do you monitor and control from that console?

Data Processing System (DPS)

How are those systems used by the Space Shuttle?

The Space Shuttle is a fly-by-wire vehicle (like the F-16). Every switch and button is connected to computers. The entire flight from launch to landing is under computer control. Astronauts are still needed to operate the shuttle, but there are computers between them and everything they do. These computers are called the Data Processing System (DPS).

DPS not only flies the shuttle, but also monitors and controls all of its systems (main engines, solid rocket boosters, power supplies, environmental control, etc.) DPS collects data from vehicle sensors and crew input, performs calculations to analyze that data, and issues commands to vehicle hardware. DPS also displays vehicle information to the astronaut crew and transmits it down to the support team on the ground.

During processing and launch at KSC, the Firing Room communicates with DPS to exchange information with the Space Shuttle. Data received from DPS is displayed on consoles so that Launch Team members can monitor their assigned Shuttle systems. They also use consoles to command DPS to control those systems.

The heart of DPS is its five General Purpose Computers (GPCs). These are small black boxes with computer chips inside that run the software to operate the Shuttle. GPCs are so important that four of them are configured as redundant to each other. They run the exact same software called the Primary Avionics Systems Software (PASS). All four stay in constant communication to make sure each is working as expected. If one fails, the crew can perform an automatic switchover to the fifth GPC. This computer is loaded with the Backup Flight Software (BFS), which as the name suggests, is a backup to the primary software.

GPCs do not directly communicate with Shuttle systems. Other devices called Multiplexer-Demultiplexers (MDMs) link them together. MDMs read measurements from vehicle hardware and translate them into the "language" that a GPC understands. They also convert commands sent by GPCs so that the destination hardware can process them correctly. Each shuttle can support up to 17 MDMs.

Unlike the PC that you use at home or school, a GPC does not have a hard-drive. All of its software is stored on an external tape device called a Mass Memory Unit (MMU). There are two MMUs on each shuttle. Because of limited storage capacity, software is loaded from an MMU into a GPC on an as needed basis.

The Multifunction Electronic Display Subsystem (MEDS) is another important part of DPS. These are the monitors and keyboards that astronauts use to view displays and input data. MEDS is located in the Shuttle cockpit.

The Heads Up Display (HUD) is a DPS unit that helps astronauts land the Shuttle. It displays critical flight data in the form of symbols projected out the front cockpit windows. This projection allows the pilot and commander to keep an eye on this data but still maintain their view out these windows while landing the Shuttle.

There are several other hardware components within DPS. The "Learn More" option at the top of this page contains links to web sites with more information about all of these components.

What are your responsibilities with regard to those systems?

The DPS System Engineering (SE) team is responsible for testing, checkout, and operation of DPS. Our goal is to make sure that all DPS hardware and software is ready to accomplish a safe and successful Shuttle launch and mission. We also support other engineers as they test and checkout their systems. When a problem occurs, we apply our expertise to help them isolate the source of the problem. During launch countdown, we perform final checkout and configure DPS for launch. Some responsibilities within DPS include Vehicle SE Lead, Vehicle SE Backup, and DPS Hardware Lead. As a DPS SE, you might find yourself working in the office, Firing Room, or even inside the Space Shuttle itself.

What was your most exciting or memorable experience while working in the Firing Room?

I think each launch is a memorable experience. It is incredible to me the amount of knowledge and expertise that is required to launch each Shuttle.