Purge system (Credit: NASA, Boeing).

Just before launch, Diana Centeno-Gomez and other key engineers work hard to ensure the safety of an important space shuttle subsystem. These engineers must be on-hand in the Mission Evaluation Room at NASA’s Johnson Space Center 11 hours before a scheduled launch to monitor the shuttle’s Purge, Vent and Drain (PVD) Subsystem.

As a NASA Subsystems Engineer (NSE) supporting Johnson’s Orbital Project Office, Diana is part of pre-launch, launch and landing activities that are used to maintain environmental and pressure control within the shuttle. Diana is one of several NSEs selected from Glenn Research Center to directly support shuttle missions.

Vent system (Credit: NASA, Boeing).

“It takes a lot of work, but being involved in this activity allows you to see how the shuttle really operates. You also realize how many people are needed to make it work,” said Diana

The PVD subsystem consists of three main functions: purge, vent and drain. Purge first occurs when air is pumped into the orbiter to get rid of any hazardous gases or particles and to provide thermal conditioning. The purge to the vehicle is a 24-hour operation that occurs while the orbiter is on the ground. The purge consists of conditioned dry air at all ground operation facilities and dry gaseous nitrogen during fuel loading.

The vent system provides the flow area to control pressure during purge, depressurization during ascent, molecular venting in orbit, and re-pressurization during entry. The drain system is used if the shuttle was rained on while on the launch pad. Water damage is prevented by releasing trapped water through many drainage holes on the orbiter.

Drain system (Credit: NASA, Boeing).

Another subsystem involved in PVD is the Window Cavity Conditioning System. Each of the 11 windows on the orbiter contains tiny cavities. The system conditions the window cavities to maintain visibility and prevent moisture accumulation on the window surfaces. 

The Purge, Vent and Drain Subsystem is vital to stabilize the shuttle’s pressure and temperature before, during and after landing when leftover gas must be purged from the vehicle. All of these operations require a great deal of expertise during shuttle missions.

“While supporting a mission, you get to see the dedication and technical expertise required for success,” commented Diana. “It’s all worth it when liftoff occurs and you feel the excitement and sense of accomplishment.”