Back to the Future

It has been quite an interesting time, unique in the fact that in the present we have seen images of the past and a look into the future. Just two months ago John Glenn recaptured the imagination of America as he rocketed once again into space and the history books. Then just one month later a new window into the future opened as we began the construction of the International Space Station.

The launch of the Space Shuttle Endeavour on mission STS-88 was first scheduled for Thursday, December 3, 1998. As the rain stopped shortly before the pickup of the countdown at the T - 9 minute point, it looked as if we were going to fly that night. The count picked up and just after passing the T - 5 minute point as the hydraulic systems were brought up, an unexpected master alarm rang in the cabin. The space shuttle has a system called the Caution and Warning System that monitors the critical systems. When something does not fall within the proper range an alarm, called a master alarm, is sounded. This alarm caused the countdown to be held at T - 4 minutes. Now, with only a five-minute launch window to work with, the launch team worked hard to identify and understand the problem. This troubleshooting continued as the clock was restarted to be once again stopped at T - 31 seconds in an effort to use the window as effectively as possible. However, in the end the team just simply ran out of available time.

Personally, I view launch scrubs not as a negative experience but as a learning experience. Clearly, it is not a desirable thing. However, to me it proves that the system works. If an alarm sounds we know the vehicle isn't ready to fly. If we don't get a problem indication, then we can place a high level of confidence in the fact that from an engineering standpoint we are ready to go. The bottom line to me is that we only fly if we are 100% sure we are ready to fly! Any less than this is sufficient reason to scrub the launch. Simply put, we can always launch another day. The TOP PRIORITY is to make sure we have as safe and successful launch as possible.

After an intensive evaluation it was determined that the problem the night before was understood, and we were ready to fly. On a beautiful clear night, less than 24 hours later, the Space Shuttle Endeavour brilliantly lit up the sky and raced into space. This was a special experience for me for another reason. My Mom and Dad came up to the Cape to watch the launch with me. It is always great to have them here for a launch. After all, they are the reason I am here in the first place. Endeavour's crew then carried out a very successful mission to start the construction of the International Space Station (ISS). The orbiter carried up the Unity module. It was connected through a series of spacewalks to the Zayra module that was launched by Russia a little over a week before. Unity will serve as a node of docking ports for additional modules to be connected later. The crew even got the chance to go into the space station to transfer equipment and setup various items for future crews. A couple of days after undocking from the ISS, Endeavour made a flawless nighttime landing at the Kennedy Space Center.

Due to the "missing of the window" and subsequent scrub on December 3, many people have been asking about launch windows. Therefore, I thought I would take a moment to discuss them. A launch window is a period of time during which the Space Shuttle can be launched. Launch windows vary in length of time for a variety of reasons. Typically, the biggest factor in determining the beginning and end of a launch window is a payload. If the payload must be delivered to a specific location in space, the window (or allowable timeframe) can be very short. Also, missions that require the orbiter to be placed into a very specific orbit, such as a docking mission, would require a precise launch window. For example, the STS - 95 medical research flight of John Glenn had a two-hour window since the mission did not require a specific orbit. In contrast, on STS - 88 Endeavour needed to dock with a space station module in orbit and had only a five-minute window to get into the proper orbit.

On the long side, a two-hour window is the longest possible. This is because the flight surgeon requires the crew spend no more than two hours on their backs awaiting launch. Windows can also be determined by conditions not only here at the launch site but also those halfway around the world. For instance, if an emergency abort landing were required in Europe or Africa, lighting conditions, such as approaching darkness, could be a factor. In addition, several other smaller factors also influence the timing and length of a launch window.

As true with most things, all launch windows are not the same. Some windows actually have "preferred launch windows" inside them. For example, those we will be using for the ISS flights. We call it a five-minute window, however, the total available window is actually 10 minutes long. In this case, the start of the five-minute window is at the middle of the total window. We could launch up to five minutes prior to the preferred launch time in the middle if necessary. However, if all is going well with the countdown and no problems are ongoing or expected we will shoot for the halfway point (start of the five-minute window). The primary consideration for this is the amount of propellant needed to complete the mission. Launching exactly halfway in the 10-minute time frame would require the least amount of propellant in space to rendezvous with the target. The earlier or later you move from this point, the more you use. With limited quantities onboard, efficiency is a very important thing.

As we move into 1999 I would like to wish all of you a Happy New Year. This year again promises to be an exciting year in the Space Shuttle Program. As we near the end of an incredible half century of spaceflight and look back upon an historic past, we near the dawn of an exciting future.