We cite these two accidents to make the point that they were caused by the other shuttle components used during ascent to orbit. The Orbiter spacecraft has never been the cause of any failures. The Orbiter has a perfect record of 123 consecutive successful missions, and we are confident that this record number will grow. We also have a dedicated team of new engineers trained by their mentors, thus insuring that the Orbiter can continue to be operated correctly.
The Orbiters are, of course, aging but have two thirds of their 100 mission design lives (per vehicle) still ahead of them. Sean O'Keefe, a former head of NASA, states in the NOVA documentary that prior to the Columbiaaccident NASA was planning to keep the space shuttles in operation till 2020. One of the members of SAT recently delivered a technical paper on the built-in space shuttle longevity and compared it to the Douglas DC-3, an aircraft that has been flying for over 70 years and is known for its reliability and ruggedness. The vehicles are well maintained and to this day remain pristine. If you look inside one of the Orbiters today, for example, it looks very similar to the first Orbiter on its maiden voyage back in 1981.
Each of the Orbiters was designed and qualified by tests and analysis for a minimum of 100 space missions. Many of the component test programs were extended to 400 missions to flush out any hidden or unexpected failure modes. The most-used Orbiter in the fleet has only performed 35 missions, so today there is plenty of useful life remaining for additional space missions.
Furthermore, the space shuttles are not old technology. The Orbiter is very similar to military and commercial airplanes, and only evolutionary changes have occurred in airplanes over the last 27 years, as opposed to radical redesigns. Furthermore, those changes are mostly in the avionics, which are readily updated. The more familiar examples of this are the Boeing B-52 and B-1 bombers and the Boeing 747 airliner, all of which are still flying after a longer period, and in the latter case the plane is still in production. The fact is if a spacecraft were designed today to do all the things the space shuttle can do, it would be virtually no different from the existing proven hardware.
A former Orbiter Chief Engineer and VP of Engineering reports, "Many people are unaware that NASA has long maintained an upgrade process to provide current technology to the Orbiter. Starting with the early space missions, many upgrades were installed to improve performance, enhance system reliability, and improve operational safety. More than $1 billion was spent after the Challenger accident on the SRBs, the ET, and the Orbiter. The successful flights after the Columbia accident also show that NASA keeps these shuttle components operating with technology that can meet the mission requirements, consistent with the available funding for modification kits and their installation. Over the years of shuttle operations, these upgrades have received lots of attention as recorded in Reference (1)." (The reference is to a 1999 National Research Council Report entitled "Upgrading the Space Shuttle," published by the National Academy Press.)
As summarized by a former Chief Engineer at Kennedy Space Center, "The Orbiter is the most fantastic flying machine built by man. Its retirement in 2010 is premature and shortsighted. What a waste of unique hardware and all the associated infrastructure and people skills that have been developed at Kennedy Space Center. (This applies as well to the other NASA Centers and to the Corporate Suppliers.) The knowledge base and support for complex space launches take a significant time to establish, and now we're planning to dismantle the talented workforce at that site, together with the software and procedures established over 123 flights, to begin a new program. Skills will be lost as we wait on the Constellation hardware to materialize—a situation very similar to the tough six years between the last Apollo launch (Apollo Soyuz) in 1975 and the drawn-out buildup for the shuttle that finally culminated in its first launch in 1981. Such an extended development with the Constellation elements in these days of budget shortfalls could seriously impact the first scheduled launch of Orion in 2015.
http://www.pbs.org/wgbh/nova/space/case-save-shuttle.htmlSent from my iPad
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