Evolution of the Space Shuttle
How 30 years changed the world's most complex flying machine.
- By Michael Klesius
- Air & Space magazine, July 2010
The shuttle main engine is the most tested large rocket engine in the world. In 1996, a turbine component (displayed here by a NASA scientist) underwent airflow tests to help engineers create more efficient aircraft engines.
NASA
The Space Shuttles's first flight, a two-day mission launched on April 12, 1981, with commander John Young and pilot Robert Crippen, was an announced test flight. So complicated was the shuttle system, it could be argued, that every mission since then has been a test. Over the years, NASA fine-tuned the system with modifications large and small. As the program’s end nears, the knowledge gained over 30 years will be flying on its 134th flight.
Reusable Solid Rocket Boosters
- After STS-5 (November 1982), the casing was made .002 to .004 inch thinner, reducing the weight of each booster by 4,000 pounds.
- After STS-7 (June 1983), engineers narrowed the booster’s throat and enlarged its nozzle. The changes increased thrust, enabling the shuttle to carry 3,000 more pounds of payload.
- During the days leading up to the launch of Challenger on STS-51-L (January 1986), freezing temperatures weakened an O-ring seal in a joint between two segments of the right booster. The weakness allowed hot gases to burn through the casing, causing the shuttle to break apart on ascent, which killed the seven-member crew. Two joints were redesigned with interlocking walls that had new bolts, pins, sensors, seals, and a third O-ring.
- In December 1994, parachutes (three per booster) were enlarged from 115 feet in diameter to 136 feet, slowing the jettisoned boosters’ descent, which reduced their damage at impact in the Atlantic Ocean. And to minimize damage during deployment, the chutes were packed in a circular, rather than zig-zag, pattern.
- Propellant grain was modified after 2003 to avoid cracks in the fuel when the boosters are stored horizontally at temperatures below 40 degrees Fahrenheit.
External Tank
- Before the loss of Columbia and its seven astronauts on STS-107 (January-February 2003), the base of the connection between the tank and the orbiter’s nose was insulated with ramp-like foam panels to prevent ice from forming (right, top). It was a piece of this foam that broke away during Columbia’s ascent and damaged the leading edge of the left wing, creating the condition that led to the destruction of the orbiter on reentry. On future flights, heaters replaced the foam panels.
- For the first two missions in 1981, the tank was painted white to protect its insulating foam from the sun’s ultraviolet rays while on the launch pad. Eliminating the paint allowed the shuttle to carry 600 more pounds of payload.
- Design changes, welding improvements, and the use of aluminum-lithium alloys have cut the tank’s weight. In 1981 and 1982, it weighed 77,100 pounds empty. STS-6 (April 1983) introduced a lighter tank: 66,800 pounds. With STS-91 (June 1998) came one even lighter: 57,470 pounds. The savings enabled the shuttle to carry increasingly heavier payloads.
- After STS-107, six cameras were added to six already on the shuttle system to monitor foam loss during ascent. They’re mounted on the boosters (three on each), on or in the orbiter (five), and on the tank (one).
Space Shuttle Main Engines
- In 1995, the power head was narrowed from a three-duct injector design to a two-duct one, and in 1998 the combustion chamber’s throat was enlarged. The changes reduced internal engine pressures and increased safety margins.
- To reduce friction from the oxidizer pump’s 23,000 revolutions per minute and the hydrogen fuel pump’s 34,800 rpm, silicon-nitride bearings were added to the two high-pressure turbo-pumps in 1995. In the oxidizer pump, the number of rotating elements was reduced from 50 to 28, while the number of bearings dropped from four to three. In the fuel pump, the rotating elements went from 30 to 14, and the bearings from five to two. The new oxidizer pump first flew on STS-70 (July 1995), while the new hydrogen fuel pump debuted on STS-104 (July 2001).
- Starting with STS-117 (June 2007), new onboard computers and sensors began providing better real-time monitoring of vibration loads in the turbopumps.
- High-precision casting during manufacturing has reduced the number of welds, cutting the number of engine inspections needed between flights.
Orbiter
- Starting with STS-49 (May 1992), orbiters used a drag chute on landing, which relieves wear on the brakes and reduces rollout distance by up to 2,000 feet.
- On the first four missions (1981-82), which each had only two astronauts, the shuttle had modified SR-71 Blackbird ejection seats. On STS-5, with a crew of four, the seats were disabled, and after STS-9 (November-December 1983), they were removed. Starting with return-to-flight STS-26 (September 1988), a telescoping slide-pole was installed to enable crew escape through the side hatch when the orbiter was below 30,000 feet and in a glide no faster than 230 mph.
- The original airlock was 150 cubic feet and located inside the mid-deck, with one hatch opening into the mid-deck and the other into the payload bay. In the early 1990s, the airlock was enlarged to 185 cubic feet and moved into the payload bay, with a third hatch at the top for docking with the Russian space station Mir (1995-98) and the International Space Station (starting with STS-88, December 1998).
- Beginning in 1995, crew seats were made with aluminum alloys, which cut their weight from 110 pounds to 49.
- After January 2003, the wing leading edges were fitted with 66 tiny sensors, each of which makes 20,000 readings per second to detect impacts. To protect against impacts, NASA hardened the tiles on wing leading edges and added reinforced carbon-carbon blankets under the nose.
- The shuttle has deployed six Tracking and Data Relay Satellites, beginning with STS-6 (April 1983). The satellites, along with three more sent up on Atlas IIA rockets, provide near-continuous communication during missions. Before TDRS, astronauts could talk to mission control only about 15 percent of the time while in orbit.
- A glass cockpit, with 11 flat panel color displays, replaced 32 dials and gauges starting with STS-101 (May 2000).
Shuttle Remote Manipulator System
- First used on STS-2 (November 1981), the 50-foot-long, Canadian-built arm was designed to deploy and retrieve payloads weighing up to 65,000 pounds. Work on the ISS, begun in the mid- 1990s, raised the requirement to 586,000 pounds, so the “wrist” got greater torque, enabling it to assist, if needed, in docking the shuttle to the station. The arm, however, was never used for that purpose.
- In 2000, all joints were refurbished, gear boxes and motor modules replaced, and, for better stability in space, asbestos brakes were swapped out in favor of ceramic ones.
- Starting with return-to-flight mission STS-114 (July 2005), NASA added a 50-foot extension to allow the crew to examine the shuttle’s belly for signs of foam impact damage.
Michael Klesius is an Air & Space associate editor.
Comments (6)
You might also mention the Flexible Reusable Surface Insulation (FRSI), quilted mineral fabric blankets that have replaced all the large white tiles that were previously used on the upper surfaces and frequently fell off. The blankets, some of which are hand-sewn, have proven remarkably durable even at Mach 25. Also, improvements to the foam insulation on the external tank have essentially eliminated foam loss and tile damage.
Posted by Dan Woodard on May 20,2010 | 11:09 PM
I'm amazed that we're seeing into the future of even publications!
A July 1st story and we just hit JUNE! (I'm just having fun with you). I love the shuttle. I am devastated that we're retiring one of the last non-partisan, patriotic, morale boosting, uniting, and dream building machines. It's not time. It's premature and it's wrong. I started the NASA Advocates Society on Face Book to bring you together and show we have a voice. I'm in the music business but these people, NASA, the minds, the crews and all at mission control are my heroes. My rock stars if you will. I think we let it slide and we can't afford to. .7% of the budget is spent on NASA. This is atrocious to think cutting HSF will change the national debt. I mean, I want privatization competition and sure, government smaller? but NASA? please let's stop picking on the brains here. We are #1 in Human Space Flight. We used to rally behind this stuff and in grade school when the first Shuttle went up, we all watched and were united. We need unifying things like this even if it costs 5% of the budget just for the morale part alone. Sure we can use SOYUZ now with the russians, thats nice we can share , but NASA, the Shuttle and our endeavors are what built this country. We need to always preserve what brought us here. Without these christopher columbus's of today, we're doomed to become more and more fragmented. It's not about government, it's about country. Let's not forget the things the ISS and SHuttle missions have done for all of us as far as the medical discoveries and advancements.
I can't tell you how much it will sadden me when and if this really is retired.
At least replace it with something to keep us going as a country instead of giving up. That's not America.
Posted by Grundmaster on May 29,2010 | 03:42 PM
I fully agree with the comments.
I cant believe in the 21st century that we are retiring 20th century inventions with no 21st century improved version to replace them. I am thinking Concorde as well as the Shuttle program here. What has happened to all the advancements in technology of world class icons we can be proud of. Is too much time and investment being spent on consumer electronics technology advancement at the expense of world-beating icons like the Shuttle and Concorde. I wonder where we will be in 10 years time? What happens after the ISS anyway? How will the ISS be repaired, upgraded or expanded?
Posted by Frosty from the UK on June 6,2010 | 10:32 AM
I would like to know what happens to the space station and the crew after the last two missions. Will the crew come home on the last mission and what would be the purpose of the space station with no one aboard. Also, how long will the space station maintain its altitude without starting to fall back to earth.
Posted by Norman Dillard on June 13,2010 | 11:43 AM
I love the shuttle program, but the comparison to the
Concorde is very enlightening. Mach 2 airline flight is
too expensive and inefficient to sustain. Concorde also
had risk factors which were judged to be unacceptable for
passenger flight.
The same issues affected the shuttle. At a billion and a half per flight, we can no longer justify the expense. Like the
Concorde, unresolved safety issues came to light, making
further flights unjustifiable.
Posted by John Ragozzino on July 10,2011 | 01:57 PM
i'm doing a space project for school and i want to find out if the design of the space shuttle has changed. get back to me as fast as you can. EDITORS' REPLY: Go to NASA's website for more detailed information on the shuttle.
Posted by will on May 12,2012 | 09:21 PM