There were a total of six space shuttles in NASA's Space Shuttle program, which was active from 1981 to 2011. These operational spacecrafts performed a variety of missions including deploying satellites, conducting scientific research, and performing service missions to the International Space Station.

Below are the shuttles and their details:

1. **Enterprise (OV-101)**: Though never flew in space, Enterprise was vital for NASA’s approach-and-landing tests within the atmosphere in the late 1970s. It's maiden flight occurred on February 18, 1977.

2. **Columbia (OV-102)**: This was the first operational space shuttle, with its maiden flight on April 12, 1981 for the mission STS-1. Columbia completed 27 missions before the catastrophic STS-107 mission, during which the shuttle disintegrated upon re-entry on February 1, 2003, leading to the death of all seven crew members.

3. **Challenger (OV-99)**: The second operational shuttle, it made its first flight on April 4, 1983 for the STS-6 mission. Challenger flew nine missions before it was destroyed shortly after launch on January 28, 1986 for the STS-51-L mission, resulting in the death of all seven crew members.

4. **Discovery (OV-103)**: Discovery's maiden flight was on August 30, 1984 during the STS-41-D mission. It completed 39 successful missions, more than any other space shuttle, with its final flight in February-March 2011 (STS-133). Discovery deployed the Hubble Space Telescope and launched the Ulysses probe to study the Sun.

5. **Atlantis (OV-104)**: Atlantis debuted on October 3, 1985 for the STS-51-J mission. It completed 33 missions, with the final one in July 2011 (STS-135), marking the end of the Space Shuttle Program.

6. **Endeavour (OV-105)**: Endeavour was built to replace Challenger and first flew on May 7, 1992 for the STS-49 mission. It flew 25 missions, with the last one in May 2011 (STS-134).

The names of the shuttles were often drawn from influential ships of exploration or scientific research. For instance, Columbia was named after the Boston-based sloop that in the 18th century became the first American vessel to circumnavigate the globe. Meanwhile, Endeavour was named to honor Captain James Cook's 18th-century ship used to explore the South Pacific.

Each of these shuttles played an integral role in space exploration and the contributions and sacrifices of the crews associated with Columbia and Challenger will forever be remembered.

The termination of NASA's Space Shuttle Program was primarily due to a combination of all three factors you've mentioned: financial considerations, technical issues, and safety concerns.

1. Financial Considerations: Operating the Space Shuttle program was expensive. Each launch was estimated to cost around $450 million, and the total program cost ran over $200 billion. Given these high costs, NASA wanted to redirect its budgets towards deep-space exploration missions, like sending humans to Mars, developing new spacecraft, and more detailed exploration of the outer planets.

2. Technical Issues: The Shuttles themselves were originally designed in the 1970s and became increasingly complex and difficult to manage and maintain over time. Issues related to aging were prevalent. They were also less efficient in comparison to newer technologies becoming available. From a design perspective, several critics questioned the Shuttle's partial reusability feature, stating that it might not have led to the cost savings initially anticipated.

3. Safety Concerns: The Shuttle Program had two major disasters (Challenger in 1986 and Columbia in 2003) which resulted in the loss of 14 astronaut lives. These tragedies raised serious questions about the Shuttles' safety. After each accident, the Shuttle fleet was grounded for over two years, and extensive reviews and upgrades were conducted. Despite improvements after each accident, doubts about the Shuttle's safety persisted.

After careful review and many deliberations, the decision was made to retire the Space Shuttle Program in 2011. The retirement paved the way for the next generation of spaceflight capabilities, where the responsibility for transporting crew and supplies to the International Space Station has been entrusted to commercial spaceflight companies, under NASA's Commercial Crew Program. Simultaneously, it also gave NASA the chance to focus resources on developing new technologies and systems needed for the Artemis program, aiming to send astronauts back to the moon and eventually, to Mars.

While the ending of the Shuttle Program marked the end of an era, it also started a new one, broadening the space industry to include more commercial involvement and propelling new possibilities for exploration and technological progress.

John W. Young and Jerry L. Ross are the two astronauts who have flown the most times with the Space Shuttle.

1. John W. Young: John Young is one of NASA's most experienced astronauts. He flew six space missions in three different programs--more than any other astronaut. Young's first two flights were on the Gemini spacecraft. He then flew two missions to the Moon on the Apollo spacecraft, one of which he walked on the lunar surface. After that, he flew two missions on the Space Shuttle. Among these, he was the Commander of STS-1, which was the first Space Shuttle mission, launched on April 12, 1981.

2. Jerry L. Ross: Jerry Ross is a retired American astronaut who is tied with John W. Young for the record for most spaceflights by a human being. He has a total of seven flights, all of which were on the Space Shuttle. His flights include the STS-61-B (1985), STS-27 (1988), STS-37 (1991), STS-55 (1993), STS-74 (1995), STS-88 (1998), and STS-110 (2002). During his career, Ross was involved in a number of milestones in the Space Shuttle Program, including the first launch of the Space Station assembly missions.

3. An additional mention should be Franklin R. Chang Díaz, who also has flown to space seven times but on different Space Shuttle missions. His missions include STS-61C (1986), STS-34 (1989), STS-46 (1992), STS-60 (1994), STS-75 (1996), STS-91 (1998), and STS-111 (2002).

Their dedication and contribution to space exploration have been instrumental in our understanding of space and have pushed the boundaries of human achievement. These astronauts have not only contributed by participating in missions but also leading them, conducting scientific research, and making significant contributions to space technology.

The Space Shuttle with the longest mission was Columbia as part of the STS-80 mission. This mission lasted nearly 17.5 days, from November 19 to December 7 in 1996.

STS-80 was a marathon science mission during which the shuttle's crew operated a variety of experiments in a self-contained module in the shuttle's cargo bay, known as the Spacelab module. Most Spacelab investigations were staffed by double-shift crews to ensure 24-hour operations, contributing to the lengthy mission time.

The mission had multiple objectives. Two significant goals were deploying and later retrieving the Wake Shield Facility and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer-Shuttle Pallet Satellite II (ORFEUS-SPAS II), both of which were separate deployable payloads designed to study novel aspects of space science.

The Wake Shield Facility was designed to create an ultra-vacuum environment in its wake (hence the name), suitable for growing thin semiconductor films for use in various technologies, while the ORFEUS was an astrophysics payload designed to observe the life cycle of stars and understand the gases surrounding them better.

Lengthly missions like STS-80 allow for extended observation and data collection times, which can provide more comprehensive outcomes and meaningful insights in such scientific investigations. It's also a testament to the increasingly long-duration spaceflight capabilities NASA was developing at the time, preparatory to stays aboard the International Space Station.

The Space Shuttle, run by NASA from 1981 to 2011, was a partially reusable spacecraft system that was instrumental in the exploration and understanding of space during its three decades of operation. Known for its distinct design and engineering capabilities, the Space Shuttle was utilized to transport a variety of payloads to and from orbit. These included:

1. **Satellites**: One of the primary functions of the Space Shuttle was delivering satellites into orbit. These included communication satellites, weather satellites, astronomical satellites, and more. Notably, in 1990, the Hubble Space Telescope was launched into space by the Space Shuttle Discovery.

2. **Spacecraft Parts**: The Space Shuttle was critical in the construction of the International Space Station (ISS). It transported various modular parts, power systems, observational devices, etc.

3. **Scientific Instruments & Experiments**: The Space Shuttle carried numerous scientific payloads for research in various fields including physics, astronomy, geology, and biology. Notably, the Spacelab module was transported for conducting scientific experiments.

4. **Supplies for Astronauts**: The Space Shuttle transported items needed for habitation like food and water supplies, oxygen tanks, space suits, and other equipment necessary for the stay of astronauts aboard the ISS.

5. **Crew Members**: The Shuttle also served as a crew transporter, taking astronauts back and forth from the ISS.

As for unique and unexpected payloads, there are quite a few interesting examples. The Shuttle carried a variety of student science experiments over the years, including an ant farm, chicken embryos, and various seeds for germination experiments. In 1992, the Endeavour carried Coca-Cola and Pepsi soda cans for a commercial experiment.

In 1984, the Discovery brought up the IMAX movie camera to film the documentary "The Dream is Alive" and in 1986, Challenger transported the first American female astronaut, Sally Ride, to space. In 2011, the final flight (STS-135) of the Space Shuttle Atlantis carried an iPhone and several LEGO sets to conduct various experiments in microgravity.

In terms of payloads, it is hard to think of any class of object that humans have sent to orbit that the Space Shuttle hasn't had a part in. The range was wide and varied, from scientific equipment and satellites to creatures, basic life necessities, and even popular culture articles, making the Shuttle an integral part of space exploration history.

The Space Shuttle program was an important chapter in the history of space exploration, operated by NASA from 1981 until 2011. It is remembered for both its significant contributions to our understanding of space and for several tragic incidents that prompted policy changes and technological advancements. Here are some key successes and failures of the Space Shuttle program:

Successes:

1. Frequent Access to Space: The Space Shuttle provided frequent and relatively cost-effective access to space, enabling the launch, repair, and retrieval of satellites.

2. Hubble Space Telescope: The shuttle was instrumental in deploying the Hubble Space Telescope in 1990, and in subsequent repair and upgrade missions. The Hubble has transformed our understanding of the universe with its detailed images.

3. International Space Station (ISS): The Space Shuttle was pivotal in the construction of the ISS, transporting segments of the Station to be assembled in orbit, as well as delivering supplies and crew members.

4. Extended duration of stay in Space: The Shuttle Program enabled astronauts to conduct experiments for extended lengths of time in space which led to many scientific advancements.

Failures:

1. Challenger Disaster (1986): The most tragic failure of the Space Shuttle program was the explosion of Challenger, resulting in the death of seven astronauts. An investigation determined that low-temperature conditions caused the O-ring seal in the right solid rocket booster to fail. This led to significant design and policy changes in the program.

2. Columbia Disaster (2003): Another dark chapter was the disintegration of Columbia during re-entry, where another seven astronauts were lost. The accident was caused by a piece of insulating foam from the external tank, which struck the shuttle's left wing during launch, and led to its break-up during re-entry due to the intense heat. This resulted in a renewed emphasis on shuttle safety and the decision to retire the shuttle fleet in 2011.

3. High Cost: The Shuttle program was exceptionally expensive. With the initial aim of affordability compromised, it impacted the scope and diversity of potential NASA projects.

4. Design Limitations: The shuttle was extravagant for many simpler tasks, limiting its use mostly to the needs of the ISS.

Despite these setbacks, the Space Shuttle program immensely contributed to the exploration of space, scientific experiments, international cooperation, and made space more accessible. Its failures led to important conversations about risk, safety, and the future direction of space exploration technology. At the time of retirement, it had flown 133 missions, carried over 350 people into space, and had paved the way for more advanced and safer spacecraft like SpaceX's Dragon and NASA's Orion.

The Space Shuttle Columbia disaster in 2003 marked a pivotal moment in the history of space exploration. The space shuttle tragically broke apart upon re-entry into the Earth's atmosphere, costing the lives of all seven crew members on board. Following the disaster, NASA and other space-related organizations worldwide enacted several safety measures intended to prevent such a catastrophe from occurring again. Here are some significant changes:

1. **Vehicle Health Monitoring**: The Columbia Accident Investigation Board (CAIB) identified the need for improved in-flight inspection and repair capabilities. NASA made changes to ensure vehicle health is stringently monitored throughout the mission.

2. **Inspections & Wing Leading Edge sensors**: They developed extensive on-orbit inspection techniques using the Orbiter Boom Sensor System (OBSS). They also installed wing leading edge impact sensors to detect and quantify potential debris strikes in future missions.

3. **Debris Assessment Team**: This group was created to make real-time decisions during launch if sensor data showed something potentially problematic.

4. **Elimination of Foam Shedding**: The root cause of the Columbia disaster was foam shedding from the external tank during ascent, which struck the orbiter's wing. NASA made substantial modifications to almost 50 areas of the external tank to eliminate foam shedding and reduce the risk of debris during launch.

5. **Changes to the Crew Module**: More survival equipment was added to the crew module, including better restraints and helmets, a better method for locating downed spacecraft and improvements to the crew module's seats to better handle impacts.

6. **Enhanced Crew Training**: The astronauts are now trained for several types of emergency landings over water and on land in various types of terrain, and at all times of day.

7. **Improvement in Organizational Structure**: Following the recommendations of CAIB, NASA worked on improving the scheduling pressure, communication problems, and dissenting opinions to ensure safety is the top priority.

As for how these changes impacted future Space Shuttle missions - they certainly helped improve the safety precautions significantly. These post-Columbia improvements saw astronauts return to space on the Shuttle a couple of years later with STS-114 mission. The emphasis has been tremendously increased on astronaut safety to minimize the risk factor during re-entry and landing procedures. Following the disaster, the remaining space shuttle missions until its retirement in 2011, had a remarkable safety record.

SEO, short for Search Engine Optimization, is a broad field that focuses on improving a website's visibility and ranking on search engine results pages (SERPs). While there are several types of SEO, on-page and off-page SEO are two of the primary categories.

1. On-Page SEO: Also referred to as on-site SEO, on-page SEO focuses on optimizing elements that are within the control of the website. At its core, on-page SEO revolves around ensuring your website has useful, relevant content and an excellent user experience. Examples of integral on-page SEO elements can include:

* Content: High-quality, well-researched, and unique content is paramount. It should address the user's needs and include the relevant keywords that users might use to find your site.

* Keywords: Proper keyword research, selection, and usage in your content increases the visibility of your pages in SERPs.

* HTML Tags: Proper use of title tags, meta descriptions, header tags, and alt tags ensure that search engines understand the context of your page.

* URL Structure: A well-defined URL structure that includes the primary keyword of the page helps improve SEO.

* Internal Linking: Linking your own pages with each other can help provide additional context to search engines about your content and can help push authority around your website.

* Site Speed: Web pages that load quickly contribute to a better user experience and are favored by search engines.

2. Off-Page SEO: While on-page SEO concentrates on aspects that you control on your website, off-page SEO refers to actions taken outside of your website. The primary goal of off-page SEO is to increase your site's trustworthiness and authority. Key elements of off-page SEO may include:

* Backlinks: These are links from other websites to your pages. Backlinks from reputable, high-authority sites can significantly improve your ranking as they signal to search engines that other credible sites vouch for your content.

* Social Media Engagement: While not a direct ranking factor, social signals such as likes, shares, and comments from social media sites can enhance your website's visibility and drive additional traffic.

* Guest Blogging: Writing articles for other blogs can help you gain exposure, establish authority, and earn backlinks.

Both on-page and off-page SEO are crucial for a comprehensive SEO strategy. On-page SEO ensures your website is user-friendly and optimized for both users and search engines, while off-page SEO improves your website's reputation and visibility online. It's a symbiotic relationship – by excelling in both, you can increase your chances of achieving higher SERPs rankings, which in turn leads to more traffic and conversions for your business.

Choosing the right URL structure is an extremely important aspect of SEO as it assists both users and search engines in understanding the nature and structure of your website. Here are some best practices for creating SEO-friendly URLs:

1. **Keep URLs Simple and Readable:** The URL should be simple and easily understandable for both search engines and users. Avoid using complicated parameters, numbers, and special characters. Use words in URLs that are relevant to your site's content.

2. **Use Keywords:** Whenever possible, use essential keywords in your URL. This demonstrates to search engines what the page is about and can help your page rank higher. However, avoid keyword stuffing as this can result in a penalty from search engines.

3. **Use Hyphens to Separate Words:** Search engines, like Google, prefer hyphens (-) rather than underscores (_) to separate words in the URL.

4. **Avoid Using Special Characters and Unnecessary Parameters:** Special characters and parameters can complicate your URL and make it less user and SEO friendly.

5. **Use Lowercase Letters:** Always use lowercase letters in your URLs. URLs can be case sensitive and can cause confusion for users and possibly even duplicating content issues.

6. **Use Canonical URLs:** Canonical URLs are used to prevent issues related to content duplication. So if you have content that's available on multiple URLs, you should choose one URL as your primary and use a canonical tag to prevent duplications.

7. **Limit Folders in URL Structure:** Overusing folders can make a URL look longer and complex. Try to limit the use of folders to a necessary minimum.

8. **SSL Certificate:** Use HTTPS, not HTTP, as it's a ranking signal for Google. To use HTTPS, you need to install an SSL certificate on your website.

Remember, while it's good to have an SEO-friendly URL, tweaking URLs unnecessarily could lead to broken links, which isn't good for SEO or user experience. It's also important to set up proper 301 redirects if you decide to change your website's URL structure.

In conclusion, an SEO-friendly URL is descriptive, gives an idea of the content of the page, is not overly long, uses hyphens to separate words, does not overuse folders, and uses HTTPS. Applying these best practices will not only make your URL structure SEO-friendly but also user-friendly.

The Cold War, stretching from the end of World War II in 1945 until the dissolution of the Soviet Union in 1991, was marked by a tense and complex series of confrontations, standoffs, and moments of detente between largely East and the West, primarily between two superpowers: the United States and the Soviet Union. Here are some defining moments and major events of the Cold War era:

1. **Formation of United Nations (1945):** Though not directly part of Cold War confrontation, the formation of the United Nations laid the foundation for many diplomatic exchanges and discussions during this period.

2. **The Truman Doctrine (1947):** This was a policy put forth by U.S. President Harry S Truman to provide economic and military aid to countries threatened by communism. It is often recognized as the official start of the Cold War.

3. **Marshall Plan (1947-1951):** This was a U.S. aid package to European countries to help them recover after World War II and prevent them from falling under Soviet influence.

4. **Berlin Blockade and Berlin Airlift (1948-1949):** The Soviet Union blocked rail and road access to West Berlin in an attempt to force the Allies out. In response, the Allies delivered supplies to West Berliners via an airlift for about a year until the blockade was lifted.

5. **Foundation of NATO (1949):** The North Atlantic Treaty Organization was established by Western powers as a collective defense pact against the Soviet Union.

6. **Korean War (1950-1953):** This war resulted from a conflict between North Korea (backed by the Soviet Union and China) and South Korea (supported by the U.S. and its allies).

7. **Cuban Revolution (1959):** The victory of Fidel Castro's communist regime in Cuba increased Cold War tensions, as communism now had a foothold in the Western Hemisphere.

8. **Construction of the Berlin Wall (1961):** East Germany, backed by the Soviet Union, built a wall to prevent East Germans from fleeing to the West.

9. **Cuban Missile Crisis (1962):** An extremely tense confrontation when the U.S. and the Soviet Union nearly came to nuclear warloads over the deployment of Soviet missiles in Cuba.

10. **Vietnam War (1955-1975):** A long and controversial war where U.S. intervened to stop the spread of communism in South-East Asia.

11. **Prague Spring and the subsequent Soviet Intervention (1968):** An attempt to establish "socialism with a human face" in Czechoslovakia was suppressed by the Warsaw Pact forces.

12. **SALT I and II (Strategic Arms Limitation Talks - 1972 & 1979):** These were landmark arms control treaties between U.S. and Soviet Union, reflecting periods of relaxation, or detente.

13. **Soviet-Afghan War (1979-1989):** The Soviet Union's costly and unsuccessful war in Afghanistan heavily strained their economy and contributed to the dissolution of the Soviet state.

14. **Fall of the Berlin Wall (1989):** This significant event signaled the beginning of the end of the Cold War, allowing East and West Berliners to travel freely.

15. **Dissolution of the USSR (1991):** The breakup of the Soviet Union marked the end of the Cold War era.

Remember, these are only select highlights. The Cold War era was complex and multi-faceted, involving a range of political, military, economic, and ideological struggles in diverse locations around the globe. It was a period that had a profound and lasting impact on global politics, societal perspectives, and international relations.