established the following ranking of the most important technological developments of the 20th century: Electrification Automobile Airplane Water supply and Distribution Electronics Radio and Television Mechanized agriculture Computers Telephone Air Conditioning and Refrigeration Highways Spacecraft Internet Imaging technology Household appliances Health technology Petroleum and Petrochemical technologies Laser and Fiber Optics Nuclear technology Materials science 21st century In the early 21st century, research is ongoing into quantum computers, gene therapy (introduced 1990), 3D printing (introduced 1981), nanotechnology (introduced 1985), bioengineering/biotechnology, nuclear technology, advanced materials (e.g., graphene), the scramjet and drones (along with railguns and high-energy laser beams for military uses), superconductivity, the memristor, and green technologies such as alternative fuels (e.g., fuel cells, self-driving electric and plug-in hybrid cars), augmented reality devices and wearable electronics, artificial intelligence, and more efficient and powerful LEDs, solar cells, integrated circuits, wireless power devices, engines, and batteries. Large Hadron Collider, the largest single machine ever built, was constructed between 1998 and 2008. The understanding of particle physics is expected to expand with better instruments including larger particle accelerators such as the LHC and better neutrino detectors. Dark matter is sought via underground detectors and observatories like LIGO have started to detect gravitational waves. Genetic engineering technology continues to improve, and the importance of epigenetics on development and inheritance has also become increasingly recognized. New spaceflight technology and spacecraft are also being developed, like the Boeing's Orion and SpaceX's Dragon 2. New, more capable space telescopes, such as the James Webb Space Telescope which was launched to orbit in December, 2021, and the Colossus Telescope, have been designed. The International Space Station was completed in the 2000s, and NASA and ESA plan a human mission to Mars in the 2030s. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an electro-magnetic thruster for spacecraft propulsion and is expected to be tested in 2015. Breakthrough Initiatives, together with famed physicist Stephen Hawking, plan to send the first ever spacecraft to visit another star, which will consist of numerous super-light chips driven by Electric propulsion in the 2030s, and receive images of the Proxima Centauri system, along with, possibly, the potentially habitable planet Proxima Centauri b, by midcentury. 2004 saw the first crewed commercial spaceflight when Mike Melvill crossed the boundary of space on June 21, 2004. By type Biotechnology Timeline of agriculture and food technology Timeline of biotechnology Civil engineering Civil engineering Architecture and building construction Bridges, harbors,