General Considerations

• The subject: By "space exploration" here we mean missions that send human-made spacecraft into space, not in orbit around the Earth (like on the International Space Station).
• Funding: In the US, the National Aeronautics and Space Administration (NASA); Many other countries now have a space agency; Main example, the European Space Agency (ESA).

  Solar System: First Accomplishments

• The beginning: Ideas had been proposed for a long time, but the first concrete steps were taken during the Cold War, motivated by US-Soviet Union competition.
• The Moon: 1968, Apollo 8 orbits; 1969, Apollo 11 landing; Several more landers (a dozen astronauts) and orbiters since.
• Terrestrial planets: 1960's, Mariner flybys of Venus; 1970's, Mariner 10 probe to Mercury, Venera landings on Venus and Pioneer Venus orbiter, Viking 1 & 2 landers on Mars.
• Jovian planets: 1970's, Pioneer 10+11 were the first to venture beyond the asteroid belt; 1979-1989, Voyager 1+2 grand tour (a once-in-175-years opportunity!); All four spacecraft are now heading out of the Solar System.
• Propulsion technology: Use solar panels and, for travel much beyond Mars, radioisotope thermoelectric generators (RTG).
• End of the "Grand Interplanetary Explorers" era: Approach changed to "faster, better, cheaper" missions after 1993 loss of 1-G$ Mars Explorer.

Solar System: Recent and Current Missions

• Planet missions: Venus, Magellan in orbit from 1990 to 1994; Mars, Pathfinder and Global Surveyor in 1997 (2 spacecraft lost in 1999), Mars Odyssey launched in 2001; Jupiter, Galileo in orbit since 1995; Saturn, Cassini started heading there in 1997, will arrive in 2004.
• Other missions: The Sun, SOHO, Ulysses, Wind, ACE, TRACE; Asteroids, EROS explored Eros in 2000-2001; Comets, Stardust, launched in 1999, is collecting dust and will meet comet Wild-2 in 2004; Pluto/Kuiper Belt, New Horizons, launched in 2006, is scheduled to arrive in 2015 [the fastest spacecraft yet, at > 83,000km/h after its 2007 Jupiter encounter].
• Current trends: Loss of Mars spacecraft may indicate NASA went too far in cutting costs, but idea still seems good. New ideas include "impact" astronomy (like with Lunar Prospector, Galileo, Deep Impact); Orbiters vs landers vs rovers.
• Plans for the near future: Mercury, NASA's Messenger in 2004, ESA's Bepi Colombo in 2009; Mars, ESA's Mars Express in 2003, several NASA missions planned; Europa, orbiter in 2003; Asteroids/Comets, ESA's Rosetta to be launched in 2003.

  Solar System: Future Exploration

• Human or unmanned missions? In particular, should we send humans to Mars?
• Launching spacecraft: Should we build them in space, or on the Moon?
• Propelling spacecraft: Need to increase speed (currently 10's of thousands of km/h, but progress could be quick), without heavy fuel; Over the next few years, NASA will develop a fleet of nuclear-powered spacecraft; Electric ion propulsion has been successfully tested; Solar sails that propel spacecraft by reflecting sunlight (rather than absorbing) are being planned, despite the Cosmos-1 setback in 2005; NASA has tested engines propelled by methane, abundant in the outer solar system; Plasmas? Matter-antimatter?
• Dangers faced by spacecraft: Radiation and cosmic rays, bursts of energy from the Sun, human-made debris, speedy meteoroids; Landing conditions.
• Communicating with spacecraft: Currently handled for NASA by the Deep Space Network, managed by JPL.
• Plans: Return to the Moon and establish bases; Set up a gateway at L1...

Beyond the Solar System: Possibilities for Interstellar Exploration

• A beginning: The Pioneer and Voyager spacecraft are already beyond the planets' orbits (Voyager 1 at 100 AU!), carrying information about us.
• Could we travel to interstellar space? The trip is too long for one crew (right now it would take 50,000 yr!), but scientists are discussing the possibility of several generation-long trips, including what the crew should be like, how their language would change over the hundreds of years the trip would take, how to communicate with them, ...
• Time travel: Can we circumvent the speed of light limit by non-conventional means? Wormholes and warp drive? Hyperspace?
• And then? Who would we meet out there?