Long ago men dreamed of travelling into space and this finally became a reality in 1961 when Yuri Gagarin made the first space flight in Vostok and remained in space for 89 minutes. Man has also, since long ago, dreamt of travelling to the Moon. This was also made a reality in 1969 when Neil Armstrong became the first man on the Moon and was on the Moon for 22 hours. Apollo 11 took him there. In total man has gone to the Moon six times and is now looking towards the planets.
The first stop after the Moon was thought to be Mars. Mars is not the nearest planet though. Venus and Mercury are nearer but they are both much too hot so Mars is the first planet we will visit. It however may not be our next step. The next stop may be even nearer.
Travelling to a 'Near Earth Asteroid' will probably be the next step before Mars. It will be a lot nearer and a lot cheaper. No asteroid has been chosen yet but there are about 200,000 to choose from. After this the next step is most likely to be Mars.
A mission to Mars will be a much longer affair than to the Moon. The first thing that will happen is a craft will go ahead, before the manned space flight, to land on the surface and produce fuel that will enable to crew to return without having to take the fuel with them.
A manned flight will then take place. The trip to the Moon took three days each way. A trip to Mars should take between six months and a year. Since a Martian year is two Earth years long, there will plenty of launch windows for a trip to take place. The crew is likely to remain on Mars for a few years before returning to Earth. Once this step has been taken more trips can be made. These will hopefully lead to the construction of a colony on the Red Planet.
After Mars, it is uncertain which of the giant planets will be the first step. Jupiter is nearer and could be reached in two years and although Saturn would take four years, it has one fact very much in its favour. Both the planets cannot be landed on so the planets largest moon will be the place where Man will probably land.
The largest moon in the Solar System is Ganymede in orbit around Jupiter. Titan however, the second largest moon in the Solar System and largest moon of Saturn, is the only moon in the Solar System that has an atmosphere. This means is could be ideal for refuelling. Jupiter's moons do however have ice, which could also be used for refuelling.
After Jupiter and Saturn, Uranus and Neptune will be the next planets that we will visit. These planets are also gas giants and can't be landed on. They also have many moons for men to touch down on. Uranus is a lot more distant to us than Saturn and due to this, combining Uranus and Neptune may be a better idea. This is uncertain since the distance between Uranus and Neptune is still huge compared to most other interplanetary distances.
The distance between Saturn and Uranus is the same as the distance between Saturn and the Sun. When Uranus was discovered, the Solar System doubled in size.
After Neptune the next stop would seem to be Pluto but Pluto is not an easy planet to reach. With its plane of orbit so inclined reaching Pluto would be difficult and since its orbit is so eccentric, the time we have to go there has to be chosen carefully. Also its year is so long that we would have to wait a long time if we miss an opportunity.
It seems that there is little question on the best time to travel to Pluto. For twenty Earth years in each Pluto year, the planet crosses inside Neptune's orbit and for that short time it means that it is no longer the furthest planet from the Sun and therefore the trip would be the shortest then. There is also another reason why Pluto may not be the next stop.
Pluto is not really a planet. It is a planetoid. It is an object in the belt of small objects out past Neptune's orbit. This is called the Kuiper Belt. This consists of planetoids, which are small objects not meant to be planets. Some of the moons of Uranus and Neptune are most likely Kuiper Belt objects and Pluto and its cosy companion Charon - its moon, are also Kuiper Belt objects. Pluto is the largest Kuiper Belt object and will only keep its status as a planet for historic reasons. This means that Pluto may not be a particularly important stop.
This leads us to the question, if not Pluto then where. I have already mentioned that Mercury and Venus are much too hot but they still are planets of our Solar System and even if it has eight or nine, I'm sure we'll want to do the complete set.
Mercury is the nearest to the Sun with temperatures that soar to 842°F (450°C) at day. Venus however, somewhat further from the Sun is much hotter. 867°F (464°C) is what Venus has to offer due to its clouds or carbon dioxide that have given the planet a runaway greenhouse effect and make it the Planet of Hell.
Mercury however has something else in its favour. Although the temperature is at rocket heights at day, the average temperature is only 333°F (167°C) because at night the temperatures plummet to -292°F (-180°C) because Mercury has virtually no atmosphere and so no way of retaining its heat.
This is what would make Mercury the next candidate. A landing could be completed on the night side where people could still walk on the surface, wearing space suits of course. A day on Mercury is 56 days but since it orbits the Sun in 88 days, it is 176 days between sunsets. This means that there would be plenty of time to make a landing and take off again before sunrise. However this doesn't have to be the case. Some of the craters on Mercury's South Pole are always shielded from the Sun. It is believed that there may be water ice in them and a base could even be either built in one of these craters or the entrance could be there with the base protected from the Sun's heat under the surface.
Venus being nearer than Mercury may be too hot to ever be landed on. However probes have been landed on Venus and even if the people on a manned ship never actually leave the ship a short landing may be possible. It is likely that even with the difficulty of getting to Pluto it may be that Pluto is the stop after Mercury. It does have the icy bodies of the Kuiper Belt that could be used for refuelling.
Venus and Mercury are near enough to make refuelling not to big a problem. Mercury is worth a visit with a view to returning, since it may one day be mined. Venus on the other hand could maybe be terra-formed. There have been plans and unlikely as this seems if it does work, Venus, being almost as large and the Earth, could be an ideal Earth #2 if we can keep the temperature down.
After Venus or Pluto we have run out of planets. Asteroids in the belt may be places to visit with Ceres, being the biggest containing one third of the total mass of all asteroids, would be the first choice. Comets may also be targets. Halley's Comet would be a favourite and has been suggested by science fiction authors. Comets in the Oort Cloud may also be a target for the ambitious. Along with a landing on Pluto and presumably Charon, Kuiper Belt objects may also be landed on. Quaoar is the most likely, after the 'Pluto - Charon' double world, since at the present it is the largest Kuiper Belt object known to exist that is not classified as a planet or planet's moon.
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