On or after January 11th the New Horizons spacecraft will be launched on a 9 year journey to the tiny planet Pluto and its moon Charon. The journey of the project to this point was as long as the actual trip is projected to be, with the mission being proposed, killed by congress, resurrected, cancelled and resuscitated again and again.
First named the Pluto Fast Flyby mission, two spacecraft were supposed to be launched. That project died and the Pluto Express was proposed. Now its New Horizons. The single spacecraft has only a 35 day launch window. If launched before February 2nd New Horizons will be able to catch a gravitational assist from Jupiter in February or March 2007 to reach Pluto in July 2015. From February 2nd to the 15th the earth and Jupiter will be out of position, and New Horizons will take a slower trajectory to Pluto without Jupiter's assistance, and will reach Pluto in 2019 or 2020. If so, it will be the first time a spacecraft would be sent past Jupiter without the gravitational assist of this largest of planets.
Ths use of planets as means to increase or decrease the velocity of spaeccraft has been a useful navigation technique since its use by Pioneer 11 in 1974, to get from Jupiter to Saturn. Then Jupiter wasn't in the best position for the assist, So the spacecraft had a long haul across the solar system to Saturn, reaching the ringed planet in September of 1979. Voyager 1, launched 4 years after Pioneer 11, reached Saturn only a year later in November 1980. Jupiter was more favorably aligned for that assist.
Planetary Navigation 101 says that to increase a spacecraft's velocity, and get it to move away from the sun, aim to encounter a planet from behind, as its orbits the sun. The planet will, in effect pull the spacecraft forward, stealing a immesurable bit of orbital energy from the planet involved. To drop closer to the sun, aim in front of the planet, you wish to use for the assist, to transfer energy from the spacecraft to the planet. This technique is being used multiple times using, the earth, Venus and Mercury itself with the MESSENGER spacecraft attempting to reach Mercury and to enter orbit of it. Launched last year, that flight will take some 7 years to get to Mercury.
This brings up the relative merits of manned vs. robotic missions. Manned missions require much heavier spacecraft to support human life, water, food, oxygen, perhaps artificial gravity. Exploration missions must be set up as round trips. Early colonization missions also must have the safety factor of an emergency return vessel until the colony becomes completely self sustaining. Humans are not considered expendable. While humans are much more versatile and have better brains that any robotic computer we are rather delacate creatures: we can't handle too high or low temperatures, high radiation or high G-forces and possibly zero G for extended periods of time.
Robotic missions are hundreds of times cheaper than human missions, lighter, quicker to develop and launch. They can journey for years, with little expendature of fuel. They needn't return to earth unless to return a sample.
In fact one robotic mission will return with a sample January 15th. The Stardust spacecraft, which swept past Comet Wild 2 (Pronounced Vilt 2) January 2nd, 2004, collecting particles from the comet, is heading home with its prize, and is scheduled to land in Utah. We're hoping the landing will be softer than the Genesis spacecraft had back in September 2004. While the parachute failed, and the spacecraft augered into the ground at a velocity that would have killed a human crew, a good percentage of the collected solar wind particles was recoverable.
I'm not against manned missions. However there will be a point when they will be practical. Since 99.9999% of us can't go along on a manned mission anyway, the vicarious experiences of say the Mars rovers over the past two years has been a thrill. As close as I'll ever get to Mars. As the rovers get more sophisticated, and the transmission bandwith increase we will get near realtime video feeds, and more sophisticated science results. It'll almost be like being there.
For the foreseeable future, manned missions will be restricted to the moon, Mars, short period comets and asteroids. In reality the asteroids are perhaps the most promising. The latter two have easily accessable organic and other material that will be useful for life support and trade, and may in the long run be better targets than planets.
But for now, let the robots fly and roll on into the blue Martian sunset.
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