Hugh Pickens writes:
The cost of getting to orbit is exorbitant, because the rocket, with its multimillion-dollar engines, ends up as trash in the ocean after one launching, something Elon Musk likens to throwing away a [Boeing] 747 jet after a single transcontinental flight. That's why on Tuesday morning at 6:20 a.m. EST his company hopes to upend the economics of space travel in a daring plan by attempting to land the first stage of a Falcon 9 rocket intact on a floating platform, 300 feet long and 170 feet wide in the Atlantic Ocean. SpaceX has attempted similar maneuvers on three earlier Falcon 9 flights, and on the second and third attempts, the rocket slowed to a hover before splashing into the water. “We’ve been able to soft-land the rocket booster in the ocean twice so far,” says Musk. “Unfortunately, it sort of sat there for several seconds, then tipped over and exploded. It’s quite difficult to reuse at that point.”
After the booster falls away and the second stage continues pushing the payload to orbit, its engines will reignite to turn it around and guide it to a spot about 200 miles east of Jacksonville, Florida. Musk puts the chances of success at 50 percent or less but over the dozen or so flights scheduled for this year, “I think it’s quite likely, 80 to 90 percent likely, that one of those flights will be able to land and refly.” SpaceX will offer its own launch webcast on the company's website beginning at 6 a.m. If SpaceX’s gamble succeeds, the company plans to reuse the rocket stage on a later flight. “Reusability is the critical breakthrough needed in rocketry to take things to the next level."
Rockets may bring a human to Mars once, but it is not the way to effectively reach other planets. I would say that a manned trip to Mars is impossible with what we have today. It will simply take too long, and the travel time, combined with harmful environment, will injure astronauts even before they reach Mars.
It's roughly six months each way to Mars. That's not particularly long especially if as you do below, take care of the radiation shielding and introduce some artificial gravity.
To survive for a year in space astronauts need artificial gravity and protection from energetic particles (space radiation) - it's the bare minimum. But in practice you'd also need life support, ideally a renewable one, and a way to protect people from going insane during the trip.
None of which has anything to do with rockets. We could develop all of these and still use current rocket technology to pull the trip off repeatedly.
Things get complicated once you try for something further away than Mars or Venus. A manned trip to Jupiter could be done with chemical rocket engines, but it's going to be a trickier problem due to having at least several years of travel time and the much more considerable delta-v involved. I wouldn't attempt it without at least a better understanding of long term human habitation outside the Van Allen belts.