The guy is right. If you can send stuff to Mars, sending stuff to Saturn isn't much harder. In fact, we already do send probes around the solar system.<p>The problem is moving <i>people</i> in space. Space is the ultimate desert. People need all kinds of supplies to stay alive and healthy (air, water, food, gravity, etc). They also need to be shielded from cosmic rays and solar events.<p>I've said it before and I'll say it again: I doubt large numbers of biological humans will ever participate in interplanetary travel. I bet brain-in-vat or uploading technology will show up before payload costs get low enough for average people to buy tickets to Mars. A brain in a vat doesn't need gravity or exercise or space to roam around in. It needs less food and water than a full human body, and it can be shielded easily.
Regarding his underplaying of fuel mass, check out the rocket equation to get an idea of how hard it is to achieve the delta-v required for various maneuvers (e.g. suborbital, orbital, escape): <a href="http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation" rel="nofollow">http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation</a><p>Essentially, your fuel mass requirements increase exponentially as you need more delta-v. It's very much harder to get into orbit than to stay sub-orbital. And you will need a significant amount of fuel left over if you wish to orbit or land at your destination. You can mitigate that with atmospheric aerobraking, but that's not possible on, say, the Moon.
Halfway to anywhere: A really good book on the subject, including an interesting story about development of low cost space launch capability. It is a bit old now with SpaceshipOne and SpaceX in progress, but still worth a read: <a href="http://www.nss.org/resources/books/non_fiction/review_013_halfway.html" rel="nofollow">http://www.nss.org/resources/books/non_fiction/review_013_ha...</a><p>I was actually expecting some analysis on interstellar space travel. But you can find an entertaining attempt at this by Charles Stross: <a href="http://www.antipope.org/charlie/blog-static/2007/06/the_high_frontier_redux.html" rel="nofollow">http://www.antipope.org/charlie/blog-static/2007/06/the_high...</a>
I think really this should be titled, 'How hard is moving an object in space, in principle'.<p>For me space travel involves humans in space and that's really difficult. Think about being in a little bubble of air surrounded by hard vacuum that would kill you in seconds. Plus the cold/radiation/general plumbing problems. Space travel is really hard.
<i>In fact, nearly all of the energy expended by modern rockets goes into lifting the rocket fuel itself, and only a small amount into the payload.</i><p>Which would mean the fuel needed is quadratic in the GPE needed, which would put Saturn right back up there at ~100 times harder to reach than the moon (ignoring constants).
"In fact, nearly all of the energy expended by modern rockets goes into lifting the rocket fuel itself, and only a small amount into the payload. An unfortunate consequence of this is that you need a lot more than four times as much fuel"<p>Yes this is where theory != practice, and why in fact, it's incredibly difficult and expensive to get somewhere like Mars.
There seems to be an assumption here that the difficulty of going somewhere is proportional to the energy required.<p>What about time, and provisions for life support during that time? What about launch windows, in terms of the amount of waiting time required before a return trip and the difficulties of a rescue mission?<p>Others have already mentioned that the amount of fuel/weight you need is worse than linearly proportional to the energy required.
Really, really good book on this subject:
<a href="http://en.wikipedia.org/wiki/The_Millennial_Project:_Colonizing_the_Galaxy_in_Eight_Easy_Steps" rel="nofollow">http://en.wikipedia.org/wiki/The_Millennial_Project:_Coloniz...</a><p><a href="http://www.amazon.com/Millennial-Project-Colonizing-Galaxy-Eight/dp/0316771635" rel="nofollow">http://www.amazon.com/Millennial-Project-Colonizing-Galaxy-E...</a><p>The book does a nice job of capturing all the hard engineering problems. His proposed solutions are interesting but a bit superficial.
If your willing to take a loooooong time, you can take the interplanetary highway. Basically, by carefully picking your path, you can essentially move from Lagrange point to Lagrange point, where changing directions is nearly free.