Some of it has to do with the mathematical realities of the solar system. Mars will be closest to Earth in 2018, but if we can't get there that quickly, after that Mars will not come nearly as close to Earth through the 20's until we get to the 30's[0]

[0]http://cseligman.com/text/planets/marsoppositions.htm

The variances in fuel over that ~15 year cycle are really minor. Normally launch windows to Mars open every ~24 months.

An unmanned probe can take an extra month or year to get there with no changes to the actual mission as long as the path is fuel efficient.

For human cargo, the time difference is as important as the fuel expenditure - extra life support supplies can be heavier than extra fuel to make the same flight faster, or the need for much longer life support may make the whole thing impossibly heavy.

The closest Mars approaches (in a reasonable time frame) occur on a roughly 15-year period. The next one is in 2018, with the one after that being 2033. See http://en.wikipedia.org/wiki/Mars#mediaviewer/File:Mars_oppo... and the associated article for a bit more detail.

That said, I agree that the plan is pretty pointless: when I was in high school, I was super-psyched that we were going to Mars in 2018. Couldn't wait. Then we got to ~2008, and we had to go from dreaming to doing. Perhaps unsurprisingly, we also decided to go to Mars in 2033. This time I'm less excited.

How big is the difference really? Another month or two travel time? Humans have spent over a year (Mir) and routinely do six month stints on the ISS. If you've got the tech to get to Mars and land there, then an extra month or two flight time is not going to kill you.

I say go as soon as we have the flight hardware built and qualified.

If you're sending humans, that's another month or two of the most expensive supplies in the history of human endeavor. It's not exactly a detail that we can currently afford to wave away.

(And I do mean afford. If we had better propulsion tech, like, oh, say, anything nuclear, we wouldn't have to worry so much about such details. But if we're going to hobble ourselves by rejecting that out of hand, we can't afford much mass.)

And nuclear thermal isn't even that good at 'only' (should I say surprisingly?) about 2x ISP, so you'd still need lots of mass.

It's not just the problem of having astronauts hanging out in their ship playing zero-gravity poker for an extra couple months. You also need to have adequate supplies for that time and make sure the crew is protected from any additional radiation exposure they'd experience during that time.

There's something wrong with the math here. 100 km/s delta-V means you go from standstill to 100 km/s. Solar system's escape velocity is 42 km/s at Earth's orbit. By the very definition, any A->B travel for any A and B within the solar system, requires less delta-V if Hoffman's orbits are used.

In reality the delta-V for Earth_surface -> Mars_surface journey is between 19 and 21 km/s (depending on the relative position of the two bodies) for Hoffman's orbits. Without using aerobreaking. If using aerobreaking, it's less by about 3-4km/s [1]

http://en.wikipedia.org/wiki/Delta-v_budget

No matter when, you are going to burn extra fuel to shorten the trip for humans. You can get down to about 6 months travel time before it starts being crazy to spend extra fuel to shave extra days off the trip.

I just watched Neil DeGrasse Tyson's word on the subject yesterday (https://www.youtube.com/watch?v=wNxnCzz5oQE) and he quite agrees with you: "We're going to Mars in 20 years" is not what NASA should be about. NASA (and other space agencies) should strive to make space re-enter our culture so its benefits can rain on all aspects of our lives. In order to do that his proposal is to double NASA's budget and focus on building a suite of vehicles able to transport whatever they want. Kind of like the space shuttle but for longer distances, such as the moon, asteroids, Mars, Lagrange points... If you have perfected a space vehicle, going to Mars is about adapting that vehicle.

I'm not sure NASA has the budget to accelerate things the way they did during the Apollo era.

Isn't it prudent to spread out the $1 trillion cost over a couple decades? After all, we have to borrow every dime of that from future taxpayers. I'm including cost overruns.

Or are you willing to pay an extra $10K a year in taxes to get to Mars sooner?

NASA's budget over a couple decades isn't anywhere near $1 trillion. It's a skimpy little agency, relatively speaking.

You don't think the budget will increase as they take on their biggest challenge yet, by a couple orders of magnitude?

Even the stupidest plan to get to Mars only got a price tag of half-a-trillion (over 30 years).

The same team that gave the sticker-shocking $300-500 billion price tag to the Space Exploration Initiative gave a price tag of about $30-$50 billion to a MarsDirect-style mission. Spread over 10 years, that's about 10% of NASA's budget.

Even if, incredibly, there are no huge cost overruns and the final tally is $30 billion, are you willing to pay extra taxes starting today so the money isn't borrowed from future generations who presumably would like to have their own space missions to enjoy in real time, rather than just read about them in the history as they struggle with high taxes to pay down the debt we ran up for them?

Yes.

Then kudos to you!

The average taxpayer pays NASA $55 per year.

I pay less for my Science Museum membership.

I would love to see NASA fixed (firstly) and fully funded (once its fixed).

Well you haven't paid a dime in NASA funding yet. All funding to date has been borrowed from people younger than you or not yet born. Presumably the gov't will borrow many times more to get to Mars, than it has for any previous mission.

You think that will pay for a human expedition to Mars and back?

If the US wasn't $17 trillion in debt, I could agree. Pretty sure all NASA funding to date fits into that debt amount. Since it's a "nice to have", I'd say the average taxpayer has never paid anything to NASA, not even interest on debt since we borrow to pay that.

We're already scheduled to spend a similar amount on simply maintaining our (US) nuclear deterrent. Not that I think we should abandon it or that it lacks strategic importance, but I do wonder about scale, in the same way that I wonder if NASA could find more efficient approaches.

So you're okay with paying extra taxes today so money needn't be borrowed from the kids (and their kids) for a Mars expedition?

Yeah, some, although I think that with 30 year t-bills at ~3% some of it should be financed by debt, as we're likely to develop multiple growth- (and thus revenue-) enhancing technologies over a 30 year period.

For perspective, Medicare and social security outlays over the same period are likely to exceed $50 trillion.

Okay, thanks for sharing your opinion on that. Myself, I'd rather see it paid off as costs are incurred, if we spend the money at all. If we weren't so in far in debt already (i.e. if future kids weren't so doomed), then we could take a chance on those revenue enhancements coming to fruition.

yes, and if weren't going to happen in my lifetime otherwise, 20-30k.

Wow, I applaud you for being among the very few people who can both support a space mission and be willing to pay for it!

don't take it as a personal demonstration, i mean it should be generally true for all

it's a small individual sacrifice for the most significant accomplishment yet of all known life

i can't think of anything larger or more important to support