We do have fusion reactors (and of course, have the tech for them). We do not have the tech for practical fusion reactors. Neither one of these positions is controversial at all.
We do have a roadmap for several decades of research and development which we hope will eventually conclude with a practical fusion reactor. But we’re not at the end of that road yet. We haven’t yet solved all of the problems. We almost certainly don’t even know what all of the problems are that need to be solved.
Which has been “ten (or maybe twenty) years away” for my entire adult life.
The OP:
Are we already capable of going to Mars this very instant but just unwilling?
A Mars rocket is not just sitting in a warehouse right now.
But could we build it and make it happen, with today’s tech, if money is no object?
Sure. No one has said what tech we lack and would need to invent to get there. We’ve already gotten there. Many times. The twist here is a human so life support but we’ve had people in space for over a year before and have people living there now.
We know how to do this. It’s just a money problem mostly but the OP specified unlimited funds.
Would it be dangerous/risky? Sure.
We know how to successfully land small rovers on Mars.
What is the tech that we already have that will let a landing vehicle, which weighs one to two orders of magnitude more than the various Mars rovers, and which contains human cargo, successfully and safely land on Mars, and be able to get those humans back off the planet?
Where did the OP say we have to land?
And even if we did why do you think it is beyond our current tech to do?
Where did the OP say that “getting into orbit was close enough?”
@Stranger_On_A_Train has shared that in this thread several times, until you started accusing him of spamming the thread by reposting what you either have not read, or do not care to believe.
Also, in the Wikipedia entry on “Human Mission to Mars,” there is this (bolding mine):
So, if NASA is having to “develop new approaches to Mars atmospheric entry,” that does kinda indicate that, no, we do not have that technology today.
In post #11 of this thread the OP said:
For sure. But my hypothetical is just asking if political and social will were no issue - everyone agrees we need to go to Mars pronto - whether we already have the means.
Per Stranger, no we do not, so my ignorance is fought.
Since @Stranger_On_A_Train to that point only addressed the difficulties of landing and retrieving a team from the Martian surface, a reasonable reader would conclude that the OP meant landing and returning.
Let me give an extremely oversimplified example. One piece of technology I own is a little plastic thingy I use as a hall pass for my students in class. I 3D printed it, of course, so you could argue that the “technology existed” for it ever since 3D printers were invented (or at least, ever since they got cheap enough that a teacher would have opportunity to use one).
But the first one I made didn’t work very well: When students handled it and occasionally dropped it and so on, it tended to chip around the edges. So I tried various ideas to address that problem. I tried making a mold, and using a soft heat-melt polymer to make it, but it didn’t show fine detail well enough. I tried using the same mold, filled with silicone. That showed the fine detail, but it was too fragile: The details tended to break off. I tried making a skeletal core for it that fit inside of the mold, and that solved the detail problem, but eventually the silicone peeled away from the rigid skeleton. Eventually, the seventh instance of the hall pass I made, years after I started, I came up with something that superficially looks almost exactly like the first version, except that by that time I had learned enough more about 3D printing to add extra internal reinforcement to the edges where the original chipped and broke, and this one has lasted five years and counting. I can now safely say that this hall pass is a fully-developed piece of technology, but I wasn’t able to say that before.
Now, if, before I had made the very first one, someone had said to me “The edges are likely to chip and wear with ordinary use; you should add internal structure to reinforce the print near the edges”, I probably would have been able to do it, and jump straight to the successful model. But the thing is, nobody did tell me that, in large part because that particular sort of hall pass is not something anyone was doing before I did it.
All theoretical stuff aside, might I point out that the one person really, really, really serious about getting people to Mars has, after years of effort, still not got one of his Mars rockets to orbit and back again intact, when he would need a dozen or so to work to get just one of them to Mars? “We” are trying to get people to Mars at this very instant, and are still a loooong way from getting it right.
Is one being built? Last I heard, we were 20 years away from being able to do that.
I think that getting there is the easy part, getting back is the hard part.
What tech do we lack? Could we build a vehicle capable of blasting off from Mars into orbit, and landing that vehicle on Mars, intact and upright?
Serious question, everyone. Could we do that? I suspect not.
Oh yeah…HUGE project, well on its way:
It should be pointed out that their project’s home page describes it as:
In other words, yes, they’re building a fusion reactor, but it’s still an experimental one; they are not, at this point, building anything that they could hope to be a practical fusion reactor.
True…
But it should also be pointed out that this is not some experiment being done in a college closet. It is a huge, $25+ billion, 20+ year project the size of an actual power plant. Heck, they’ve even expanded whole highways and re-enforced bridges to be able to get the massive equipment to the site. It may even eclipse CERN in terms of size and complexity (not sure about that but that is the realm both are in).
Be clear. iTER is not a useful fusion reactor. It doesn’t contain any mechanism to extract power from any fusion that occurs. Even if it did, and even if it works as well as hoped, it uses many times more power from the grid to operate than it could ever generate in practice. They will claim a break even and later net power gain as they get it going. But that will deliberately neglect the tiny detail of the ridiculous power needed to support the infrastructure and the inherent inefficiency in any recovery of power. Nor is it capable of continuous operation. It is an end to end experiment addressing really only one problem. Nobody really knows how to build a useful fusion reactor. There are still a ridiculous number of unsolved problems.
There are a slew of private companies looking to take investor’s money claiming breakthroughs. There are going to be some very unhappy investors.
Certainly; There are also large-scale fusion experimental projects going on elsewhere, such as the National Ignition Facility at Lawrence Livermore National Laboratory in California (which was profiled on 60 Minutes two years ago).
Breakthroughs have been made at some of these facilities in recent years, but AIUI, those breakthroughs are on the order of succeeding at fusion ignition for extremely brief periods of time (i.e., fractions of a second), and at levels in which the energy output is a very small fraction of the energy that had to be put into the system to achieve it.
Barring a tremendous (and, probably, unlikely) sudden breakthrough, a practical fusion reactor – one that can function on an ongoing basis, rather than for a moment, and has a net positive energy output – appears to still be a long ways off, and is certainly not something that could be used on a manned mission to Mars, either now, or in the foreseeable future.
Edit: @Francis_Vaughan said it better than I did, while I was writing. 
FWIW the National Ignition Facility at Lawrence Livermore National Laboratory in California recently (several months ago) managed to get more energy out than was put in. There was no way to capture that extra energy (they weren’t even trying) but it was/is a milestone in fusion research.
To the OP I think this illustrates that we have the tech and know-how now to go to Mars. If (per the OP) money is no object I see no reason why we could not manage it. The caveat being we can’t do it tomorrow…it’d take some years to pull it off. But with unlimited resources I do not think we need to invent any new tech. Just use the tech we have now and get busy.
In all fairness, when it comes to fusion (among other things) – no, it really doesn’t illustrate that.
Yes, we know how to make a very brief fusion reaction. We do not have the technology today to make a practical, useful fusion reactor. Breakthroughs in recent years are steps along the way, but are absolutely not the end technology. If and when we get to a practical fusion reactor, the technology may well be only distantly related to the technology used today at reactors like NIF.
I didn’t mean to post…my fault.
Just for the record, while technically correct, this is misleading. They did get more energy out (briefly) than the lasers were putting in, but ignored the energy it took to create said laser output. IE just the energy to run the lasers was approximately 100 times the energy generated.
On December 5, 2022, after further technical improvements, NIF reached “ignition”, or scientific breakeven, for the first time, achieving a 154% energy yield compared to the input energy.[12] However, while this was scientifically a success,[13] the experiment in practice produced less than 1% of the energy the facility used to create it:[14] while 3.15 MJ of energy was yielded from 2.05 MJ input,[15] the lasers delivering the 2.05 MJ of energy took about 300 MJ to produce in the facility.[13]
Back to Mars though, the way I examine it internally (and YMMV of course) is that a trip to Mars for a measurable duration (plant the flag, run some experiments, secure samples) and the return is currently in the realm of hard science fiction, where we have as the OP would suggest, all the conceptual technologies are available or at least likely in the near future, given the claimed unlimited budget, but requires multiple story conceits to pull off. The common one for such fiction is hard evidence of life (local or alien) on Mars to justify such a new space race, and even then, it’s a fertile field for speculative disasters. And most of it involves quite a lot of handwaving or breakthroughs to make some of the currently more speculative approaches work (such as super long high strength carbon nanotubes for a “bola-style” gravity generation.