Are we already capable of going to Mars this very instant but just unwilling?

Factual Questions
161

This is a very very skewed version of more power out than in. The fusion reactions created more energy than was contained in the laser pulse that reached and collapsed the pellet. Nowhere does it take into account the energy needed to create the laser pulse. You will hear these claims all over the place. But they are still at least one order of magnitude short of real break even. The lasers are inefficient, and losses in the optical path rob the system of significant energy as well. These are not trivial problems to fix. They are already using systems at the leading edge of technology. They need fundamental breakthroughs, not just more engineering.

ETA, ninjed above. Two orders of magnitude short.

And nobody has even started serious work on developing a viable energy recovery systems for any reactor. There are paper designs of in-principle ideas. Getting useful energy out of a fusion reactor is a huge step up from a fission reactor. There are a slew of desperately difficult problems to solve. Fission reactors have the luxury of thermalising neutrons in a cooling medium directly integrated into the core. Fusion reactors can’t do this. The full neutron flux passes outside before it can be used. This means that the entire reactor has to be engineered to work in the face of this flux. It really isn’t clear how you make a viable reactor that can survive this for an economic time. And claims of a-neutronic fusion reactions as a solution neglect another slew of problems, not the least of which is that they require nearly an order of magnitude more energy to initiate, and they are only a-neutronic on one of the reaction pathways present, so still deliver a significant neutron flux.

162

So the NIF thing was just a bullshit milestone? They are just messing with us and didn’t really achieve anything?

163

Mostly it was about pubic perceptions. But the NIF’s job isn’t actually to prototype nuclear fusion for energy generation. The real job (from their web page):

NIF is a key element of the National Nuclear Security Administration’s science-based Stockpile Stewardship Program to maintain the reliability, security, and safety of the U.S. nuclear deterrent without full-scale testing.

Experiments to understand fusion are important.

164

There’s a big difference between “We are currently working very hard to develop the technology” and “We currently have the technology”.

There’s even a difference between “We think we have everything we need for the technology” and “we actually do have everything we need for the technology”.

Until you actually do the thing, you can never be sure that you’ve caught all of the “unknown unknowns”. Sometimes, someone gets an idea to build something new, builds it, and it works right on the first try. Maybe, in such a case, you could argue that the technology existed as soon as the person got the idea. But usually, when something new is built, it doesn’t work right on the first try, for some reason that the designer didn’t even anticipate beforehand.

165

When President Kennedy announced his project, he mentioned a detail which added greatly to the difficulty:

166

The state of technology of controlled nuclear fusion for power production has been thoroughly (and correctly) addressed so I won’t rehash that but it does serve as a useful example for the difference between having an idea that could work, having a ‘proof of concept’ level of development, and having an adequately mature technology sufficient that it can be used in a ‘production’ setting where lives or mission-critical objectives are at stake. NASA (and the US Department of Defense for space applications) uses a scale of evaluation of development called the Technology Readiness Level (TRL) which looks like this:

The purpose of this is to provide an assessment of the maturity of a technology for use in applications and its suitability for use compared to the risk posture (the acceptable threshold of risk based upon a matrix of likelihood and severity of a failure). The TRL of controlled nuclear fusion for power production is somewhere between a 3 (“Analytical and experimental critical function and/or characteristic-proof-of-concept”) and a 4 (“Component and/or breadboard validation in laboratory environment”). The purpose of ITER (as opposed to the National Ignition Facility, which as already noted is really intended to simulate fusion conditions seen in a nuclear weapon and is only incidentally a scientific testbed unsuited for power generation) is actually to validate materials compatibly and durability, methods for controlling hot and (hopefully) burning plasma at this dimensional scale and power levels, extraction of power to be transformed into electricity, and general experience in the problems that can come up during construction of a device of this size. It is not intended to be an actual power generation system itself, and although it is hoped to produce a power factor of Q>10, it still probably isn’t sufficient for a truly sustainable fusion system. The conceptual successor, DEMO, is still in its infancy in terms of development (basically at a TRL of 2) and will probably be on the order of a magnitude larger with corresponding input power requirements. (It is also, frankly, a counterexample to this approach of nuclear fusion for power generation, as the costs, complexity, and problems have just grown and the schedule has slipped out over a decade and counting; even if ITER is successful in its goals and leads into DEMO, it is unlikely to even sustain a burning plasma until well passed the latter half of the century (current estimates are ~2060), and at this scale may never be cost effective or practicable given the capital and tritium fuel requirements unless a way is found to breed more tritium than is consumed.

Getting back to a Mars mission, most of the critical technologies required to send a viable crewed mission to the surface of Mars and return them safely to Earth (solar electric or nuclear thermal propulsion, entry/descent/landing of a multi-ton landing and return vehicle, deep space and surface habitation, mitigation of physiological issues of interplanetary transit and extended stay in fractional gravity, in-situ resource utilization and/or sufficient recycling and food production to make the consumables budget manageable) are at a TRL of between 3 and 5. Even the experience on the ISS does not really provide “demonstration in a relevant environment” as it is protected against energetic solar charged particles by the Earth’s magnetosphere, and providing enough shielding to protect a human crew would be prohibitive, much less protection against high energy cosmic radiation both in transit and on the surface of Mars. A crewed mission would have to have at least a TRL of 7 (and preferably 8) in all essential elements before we could practically consider such an inherently risky and long duration human mission to Mars.

It should be noted that without advanced constant thrust or high impulse propulsion there are two essential mission profiles: the opposition class (“Short-Stay”) mission with a stay of generally 30-40 days, and the conjuction-class (“Long-Stay”) mission with a stay time of ~550 days. (The linked presentation has somewhat different values based upon higher Δv values that can avoid the inbound Venus swing-by maneuver and the possibility of 60 day transits which are based upon the use of nuclear thermal propulsion (NTP) but we aren’t anywhere close to actually demonstrating that in practice, and frankly I’ve come to the conclusion after research and modeling that NTP is likely a pipe dream given the required mass and inherent complexity of the system. NEP and NTP are at best a TRL of 3 even assuming that we can leverage practical work done in the ‘Sixties and ‘Seventies that has been abandoned for so long that the base of specific expertise is gone.) With those mission profiles, a human crew is exposed to freefall and fractional gravity as well as radiation in interplanetary space for at minimum the better part of two years, and what we have learned from the ISS and other long duration stays in space does not give confidence to the health and well being of human crew for that duration or the ability to function on Mars without support.

While we could send a crew to Mars orbit to operate rovers and probes without the time delay we have from Earth with a substantial reduction in cost, complexity, and risk (albeit still at costs in the nine figure range in US dollars) the benefits of doing so are highly questionable versus using advances in machine intelligence to provide more autonomous operation of remotely-operated missions to Mars. From a cost standpoint, exploring the surface of Mars with probes and rovers makes vastly most sense as we could place dozens (or at a production scale even hundreds) of remotely operated devices across the vast surface of Mars far beyond the reach of a human crew for the same cost as a single crewed mission, and take the risk of landing them in difficult and dangerous locations where we would never risk trying to land people. This is not to say that there isn’t utility in advancing the technology for human habitation in space (although I have doubts that this will ever support anything but small crews of people doing technical work, not for recreation or having some kind of safe haven if the Earth were to somehow become uninhabitable) but from that standpoint it makes far more sense to develop the infrastructure to support human crew safely for long durations first before trying for a desperate “flags and footprints” mission straight to Mars, and to that end autonomous systems will need to be developed and used to do essentially all of the heavy labor and advanced exploration.

Stranger

167

I believe there is a fundamental disconnect over what it means to “have the technology”.

We may not have any fundamental science to overcome in launching a large rocket, but we do not have a working rocket, and the latest attempt has blown up twice. That means there is something missing in the technical details.

The point of contention seems to be what are “engineering challenges”, and how do they apply to “have the technology”.

As an engineer, I would come down on the side of “engineering challenges” meaning we do not have the technology.

Technology is at its heart applied science, which basically means of it isn’t working, it’s not considered ours to use.

To give a concrete space example, consider countermeasures for low gravity. The simplest answer is spin the spacecraft, right? Straight out of 2001. Well, nobody had done that and shown it works.

Science tells us that we just can’t take a Lunar Service Module or Skylab and spin about the long axis. While we can get a high enough rotational rate to get to 1g, the coriolis force affects the human balance system.

In order to get the coriolis low enough, you need a diameter of 450 meters. The ISS main truss is 109 m long.

No one has built any thing to that scale in space. Saying that we have built a 100 m structure, so a 450m structure is just an extension of a what we know fails to grasp the challenges of building that 109 m truss, and that the difficulties compound with length.

We need a fundamentally different assembly method than the ISS used.

Just use steel cables, you say. We have very little experience using cables in space, and the main experiment we tried failed twice. The first time didn’t deploy, the second burned through and broke.

This is not mature technology. This is not somewhat developed technology. This is “We’ve never done this before”.

We do not currently have even the component elements of assembling this scale of a vehicle, nor making it work. This is not existing technology.

168

Again, though, that’s a limitation of COST. The conditional I mentioned was unlimited budget and willingness. Even getting a heavy lift rocket that doesn’t blow up is just a matter of cost and, I admit I’ll throw this one in now, getting profiteering scam artist billionaires out of the program.

I mean, we are talking about a project of staggering cost - something that would beggar the world’s economy as it stands. A 40-foot cylinder isn’t big enough for practical artificial gravity? Make it 160 feet. It’d cost you a hillion-bagrillion dollars, that’s all.

The health of the astronauts is, of course, just a cost.

169

Not really. The assumption you (and others) are making is that spending can overcome any obstacle. That’s only true when you know what to spend it on and how to apply spending in a way that moves that part of the whole solution forward.

All the world’s GDP cannot build a warp drive. We don’t know how. All the world’s GDP in e.g. 1880 cannot build a USB stick because they did not know how. We make 'em now for a nickel a GB.

The difference is not willingness to spend. It’s knowing how.

Amplifying that problem, stuff does not scale simply. A bar of steel 2 feet long x 1" cross section is stiff by human standards. Support it only at both ends and you can drive a car over it without deformation. Make that same unsupported bar 20 feet long and a car driving over it will kink it. Make it 5 miles long and it can be readily tied in a knot.

170

It’s not just a cost; an astronaut who is injured or becomes ill during the mission becomes a substantial burden on the ability of the rest of the crew to perform critical mission activities, and if the entire crew is incapacitated the mission may just be a complete loss. Although people often find The Martian (novel and film) an inspiring tale of improvisation and devotion, they also basically threw away an entire mission and put the other five crew members at risk (their choice but still potentially creating more victims) in a desperately risky attempt to rescue Matt Damon. The lesson that should be taken away from that is that it is far better to develop an infrastructure which can support crewed space travel and has options for recovery that doesn’t have so many unrecoverable failure points rather than to place the success of a mission and safety of the crew in one very linear mission.

Stranger

171

You are ignoring TIME. You cannot speed up development by an arbitrary amount by throwing more money at it. Like the old chestnut says, nine women cannot produce a baby in one month.

You are also ignoring the interplanetary radiation issue which Stranger has brought up many times (and I may have mentioned). We do not have a solution for that. It may be that interplanetary manned spaceflight is impossible due to radiation, let alone interstellar manned spaceflight at a significant fraction of c where the sparse interstellar hydrogen becomes high-energy protons pounding on the ship for years.

172

At the most desperate-to-satisfy-the-hypothetical extreme, humanity can probably put something together that replicates Opportunity or Spirit to softland a coffin containing one human corpse on the surface of Mars. Which, even by the standards of much modern planetary exploration, is as pointless and counterproductive gesture as it gets.

173

I never said by when it would be done. Time is also a resource.

174

That is a gross misrepresentation of the design process and engineering realities. To some extent, funding is important, and more funding means more people working in each part of the problem, and maybe parallel development tracks. Funding can accelerate production.

But funding doesn’t overcome every engineering challenge. It takes creative effort. It takes gaining knowledge.

Think about cancer research. How much funding has gone into curing and pendent preventing breast cancer? And how many women still die every year from it? Fewer than used to, but still a lot.

@LSLGuy has a great example. Things don’t scale up linearly. For example,

160 feet is too small. 450 meters. You couldn’t launch something that big with chemical rockets. Cost is irrelevant. We don’t have the controlled energy to do it.

Money may help you solve problems faster, but money doesn’t solve the problems. Knowledge we don’t have is “can’t do our with existing tech”.

Could we figure all this out with enough funding to do enough testing and research? I think so. But we can’t now without learning more things.

175

Let’s start with the basics. If D.D. Harriman wanted to go to Mars Referencing Requiem, could we do it?

176

By the time of that story, Harriman’s company was already mass-producing nuclear-fueled rockets. Harriman could do it. That doesn’t mean that Musk can.

177

Harriman barely survived the three day trip to the Moon. Eight to nine months of a pseudo-Hohmann transfer from Earth to Mars in a confined space and freefall would be stressing for a young and healthy person, much less and elderly man in poor health.

Something that is also not appreciated by most people is just how unhygienic freefall conditions are. When you are on Earth, dirt, discarded hair and skin cells, mucus excretions, urine and feces, et cetera, all fall down and generally rest upon horizontal surfaces that can be readily cleaned. In freefall, everything must floats around until it is sucked through a filter or sticks on any random surface. If you don’t have a hardy immune system (and one effect of freefall conditions is to suppress immune response) and are prone to infection then it is the worst possible environment, as it would be for anyone with a heart condition due to fluid retention, notwithstanding how much more damaging ionizing radiation is to older people whose cellular metabolism is already in decline.

Stranger

178

Build it in sections, rocket each section into space, and assemble in orbit. It would be like the largest IKEA kit in history. Expensive, but do-able.

179

Do you even need a 160-foot cylinder at all? How about a capsule spinning round and round on the end of a 160-foot cable? Or 450 metres, if needed?

180

You aren’t paying attention. I’ve mentioned doing it in sections. That comment was in response to the idea we could just launch a bigger cylinder, easy peasy, it just takes money.

As for doing it in sections, again I point out it hasn’t been done yet. The ISS was built in piecemeal assembly like that, but used the Shuttle as the primary launch vehicle and assembly platform. The first components (Russian) were assembled in Nov 1998. It took until Feb 2011 to complete assembly. It took over 159 EVAs for over 1000 hours of work. And ISS is only 109 meters.

We need a fundamentally different approach. Flying larger modules on a heavy lift rocket would still require extensive on- orbit assembly time with numerous EVAs to connect avionics. Central power and environmental control can’t be created by just fixing modules.

There’s never been anything of this scale in space. We need to make new techniques. We need to create experience handling new equipment like cables and trusses. ISS experience is a starting point, but like crawling when we need to be able to run. A lot of what it taught us was the scope of that kind of project, and how our choices hindered the outcome.

Again I state nothing like that has ever been done in space. The one experiment in handling cables was an electrically conductive cable that dangled 12 miles off the Space Shuttle. Except it burned through from electrical current generated by traveling through low Earth orbit before it reached 12 miles.

We have miniscule experience handling cables in space. Building a spinning assembly connecting two distant modules with cables is even further from our knowledge than slamming modules together.

Think of it like learning how to build the Golden Gate Bridge when you’ve never built a suspension bridge before, attempted a suspension bridge before, done even know how to make cables large enough to hold the weight, nevermind how to string them across the Bay. Now do it in space.