They were crazy enough to conceive of a manned Venus flyby using a modified Saturn V:
This has pretty much been answered up thread, but this is the funniest response to me that concerns the, umm, meat of the problem. I’ve come back a couple of times to re-read it, just because it makes me chuckle.
Because landing there is no easy feat, and even more difficult if you’re squishy meat.
Landing on and taking off from the Moon is really easy. There’s no atmosphere, and a very shallow gravity well. Mars has both an atmosphere, and a significantly deeper gravity well. You could neither land on nor take off from Mars with just a lunar lander.
I think there’s a lot of wishful thinking in this thread. I’ve been doing that myself over the years, having OD’d on SF in my younger years. However, Veritasium just uploaded a really good video about Ingenuity (the Mars drone), which is worth watching for its own sake. But also as a reminder of where we actually are today.
So no. We’re not able to send humans to Mars, for a safe return, anytime soon.
Can’t remember if this point has been raised in this thread: recent research indicates that the kidneys may not survive the trip to Mars, due to radiation damage:
Who else wants pics of @Chronos’s hall pass?
This is the state of hall passery in 2017
(From this thread)
The other thing I haven’t seen mentioned llot is rocket fuel. Everyone discusses the fuel they’ll need. But watch a Starship launch, or any launch. The outside frosts up, because they’re pumping cryogenic fuels into the rocket.
I realize that is space, there is the equivalent of a single-wall vacuum flask, but how likely is it that those cryogenic fuels will last the year or so it will take to get to Mars, let alone the return trip delta-V when the ship returns to earth? Just one of thousands of individual engineering issues needing to be solved.
As for radiation - how much shielding is called for and for how long, and does it have to be 360°? Could they build a shelter shaped like a coffin or freezer, oriented with the back to the sun, using the water borught along for the extended journey. How much water is needed for shielding? would a foot or two thick suffice? AIUI, it is necessary for the occasional solar storms that happen for a day or so at a time.
I saw some discussions on Starship - it seems the new version, last 2 launches, replaced a single fuel pipe through the lower tank with separate pipes to each outside engine. The belief is that these thinner individual feed pipes built up resonance and broke, creating an interesting problem. One analysis points to the last few seconds of camera feed indicating 2 starship rocket engines are “no longer present in the engine bay” Allegedly fixed for the next launch, in a week or two. We shall see.
This is the difference between “we have the technology” and “the technology is proven”.
For long voyages, such as going to Mars on a Hohmann transfer orbit, shielding for cosmic rays becomes more important than shielding for solar flares. And there’s no way they can bring enough mass to shield from cosmic rays, which are much more energetic. There’s been some progress on developing a shield for a Mars mission. Here’s an article from a year ago. It seems the most promising is to use electrostatic shields.
For cosmic rays, the big concern isn’t that you’ll have too little shielding. It’s that you’ll have too much. Cosmic rays consist of a very small number of very energetic particles. Once you get above the ionization threshold, though, it doesn’t much matter how much energy a particle has: A super-beyond-ionizing particle will do the same damage as a just-barely-ionizing one. The increased danger from high-energy particles is spallation: If it hits some other matter, that interaction can result in a shower of other, lower-energy particles. And if you have enough energy to start with, you can end up with a lot of other particles in that shower that are all above ionization energy. So each of those particles in the shower can now do one particle’s worth of damage. The solution to this is to have as little shielding as possible, so you only get exposed to the few original particles, not the many spallations.
But a spacecraft has to have enough shielding to protect against solar energetic particles (only facing the Sun but galactic cosmic radiation comes from all directions), and to protect against micrometeorite impacts (infrequent, especially in interplanetary space but it only takes one impact or inaccessible leak to create a really bad day), as well as the structure required to contain habitat pressure, hold all of the elements of the spacecraft (habitat, propulsion system and propellant tankage, stores, instrumentation, et cetera) and perform any kind of aerobraking maneuvers to slow the vehicle from interplanetary speeds to a stable orbit or reentry profile. So, spallation of cosmic particles is going to be experienced by astronauts regardless of the amount of shielding that is or is not applied. Energetic cosmic radiation is just a ‘fact of life’ of extraterrestrial habitation that can’t be handwaved away, and either has to be accepted as a risk or mitigated in some fashion that is beyond current technology, either by adding meters of material to absorb the majority of spallated particles or by concocting some kind of active ‘shielding’ that is currently still in the realm of science fiction regardless of popsci articles about concepts for it.
Stranger
And travel to Mars might only happen as a crapshoot during the low spot of the 11-year solar cycle.
Cryogenic fuels aren’t the only options. They just work best for the high-energy needs of liftoff without toxic by-products.
Space vessels tend to use nasty chemicals with toxic residue because they can be ignited by contact and don’t require a spark.
Cryogenics like liquid hydrogen and liquid oxygen offer the lowest molecular weight and a good yield of specific chemical energy at the cost of having to keep them at liquefaction temperatures (and for hydrogen, the low density even when in liquid state). For nuclear thermal or nuclear electric propulsion, hydrogen is the clear choice despite the downsides for providing high specific impulse; virtually anything else renders these systems as not much of an improvement over thermal combustion propulsion systems in terms of specific impulse.
Hypergolics like nitrogen tetraoxide and hydrazine are useful not only because they do not require an ignition source but because they are storable at room temperature and are also quite dense, but their performance is lackluster. The were used for early ICBM (Titan II) and space launch systems because they could be loaded and have the vehicle at ready for long durations but the toxicity, corrosiveness, inadvertent combustion hazards, and ultimately the costs were just prohibitive for main combustion systems. The STS ‘Space Shuttle’ Orbital Maneuvering System (the ‘pods’ on the back of the Orbiter Vehicle above the Space Shuttle Main Engines and straddling each side of the vertical stabilizer) using monomethylhydrazine and mixed nitrogen oxides were used for orbital insertion and deorbit, as well as on-orbit trajectory changes but ultimately limited the altitude and adjustments the OV could make. For propellants that can be synthesized in situ, the complex hydrocarbon hypergolics are a non-starter because of the energy and complexity of synthesis; any synfuels produced from space resources will be basic elemental compounds (diatomic hydrogen or oxygen, hydrogen peroxide) or very simply hydrocarbons like methane or ethane.
The absurdity of transshipping massive amounts of propellants from the surface of Earth into orbit and then transferring to an interplanetary shuttle is evident when you start to look at the logistics of it. Even with high reusability of a hypothetical tanker rocket, it just requires so many launches, on-orbit transfer operations (which have not been done at anything like this scale and require complex maneuvers), and all of the labor support required that it is just a nonsensical proposal to send large masses of consumables and hardware, much less crewed vehicles to Mars or even the Moon. The feasibility of large scale ‘outposts’ are predicated on in-situ resource utilization (ISRU) which is still in a very nascent stage of development even for basic elements and compounds much less anything that needs to be synthesized or manufactured.
Stranger
Glad I didn’t go off too far on their abilities. I know of their use on Shuttle, and satellites, but wasn’t sure about overall performance.
Yes. Apollo and the predecessor Gemini (which was really just early prep for Apollo) were barely sustainable on resource use because of the Cold War justification, and I doubt even a renewed Cold War with Russia or even China would really sell it now.
And ISS has done one thing for the US Space Program - it has illuminated the complexity, the time and expense, and the lack of knowledge that needs to be overcome. From underestimating the amount of storage space to the challenges of connecting avionics lines by spacewalk to the ability to maneuver multiple vehicles in close proximity without creating more hazardous debris to then have to track and avoid.
The crew has been an ongoing experiment in trying to figure out how to deal with the effects of space travel, and we don’t have all the answers. Radiation is a big hurdle.
Yes. 3-D printing offers a new tool to apply to a lot of different fabrication challenges, but that can’t solve all the problems for a complex electro-mechanical system, nevermind a whole habitat and environmental enclosure.
Air and water recycling and purification will be a must, but they can’t even close the loop on ISS now.
Here is a visual chart comparing the specific impulse (Iopt in this table). These are sea level specific impulse (14.7 psia of back pressure) but hydrogen gets even better in vacuum because the low molecular weight facilitates a higher expansion rate to recover more of the thermal energy into momentum transfer (assuming you have a large enough nozzle) to get closer to the theoretical value. Braeunig has a pretty comprehensive table (again, unfortunately for sea level because it is focused on launch vehicles) which shows that LH2 and LOX are far and away better from a mass performance standpoint than any other common propellant; the only thing that beats it in that table is liquid fluorine (F 2), which has to be kept below 85 K, is extremely toxic, and highly reactive.
Of course, specific impulse is not the only metric of consideration for a fuel—oxidizer combination; energy mass density, storage temperature, reactivity, potential for instability and coking, ignitability, et cetera are all important considerations, but for moving large payloads around interplanetary space hydrogen has clear advantages, and provided you can shade tanks from directing impingement of sunlight it isn’t difficult to keep them at cryogenic temperatures even for extended durations, but shipping that volume of liquid hydrogen from Earth’s surface to orbit with all of the inert mass of tankage and insulation becomes its own problem. SpaceX and others have defaulted to using methane, which provides decent performance and can be used in an expander cycle with less stringent cryogenic limits and greater density as a liquid but it would still be onerous to ship dozens of tankers in order to fill up a single large interplanetary chemical rocket for a transit to Mars, and essentially impossible to go any further using chemical propulsion without the mission duration being prohibitive.
Stranger
Still, it’s one thing to talk about “long term” as in a few weeks or a month to the moon and back, or storage in taks in the shadows on the moon; it’s another order of magnitude to consider Mars returns with times of 2 years or more. I assume this is one of the topics that will need to be studied once they start building a tank farm in orbit. (And how do you chill your stored fuel if you need to? Is dispensing of the pumped-out heat by radiant fins feasible?)
I would presume that generating fuel (oxygen and methane) given a solar farm and robotic control would simply be a matter of landing sufficient equipment on Mars, in ships sent long before the first human attempt. But the storage tanks would be the key problem - how much volume does a refuel need? That’s before we get to the refueling problem, landing close enough to the facility that the amount of piping sent there is sufficient to reach the ship.
Every concept invites more problems to solve. We sneed several orders of magnitude greater resources before it’s safe to even consider a human mission.
“Attention, Space Force Special Envoy to Mars! Mr. Musk, good news, you’ve gotten your wish!”
Well, Mars Sample Return is formally removed from the NASA budget:
Stranger
No, when the U.S. sends astronauts to Mars, they will bring samples back on the return trip.