Excluding the fact that we can certainly make faster probes, the study of habitable exoplanets is not and never has been contingent on the ability of people to visit them. We can still gather data and that data is still useful.

> . . . I've read that the spinning spaceship (Circular disc) will not be useful, because; issues

There's nothing that makes spin-gravity a show stopper unless the habitat in question is very tiny and rotating fairly quickly, but it's also not a strict requirement for a mission to Mars and that's why it's seldom considered in detailed plans for manned missions to Mars in the near future.

Assuming the slowest normal trajectory (assuming you're not using a very low thrust but still man-rated electric rocket), going to Mars or returning from it takes about eight and a half months. There have already been human beings that have spent more time than that in space within individual missions, and they also fully recovered from any negative effects.

There, however, remains a question mark in regards to how deleterious Mars gravity may or may not be towards the human body. It's quite possible that some gravity, however low, may be enough to stave off the effects typically seen with extended periods of living in zero gravity. Very little observational data on the subject exists, however.

While there have been recent breakthroughs in improving the thrust of ion drives, they and all other electric rockets still invariably have inferior thrust when compared to chemical rockets.

That doesn't mean they aren't competitive, however, or that there are not drives with decent thrust.

Magnetoplasmadynamic drives, for instance, could boast better thrust and specific impulse than existing electric rockets, and some electro-thermal rocket motors coule have impressive thrust at the cost of specific impulse.

However, higher performance electric rockets in turn require more electricity and operating temperatures. While this may require the use of nuclear power plants per given mission requirements (increasing cost and vehicular mass), their higher specific impulse relative to chemical rockets means they could employ higher energy trajectories and ultimately get to their destinations faster for less propellant.

Some kinds of nuclear rockets can also rival chemical rockets in terms of thrust, but they also tend to be very heavy (courtesy of the reactor and shielding) and expensive. Nuclear thermal rockets have been tested on Earth, though, and NASA has recently shown renewed interest in their use.

While it was in a still pressurized section, the long-since destroyed space station Mir also had a fire nearly twenty six years ago to the day!

I will note, though, that the penultimate battle of the sequel movie Serenity incorporated sound effects, but it was visually handwaved because it took place in a space cloud.

Zathras is simple man.

Zathras see Babylon 5, Zathras upvotes.

>"the situation kind of reminds me the issues we have trying to achieve fusion energy, in both cases we know the that phisics work, we know is a desirable outcome but we need to workout the engineering problems"

Sometimes, engineering problems can themselves be insurmountable or simply not worth implementing. It's not a great feeling, but it's happened in the past and will happened again.

Nonetheless, the low payload capacities of SSTOs are a big risk because there may simply not be a worthwhile market for such small sizes. So many people focus on kilos to Low Earth Orbit while failing to take into account any other factor. It matters very little if you can get 1 kilogram to orbit for mere pennies at a time if no one wants to launch something that small, and a lot of payloads require additional space or higher orbits that any near-future SSTO would be hard pressed to accommodate.

Single stage to orbit is highly unlikely to happen (or at least become common) in the foreseeable future. Even very optimistic concepts have very small payloads for the masses in question, and any weight gained during development could compromise that capacity. Moreover, there's a case to be made against SSTOs given other potential designs.

Reaction Engines Limited 2014 concept detailing the Skylon D1, for instance, has a 325,000 kilogram fully fueled SSTO delivering a 53,500 kilo vehicle (empty) into the lowest possible equatorial orbit with 15,000 kilos of worth of payload. That 53 1/2 ton vehicle is a larger penalty against the payload mass than the STS' Orbiters were, and the payload capacity itself is inferior to modern, partially reusable Falcon 9s. Yes, they're not totally reusable, but one wonders if the savings of reusing that expended mass would be worth the added developmental costs.

If the SABRE engines are not as good as thought or if new features and their extra mass must be added (as had happened in the aftermath of the Falcon 9's initial landing failures), the resulting payload mass reductions would be larger than they would be for multi-stage craft. Hypersonic engine research is also very difficult and very expensive, and that high R&D means there would have to be a significant frequency of flights and low turn around time for the vehicle to be competitive. Additionally, Skylon D1s delivering payloads to higher orbits would invariably rely on independent upper stages that would likely be disposable.

However, as far as plasma jet engines go, the largest bottleneck for them is energy storage. Amusingly, Gerard K. O'Neill's 2081: A Hopeful View of the Human Future had launch vehicles conveniently get around this issue by using Solar Power Satellites as their energy source during airbreathing mode in lieu of storing it all onboard. Not bad for a book published in 1981! While we are currently in want of SPSes, the idea has finally gotten real traction in the last decade with the entities within United States, China and Europe having committed to launching SPS testbeds into orbit in the next few years.

Ehhhhh . . . That's kind of misleading. While the risks of nuclear fuel dispersal is generally overblown (coal plants are hard to beat in this regard), there is not a zero risk of dispersal and there have been historic releases of fissile material.

In the 1970s, the Soviet Union's US-A radar imaging satellites (often known as RORSAT) depended on nuclear reactors to power them in lieu of RTGs and Solar panels. An unnamed launch failed to reach orbit in 1973 and resulted in the reactor entering the Pacific Ocean. Kosmos 954 and Kosmos 1402 had their cores reenter the atmosphere in 1978 and 1983 respectively, with the latter dispersing its debris over Canada. More recently, the Russia Federation's Mars 96 launch failure resulted in the reentry of its onboard plutonium-238.

The United States also had plutonium-238 enter the Earth's atmosphere during Apollo 13. As this material was originally intended to remain on the Moon to power surface instruments, it remained onboard since a landing attempt was aborted.

Only a small handful of launch providers can claim a 100% success rate, and nuclear reactors for man rated thermal rockets or electric rockets must inevitably much larger than any of those involved in the beforementioned incidents.

I also caution against people arguing that nuclear fission is the only way forward for space travel. There have been very encouraging developments in Solar electric propulsion in recent years, and nuclear power for spacecraft comes with engineering headaches that tend to be ignored more often than not. Nuclear reactors must have heavy shielding to protect the crew, and this shielding increases their already large minimum engine mass. Reactors generating electricity must also have significant mass dedicated to generating said electricity and then shedding the large amounts of waste heat produced as a result.

Moreover, nuclear reactors can only be reused so many times before they accumulate too many poisons and can no longer produce useful levels of energy. Once a reactor has also been used, they will also continue to generate radiation. This can make docking in particular very problematic, as economical shielding can only cover a certain 'cone' in front of the reactor and thus forcing other vehicles to enter via that safe zone once they've come within a certain distance of the nuclear-armed target.

I think people tend to underestimate just how many Shuttle launches there were in the past in spite of its great size and cost!

There are two important things to keep in mind, however.

Firstly, several Soviet missions failed merely because autodocking of Soyuz spacecraft failed. Even when it did work, there were many issues that persisted for years.

Secondly, many Salyut 6 and 7 launches existed for no other sake then to give the incumbent station crews a new spacecraft.

At the time and even now, Soyuz spacecraft only have a limited recommended amount of time they can safely remain fueled and active before they 'retire' and must return. To overcome this, the Soviets launched fresh spacecraft with, "guest" cosmonauts who would swap seat liners and return to Earth with the old spacecraft. The Soviets in turn tended to fill these fresh Soyuz with foreign provided cosmonauts under the Interkosmos program. Rather cynically, they were not expected to do much and given little-to-no training on operating the actual spacecraft; such tasks were left solely to the Soviet cosmonauts who accompanied them.

On a related note, the Soyuz 12 and 13 "free flights" occurred in the wake of Salyut 2's failure, as the Soviets had already prepared the spacecraft for flight and would not have Salyut 3 up in orbit before they reached their sell-by-date.

While Solar Power Satellites for Earth are normally depicted as being used from a geostationary orbit, you can conceivably use them in other orbits provided you have at least two or three or so to provide continual coverage. Molniya orbits, for example, are a popular suggestion for Earth SPS to provide energy directly to higher latitudes.

It worked for the Telvanni up until Red Mountain erupted and the Argonians decided to reduce them from a Great Tree House into a charred stump.

Separating aluminum from oxygen on the Moon in the first place is a little tricky

Unlike Earth, where most aluminum is recovered from bauxite using the Bayer process (producing alumina, or aluminum oxide) and then the Hall–Héroult process, aluminum on the Moon is overwhelmingly anorthite that cannot be processed in the same way.

Instead, more energy intensive methods must be used. Perhaps the most favored alternative is using the FFS Cambridge Process (typically used on titanium oxides), as detailed in Ellery et al.'s FFC Cambridge Process and Metallic 3d Printing for Deep In-Situ Resource Utilization - A Match Made on the Moon. Energy production may be an issue, especially if all the refining has to take place on the Moon, where nuclear power would have to employ enormous or very high output radiators to shed their waste heat and where Lunar nights can reduce Solar power input.

It's that one mod from #KSPOfficial!!!

Pandora is probably tidally locked, but the kind of tidal forces responsible for prolonged geological activity for moons like Io also require special resonance orbits with other satellites. Europa and Ganymede have a 2:1 and 4:1 orbital resonance with Io respectively, and these resonances maintain Io's orbital eccentricity. Without this elegant dance of moons, the same tidal forces that physically distort Io would also circularize its orbit.

Interestingly, though, Pandora is also reliably depicted as being fairly close to Polyphemus (a planet that is itself slightly less massive than Jupiter). While there doesn't appear to be a canon figure available on the internet in regards to its orbital period (and, thus, lengths of its days), there is no doubt in my mind that James Cameron has figures to this end for use by the production team.

Pandora is not actually so small that its core would necessarily be solid. Jupiter's largest moon, Ganymede, is known to have its own magnetic field brought about by a partially molten core, and it's only 2.5% the mass of Earth! By contrast, Pandora is said to be 72% the mass of Earth, which makes it significantly more massive than Mars and slightly less massive than Venus. What really determines whether or not a celestial body's core stays molten on its own probably boils down to a favorable amount of transuranic elements in addition to size. After all, half of Earth's own interior energy can be attributed to the decay of radioisotopes and the occasional natural fission reactor. The presence of tectonic activity might also be important, which could explain some differences between Earth and Venus in regards to their interior activity.

It can also take a very long time for stellar winds to strip away another celestial body's atmosphere, and there are means to replenish any losses like volcanic outgassing.

Given the recent issues with Roscosmos, it could've just as easily been poor quality control as a meteor.

All they need is for Paul Reubens to voice the thing and we're all set!

My point was that you're using data that's taken out of context and ignores the many improvements which make the old failures; often which were the result of quality control and immature spaceflight technologies. Including the failures of the Soviets' programs would be like using boiler explosions from steam engines to say diesel engines are unsafe.

Heck, even your revision is not terribly accurate. Aside from NASA, the ESA, China, India and even the United Arab Emirates have all had successful missions to Mars. China's even got a functioning lander and rover.

Again: Many of the failures are attributable to a single nation which doesn't even exist anymore, and this really messes with our understanding of spaceflight as a whole by ignoring improvements in reliability.

As it stands, however, deep space exploration really is dominated by NASA. The agency is and will likely remain the front runner in terms of technology and mission volume for many years.

The, "50%" figure is very misleading. General spacecraft reliability has increased tremendously since the 50's, and many of the failed landers are attributable to the Soviet Union's old and very troubled exploration program (something which extended into the Russian Federation's attempts). Indeed, NASA hasn't had a Mars mission failure since the loss of Mars Polar Lander in 1999.

Technically, a ~1,000 day mission to Mars (including ~500 days spent on the planet's surface) would entail about 1 Sievert of radiation. That's only a death sentence if you're getting it within a very short period of time, but it's quite survivable when spread out over the given timeframe. While there would be an increased tumor risk over the remaining lifetime of a Martian astronaut, it would be far from a guarantee.

However, that given radiation figure does not include the use of shielded habitats or spacecraft. If need be, local dirt could provide very effective protection, but radiation exposure on the surface of Mars is less of a problem relative to that encountered in deep space. For that, there are promising, lightweight albeit bulky materials that could provide a significant risk in radiation absorption. Some people have also suggested the use of reusable shields or shielded Aldrin cyclers in perpetual transfer orbits: The idea being that interplanetary vehicles would 'dock' with these structures after burning towards Mars.

Venus' modern retrograde rotation is most likely the product of atmospheric braking combined with a slow initial rate of rotation.

However, slow rotation and even outright tidal locking does not necessarily rule out long-term habitability. Oceans and atmospheres can transfer absorbed energy, for instance. In "Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate", Yang et al. argued that a slower rotation rate is beneficial the closer a planet is relative to its host star.

ISRU typically means producing stuff for immediate use, rather then large scale extraction and export.