shynung

The London-New York route is just above open ocean, on which supersonic flight is permitted. In that case, a Concorde could take advantage of its speed to zip through quickly without the need for LOX or LH2. The routes that are viable for suborbital airliners would be London to Tokyo, or London to Sydney, where most of the route goes over land. Here, supersonic transport is not permitted due to noise from sonic booms. The A2 plan to get around it by travelling northwards, over the North Pole, through the Pacific, then arriving at Sydney from the North. A suborbital airliner could, in theory, simply fly over them at the upper atmosphere, where the air is too thin to transmit the sound to the ground, therefore taking a much shorter direct route. Also, air-augmented rockets are flexible on the fuel. Jet-A/LOX could be used, eliminating the LH2 infrastructure necessity. Jet-A/N2O4 is also possible, if cryogenic tanks are to be avoided.

I recently read about Reaction Engines A2, a hypersonic (Mach 5+) airliner using the Scimitar engine, which is essentially a precooled turbofan engine. Then, I came up with a slightly different idea. Rather than going hypersonic, why not go suborbital? Such a plane, I think, would look similar to A2 or Skylon, but would need hybrid engines, such as SABRE or air-augmented rockets. It would take off from a typical runway, then quickly accelerate upwards, setting itself on a semi-ballistic trajectory aimed near the destination airport. After that, it would turn off its engines completely, gliding at the thin part of the atmosphere, then fire its engines once more at final approach. Electricity demands in the gliding phase could be met from either fuel cells (if using LH2/LOX), or deployable solar panels (if apoapsis is high enough). If using air-augmented rockets, it could either take off on fuel-oxidizer mix, or use some sort of bypassable turbocompressor mechanism. Then, it would transition to ramjet mode at about Mach 3, then to rocket mode when the air becomes too thin for jet engine operations. Possible advantages include the capability to fly hypersonic over land, something which is forbidden under current laws. However, the need to carry oxidizer, along with the plane needing a heatshield for reentry, and a possibly complicated electrical system could offset it. Although, if the goal is going over very long distances for the shortest time possible, this design could do much better than Concorde or A2, at the cost of complexity. What do you guys think?

I concur. Binary systems are far too complicated for use even on simple everyday mathwork, let alone complex calculations. The majority of computer programmers and scientists never use this systems for their entire life ever since the programming language were invented.

On hard drives, I would recommend HDD over SSD, as I believe an SSD has limited write cycles, and cease to function properly when it is reached (though various software countermeasures against it has been devised). As for RAM, for primarily KSP usage, 4GB should be enough. It is also good enough to run most recent games up to the 2012 era. If you're willing to drop Windows, KSP has a version for 64bit Linux OS, which effectively skips the 4GB limit. EDIT: I've been convinced by the posts below about the SSD's working life, which I may have grossly underestimated. I would still avoid it for now, though, as prices per GB are still high.

Throttling is definitely possible on hybrid rocket designs. The key here is that the fuel cannot burn itself without presence on the oxidizer, therefore throttling the oxidizer flow would throttle the rate of fuel/oxidizer reaction, hence throttling the thrust. Problem is, these designs necessitate an additional tank for the oxidizer(which, if we're talking about liquid oxygen, would be HEAVY due to the insulation), ultimately lowering their thrust-to-weight ratio with little increase in ISP. As such, it would be useful only in very specific situations.

This particular trait has happened already; elephants' ears double as radiators. In my opinion, intelligence is probably nothing more than a nice-to-have to an evolving organism. Other than the aforementioned dinosaurs, lifeforms such as bacteria managed to thrive without it for millions of years, all the way to the present day. Other possibilities include the appearance of something I would call a superorganism; that is, an organism that is comprised of smaller organisms that act as a single individual. While multicellular organisms may already fit into this category, I'm more inclined to use it on animals such as ants or bees, that individually is not very powerful, but have considerable impact on its environment when formed into a hive. Regarding the effects of human presence on the environment, I think there might be organisms that evolved to take advantage of it to thrive. What was ancient wolves and ocelots (small feline predators, basically miniature tigers) followed early humans around to eat their food scraps. When the humans took notice, they brought them around as pets, to help them hunt, guard their belongings, and so on. Eventually, these ancient predators evolved into dogs and cats as we know today. Also, due to global warming from greenhouse effects, I'm guessing that darker-coloured organisms (including humans) would fare better in the future, pigments being the natural shield against (weak) solar radiation.

Thanks a lot for the explanation, I really appreciate it.

So, you're trying to tell me that, in order to get effective ISP, I must assume all power-generating parts as propellant mass? The reverse of payload mass fraction? I think I'll make an example, just to be clear. I'll assume an ion-drive satellite in polar orbit around Kerbin, carrying a gravity meter and an antenna. The orbital plane is perpendicular to the Sun's direction, so it has sunlight coverage all around. It has a radial xenon tank, a Gigantor XL panel, and a PB-ION thruster (the bare minimum for it to work). Stats straight out of the Wiki: A QBE probe(80 kg) + GRAVMAX sensor(5 kg) + Comm16 antenna(5 kg) totals for 90 kg of payload mass. A Gigantor XL panel(350 kg) + PB-X-50R tank(70 kg full, 30 kg dry) + PB-ION thruster(250 kg) totals 630 kg of engine+generator mass, and 40 kg of propellant mass. Using standard Tsiolkovsky equation, I get 4200*9.81*ln(760/720) = 2227.67 m/s2 of ÃŽâ€V. However, to get this ÃŽâ€V, I still have to lug around 630 kg of parts, which I assume is completely useless once all propellant has been used (immovable sats are dead sats). Using the above ÃŽâ€V and the modified equation, the effective ISP of the entire propulsion system is 2227.67/(9.81*ln(760/90)) = 106.44 seconds, if I'm correct. As a comparison, the same probe is now powered by a chemical rocket (LV-909), carrying fuel in an FL-T100 tank. It also carries the lightest solar panel (OX-STAT), just to keep it alive. The LV-909(500 kg) + FL-T100(562.5 kg full, 62.5 kg dry) totals 562.5 kg of engine mass, and 500 kg of propellant mass. The OX-STAT add only a measly 5 kg to the payload mass. Again, using the standard equation: ÃŽâ€V = 390*9.81*ln(1157.5/657.5) = 2163.83 m/s2, losing to the ion drive by 63.84 m/s2. Plugging it to the modified equation yields: 2163.83/(9.81*ln(1157.5/95)) = 88.22 seconds of effective ISP. The difference of effective ISP between the two systems are just 18.22 seconds. That's kinda disappointing...

Whenever I ask about rocket engine efficiency, I often found the answer in the form of specific impulse (ISP), given in seconds, representing impulse per unit of propellant weight. However, there is a problem. Some rockets, namely electrically-powered ones, have high ISP values, but also have considerable power requirements, often necessitating heavy power generators, which could nullify mass loss from needing less propellant mass. In short, I ask this: How to calculate rocket efficiency from energy usage perspective, including energy generated from sources other than the propellant? Thanks in advance.

While that particular company's approach may be expensive (reusable launchers are the trend nowadays), the concept is actually really simple. The only thing a rocket engine needs to be air-augmented would be installing some sort of shroud around the engine that has an intake scoop. That's it.

I've recently come across this interesting concept on a poorly-cited Wikipedia page: https://en.wikipedia.org/wiki/Air-augmented_rocket Basically, it describes a type of rocket that collects additional reaction mass in the form of ambient air whenever in an atmosphere, mixes it with exhaust from the rocket nozzle while not necessarily combusting it, and exhausts this mixture through another nozzle. Possible advantages from this design would be increased ISP and/or thrust compared to a conventional rocket in atmospheric conditions, flexibility to work with virtually any type of fuel (even solid fuels), and the relative simplicity compared to designs such as SABRE. Disadvantages would be no increase in ISP and/or thrust at zero airspeed, slightly lowered TWR due to the air duct's weight (though they could be discarded once out of the atmosphere), and maybe cooling problems. I'd like your opinions on the feasibility, expected gains and losses, and possibility of this design actually flying in the near future. BTW, here's one company's take on it: http://www.sei.aero/eng/papers/uploads/archive/SEI_SCAAT-2013_PublicBrief.pdf No intentions to advertise, but their launch vehicle looks really cool.

@MrZayas1, While quantum mechanics may not make sense in car dynamics, gravity and aerodynamics is certainly important in several cases. This one, a car going uphill, is one case where gravity is not negligible. A car, no matter where it is, experiences gravity on a constant direction (downwards). This is opposed by the Earth's normal force pushing on the car, as the result of its downward force via gravity, by Newton's third law. The normal force, however, is always perpendicular to the surface being applied force, no matter at what angle the force was applied. As a result, when the car is on a sloped surface, this normal force has a horizontal component, facing away from the upper side of the slope. If a car is to stand still on this slope with no brakes, it would have to counter this force with energy from its engine, lest it would roll backwards. As you pointed out, disregarding the aerodynamic components, cars spend more energy per unit of distance when going at higher speed, due to various internal friction losses. Logically, going slower, in such cars, means getting more fuel efficiency. On the uphill scenario, there is a dilemma. Go too fast, and you'll waste fuel via internal losses inherent from high-speed driving. Go too slow, and you'll lose too much energy trying to overcome the normal force's horizontal component as explained, by staying on the hill area for too long. If the car were to stop in the middle of the hill without using the brakes, it would waste fuel keeping itself still, despite not moving at all. As previous posts explained, there is a sweet spot; an optimal, most efficient speed at which to climb a hill, specific to the car model and the gradient/steepness of the hill.

Thanks. Looks like I'm stuck with more SRBs for the moment.

Quick question. Is it possible for a thermal rocket nozzle to take so much power from a reactor, the generator next to it produces absolutely no power? I once launched a rocket using 2 3.75m fission-powered NTR and a D-T Vista engine. According to the megajoule screen, they would theoretically be able to produce around 9GW, yet they cease to generate power about 3km over the pad. Is this normal?

The Wikipedia article referred to this journal:http://path-2.narod.ru/design/base_e/nswr.pdf The design outlines a system with at least 10,000 seconds of ISP with comparable thrust to chemical systems, which is quite impressive. Regarding technical challenges, isn't it enough to simply use a shielded combustion chamber? The system uses liquid-based fuel (mostly water), so I believe even turbopumps would still work.

For the sake of the argument, let's disregard all political factors in this discussion. Let's talk only about technical matters of the subject. Whenever I think about nuclear propulsion systems, two designs often came to my mind: Nuclear Thermal Rocket or Nuclear Pulse Propulsion, both having been studied as project NERVA and Orion, respectively. Later, I thought of a different design. This one would work similar to NTR systems, in which nuclear fuel is reacted to heat a different propellant(say, hydrogen). However, instead of a typical nuclear reactor, it had a simpler combustion chamber with no means to retain the fissile material. Instead, products of the nuclear reaction is ejected, being part of the exhaust, hence open-cycle. What are the possible advantages and disadvantages of such propulsion systems? How would it perform in comparison to NERVA and Orion systems? Also, what technical challenges the propulsion system might impose?

Muscle loss can be reduced by exercise regimens, but unfortunately not bone density loss. To reduce the latter, there must be some way to do weight-bearing exercise that covers the whole body, in order to compress the bones. Strapping the astronauts' hips to the treadmill won't do it, since this leaves upper body bones from having to bear weight. Strapping them by the shoulder leaves the neck bones vulnerable, and so on. Also, human arms normally hung from the upper body sections, which means they have to be given exercise separately (bones need pressure to maintain density, not tension). In the end, some sort of centrifuge would still be necessary, otherwise we're looking at an extensive exercise regime. Then again, considering the amount of time the astronauts have off duty, such exercise regime would still make sense.

As much as I hate to, I have to agree with lajoswinkler's opinion. As a biological creature, humans evolved, at first, to ensure only their own kind's survival, then extending it to other animals and plants when the humans deem them necessary for survival, which is embodied by the discovery of farming. In farming, one would wish to have good produce all around. To do this, they remove the 'unfit' from the population, only breeding ones deemed 'fit'. Almost in the same way, humanity (in this case, the collective society) wishes that all of its individuals would be 'fit', according to the population's definition of 'fitness'. That way, human beings don't mate (or even socialize) randomly, instead centering on the 'fit' portion of the population. The rest, deemed 'unfit', is usually either negatively discriminated, have their rights or belongings taken, or be killed altogether. This 'unfit' population would mean the sick, the insane, and people who have any differences to the majority's definition of 'fitness'. This, I think, is one of the main reasons people don't always accept diversity easily, even within technologically advanced populations. I must, however, stress that the definition of 'fitness' here does not imply some physical capability. This merely means that a 'fit' individual is considered passable to be present in the population. If, at any point, people think that some individuals are unacceptable to be around, say from wearing a set of Google Glass device, it is safe to say that such individuals are considered 'unfit' by that population standards, no matter the reason. Regarding how humanity reacts to self-aware machines, it highly depends on how they present themselves to the humans. If they were to come across as helpful and understanding, in my opinion, people will, given enough time, think of them as 'fit' individuals, despite being inhuman, and coexist without much difficulty. On the other hand, if they were to be viewed as objects that present difficulties to the population's survival (think of robots replacing humans in every aspect), their chances of acceptance would be little, if any.

Antimatter particles are very expensive. Anything using it for fuel would have been limited by funding to carry only small amounts. Fusion rockets and electric propulsion systems ran into similar problems, which is the available quantity of energy immediately usable. Propulsion systems almost always trade one performance for another. Either it would be very efficient (high specific impulse), or very powerful (high thrust-to-weight ratio). If both parameters are high, there's usually another drawback (antimatter rockets using expensive fuels, nuclear pulse propulsion giving the payload rough impulses rather than a gentle push). Also, some propulsion systems cannot (or isn't allowed to) be used on Earth, for various safety reasons. Most likely, standard Hohmann transfers would still be widely used.

I was thinking that the fuel requirements would be cut by half due to the fact that the spacecraft, including the Mars-injection engines, would never come back to Earth. If nuclear propulsion systems are to be used, it's more likely that the nuclear reactor would be carried along to the surface, for use as power plant. Whatever remains of the Mars-injection spacecraft would be left in orbit, or crash-landed somewhere else. That is, of course, if the mission is a one-way trip. Which means, anyone going for Mars would start a colony, and stay there for the rest of their lives, away from the rest of humanity, except for a 30-minute-lagged communications system. BTW, when I said 'the post above', I meant Ralathon's. Sorry for that.

I suppose I did not take the ship's resource extraction capability into account. Yes, that would significantly lower the launch mass of the ship, and its size along with it. The only other problem I could think of is dealing with zero-g effects on the astronauts, but it is solvable by deploying centrifuges, which are possible using today's technology. So, to answer the OP's question, a slighty scaled-up Apollo-style mission to Mars by 2025 using technology available today is certainly feasible, although I doubt NASA or anyone would actually do it that way. EDIT: I agree with the post above about combining landing and colony mission in one shot. This would cut fuel use for the trip at least by half, as there wouldn't be any need for a return trip.

Consider this: The signal from the rover took about 14 minutes to reach the control stations on Earth. Any astronaut going that distance would be reduced, in terms of communications, to sending emails. This communication lag could put mental pressure on the astronauts, especially those used to ISS missions where direct video-and-voice comms are available. Also note that abort modes after going to interplanetary space is going to be scarce. Should the mission be cancelled for any reason, the poor souls onboard have little chance of survival. Going on this sort of mission is bordering on suicide; should any error occur, that would be it. I agree that the ship may not need to be skycraper-sized, but I'd guess it would still be big. The ISS have regular supply launches to support them, which is why it is habitable for quite some time. A Mars-bound ship have no access to this sort of resupply, and have to carry everything from LEO. Add scientific equipments, labs, landers, and all sorts of thing needed for a Mars manned mission, and that would result in a very heavy ship. This would necessitate plenty of fuel, both to get itself there and back, and to fuel any landers they carry. Add the fact that it has to carry everything on its own, and that results in a large ship.

Two years ago, on August 6, a 900kg rover the size of a car, named Curiosity, landed on the surface of Mars. This fact alone proves than we, as a civilization, are able to travel to Mars on current technology. However, to get there, it had to travel over a period of approximately 9 months (it was launched on November 26, the year before). The problem of conducting manned missions over this sort of time distance is not technical, but logistical. How do we feed and take care of astronauts/cosmonauts, inside a (typically) cramped spacecraft, isolated from the rest of humanity by space and time? Even more, how do we ensure they do not kill themselves, or otherwise render themselves inert, before their mission is complete? Regardless of our solutions, what are the ethics of conducting this sort of missions? More advanced propulsion systems may drastically shorten the time taken for such missions, but they have their own problems. As mentioned by countless posts above (and in other threads), nuclear-powered systems are not politically viable solutions. This is a problem, because nuclear fuels are one of the densest forms of energy storage accessible to mankind. Any alternative electric propulsion systems that promises comparable performance have power requirements so high, you might as well bring nuclear-powered generators in the first place. In short, we have the technological means to carry manned missions to Mars by 2025, with the catch that it will be a very long trip. Some people (like me) would respond by building spacecrafts the size of skyscrapers, carrying enough supplies for such a long trip, and back again. Only if political holds are released, are we able to build more powerful and exotic propulsion systems, up to and including the ever-infamous nuclear pulse propulsion. By then, the time distance to Mars would be measured by weeks (or even days), rather than months.

I suppose that explains why the rocket would go boom 1/3 of the time. I noticed that they plan to use the GH2 as cold-gas thrusters when the LH2/LOX runs out. Simply switching the plumbing means the GH2, instead of going through the central injector, would go through the vortex injector, nullifying this effect. That might be the reason they used LOX as coolant. Bypassing this problem would have meant additional injectors for cold-gas thrusters, or a more complicated valving system. Why they skipped this idea and simply use LOX as coolant, I have no idea.

In the engine diagram further in the PDF, it is shown that the LOX, now gas,travels through the combustion chamber in a vortex (hence the name) after the cooling jacket. This vortex protects the chamber walls from the combustion itself, keeping its temperatures low. I think the decision to use LOX as coolant has something to do with the engine's use of hydrogen gas (boiloff of the LH2), but I do not understand the specifics of the matter.