Armchair Rocket Scientist

This all makes sense - I figured the mass of associated equipment would be approximated by the case mass and/or the density used for the part. However, the results I'm getting don't seem consistent with it just using the area density and canopy area. As an experiment, I edited ParachuteMaterials.cfg to reduce the area density of all materials by a factor of 100, then made a RealChute with an extremely small size, and a ridiculously small parachute with a 3 meter diameter. The parachute mass should be negligible - which was confirmed by the part mass hardly changing at all with changing chute diameter, and the case mass is only 3 kg. However, the total part mass is still about 0.303 tons. Do you have any idea where this extra mass could be coming from? Screenshot showing the anomalous part mass.

How is the parachute mass calculated? My chute masses don't seem realistic. I am using RealChute, FAR, and Realism Overhaul, and attempting to make an Orion-like spacecraft. According to various NASA articles, each of the Orion's three main parachutes weighs about 300 lb (136 kg), is 116 ft (35 m) in diameter, and slows the approximately 9 ton capsule down to around 20 mph (9 m/s). However, testing with a 35m diameter nylon RealChute, using the Radial RealChute at the default size, with an approximately 3 ton spacecraft, the part mass was approximately 0.43 tons. Its performance was close to reality, reducing the craft to 7 m/s at sea level. Additional testing using a 3m conical RealChute with a 71m diameter (equivalent area to the three parachutes on the space shuttle SRBs) and a landing mass of 90 t (equivalent to the descent mass of an SRB) resulted in a total chute mass of 0.512 t, of which 0.288 t was the case - this is compared to the SRB main parachutes weighing 3 tons in total. Again, the parachute's performance was realistic, with an impact speed of 20 m/s, but the mass was far different from reality. Is there a way of fixing this to get parachute masses comparable with real spacecraft?

Is there a way to use Realism Overhaul for realistic solar panels, electricity consumption, and so on, but without rescaling parts like command pods to human-size, and using the Stockalike RF engine configs? I'm working on an install with roughly 10x upscaled planets, and I want all the physics and part performance to be as realistic as possible, but keeping the multiples-of-1.25m scale factor, as appropriate for meter-tall Kerbals. I know the answer is probably somewhere in the configs, but I wanted to confirm that deleting the Engine_Configs folder that comes with RO and replacing it with something else won't break everything, and I can't find which config has the changes to parts like command pods and reaction wheels.

[quote name='wumpus']Just how many pound draw do you need to fire an arrow at orbital velocity? You aren't going to hit the Earth from ISS with any bow pulled by mortal man (ignoring slow, slow air resistance).[/QUOTE] No amount of draw. As you make the bow larger, it gets heavier, and the body and string of the bow have significant inertia. Ultimately, for a given bow design the speed will be limited by material strength and density. Maybe with some extremely complex design you could get an arrow to go supersonic, but orbital velocity is comparable to the detonation speed of high explosives. I'm not sure how you'd get any material to elastically rebound at those speeds.

[quote name='Cirocco']I made a thread about this in the space lounge as well and I'll repeat the same arguments here: this landing has almost nothing in common with what SpaceX is trying to do. The falcon 9 is designed to boost a payload + upper stage halfway to orbit. It's far, far, FAR bigger, heavier, more flexible, its engines don't allow it to hover like the New Shepard, etc. SpaceX has to overcome a whole lot more difficult problems. That being said, this [I]was[/I] a historic event: it was the first rocket that passed the Karman (I swear I almost typed Kerman there) line and come back down to land safely. The team behind it definitely deserves all the recognition and credit for that. And I definitely agree that the civil response from musk would have been to say "hey, good job on achieving your goal. Now we're going to go back to work on ours". I have great admiration for what Elon Musk has done and continues to do to drive technology forward to a more sustainable future, but I really dislike how he reacts to these sort of things, or to people investigating technologies or things he considers not worth researching.[/QUOTE] It was the first rocket that passed the Karman line and safely performed a propulsive landing. Sounding rockets (and amateur ones) have made safe parachute landings from beyond the Karman line.

The simplest answer: you can't simply "deal with" this problem because it's part of physics. If a vehicle is aerodynamically stable flying nose-first, then it will be travelling nose-first when the parachute deploys, and subsequently have to "flip" around. There are only two ways to "fix" this. 1. Deploy the parachute from somewhere other than the nose, resulting in an "on-its-side" descent attitude. This is similar to the "rogallo wing" concepts for Gemini, as well as ballistic chutes for airplanes. For a capsule, you're lying on your back in normal flight, so with the capsule on its side you're sitting upright. For an airplane, the vehicle is in close to its level flight attitude. You can also deploy the chute from the tail, but for a manned vehicle you'd be hanging upside down for the descent so this is usually avoided. 2. Make the vehicle aerodynamically stable flying tail-first. This is what all "capsule-style" manned spacecraft do: during a normal reentry and descent, when the parachute deploys the spacecraft has already jettisoned the launch vehicle, service module, etc. and is already falling with the heat shield pointing downward. The only time something like this could come up in manned flight is during a launch abort scenario. In [URL="https://www.youtube.com/watch?v=AMdYAg5mrnU"]this video[/URL] of the DragonRider's pad abort test, when the trunk, which includes fins to keep the vehicle stable nose-first during the LES burn, is jettisoned, the capsule violently flips over, although this is due not to the parachutes but due to it now being stable in a heat-shield-first attitude. The parachute deployment causes additional rocking and swaying. However, while it might be uncomfortable, this is definitely survivable, and would only occur in a launch abort scenario where crew discomfort and minor injuries are acceptable.

[quote name='SomeGuy12']If you wanted to dock to a rotating station along the rim, cuz you're crazy...can it be done? Let's see...if you draw an imaginary line out in space representing a tangent coming off the rim, and then position your spacecraft along that line, I think it would become an intercept problem. Suppose there's a particular docking port that passes a point on the tangent line with every revolution. You want to match velocities with the rim speed, and then arrive at the intersect point between the tangent line, the station, and the docking port at exactly the right instant. Assuming constant station velocity and a known distance, this is a pretty simple intercept problem. So you just jet on over, matching velocity during the initial burn, then at the very instance your docking apparatus (something that can grab really fast, like big honking electromagnets I guess) achieves closest approach to the station, at that exact same instance, the docking port revolves underneath it. A gigantic surge of current and the magnet sticks you to the station. The problem is you go from 0 acceleration (just coasting through space headed for the rendevouz) to 1 G instantly. A huge jerk. It seems like this might also be bad for the structure of your spacecraft and the station. Maybe shock absorbers could smooth it out? On the bright side, the actual rendevouz is easy. You can trivially monitor the relative position of the station wheel as you approach on computer control, via optically checking against markings on the wheel. Radars give your exact velocity of approach. You can easily fine tune your approach as you get closer, and if something happens to where the rendevouz will be missed, you just need a puff of RCS to push you away from the station so the closest approach is more than 10 meters separation. The timing is only difficult if humans have to do it. The hard part is the mechanical coupling and the whiplash.[/QUOTE] Docking with the rim of a rotating station would be incredibly easy. Just make the rim significantly wider than the spokes, or build it without a hub. Then put maglev rails on the inner rim. The docking spacecraft maneuvers up to the rails as slowly and carefully as it wants, then clamps onto the rails and a braking system on the station automatically slows it down, at which point it is switched off the main rails to a docking bay. For undocking, the process occurs in reverse, with the spacecraft being catapulted backwards until its "true" velocity is zero, then unclamp from the rails and fly off with RCS. Heck, you could even build an actual runway on a station and land a spaceplane on it, although taking off would still need a catapult.

Depends on how much payload and how much time. A major constraint on a mission like this is that the power output of RTGs gradually declines: making a probe that gets to Sedna 50 years after launch isn't necessarily that useful. How big is your course correction? Your probe is going to be going FAST when it flies by Quaoar if you want to reach Sedna in a reasonable timeframe. Even a tiny change in direction could end up costing multiple km/s of dV (which is a big deal for a small probe). Now, I have a question of my own: Why Sedna? We've already done a flyby of Pluto, so we have a decent idea of what TransNeptunian objects look like. Yes, Sedna's weird orbit raises a lot of questions, but how many of those could be answered by a flyby lasting just a few hours? And there are many other promising targets for flagship missions, including long-duration exploration of Europa, Titan, Enceladus, Uranus, or Neptune. If you want to make a serious mission proposal, you need to do two things: first, show that it is technically feasible, and second, justify spending money on your mission instead of the other mission proposals competing for the same funding.

Real-world spaceflight news always goes in this subforum.

https://en.wikipedia.org/wiki/1997_Pacific_hurricane_season https://en.wikipedia.org/wiki/1997_Atlantic_hurricane_season

Environmentally a terrible idea, and according to the wikipedia page it would have required "six new nuclear power plants" to pump the water over the Rockies. Desalinization plants would likely be cheaper and more environmentally friendly, especially since much of the infrastructure could be built in desert areas.

I don't think 57 solar masses is enough to exceed the Eddington limit, since there are stars over 100 solar masses.

How do you know it isn't behind us? Say, that the probability of a species developing to the point where it's capable of forming a technological civilization is extremely low, and very few planets have agriculture, much less Dyson Spheres.

There are plenty of altimeters designed for amateur rockets that will read up to 100,000 feet with barometric sensors. Note: Don't use these on a balloon. They have high sampling rates (meaning they probably won't record hours of flight) and use accelerometers to detect a launch: the gentle ascent of a balloon probably wouldn't do much. You should be able to find Arduino-compatible pressure sensors with that resolution. I'd also advise asking this question on DIYDrones or another amateur weather balloon forum: they'll be much more able to help you than this forum.

There are several problems. 1. Your grid must be separated from the floor by at least a few millimeters, be strong enough to support the weight of people and furniture, and be fine enough to not be unpleasant to walk on. Does this even exist? 2. You still have to clean the grid itself. Using GMO organisms for more efficient disposal of trash is a decent idea, but it's better to just use a composting vat. If you want an environmentally way of cleaning off objects, don't bother with a whole slime mold in your house: farm the desired microorganisms for their digestive enzymes and use the enzymes in cleaning fluid to replace less environmentally-friendly chemicals. I'm pretty sure there are already enzyme-based dish and laundry detergents, pet urine smell removers, etc.

To create such an organism? Probably fairly easy to make something that would survive in a humid house - arid climates I'm not sure. However, an organism that eats household debris like pet hair, dead skin cells, and crumbs will also eat a lot of other stuff. The hard part would be making sure the modified organism doesn't become an invasive species. Conservation of mass isn't that big an issue - I'd imagine a slime mold's metabolism would convert most dead organic stuff into gases such as CO2, water vapor, maybe something like ammonia. Another problem is that slime molds are, well, slimy. I don't think most people would want a wet microbial mat growing on their floor - if nothing else you could slip on it and break your neck.

Wait... in North Carolina? I like a good joke about the South, but that's ridiculous. I might expect those attitudes in rural Tanzania or something, but that's crazy for the US.

China might be the only one with an operational launcher of this type, but a bunch of countries have been working on developing them: http://seradata.com/SSI/2013/09/small-and-sweet-nasa-wants-a-dedicated-launch-vehicle-for-cubesats/

Is there ANY jurisdiction where jet or rocket engines are street legal? I think a few people have built pulsejet vehicles, but they're generally either something small like a shopping cart or they only actually run the jets at a track. The noise generated by running a jet engine on a public road might well incapacitate other drivers. But yeah, think about how road-worthy a top fuel dragster is. This vehicle is less useful in every way. I should qualify that: I mean impractical for the application the articles say it's meant for. A rocket-powered vehicle is definitely practical for breaking the land-speed record, which is this vehicle's only intended application. On the other hand, this: http://www.gizmag.com/vv-plane-vtol-cargo-ducted-fans/33296/ is an impractical concept. It has four clusters of EDF units (inherently less efficient than larger propellers), the rendering has ridiculous spindly engine mounts which couldn't withstand the weight of the engines, let alone 30+ tonnes of thrust, and the company makes an implausible claim that it would be cost-competitive with trucks when they don't even have a working small-scale prototype to base things on. There is a difference between "bogged down in development" and "nonexistent product which anyone with a basic grasp of physics, let alone an engineer, can tell you won't work as promised."

Not even in an infinitesimal way. The only reason you don't move when you throw a stone is that normal and frictional forces between your feet and the ground transfer the momentum to the Earth, which is so heavy its mass can usually be treated as infinite for those calculations. If you threw a stone on roller skates, you'd start moving backwards: according to my calculations a 75 kg pitcher throwing a baseball at about 80 MPH (yes, I converted the units) would send himself backwards at about 7 cm/s. That isn't high, but you'd definitely notice it. Throwing a baseball in space would also probably cause you to start spinning because the throw won't be aligned with your center of mass. If we use a device to throw the object backwards even faster, you can get greater accelerations. For example, with a total mass of 75 kg a .22 rimfire cartridge will only send you backwards at 1.3 cm/s. A 30-06 rifle will send you backward at 12 cm/s, a .38 special will give you 4.5 cm/s, and a .50 BMG will send you backward at over 0.5 m/s. You could potentially get a full meter per second of delta-V by using a double-barreled 12 gauge shotgun with appropriate ammunition. Beyond that, the guns get so heavy they'll be a significant portion of your mass, making the calculations more complicated. XKCD did a "what if" comic about using machine guns as jet packs, but that was more concerned with getting enough thrust to lift off the ground. Unfortunately, chemically-powered firearms rarely have muzzle velocities above about 1 km/s, which translates to an Isp of 100 s (assuming we're firing hundreds of bullets, treating them as a continuous flow of mass is a decent approximation). This is barely better than an Estes rocket motor, and can be beaten by homemade "rocket candy" motors. Railguns are expected to have muzzle velocities of 2-3 km/s. At the low end, this is comparable to commercially available high-power rocket motors using solid fuels. At the high end, it's comparable to kerolox rocket engines. Just for fun, let's say our major league pitcher from the first example has a large magazine of balls, and throws until his arm gets tired. Typical pitch counts are about 100 pitches per game, so our pitcher will throw that many balls, with a velocity of about 90 MPH for an ISP of 4 s (ha!). The balls have a total mass of about 15 kg, so with a "dry mass" of 75 kg, the pitcher's total dV is: 7.3 m/s. He could probably run faster than that, and that figure assumes no losses from friction.

You're making it sound like they're trying to develop a rocket-powered luxury vehicle for the super-rich, which is completely inaccurate. This is an attempt to break the land-speed record, and their options are basically limited to jets or rockets. You really shouldn't put such a negative spin on tech articles unless a company is touting some obviously impractical vaporware designed by business majors (like that ridiculous aircraft concept a few months ago with sixteen ducted fans).

Another factor people haven't mentioned: Mars has water. Water, Nitrogen, and CO2 can be used to make a variety of different rocket fuels and oxidizers, including hydrogen, methane, and even hypergolics or monoprops like N2O4 and hydrazine derivatives. Venus has very little atmospheric water: Wikipedia says 20 ppm, which would be a pain in the ass to harvest. There aren't other sources of elemental hydrogen (which is a component in nearly all fuels that don't suck). Without hydrogen-containing fuels, your only option for orbital launch is running an NTR off nitrogen or CO2, which gives you ISP in the 500s IIRC. Basically, this means that a Mars surface colony with sufficient infrastructure can send stuff into Martian orbit and back to Earth with a fleet of reusable SSTOs, or even mass drivers (harder on Mars than the moon, but its atmosphere is pretty thin which makes it easier to fling stuff to hypersonic speeds at the surface without it disintegrating). This is unlikely to be possible on Venus without exotic drive systems like gas-core NTRs.

My point is that an unmanned glider could just as easily reach the same altitudes and ranges carrying the same instrument package, and probably be less expensive. Not to mention that a solar-electric UAV could potentially maintain stratospheric altitudes for weeks or months at a time, while a manned glider would probably have less endurance than a zero-pressure balloon (although with more cross-range control).

Hang on... are these "27 cubic meters per person" figures based on astronauts or the general population? Because a spacecraft crew is automatically be made of individuals with a very high tolerance for close quarters and no privacy. 27 cubic meters is a 3m x 3m x 3m box, or with 8 ft ceilings a room less than 11 by 11 feet on a side. That's an average bedroom in America. Probably most prisons have FAR more space per person once you count all the "public" spaces, structure, etc... and they're far from a "comfortable" environment. You're also forgetting that a city with a high population density will already be built up vertically, so there's more "habitable volume" than you'd think. And actually a habitable volume study is only relevant for spaceships: on Earth you need to think about habitable area: spaces will usually be a mixture of heights, from 2.5 m (comfortable personal/family quarters, offices, etc) to 10 meters and above (large public spaces). The city you are proposing would most likely have concentration-camp-like conditions. EDIT: There's something very wrong with your math. A city with 3000 people per square km has 333 m^2 of area per person. Not all of this is habitable, but buildings have multiple stories. For any "sky-like" ceiling height that works out to thousands, or even tens of thousand of cubic meters per person.

I'm not sure what sort of data this vehicle could obtain that couldn't be obtained with an unmanned vehicle like NASA's old Helios program, aside from "can we get a manned glider to 90,000 feet?" Also, I found this in the comments in response to the "why can't we launch stuff to orbit this way" question that someone posts in every thread about upper-atmospheric flight: