# Tag Info

67

Because space isn't about going high; it's about going fast! For example, in a 400 km orbit (like ISS) you need a speed of about 27,500 km/h or 7.66 km per second. So if you would extend a pole, winch or anything else into the lower parts of the atmosphere, it would also move at about 27,500 km/h (if we ignore atmospheric drag and all other ...

53

Interesting but no, it wouldn't work for the same reason that astronauts in the International Space Station, other space stations, or orbiting shuttles or capsules do not "feel" gravity with respect to their station or capsule. When you are inside an object which is in orbit, you are in orbit too! The Earth pulls on the station with nearly 1 g and it pulls ...

44

Take a look at the SABRE engine. The goal is to achieve single stage runway liftoff/land to/from orbit with a hybrid engine capable of breathing air at low altitude but switching to stored oxidizer and operating like a rocket when it is not practical to use ambient air. The limitations of an air-breathing engine for space launch are that You can't go very ...

42

Systems that do this exist and more are being introduced. It's just that they hide their appearance and look somewhat different to what would be expected from what you describe. Orbital Sciences Corporation (now owned by Northrop Grumman) have been air launching the Pegasus satellite launcher since 1990 (almost 30 years). Virgin Galactic's 'White Knight' ...

35

The main engineering challenge in implementing your proposal is that in order to be competitive with a chemical rocket engine, the grinding wheel must rotate at an extremely high velocity. A typical chemical rocket might have a specific impulse between about 250 and 450 seconds; therefore, the exhaust velocity is about 2500-4500 m/s. In a competitive ...

26

A flywheel is so efficient because it is big and heavy, both of which you don't want to add to a spacecraft. As for spinning an existing component, the only parts of a rocket that really have any significant mass (would justify the additional bearings and generator) would be fuel tanks. Spinning a fuel tank with liquid fuel in it would be tricky though, ...

20

It absolutely could! First of all, water can be split in to hydrogen and oxygen, which can be enough to launch a rocket. Hydrogen requires a very low temperature, and the rocket engine doesn't have as much thrust as other options out there, but it is the same fuel that ran the Space Shuttle main engine, among others. Water and carbon dioxide, easily ...

19

There are two major barriers: one is that thrust-to-weight ratio of jet engines is pretty poor (2 J58s massing more than 15 times what 9 Rutherfords do), the other is that it's hard to make an engine that performs efficiently over the wide range of speeds and altitudes that a first stage wants to cover. That said, Boeing at one point toyed with a concept ...

18

As an alternative to DarkDust's answer, if you start higher, at the classic altitude for space elevators, the end of your cable is indeed stationary to the air. But your cable needs to reach from geostationary orbit to the upper atmosphere, something like 35,700 km. The clipping off the last 20-60 km does not make a big difference in the overall ...

18

I don't know if it has ever been considered by anyone. In my view, this is not a good idea for at least the following reasons: It is equivalent to mechanically throwing things retrograde. See this video for an overly simple example. This is obviously not a good way for propulsion, as the specific impulse is very low. Let's talk just about the impulse $$p=... 16 Have the object tidally locked into its orbit around the sun This way we would get the 1g gravity from the sun on the opposite side of the asteroid Interesting idea, but you missed something in your math. You'd only get the tidal difference between the sun's gravity at the centre of mass vs. the sun's gravity 1 object-radius farther away. This varies ... 14 The VASMIR 200 is listed as having a thrust of 5.4 newtons, and you need 9.8 newtons to lift 1kg against earth's gravity. So 700 tonnes is going to need more than a million engines and be consuming more than 254 GW of electricity. So even if the engines are weightless this is not lifting off from earth without co-opting the power generation of a sizable ... 13 Before I start my answer: This is not a rockoon anymore, since there is no balloon part. It's just a quirky air launched rocket. My answer: No. What you are doing is: Phase 1: Climb with a plane Phase 2: Descend with a plane Phase 3: Climb without a plane So yes, Phase 3 climb will begin with higher speed. However, since it's all energy that was gained ... 12 In principle, this should be possible. The question is, is it practical? An example flywheel used in car racing (i.e. a high-performance, cost-no-object application) weighs 18 kg and stores 400 kJ = 400 kWs, is 111 Wh, or 6.1 Wh/kg. A Li-ion battery has a specific energy of 100–265 Wh/kg, 16-44 times higher. So the flywheel solution needs far more ... 12 Any multi-stage rocket design has to obey three rules to achieve good performance: The fuel should have a high specific impulse. A real rocket will achieve a fixed percentage thereof, depending on structural weight and payload. Each stage's payload (which can be another stage) should outweigh the stage's structure, otherwise most of the energy is wasted ... 12 Effectively it has been done, but not in the way you're thinking (or probably intending). The USAF launched its ASAT missile into space from an F-15 fighter aircraft. While not an orbital rocket, it's close. And for orbital rockets, there's Pegasus, launched from a converted L1011 Tristar mother aircraft. It's not a concept that ever really took off, ... 12 Pipelines two orders of magnitude shorter on Earth are usually divided into many compressor stations. But let's take a look at how feasible it is. At the very least, a compressor station would have to provide a pressure greater than the pressure at the bottom of the pipeline. Fortunately, the pressure calculation needed is unusually simple for a CR3BP ( ... 11 Have you ever flown a kite with a tail? The tail flies almost horizontally, kept up by the wind. It would hang at a steeper angle if you made it heavy, but what would then happen to your kite? Now imagine that wind to be Mach 20 or so. Even if you had a rope made of unobtainium and hence able to withstand the heat created by atmospheric compression it would ... 11 You may not send a nuclear bomb into space if you're one of the 105 countries that have signed the Outer Space Treaty that, among other things, forbids deploying nuclear weapons or any other kinds of weapons of mass destruction in outer space. Even disregarding that... By measuring the craters of bombs we exploded in the 1950's, we found that a crater ... 10 No Even if overall design makes a helicopter lifted first stage sensible you still need good energy density (power per KG of energy storage). Super capacitors have a special properties that make them useful but energy density by weight is not one of them. Going off the linked (and plausibly out of date) table they would need to be ten times better to equal ... 10 Yes or no, depending how you define realistic. Like many other fantastical future technologies like space elevators, cylinder habitats, and nuclear lightbulb drives, there's nothing wrong with the underlying concepts. Physicists have written papers, done the math, and found that it mathematically could work. There are no known laws of physics that prevent ... 10 Conceptually, staging is getting rid of hardware we no longer need. Keeping useless hardware attached to the rocket is expensive, since added mass reduces acceleration. Ideally, we would want to get rid of hardware as soon as it gets useless, instead of piling it up to a "batch", which is essentially what the question boils down to. Rockets are very simple*... 9 From a mechanical, engineering view, having a brush on a robotic arm to clean the solar panel is more favorable, than rotating the panel. Having a current transfer between the rotating solar panel and the standing probe is highly problematic and would cause likely more problems, than the dust itself. Note, although that dust played a role in the end of life ... 8 It would not be feasible. Compressed-gas thrusters have a very low specific impulse (a measure of fuel efficiency), and the ratio of launch mass to payload mass goes up exponentially with lower specific impulse. Achieving the horizontal speed needed for orbit is much harder than just gaining altitude, so the 50km start isn’t enough to make it work. One ton ... 7 The end of the cable would be destroyed by the heat of reentry from a low orbit when reaching the height where planes may fly. But if you try to drop a cable from a low orbit it would not drop, it would stay in orbit. There is no dropping of things in zero gravity. Pulling up a load to the spacecraft in low orbit would slow down the spacecraft. It would ... 7 Since specific impulse and exhaust velocity are directly related via$$I_{SP}=\frac{V_e}{g_0} anything that increases the exhaust velocity necessarily increases the specific impulse. The issue is: do you gain anything from it? That depends on what "gain" you're looking for. Rocket engines of any type are momentum devices. The impulse imparted to the ...

7

Could liquid metal be made ferromagnetic by externally inducing an internal magnetic field? No. Metal is either ferromagnetic or not; this is a result of the quantum-mechanical interaction of neighbouring atoms in the metal's crystal lattice. Even non-magnetised iron at room temperature is ferromagnetic, only, the Weiss domains are randomly oriented and ...

7

You don't need a laser to do this. The technique you describe is known as spectroscopy, and it can use any light source, including light from the planet's star. This is a common technique for studying Earth's atmosphere from space, and to study stars and planets from Earth. This even works on planets in other solar systems. In a few years, an ESA mission ...

7

The Sprint missile could get up to 3 kilometers a second very briefly and with the outside shell going white hot. https://en.wikipedia.org/wiki/Sprint_(missile) That is approximately 1/3 orbital velocity or 1/4 earth escape velocity, depending on which one you meant. Going faster will involve exponential increase in needed power to overcome drag. And ...

7

The forces involved in spinning a wheel at high speeds are enormous. At 1600 km/h rim speed, the wheels on the Bloodhound SSC experience 50,000 G. Even the slightest imbalance (from, say an abrasive particle coming loose) would be catastrophic.

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