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As other answers say, if someone just jumps off of the international space station(ISS), they would still be in orbit around the earth since the ISS is traveling at 17,000 miles per hour (at an altitude of 258 miles). Instead of just jumping, imagine the astronaut had a jet pack that could cancel that speed of 17,000 miles per hour in a very short time ...

19

It's all a question of if they need it. Most that are staying within a couple AU of the sun can get sufficient power from solar panels. It's when they start getting further away that they use an RTG. For example, New Horizons, which launched in 2006 (which is considered to be 'modern' when you only launch a few probes per year) is going to Pluto, so it ...

15

Somebody has to put the pieces together somewhere. If you do it in the ground, you can work in shirtsleeves, with easy access to supplies, tools, equipment, and other workers. If you need a tool, you can probably walk next door to get it, or ask someone to bring it to you. If you drop a tool, you can pick it up. In orbit, you have to work in a bulky ...

15

edit: I originally had some points about the inefficiency of RTGs, but after some more research prompted by @Jeremy I found that it's not really a valid point when they're used appropriately for the spacecraft's mission. The RTGs used by Galileo at Jupiter generated 300W of power, whereas the solar panels that will be used by Juno at Jupiter will generate ...

15

It's a great way to get gyroscopic stability. NASA has been using this technique for a long time. For instance, the Pioneer spacecraft used this method. Another example is the Juno spacecraft as well. I hope that answers your question sufficiently.

15

The basic tragedy of space travel is expressed by the Tsiolkovsky rocket equation, which says that the amount of reaction mass you need grows exponentially with your $\Delta v/v_e$, where $v_e$ is the exhaust velocity. The advantage of antimatter propulsion is high energy density, but energy density doesn't have any direct, major effect on the amount of ...

12

It depends on how you define the problem. Humans have re-entered the atmosphere from the International Space Station many times, by riding in either a Space Shuttle or a Soyuz capsule. Someone re-entering without a spacecraft of some sort would obviously have to wear some kind of pressure suit (as Felix Baumgartner did in his jump). How elaborate is the ...

12

Two points that may help Think about what is required in order to accelerate. You have to throw something overboard.1 However your engine works you will eventually run out of fuel and at that point you are done accelerating. There is an exception to the "run out of fuel" claim and a possible loophole. The exception is a photon drive: just point a laser ...

11

The real problem with RTGs is that the US stopped making Pu238 in the 80s and has been very slow to start up production again, purchasing all our spacecraft Pu238 from the Russians (who have now also run out). I don't know about the byproducts from the breeder reactors, but Pu238 itself is actually not that dangerous to handle, and only toxic if ingested.

8

I wrote a semi-popular book on this subject a couple of years ago: http://www.amazon.com/Can-Star-Systems-Be-Explored/dp/9812706178/ref=sr_1_3?ie=UTF8&s=books&qid=1297567209&sr=8-3 A lot of this was worked out. I illustrate the relativistic rocket and the photon sail. The photon sail is clearly the most reasonable of these two. I also ...

8

In a lot of ways this is a technology---rather than physics---question, but lets look at some limits imposed by physics. For rockets there are two numbers that matter: the velocity relative the spacecraft with which the fuel can be expelled (called the specific impulse) and the fraction of the original mass that is fuel. For very high mass fractions the ...

8

Stabilization. Example: Pioneer Equalize heating (barbecue mode). Example: Apollo Deploy antennas & booms (via centripetal force). Example: IMAGE Maintain tension in a solar sail. Example: Cosmos 1 Test general relativity. Example: LAGEOS Create artificial gravity. Example: Gemini Simplify or reduce weight of sensors (e.g. star trackers). ...

8

The reason the donut is heavier when it's spinning is that it contains more kinetic energy, and this energy has mass. (Or at least, it does if you use the word "mass" to mean "relativistic mass" rather than "rest mass", which is somewhat out-dated language, but I'm going to keep using it anyway.) The question is, where does that energy go when the donut is ...

7

The distance between Earth and Alpha Centauri is $4.4\,\text{ly}$. Dividing by $60\,\text{years}$ it's approximately $22000\,\text{km/s}$. The relativistic factor (I mean $\gamma = \frac{1}{\sqrt{1-v^2/c^2}}$ for this is almost $1$. If we take a constant acceleration of $2g$ (it's possible) it would take only $320\,\text{hours}$ to reach this speed (and, ...

7

If you are not interested in relativistic effects, the answer to your question is easy to workout. According to Wikipedia, Alpha Centauri is 4.24 ly away (4.0114x$10^{16}\mathrm{m}$). So to get there in 60 years ($1892160000\mathrm{s}$). So your non-relativistic answer is $v = \frac{d}{t} = \frac{4.0114 \times 10^{16}}{1892160000} = 21200000 ... 7 As long as you have useable energy in your ship, you can use it to accelerate indefinitely your propellant in the opposite direction you want to accelerate; this is how rockets work. The propellant is basically something that carries away linear momentum in one direction so that the ship can gain momentum in the opposite direction. Indeed, as you realise, ... 7 Suppose the spaceship was accelerating constantly at 1g, what would that feel like? Well Einstein gave us the answer to that: it would feel exactly like standing on the surface of the Earth where the acceleration due to gravity is 1g. This is (one statement of) Einstein's equivalence principle. If the acceleration were continued for many hours that wouldn't ... 6 You would use the stars as your reference. Of course, some stars are more suited to this than others. For example, the Voyager Golden Records had pulsar maps, that in theory some alien civilisation could use to locate Earth (what could possibly go wrong?). So, stars with unique and easily recognisable characteristics make good 'landmarks' (in particular, ... 6 Assuming you're in orbit around the Sun (presumably a highly elliptical orbit) you won't feel any force due to gravity. In principle you might feel tidal forces, but for an object the size of a spaceship these are negligable even if you graze the surface of the Sun. The most obvious problems are the heat from the Sun and the radiation it emits. The ... 6 1) Motors orient the camera independently of the satellite. The satellite has to be oriented so its big dish antenna is pointed toward Earth. 2) Yes they know the position, and they pre-program the photographs, because instructions take hours to get there. 3) is there a gravitational sensor? Not for pointing cameras. 4) For orientation, they have inertial ... 6 Right, well someone check my math but starting from equations 4.16-4.17 and 4.73 of the link Ben Crowell posted I work out that the delta-v of a boost/plane change/circularize relative to the direct plane change is$\$ \frac{\Delta v}{2v\sin(\frac{\theta}{2})} = ...

5

Depends how much fuel you have. The space shuttle and other craft need such large heat shields because they use it to dump all their kinetic energy 'for free'. The shuttle only uses it's engines for takeoff and has only some small thrusters available in orbit. If you also had some form of propulsion as well as a space suit and could generate all the thrust ...

5

The ISS is using electrolysis, in the "Elektron" oxygen generator, http://en.wikipedia.org/wiki/Elektron_(ISS)#Elektron to separate water to hydrogen and oxygen. NASA claims that those devices don't work well and prefers bottled oxygen delivered from Earth which the Russians only consider a backup option. Another backup option are solid fuel oxygen ...

4

If I decided to leave for Neptune today (using gravity assist), how would I find a good route and are such tools available on the desktop? I don't know about the 'find[ing] a good route' stuff, but my understanding is that the main tool used for these calculations is the SPICE Toolkit, and if I understand correctly, it's no longer ITAR controlled, so ...

4

The most comparable thing would be constructing a submarine, not a house. Let's bring a few things to consider. They must be air tight. They have complex electronics to regulate systems. They both operate in non-typical environments. Submarines are typically constructed in dry docks, and then placed in the water. That way they can get everything welded ...

4

Optical diodes (aka isolators) are nothing new http://en.wikipedia.org/wiki/Optical_isolator Recent work like the one you cite is not about demonstrating that optical diodes are possible, it is about making optical diodes that are compatible with silicon-based integrated circuits. Here is more about that. A solar sail does not need to be a special ...

4

The trans-lunar injection doesn't achieve escape velocity. Instead it changes the orbit of the spaceship to an elliptical orbit that intersects the Moon's orbit. The Wikipedia article on Hohmann transfers explains this very nicely. The spaceship starts out in a circular orbit around the Earth. The Moon is also in a circular orbit, except of course the ...

4

Privět. These are real-world questions that NASA, Russian/Soviet space program, and others of course had to be solving – if you kindly believe that astronauts are real – when they were designing space suits, see e.g. http://en.wikipedia.org/wiki/Spacesuit Actually these 8 pages about space suits could be more useful (buttons 1-8 are at the bottom): ...

4

UPDATE 2: If allowed to freely design the spacesuit the answer is yes.(see below) Initial answer before clarification The short answer is no. (SEE UPDATE) The longer answer is that there are a few key obstacles. One is that the person on the space station is in a relatively stable orbit around the planet. So while jumping from the space station would ...

4

You don't say how much you know about special relativity, and the calculations involved in handling acceleration are a bit involved unless you are already fairly familiar with the subject. The calculation is described in chapter 6 of Gravitation by Misner, Thorne and Wheeler, or if you just want the results see John Baez's article on the relativistic rocket. ...

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