# Tag Info

## Hot answers tagged rocket

32

In space you don't just "go somewhere". You have to match orbits, while not wasting too much fuel. If you're in a low circular orbit, and you want to get to a high circular orbit, it takes two tangential burns, one to elongate your orbit into an ellipse, and another at the high point of the ellipse to make it circular again. This is called a Hohman ...

15

At constant 1 g acceleration half-way through, then constant 1 g deceleration the remaining half, it takes 7 years in rocket time, 38 years in Earth time: http://www.cthreepo.com/lab/math1.shtml Scroll down to Long Relativistic Journeys and enter your data. To the Andromeda Galaxy (2.5 mil ly) it's 29 years in rocket time! :)

14

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.

14

Aircraft rely on lift generated by interacting with the atmosphere and on using atmospheric oxygen to burn with fuel they carry. Orbits aren't stable until you are high enough that there isn't enough atmosphere to interact with, and long before that the oxygen content drops too low to be useful. So, to get to a stable orbit, you will need rockets ...

11

Nowadays, rockets use Gimbaled Thrust System. The rocket nozzles are gimbaled (An appliance that allows an object such as a ship's compass, to remain horizontal even as its support tips) so they can vector the thrust to direct the rocket. In a gimbaled thrust system, the exhaust nozzle of the rocket can be swiveled from side to side. As the nozzle is moved, ...

9

Here is a visualization: Momentum is mass times velocity, so draw it as the area of a rectangle: If we change the mass and velocity a little, we change the momentum: The total change in the momentum is the sum of green, blue, and purple rectangles. Their sizes are just length times width, so overall we have $\Delta p = m\Delta v + v\Delta m + \Delta ... 8 This is a hugely open ended question and a very big subject, it's a bit like asking "what automobile is best for use on Earth?" I'll try to fill in some details. There's the unique environment of space: zero-g, potentially very cold temperatures, vacuum, potentially long travel times (months or years), varying delta V requirements, etc. Each of those need ... 7 Rather than leaving a brief comment on this topic, let me just point at this wikipedia page which is very comprehensive: http://en.wikipedia.org/wiki/Interstellar_travel My own comments: Once we learn to control fusion, that would be an attractive candidate for the engine. The nice thing is that there might be no need to convert the reactor's energy into ... 7 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). ... 6 It isn't needed in a rocket, however if you are going to the effort of sending something up outside the atmosphere (or even just high up within the atmosphere) you might as well try and get some useful data out of it. This might even help you get sponsorship for your rocket, as data from climbs through altitude is useful to a number of academic institutions. ... 6 For what it's worth, even though a rocket starts its flight going straight up, once it has traveled through most of the atmosphere it soon starts to change its direction so that it spends most of its flight accelerating in the "around the earth" direction (i.e. basically horizontal). Also, to reach orbit a vehicle either has to reach a high enough speed, or ... 6 Pretty straightforward, really: Accelerating upwards, the rocket can accelerate at T-g, where T is thrust, and g is the acceleration due to Earth's gravity. Accelerating downwards, the rocket can accelerate at T+g Accelerating horizontally, the acceleration will be T So you can see that it will accelerate fastest downwards. 6 There are two concepts here that may be getting mixed together, namely, conservation of linear momentum and conservation of angular momentum. Newtons laws state that an object in motion will say in motion unless acted upon by an external force. So unless interstellar friction is a problem, the spaceship will keep travelling linearly in the same direction ... 5$M$is reducing. Thus,$\mathrm dM$has a negative value. In contrast, in the above equations, you can see an$M-\mathrm dm$term. Here, we can see that$M$will reduce only if$\mathrm dm$has a positive value. In other words, when time goes forwards, the mass that got thrown out ($m$) is increasing, thus$\mathrm dm$is positive. In contrast,$M$... 5 A 747 - can get you to around 35,000 feet. Still very much within the atmosphere. So what do you do then? Launching a rocket from that point still requires an awful lot of kit, so while you have reduced your propellant requirements a little, the 747 still has to carry a launch platform, so you're not really getting anything out of this. New technologies, ... 5 To the best of my knowledge there aren't any platforms currently targeting a payload that small. The only platform I'm aware of targeting satellites that small is CubeSat which has a 1.33 kg mass limit and 10x10x10 cm volume limit. However CubeSats are launched as secondary payloads on larger rockets being used for other purposes. 5 Rory Alsop explained why the idea is wrong, but it may originated from the following reasoning. When a space rocket takes of, it does so vertically. At that time it is fully loaded with fuel and hence its acceleration is slow. When you watch a video of a space rocket take-off, it seems to crawl along the launch tower. However, in order to achieve orbit, ... 5 The barbecue roll and the roll program are not related. The former is for passive thermal control when the spacecraft is exposed to the Sun and the latter is a maneuver early in the launch sequence to orient the launch vehicle to the proper heading. For a number of reasons, the space shuttle launch vehicle needs to be oriented "heads down" (the shuttle is ... 4 The idea about this school book derivation is that you can change moment by changing velocity (common case) or by changing mass. Since you can change the momentum of the system (rocket plus gasses) only by the external force, and in case of the rocket there is no external force (neglect gravity for a moment), so the question is, why is rocket getting faster ... 4 It's only true when the changes$\Delta t$,$\Delta v$,$\Delta m\$ are small and then it is known as the Leibniz rule, the rule for the derivative of a product, which Leibniz (but also Newton) discovered when they invented the calculus 3 centuries ago. Just look at this proof: $$\frac{\Delta (mv)}{\Delta t} = \frac{(mv)_{new} - (mv)_{old}}{\Delta t} ... 4 The answer is no, according to Einstein's Theory of Relativity. As an object approaches the speed of light, more and more energy is needed to accelerate it further. To reach the speed of light an infinite amount of energy would be required. Also, there is wind/friction in space. There is no absolute vacuum, there is an interstellar medium. Indeed, ... 4 The basic design difference between atmospheric and vacuum rocket design is its nozzle. The rocket thrust equation is http://www.braeunig.us/space/sup1.htm,$$ F = q \times V_e + (P_e - P_a) \times A_e $$where$$ \begin{eqnarray} F &= &\mbox{Thrust} \\ q &= &\mbox{Propellant mass flow rate} \\ V_e &= &\mbox{Velocity of ...

4

Since you're doing the thought experiment anyway, there are at least two important engineering considerations that limit this more severely than what accelerations humans can stand (which is trivially solvable with robots anyway): (1) The energy needs would be huge. What percentage of the total mass would have to be fuel in order to supply enough energy to ...

4

A 747 moves at approximately 1,000 km/h, a satellite in orbit travels at 28,000 km/h. So, after your rocket is released from the 747 it still needs enough fuel to accelerate a further 27,000km/h. That requires a lot more fuel than the 747 is capable of carrying. Remember that the shuttle lift-off weight is about 2,000 tons - far more than the 747 can carry. ...

4

More fundamental than the gimballed thrust system or verniers is the relationship between the "center of gravity" and "center of pressure" on a rocket (or any kind of projectile (e.g., bullet). For the rocket to fly nose-forward and not flip around, the center of gravity must be ahead of the center of pressure. In building small amateur or model rockets, ...

4

The trivial answer is that space is a vacuum, and is therefore largely devoid of a substantial amount of oxygen in sufficient densities to be freely usable by a spacecraft. A little more advanced response would require us to look at a concept like partial pressures. First we would identify the pressure in space which some might think is zero, which would ...

3

The Saturn V payload mass to LEO was 118,000 kg. Wikipedia has a decent comparison of Super-heavy launch systems with a payload mass to LEO of 50,000 kg or more. None are in current use, and only two systems are in development. There is also a "Heavy" lift launch system list which includes the Delta IV and Ariane 5 you mentioned. The top operational system ...

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