Questions tagged [propulsion]

Systems for propelling a spacecraft from one place to another, such as rockets.

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65
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17answers
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Why is using a space elevator cheaper than rocket power?

Why is rocket power so much less efficient? In both cases you want to lift a given weight a certain height. What does climbing a tether give you that you don't have when using rockets? Wouldn't a ...
59
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4answers
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Can gunpowder get you to the moon?

In 'From the Earth to the Moon' (1873) by Jules Verne, A huge cannon is used to send a spaceship to the moon. A lively discussion in chapter IX leads to using 400,000 pounds of fulminating cotton to ...
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6answers
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Can you tack against the sun using a solar sail?

Solar sails are a great, inexpensive way to move out from the sun, if you’re not in a hurry. Ocean going ships are able to tack against the wind, and to move up wind. Could a solar sail gain inbound (...
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3answers
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How fast will 1g get you there?

If you have the energy for a constant 1G thrust, how long would it take to get to the planets in our solar system? How long for the 5 nearest solar systems? Assuming turn over and decelerate at ...
42
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1answer
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Do booster stages run out of fuel, or are they purposefully shut off?

When an expendable booster rocket stage nears the end of its burn, does the guidance computer shut the engine(s) off at a certain velocity/altitude for the mission, or does the stage completely ...
39
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4answers
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When the ISS accelerates, do the astronauts feel it?

The ISS has thrusters to avoid debris and to combat orbital decay. Do the astronauts feel the station accelerating? Do they have to hold onto something and is it the same when they rotate the station ...
37
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3answers
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If the Apollo mandate were delivered today, would the mission vehicle(s) and profile be similar?

Among a variety of alternatives considered at the time, the Apollo configuration of 3-person CSM and 2-person LM, launched atop a single vehicle was considered the optimal choice for its day. With ...
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4answers
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Is this really Rosetta's orbit around 67P?

From this link I fount the following representation of Rosetta's orbit relative to 67P: A video from ESA depicts a similar orbit. My questions are: is that really the relative orbit? If yes: why ...
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4answers
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Is warp drive a legitimate avenue of scientific investigation?

I've been reading a number of online "pop-sci" articles on the subject of "warp drive" - derived from work done initially by Alcubierre. Some of the most recent articles say that there are ...
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3answers
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Has in-space refueling been done?

Before the Apollo program committed to the lunar orbit rendezvous mode, one of the Earth orbit rendezvous proposals involved launching two Saturn Vs, one with the Apollo spacecraft and large lunar ...
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3answers
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Starting a liquid fuel engine in zero gravity

In zero gravity, the liquid in a fuel tank tends to form a blob in a random location, so you'd have to take precautions to make sure the fuel pump can draw fuel. In a recent question about spinning ...
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9answers
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Would a grinding machine be a simple and workable propulsion system for an interplanetary spacecraft?

I am wondering if any space agency has ever considered using a grinding machine as a propulsion system for an interplanetary spacecraft. This system would not be used to lift the spacecraft off of a ...
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8answers
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Why aren't linear aerospike engines in common use?

Linear aerospike engines are an old idea that seem so full of promise. Why are they not widely used today by the likes of Boeing, SpaceX, etc.?
22
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4answers
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Why does the Falcon 9 use RP-1/LOx and not LH2/LOx?

Why does SpaceX use RP-1 in the first and second stages of their rockets? In my view at least the second stage could use hydrogen as it currently is not being reused. I am aware that you have higher ...
22
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6answers
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Why are Ion Thrusters so energy hungry?

Ion thrusters need a lot of energy. But I don't understand why. So, one thing I understand is that it takes a lot of energy to achieve a high exhaust velocity (since kinetic energy is proportional to ...
22
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3answers
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Has any CubeSat flown with an active propulsion system?

CubeSats are small, but so are some propulsion systems (cold gas thrusters, for instance, really aren't too complex and can be low volume/mass). Has any CubeSat actually flown with its own propulsion ...
21
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3answers
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Why don't we use Cavea-B

Raiz Aerospace raised an interesting question during one of his KSP Realism Overhaul play throughs. If the RCS propellant Cavea-B is better than hydrazine and less toxic why does no one use Cavea-B, ...
21
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1answer
701 views

Is there any ongoing research in nuclear pulse propulsion?

Nuclear pulse propulsion seemed to be quite actively researched up until the 1990's, with a few projects that saw some rather promising results (some that could theoretically reach over 4% light speed....
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7answers
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Can ion thrusters be scaled up?

All ion thrusters are quite small. Having read through the more approachable information about them, as they use physics pretty beyond me, I don't understand what it is about them that makes it ...
19
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6answers
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What limits the speed of space probes currently?

...other than budget, obviously. Our computers nowadays are good enough that we should be capable of sending a probe to a neighbor star system and back, and get some pretty good analysis reports. We ...
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2answers
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Where does the thrust act in a rocket engine and how is it transferred to rocket structure?

A rocket engine is basically a device that generates a high pressure inside the chamber and the pressure difference creates a force. A nozzle helps in effectively accelerating the flow and increases ...
19
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3answers
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What exactly causes stranded upper stages to explode?

Usually if an upper stage experiences a failure before it can "passivate" itself (empty tanks, drain batteries, etc.), it's only a matter of time before it explodes. For recent examples, see any of ...
18
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2answers
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What powers New Horizons?

What does New Horizons use to keep itself traveling (so far), while keeping all of its monitoring and communication systems active? I did read that it leveraged force from a gravity sling shot from ...
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4answers
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How does a Spacecraft change its orbit?

I am a high school student. I saw the latest Indian spacecraft "CHANDRYAANN 2", which was in orbit around the Earth for 14 days..... I am so curious to know how a spacecraft changes its orbit. I ...
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6answers
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Methods for propulsion other than rockets for leaving Earth's atmosphere?

Due to the large amount of energy required, the standard method for leaving the Earth's atmosphere is rocket propulsion. Is there any other methods in development that don't involve rockets? E.g. ...
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4answers
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How much does it cost to fill an ion thuster with Xenon for a spacecraft propulsion system?

Ion engines are touted as a great source of propulsion for high deltaV missions that can afford an ample power supply and need low thrust maneuvers; and they are great. But I'd like to know how much ...
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2answers
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Why is the “impossible” space drive impossible?

So apparently NASA just built an impossible propulsion device: Sawyer's engine is extremely light and simple. It provides a thrust by "bouncing microwaves around in a closed container." The ...
17
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2answers
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What factors determine whether a spacecraft/probe/satellite uses gyroscopes or propellant thrusters to rotate?

Say I'm designing a probe or satellite. To control its attitude, I can add some gyros, or I can put thrusters on each corner, or I can add both and pick one in flight according to the situation. How ...
17
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1answer
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Why the non-symmetric design of rocket nozzles?

Although I have seen many perfectly symmetric nozzles, I have also seen designs such as this (Virgin Galactic) which is only symmetrical about one axis: Why is this?
17
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1answer
699 views

What contributes the majority of the mass in an ion drive?

In another question I've been corrected that batteries don't weigh that much in ion drive powered probes. Well, I thought a can of xenon would have a chance to be lighter than a solid block of ...
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4answers
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Why aren't there any space tugs in use?

Ion thrusters are capable of providing the same amount of delta-V for far less fuel (e.g. Falcon 9 v1.1 second stage specific impulse is 340 seconds, while some ion-thrusters have a specific impulse ...
16
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3answers
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What limits the speed at which rocket fuel is expelled?

Rocket propulsion is based on Newton's laws. The faster propellant is expelled, the faster the rocket is accelerated. At what speed is propellant expelled in a normal rocket? What are the factors ...
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4answers
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Could a ship take off from Earth using ion thrusters?

If you had enough ion thrusters, could you take off from Earth's surface into low Earth orbit? If not, why not?
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2answers
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How do you confirm ignition in the combustion chamber of a rocket?

Is ignition confirmed using a temperature sensor, pressure sensor or another device?
16
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2answers
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Is it more efficient to assemble spacecraft in orbit, or assemble on the ground and launch?

My friends and I were trying to figure this out a while ago. I was thinking that by transporting smaller pieces into space via a lighter re-entry spacecraft, there would be overall less fuel used ...
16
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3answers
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Pumped propellant propulsion - is it viable?

A recent article on Slashdot got me thinking. While the article is about using electric turbopumps for moving fuel from tanks to engines during launch phase and is just a small, incremental ...
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1answer
716 views

How important is plume impingement in rendezvous operations?

When performing space rendezvous operations close to the target vehicle (0-5 m relative distance), pursuer thruster escape nozzle gases can hit the target if firings are done in the direction of ...
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4answers
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Why is Philae not provided with a propulsion system?

Rosetta is en route to rendezvous with Chury. Briefly, the mission comprises an orbiter, and a lander. The latter named Philae. Wikipedia writes to say ... The lander is designed to touch down ...
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2answers
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Space travel using constant acceleration drive: Earth to Europa

Long story short: I'm writing sci-fi and taking my protagonist to Europa. He's got 2 weeks to one month to get there from Earth, give or take a few days. That sounds, of course, preposterous in this ...
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2answers
944 views

What are the economics of Nuclear Thermal Propulsion?

Can anyone breakdown the cost of developing and implementing an upper stage nuclear thermal engine? After development, what could the price be of each engine produced?
14
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2answers
3k views

Could a complex system of reaction wheels be used to propel a spacecraft?

I was think about different ways spacecraft could feasibly move around and I came across Reaction Wheels as a way they can rotate. So I was curious if a complex system of them could be used to propel ...
14
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5answers
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If LOX/LH2 were used in a fuel cell powering an ion engine could it provide a greater delta-v than with a conventional engine?

Question: If LOX/LH2 were used in a fuel cell powering an ion engine could it provide a greater delta-v than with a conventional engine? Conditions: Start in space in a stable heliocentric orbit (no ...
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2answers
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What is the “specific impulse”?

One of the most important values when talking about rocket engines is the so-called specific impulse. I have read the Wikipedia article but still have trouble understanding what it really is and what ...
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2answers
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Why is (conventional) ramjet not used for 2nd stage of rocket propulsion?

Due to nature of space-rocket launches using "conventional" rocket fuel (fuel+oxidizer, e.g. hydrogen+oxygen), every kilo of fuel that has to be carried impacts the rocket's range in a very nonlinear ...
14
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3answers
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Why do we use the gravitational acceleration at the Earth's surface when calculating the specific impulse of an engine?

So one of the ways of calculating Isp is: Isp = Ve/g0 You divide the effective exhaust velocity by acceleration at earth's surface. This gives you a number in seconds, and is generally considered ...
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1answer
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Can I derive a combined equation for velocity of solar sail?

In this article on The Planetary Society website, I read this about solar sails: At an acceleration rate of 1 millimeter per second per second (20 times greater than the expected acceleration for ...
14
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1answer
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Are MMH and UDMH interchangeable?

Can Monomethylhydrazine and Unsymmetrical dimethylhydrazine be used one in place of another for the class of the existing orbital maneuver engines (with reduced performance may be)? Such as Shuttle's ...
14
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3answers
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Why do pump and pressure fed liquid engines need to operate at high pressures?

There is apparently some confusion as to why pump or pressure fed liquid rocket engines need to operate at high pressure to product significant thrust, based on the comments to this question about ...
14
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1answer
414 views

How far have autophage rockets been developed?

Ars Technica reports on a May 24 phys.org press release/precis on a University of Glasgow paper in Journal of Spacecraft of Rockets about a solid rocket intended to consume itself during use rather ...
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9answers
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Tiny emergency propulsive device if stuck floating in a large volume in microgravity

The questions here in SXSE Can you swim in space? and in Physics SE How to escape the center of a room without gravity? [closed] both address aspects of how to move if stuck floating in the center of ...

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