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Questions tagged [propulsion]

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

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70 votes
17 answers
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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 ...
Xavier Aaron's user avatar
66 votes
3 answers
173k views

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 ...
James Jenkins's user avatar
59 votes
4 answers
8k views

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 ...
James Jenkins's user avatar
51 votes
7 answers
9k views

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 (...
James Jenkins's user avatar
42 votes
1 answer
7k views

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 ...
Jake Blocker's user avatar
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41 votes
4 answers
5k views

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 ...
matt's user avatar
  • 513
40 votes
3 answers
5k views

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 ...
Anthony X's user avatar
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36 votes
5 answers
5k views

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 ...
Anthony X's user avatar
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34 votes
4 answers
4k views

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 ...
Federico's user avatar
  • 980
32 votes
3 answers
9k views

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 ...
Russell Borogove's user avatar
29 votes
8 answers
7k views

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 ...
user avatar
29 votes
3 answers
8k views

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 ...
Hobbes's user avatar
  • 128k
27 votes
8 answers
21k views

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.?
Travis Bear's user avatar
24 votes
6 answers
8k views

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 ...
Chandrahas's user avatar
23 votes
4 answers
10k views

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 ...
CKA's user avatar
  • 546
23 votes
6 answers
5k views

Why is it not concerning from a cost perspective to have so many engines on Starship?

Starship is meant to imitate (to a degree) the affordability of passenger jets. This applies to Earth-to-Earth travel as well as space travel. Jetliners started with 4 engines, but have since migrated ...
Abdullah is not an Amalekite's user avatar
22 votes
3 answers
1k views

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 ...
user avatar
22 votes
5 answers
17k views

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 ...
marked-down's user avatar
  • 8,951
21 votes
3 answers
4k views

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, ...
DJ319's user avatar
  • 405
21 votes
7 answers
13k views

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 ...
kim holder's user avatar
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21 votes
3 answers
1k views

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 ...
user avatar
21 votes
1 answer
835 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....
berry120's user avatar
  • 2,043
20 votes
4 answers
6k views

Why can't you travel to Mars in a straight line?

I had two questions regarding choosing a path to Mars. Firstly: I wanted to have a look at the mathematics behind the reason as to why we choose Hohmann's transfer over a journey that is a straight ...
Ryan's user avatar
  • 459
20 votes
2 answers
4k views

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 ...
karthikeyan's user avatar
  • 4,479
19 votes
4 answers
6k views

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 ...
आर्यभट्ट's user avatar
19 votes
3 answers
4k views

How is the Quantum Drive performing on board the BARRY-1 cubesat?

Since 2001 there has been chatter about reactionless “quantum drives” such as the EmDrive developed by Satellite Propulsion Research Ltd. These drives supposedly produce thrust without consuming ...
Woody's user avatar
  • 22.4k
19 votes
6 answers
9k views

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 ...
SF.'s user avatar
  • 55k
19 votes
1 answer
838 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 ...
SF.'s user avatar
  • 55k
19 votes
1 answer
739 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 and Rockets about a solid rocket intended to consume itself during use rather ...
Erin Anne's user avatar
  • 12k
18 votes
2 answers
12k views

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 ...
Ricky's user avatar
  • 453
18 votes
6 answers
3k views

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 ...
user avatar
18 votes
6 answers
6k views

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. ...
Marmstrong's user avatar
  • 1,093
18 votes
2 answers
1k views

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 ...
JKor's user avatar
  • 840
18 votes
1 answer
3k views

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?
Jonny's user avatar
  • 303
18 votes
1 answer
1k 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 ...
Julio's user avatar
  • 1,732
17 votes
4 answers
1k views

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 ...
Everyone's user avatar
  • 13.6k
17 votes
2 answers
3k views

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 ...
xmp125a's user avatar
  • 367
17 votes
3 answers
3k views

Could radiated heat propel space-craft in outer space?

The comment chain on What is the feasibility of launching a probe to Sedna? indicates RTG thermocouples decay. With the passage of time the thermocouple may even have the ability to transduce an ...
Everyone's user avatar
  • 13.6k
17 votes
3 answers
2k views

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: $$I_{sp} = V_e /g_0 $$ You divide the effective exhaust velocity by acceleration at earth's surface. This gives you a number in seconds, and is generally ...
David Fourman's user avatar
17 votes
2 answers
2k views

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 ...
user avatar
17 votes
2 answers
2k views

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 ...
Dan Hulme's user avatar
  • 535
17 votes
1 answer
8k views

What are the advantages of Ox-rich staged combustion?

In the context of staged combustion, I understand that burning ox-rich creates complications associated with having hot, high pressure, oxidizer. Some engines, notably the RD-170 and RD-180 family run ...
randomUsername's user avatar
16 votes
3 answers
6k views

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 ...
user332336's user avatar
16 votes
4 answers
5k views

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?
Joe's user avatar
  • 3,950
16 votes
3 answers
16k views

What propulsion methods does the ISS use for station-keeping?

The International Space Station is constantly losing orbital energy due to atmospheric drag. How does station-keeping work for the ISS? What sort of propulsion system is used to keep it in the desired ...
Stu's user avatar
  • 5,928
16 votes
2 answers
2k views

How do you confirm ignition in the combustion chamber of a rocket?

Is ignition confirmed using a temperature sensor, pressure sensor or another device?
Edward Jane's user avatar
16 votes
2 answers
4k views

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 ...
adamholtwrites's user avatar
16 votes
3 answers
1k views

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 ...
SF.'s user avatar
  • 55k
15 votes
2 answers
3k views

Could the Space Shuttle launch with two engines?

In a movie, they need to launch the Space Shuttle, but one engine is not ready to go in time, so they decide to launch with the booster and two of the shuttle's engines - Could the shuttle Launch with ...
nycynik's user avatar
  • 763
15 votes
3 answers
2k views

Using nuclear detonations for propulsion

The proposed orion propulsion system used nuclear explosions to push against a giant shock absorber and propell it, but from my understanding, nuclear explosions only produce heat and rely on the ...
R. Hall's user avatar
  • 822

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