We’re rewarding the question askers & reputations are being recalculated! Read more.

# Tag Info

5

The nozzle is there to maximize thrust, which is the same thing as maximizing the backward-going momentum of the exhaust gas. To increase that momentum, Newton's 2nd and 3rd laws means that the gas has to be exerting a forward-going force on the nozzle, i.e. generating thrust. If you have the numbers, you can directly calculate this part of the total ...

4

From Sutton, 4th edition, page 36 The axial thrust can be determined by integrating all the the pressures acting on areas that can be projected on a plane normal to the nozzle axis. I think your injector area X chamber pressure is a rough approximation but you'd have to take the pressure on all the surfaces including the nozzle to get it exactly.

0

Other answers have focused on the fact that you wouldn't want to run a rocket engine on gases because the tanks would be too large. One thing that hasn't been mentioned yet is the turbopumps. Turbopumps consist of a turbine which runs on burned fuel and oxidiser. This runs a pump which pumps the liquid fuel from a low pressure tank to the high pressure ...

0

Burning gases is an aim. Carrying fuel of maximum density is another. Propellant density and thus increased propellan payload was (and is) of such interest that in the 1990s the use of "Slush Hydrogen" was propoesed - ex mix of Solid (!) and liquid Hydrogen which increased Hydrogen payload by about 20%. The problems proved to be considerable. A summary of ...

15

Yes, and it is currently being done on a few engines, notably SpaceX's Raptor engines. They run on liquid oxygen and liquid methane. These are run through turbopumps in two different mixture ratios, burning a small part of the fuel which spins the pumps and vaporizes the rest of the fuel. When they enter the combustion chamber they are both in gaseous form. ...

0

You need a liquid to cool a large and hot combustion chamber efficiently. Ablative cooling has been used for smaller engines only. Heat transfer from the solid chamber walls to a gas is too small for cooling.

6

To complement the answer: 1 L contains 1141 g of liquid oxygen 1 L contains 1 g of gaseous oxygen (at 1ATM) Of course you can compress it but the container will add more weight (highly undesirable). But that's not over! Rockets consume not only a lot of propellant, but they consume it fast. A Saturn V consumes 18000 kg every second. That would be ...

25

Possible: yes. Feasable: not really (at least not for power applications). The main trick is energy density (per volume) - gases tend to be quite significantly less dense than liquids - and thus the tanks would need to be much larger and heavier - so they are commonly used in their condensed liquid form. For small engines gases have been used - both as ...

4

In general, heavier launchers can send more mass to LEO, but as described in this QA, the correlation isn't very strong. Different engine technologies used in modern rockets have different mass/impulse/cost tradeoffs. One particular example is Delta IV Heavy versus Ariane 5. Delta IV Heavy is 733 tons on the pad, 28 tons to LEO, for a payload mass ratio ...

0

Amount of fuel/propellant needed to get the ship up to 0.05C (and then back down to stationary) for a 4.7ly trip. Russel Borogrove covered this nicely above. The answer is unambiguously "too much". When your required delta-V exceeds your exhaust velocity, your mass ratio shoots up exponentially. 0.05c is pretty gosh-darn fast... about the speed that fusion ...

6

In addition to Russell Borogove's good answer there is another factor here to keep in mind: When you are dealing with planets you can't just add together separate burns. If you add up the energy needed to escape Earth, the energy needed to go from Earth's orbit to Mars' orbit and the energy needed to enter Mars' orbit you will get more than 16 km/sec. In ...

6

16 km/s is about right for Earth surface to low Mars orbit, summing up a few entries in this table. I am not sure as how he did it though, and was unsure if he used the escape velocity of Earth, the Hohmann Transfer, and also if that was only that velocity computed needed to be obtained once At a minimum, this would be split into ascent to LEO (~9.4 km/...

2

It’s completely impractical to get to even .05c with either chemical or ion rockets. Here’s the rocket equation, rearranged to “mass fraction form”: $$M_f = 1 - \frac{m_1}{m_0} = 1-e^{-\Delta V / v_\text{e}}$$ where $M_f$ is the propellant mass fraction (the part of the initial total mass that is turned into rocket exhaust). The delta-v term is 15,000,...

-1

Well now, I think that is an interesting question. The key to the answer is that nature is a complex and messy place. We represent that complexity with a mental image that represents it, but is always a compromise. The reality is that the space above us is extremely energetic, as has been pointed out by others, contains a constant wind of high energy ...

0

The International Space Station leaks a little air, and enough stays in the orbit to limit the experiments that can be done there. My former colleagues in Harwell make vacuum better than that to support high power laser experiments etc. So it is possible to pollute space.

8

The short answer is no. In space the rocket exhaust isn't really a gas it's more like a molecular dust, where all of the molecules (CO, CO2, H2O, etc) are travelling on their own divergent trajectories. In order for a 'gas' pocket to form those molecules would need to be held together in some way, and there's just nothing acting on them to do this. ...

23

The Sun ejects as Solar wind about a million metric tonnes per second. The ejection of some tonnes per minute occasionaly from a second stage rocket engine above the atmosphere of Earth is neglible small compared to Solar wind. A planet like Earth needs a huge mass to hold an atmosphere by its own gravity. There is no force that would hold such a gas ...

4

I would think it would be pushed out of our solar system by the sun's radiation just as the atmosphere of mars (or earth would be if we didn't have a magnetic field). In regards to distances further away from our sun, I believe it would act as described above. In a vacuum gas molecules dissipate. Lets be extreme and assume the hwy gets used ALOT - would the ...

55

Interplanetary space is a pretty good vacuum. Any gas introduced into that vacuum will be at a higher pressure than that vacuum. Gas expands until its outward pressure is in equilibrium with the inward pressure exerted on it by its surroundings, so rocket exhaust will rapidly dissipate until there's no noticeable trace left. The gas leaving the rocket ...

0

Adding to other answers, if you have a small launcher you can put in orbit your very own small satellite without sharing a great deal of information about it with the big rocket operator and/or the public in general.

1

Welcome to the site! I am afraid the answer you are looking for is not the one you want. Long story short, the optimal gravity turn must be calculated numerically, because the atmospheric density profile and velocity field is inherently numerically defined based on local conditions at the time of launch. (There's the standard atmosphere, and then accounting ...

14

Apparently lining up a lot of smallsats for a dedicated big rocket launch is like herding cats. Delays on any of the smallsats delay the overall launch. Hence SpaceX's recent announcement that their planned Falcon 9 dedicated smallsat launches will launch on schedule regardless of whether all the satellites are ready. https://spacenews.com/spacex-says-...

24

Why hasn't the small-lift launch vehicles completely replaced by the medium and heavy-lift launch vehicles? Because small launchers can provide several things: A small launcher is much cheaper than using a large launcher to launch a single small satellite. a dedicated launch, instead of having to share a launch which reduces your choice of final orbits a ...

3

The classic expander cycle engine, the RL-10 starts as follows: The RL-10 engine starts by using the pressure difference between the fuel tank and the nozzle exit (upper atmospheric pressure), and the ambient heat stored in the metal of the cooling jacket walls. The engine “bootstraps” to full-thrust within two seconds after ignition. A typical ...

14

It is purely down to trajectory. The side cores detach relatively early after the launch. This means that they are not so high nor do are they travelling so fast Eastbound. There is therefore enough fuel left in the side boosters to allow the "boost back burn" that allows them to change direction and get back to the original landing site. The centre core ...

44

Because of accidents of geography and history. Both of the main US launch sites are where they are because rockets occasionally crash, and, for fully fueled heavy lift vehicles, worst-case impacts have yields approaching that of nuclear detonations. So they were sited to fire out over the ocean for the longest possible distances to minimize potential ...

13

Falcon is launched over sea, partly for safety reasons (to avoid rocket stages falling on people's houses - which happens in China). The first stage is in a ballistic trajectory and simply does not have the range to reach solid land before falling back to Earth. Only the second stage reaches orbital velocity - which ironically means it can't be recovered at ...

Top 50 recent answers are included