155 votes
Accepted

How much bigger could Earth be, before rockets wouldn't work?

Because linear increases in delta-v require exponential increases in mass, small changes to the assumptions you make about fuel tank structural mass and engine thrust-to-weight ratio start to make ...
Russell Borogove's user avatar
115 votes
Accepted

Why is it easier to escape the solar system than get to Mercury or the Sun?

Because the earth goes very fast around the sun. If you want to get to the sun, you need to slow down almost completely so that your speed relative to the sun becomes almost zero. If you don't slow ...
Speedphoenix's user avatar
  • 5,324
87 votes

How many times do you have to circle the Earth to break orbit?

This depends on how much thrust you have available. With enough thrust, you don't need to be in Earth orbit at all: you can launch straight into an escape trajectory. New Horizons did this, more or ...
Hobbes's user avatar
  • 127k
75 votes
Accepted

Has any human ever had the choice to leave Earth permanently?

Of the 533 humans who have been in orbit, have any of them been sent into space with enough propellant to actually escape Earth's grasp, should they have chosen to use the fuel in that manner? Has any ...
Russell Borogove's user avatar
48 votes
Accepted

Why is it so hard to build crewed rockets/spacecraft able to reach escape velocity?

Delta-V to LEO is about 10 km/s. From there to C3 (Earth escape) is another 3.2 km/s. It's just another 30% delta-V. The problem is the Tyranny of the Rocket Equation. More delta-V means more fuel. ...
Schwern's user avatar
  • 8,006
47 votes

Why didn't Voyager 1 and Voyager 2 crash on into Jupiter or Uranus when they approached near to these massive planets?

why weren't they completely attracted by their gravitational field? How much a trajectory is changed, depends on 3 factors: the mass of the planet, the speed of the spacecraft, the distance between ...
Hobbes's user avatar
  • 127k
46 votes

How many times do you have to circle the Earth to break orbit?

Zero See at: https://en.wikipedia.org/wiki/Escape_velocity for theory. Once you build enough velocity to surpass gravitational attraction, you will leave planetary orbit. A spacecraft simply ...
ingconti's user avatar
  • 499
46 votes
Accepted

How could an object barely exceeding escape velocity from the Moon eventually reach the Earth?

http://nbviewer.jupyter.org/gist/leftaroundabout/3955d27877e19be39d0f61fdafce069e Barely achieving escape velocity means you take a parabolic orbit. The thing with parabolic orbits is that they ...
leftaroundabout's user avatar
37 votes

Why is it easier to escape the solar system than get to Mercury or the Sun?

Changing orbits requires delta-v. To reach the Sun, you need to subtract delta-v such that your velocity relative to the Sun is near zero, which allows you to "fall straight down" into the ...
Nuclear Hoagie's user avatar
36 votes
Accepted

Non-orbital takeoff and landing?

TL;DR: it is inefficient. You should play some Kerbal Space Program and see for yourself the effects of travel in this way. Assuming, of course, you didn't really want to enter the orbit, but ...
Starfish Prime's user avatar
34 votes

Why is it so hard to build crewed rockets/spacecraft able to reach escape velocity?

It's not hard, it's just expensive. We know exactly how to do it. Compare this to building computer processors with 1nm transistors, or making reliable self-driving cars. Those are both things that we ...
spacetyper's user avatar
32 votes

How much bigger could Earth be, before rockets wouldn't work?

First, let us look at the rocket equation: $$\Delta v=\ln \left(\frac{m_0}{m_f}\right)v_e$$ That tells how much a rocket can change its velocity (the $\Delta v$). The requirements for reaching a ...
SE - stop firing the good guys's user avatar
32 votes

Has any human ever had the choice to leave Earth permanently?

Soyuz 11 The crew did not return to Earth in their lifetimes. This interpretation is obviously not what you are talking about though. Instead what is of interest is human's remains that do not return ...
Lex's user avatar
  • 1,338
30 votes

How fast is fuel escaping a rocket for it to reach the escape velocity 11 km/s?

The velocity of a rocket can exceed its exhaust velocity. It is possible for the velocity of a rocket to be greater than the exhaust velocity of the gases it ejects. ...The thrust of the rocket does ...
Organic Marble's user avatar
27 votes

How fast is fuel escaping a rocket for it to reach the escape velocity 11 km/s?

An intuitive way to think about it: You have a big rocket, composed of two parts of equal mass: the payload part and the fuel part. You launch the exhaust (fuel) backwards at 1 km/s (for simplicity: ...
SF.'s user avatar
  • 55k
25 votes

How many times do you have to circle the Earth to break orbit?

Think of this as a slightly different question, and the answer becomes more clear. How many times do you have to circle the Sun to leave orbit? The Earth has been orbiting our Sun for about 4.5 ...
James Jenkins's user avatar
25 votes

Why is it easier to escape the solar system than get to Mercury or the Sun?

Escaping the solar system requires adding orbital velocity to the spacecraft. Similarly, getting closer in the solar system requires removing orbital velocity. It turns out Earth is more out of the ...
Phil Frost's user avatar
  • 1,033
24 votes

Could a human jump off Mimas without return?

tl;dr: No chance, not even close! The escape velocity from the surface of a round (spherically symmetric) body is given by $$v_{esc} = \sqrt{\left(\frac{2 GM}{r_0} \right)}, $$ showing that it is ...
uhoh's user avatar
  • 149k
24 votes
Accepted

What is the most fuel efficient way out of the Solar System?

The most fuel efficient way to leave the solar system at present, is to launch into a trajectory that (like that used for Gallileo) may well involve one or several gravity assists from Earth or Venus, ...
Steve Linton's user avatar
  • 19.6k
21 votes

Why didn't Voyager 1 and Voyager 2 crash on into Jupiter or Uranus when they approached near to these massive planets?

To add to the answers @Hobbes & @Steve Linton posted, the mission designers indeed knew Jupiter's gravity field quite well from the orbits of Jupiter's moons. But before the Voyagers arrived they ...
Tom Spilker's user avatar
  • 18.3k
19 votes

What kind of mission objective would make a parabolic escape trajectory desirable?

Why zero excess velocity? Well, with almost zero excess velocity you can stay near Earth, but not too near. For example, the Spitzer space telescope did this to communicate with Earth while avoiding ...
Camille Goudeseune's user avatar
19 votes
Accepted

Is escape from earth, hyperbolic in reality?

Sure, it's an approximation. Perfect conic trajectories only happen in 1 or 2 body systems, a 2 body system can be reduced to an equivalent 1 body system. When $n>2$ in an n-body system, the ...
PM 2Ring's user avatar
  • 2,564
18 votes

Would it be possible to go beyond Jupiter without making any slingshot?

It is absolutely possible, just not advised. New Horizons was launched at Solar System Escape Velocity, meaning it could have visited anywhere beyond Earth without stopping. It did visit Jupiter, ...
PearsonArtPhoto's user avatar
  • 121k
18 votes

Apollo 11 mission report shows velocity well below escape velocity thousands of km on the way to the Moon

As @Rikki-Tikki-Tavi points out escape velocity is the velocity you would need at (or near) the surface of Earth to make out out of Earth orbit. Of course, just like anything thrown up into the air, ...
uhoh's user avatar
  • 149k
17 votes

Couldn't I escape Earth's gravity traveling only 1 mph (0.45 m/s)?

Escape velocity is the speed at which you'll leave the Earth and not return if you don't continue to propel your craft. Below that speed, gravity will pull you back down. If you want to keep ...
Russell Borogove's user avatar
15 votes

How could an object barely exceeding escape velocity from the Moon eventually reach the Earth?

It would be lost in space. If you barely reached the moon escape velocity, it means that your object will reach an orbit somewhat similar to that of the moon. From there, the orbit will be unstable ...
Antzi's user avatar
  • 12.7k
15 votes

Why didn't Voyager 1 and Voyager 2 crash on into Jupiter or Uranus when they approached near to these massive planets?

Let's try and understand how gravity works in space. This is kind of key idea to understanding lots of issues in space travel and astronomy. So imagine a space probe, or rock, which is heading in ...
Steve Linton's user avatar
  • 19.6k
15 votes
Accepted

Are there any accurate velocity plots of all spacecraft that achieved escape velocity from the solar system? (Pioneers, Voyagers, & New Horizons)

Wikimedia has the following graph for the heliocentric velocities of both Pioneer probes: (SVG) As far as I can tell it's accurate, since it clearly shows the velocity change of Pioneer 10 during its ...
SE - stop firing the good guys's user avatar
14 votes
Accepted

Why can't deep-space missions escape orbit by skipping off the atmosphere?

Skipping off the atmosphere can only lead to an escape if your speed going in was above the escape speed. The skip changes your direction, and it reduces your speed a bit. So if you enter a skip below ...
Hobbes's user avatar
  • 127k
14 votes

How much bigger could Earth be, before rockets wouldn't work?

note: I've accepted an answer 2.5 years ago. This paper was published recently so I thought I would add this supplemental answer since it may be an interesting reference for future readers. The Space....
uhoh's user avatar
  • 149k

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