74

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 human ever had the choice to never return to Earth? Apart from the Apollo missions, no crewed spacecraft has had anything like enough propellant to leave ...


35

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 wanted to e.g. go to the Moon or deep space probing. Especially in conjunction with Wikipedia's note about not having to attain escape velocity to leave gravity well....


30

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 to Earth ever. In this case there is also a definitive answer. Clyde Tombaugh Tombaugh died on January 17, 1997, when he was in Las Cruces, New Mexico, at ...


22

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, but which eventually gets you to Jupiter. If you can get to Jupiter you can almost certainly do so in such a way as get a slingshot into a solar escape ...


19

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 radiant heat from Earth. It's been drifting away, but slowly enough that other factors first reduced its effectiveness.


12

Why would one want to choose zero excess velocity upon escape? If you aren't in a great hurry, and you have a small delta-V budget, and you want to visit the Trojan points L4 or L5, you can do so by getting just outside of Earth's sphere of influence, then lowering or raising your solar orbit very slightly to get ahead of or fall behind Earth. You wouldn't ...


12

If you want to avoid gravity assists, the most fuel-efficient way out of the Solar System is to launch due East from from a launch site in the Ecuadorean Andes, sometime before local midnight on a January 3 when there's a new moon. This gives you the maximum possible benefit from the Earth's movement, leaving only about 12,000 m/s of delta-V needed in ...


12

Escape velocity is the velocity at a given altitude (usually the surface) that is enough to leave the body's sphere of influence with a positive net velocity. But if you leave a body at exactly escape velocity, your velocity bleeds off as you climb in exchange for gaining gravitational potential energy, and your velocity tends to the limit of zero at ...


10

Your question is, as I understand it, pointing out that there are two ways to get from the surface of the Earth to the surface of the Moon. Way one: Burn upwards until through the thickest part of the atmosphere to avoid aero drag. Burn sideways to attain orbital velocity and raise apogee and perigee into space. From Earth orbit, burn prograde to attain ...


9

Earth departure burns can be relatively leisurely, so the acceleration tends not to be extremely high. There is some tradeoff between doing the burn over a short timeframe to maximize the Oberth effect, versus using a smaller, lighter engine and maximizing crew comfort. At the start of the Apollo TLI, acceleration would be about 0.6g, increasing as fuel ...


7

This image is from Quora because the picture I took from my Saturn V Haynes Manual was too big to upload. Anyway, you can see that the acceleration is by no means constant, but it peaks at just under 40 m/s^2, or around 4g. And it was a wild ride. In particular, when the first burn ended the entire structure, which had been compressed, snapped back. ...


7

The Sprint missile could get up to 3 kilometers a second very briefly and with the outside shell going white hot. https://en.wikipedia.org/wiki/Sprint_(missile) That is approximately 1/3 orbital velocity or 1/4 earth escape velocity, depending on which one you meant. Going faster will involve exponential increase in needed power to overcome drag. And ...


6

Developing on Nathan's answer, let's do some math. For simplicity we suppose here that we are not really going to the Moon, that only Earth's gravity us relevant. We leave at escape velocity, 25,000 miles per hour from an altitude of 4000 miles above the Earth's center, and climb straight up. As we do so our velocity decreases against Earth's gravity but ...


6

Let's focus on the "why weren't they completely attracted by their gravitational field" question here. You've probably seen Newton's cannonball diagram before: In this diagram, the distance from the object to the planet is fixed, and it's the speed that changes, and gives different results: too slow (A or B, below orbital speed): it will indeed be pulled ...


5

No and yes. Rockets are costly things and no human ever left Low Earth Orbit, except the Apollo astronauts. Others had not enough fuel to do that. The Apollo astronauts had theoretically the option to contradict their mission requirements and choose death on the Moon on Moon orbit or somewhere between the Moon and Earth by commiting a suicidal sabotage. ...


5

At the heart of this question is how the gravity assist 'works', at least an intuitive understanding of it. When a space probe uses gravity assist from a planet, it gets some energy from it, which (yes) incidentally slows the planet down slightly. How does it do it? Imagine a tennis ball in flight towards an ideal moving tennis racket. The ball rebounds ...


5

Parabolic escape trajectory is only theoretical, it only "works" in a two body system, and in a two body system "escape" is a meaningless practice anyways. In a multi body system the forces from other bodies, especially around the edge of the gravity well, make parabolic escape impossible: before you'd have zero velocity the other body would've already ...


5

For getting to the moon specifically, there's an extra problem, on top of what's already been mentioned: presumably, your objective when you get to the moon is to either orbit it or do a nice gentle landing on it (if your objective is to turn yourself into a cloud of shrapnel spread over a large area of regolith, feel free to take your approach). That is: ...


4

Probably it will not work. The problem is that gas molecules have a wide distribution of velocities; most molecules in a gas are not really close to the rms velocity. Over the course of billions of years we should expect faster molecules to escape. At some point all the molecules have become "faster" at one time or another and make a run for it. To ...


4

I can't think of one. For mission planning there is nothing special about parabolic velocity. There is something special from the perspective of teaching orbital mechanics as it is the boundary between closed and open orbits, but from a practical mission point of view it looks just like a very long ellipse or a barely open hyperbola for many, many years. ...


4

Newton discovered gravity (and invented mathematical laws to describe it) a long time before Pioneer 10 flew! It has been possible to calculate the mass of the planets with a fair degree of accuracy for a very long time, based on their effects on each other, as well as on their moons, and on passing NASA space probes. There were very well worked out laws ...


4

In addition to the answers above, one should add that assuming you can get to Mars very, very fast, you will therefore arrive there with a very high velocity relative to Mars. This makes the problem of landing on Mars much harder. Also, if something goes wrong at Mars insertion, the Martian explorers are hurtling off into deep space with no way back. The ...


4

By combining two answers (18.25km/s dV is a reasonable launch to solar escape and ~18km/s total dV of the Saturn V (before the lunar lander)) means yes, the Saturn V could have without any gravity assists. But the second post makes it clear they are not including payload, like the Apollo spacecraft, so lets do that math: | Individual stage | Total ...


4

According to Wikipedia: Escape velocity is actually a speed (not a velocity) because it does not specify a direction: no matter what the direction of travel is, the object can escape the gravitational field (provided its path does not intersect the planet). It may seem nonintuitive that an escape trajectory directed “downward” could escape just as easily ...


4

Going to a celestial body, entering orbit, then having to shed all that orbital velocity. If you were travelling slow enough as it is, and slowly decelerating all the way, counteracting gravity, it would take you loads of time probably, but surely there must be another reason why it can't be done, else why wouldn't we do it. Since others (specially Starfish ...


3

I do not have the book, so lets look at the script, in particular page 99 and following: JOHANSSEN Velocity 850, altitude 1843 -- [...] JOHANSSEN He’s well below target altitude. LEWIS How far below? JOHANSSEN Working on it [...] JOHANSSEN I have interval pings. Intercept velocity will be 11 meters per second... BECK (OVER COMMS) I can make ...


3

As everyone else has mentioned, there doesn't seem to be a mission for a true parabolic escape, especially since an exact parabolic trajectory is a target of zero size and therefore there is a zero chance of hitting it exactly. Also, a true parabolic orbit only makes sense in a two-body model. Once you consider the gravity of anything else, the orbit ...


3

Here is a list of equations you'll need to determine orbital velocity at different points, orbital velocity required to orbit, apoapsis, periapsis, mean anomaly, true anomaly, and eccentricity. This is the best I can give you as there is no formula that calculates fuel consumption because it entirely depends on the type of engine and etc. To determine the ...


2

The short answer is that ruling out world-building thought experiments to increase mars' escape velocity; nothing can be done to prevent water vapor from escaping which is precisely why it has so little water compared to Earth. With that said, Mars' water escapes on astronomical timescales while the goal of any type of terraforming activities would be to ...


2

If we interpret the question as asking for the highest speed relative to the primary of any closed orbit, then it becomes answerable. The orbit you want will basically skim the surface of the body (or the top of its atmosphere) at closest approach, and recede as far as possible before the perturbing effects of other bodies mean it would no longer be a ...


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