Spaceships

[Shauney]

What causes a spaceship to be launcehd into space?

[rjkh]

nasa

[snook]

Thrust. The fuel, once ignited, causes a downward thrust that propels the vehicle upward. Huge amounts of fuel are necessary since it has to keep climbing vertically until it's reached escape velocity (about 7 miles a second I seem to remember) and can reach the upper limits of the Earth's atmosphere where the gravitational pull is negligible.

[Robert G]

PART 1 of answer:

I think snook is largely correct. However, I would like to make some comments relating to gravity and the practicalities:

While the craft has to keep gaining vertical height it does not do so vertically. Rather, its angle of ascent continuously departs from its initial vertcal position on the launchpad until it enters Earth orbit (at which time it is travelling horizontally, of course).

So far, so good. The craft, or what remains of it, has been launched.

Then, at the previously, and precisely, determined moment, which could be after a number of orbits, the rocket is fired to further increase the speed in order to overcome Earth's gravity which, contrary to what snook says, is most certainly not negligible at the orbiting altitude. Far from it, for the craft, being only a few hundred miles up, is still in close proximity to the Earth. (While in its orbit It may be in space - ie where there is no atmosphere - but it is helpful to think of it as being above the Earth's surface, not away from the Earth).

It helps, of course, that by now the mass of the remaining portion of the spacecraft is considerably less than that of the original craft which sat on the launchpad; it has spent a huge mass of fuel, and large portions of its structure (essentially fuel tanks and main thrusters in one or more stages) have long since been jettisoned as part of the launch process.

(Continued in Part 2)

[Robert G]

PART 2 of answer:

The thrust introduced during orbit propels the craft not vertically away from the Earth, but increasingly farther away from its orbit in a sort of unwinding spiral (ever straightening) trajectory.

The calculations necessary to achieve all this are hugely complex due to the continuously changing mass, changing gravitational pull, and changing speed. And, of course, the spacecraft never really travels in a dead straight line through space because it is always acted upon by the changing gravitational pull of stars, planets, and moons, drawing in all sorts of changing directions.

This is why occasional course corrections have to be applied through multi-directional thrusters on the craft. This is extra complex If the craft is unmanned because, in signalling the correction instructions from the base (which so far has been on the Earth) allowances have to be built in for the time it takes for the signals to travel the increasing distance between the base and the craft.

Welcome to astronautics, Shauney!

[Postdog]

And I thought it was a guy at the bottom lighting the blue touch paper. Just goes to show you, dunnit?.

[halfadaily]

very interesting Robert, and I thought it was Flash Gordon pushing the big black lever thingy!

[snook]

That's what I meant to say, Robert G! But you have to understand, Shauney's new to all this and I didn't want to intimidate him with so much detail.

By the way, the fact that it really is so complicated (and I don't doubt that it is) does tend to make one wonder if there's actually some truth in the conspiracy theory that there never really was a Moon landing. I mean, did we really have any computers that could have coped with those calculations back in the Sixties? I have trouble working it out in my head even now, and I've got a calculator.

[Caladon]

Snook, a calculator... but do you have a first in physics and mathematics from Cambridge ;o)

[Robert G]

Ha, ha! Sorry, Shauney, I didn't mean to blind you with science - or should I say with my pseudo-scientific thoughts on how it's done. I'm sure it is more complicated than I have tried to indicate.

And to get to the point where your spaceship is travelling through space, having successfully escaped the Earth's gravitational pull, is one thing. What I really marvel at is how we are able to approach other (orbiting - ie moving) planets on the right trajectory, at the right speed, so as to go into orbit around them, and then to descend from that orbit and actually land on the surface of the spinning planet at a predetermined location. Without a pilot on board. Even with all the computing power available today, it's still mind boggling.