why do spacecrafts need continuous propulsion systems whereas there is no any other force to slow them down?

Answer 1

You have great answers, I debated about whether or not any more information was necessary.

Most current spacecraft do NOT have continuous propulsion systems. They boost for a short time to achieve escape velocity. They also boost around other planets to take advantage of gravitational slingshot effect. Cassini, for example, boosted from earth to Venus and back to earth again before heading off to Jupiter for yet another gravity assist. In between each planet it was not burning fuel--only at the planets themselves. It used more fuel braking into the Saturn system. So the fuel was used primarily at takeoff and final approach.

To shorten trip times, a spacecraft could boost continuously, but this would require a huge fuel supply, if chemical rockets are used. Ion drives have extremely low thrust--you cannot achieve escape velocity with them. However, the advantage is that the fuel is very light weight--you can boost with ion engines during an entire trip. Although the acceleration is small, it adds up over time.

In summary, the longer you can leave the engine running, the shorter your trip time will be. But only half way--half the fuel used must be to slow the ship down for the landing. Otherwise, you could just boost straight the entire trip, making a really short trip, but a really big impact crater upon arrival...

Answer 2

So far all the answers that have been given are correct. I saw in a book one time about a type of propulsion system that would work in space where it thrust itself by electrons and with the experiment they did with the copper trailing cable that was dragged behind the space shuttle that produced thousands of volts so much so that it burnt the cable in two. So if they could combine the two technologies they could produce thrust without fuel and just use the magnetic field of most of the planets to get around. Oh and yes they could also use this force to slow down the spacecraft also before they run into a planet! What I can't figure out is why haven't they done this before now since the information already exists? I guess we need a non college educated type like Orville and Wilbur Wright to show them, I mean after all you don't really need to go to college to be very intelligent now do you?

Answer 3

Gravitational pull is very much there to slow them down. That is why continuous propulsion is needed. Once they are in stable orbit or are in free fall, the propulsion system is switched off and is restarted only when again nearing a gravitational field. And sometimes, a low power system is kept on so that a small but steady acceleration is provded to increase the speed of the spacecraft and thus reduce the travel time. Such systems are usually based on solar sails (light exerts a small but definite pressure on the sail and pushes the spacecraft away from the sun) and nuclear isotope based (a small stream of alpha particles or some similar particles is continuously ejected from the rear giving a thrust to the spacecraft).

Answer 4

Partly so that the spacecraft can continue to increase its forward velocity. In addition, a spacecraft does not usually travel in a straight line; it needs the propulsion system to correct its course or change its direction of travel.

Answer 5

Present day Spacecraft do not use continuous propulsion systems.
They cannot carry enough fuel to use it continuously.
The main fuel tanks are all jettisoned after using up their fuel.

As it is they are lucky to have enough fuel stored to be able to steer themselves into orbit, or to make small course corrections, and still have enough left for docking, and returning.

Even the mars probes coast almost all of the way once they are headed in the right direction.

Answer 6

The Ion stuff is exceedingly a lot it top now. yet something that could convert power from nuclear reaction into kinetic stress eminating from the returned of the craft might artwork. It purely seems now that the stream of Ions is the proper selection for it. there is been some talk of image voltaic "sails" which would be pushed via image voltaic wind like the tail of a comet, yet they might might desire to be inconcievably huge and can take forever to enhance up with out tips at launch from something like an Ion force.

Answer 7

They don't. Even the crafts that went to the moon coasted most of the way without power. they only need propulsion to escape gravity or change direction. If we send a craft to mars, it will coast most of the way.

Answer 8

I like the other answers, but I am going to go a different route. You use continuous thrust because you can only carry so much oxygen, food, water, etc... So you get there and get back in a hurry so you don't run out.

Answer 9

mainly to keep them in the right direction. even in the vacuum of space forces from various bodies of mass (stars, planets, debris and space gas) still act on the spacecrafts