moving in space?

How come in space you need an engine? i was reading an article and it said to get to Mars or beyond we would need the engine to be on the whole time. I thought that in space you didnt need an engine to keep going? Just like a first little "push" to get going the speed you wanted to go, and then you would keep that speed. im confused about that. someone explain.thanks

I think it's because constant thrust (well, at least half-way) would reduce the time required to get there. Also, the engine has to be on to slow down, so the end of the journey would require thrust too.

Perhaps they mean that a quick burst, then a long drift phase would mean a journey that would take a grat length of time.

You are right, in space, there is very, very little friction. I think I remember reading the density of space is a handful of atoms per square mile, so almost negligable.

Engines arent on in space. The aircraft sort of drifts. If they want to get somewhere fatser or land then they use the engine of the aircraft.

[Edited on 8-5-2004 by AD5673]

ya i heard theres about Zero percent of friction out there. My old teacher said that if you took a square foot of Space, that there would only be about 2-3 atoms of Hydrogen. And i also heard that if you were in space and gave succesive boosts of alittle bit more power, you would be able to go faster and faster. I saw a theory on tv of putting out a parchute on a spacecraft then using a bomb of somesort(probly atomic) to make the ship go extremly fast.

btw, is it possible to come to a complete stop in space?

Originally posted by masterofpuppets
btw, is it possible to come to a complete stop in space?

An object in motion tends to stay in motion unless acted on by an outside force

www.grc.nasa.gov...


I guess if you were good enough with thrusters you could totally stop a ship in space , but I think there would still be a very small amount of drift

btw, is it possible to come to a complete stop in space?

We had a brief discussion on this in an earlier thread:

www.abovetopsecret.com...

Basically, motion can only be considered relative to a given reference frame. So, if you're not moving within the reference frame, you have "stopped" in space. Is there an absolute reference frame? That's a good question. If the universe is infinite, I'd have to guess that there's not. Therefore, you could never really "stop." You'd always be moving relative to something else.

music playing in background Scorpions: We Burn the Sky

Quote "btw, is it possible to come to a complete stop in space"

Yes, if a force with a magnitude equal to the thrust and opposite in direction is applied to the object. This results in a net force of zero.

see the (c) in action with a game. Download maelstrom, a macintosh classic (Back when the LCII was popular), for windows by clicking the following link.

www.devolution.com...

Yes, if a force with a magnitude equal to the thrust and opposite in direction is applied to the object. This results in a net force of zero.

You're mixing velocity and acceleration here. Thrust applies a force, hence acceleration (force=mass x acceleration). If the net force on an object is zero, the acceleration is zero, but the velocity may not be. A complete stop means zero velocity. Again, velocity is relative. If you're sitting in a car going 45 mph, your velocity relative to the car is zero, while your velocity relative to the earth is 45 mph.

there are posts about this very topic. Yes, the only true reason for an engine is escape velocity.....motion to direct the craft, and motion to slow down.

Once we have a better grasp on solar wind theory moving out into the galaxy and beyond will prove much more reliable. Cheaper too.

Solar wind is created as the sun gives off heat. If we put a craft with a large sail above the gravitational pull that would return it to earth. All it takes is a small thrust to initiate the motion. (Like a hot air balloon rises, the expanding heat from the sun continues to produce thrust.)

Don't get excited yet. You still have to have some way of directing your path. And the initial motion is not going to get you very far at the outset.

Here's the great part.

We know that all orbiting bodies have a gravitational pull. That pull doesn't just disappear.
But at a certain point between all orbiting bodies there is a point where gravitational pull equals keeping everything in place. (This is why you don't wake up and find the moon landed in Omaha.)

It gets better. Once we have our craft moving and directed to our destination, we are going to penetrate this dead zone. It might take three days to get there by solar wind alone, but once we do the gravitational pull of the destination takes over!

So now we've got gravitational pull and solar wind moving us toward where ever we want to go!
Two froms of propulsion must be better than one when one is pushing and the other pulling. So our speed dramatically increases!

This leaves all our fuel for retro firing to decelerate.

Make any sense?

BTW, E=MC squared confuses me.
C= maximum constant speed in the formula.

Do you see the problem?
If we obtain the MAXIMUM CONSTANT speed, how do you SQUARE the maximum?
If you can square it, it's not the maximum, is it?

G

MoP: the Rovers did not have their engines on during the transit from Earth-Mars. After the insertion into an interplanetary orbit, only 3 course correction burns were scheduled in the cruise phase and 3 in the approach phase. (As well as a few small corrections to keep the solar panels/antenna pointed at the sun/earth respectively. Spirit skipped the last 2 corrections in the Approach phase and Opportunity skipped some of its corrections as well.

marsrovers.jpl.nasa.gov...

If we obtain the MAXIMUM CONSTANT speed, how do you SQUARE the maximum?
If you can square it, it's not the maximum, is it?

Why not? It's just a number that we're applying a mathematical operator to. Anyways, after you square it you don't have velocity anymore - I don't think there is a term for the resultant dimensions (m/s)^2=m^2/s^2.