I still don't understand why our current spacecraft travel so slow in space. Can anyone explain?

Question

For example a 500 day trip to Mars, with Mars at close approach of 35 million miles works out to 2900mph. That's no better than our top military jets that have to 'swim' through our dense atmosphere, whereas space is a vacuum!
Also, we regularly go 17,200mph just to reach orbital velocity, and need 25,000mph (?) to escape earth entirely.
So, how do we end up with a turtle 2,900mph once in space?
Is it a matter of fuel? If so, why can't we just shoot big tanks of liquid hydrogen into earth orbit, send up our space craft, bolt the tanks on, ignite the fuel and zip along at 25,000mph or even 100,000mph, at least until the fuel runs out?

Answer 1

mass accretion increases exponentially with V,,  the fuel required makes travel at C impossible,,at present,when basic forces in the universe are understood,a method to negate or minimize mass will help us go xxxxxx  times faster

Answer 2

To go faster takes more fuel, a lot more fuel.  Look at the size of the Apollo spacecraft that launched from Earth versus the bit that came back.

 

And there are no tankers in space.  

Answer 3

The speed of the motion is dictated by the amount of power  given to the space ship

Answer 4

The closest approach of Mars may be 33 million but the trip taken by the space ship is a portion of an ellipse so the actual distance can be many times more

Answer 5

First, your math is wrong. Try the estimated 186 day trip to mars.

We get 25,000 MPH now using slingshot maneuvers for acceleration, then just a coast with a touch of course correction. And not in a straight path, you forget gravity is still there.

That escape velocity takes the fuel and power of like the Saturn 5.

NASAs new HLV matches that with solid fuel.

Look what it takes the shuttle just to get into low earth orbit. Just enough fuel left to slow down to reentry and attitude rockets. Then it is a flying brick.

The smallest rocket to even get to orbit was a Japanese job that carried just a Kg payload:

https://global.jaxa.jp/projects/rockets/s_rockets/images/projects_07.jpg

Answer 6

You have to consider the size of the rocket, its fuel and its payload. If the payload is big (i.e., you, and enclosure food water etc.) then it takes 1 rocket a fifty to a hundred times bigger to hold the fuel just to get you out beyond eartth's orbit.  And even then you're just coasting the rest of the way having used up all or most of your fuel.  This is why we need new technologies which are lighter and longer lasting so we can build ships that aren't out of fuel by the time they leave earth's orbit.



Or we go on with unmanned missions which are lighter and so require less fuel to push them on their way. A robot probe does not need to carry food and water, air filtration systems etc. 

Answer 7

The Velocities and distances you are explaining are Relative

Space Travel is not just so Straightforward

Gravity really plays a roll despite being the weakest force in the Universe

A linear Velocity of 17. 500 mph is needed to reach orbital Speed above Earth's Atmosphere

To achieved that, Vertical Take off is still the shortest and most fuel efficient way

The Shuttle quite cleverly used a detachable fuel tank and two Rocket Boosters

All jettisoned as dead weight when empty

 Staged Rockets were the most efficient because of that idea

The idea of placing Fuel Tanks in space would be all fine and Dandy, but there is extra costs and the problem of getting to it

 There could be power and fuel wasted if it had to power down then up again

Attaching it adds mass and Momentum and not essentially velocity

Since Apollo, Earth Orbit has followed Newton's Third Law of Motion

An Object in Orbit will remain at its Velocity and Vector until an extra Force is applied to it

Acceleration gains Altitude, and Deceleration Looses Altitude

This Gravitational Arc is continually used

Apollo used it for the Moon and Back

It meant that the minimal Fuel could be used

In the Sixties, Nasa sent 6 Viking probes to experniment on the Moon for its suitablility for Landing

One even had a Scoop to test the depth of the Substrate

Shot Vertically out of the Atmosphere on a direct Vector to the Moon, they took 3 days for the trip

Retrorockets slowed them down and were stopped short of the Lunar Surface so they didn't cause any disturbance of the Regolith

Out of the 6, 2 craft Crashed

Apollo 12 were able to visit one of the Crash Sites and deduce that the retrorockets failed

 Traveling to any of the Planets requires a Hyperbolic Route, known as the Hohman Transfer

Voyager Two went on the Grand Tour using the Hohman Transfer with Gravity assists and a Special alignment of the Big Four to Visit them all

 New Horizons is the latest probe to Go into the Kuiper Belt

Launched in 2006 before the AIU's fateful decision

It has visited Pluto to give us photos of all Nine 

Then visited Ultima Thule that thrilled us by its weird appearance

It is finally travelling towards another known KBO where it will use a Gravity assist and its remaining Fuel to set course for the Oort Cloud

Answer 8

Jets don't go that fast.  Nor is a trip to Mars that slow.  You also forget that you can't go there in a straight line - Mars is moving all the time so you have to aim ahead of it.

Answer 9

>>I still don't understand why our current spacecraft travel so slow 

>>in space. Can anyone explain?

I'm not sure "slow" is the word... Most would leave Earth in excess of 30,000 to 32,000 mph with respect to Earth.



>>For example a 500 day trip to Mars, with Mars at close 

>>approach of 35 million miles works out to 2900mph. 

That's true, but... no one is talking about a year and half mission to Mars.  To *get* to Mars, it's estimated to be a 6 to 9 month mission - about 180 to 270 days.  





>>That's no better than our top military jets that have to 'swim' through 

>>our dense atmosphere, whereas space is a vacuum! 

Agreed, but there are two things to consider: Fuel needed to boost the speed of the craft to reach Mars, and then - fuel needed to *slow down* for arrival at Mars... When Apollo went to the moon, they left Earth on a 'free-return' trajectory, meaning, if the engine failed, they'd loop back around towards Earth.  It was a safety issue in case there were problems. (Apollo 13, for example, left Earth on Free-Return, then burned their engine to *leave* the free return trajectory... after the accident, their primary focus was to return to the trajectory to get back home...) 

For Mars, there was a discussion about a proposed design that - if the engine failed at Mars Arrival, the speed of the craft would allow solar gravity to pull it back towards Earth - a 'fail safe' trajectory.  But - the caveat is, you need to travel at a slightly slower speed than what's possible if you don't have 100% faith in your engine(s). 



>>Also, we regularly go 17,200mph just to reach orbital velocity, 

>>and need 25,000mph (?) to escape earth entirely. 

Not precisely true; you need 25,000 mph to reach the moon, but it's not truly escape velocity... 



>>So, how do we end up with a turtle 2,900mph once in space? 

So... your 2,900 mph is based on an Earth/Mars straight line distance at closest approach.  And, that's not the way to think about it. Below is an example of the trajectory a spacecraft would use... You'd launch about 6 months prior to closest approach, then intersect Mars' orbit on the other side of the Sun.  It's a much longer journey than 35 million miles. 



>>Is it a matter of fuel? If so, why can't we just shoot big tanks of liquid 

>>hydrogen into earth orbit, send up our space craft, bolt the tanks on, 

>>ignite the fuel and zip along at 25,000mph or even 100,000mph, at 

>>least until the fuel runs out?

Partially - how much you can carry to boost your speed, versus how much you can carry to *cancel* your speed upon arrival.  (And - the consideration of having a mass of volatile fuel on board for 6 to 9 months...) 

Answer 10

In the first place, it doesn't take that long as you said (500 days) but about 6 to 9 months. Then one more thing, the craft will not go straight to the red planet as it leaves Earth. It takes a round curve around the sun in order to obtain a rendezvous in space far away from its launch position. You see, Earth takes 1 year to go around the sun while Mars takes almost 2 years. Therefore, there can never be a straight line travel to the planet, otherwise it would  miss it.

Answer 11

Sorry but that is due to the laws of physics, which we cannot change.



Spacecraft travel at enormous speeds, but planets like Mars are enormous distances away. That is why it takes so long.

Answer 12

That might break the ship apart. Plus, once they burn up most of the fuel

to escape the Earth's gravitational pull, they have to coast on what

they have left.

Answer 13

First, it takes roughly 6 to 8 months to travel to Mars, not 500 days.  Second, the 35 million miles is the straight line distance at the closest approach.  Nothing in space travels in a straight line and neither Earth nor Mars are standing still.  If you launched the spacecraft toward Mars at it closest approach, the Mars would have moved quiet a distance by the time the spacecraft gets there.   Normally you launch some time before the closest approach; the probe travels on a curved trajectory and catches up to Mars.  And third, you don't want to be going too fast if you want to actually orbit Mars, not wave at it as you zip by.  You will actually have to slow down a little to enter the orbit.

Answer 14

The expense and flammability of putting hydrogen. Into space. Hydrogen is highly flammable. Watch the Hindenburg burning 50 times. The expense of putting ANY mass in orbit is a  trade off between how much fuel it takes to get it out of Earth's gravity well and how much fuel it will take to accelerate that mass to higher velocities.



2900 mph RELATIVE TO WHAT once it gets into space? Earth, Mars, the Moon, Jupiter, Titan, the Sun? It also takes fuel to SLOW down to be able to go into orbit or land once it gets there. You have to aim to where the planet or moon WILL be, not where it is when it takes off. There are no gas or hydrogen and oxygen in space. Fuel will not burn without oxygen. Look at the Voyagers, still going more than 43 years later after at least one or more gravity assist trajectories around one or more gas or ice giant planets on radioactive fuel. There is NO friction in a near vacuum to slow them down. It will still take them more than 44,000 YEARS to get anywhere NEAR another

Answer 15

we need twice as much fuel...one to speed up and 2 to slow down...the faster you go the more fuel you need in the reverse in order to stop

Answer 16

they don't travel to mars by taking the shortest, straight line course you're describing.  that would cost a whole lot more fuel than they're willing to haul along.  they spiral out there until they catch up with mars



a straight line course, with some kind of appropriate engine and fuel to power that kind of extravagance, would take a lot less time