Why cant the Falcon Heavy fly in a straight line to orbit?

[SVBarnard]

from twitter: https://twitter.com/elonmusk/status/330395232564826112

"Speaking of F9R, how do you plan to recover the FH center core? Seems it would be going too fast/far for direct boost-back."

Elon: "Yeah, that is super tricky. Will have to sacrifice a lot of payload to boost back or land on ocean platform."

"Is it possible to launch from Texas and land in Florida?"

Elon: "Side boosters fall short & center core goes too far + Florida is heavily populated. Landing permission tricky "

So someone please explain to me why the Falcon Heavy cant just fly straight up, directly up, in a straight line to orbit? Seems this would solve their boost back problem?

So the rocket flys diagonally across the sky, it doesn't fly straight up? There must be a good reason for this, please explain?

does the falcon 9 also fly downrange, if so how come they're able to have the first stage boost back to land and not the falcon heavy's?

Its just that I intuitively thought that rockets fly straight upwards to orbit.

[Robotbeat]

Because it's very inefficient... A lot greater gravity losses.

[SVBarnard]

I mean if the rocket just flew straight up, there would be no boosting back to do, all it'd have to do is fall straight back down to the landing pad, so why  in the hell do they fly it at an angle across the sky?

I've been racking my brain over this.

[Robotbeat]

Read this: https://what-if.xkcd.com/58/

[SVBarnard]

Because it's very inefficient... A lot greater gravity losses.

So you're saying there is more of a tug-o-war with the earth's gravity is they fly straight upwards?

Doesn't the falcon 9 fly in a pretty straight line to orbit though?

[Robotbeat]

Seriously, read this: https://what-if.xkcd.com/58/

[Burninate]

Because it's very inefficient... A lot greater gravity losses.

So you're saying there is more of a tug-o-war with the earth's gravity is they fly straight upwards?

Doesn't the falcon 9 fly in a pretty straight line to orbit though?

*Orbit* is not a place.  It's the combination of gravitational relationships, position, and very importantly, velocity.  Something in Low Earth Orbit is flying a circular orbital path - the Earth's gravity is bending its orbit at a certain amount per second, and it's flying past the Earth very rapidly, changing its orientation at just about the same amount per second.  It's not very high above Earth - 1/20th of an Earth radius - and the *only* reason it's staying up there, is because it's moving very fast.  Something that was stationary at ~300km above, say, the North Pole, would drop to the Earth at an initial acceleration of something like 99% of the acceleration it would feel on the surface - you don't save much gravity in low orbits, for that you need many Earth radii of distance.  The *horizontal velocity* is what's required to keep it up there, to fight gravity.

[kch]

... I intuitively thought that rockets fly straight upwards to orbit.

If they just flew straight up, they'd fall straight down again -- along with whatever they were carrying.  There are rockets that do exactly that ... they're called sounding rockets.  They never build up much (if any) sideways speed, so they never achieve orbit.  You may find these links helpful:

http://www.braeunig.us/space/orbmech.htm#launch

http://en.wikipedia.org/wiki/Orbit#Understanding_orbits

 

[Damon Hill]

Altitude is necessary to get out of the atmosphere and eliminate drag.  Velocity (17,000+ mph) tangental to the Earth's surface is necessary to stay up there, essentially falling at a right angle to Earth's gravity.

The first stage's main job is to get the upper stages/payload up and out of the atmosphere, and started downrange to get going on the velocity.  It might be possible to mostly go straight up to orbital altitude and let the upper stages do nearly all the velocity gain, but I think that's highly inefficient.

[Burninate]

I would also strongly recommend Kerbal Space Program, if you want to learn orbital dynamics to a very intuitive level, and have fun doing it.

[Burninate]

Altitude is necessary to get out of the atmosphere and eliminate drag.  Velocity (17,000+ mph) tangental to the Earth's surface is necessary to stay up there, essentially falling at a right angle to Earth's gravity.

The first stage's main job is to get the upper stages/payload up and out of the atmosphere, and started downrange to get going on the velocity.  It might be possible to mostly go straight up to orbital altitude and let the upper stages do nearly all the velocity gain, but I think that's highly inefficient.

And altitude is *cheap*.  About 85% of velocity is spent increasing horizontal velocity, ~1% is spent fighting aerodynamic drag, ~12% is spent fighting gravity, something we have to do temporarily to stay above the atmosphere while we build up enough speed to orbit, and only around ~2% is spent on a Hohmann transfer to a few hundred kilometers higher above the Earth than the surface.

[Nibb31]

Getting to orbit isn't about altitude, it's about speed. To reach orbit, you need to be travelling parallel to the ground at ~27000km/h/17000mph.

The reason we go above the atmosphere to reach orbit is because the drag would slow us down and make us fall back. Other than that, you could orbit at sea level as long as you went fast enough.

And straight lines don't exist in spaceflight, you are always orbiting something.

[Tnarg]

As others have pointed out you seem to misunderstand what orbit is.  Let me try to explain. Imagine you're standing on a 1 meter high table in the middle of an open landscape.  Look to the horizon.  To get into orbit at this height you are going to have to run off the table so fast that you reach the horizon before you hit the ground.  Thats what orbit is.

Now if you were to travel that fast air friction would slow you down very quickly which is why you can only really be in orbit in space.  Orbit is not a height it's a sideways speed.

A rocket could fly straight up then turn 90 degrees drop it's stage and then start flying sideways and yes that would make recovering the stage easier,  It has been take about on these forums, but it's not an efficient way to get into orbit.

[pagheca]

I mean if the rocket just flew straight up, there would be no boosting back to do, all it'd have to do is fall straight back down to the landing pad, so why  in the hell do they fly it at an angle across the sky?

I've been racking my brain over this.

Let me try too...

A "useful" orbit require 2 conditions to be respected:

(1) reaching the orbital speed at the point where you switch off the engines (you have to, soon or later, as fuel is limited).

(2) injecting the payload on a trajectory that doesn't intersect other bodies and in particular the Earth.

To explain this better, let me ask to jump on your feet. Now!

Some people can't see that easily, but while you are on air you already respected condition (1): you are orbiting the Earth as you reached orbital speed for that point. If you could pass through the Earth with no friction (imagine there is a vacuum tube copying exactly your trajectory and getting across the Earth), you would fall down toward the Earth center, acquiring speed, than you would re-emerge on the other side etc. and continue forever oscillating between these two points (actually I'm simplifying and the trajectory would be a bit more complicated but the core of my reasoning is correct): you would be in orbit.

So, the real problem is not only reaching orbit, but doing this in such a way that you are on a trajectory not colliding with the Earth any soon (I'm now neglecting the atmospheric friction).

If you launch a vehicle straight up, the problem is NOT really the gravity factor (you would just sacrifice some payload but the balance if you want to recover could be positive), but the fact that the payload would be injected on a trajectory that would make him going up up up and then... down down down, ending up in a crash near the launch site (not really, as the rotation of the Earth would move it toward Earth, but this is not essential).

In other words, the trajectory of a launch vehicle is designed in such a way to minimize the use of propellant required to put a given mass in a trajectory not intersecting the Earth (or other celestial bodies) any soon, apart from secondary correction requiring a relatively limited amount of fuel.

Launching straight up would mean your payload would soon or later, independently from the speed acquired, return to Earth.

In some way, the problem of rocketry is not to reach a VERY high altitude (that could be done also by a modified nazi V2 rocket), but injecting the payload on a trajectory that doesn't intersect that Earth. This, in turn, requires VERY high speed and therefore kinetic energy. But giving that kinetic energy to the payload is not enough if you are not on the proper trajectory.

I would be curious to know if you got my point.

[K-P]

So someone please explain to me why the Falcon Heavy cant just fly straight up, directly up, in a straight line to orbit? Seems this would solve their boost back problem?

So the rocket flys diagonally across the sky, it doesn't fly straight up? There must be a good reason for this, please explain?

Oh dear...

This must be trolling.

Please let it be just that.

[Jarnis]

...and before the OP asks, yes it is theoretically possible to launch a rocket that is going to leave Earth completely (interplanetary trajectory) by flying it straight up.

However, this is highly inefficient due to additional gravity losses (energy spent fighting gravity instead of adding velocity). So such a trajectory is not used.  Get Kerbal Space Program to experiment yourself and see why not

It is possible to launch on a more "lofted" trajectory - steeper than normal - to keep returning stages closer to the launch pad but this is a tradeoff - you'll rely more on the second stage to do the big job of reaching orbital speed and eat more gravity losses. Less payload. Orbcomm launch actually flew a bit like this, partly because it was heading to a fairly high orbit, partly because there was a ton of extra margin on the launch (very light payload compared to F9 v1.1 capabilities).

Also for any manned launches, "lofted" trajectories add an extra kink - if you need to abort and separate the crew capsule from the rocket before the trajectory starts to flatten, it will emulate a sounding rocket - go up and then come down very steeply potentially too steeply for the heat shield and/or the crew (G-loads) to be able to take it. So such a trajectory wouldn't work for manned launches.

Normal re-entry is gentler because the capsule gets to shed a lot of speed "skimming" the thin upper atmosphere before hitting the lower parts. No such luck when coming in very steep.

[Jarnis]

So someone please explain to me why the Falcon Heavy cant just fly straight up, directly up, in a straight line to orbit? Seems this would solve their boost back problem?

So the rocket flys diagonally across the sky, it doesn't fly straight up? There must be a good reason for this, please explain?

Oh dear...

This must be trolling.

Please let it be just that.

Personally I'd place my bet on "general level of education in [insert country of the original poster here]".

Not a big deal, plenty of people ready to educate a new guy in these forums

[K-P]

Not a big deal, plenty of people ready to educate a new guy in these forums

True.

I also HAD a girlfriend asking me in the middle of some space-related conversation (or monologue as I am usually the only space-geek in the group) that "But how can they drive rovers on Mars because there's no gravity there, because space is weightless place?".

So, no need to tell, soon after this we just had to break up. I mean, really, we had to.

[pagheca]

This must be trolling.

Maybe. But I noticed that If you speak to 100 people, including some with an high level degree, you will find that most of them think that space exploration is about altitude, not speed.

[pagheca]

Not a big deal, plenty of people ready to educate a new guy in these forums

I also HAD a girlfriend asking me in the middle of some space-related conversation (or monologue as I am usually the only space-geek in the group) that "But how can they drive rovers on Mars because there's no gravity there, because space is weightless place?".

I will start a thread about most funny questions and misconceptions we got about space right now. Hope Chris and moderators will find it usefuls.