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. 

[K-P]

you will find that most of them think that space exploration is about altitude

It's about attitude. (like Elon Musk & co.)

[QuantumG]

Rockets are like women Billy...

[Jet Black]

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

I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

[K-P]

I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

Yes...

And I think they definitely should.

Considering how much e.g. the Sun is affecting our daily lives, it is truly devastating to see how little comprehension people do have about its structure, mechanisms or even size and distance from us.

Or space in general. We are constantly "in space". Space is around us. Still, lot of people see space as a separate thing from our existence and life on planet Earth. Just like the legendary gravity. That somehow "in space" the gravity works in different ways or does not exist...

Even I had only 1 astronomy-class in high school, and I went to a "mathematical/scientific" high school...!
And in elementary school we had maybe a 15 minute session about astronomy and planets at the beginning of geography book. And teacher very professionaly backed this up by saying "ok now, everybody interested in this stuff can read it at home, now then, let's start with geography of the Benelux-countries...".

OK, this is clearly a topic of its own already, but still... I can't imagine how people deciding about the guidelines of education in our country (and countries worldwide) do not recognize the importance of space sciences / astronomy even today and it's wider meaning to young people in understanding the scales of universe and opening up fresh perspectives. It is sad.

Those who have natural interest in these things will find the information and learn. But those who never get the initial spark by themselves propably will never find it in the school either. After all, it is far more important to know the geography of the Benelux-countries at that moment when solar storm is wiping out half the civilization...

[R7]

Rockets are like women Billy...

So true.

Gorgeous outside, ice-cold inside.
Awful lot of planning ahead and everything including the positions of celestial bodies must be in order to get them excited.
Then will liquids flow down-there, sparks fly and they are on fire.
Their bodies tremble and a few minutes of fierce thrusting ensues, ending abruptly with a vision of bright stars.
After excitement calms down you notice she's left you for good.


("but ... but F9R returns!?" you say? Yes, there's hope in the rocketry...)

[ncb1397]

People on this forum should remember that all the most brilliant minds in human history didn't understand orbital mechanics and gravity until a few hundred years ago - a small slice of time on the scale of human civilization. It is certainly not obvious and all the people here still wouldn't understand it without someone explaining it to them.

[Jet Black]

I think people sometimes get caught up in the idea of zero-g meaning weightless, and thinking that things just float there, when in reality things in orbit are actually falling towards the earth. The thing is they are also moving sideways so fast that by time they have fallen 10m, the surface of the earth has also fallen 10m, and because the earth is a sphere, down is now in a slightly different direction.

[Ben the Space Brit]

Um... All rockets, even over-powered giants like Saturn-V, N-1 and Energia fly pitch-over trajectories into orbit. It massively reduces the amount of fuel they use. By  slowly pitching over to horizontal flight, they get a free boost from Earth's rotation. If they tried to fly the core straight up and then used the upper stage for the transition to horizontal flight, they'd need much more fuel in the upper stage and would be able to carry less payload.

[R7]

I think people sometimes get caught up in the idea of zero-g meaning weightless, and thinking that things just float there, when in reality things in orbit are actually falling towards the earth. The thing is they are also moving sideways so fast that by time they have fallen 10m, the surface of the earth has also fallen 10m, and because the earth is a sphere, down is now in a slightly different direction.

Personally I found this introductory explanation of orbits always confusing (and wrong for circular orbits). In my mind "falling towards earth" denotes acceleration of velocity. Circular orbits have constant velocity speed. Only non-circular orbits feature velocity increase while approaching perigee.

A person who is taught centrifugal force will probably understand that in circular orbits it's magnitude equals the force of gravity.

The revelation comes when you explain the person that force perpendicular to velocity does not accelerate nor decelerate, just turn direction. Then the person realizes that in circular orbits velocity is matched to gravity so that latter just keeps bending the trajectory turning it into a circle.

edit: cheers, AnalogMan 

[Nomadd]

 If Elon's vacuum train was fast enough, you could be in orbit 10 feet off the ground. In fact, if it could go about 27,000 mph, you'd have normal gravity in the wrong direction.

[AnalogMan]

... Circular orbits have constant velocity.

I'm sure you meant to say "Circular orbits have constant speed"   

[K-P]

If Elon's vacuum train was fast enough, you could be in orbit 10 feet off the ground.

Wouldn't it be great to have a probe (or manned spaceship) on orbit of a really regular body, like Europa (and no gravity mascons like Moon has) and with no atmosphere (and drag) so you could have a stable orbit few meters above the ground and still in a freefall-state (xxxxx km/s). Maybe that would clarify things to some...?

But hey, why we just don't build ladders tall enough to get to orbit?
Much cheaper than burn fuel.

[JasonAW3]

If Elon's vacuum train was fast enough, you could be in orbit 10 feet off the ground.

Wouldn't it be great to have a probe (or manned spaceship) on orbit of a really regular body, like Europa (and no gravity mascons like Moon has) and with no atmosphere (and drag) so you could have a stable orbit few meters above the ground and still in a freefall-state (xxxxx km/s). Maybe that would clarify things to some...?

But hey, why we just don't build ladders tall enough to get to orbit?
Much cheaper than burn fuel.

Um, not too sure how that would work, as between surface features that range from a few centimeters to several kilometers in height, as well as random Water Geysers that can extend between a dozen and a hundred kilometers high by hundreds of kilometers long.

It might work at a few kilometers up, but you might still have to adjust your altitude from time to time because of geysers. (Ice build up changing the mass of teh probe, plus smacking into the ice blown out of a geyser is bound to eat away at the kenetic energy needed to maintain orbit.  Assuming a nuclear thermoelectric generator for power, melting the ice away should't be a problem).

HOWEVER; This does present an interesting possibility that I doubt has occured to anyone.

     With Europa venting water ice out into space, would the density of the ice cloud be sufficent to warrent scooping the upper plume of one of these geysers for ice that can be converted to fuel?  Assuming a scoop tanker that gathers up water ice from the geyser plumes over Europa, or one of teh other icey moons that vent geysers of water ice, orbits for several months, maybe up to 6 months, could a sufficently large quantity of water be gathered to justify the operation?  It also occures to me that this might also work with comets, should one be passing close enough by a scoop equiped probe, that a fuel gathering might be worth it, so long as good science and a sufficent amount of fuel (or in this case, simple reaction mass) could be gathered to extend a particular probe's range and duration, sufficently to warrent the risk of gathering reaction mass in the Comet's coma.

   I Know that this is a bit off topic, but the quoted comment got me thinking of ways of lowering costs for extending missions in deep space.

     By the way, Has anyone ever thought of using a Nuclear Theromoelectric generator's excess heat as a means of heating up a reaction mass, (water or some otehr gases) sufficently to act as a reaction mass?  I know we have Ion Drives now, but why not try to use as much energy produced by Nuclear Isotopic Theromoelectric Generators as possible?  the excess heat generated over and above what is needed to power a probe's electronic systems is generally dumped as waste heat, so, can it be used for something else?

[JasonAW3]

[I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

MAYBE Japan, but that's more likely an elective.  Most kids have to pick it up on the streets.

     You know the type; Punk haircuts, wire rimmed glasses, wearing white leather labcoats and sneaker soled boots.  Walking around with kluged together calculators or tricked out laptops, running pirate copis of spreadsheets and databases, while drinking stove top brewed versions of Jolt Cola and overcaffinated Mountian Dew. Using abandoned warehouses and old barges to build and launch rockets that they put together with salavged sheet metal and hand built rocket engines using windshield wiper motors as fuel pumps.

You know... The Rocket Punks...

[llanitedave]

People on this forum should remember that all the most brilliant minds in human history didn't understand orbital mechanics and gravity until a few hundred years ago - a small slice of time on the scale of human civilization. It is certainly not obvious and all the people here still wouldn't understand it without someone explaining it to them.

And most of the most brilliant (male) minds in human history didn't and still don't understand women.  Which does make them a bit like rockets.

[Rocket Science]

[I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

MAYBE Japan, but that's more likely an elective.  Most kids have to pick it up on the streets.

     You know the type; Punk haircuts, wire rimmed glasses, wearing white leather labcoats and sneaker soled boots.  Walking around with kluged together calculators or tricked out laptops, running pirate copis of spreadsheets and databases, while drinking stove top brewed versions of Jolt Cola and overcaffinated Mountian Dew. Using abandoned warehouses and old barges to build and launch rockets that they put together with salavged sheet metal and hand built rocket engines using windshield wiper motors as fuel pumps.

You know... The Rocket Punks...

Oh you mean like this guy?

[Nine_thermidor]

This thread is fascinating. I'm pretty much a noob/long time lurker here, and despite being really interested in planetary science and exploration, and in Spacex's exciting plans, I've never really understood this stuff. I'm reasonably well educated in science (a masters and doctorate in geology) but I was never much of a fellow for physics and maths and such. Anyway, thanks to those who have taken the time to do simple explanations here, and any other suggestions for simple introductions to orbital dynamics/rocket science much appreciated. Love reading NSF, but the jargon can be a bit overwhelming at times. I'll have to get involved with Kerbal Space Program.

[Tuts36]

With Europa venting water ice out into space, would the density of the ice cloud be sufficent to warrent scooping the upper plume of one of these geysers for ice that can be converted to fuel?

You would promptly be murdered by a screaming mob of would-be exobiologists.

[thebluemarble]

I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

Even if they did, most people simply don't care about things like that when they are in high school, if they don't want to study physics or something.
They might become interested in spaceflight later on and discover how fascinating it is etc., but they don't remember a single thing from their physics classes, usually because it was presented to them in a very boring way. And people who don't consider certain subjects to be their lifelong passion need a slightly different approach.
High schools in my country actually teach some very basic orbital mechanics, even to those who choose to focus on human arts, just like I did. I remember explaining spaceflight to my classmates. I don't consider myself a good teacher, but I don't think many of them would be able to understand anything of it without help from someone who is actually interested in spaceflight and has enough patience. The teacher clearly was not patient enough and had no idea how to explain these things to people who prefer reading Dostoyevski to reading Hawking.
If your country is not a space power, it also doesn't help, because the topic of spaceflight hardly ever appears in the media.
So it's not only about the educational system, it's about individual people and the overall attitude of the society.

[K-P]

any other suggestions for simple introductions to orbital dynamics/rocket science much appreciated.

I don't know about others but for me just playing with Orbiter Space Flight Simulator and flying around in near-Earth space with Delta Glider has been a true hands-on lesson of orbital mechanics. Taught even to me some new things about slingshots and orbital burns. And yes, landing on Venus... more like diving in an ocean.

(don't mean to promote/advertise anything, just enjoyed Orbiter)

[oiorionsbelt]

This is probably a nob question but, I've always wondered why rockets such as the Shuttle performed the early roll manouver shortly after launch. I noticed the Ares V simulations have the same manouver. Can this not be achieved by orienting the vehicle on the pad?

[Joffan]

I think we've beaten this question almost to death, but I'll just add a link to Jon Goff's assessment of "pop-up" first stages, where the first stage goes straight up and the second stage does all the orbital velocity work.

[Jim]

This is probably a nob question but, I've always wondered why rockets such as the Shuttle performed the early roll manouver shortly after launch. I noticed the Ares V simulations have the same manouver. Can this not be achieved by orienting the vehicle on the pad?

The pads were built for the Saturn V.  Use of the VAB and pad dictated a certain orientation which was not the same as the Saturn V's and hence the need for the roll.

[Jim]

Even if they did, most people simply don't care about things like that when they are in high school, if they don't want to study physics or something.

Orbital Mechanics are beyond what is done in high school.  I had calculus and analytical geometry in high school (but my physics course only used algebra.  We touched on it a little but my courses were the most advanced ones and there were only 30 of us in it out of a class of 600.

[veedriver22]

 Here is the simple explanation.  To be in orbit you need 2 things.   #1 is speed. You need speed and lots of it,  like 17000 MPH.  #2 is Direction.  You must be travelling in a direction that is parallel to the earth surface.

 If you go straight up you can build lots of speed, but your momentum will want to keep going straight up.  You can't just take a right turn.   That's even true with a car.   If you are going very fast and try to make a sharp turn you will spin and the car will pretty much keep going in the direction you were going until the friction of the tires stops you.

 Once you get up to the orbit altitude you can then make a gradual turn to achieve orbit, but to do that you need lots more fuel.  The rocket wants to keep going straight and it takes fuel to change the momentum.  Fuel is cheap, but the problem is its heavy.
 

[rpapo]

Orbital Mechanics are beyond what is done in high school.  I had calculus and analytical geometry in high school (but my physics course only used algebra.  We touched on it a little but my courses were the most advanced ones and there were only 30 of us in it out of a class of 600.

My experience in high school was the same.  If you intended to go on to college, you took the toughest courses available, period.  Most of the others in the high school didn't care to work that hard.

I learned some orbital calculations on my own in college, and bought computer time to play with it.

[strangequark]

... Circular orbits have constant velocity.

I'm sure you meant to say "Circular orbits have constant speed"   

No, he's clearly using a spherical coordinate system.

[Owlon]

Orbital Mechanics are beyond what is done in high school.  I had calculus and analytical geometry in high school (but my physics course only used algebra.  We touched on it a little but my courses were the most advanced ones and there were only 30 of us in it out of a class of 600.

My experience in high school was the same.  If you intended to go on to college, you took the toughest courses available, period.  Most of the others in the high school didn't care to work that hard.

I learned some orbital calculations on my own in college, and bought computer time to play with it.

I think most states in the US require some sort of physics course, and most of those cover the basic concept of orbit using algebra [F=GmM/r^2, v=(GM/R)^(1/2)] --but not much of anything beyond that. Whether most people understand or remember that bit is another question entirely.

[rpapo]

Orbital Mechanics are beyond what is done in high school.  I had calculus and analytical geometry in high school (but my physics course only used algebra.  We touched on it a little but my courses were the most advanced ones and there were only 30 of us in it out of a class of 600.

My experience in high school was the same.  If you intended to go on to college, you took the toughest courses available, period.  Most of the others in the high school didn't care to work that hard.

I learned some orbital calculations on my own in college, and bought computer time to play with it.

I think most states in the US require some sort of physics course, and most of those cover the basic concept of orbit using algebra [F=GmM/r^2, v=(GM/R)^(1/2)] --but not much of anything beyond that. Whether most people understand or remember that bit is another question entirely.

That formula was the basis of the program I was playing with...

[Soralin]

I like newton's cannon for a simple understanding of orbits:

http://en.wikipedia.org/wiki/Newton%27s_cannonball


If you fire a cannonball out of a cannon, it will move to the side, and curve toward the ground, due to gravity.  Get it moving fast enough, and it will be moving so fast to the side, that by the time it would have hit the ground, the ground has curved away from under it, due to the curvature of the Earth, and it misses it.  Since the ground is now in a different direction, it gets pulled in that direction, and again misses hitting it due to the curvature of the Earth, etc.

That's basically just what an orbit is: Falling, but moving so fast to the side that you miss hitting the planet.  The only reason for the height, is to get out of the atmosphere, so that you don't have to deal with air resistance slowing things down.  If you don't have any air, and there aren't any mountains or such in the way, you could get something into an orbit arbitrarily close to the ground.

There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss.

[Nindalf]

The only reason for the height, is to get out of the atmosphere, so that you don't have to deal with air resistance slowing things down.  If you don't have any air, and there aren't any mountains or such in the way, you could get something into an orbit arbitrarily close to the ground.

This is correct in principle, but not actually true.  If you get too low around an airless world, you encounter gravitational variations as you travel over it, due to it not being a perfectly uniform sphere.  You wouldn't notice them standing on the surface, but they're enough to make your orbit unstable.

This is a real practical consideration in low lunar orbit, as seen in the example of LADEE:
http://www.gizmag.com/ladee-moon-probe-impact-nasa/31708/

[SVBarnard]

So the first stage is going to literally fly hundreds of miles back to shore? There is no way in hell it has enough fuel to travel that much distance! I am totally confused! There is no way in hell they're ever gonna land back on shore it'll have to be a barge.

Surely I'm mistaken?

[SVBarnard]

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.

How could someone be so dense? lol i laughed so hard!

[Ludus]

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

The OP started with an older Elon Musk tweet, this link was a more recent Musk retweet that's precisely the answer to the difference between going into space and going into orbit the OP is asking about.

What Virgin Galactic is promising to do is take passengers straight up into space, which is a heck of a lot easier than taking them into orbit.

[rockettrey]

I love this topic and have also recently posed a related question on it elsewhere in the vast realm that is NSF.   It has also bugged me for years.  Thanks to all the experts out there helping out us orbital mechanics-deprived individuals!   

We all know boost back reduces the amount of payload to orbit. Gravity losses associated with just going vertical also have associated payload reduction, not to mention all the work the 2nd stage now has to do to build up velocity.  Which loss type is greater- gravity v.s. boost back? 

The reason I ask is this- instead of going vertical to whatever orbital altitude is desired (for easy RTLS) and then work on the necessary orbital velocity (which we all now know is really inefficient), why not go vertical to say 500% of the desired orbital altitude (wild guess to make my point), separate the booster stages (or first stage in F9R), and let GRAVITY (along with 2nd stage) help to achieve the necessary orbital velocity?  The boosters/first stage could then RTLS with minimal corrections due to Earths rotation and the important parts would have a nice long downhill ride to pick up speed.

[Burninate]

I love this topic and have also recently posed a related question on it elsewhere in the vast realm that is NSF.   It has also bugged me for years.  Thanks to all the experts out there helping out us orbital mechanics-deprived individuals!   

We all know boost back reduces the amount of payload to orbit. Gravity losses associated with just going vertical also have associated payload reduction, not to mention all the work the 2nd stage now has to do to build up velocity.  Which loss type is greater- gravity v.s. boost back? 

The reason I ask is this- instead of going vertical to whatever orbital altitude is desired (for easy RTLS) and then work on the necessary orbital velocity (which we all now know is really inefficient), why not go vertical to say 500% of the desired orbital altitude (wild guess to make my point), separate the booster stages (or first stage in F9R), and let GRAVITY (along with 2nd stage) help to achieve the necessary orbital velocity?  The boosters/first stage could then RTLS with minimal corrections due to Earths rotation and the important parts would have a nice long downhill ride to pick up speed.

Because velocity is a vector (represented by three quantities, possessing orientation and magnitude), not a scalar speed represented by one quantity.  Achieving extra velocity towards the ground doesn't help you much.

Gravity is accelerating the spacecraft towards Earth, while to raise periapsis, the closest-approach of the orbit (which starts out deep down near the core of the Earth, and which we are trying to get above the atmosphere), we need to thrust perpendicular to that acceleration vector.  The problem with explaining it this way, is that Earth's gravity *does indeed* get weaker with altitude, the higher the vehicle is at apoapsis, the "cheaper" raising periapsis is - and this sounds a lot like your (incorrect) idea.  The thing is, gravity fades out so very, very slowly.  You don't need 500% of the height of a low earth orbit, you need 500,000%, for it to take a lot less velocity to raise periapsis above horizon - and getting there takes extra energy;  Energy you're just going to slowly aerobrake away (itself a problem for things like solar panels) if you want to achieve a low earth orbit.

A direct injection ascent, which skips LEO, is something that would theoretically save some fuel, but seems to be prohibited through some combination of being very, very inconvenient from an operations perspective, and requiring significantly higher thrust engines for more of the mission, which cost a lot more and are heavier in an upper stage than the alternative.

[Damon Hill]

So the first stage is going to literally fly hundreds of miles back to shore? There is no way in hell it has enough fuel to travel that much distance! I am totally confused! There is no way in hell they're ever gonna land back on shore it'll have to be a barge.

Surely I'm mistaken?

Well, there's a performance hit for sure but the (nearly) empty first stage is MUCH lighter than when it started out.  It depends on how far downrange the core travels and its velocity, which will be higher.  The boosters have it much easier as they drain very rapidly with propellant cross-feed to the core and spend most of their ride just gaining altitude for the core rather than downrange velocity.

I sort of think a core stage barge landing is more likely.  There's going to be enough excitement with two boosters coming back for a landing at the launch site, never mind the core making it three.

--Damon

[Owlon]

So the first stage is going to literally fly hundreds of miles back to shore? There is no way in hell it has enough fuel to travel that much distance! I am totally confused! There is no way in hell they're ever gonna land back on shore it'll have to be a barge.

Surely I'm mistaken?

While physics normally manages to make everything about space and rockets difficult, it this case it is helpful in a few convenient ways.

When your second stage separates from the first stage, both stages are still moving upwards and away from the launch site in a parabolic arc. Your first stage doesn't need to "fly hundreds of miles back" per se, it just needs to impart enough velocity change on itself to reverse direction such that it by the time it has reached the peak of it's trajectory and fallen back to land, it has traveled backwards just as far as when stage separation happened.

I don't know off the top of my head what realistic numbers here might look like, but these are probably relatively close: say your first stage is moving away from the launch site at 1000 m/s and upwards at 200 m/s upon stage separation; you might only need to accelerate by 1500 m/s back towards the launch site in order to make it back.

Fortunately, that 1500 m/s velocity change is not actually as difficult as it might seem. Due to the exponential nature of the rocket equation (http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation), the less propellant you have left, the more punch you get out of each kilogram, because you no longer have to push along the weight of the propellant that has already been burned. If you assume the empty F9 first stage masses about 25000 kg, then, using the rocket equation, the last 25000 kg of propellant is enough to impart about 2100 m/s of velocity change.  The first 25000 kg that is burned in the first few seconds of a launch only accelerates the rocket to about 150 m/s, because you have all the fuel, the full second stage, and the payload weighing the rocket down.

I believe it has been said by Elon Musk and/or other SpaceXers in the past that for every 7 kg of mass added to the first stage, the payload to orbit is cut by about 1kg. Saving 25000 kg of fuel for the boost-back and landing reduces the payload by 25000/7 = 3570 kg. That adds up to roughly what the expected payload hit will be: the Falcon 9 is supposed to deliver nearly 17000 kg to LEO, but the SpaceX website only lists it as lifting 13150 kg. 13150kgkg + 3570kg = 16720
(Wow, the numbers I pulled from thin air actually worked!)

The situation with Falcon Heavy is worse. With the Falcon 9, much of the first stage propellant is used fighting gravity just to lift the rocket up; with the Falcon Heavy, the side boosters do that and the core actually picks up a lot of downrange velocity before second stage separation, so it needs much more propellant to boost back to the launch site.

This nifty graphic of another boost-back design that others have posted in the past was helpful to me in visualizing this:

[Burninate]

The situation with Falcon Heavy is worse. With the Falcon 9, much of the first stage propellant is used fighting gravity just to lift the rocket up; with the Falcon Heavy, the side boosters do that and the core actually picks up a lot of downrange velocity before second stage separation, so it needs much more propellant to boost back to the launch site.

FH is designed, really, around the concept of side-booster flyback to the launch complex being very easy.  Falcon 9 is in an uncomfortable situation where the first stage separates late enough that flyback does take significant amounts of fuel.  For the center core?  The center core will, IMO, probably never fly back all the way to the launch complex in the course of normal operations - it's that impractical.  I think SpaceX want to try it for testing purposes, and that's why they were advertising 6T to GTO prices (less than a third of maximum capability).
In normal practice, I think the center core will either be expendable (which essentially triples the payload for the price of a Falcon 9 non-R), or it will land on something like a barge or an uninhabited island, far from humanity and much closer to its natural unpowered landing zone.  In normal operations, then, probably FH will spend less capability on flyback than F9R.

[Aerospace Dilettante]

The Dry Tortugas are about 1500km slightly south of due east from Boca Chica, tailor frickin' made for our purposes I'd think.

Loggerhead Key isn't being used for anything, put it to use. 

[Jim]

The Dry Tortugas are about 1500km slightly south of due east from Boca Chica, tailor frickin' made for our purposes I'd think.

Who is "our"?

[ThereIWas3]

I learned orbital mechanics by the seat of my pants, playing the original SpaceWar on a PDP-1.
You quickly learn that you can't thrust straight out of a deep gravity well.

[nadreck]

On the educational issue here, by the time everyone has graduated from high school they have been given the option of being exposed to everything they need to know to go on on their own and learn just about anything. However, to do that you have to be motivated, to do that in a lot of different areas you have to be motivated and more intelligent than average, to do that and go on to make new contributions to human knowledge you need to be motivated, significantly more intelligent than average, and be stubborn about accomplishing what you want to accomplish.

So the motivation part, you will find that levels of motivation vary greatly from person to person irrespective of their intelligence. And within the same person varies across goals and time. So if 1 in 100 people in high school are motivated to learn more about rockets (like I was, enough to be president of the high school rocketry club) only one in 10,000 has a higher IQ than 150 and could go on to make rockets that are new and different than what we have today - if they don't get distracted by a myriad of other things in life.

So there are lots of smart, contributing people in society who don't know much about orbits, but it is not because high schools don't cover it, it is because they aren't interested.

When I was president of the rocketry club we had lots of members who had the patience to sand and polish balsa fins, painstakingly dope them and then align them on the rocket bodies, and even painstakingly paint them to match a particular historical design or futuristic artists impression that Estes or Cox had illustrated the kit with. Then they wondered why I spray painted mine black on one side and white on the other. However most of our members didn't want to learn the physics of it, they just wanted to build and launch rockets. The few of us interested in the physics had no trouble learning about it.

Oh and I recommend both Kerbal Space and Orbiter to any and all.

[The Amazing Catstronaut]

Oh and I recommend both Kerbal Space and Orbiter to any and all.

Kerbal is a wonderful simulator if you'd like a layman's model. Apart from the fact that very few of the physics are scaled accurately (the game is designed to be playable, after all), and appears to have a slightly differing comprehension of mass, relativity, the light barrier, conservation of momentum, newtonian principles, ecetera, it serves as a majestic introduction to the wonders of real-world spaceflight. Barring a few reasonable balance reductions (that can easily be modded back in), such as simplified aerodynamics, aerobreaking and… ah, none-incendary meteoric re-entries,

Orbiter is older than much of the ISS, a number of prominent STS missions and that SpaceX thing we all know and love, yet is still without equal. However, it only models Newtonian physics, and is heavily unpermissive of in game craft design, which is much of Kerbal's thrill.

(I personally advocate Kerbal).

[Avron]

I would think its time to optimise the flight profile to maximise the mass to orbit etc and also constrain the flight path so that the first stage can land back at the pad. Yes its gonna take more gas, and/or the mass to orbit will reduce but the overall efficiency of the vehicle will improve from a cost prospective as gas cost less, bigger rockets cost more, but are very cheep if you can reuse . So yes, there will be gravity losses etc but all in all the efficiency must increase, taking into account that a reused stage overall will lift many times a given flight. all depending on usage. so when the calcs are done, take multiple flights into account, add in the added gas needed at less that 1% of cost and while ur at it add in reduced time to market for any core..  doglegs are us .. straight lines all depend on point of reference

[aceshigh]

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.

actually, the amount of people who don´t really stop to think about it, and think that orbit and space are the same thing, and that you could get straight up and somehow "gravity disappears" and stuff like that... I think it´s actually the majority of people. Just another day I was teaching a friend about it. I started making him questions like "if there is no gravity, why does the moon and the artificial satellites stay circling the Earth instead of flying straight away?" to make him THINK about these things, instead of just telling him.

[Donosauro]

[I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

MAYBE Japan, but that's more likely an elective.  Most kids have to pick it up on the streets.

     You know the type; Punk haircuts, wire rimmed glasses, wearing white leather labcoats and sneaker soled boots.  Walking around with kluged together calculators or tricked out laptops, running pirate copis of spreadsheets and databases, while drinking stove top brewed versions of Jolt Cola and overcaffinated Mountian Dew. Using abandoned warehouses and old barges to build and launch rockets that they put together with salavged sheet metal and hand built rocket engines using windshield wiper motors as fuel pumps.

You know... The Rocket Punks...

If I remember correctly, OTRAG actually did use windshield wiper motors to control propellant valves.

[Nilof]

My one size fits all answer to questions like these is to link this excellent blog post by Matt Strassler.

[Lobo]

... 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

 

Yes, it would do exactly what SpaceShipTwo will do.  Go straight up and come straight down, without expending all of the energy necessary to gain the 17,500MPH speed nessesary to achieve stable low each orbit.
Getting "up" is only a small part of what's needed.  The Shuttle SRB's essentially got the Shuttle to space, but the SSME's needed to burn the hydrolox in the ET for another several minutes to get going fast enough to achieve orbit, after jettisoning the SRB's.

[Lobo]

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.

I believe there's been talk of a more "lofted" trajectory this way to help the boosters of FH or F9R return to landing site.  I'm not expert on orbital mechanics, but from what I've read being discussed, yea, that's not a very efficient trajectory.  But it might work...to a degree (it won't be "straight" up, but lofted)...with FH as it will have a lot of capacity to spare.  Getting the boosters back as cheaply as possible is more important than wringing every spare ounce of capacity out of the LV. 

[Lobo]

So the first stage is going to literally fly hundreds of miles back to shore? There is no way in hell it has enough fuel to travel that much distance! I am totally confused! There is no way in hell they're ever gonna land back on shore it'll have to be a barge.

Surely I'm mistaken?

Well, there's a performance hit for sure but the (nearly) empty first stage is MUCH lighter than when it started out.  It depends on how far downrange the core travels and its velocity, which will be higher.  The boosters have it much easier as they drain very rapidly with propellant cross-feed to the core and spend most of their ride just gaining altitude for the core rather than downrange velocity.

I sort of think a core stage barge landing is more likely.  There's going to be enough excitement with two boosters coming back for a landing at the launch site, never mind the core making it three.

--Damon

If it flies a less efficient lofted trajectory, where it goes more up than over before staging, it's not as far down range or going as fast.  A large part of it's velocity will be a vertical componant that gravity will "brake" for free.  The boost back burn helps slow down the horizontal velocity, as does the atmosphere when it hits is.  Meanwhile the Earth is rotating under the booster, bringing the launch site to the booster essentially.  So by the time it comes down it's much closer to the launch site than you'd otehr wise think.  The boost back burn needs to be long enough to put the booster right over the launch site by the time it fully decends.

For the center core of a FH to return to the launch site, it would need to stage not too long after the boosters, and do more boost back.  Which would really start to kill payload.  However, how much payload capacity do you need?  That's the question.  If a FH sending all of it's cores back to the launch site could put 23mt into LEO and 11mt to GTO (1500m/s to GSO), then it would match D4H (prior to RS-68A) and would be capable of launching the largest unmanned payloads ever launched outside of Saturn V.  I don't think there's bee a payload yet on D4H that needed it's additional capacity.  (someone please correct me if I'm wrong).
And you get all 3 cores back to the launch site, with basically just an upper stage expended.  Horribly inefficient from a performance standpoint, but very efficient from an economics standpoint.  And you have an LV that can launch any payload out there for the cost of an upper stage.

I don't really see the problem with that, if that's the case.  IF that FH cannot put 11mt to GTO, but say 7mt to GTO (1500 m/s to GSO), that's still as much or more capacity as an Atlas V-551 and every other LV out there except D4H and Ariane V with the ECA upper stage.  And the D4H is the only LV to fly a single payload that needed more than 7mt to GTO.  Ariane V has only flown dual payloads to GTO.  Unless flying dual payloads, a FH with all 3 reusable boosters at 7mt to GTO could fly anything that's ever flown outside of Saturn V's payload, and 5 NRO payloads on D4H.

If they want more performance, they expend the central core, or recover it farther down range on a barge or something.  If they want even more performance, they crossfeed the boosters, but still recover them, and expend the core.
If they want even more performance, they crossfeed the boosters (so they are empty at separation) and expend them as well as the central core.  But payload would have to grow far larger than any are now to need that.

[deruch]

So the first stage is going to literally fly hundreds of miles back to shore? There is no way in hell it has enough fuel to travel that much distance! I am totally confused! There is no way in hell they're ever gonna land back on shore it'll have to be a barge.

Surely I'm mistaken?

Yes and no.  Yes, the first stage is going to fly a considerable distance down range, then turn around and come back, but it won't be hundreds of miles (closer to just 100 miles).  This is made potentially possible by a few factors.  The first is sort of counter intuitive and where I think many people get confused.  It doesn't have to fly as fast to get back.  It can fly back much slower.  To illustrate, on the Orbcomm OG2 launch, the booster touched down 8 minutes after the stages separated.  Even allowing for time for the stages to move apart and for the booster to turn around, it should have about twice the amount of time to fly back that it took going downrange.  Consequently, it can cover the same distance at a slower speed.  Slower means less acceleration needed--->take less force and therefore less fuel to accomplish this.  The second factor that makes RTLS potentially possible is mass changes.  On it's outbound trip, the first stage is pushing the mass of a full second stage as well as the payload.  It also starts with full tanks of its own.  By the time it turns around to come back to land, it has already separated from the second stage and its own tanks are much closer to being empty.  Hence, for the return trip, the amount of mass needing to be propelled back is way, way less.  Consequently, it will take way, way less force to accelerate the stage back towards the launch site (F=m*a or a=F/m. i.e. For a given amount of acceleration needed, lowering the mass means it will be accomplished with less force).  Less force needed means less fuel required for that burn. 

So, because it doesn't need to fly as fast, it needs much less acceleration.  And because it has so much less mass at boost-back, it will take much less force to accelerate it to the required velocity.  Both of those factors together mean that there is sufficient propellant remaining to accomplish boost-back to land.  Whether there is sufficient margin to boost-back, control reentry, and land safely at a specific point remains to be seen.  At this point I would say that it's very likely possible for at least some payloads flown on the F9v1.1.

If you want to see what it may look like, there a decent demonstration from a modded Kerbal Space Program:

[MP99]

If a FH sending all of it's cores back to the launch site could put 23mt into LEO and 11mt to GTO (1500m/s to GSO), then it would match D4H (prior to RS-68A) and would be capable of launching the largest unmanned payloads ever launched outside of Saturn V.

SpaceX quotes to a GTO at 27 degrees, which is 1800m/s short.

FH is 7t with all-RTLS and 14t with centre core expended.



Note that F9E's payload drops to 3.5t when delivering to a minus-1500 orbit, which they call "SuperSynchronous", or SSO.

There is some question whether FH with core expended could loft 11t to SSO.

Cheers, Martin

[Lobo]

If a FH sending all of it's cores back to the launch site could put 23mt into LEO and 11mt to GTO (1500m/s to GSO), then it would match D4H (prior to RS-68A) and would be capable of launching the largest unmanned payloads ever launched outside of Saturn V.

SpaceX quotes to a GTO at 27 degrees, which is 1800m/s short.

FH is 7t with all-RTLS and 14t with centre core expended.



Note that F9E's payload drops to 3.5t when delivering to a minus-1500 orbit, which they call "SuperSynchronous", or SSO.

There is some question whether FH with core expended could loft 11t to SSO.

Cheers, Martin

Understood.  I was just using speculative numbers as I didn't know for sure what the predicted performance for an FH with all 3 cores RTLS and with a central core expended were.
Just saying that even with the obviously large performance hit of all 3 cores RTLS, it's fairly immaterial if the majority of the payloads FH would be launching don't need more than that, and you get to reuse all 3 cores.
So if FH with all 3 cores RTLS actually can do 7mt to GTO (1800m/s to GSO), then that's right on par with Atlas V-531 and Delta IV (5,4) (about 1/2mt short of each).  So the only payloads that have every been flown that require -more- than that to GTO have been the 5 D4H missions (the first was only a test), and 5 Atlas-541/551 total launches. 
So while very inefficient to bring all 3 cores back to the launch site, it would still cover about 86% of all the EELV launches every done.  By expending just the core, it looks like it would cover at least most of the rest of that. 
Ariane V can do more, but it doesn't look like it's ever launched more than 9.4mt payload to GTO, but those were always dual payloads, so no single payload to GTO of more than probably 5-6mt.  So FH with all 3 cores RTLS would be able to launch any of those payloads as single payloads....or perhaps dual payloads with an expended central core, if that would be more cost effective.  Not sure if SpaceX is looking to do dual payloads to GTO the way Ariane V does though?



 

 

[FinalFrontier]

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

I doubt most high schools all around the world teach even basic orbital mechanics to be honest.

Ha. They don't. Math and science in america in k-12 doesn't exist, its a myth. What they teach now is whatever is "politically correct" to teach. Spaceflight is considered by many not to be politically correct (don't ask its beyond the scope of the thread).
This being said I was not at all surprised to see this thread.

[ChrisWilson68]

Ha. They don't. Math and science in america in k-12 doesn't exist, its a myth. What they teach now is whatever is "politically correct" to teach. Spaceflight is considered by many not to be politically correct (don't ask its beyond the scope of the thread).
This being said I was not at all surprised to see this thread.

That's nonsense.  The level of math and science education is uneven, varying from place to place in the U.S. but to just make blanket attacks on it is wrong.

[Owlon]

Ha. They don't. Math and science in america in k-12 doesn't exist, its a myth. What they teach now is whatever is "politically correct" to teach. Spaceflight is considered by many not to be politically correct (don't ask its beyond the scope of the thread).
This being said I was not at all surprised to see this thread.

That's nonsense.  The level of math and science education is uneven, varying from place to place in the U.S. but to just make blanket attacks on it is wrong.

This.

I got a solid foundation of physics, chemistry, and calculus in my Texas high school (hint: Texas is not renowned for it's excellent k-12 education). I did seek out AP classes and whatnot, but the minimum graduation requirements would have you taking very similar chemistry and physics classes. As I mentioned previously in the thread, my regular physics class that everyone had to take covered the basics of orbit and gravitation using algebra. You would have failed that unit if you didn't understand the difference between space and orbit.

[cleonard]

You could launch in a straight line and get into orbit.  The catch is what you are orbiting.  Launching from the surface of the earth you could go in a "straight line" directly into solar orbit by getting just past escape velocity. 

[Dave G]

Can we kill this thread already?

[M_Puckett]

Isn't straight line orbit an oxymoron?

[Jcc]

Isn't straight line orbit an oxymoron?

Yes. Yes it is.

[DecoLV]

OK, I'm going to slightly bend the trajectory of this thread by asking a related question of my own. Can you achieve orbit via direct rendevous?

Try this. The space shuttle is orbiting at 115 miles, payload bay toward Earth. Freedom 7 with Alan Shepard is launched at the perfect moment so that the peak of the capsule's path (115 miles) intersects with the shuttle. The Mercury capsule flies into the cargo bay where is it seized by [insert relevant technology here] and captured. Mercury Freedom 7 and Al Shepard are now in orbit. Without an Atlas.

Right?

[WmThomas]

The space shuttle in your example would be decelerated by the capsule. Whether the united vehicles would stay in orbit is an open question.

[AS-503]

OK, I'm going to slightly bend the trajectory of this thread by asking a related question of my own. Can you achieve orbit via direct rendevous?

Try this. The space shuttle is orbiting at 115 miles, payload bay toward Earth. Freedom 7 with Alan Shepard is launched at the perfect moment so that the peak of the capsule's path (115 miles) intersects with the shuttle. The Mercury capsule flies into the cargo bay where is it seized by [insert relevant technology here] and captured. Mercury Freedom 7 and Al Shepard are now in orbit. Without an Atlas.

Right?

Okay, I'll drive my pickup truck by you at 17,500 MPH and you just hop in when I drive by;)



 

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

[NovaSilisko]

OK, I'm going to slightly bend the trajectory of this thread by asking a related question of my own. Can you achieve orbit via direct rendevous?

Try this. The space shuttle is orbiting at 115 miles, payload bay toward Earth. Freedom 7 with Alan Shepard is launched at the perfect moment so that the peak of the capsule's path (115 miles) intersects with the shuttle. The Mercury capsule flies into the cargo bay where is it seized by [insert relevant technology here] and captured. Mercury Freedom 7 and Al Shepard are now in orbit. Without an Atlas.

Right?

The Shuttle impacts poor Freedom 7 and Al with a relative velocity comparable to the shuttle's orbital velocity. Both are blasted apart in an instant. A small meteor shower occurs slightly downrange of the cape as bits of Freedom 7 burn up in the atmosphere.

The cloud of debris in orbit from the Shuttle renders LEO unusable for some time.

Program subsequently cancelled due to being "a really terrible idea"







...however.

If you were to perhaps fire a grappling hook out of the payload bay in a retrograde direction, kept the cable unspooling at 8 km/s, latched the hook onto the Mercury capsule, and then slowly reversed the unspooling to winch it in, you could indeed drag the capsule to orbit, at the expense of some of the Shuttle's orbital velocity.

All the mass allocated to the gigantic hypervelocity winch system means however that the Shuttle couldn't carry any deorbit propellant, and the stack reenters on its own after a few weeks due to orbital decay.

This program was also cancelled.

^{(I wonder if this would work for slower speed flybys of asteroids for sample return? Fire a scooper on a long cable at the asteroid when flying past at something like 500 m/s, then unlatch it from the asteroid and yank the thing out before slowly winching it back in)}

[Lee Jay]

OK, I'm going to slightly bend the trajectory of this thread by asking a related question of my own. Can you achieve orbit via direct rendevous?

Try this. The space shuttle is orbiting at 115 miles, payload bay toward Earth. Freedom 7 with Alan Shepard is launched at the perfect moment so that the peak of the capsule's path (115 miles) intersects with the shuttle. The Mercury capsule flies into the cargo bay where is it seized by [insert relevant technology here] and captured. Mercury Freedom 7 and Al Shepard are now in orbit. Without an Atlas.

Right?

The Shuttle impacts poor Freedom 7 and Al with a relative velocity comparable to the shuttle's orbital velocity. Both are blasted apart in an instant. A small meteor shower occurs slightly downrange of the cape as bits of Freedom 7 burn up in the atmosphere.

The cloud of debris in orbit from the Shuttle renders LEO unusable for some time.

Program subsequently cancelled due to being "a really terrible idea"

If I understood the question asked, Freedom 7 would be orbital via direct insertion.  Assuming apogee is the same but perigee is lower, there would still be a relative velocity, but it would be no where near orbital velocity.

[NovaSilisko]

If I understood the question asked, Freedom 7 would be orbital via direct insertion.  Assuming apogee is the same but perigee is lower, there would still be a relative velocity, but it would be no where near orbital velocity.

Well, I was interpreting it as being launched by a Redstone rocket into a steep suborbital trajectory with the apogee at the Shuttle's orbital altitude, not unlike the actual Mercury suborbital flights. It would a bit less than orbital velocity though, unless you launched the capsule north or south.

[kch]

OK, I'm going to slightly bend the trajectory of this thread by asking a related question of my own. Can you achieve orbit via direct rendevous?

Try this. The space shuttle is orbiting at 115 miles, payload bay toward Earth. Freedom 7 with Alan Shepard is launched at the perfect moment so that the peak of the capsule's path (115 miles) intersects with the shuttle. The Mercury capsule flies into the cargo bay where is it seized by [insert relevant technology here] and captured. Mercury Freedom 7 and Al Shepard are now in orbit. Without an Atlas.

Right?

Okay, I'll drive my pickup truck by you at 17,500 MPH and you just hop in when I drive by;)



 

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

Yup.  Basically, [SPLAT] and resulting pieces-parts all over Hades ... nasty.  Wouldn't wish that on my worst enema. 

[Patchouli]

Oh and I recommend both Kerbal Space and Orbiter to any and all.

Kerbal is a wonderful simulator if you'd like a layman's model. Apart from the fact that very few of the physics are scaled accurately (the game is designed to be playable, after all), and appears to have a slightly differing comprehension of mass, relativity, the light barrier, conservation of momentum, newtonian principles, ecetera, it serves as a majestic introduction to the wonders of real-world spaceflight. Barring a few reasonable balance reductions (that can easily be modded back in), such as simplified aerodynamics, aerobreaking and… ah, none-incendary meteoric re-entries,

Orbiter is older than much of the ISS, a number of prominent STS missions and that SpaceX thing we all know and love, yet is still without equal. However, it only models Newtonian physics, and is heavily unpermissive of in game craft design, which is much of Kerbal's thrill.

(I personally advocate Kerbal).

I played with Orbiter before KSP.

Probably why I made it to orbit in KSP on my third try.

As for learning basic orbital mechanics I learn about them when I was 13 by reading books and watching educational programs.
I remember in science class being taught about Newton's cannon.

[puetzk]

If you were to perhaps fire a grappling hook out of the payload bay in a retrograde direction, kept the cable unspooling at 8 km/s, latched the hook onto the Mercury capsule, and then slowly reversed the unspooling to winch it in, you could indeed drag the capsule to orbit, at the expense of some of the Shuttle's orbital velocity.

All the mass allocated to the gigantic hypervelocity winch system means however that the Shuttle couldn't carry any deorbit propellant, and the stack reenters on its own after a few weeks due to orbital decay.

This program was also cancelled.

^{(I wonder if this would work for slower speed flybys of asteroids for sample return? Fire a scooper on a long cable at the asteroid when flying past at something like 500 m/s, then unlatch it from the asteroid and yank the thing out before slowly winching it back in)}

Designed in a slightly more workable fashion, this is known the Rotovator or momentum exchange tether

[GORDAP]

I guess there is one way that you could launch 'straight up' and achieve Earth orbit:  Launch from the equator on a trajectory that looks like straight up to an observer near by on the surface, and which tops out at exactly geosync height.

I think you'd have to accelerate eastward to make this happen, and it wouldn't be a particularly fuel efficient way to get to geosync orbit, but again I think it would look like a launch straight up to orbit, right?

[Nomadd]

 This can't be right. All you have to do to get from one place to another in space is look for where you want to go and scoot over in an MMU. I know because I saw it in Gravity.

[Dave G]

Isn't straight line orbit an oxymoron?

Yes. Yes it is.

According to Einstein, all orbits are straight lines, but gravity warps space-time to make them appear elliptical.

Of course, that's about as useful as anything else in this thread...

[matthewkantar]

 Straight up, bee line to a place near where the moon will be when you get there. slingshot around the moon so that you go near where the earth will be when you get there, aero braking, thrusters, blah blah, kabam,  earth orbit.

Worst thread ever maybe?

Matthew

[andrewsdanj]

I guess there is one way that you could launch 'straight up' and achieve Earth orbit:  Launch from the equator on a trajectory that looks like straight up to an observer near by on the surface, and which tops out at exactly geosync height.

I think you'd have to accelerate eastward to make this happen, and it wouldn't be a particularly fuel efficient way to get to geosync orbit, but again I think it would look like a launch straight up to orbit, right?

So...... a space elevator without the elevator? :-)

[DecoLV]

"Second star to the right, and straight on 'til morning."









Well, someone had to say it. 

[CuddlyRocket]

OK, this thread appears to have morphed into a general Q&A thread about orbits and there's a dedicated Q&A Section of the forum for that. Locked.