QUESTION: about rockets turning eastward after launch...

Dear Gurus Somewhere On The Internet...

This posting is related to a well known question about why rockets
turn eastward soon after launch.

Many answers to that question state something along the line of
"...objects on earths SURFACE move at a speed of...."

The question I wanted to ask is, what does this have to do with a
rocket that is not on the surface but somewhere up in the atmosphere?

Is the reason that earths atmosphere (meaning the gases in it) is also
in a constant movement eastward?

Or is there some other reason and in that case which?

Thanks in advance for enlightening me again:-)

On Jun 22, 10:07*am, JJ wrote:
Dear Gurus Somewhere On The Internet...

This posting is related to a well known question about why rockets
turn eastward soon after launch.


Most launches are timed and oriented to put a vehicle in
a specific orbit. Angle, direction, distributed thrust and timing
are all chosen to achieve the desired orbit. It goes without
saying that it takes less fuel if the orbital motion is in the
same direction as the earth's rotation.

Dear JJ:

On Jun 22, 8:07*am, JJ wrote:
....

This posting is related to a well known question about
why rockets turn eastward soon after launch.

From the east coast, they do. From the west coast, they usually head
for ocean. Depends on the orbit sought.

Many answers to that question state something along
the line of "...objects on earths SURFACE move at a
speed of...."

The question I wanted to ask is, what does this have to
do with a rocket that is not on the surface but
somewhere up in the atmosphere?

Conservation of momentum. Once moving at 1000+ miles an hour
eastward, would be nice to use that "free" momentum and just add to
it. The gases have naught to do with it, as we have to tear through
them to get to space.

Is the reason that earths atmosphere (meaning the
gases in it) is also in a constant movement eastward?

They move a little faster, since they have to keep up, but there is
also the jet stream.

Or is there some other reason and in that case which?

Using the free momentum,
Taking off so that an abort will land in ocean, rather than on land.

David A. Smith

"JJ" wrote in message
...
| Dear Gurus Somewhere On The Internet...
|
| This posting is related to a well known question about why rockets
| turn eastward soon after launch.
|
| Many answers to that question state something along the line of
| "...objects on earths SURFACE move at a speed of...."
|
| The question I wanted to ask is, what does this have to do with a
| rocket that is not on the surface but somewhere up in the atmosphere?
|
| Is the reason that earths atmosphere (meaning the gases in it) is also
| in a constant movement eastward?
|
| Or is there some other reason and in that case which?
|
| Thanks in advance for enlightening me again:-)
|

To orbit the Earth the vehicle has to reach orbital velocity
(about 17,000 mph), independent of the Earth spinning
beneath it. Since the Earth is already spinning eastwards
it can give the rocket a boost of about 1000 mph so the
rocket only has to accelerate a further 16,000 mph.
A westward launch requires the rocket to accelerate
to 18,000 mph, the first 1000 mph only stops it.
A polar orbit is best accomplished from a site near to
one of the poles. So the simple answer is: to save fuel
or increase payload.

JJ wrote:

Dear Gurus Somewhere On The Internet...

This posting is related to a well known question about why rockets
turn eastward soon after launch.

1) 1000 mph equatoral free velocity addition.
2) Not true for polar orbits (Vandenberg).

Many answers to that question state something along the line of
"...objects on earths SURFACE move at a speed of...."

The question I wanted to ask is, what does this have to do with a
rocket that is not on the surface but somewhere up in the atmosphere?

Is there a 1000 mph ground speed wind up there? No. The atmosphere
turns with the Earth - or faster (jet stream).

Is the reason that earths atmosphere (meaning the gases in it) is also
in a constant movement eastward?

Ever do a sailboat?

Or is there some other reason and in that case which?

Momentum is measured vs. the fixed stars.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz4.htm

On Tue, 22 Jun 2010 08:07:08 -0700, JJ wrote:

Dear Gurus Somewhere On The Internet...

This posting is related to a well known question about why rockets turn
eastward soon after launch.


How soon is "soon?" Rockets don't turn. They go straight up.
This minimizes the thickness of the atmospheric layer which they
must traverse. The atmosphere imparts aerodynamic drag and
stress which can be damaging. Did you ever hear of "Max Q?"

Once clear of any significant atmospheric effects, the rocket
must turn to achieve orbit. An orbit is an elliptical trajectory
that does not intersect the earth and a rocket must be positioned
(via staging) at the proper altitude, direction, and velocity to
match the required parameters of that ellipse.

But even a ballistic missile, which enters an elliptic trajectory
that *does* intersect the earth, is fired straight up vertically.
Once high enough, it then maneuvers to enter the intersecting
elliptical orbit.

The reference frame for rocket launches is relative to the
fixed stars. The rotation of the earth is accounted for
separately.

On Jun 22, 6:45*pm, rabid_fan wrote:
On Tue, 22 Jun 2010 08:07:08 -0700, JJ wrote:
Dear Gurus Somewhere On The Internet...

This posting is related to a well known question about why rockets turn
eastward soon after launch.

How soon is "soon?" *Rockets don't turn. *They go straight up.
This minimizes the thickness of the atmospheric layer which they
must traverse. *The atmosphere imparts aerodynamic drag and
stress which can be damaging. *Did you ever hear of "Max Q?"
....

Did you ever hear of a dog-leg maneuver?

The NASA rocket launch that I witnessed with my own eyes did not go
"straight up."

CM

rabid_fan wrote:
On Tue, 22 Jun 2010 08:07:08 -0700, JJ wrote:

Dear Gurus Somewhere On The Internet...

This posting is related to a well known question about why rockets
turn eastward soon after launch.


How soon is "soon?" Rockets don't turn. They go straight up.
This minimizes the thickness of the atmospheric layer which they
must traverse. The atmosphere imparts aerodynamic drag and
stress which can be damaging. Did you ever hear of "Max Q?"

Once clear of any significant atmospheric effects, the rocket
must turn to achieve orbit. An orbit is an elliptical trajectory
that does not intersect the earth and a rocket must be positioned
(via staging) at the proper altitude, direction, and velocity to
match the required parameters of that ellipse.

But even a ballistic missile, which enters an elliptic trajectory
that *does* intersect the earth, is fired straight up vertically.
Once high enough, it then maneuvers to enter the intersecting
elliptical orbit.

Rockets that launch satellites *do* tilt (usually towards the East) within a
minute or so of launch; they are trying to get above the thickest parts of
the atmosphere, and at the same time they are trying to use the thrust to
increase speed to reach orbital velocity at the correct altitude. If they
expended all their thrust vertically, they would fall back to Earth; if they
turned horizontally immediately, the atmospheric resistance would cause them
to fail to reach orbit. It is a gradual manoeuvre, a compromise between
extra exposure to atmospheric resistance and reaching orbital velocity going
the right direction.


The reference frame for rocket launches is relative to the
fixed stars. The rotation of the earth is accounted for
separately.

--
Mike Dworetsky

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