APOD: The Falcon and the Redstone (2023 Aug 03)

[APOD Robot]

The Falcon and the Redstone

Explanation: In a photo from the early hours of July 29 (UTC), a Redstone rocket and Mercury capsule are on display at Cape Canaveral Launch Complex 5. Beyond the Redstone, the 8 minute long exposure has captured the arcing launch streak of a SpaceX Falcon Heavy rocket. The Falcon's heavy communications satellite payload, at a record setting 9 metric tons, is bound for geosynchronous orbit some 22,000 miles above planet Earth. The historic launch of a Redstone rocket carried astronaut Alan Shepard on a suborbital spaceflight in May 1961 to an altitude of about 116 miles. Near the top of the frame, this Falcon rocket's two reusable side boosters separate and execute brief entry burns. They returned to land side by side at Canaveral's Landing Zone 1 and 2 in the distance.

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[Roy]

Reusable boosters! Reentry burns! Land side by side! Sci-fi made real.

[orin stepanek]

Launching Falcoln!

Landing the boosters!

[johnnydeep]

It's amazing to me that these SpaceX launches have become so routine now that they barely ever make the evening news. Except the manned ones of course. And the rare malfunctions. I long for the day when those too are equally routine.

PS - those flawless booster landings never fail to blow my mind. SpaceX has been doing yeoman's work for sure.

[Chris Peterson]

It's amazing to me that these SpaceX launches have become so routine now that they barely ever make the evening news. Except the manned ones of course. And the rare malfunctions. I long for the day when those too are equally routine.

PS - those flawless booster landings never fail to blow my mind. SpaceX has been doing yeoman's work for sure.

Absent much if any use for manned flights, I hope they never become routine!

[johnnydeep]

Also, from the geosynchronous orbit in the text, we have:

Geosynchronous Orbits

A geosynchronous orbit (GEO) is a prograde, low inclination orbit about Earth having a period of 23 hours 56 minutes 4 seconds. A spacecraft in geosynchronous orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south. The spacecraft returns to the same point in the sky at the same time each day.

Geostationary Orbits

To achieve a geostationary orbit, a geosynchronous orbit is chosen with an eccentricity of zero, and an inclination of either zero, right on the equator, or else low enough that the spacecraft can use propulsive means to constrain the spacecraft's apparent position so it hangs seemingly motionless above a point on Earth. (Any such maneuvering on orbit, or making other adjustments to maintain its orbit, is a process called station keeping.) The orbit can then be called geostationary. This orbit is ideal for certain kinds of communication satellites and meteorological satellites. The idea of a geosynchronous orbit for communications spacecraft was first popularised by science fiction author Sir Arthur C. Clarke in 1945, so it is sometimes called the Clarke orbit.

But I'm having a hard time understanding the subtleties here. Geostationary is a sub-class of geosynchronous, that's clear. But:

Are all these orbits at the same height? (No, I guess not since it depends on eccentricity?)

Would there be any advantages in using a retrograde instead of a prograde orbit?

What about high inclination orbits?

What about an orbit that passes over a (geographic) north or south pole (inclination = 90 degrees)?

Isn't an inclination of zero identical to being "right on the equator" (by definition)?

How eccentric could an orbit be and still be either geosynchronous or geostationary?

[johnnydeep]

The Falcon and the Winder Soldier - https://www.imdb.com/title/tt9208876/

The Falcon and the Snowman - https://www.imdb.com/title/tt0087231/

[Rauf]

Also, from the geosynchronous orbit in the text, we have:

Geosynchronous Orbits

A geosynchronous orbit (GEO) is a prograde, low inclination orbit about Earth having a period of 23 hours 56 minutes 4 seconds. A spacecraft in geosynchronous orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south. The spacecraft returns to the same point in the sky at the same time each day.

Geostationary Orbits

To achieve a geostationary orbit, a geosynchronous orbit is chosen with an eccentricity of zero, and an inclination of either zero, right on the equator, or else low enough that the spacecraft can use propulsive means to constrain the spacecraft's apparent position so it hangs seemingly motionless above a point on Earth. (Any such maneuvering on orbit, or making other adjustments to maintain its orbit, is a process called station keeping.) The orbit can then be called geostationary. This orbit is ideal for certain kinds of communication satellites and meteorological satellites. The idea of a geosynchronous orbit for communications spacecraft was first popularised by science fiction author Sir Arthur C. Clarke in 1945, so it is sometimes called the Clarke orbit.

But I'm having a hard time understanding the subtleties here. Geostationary is a sub-class of geosynchronous, that's clear. But:

Are all these orbits at the same height? (No, I guess not since it depends on eccentricity?)

Would there be any advantages in using a retrograde instead of a prograde orbit?

What about high inclination orbits?

What about an orbit that passes over a (geographic) north or south pole (inclination = 90 degrees)?

Isn't an inclination of zero identical to being "right on the equator" (by definition)?

How eccentric could an orbit be and still be either geosynchronous or geostationary?

A retrograde GSO? Is that even possible?

[Chris Peterson]

Also, from the geosynchronous orbit in the text, we have:

Geosynchronous Orbits

A geosynchronous orbit (GEO) is a prograde, low inclination orbit about Earth having a period of 23 hours 56 minutes 4 seconds. A spacecraft in geosynchronous orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south. The spacecraft returns to the same point in the sky at the same time each day.

Geostationary Orbits

To achieve a geostationary orbit, a geosynchronous orbit is chosen with an eccentricity of zero, and an inclination of either zero, right on the equator, or else low enough that the spacecraft can use propulsive means to constrain the spacecraft's apparent position so it hangs seemingly motionless above a point on Earth. (Any such maneuvering on orbit, or making other adjustments to maintain its orbit, is a process called station keeping.) The orbit can then be called geostationary. This orbit is ideal for certain kinds of communication satellites and meteorological satellites. The idea of a geosynchronous orbit for communications spacecraft was first popularised by science fiction author Sir Arthur C. Clarke in 1945, so it is sometimes called the Clarke orbit.

But I'm having a hard time understanding the subtleties here. Geostationary is a sub-class of geosynchronous, that's clear. But:

Are all these orbits at the same height? (No, I guess not since it depends on eccentricity?)

Right. Unless the eccentricity is zero, the height varies.

Would there be any advantages in using a retrograde instead of a prograde orbit?

I believe satellites have occasionally been launched to the west to prevent launch debris from coming down over populated areas. But in general, no.

What about high inclination orbits?

What about an orbit that passes over a (geographic) north or south pole (inclination = 90 degrees)?

What about them? They are common, of course. Polar orbits in particular are popular for Earth observation satellites.

Isn't an inclination of zero identical to being "right on the equator" (by definition)?

Yes.

How eccentric could an orbit be and still be either geosynchronous or geostationary?

There is no limit on eccentricity for a geosynchronous orbit (theoretically... there are certainly practical limits). A geostationary orbit must have an eccentricity of zero.

[johnnydeep]

It's amazing to me that these SpaceX launches have become so routine now that they barely ever make the evening news. Except the manned ones of course. And the rare malfunctions. I long for the day when those too are equally routine.

PS - those flawless booster landings never fail to blow my mind. SpaceX has been doing yeoman's work for sure.

Absent much if any use for manned flights, I hope they never become routine!

I knew you'd say that. But besides employing manned space missions whose sole purpose is scientific discovery (best done robotically as you often state), there is also space tourism and long term colonization, with destinations of Earth orbiting space stations, and Lunar and Martian exclaves.

[johnnydeep]

Also, from the geosynchronous orbit in the text, we have:

Geosynchronous Orbits

A geosynchronous orbit (GEO) is a prograde, low inclination orbit about Earth having a period of 23 hours 56 minutes 4 seconds. A spacecraft in geosynchronous orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south. The spacecraft returns to the same point in the sky at the same time each day.

Geostationary Orbits

To achieve a geostationary orbit, a geosynchronous orbit is chosen with an eccentricity of zero, and an inclination of either zero, right on the equator, or else low enough that the spacecraft can use propulsive means to constrain the spacecraft's apparent position so it hangs seemingly motionless above a point on Earth. (Any such maneuvering on orbit, or making other adjustments to maintain its orbit, is a process called station keeping.) The orbit can then be called geostationary. This orbit is ideal for certain kinds of communication satellites and meteorological satellites. The idea of a geosynchronous orbit for communications spacecraft was first popularised by science fiction author Sir Arthur C. Clarke in 1945, so it is sometimes called the Clarke orbit.

But I'm having a hard time understanding the subtleties here. Geostationary is a sub-class of geosynchronous, that's clear. But:

Are all these orbits at the same height? (No, I guess not since it depends on eccentricity?)

Would there be any advantages in using a retrograde instead of a prograde orbit?

What about high inclination orbits?

What about an orbit that passes over a (geographic) north or south pole (inclination = 90 degrees)?

Isn't an inclination of zero identical to being "right on the equator" (by definition)?

How eccentric could an orbit be and still be either geosynchronous or geostationary?

A retrograde GSO? Is that even possible?

By the definition I quoted, I guess not, since a retrograde GSO, would return to the same point in the sky more often (or less often???) than once per Earth rotation. Hmm, in the simplest case of zero eccentricity and zero inclination, what would the path of such an object be as seen from the ground and how often would it return to the same position in the sky (relative to the stars)?

[johnnydeep]

Also, from the geosynchronous orbit in the text, we have:

Geosynchronous Orbits

A geosynchronous orbit (GEO) is a prograde, low inclination orbit about Earth having a period of 23 hours 56 minutes 4 seconds. A spacecraft in geosynchronous orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south. The spacecraft returns to the same point in the sky at the same time each day.

Geostationary Orbits

To achieve a geostationary orbit, a geosynchronous orbit is chosen with an eccentricity of zero, and an inclination of either zero, right on the equator, or else low enough that the spacecraft can use propulsive means to constrain the spacecraft's apparent position so it hangs seemingly motionless above a point on Earth. (Any such maneuvering on orbit, or making other adjustments to maintain its orbit, is a process called station keeping.) The orbit can then be called geostationary. This orbit is ideal for certain kinds of communication satellites and meteorological satellites. The idea of a geosynchronous orbit for communications spacecraft was first popularised by science fiction author Sir Arthur C. Clarke in 1945, so it is sometimes called the Clarke orbit.

But I'm having a hard time understanding the subtleties here. Geostationary is a sub-class of geosynchronous, that's clear. But:

Are all these orbits at the same height? (No, I guess not since it depends on eccentricity?)

Right. Unless the eccentricity is zero, the height varies.

Would there be any advantages in using a retrograde instead of a prograde orbit?

I believe satellites have occasionally been launched to the west to prevent launch debris from coming down over populated areas. But in general, no.

What about high inclination orbits?

What about an orbit that passes over a (geographic) north or south pole (inclination = 90 degrees)?

What about them? They are common, of course. Polar orbits in particular are popular for Earth observation satellites.

I know those exist, but by definition then, they wouldn't be either geosynchronous (because inclination = 90 degrees) or geostationary (obviously), when naively, I'd say they should be geosynchronous.

Isn't an inclination of zero identical to being "right on the equator" (by definition)?

Yes.

How eccentric could an orbit be and still be either geosynchronous or geostationary?

There is no limit on eccentricity for a geosynchronous orbit (theoretically... there are certainly practical limits). A geostationary orbit must have an eccentricity of zero.

[VictorBorun]

a retrograde GSO, would return to the same point in the sky more often (or less often???) than once per Earth rotation. Hmm, in the simplest case of zero eccentricity and zero inclination, what would the path of such an object be as seen from the ground and how often would it return to the same position in the sky (relative to the stars)?

there are 2 ways to return a satellite to the same point in the sky every 12 hours:
1) make its orbit lower that the geostationary
2) make its orbit retrograde but keep the same radius

something like (1) is in fact used by the GPS crowd but the orbits are not equatorial.

That incline has no effect for the orbit period though; the only effect for the point in the sky is that the visits, every 12 hours, are not in the equatorial plane. Which is welcome by GPS users in high latitudes

[ErasmusRoterodamus]

Magnificent what man can accomplish with a disciplined mind; frightening what we can't do without the discipline!!

[Rauf]

a retrograde GSO, would return to the same point in the sky more often (or less often???) than once per Earth rotation. Hmm, in the simplest case of zero eccentricity and zero inclination, what would the path of such an object be as seen from the ground and how often would it return to the same position in the sky (relative to the stars)?

there are 2 ways to return a satellite to the same point in the sky every 12 hours:
1) make its orbit lower that the geostationary
2) make its orbit retrograde but keep the same radius

something like (1) is in fact used by the GPS crowd but the orbits are not equatorial.

That incline has no effect for the orbit period though; the only effect for the point in the sky is that the visits, every 12 hours, are not in the equatorial plane. Which is welcome by GPS users in high latitudes

I am wondering if it's possible to be in a similar orbit around the moon. I am not sure what it's called, Lunar Stationary orbit? If my calculator is correct, an orbit around 86700 km above the lunar surface with 0 eccentricity and inclination has an orbital period equivalent to one lunar sidereal day.
But achieving that orbit, is it possible? I mean with Earth so close, will the satellite gets affected by Earth's gravity?

[johnnydeep]

a retrograde GSO, would return to the same point in the sky more often (or less often???) than once per Earth rotation. Hmm, in the simplest case of zero eccentricity and zero inclination, what would the path of such an object be as seen from the ground and how often would it return to the same position in the sky (relative to the stars)?

there are 2 ways to return a satellite to the same point in the sky every 12 hours:
1) make its orbit lower that the geostationary
2) make its orbit retrograde but keep the same radius

something like (1) is in fact used by the GPS crowd but the orbits are not equatorial.

That incline has no effect for the orbit period though; the only effect for the point in the sky is that the visits, every 12 hours, are not in the equatorial plane. Which is welcome by GPS users in high latitudes

I am wondering if it's possible to be in a similar orbit around the moon. I am not sure what it's called, Lunar Stationary orbit? If my calculator is correct, an orbit around 86700 km above the lunar surface with 0 eccentricity and inclination has an orbital period equivalent to one lunar sidereal day.
But achieving that orbit, is it possible? I mean with Earth so close, will the satellite gets affected by Earth's gravity?

I didn't check your 86700 km figure, but if accurate, it would seem that such a satellite of the moon would get too close to the earth at some points in its orbit, at which the Earth's pull would exceed the Moon's, judging by the long detailed discussion here:

https://physics.stackexchange.com/quest ... to-the-moo

A short and likely far too simplistic a synopsis is:

Earth is about 100x more massive than the moon, and since F∝M/r2
, the distance from Earth to the astronaut would have to be about sqrt(100)
= 10x further than from the moon to the astronaut. Therefore, the astronaut falls "up" about 90% of the way to the moon.

[Chris Peterson]

there are 2 ways to return a satellite to the same point in the sky every 12 hours:
1) make its orbit lower that the geostationary
2) make its orbit retrograde but keep the same radius

something like (1) is in fact used by the GPS crowd but the orbits are not equatorial.

That incline has no effect for the orbit period though; the only effect for the point in the sky is that the visits, every 12 hours, are not in the equatorial plane. Which is welcome by GPS users in high latitudes

I am wondering if it's possible to be in a similar orbit around the moon. I am not sure what it's called, Lunar Stationary orbit? If my calculator is correct, an orbit around 86700 km above the lunar surface with 0 eccentricity and inclination has an orbital period equivalent to one lunar sidereal day.
But achieving that orbit, is it possible? I mean with Earth so close, will the satellite gets affected by Earth's gravity?

I didn't check your 86700 km figure, but if accurate, it would seem that such a satellite of the moon would get too close to the earth at some points in its orbit, at which the Earth's pull would exceed the Moon's, judging by the long detailed discussion here:

https://physics.stackexchange.com/quest ... to-the-moo

A short and likely far too simplistic a synopsis is:

Earth is about 100x more massive than the moon, and since F∝M/r2
, the distance from Earth to the astronaut would have to be about sqrt(100)
= 10x further than from the moon to the astronaut. Therefore, the astronaut falls "up" about 90% of the way to the moon.

Consider that outside of a few very specially constructed cases, any three-body system is, at best, metastable.

[johnnydeep]

I am wondering if it's possible to be in a similar orbit around the moon. I am not sure what it's called, Lunar Stationary orbit? If my calculator is correct, an orbit around 86700 km above the lunar surface with 0 eccentricity and inclination has an orbital period equivalent to one lunar sidereal day.
But achieving that orbit, is it possible? I mean with Earth so close, will the satellite gets affected by Earth's gravity?

I didn't check your 86700 km figure, but if accurate, it would seem that such a satellite of the moon would get too close to the earth at some points in its orbit, at which the Earth's pull would exceed the Moon's, judging by the long detailed discussion here:

https://physics.stackexchange.com/quest ... to-the-moo

A short and likely far too simplistic a synopsis is:

Earth is about 100x more massive than the moon, and since F∝M/r2
, the distance from Earth to the astronaut would have to be about sqrt(100)
= 10x further than from the moon to the astronaut. Therefore, the astronaut falls "up" about 90% of the way to the moon.

Consider that outside of a few very specially constructed cases, any three-body system is, at best, metastable.

From Wikipedia:

In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it will settle back into its hollow, but a stronger push may start the ball rolling down the slope. Bowling pins show similar metastability by either merely wobbling for a moment or tipping over completely.

So, a three-body orbital system is "metastable" in that it can continue to exist indefinitely in isolation, but any sufficiently strong perturbation will cause it to deteriorate?

[Chris Peterson]

I didn't check your 86700 km figure, but if accurate, it would seem that such a satellite of the moon would get too close to the earth at some points in its orbit, at which the Earth's pull would exceed the Moon's, judging by the long detailed discussion here:

https://physics.stackexchange.com/quest ... to-the-moo

A short and likely far too simplistic a synopsis is:

Consider that outside of a few very specially constructed cases, any three-body system is, at best, metastable.

From Wikipedia:

In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it will settle back into its hollow, but a stronger push may start the ball rolling down the slope. Bowling pins show similar metastability by either merely wobbling for a moment or tipping over completely.

So, a three-body orbital system is "metastable" in that it can continue to exist indefinitely in isolation, but any sufficiently strong perturbation will cause it to deteriorate?

No, it self-perturbs. Even in isolation it is not stable.

[johnnydeep]

Consider that outside of a few very specially constructed cases, any three-body system is, at best, metastable.

From Wikipedia:

In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it will settle back into its hollow, but a stronger push may start the ball rolling down the slope. Bowling pins show similar metastability by either merely wobbling for a moment or tipping over completely.

So, a three-body orbital system is "metastable" in that it can continue to exist indefinitely in isolation, but any sufficiently strong perturbation will cause it to deteriorate?

No, it self-perturbs. Even in isolation it is not stable.

Alright. So, "autometastable" perhaps. Or just "chaotic".

[Chris Peterson]

From Wikipedia:



So, a three-body orbital system is "metastable" in that it can continue to exist indefinitely in isolation, but any sufficiently strong perturbation will cause it to deteriorate?

No, it self-perturbs. Even in isolation it is not stable.

Alright. So, "autometastable" perhaps. Or just "chaotic".

Metastability and chaos are closely related. Mathematically, all physically realized n-body systems where n>2 are chaotic.

[johnnydeep]

No, it self-perturbs. Even in isolation it is not stable.

Alright. So, "autometastable" perhaps. Or just "chaotic".

Metastability and chaos are closely related. Mathematically, all physically realized n-body systems where n>2 are chaotic.