Sun-synchronous orbit spacecrafts

Have you ever heard about Sun-synchronous orbit spacecrafts? According to the information I`ve found such name have weather satellites and some kind of scientific satellites. Also, I`ve heard that there are not only weather satellites and scientific satellites that are used in Sun-synchronous orbit. Do you know which kind of sats or maybe other spacecrafts are used for Sun-synchronous orbit?

a reply to: james00

A "heliosynchronous" orbit is basically just a polar orbit canted a few degrees (roughly 2 degrees). The orbits are useful for any type of an imaging satellite because the surface of the Earth under the satellite will always be light or dark, depending on the type of imaging to be done.

a reply to: james00

Do you know which kind of sats or maybe other spacecrafts are used for Sun-synchronous orbit?

Black knight

a reply to: keukendeur

C'mon, man!

Be nice.

It was an innocent enough question.

a reply to: Flyingclaydisk

It was an honest answer...Black knight was said to have a near polar orbit if I remember correctly.

But if it was really a thread worthy question?

Usage

Polar orbits are often used for Earth-mapping, Earth observation, capturing the Earth as time passes from one point, reconnaissance satellites, as well as for some weather satellites.[2] The Iridium satellite constellation also uses a polar orbit to provide telecommunications services. This differs from a geosynchronous orbit in which one spot on the Earth's surface can be sensed continuously from a satellite.
Sun-synchronous orbits

Near-polar orbiting satellites commonly choose a Sun-synchronous orbit, meaning that each successive orbital pass occurs at the same local time of day. This can be particularly important for applications such as remote sensing atmospheric temperature, where the most important thing to see may well be changes over time which are not aliased onto changes in local time. To keep the same local time on a given pass, the time period of the orbit must be kept as short as possible, this is achieved by keeping the orbit lower around Earth. However, very low orbits of a few hundred kilometers rapidly decay due to drag from the atmosphere. Commonly used altitudes are between 700 and 800 km, producing an orbital period of about 100 minutes.[3] The half-orbit on the Sun side then takes only 50 minutes, during which local time of day does not vary greatly.

To retain the Sun-synchronous orbit as Earth revolves around the Sun during the year, the orbit of the satellite must precess at the same rate, which is not possible if the satellite were to pass directly over the pole. Because of Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque, which causes precession. An angle of about 8° from the pole produces the desired precession in a 100-minute orbit.[3]

I have no idea what Wiki doesn't answer in regard to the OP's question.

a reply to: Flyingclaydisk

Why the 2 degrees?
Why not polar?

a reply to: Terpene

See previous post...

To retain the Sun-synchronous orbit as Earth revolves around the Sun during the year, the orbit of the satellite must precess at the same rate, which is not possible if the satellite were to pass directly over the pole. Because of Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque, which causes precession. An angle of about 8° from the pole produces the desired precession in a 100-minute orbit.[3]

originally posted by: Terpene
a reply to: Flyingclaydisk

Why the 2 degrees?
Why not polar?

You need the satellite to advance just a tiny fraction more than 1 degree in each 24 hour period. In one calendar year the satellite will make one revolution around the equator much the same as the Earth will take one year to revolve around the Sun. A polar orbit would have the satellite pass over the same two points on the equator all the time.

ETA - Sorry, I bumped my head on that last part; that was incorrect. It's a torque vector as noted in the wiki C&P above. I was doing it from memory.

ETA 2 - Wait, that was correct after all. **removing the strikethrough**

a reply to: james00

I first thought you meant a LaGrange point to where two or more bodies have gravitational points that will effectively cancel each other out. However, I learned that within the LaGrange points the gravity is unstable but, the spacecraft orbit the LaGrange point as a "halo" orbit. Further explanation is in the Wiki entry: LaGrange Points
I learn sumthin' knew eech day...

a reply to: Flyingclaydisk

If the main reason for this technic is to have the same lighting why not put it equatorial and fly counter earth spin at the same speed? Let earth turn, while the satelite sits where the sun is, sort of...

a reply to: NightFlight

Lagrange... Oh the memories... Back in high-school I dated a girl called lagrange. We were so attracted to each other, it didn't work.

I always wonder is gravity at the center of the mass biggest or absent?

originally posted by: Terpene
a reply to: Flyingclaydisk

If the main reason for this technic is to have the same lighting why not put it equatorial and fly counter earth spin at the same speed? Let earth turn, while the satelite sits where the sun is, sort of...

The satellite aren't flying high enough to capture everything that's lit at the same time - they're usually getting a small chunk at a time. These kind of orbits allow them to take a photo of one section, then the next, then the next and so on. If you look at the images the ISS sends back, each photo is roughly the same sort of area, maybe even less.

Edit to add:

This image from 1969 is from a NIMBUS 3 satellite. Each side is roughly 1000 miles.

One frien of mine shared an article with me about one of Sun-synchronous orbit spacecraft . It`s called xl rocket This is a three-stage light class launch vechicle. It is aimed at placing pay loads into Sun-Synchronous Orbit over range of 500 km altitude. As far as I know this type of rocket deliver space weather satellites or satellites related to Earth observation.

originally posted by: keukendeur
a reply to: james00

Do you know which kind of sats or maybe other spacecrafts are used for Sun-synchronous orbit?

Black knight

In your dreams.

a reply to: james00

I discuss the concept in an appendix I wrote for the US Space Command some time ago.

“Orbitology” Explained [for US Space Command book, ‘Space Power Theory’]
" www.jamesoberg.com...

The fundamental principle is that satellites will orbit Earth in a fairly constant plane, tilted to the equator.

Because there is a slight bulge around the equator, the path of satellites crossing the equator are displaced slightly on each pass, in on direction during the approach and in the opposite direction during the departure from the equator ... the result is that the plane of the orbit in inertial [galaxy-relative] terms shifts, usually westward for crossings from southwest to northeast.

For typical satellites in low orbits and moderate inclinations [30 to 60 degrees] this can be as great as 5 or 6 degrees westward every day.

If you are on a long-duration earth surface observation mission it's useful if you get the same photos of areas over the year with the sun angles similar so you can compare like-to-like.

But since Earth circles the Sun, in 365 days the direction to the sun shifts 360 degrees in the earth-centered reference frame -- about a degree per day.

So you would like your observation satellite to ALSO shift its orbit that much to match the sun's shift in the sky. That requires the satellite to travel somewhat 'backwards' -- south-south-east to north-north-west, which twists its orbit exactly counter to the twist induced by Earth's motion around the sun.

The result is very useful ground observation historical records, very comparable season-to-season because shadows are about the same.

a reply to: JimOberg

I have no idea why I would dream about this, probably picked it up right here on ATS but so far it has been the only attempt at trying to answer the OP.

I`ve heard that there are not only weather satellites and scientific satellites that are used in Sun-synchronous orbit. Do you know which kind of sats or maybe other spacecrafts are used for Sun-synchronous orbit?

I could say it was a thermal blanket lost during an EVA but that wouldn't fall in the category of "sat or spacecraft" the OP was looking for.

a reply to: keukendeur
There is another interesting point to be discussed about XL rocket. The third stage for this rocket is manufactured with the help of 3D printing technology.