[bearnard1212 (OP)]

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?

[Halc]

There are actually none.  We currently lack the technology to deliver sufficient delta-V to put an object into a sun-synchronous orbit (an orbit that hangs over a fixed point on the surface of the sun).  Such an orbit would seem to serve no purpose.

Perhaps you mean something else by the term.

[Janus]

There are actually none.  We currently lack the technology to deliver sufficient delta-V to put an object into a sun-synchronous orbit (an orbit that hangs over a fixed point on the surface of the sun).  Such an orbit would seem to serve no purpose.

Perhaps you mean something else by the term.

He seems to be referring to a Solar-synchronous orbit.   This is a polar orbit which precesses at a rate equal to a Solar day.
The object is to have the satellite pass over the same point of the surface when the Sun is illuminating it at the same angle.
It is useful for weather and surveillance satellites because the lighting will be the same for each pass. 

[Halc]

He seems to be referring to a Solar-synchronous orbit.   This is a polar orbit which precesses at a rate equal to a Solar day.

Ah, I was picturing something that hovered over one point on the sun, for some unfathomable reason. This is something orbiting Earth, not the sun.

How do they get a polar orbit to precess all the way around once per year? Expend energy?
Seems like it would be at geosync altitude on average, but different orbital axis.
It need not be a circular orbit at all, and would benefit from being furthest from Earth in the day to give more time to measure stuff. Such an eccentric orbit also keeps it out of the high-contention geosync path.

[Bored chemist]

I can, in principle, put a satellite in orbit above the Earth's equator such that it is, for example, directly above Singapore.
If I put a camera on that satellite I can point it at Darwin in Australia and it will pretty much stay pointed at Darwin.
All I have to do is ensure that the orbital period is equal to the time it takes the Earth to rotate on its axis (WRT the fixed stars I think).
But I can't really do that for the Sun. I could (in principle) put a satellite in orbit round it with a period of 27 days which is "the rotation period of the Sun".
But it won't work- because different latitudes of the sun rotate at different rates. Ignoring the fact that a "Darwin" on the Sun would boil, it would also drift out of the view of my camera because the rotation of the Sun depends on latitude.
It's a big blob of gas , not a solid.

What I can do is put a satellite at one of the Lagrange points.
https://en.wikipedia.org/wiki/Lagrange_point
If I do that, then from my perspective, here on Earth, it looks like the satellite is always lined up with the Sun.

Such a satellite might be very useful if I was studying weather.

[Janus]

He seems to be referring to a Solar-synchronous orbit.   This is a polar orbit which precesses at a rate equal to a Solar day.

Ah, I was picturing something that hovered over one point on the sun, for some unfathomable reason. This is something orbiting Earth, not the sun.

How do they get a polar orbit to precess all the way around once per year? Expend energy?
Seems like it would be at geosync altitude on average, but different orbital axis.
It need not be a circular orbit at all, and would benefit from being furthest from Earth in the day to give more time to measure stuff. Such an eccentric orbit also keeps it out of the high-contention geosync path.

They fine tune the inclination of the orbit according to its altitude ( in other words, it is not a perfectly polar orbit).  That way, the Earth's own equatorial bulge produces the desired precession.  Solar synchronous orbits are not put at geo-sync altitudes.  They are much lower.  They can orbit the Earth multiple times a day. (for weather and surveillance satellites this means you can image multiple points on the Earth's surface)  You just want consistent lighting for any given region on every pass.

[bearnard1212 (OP)]

There are actually none.  We currently lack the technology to deliver sufficient delta-V to put an object into a sun-synchronous orbit (an orbit that hangs over a fixed point on the surface of the sun).  Such an orbit would seem to serve no purpose.

Perhaps you mean something else by the term.

Actually, I found out that Sun-synchronous orbit is useful for weather satellites, for some microstellites and for some launch vehicle that are used for microgravity missions and experiments I guess
https://en.wikipedia.org/wiki/Sun-synchronous_orbit

[bearnard1212 (OP)]

There are actually none.  We currently lack the technology to deliver sufficient delta-V to put an object into a sun-synchronous orbit (an orbit that hangs over a fixed point on the surface of the sun).  Such an orbit would seem to serve no purpose.

Perhaps you mean something else by the term.

Also, I`d like to mention   It is a light class launch vehicle, intended for placing payloads into Sun- Synchronous Orbit. As I have alredy mentioned Sun-synchronous orbit is useful for weather satellites, scientific satellites and microsatellites, for some microstellites and for some launch vehicle that are used for microgravity missions and experiments

[Janus]

There are actually none.  We currently lack the technology to deliver sufficient delta-V to put an object into a sun-synchronous orbit (an orbit that hangs over a fixed point on the surface of the sun).  Such an orbit would seem to serve no purpose.

Perhaps you mean something else by the term.

Also, I`d like to mention rocket XL  It is a light class launch vehicle, intended for placing payloads into Sun- Synchronous Orbit. As I have alredy mentioned Sun-synchronous orbit is useful for weather satellites, scientific satellites and microsatellites, for some microstellites and for some launch vehicle that are used for microgravity missions and experiments

By now, it should have been obvious to you that Halc originally thought you were talking about putting an object in orbit around the Sun, so that it remained over one point of its surface, and that he is no longer under that impression. It no longer makes sense to reply to this particular post anymore,  as it pertains to this original assumption.