Talk:STEREO

Orbital Positions

The original text had the A and B satellites orbiting at 22° fore and aft of the earth. At the same time the orbits are described as having periods of 347 days and 387 days (respectively). These orbits will cause the sats to gradually move away from the earth, so while the 22° positions may be *starting* positions, or *final* positions, or positions at *such-and-such* a date, or even *average* (over the working life) positions, they cannot be *fixed* positions.

True, the sats could be placed in quasi-stable orbits at plus and minus 22°, with the A sat orbiting just far enough inside earth-orbit that the earth's gravity just balances the tendency to advance ahead of the earth, and vice-versa for the B sat, but I don't think that is the case. Anyway, if if this alternate supposition was true, then the orbital periods section would need to be rewritten so that both sats had 365.24 day periods.

Xpi6 10:26, 13 December 2005 (UTC)

Yeah, I was wondering about that when I wrote the article, and I can't find where New Scientist got the 22° figure from. From the orbital times, it's basically 22°/earth year, which is probably where they got the figure from. JamesHoadley 11:03, 17 December 2005 (UTC)

So then its that they move 22° every year? I wonder could they every be placed in L4/5 orbits--BerserkerBen 19:36, 27 October 2006 (UTC)

The information about the current position of the STEREO spacecrafts can be found here : http://stereo.gsfc.nasa.gov/where.shtml I think they move at about 22&deg every year but their angular speed vary greatly within a year.

The two spacecraft continually move away from the Earth, one ahead of the Earth, the other behind, so that the Earth-Sun-spacecraft angle for each spacecraft increases by around 22 degrees per year. 130.246.132.26 (talk) 15:54, 7 May 2008 (UTC) Chris Davis, Project Scientist, STEREO Heliospheric Imagers.

Final positions - no

The intent is to be able to view the entire Sun at the same time. One NASA article that I read stated that they are slowly approaching their 180° point. That is, they will be opposite of each other in relation to the Sun. However, the statement was "approaching," not that that is the final destination. While a 180° position would allow the "entire" Sun to be viewed by the two satellites alone, their view will be not that great at the points on the Sun that are tangental to their view points. This makes me think that their final positions are to be at 1/3 earth-orbit in front and 1/3 earth-orbit behind the Earth (A, B, and Earth formaing a right-ish angled triangle around the Sun), their view of the "dark side" of the Sun will overlap each other slightly, and Earth based observations would make a 3rd viewpoint that would slightly overlap with each satellite. This would give a clear view of the entire Sun along the orbital path with only the very top and very bottom of the Sun having less than preferred imaging. If the above per year degree separation -- that someone here mentioned -- is correct, then they should reach the 180° point from each other in early 2011 (at that point, most of the surface will be visible). If they are going for a 1/3 separation between STEREO-B=Earth=STEREO-A, then they should reach their point around around the beginning or middle 2013. All of this I'm stating here is mostly based on what information I have gleaned here and elsewhere, my best guess on their intentions, and my ad hoc in-the-head calculations based on what very little I know. If someone can find information about their final orbital positions, it would be greatly appreciated by a number of people here if that can be added to the article (graphics even better appreciated). 67.177.214.210 (talk) 06:34, 26 January 2009 (UTC)

There is no final position for the STEREO spacecraft. There is insufficient fuel onboard to change their orbits in any significant way, e.g. to stop at the L4/L5 points. All maneuvers were performed before the lunar fly-bys, to make maximal use of the slingshot effect. Each spacecraft will continue to separate from Earth at 22°/yr. Eventually, they will pass behind the Sun, in 2015, and then come back toward Earth again. —Preceding unsigned comment added by Wtthompson (talk • contribs) 20:43, 25 February 2009 (UTC)

The article has a sentence about "the advent of constant 360-degree views of the sun" which should be changed to more accurately reflect that this 360-degree view is only momentary, though I assume that having two off-Earth perspectives will be highly useful to predicting CMEs at almost any phase. Wnt 16:56, 8 February 2011 (UTC)

Corrections on earlier comments

Regarding earlier comments: A "fixed" orbit is a layman's term (ie, scientists don't describe orbits this way) that refers to one in which the object's orbit does not enter the SOI (sphere of influence) of any other celestial body other than the one it is orbiting and the perturbations of orbit are minimal -- such as gravitational anomaly, aero-braking, solar radiation pressure, etc. Put another way; the Kepler orbital elements of the object is not expected to change anymore. A more technically-correct term would be a *stable* orbit.

A "final" orbit is one in which the craft either has insufficient propellant to alter its orbit further, or only station-keeping maneuvers are anticipated; For example to counter the effects of atmospheric drag, or to maintain its position through a LaGrange point. Prior to its final orbit, there are parking orbits, transfer orbits, initial orbits, etc. All of these descriptors are indicators of what is planned for the mission... it does not mean anything else.

People seem to be confusing the mission objectives with what is physically happening with the satellite; and I believe much of that confusion is due to the non-intuitive nature of orbital mechanics. Everything in motion (orbit) is constantly changing its position relative to anything else. We do not shoot satellites at the Sun and then they "stick" to specific points on that sheet of paper surrounding the planet and then never move again. When discussing orbital mechanics with lay-persons, it is helpful to create a simple animation showing the relative motions of each body... simply telling them what is happening does not work.

The "22 degrees" appears to be misunderstood; This number is derived from the number of degrees each craft is moving apart relative to the *Earth*'s orbit per *Earth year*. It's an attempt to describe to a layperson the relative motions of the two satellites. They were launched onto the same plane, but "behind" has a slightly higher aphelion and longer orbital period. Which means "behind" will continue to drift farther apart on each complete orbit relative to STEREO "ahead. This video provides a visual explanation: https://www.youtube.com/watch?v=yAo0lTo4qC0

People believe that STEREO has the same orbital period of Earth (365.24 days), but this is not true. If this were the case, the satellites would never move out of communications range of Earth by going behind the Sun. But don't take my word for it: https://stereo-ssc.nascom.nasa.gov/where.shtml Again, animations seem to be useful here for people who are not well-versed in orbital mechanics. — Preceding unsigned comment added by 76.17.167.78 (talk) 19:09, 1 November 2016 (UTC)

Exact Launch Time

I saw the launch live, and one of the mission collaborators said that STEREO launched at 00:52:00.339 (UTC). Can we put this in or is it useless?

Error in Page Formatting?

There seems to be something wrong with the formatting of the STEREO page. There is content that is (apparently) not available from any of the edit links.

Fuel to stop

Can anyone say how much more fuel would have been needed to stop the craft in L4 and L5 ? Rod57 (talk) 01:36, 29 May 2009 (UTC)

A&B orbital velocities relative to earths are 1.8 km/s; mass 620kg. Rod57 (talk) 23:17, 7 February 2011 (UTC)

Life of mission

Is anything likely to end the mission before the attitude control propellant runs out ? When is that likely ? Rod57 (talk) 01:53, 29 May 2009 (UTC)

STEREO interview, Feb 2011 says "The STEREO mission is currently funded until 2013. “The probes have enough fuel to last 100 years,” ... “The lifetime limiting factor is the spacecraft electronics and funding. The solar arrays will only gradually degrade over decades.”" Rod57 (talk) 20:53, 7 February 2011 (UTC)

Then why go around the backside of the sun? Do they have enough fuel to maintain a constant position at 120 degrees from the Earth? Something like Rod57 had mentioned immediately above. DAVilla (talk) 10:01, 9 February 2011 (UTC)

Presumably they don't have anywhere near enough fuel to change velocity by 1.8 km/s get back to a 365 day orbit. - Rod57 (talk) 13:19, 1 December 2019 (UTC)

Interesting that the reaction wheels on STEREO-A are apparently still working after 13 years. - Rod57 (talk) 13:19, 1 December 2019 (UTC)

Need more on EUVI

Many the STEREO images come from the 4 narrow band filters of the Extreme UV Imager (EUVI) which surely needs much more content in this or even its own article ? Rod57 (talk) 23:02, 7 February 2011 (UTC)

Orbital Direction

The article states that spacecraft B ejected itself from earth orbit in the opposite direction from spacecraft A. I thought that both spacecraft are orbiting the sun in the same direction as the earth, and that they are both "receding" or changing position relative to the earth because one has an orbital radius slightly more than 1 AU and one has an orbital radius slightly less.192.249.47.195 (talk) 15:56, 8 February 2011 (UTC)

That's a good clarification. DAVilla (talk) 10:00, 9 February 2011 (UTC)

I'm confused about the orbits

I'm still a bit perplexed as to the orientation of the two satellites' orbits, and how they could achieve a simultaneous view of the sun. An animation, or even just a diagram, would help this article a lot.

I understand that these satellites are orbiting the EARTH. But I don't see how two satellites orbiting the earth could obtain simultaneous views of BOTH sides of the sun. Wouldn't they have to be situated at opposite sides of the sun, in order to achieve that? What am I getting wrong?

Thanks, 75.4.194.121 (talk) 02:21, 11 February 2011 (UTC)

Check out the video at this website: [1] --Xession (talk) 02:23, 11 February 2011 (UTC)

The only thing you're not getting is that they ARE on opposite sides of the sun. — Preceding unsigned comment added by FoxBee (talk • contribs) 18:47, 1 November 2011 (UTC)

Sun rotation

The article says sun rotates every 25 days, while the video says its around 27 days. Both seem to be correct, but the article could be clarified, e.g. link to Solar_rotation#Sidereal_rotation or another way. Do you think the following is a good clarification?

Since the sun rotates every 25 or 27 days (depending on how you define solar rotation), ...

Could a more experienced editor please update the article?

Thanks, Ms937 (talk) 21:55, 29 December 2011 (UTC)

Lifetime

The article is confusing regarding the expected lifetime of the project. the infobox say "5 years" but these are over, and the mission seem to be still ongoing? thanks 79.177.231.197 (talk) 06:44, 29 May 2012 (UTC)

Subsystems - detail

Could add:

• Is the communications dish (high gain antenna) steerable ?
• Is there an omni-directional antenna (as backup) ?
• What propellant and thrusters are on board ?
• What type and number of reaction wheels ?
• Does it have to interrupt sun observations to observe another star for 20 days ?
• - Rod57 (talk) 13:53, 1 December 2019 (UTC)

Why was STEREO-B lost

Article says STEREO-B started to spin. Did NASA say why they thought it started spinning, and why it wasn't able to stop by itself ? - Rod57 (talk) 19:23, 13 November 2020 (UTC)