Tag Archives: Earth

DIY Space: Eyes On NASA

NASAs Eyes

There are several great tools available online designed to educate the public about space discoveries.  The best ones use data gathered by our space faring machines and help put it all into an understandable form.  Which is why NASA has developed the “NASA’s Eyes” program.

NASA’s Eyes is a program that can be used for multiple uses regarding virtual planetary exploration and understanding.  The program can be downloaded from this link.  It is a good tool to use to help in our understanding of some of the things going on here on Earth, too.  Honestly, the more I play with this particular program, the more I like it.  There’s a lot of data NASA has collected over the years about a lot of things, and it’s great that I can look at it in this form and play around with it.

NASAs Eyes Grav

Gravity map of the Earth. Note the GRACE satellites on the left side.

There are three primary topics of the NASA’s Eyes exploration tool.  “Eyes on the Earth” focuses on the Earth, the Earth’s environment, characteristics, the satellites looking at the Earth, and the payloads on the satellites used to gather data all about the Earth.  You can load what NASA calls “datasets,” data about a particular topic, such as ocean salinity, that’s been put together over the years.  The dataset then is displayed to show some interesting characteristics about things we take for granted, like gravity (image above).

NASAs Eyes Kepler

Eyes on the Solar System” has different kinds of datasets you can play with, but instead of the Earth, you can generally explore the Solar System.  There are different missions you can focus on, and see in great detail.  The Cassini mission (below)  around Saturn is pretty nifty.

NASAs Eyes Cassini

If you do get tired of the planets in our Solar System, there’s always the opportunity to look beyond, which is what the third set of datasets, called “Eyes on Exoplanets,” allows you to do.  Whether you wish to see exoplanets up close or just zoom out to admire the beauty of the galaxy we live in (below), Eyes on Exoplanets will help you.

Have a great time exploring space and please don’t forget to send a postcard :-).

Why Space Matters: GEO Satellite operations, Part 6–Eclipse

Eclipse

All that you touch, all that you see…

Yep, you guessed it!  We’re going to talk about another issue common to geostationary (GEO) satellites:  the eclipse.  This issue is almost opposite from the problem discussed in Part 5 of the GEO lesson series.  Instead of being overpowered by the sun’s energy, the satellite can’t function because of a lack of it.

Here’s how that works.

Twice a year, the Earth gets in the way of the GEO satellite’s view of the sun.  Those two periods occur around the vernal and autumnal equinoxes.  The eclipse period starts in very small time increments at first, gradually increasing over a period of days.  Eventually the eclipse peaks for nearly 70 minutes, then starts decreasing over the next few days.  Each eclipse period during each equinox lasts a total of 45 days.  For some satellites, though, these periods can be too long.

Forever’s gonna start tonight…

You see, the satellite’s systems are powered by electricity.  There’s no extension cord long enough to plug the satellite in, but the satellite must be powered somehow.  The common engineering answer has been to use the sun’s energy, absorbed and changed to electricity through a satellite’s solar panels.  The power is then saved in the satellite’s batteries.  The batteries then power the rest of the satellite, sub-systems, payload, etc.  But what happens when there is no sun as a source of energy for the satellite solar panels to convert?  Well there’s nothing I can say other than it’s a total eclipse of the part (of the satellite).

Again, you may be thinking, “No biggie.  I have a cell phone in my pocket that has more capability than a satellite, and it can last for days.  Surely satellite weighing tons can last longer on batteries than my tiny phone.  Right?  Right?”  The answer to this is:  It’s complicated.

You would think the designers of these very expensive satellites would put enough batteries on board a satellite to compensate for an eclipse.  They try, but here’s a question for you:  Have you ever lifted a car battery?  Now pretend the satellite has same car battery weighing at the low end of 15lbs—and multiply that weight by 103.  That’s about what the Nickel Hydrogen batteries of a modern GEO satellite weigh.

…Everything under the sun is in tune…

What this heavy fact means is there are only so many batteries that can be put on a satellite before it becomes too heavy, and therefore, too expensive to launch.  So batteries are part of a price/weight/required power/risk management balancing act.  For most satellites, the eventual design is just fine.  When eclipses come around, the satellites can rely on the battery to eventually get them through the full 70-minute eclipse.  Operations can continue without a hiccup.

But what can be done if an operational satellite’s batteries start going south?  Or if some other part of the power sub-system starts degrading or just stops working?  Suddenly the capacity to power a satellite is greatly diminished.  Suddenly the satellite may not have enough power to not even turn itself on again (at least until the sun charges them up again—but totally depleting a battery is sometimes not a good thing either).  There are also certain preventative maintenance functions a satellite operator uses to help with satellite battery life.  But all of this is what makes the battery balancing act tricky.  Now, here’s another question for you:  How long do batteries last in your household?  Especially the rechargeable ones?

I don’t know what to do, I’m always in the dark…

There’s no Walmart satellite servicing garage in space just now.  Satellite servicing and battery change capability aren’t available to satellites (yet—see this interesting tidbit).  The batteries that are designed and eventually loaded onto a satellite’s bus must be robust, long-lasting, and reliable.  If any of those criteria are violated, the satellite just becomes a very expensive man-made star.  Since satellites are so pricey to get into orbit to begin with, quite a few owners expect the satellites to be designed to last a long time–some as long as 15 years.  So guess what also needs to last that long?  Would it amaze you to know the batteries do last this long on some satellites?  They do, but eclipses still cause power issues.  At least they are predictable.

Of course, this sort of problem isn’t only the province of the GEO satellite.  The other satellites also have some power issues to deal with, including eclipse.  But this problem is very obviously seen on GEO satellites, especially since a lot of the public relies on communications and weather from those sources.

There is another problem GEO satellites do face, but that’s a lesson for another day.

HOLD ON!!!  I JUST ADDED THIS:  It seems appropriate for my readers, and I like DIY things.  Those of you from a different age might recognize Patrick Norton from ZDTV.  He’s been for the longest time a podcast host on Revision3.  The particular episode (below) posted on 27 Jan 2014 is all about making your own batteries to charge a cell phone–without lemons.

Why Space Matters: GEO Satellite operations, Part 5–Lights & Music

During the last few lessons, the great advantages of satellites in a geostationary orbit (GEO) were espoused about ad nauseum.  The characteristics of persistence in communications and observations are the direct benefits of using a satellite in GEO.  Include the huge field of regard and simplified ground system requirements, and it’s really a no-brainer to use GEO satellites for communications, remote sensing, observations, etc.

But, there are also a few disadvantages affecting satellite operations.  Problems with names such as “solar interference,” “eclipses,” “latitudinal limitations,” and “space weather.”  And while being at such a high altitude (35,786 km (22,236 mi)) from the Earth’s surface is good for seeing the whole world, a GEO satellite won’t “see” the details (technology is getting better, however).  What exactly, then, do these problems pose to satellite operations?  And how do some satellite operators deal with them?

Solar influence (or sun fade/solar transit) sounds somewhat benign.  It is also fairly easy to explain, and we’ll explain it with music.  Specifically, loud music.  If you’ve ever been to a rock concert, rave, etc., you understand the meaning of “loud music.”  You and your friends stand in front of the stage while your ears are sonically overpowered.  One of your friends tries to talk with you during this sonic assault.  You can’t hear the conversation.  So your friend tries yelling.  You still can’t hear the conversation.  Your friend’s voice simply can’t compete with the band’s amplified speakers.  Attempts at conversation stop until a lull.

This is essentially what occurs during solar interference, except it’s happening with radio waves.  There are times when the sun is directly behind the GEO satellite and above the satellite’s ground station.  The sun emits a lot of noisy radio wave energy.  It’s the equivalent of the amplified speaker overpowering your friend, the satellite.  During this alignment of the sun, GEO satellite and ground station, the ground station is unable to sort out the satellite’s communications signal from the sun’s noisy radio wave assault.  The video below shows the alignment occurring.  During that time of alignment, no signal could be received from the satellite.

This communication “outage” (no satellite communications), is predictable and typically starts gradually—a few minutes at first.  Slightly longer when it’s in direct alignment.  It’s the reason why certain agencies issue notifications like the one below.

As the Earth and satellite rotate, the sun will slowly come into alignment, with the time of the communication outage peaking at the exact time of the alignment of the sun, satellite, and ground station.  Then the communication outage shortens as the sun slowly moves away from the alignment, until it’s not even close to the alignment anymore.  Contact between the ground station and GEO satellite means satellite operators will be able to conduct 24/7 operations once again.  For more detailed information about this, please go to this Intelsat page and this Celestrak page.

Now you satellite television subscribers know why your signal goes out about twice a year.  You’re under the influence–solar influence, that is.  It’s only for a few minutes and hopefully you’re watching nothing terribly important.

More about the other GEO satellite disadvantages next week.

Why Space Matters: GEO Satellite operations, Part 3–Revolution Earth

“Endless Distance, Wildlife and Stars, Blanket the Night…”

The last lesson was about Field of View (FOV) and Field of Regard (FOR).  It was intended to help with understanding the next few lessons regarding satellites in geosynchronous orbit (GEO).  All mentions of GEO on this blog, unless otherwise stated, refer to a particular type of orbit:  it is an orbit above the Earth’s equator matching the revolution, or rotation, of the Earth.

Just in case there are people reading this blog poised with a “well, actually”—yes, yes—there are other orbits associated with GEO.  You can go here to read all about those—the article is mercifully short, so if you’re curious, go ahead and read it.  But we’re not going to cover those other geosynchronous orbit types in these particular lessons.  The geosynchronous orbit type we will be focusing on is the geostationary orbit.  As stated before, we will use GEO as the term for that orbit type.

“…You lying beside me darling, Eyes open wide…”

Hopefully the concept of a GEO weather satellite being able to see more with its “eyes” in its FOR than a Low Earth Orbiting (LEO) satellite is an easy concept to grasp.  This main FOR distinction means a few things:  with GEO satellites, you can see the patterns of the clouds, instead of just cloud cover, which LEO satellites will give you.  With GEO weather satellites, you can see where a weather pattern is trending towards—so they are important for hurricane warnings and such.  The GEO satellite’s “eyes” cover a wider area.  The resulting images from such a vantage point are like the next image:

Image from “ThisIsMoney.uk” but they got it from NASA.

But one of the most important advantages is associated with the GEO’s orbital period (how fast it goes around the Earth).

While the wide arc of the globe is turning, We feel it moving through the dark…”

In the LEO satellite lessons, you found there were some variations in the orbital period of LEO satellites.  This has to do with the variations in altitude of the different satellites and you can just go to these posts to read more about them.  A GEO satellite is, obviously, at a much higher altitude and directly “above” the Earth’s equator:  35,786 km (22,236 mi) from Earth’s surface—or 26,199 miles if you go to the Earth’s core.  This altitude, and its position above the Earth’s equator, means the GEO satellite’s orbital period will match the Earth’s rotation.  Below is a decent animation of what’s happening:

GEO animation from Wikimedia

The satellite will arc through the sky, matching the globe as it turns.  So, what is the benefit of this orbital characteristic?

It means a weather satellite (or any kind of satellite, really) in a GEO position will observe the part of the Earth the satellite is orbiting above 24 hours a day.  This one aspect describes the concept of “persistence” in satellite operations.  Persistence is how weather satellites in GEO can “track” a weather system.  Instead of seeing small, swiftly passing “weather trees” that a LEO weather satellite can see, a GEO satellite sees the entire “weather forest.”

“…On a voyage between dusk and dawn, Space and time…”

And the GEO satellite can observe that “forest” for 24 hours a day, seven days a week, etc.  A LEO satellite, because it’s moving so quickly, and the Earth is rotating as much as 2,200 km (1,367 miles) per 90-minute low earth orbit, doesn’t have this kind of persistence.  Is it possible for a LEO satellite to have persistent observation of a single point of the Earth?  Well, kind of—you have to have more than one LEO satellite to accomplish persistence.  But, as discussed in previous lessons, this kind of LEO satellite constellation introduces complicated ground system requirements, communications interlinks, etc., which is why using only one GEO satellite is the option selected by many organizations to do the job.

There is another advantage regarding this orbit, though, and we’ll get into that next week.

The interspersed lyrics are from the B-52’s song, “Revolution Earth.”  Disappointing video, but great song from their album “Good Stuff.”

Skybox: Youtube videos from space?

Skybox launched their satellite (with a few others) November 22.  But they are beginning to get sample videos in from their SkySat-1 satellite out to the public.  SkySat-1 is a sun-synchronous Low Earth Orbiting (LEO) polar satellite going around the Earth around 450 Km (280 miles) from Earth’s surface.  Skybox notes this satellite’s expected orbital lifetime is 2.5 years.  Whether that’s just a limit they’ve figured out because of components or atmospheric drag, is unknown.

Here’s the video of what they’ve done so far:

I don’t know if they’ve slowed down the videos, but they certainly do look pretty good.  There doesn’t seem to be any sort of stabilization problem–in other words, the videos look rock-steady.  Considering how fast the satellite is flying (a little over 4 miles per SECOND) over those areas, it’s a pretty damn good feat.

The satellite’s imaging payload is reportedly able to record full High Definition (HD) video at a 1080p resolution for 30 frames per second.  The satellite’s payload can record a a single video clip for 90 seconds.  The actual resolution to the ground (don’t confuse this with the image screen resolution) is supposed to be less than a meter.  Skybox say the satellite can generate up to one terabyte of data in a single day, so this video information has to be stored on board a huge hard drive (for satellites)–768 Gigabytes, according to this FCC license application.

There isn’t much information about the ground stations aside from what’s in the FCC application.  But they do have an operations center in Mountain View, California, and control the satellite and payload with commands from there.  It sounds like at least one of the remote ground terminals for sending and receiving information from the satellite is located in Fairbanks, Alaska.

The interesting thing to note is Note 6 in the FCC application, which comes down to this:  other ground stations outside the US will be able to send imagery commands to the satellites to tell them where to look.  But those commands will always originate in Mountain View’s mission operations center.  So there will be some sort of sharing agreements with other ground stations to get the video taken (and perhaps eventually, downlinked).