Category Archives: LEO

Low Earth Orbit=LEO

Launching satellites is getting cheaper?

Last year was pretty good for small satellites weighing less than 10 kg (22 lbs).   46 percent of all satellites launched in 2014 weighed less than 10 kg. A LOT of satellites were launched in 2014. Heck, just one Russian Dnepr rocket deployed 37 satellites during one launch last year. Many were deployed from the International Space Station. But while small satellites seem set to grow even more this year, one of the big limiting factors to that growth is the number of rockets that can launch them, inexpensively and reliably. And little oopsies such as what happened with the Antares and Falcon rockets aren’t doing much to increase the opportunities to launch small satellites.

However…

…there’s a company trying to join what appears to be the growing small satellite market business through providing cheaper prices for launching satellites. Rocket Lab, founded about eight years ago, is building a new rocket and is offering to launch a satellite for as low as $80,000. And that satellite has to be quite small–a 1U cubesat. 1U means 1 unit, the satellite, that is 10 cm (3.94 inches) by 10 cm by 10 cm big and weighs no more than 1.33 kg (2.93 lbs).

A person has the option to go bigger, but will need to pay more. Rocket Lab will graciously launch a 3U cubesat for $250,000. They will launch either one on their yet-to-be-launched Electron rocket. The rocket can only hold so much–8 1U cubesats and 24 3U cubesats per launch. It looks like there’s a bit of interest in the launch opportunities, which they’re projecting to start in the third quarter of 2016. Peter Beck, Rocket Lab CEO, explains some of the rationale for why their system will work in the video below.

The Electron rocket is new and full of interesting tech to make launch cheaper, and you can read about the rocket, here. But Rocket Lab is also building a commercial launch site in New Zealand. Part of the problem Rocket Lab has identified with the current active spaceports is how busy they are and how active the airspace is around those spaceports. In the U.S., certain transportation such as boats, trains, and planes are restricted from moving through spaces in which a rocket can launch and/or fail.

Rocket Lab also believe the location is perfect for launching satellites into “high inclination” orbits. Those orbits will probably be at angles of 90 degrees plus from the Earth’s equator since they’re specifically mentioning sun-synchronous orbits as the target for the satellites they’ll be launching. What, you don’t know what sun-synchronous is? You can go here to read about the sun-synchronous low earth orbit if you want to learn more.

Rocket Lab isn’t the only company focused on catering to the small satellite market. Firefly Space Systems is building their Alpha rocket, which will be able to launch at least 12 3U satellites and a bigger primary payload into sun-synchronous orbit. No advertised prices per satellite yet, but since there are less cubesats launched, and their CEO was quoting $8-9 million to launch an Alpha (vs. Electron’s $4.9 million per launch), the pricing might be slightly higher to launch a cubesat on an Alpha. And Firefly will still have to deal with the problems of current spaceports, unless they build their own (or perhaps lease from SpaceX?). But the Alpha can carry more mass.

Either way, it seems like more competition is coming to the small launcher market. I might be able to afford my small satellite fleet yet…

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Gravity Check: Thousands of Satellites Orbit Earth

Counting Satellites

Quick–just how many satellites, operational or not, are orbiting Earth?  Pretend you’re trying to impress your fellow engineers.  Even better, pretend you’re trying to impress people in a bar (although that strategy might backfire).  Have you guessed?  Do you really want to know if you’re correct or are you satisfied with impressing the folks in the pool hall?  If it’s the former, then this Talking Points Memo post helpfully gives several numbers regarding satellites orbiting the Earth.  So next time, you’ll be very accurate and the biker in the leather jacket will buy you that beer for your numerical diligence.  Well, it might helpful, at least, for those who love minute details and numbers.  Maybe you should bring it up at an accountants meeting instead?

But before you go over to the post, did you guess a number?  You’d be closer if the number were in the thousands.  Do you know who owns all of them?  What countries do they belong to? Remember, you’re going to have to include cubesats, small sats, GEOs, LEOs, MEOs, and HEOs.  It might help during your counting if you have some excellent optics and a pad and pen.  Or you could just go to Talking Points Memo’s post and find out.  That would certainly be easier, and take less time.  But if you’re like me, maybe you’re not so busy…

The Earth’s “Love Handles”

Womencitizen is focusing on the Earth’s “Love Handles” with this 2 February post.  University analysts are finding the odd shape of the Earth is keeping satellites in orbit longer than if it were a perfect sphere.  If you’ll remember, the Earth isn’t shaped like a perfect sphere, but more like a squashed Halloween pumpkin.  Such a shape creates a “bulge” (or “Love Handles” in Womencitizen-speak) around the middle of the Earth.

I’ve talked about this sort of phenomena in the LEO lessons.  So go there for a longer explanation.  The bulge at the Earth’s equator helps sun-synchronous low earth orbiting (LEO) satellites fly over certain points of the Earth’s surface at certain times.  But now there’s more.  Apparently the Earth’s bulge has more influence over satellites orbiting it than the sun or moon.  Because of such influence, the satellites remain in orbital equilibrium much longer than they would if they were orbiting a sphere-shaped world.

To see why the Earth bulges, you can also go to this site.  It demonstrates, quite nicely, why the Earth is the shape it is.  With more satellites projected to launch into space, and more space operators dealing with the realities in space, we’re about to learn a lot more.

Why space matters: Imaging satellite operations, part 9–cutting the cheese

Hopefully the beer was tasty and nutritious.

The question I posed in my previous post to you, dear (inebriated?) reader:  Why is it that moving the plane of a satellite’s orbit against the direction of the Earth’s rotation (backwards) is helpful to those operators of imagery ilk?

Let me clarify some terms here before we go on.  A satellite’s orbital plane is NOT a toy airplane flying around the satellite.  Instead, imagine a ball of mozzarella cheese representing the Earth, with that gosh-darn coin orbiting it representing the satellite.  If you attached a very long blade to the coin, insert the blade to the center of the cheese, then moved the coin in one orbit, you would likely cut the cheese in half.   So here’s the setup:

Getting ready to cut that cheese

Getting ready to cut that cheese

The nice flat surface of either half extended to the coin’s orbit around it now looks like a disk and represents the satellite’s orbital plane.  It’s a line extending through three different points: from the center of the coin at one part of the orbit, going through the center of the heavier object (the cheese/Earth) near the orbit’s center, and then extending to a point representing the center of the satellite in a different part of the orbit.  Like so:

Plane cheese

Plane cheese

Coin cheese

See, I didn’t have to use terms like inclination and longitude of the ascending node to explain this part.  Read more here, if I’ve successfully convinced you to drink again.  Read it before you drink.

Why discuss those?  Well the Earth rotates on one plane and zips along another as it orbits the sun.  The satellites in our situation zip along a different plane, one nearly perpendicular to the Earth’s rotation.  Because these inclinations are slightly past perpendicular, the orbital plane of these imagery satellite orbits rotate opposite the Earth’s rotation at a rate around 1 degree of longitude per day.  In the space world, this is backwards rotation is called precession and it is the result of torque.  There’s more here that explains this better.

So that was a lot of jibber-jabber and maybe your brain is mushy, but hang in there.  The answer to the question at the beginning is simple, really.  The sun-synchronous orbit assures imagery operators the areas they are taking photos of have nearly the same kind of light every time they want to get a snapshot.  Does the interested organization want the satellite to always skirt the dusk/dawn lines of the Earth?  Or do they want to see certain surface areas in the morning or afternoon, when shadows might be helpful?  The sun-synchronous low earth orbit can do either one, and again, cuts down variables a notch.

So, you’re an imagery operator.  Up to this point, you know you might have 11 ground terminals (thanks to Digitalglobe) to upload and download data between your satellites and operations center.  And you have at least five satellites, all zipping around the Earth in a sun-synchronous low earth orbit.  Because you’re interested in changes to the Earth’s surface and recording them over time, you think that having those satellites crossing San Francisco’s latitude (37.78 degrees) at mid-morning would be useful.  You’re almost ready for your mission.

Or maybe not.  What to do, what to do…?  I think I’ll write more in another post, maybe about satellite sub-systems and imagery payloads.  Go have a beer, and I’ll see you then!

Why space matters: Imaging satellite operations, part 8–synchronizing flying pumpkins and suns

Sorry, this isn’t about a tribute band for 90’s alternative/grunge music, at least not “Today.”  This is all about polar orbits and polar sun-synchronous orbits.

But before I get into those topics, let me warn you that if you delve too far into this, understand the math involved, the terms used, and worst of all worlds—enjoy it–you risk becoming pariah.  It’s one of the reasons I chose not to be as smart as some of you readers—I couldn’t risk becoming a giant among men—it’d be socially irresponsible.  So once you’re done reading and you understand all the references, maths, pictures, my writing, etc., go have a beer and kill some brain cells.  For the “normals,” what I’m about to write might be a little complicated.  I sometimes have trouble with it myself and the funky symbols certainly don’t help.

Polar orbits are cooler than cucumber daiquiris and perhaps more useful (depending on your need).  With one imaging satellite, you can take a boatloads (payloads?) of pictures and eventually get a portrait of the whole planet’s surface.  But how do you guarantee that the location on the surface will be in sunlight at a particular local time of day?  You put the satellite into a polar sun-synchronous orbit.

Both Digitalglobe and RapidEye use this orbit for their satellites (there’re, as of this writing, five satellites per company, remember).  Even though the orbit is close to polar, it’s not quite there—more like a little past polar.  For RapidEye and Digitalglobe both, the inclination is listed as around 97 (97.8 for RapidEye and 97.2 for Digitalglobe) degrees.  Sun-synchronous orbits can be as low as 96.5 degrees from the Earth’s equator, to as high as 102.5 (JPL paper page 1 Intro, para 2).  Why would they choose such weird inclinations for their satellites?

Well, one reason both companies are so inclined (see what I did there?) is because what I told you two paragraphs ago:  to ensure the satellites will always cross the same latitude (the line that parallels the Earth’s equator) at the same local time for that part of the planet.  If you’re trying to take atmospheric measurements, document changes on the Earth’s surface, etc., this sort of orbital consistency helps take a variable or two out of the imagery equation.

Another reason to use these inclinations is because of the Earth’s shape.  Most studied space scientists now agree the Earth is shaped more like a squashed pumpkin (oblate spheroid) rather than an orange (sphere).  So there is a little extra mass along the Earth’s equatorial area (the Earth has a beer belly!).

Oblate Spheroid vs. sphere

Orange oblate spheroid vs. orange sphere

This extra mass causes some interesting influences to a satellite’s orbit, especially one inclined between 96.5 and 102.5 degrees.  Remember, most polar low earth orbiting satellites are moving in the direction of the Earth’s rotation, and they are zipping over the Earth’s surface, completing one orbit, or period, between 90 to 120 minutes.  But, their orbit stays in place, relative to the Earth’s rotation.  Sun-synchronous low earth orbiting polar satellite orbital planes are actually moving slightly BACKWARDS relative to the Earth’s rotation.

So, why is this helpful to satellite imagery operators?  Okay smart guy (gal?), before you answer, go have a beer and get back to me later.