Category Archives: Orbits

A Motorcycle Rider Defines Space Situational Awareness


There’s been a lot of hand-wringing in recent years regarding space situational awareness (SSA). Almost every month another article appears, portending of the upcoming calamity in space–the point in which one rogue satellite or a chunk of debris hits another satellite or chunk of debris. These two chunks initiate a celestial version of pool. As in pool, one chunk will hit another chunk which speeds on to hit another chunk or cluster of chunks. The struck chunks fan out, hitting other chunks, and then those chunks hit even more chunks, and so on.

Invariably the hand-wringing prompts online conversations about whether this space-snooker-based scenario is realistically depicted in the movie “Gravity” (that Sandra, she floats so gracefully in space). Inevitably, a new round of blog posts use the computer-generated picture showing thousands of pixels surrounding the Earth–with each pixel representing one of the tens of thousands of objects, normally junk, orbiting the Earth.

The resulting picture from these conversations and blog posts is clear–the end is nigh, space-wise. Humanity has once again junked up another environment, and will soon reap what’s been sown. Unless we stop those smaller, less expensive satellites from messing it all up. Or something like that anyway.

According to some people, the number of objects (satellites, debris, rocket bodies, etc.) in orbit is reaching scary levels–tens of thousands–which is why they are verbally wringing their hands for public consumption. Is this a “chicken-littling” of space, or is there really something to worry about here? Is the blame for debris really so clear cut? Before getting to the answer, it’s probably useful to define SSA, particularly for readers new to the space arena.

There are many folks with specific definitions of SSA. The U.S. military is interested in the position, identification, and activities of objects orbiting the Earth which might potentially compromise the U.S. ability to defend itself or carry out global missions. The Europeans encompass some of the U.S. military SSA definition, but include discovering and identifying Near Earth Objects–things in space that might eventually literally have an impact on Earth if they get too close–and space weather.

For this post’s purposes, I will use my motorcycle and traffic survival skills to demonstrate SSA, but if you’re a car driver, you’ve been using aspects of SSA already.

When I first bought my motorcycle, I went through a motorcycle safety class (it’s a useful class–take it if you can). The class imparted one particular acronym that stays with me even now, 17 years later: SIPDE. Each word in the acronym suggests a way to survive on the road and hones great habits for motorcycle riding. S–Scan; I-Identify; P-Predict; D-Decide; E-Execute.

SIPDE reminds a rider to constantly use the tools at hand– eyes, brain, and motor skills-to make a rider aware of what’s happening close by, and then do something to keep the rider safe. Eyes scan for anything that may literally impact the rider. Once a rider’s eyes see something, the rider’s mind identifies it, internally racking and stacking the “threat.”

A rider then predicts what the object may do (a dog or child might run obliviously into the road, a self-righteous cyclist might blow through the stop sign from the left, a truck driver in the rear view mirror is on the phone and might not even see the rider). Once the prediction is made, the rider decides on a course of action, and then does it. This kind of cycle goes on if it’s ingrained in the rider, and it all will take place in seconds.

So, how do motorcycles and SIPDE have anything to do with space?  Essentially the same actions help define SSA, except a satellite takes the place of the rider. The orbit is the “road” the satellite is on. The tools for scanning, instead of a rider’s eyes and brain, are networks radars and telescopes on Earth’s surface–although some nations have a few space-based SSA “eyes” too. The brains are the people and computers trying to make sense of what’s nearby in orbit (is an object at the same altitude, is it on a path to intersect with another satellite’s “road,” etc.).

These people and computers are also attempting to identify objects close to the satellite’s “road”–its orbit (is it the body of a rocket, is it small debris, is it a satellite that seems to be moving from it’s orbit). Once they figure out what an object is, then they must decide whether the object is a threat, and predict possible actions of the object. The people in this SSA network must then decide what to do and then do it. This may be as simple as notifying satellite owners about a possible collision, or just monitoring the same objects to see if anything changes.

But how bad is it really, out there? Exactly how many objects are orbiting the Earth? Again, is this a “chicken-littling” of space, or is there really something to worry about? Is the blame for debris really so clear cut?

The answer, as it always seems to be, is: it depends. That’s where I’ll end it today, but my next post should hopefully give some perspective.


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.


…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…

Why Space Matters: HEO Satellite Operations, Part 5–Spysats, IR, and MMS

The Molniya orbit, a type of highly elliptical orbit (HEO), was the focus of the last HEO post.  And it was noted that the Molniya is an orbit perfectly suited to communication.  But what other missions and satellites use the HEO?

Believe it or not, the US has organizations that use the HEO for a few missions.  The most recent launch of the NROL-33 “spy satellite” is kind of related to the HEO, in that it’s part of a possible satellite communications and data constellation using a combination of HEO and geosynchronous (GEO) satellites called the Space Data Segment (SDS).

SDS-3 Constellation. Image on

In the illustration above, they call this particular combination of HEO and GEO satellites the “SDS-3 Constellation.”  Does anyone really know what’s on these satellites, aside from the people working with them?  One observation:  realize the government likes to maximize on their investments with additional payloads on satellites.  Just look at what NASA has done with their satellites and payloads to get an idea.  There’s nothing to prevent the installation of some kind of extra monitoring payloads on any of these satellites.  As discussed before regarding why the Russians use this kind of orbit, the view of areas that might be interesting to the US is pretty good.  Only the people working with this constellation really know what it’s all for, though.

Image from Wikipedia. SBIRS constellation. Old picture, as SBIRS LEO is now STSS.

A few more HEO birds owned by the US are the overpriced Space Based InfraRed System (SBIRS) HEO satellites.  There are currently two in orbit, with a third theoretically on the way.  This system is a little more straightforward in purpose, as it’s part of the early warning system for missile launch detection.  Why would the US want two to three missile launch detection satellites in highly elliptical orbit?  The Russians/Soviets also did and still do use satellites in HEO for early warning.  But the SDS, SBIRS, and OKO (Russian) satellites have to do with terrestrial activities and likely are trying to give their corresponding militaries an edge on terrestrial battlefields.

The most interesting mission using the HEO is one that’s coming up and has nothing to do with human activities on Earth:  NASA’s Magnetospheric MultiScale mission (MMS).  The focus of this two-phase mission isn’t necessarily the Earth, but the Earth’s magnetic field.  And not just the Earth’s magnetic field, but the Sun’s, too, and observing the interplay (NASA say the connecting and disconnecting of the fields) between the two fields.  The mission uses four satellites that will be “flying” in formation and placed in a “low-inclination” elliptical orbit of 28 degrees.  This means the orbit’s tilt is at a 28 degree angle to the Earth’s Equator.

Different phases, different elliptical orbital periods. Image on MMS site.

During phase 1, the satellites will have a perigee (point of orbit closest to the Earth) of 7,645 kilometers (4,750 miles) and an apogee (point of orbit furthest away from the Earth) of 76,452 kilometers (47,505 miles–at least I think NASA means apogee—on their website they say perigee twice).  During Phase 2, the perigee’s the same, but apogee increases to 159,274 kilometers (a little over 98,968 miles).  Seems like that’s pretty far, but believe it or not, the Moon is still further away, at over 238,857 miles average distance from Earth.

The two different orbits are designed to pass through the reconnection points of the magnetic fields of the Earth and the Sun.  So they are necessarily big.  But such an orbit also allows the satellites to “sample” different portions of the magnetic fields.  And they fly in a pyramid formation to help map out the reconnection events in 3-D.  Why go through all of this just to observe these reconnection events?  The reconnection events tend to release energy, and the energy can impact the electronics here on Earth and on the satellites orbiting around it.  There’s more to the science of these satellites on the MMS website.  As a side note, the MMS satellites will be controlled out of the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, Colorado (same place the Kepler mission is run out of).  Worth visiting, if only just to walk around the campus in Spring.

And while you’re in Boulder, enjoy the offerings of the Avery Brewing Company, which has a terrific Belgian Wheat (White Rascal) beer and a tasty Imperial Oktoberfest (The Kaiser) beer.  Sadly, there are no beers for HEO—which means we are now at the empty bottle part of the lesson.

Why Space Matters: HEO Satellite Operations, Part 4–Moley, Moley, Moley, Molniya!

During the last lesson, you might have been enlightened with the information that even though the Soviets have used, and Russians do use, geosynchronous (GEO) orbits for satellites, they seem to have a special place in their vodka-filled hearts for the highly elliptical orbit (HEO).  And that last lesson enumerates the reasons why they like it.  For one particular instance and for one particular HEO, they liked it so much, they gave the orbit a name.

Soviet satellite scientists were very clever when they first started using the HEO.  They already knew the Earth’s squashed pumpkin shape (its oblateness) normally “spins” (or perturbs) a satellite’s orbit slowly about the Earth’s axis.  But, they somehow figured out that a HEO satellite with a 12-hour orbital period using a specific inclination of 63.4 degrees nearly nullified that perturbation.  That particular period and inclination is a special kind of HEO the Soviets named “Molniya.”  By the way, they named their communications satellites in this orbit AND a rocket (a modified R-7), Molniya, too (so no potential for confusion there, I guess).

The Molniya orbit. Image from Wikipedia–click on it–you know you want to…

Let’s translate all that scientific “hoo-haw” into English a little bit.  The angle between the path of the satellite’s orbit, as it passes from south to north over the Earth’s equator, and the Earth’s equator itself is 63.4 degrees.  The satellite’s particular HEO is a 12-hour long trip around the Earth, which means the Molniya satellite orbits the Earth twice a day.  And the inclination was specifically chosen by Soviet scientists because it’s a very stable orbit.  The satellite seems to be rising, flying over the Earth, and setting at about the same spots over the globe every single orbit (there’s a slight shift backwards around the Earth of about -.07 degrees per orbit).  These characteristics are very specific to a Molniya orbit.

But the best thing about the Molniya is when a satellite in that orbit is near and at the Molniya’s apogee.  The satellite appears to “hover” over the Earth (no mystery why—read this lesson for a refresher).  Of a 12-hour period, there’s nearly 8-9 hours of time when the satellite can “see” most of a particular part of the northern hemisphere.  This characteristic means that for about 8-9 hours, the HEO/Molniya satellite can maintain contact with a ground station, broadcasting messages from that ground station to all receivers within that satellite’s Field Of Regard (FOR), which includes areas above 70 degrees north latitude.  Below are a few Wikipedia-cribbed pictures showing a satellite’s FOR in a Molniya orbit four hours before apogee, at apogee, and four hours after apogee.  As you can see, there’s a lot of the Earth in view during all that time (Russia, China, India, Koreas, etc.).

View of Earth four hours before apogee in a Molniya orbit. Image from Wikipedia–click to embiggen.

View at apogee in a Molniya orbt. Image from Wikipedia–click to embiggen.

View of Earth four hours after apogee in Molniya orbit. Image from Wikipedia–click to embiggen.

There’s one obvious problem for people wanting to broadcast 24 hours a day with a Molniya satellite:  communications only lasts about 8-9 hours from a Molniya satellite’s “rise” to its “set” on the opposite side of the Earth.  This means there is “dead air” for their broadcast area for nearly 15-16 hours each day.  Yes, 15-16 hours—a broadcaster’s nightmare (unless they’re union).  The gap is because the Earth has continued rotating, and by the time the Molniya satellite rises again for the second orbit of the day, the other side of the planet is now in the satellite’s FOR.

There is an answer to this problem, though.  If 1 or 2 more satellites are put into different Molniya orbits, ones in opposing orbits (so the orbits create an “open scissors” if you traced their paths—see below), then the broadcast coverage is 24 hours.  And this is what the Soviets did, successfully starting the Molniya constellation by launching the Molniya-1 satellite in 1965 (after two satellites had been destroyed in previous launch attempts).  And even as the Soviet empire fell, the Russians used and continue to use the Molniya orbit today.

Moley 1

The upshot of the Molniya orbit is that it’s an orbit perfectly suited to help a communications satellite (or satellites with other missions) keep sight of countries at very high latitudes.  Using multiple satellites in a Molniya orbit provides a very good, very big, FOR and can be extremely useful for communications, especially with stations and vehicles working within the Arctic Circle.

But what are some of the other things being done with satellites in HEO?  Maybe Part 5 of this HEO Series will answer that question.


Why Space Matters: HEO Satellite Operations, Part 3–What’s the Frequency, Komrade(th)?

The previous lesson left you hanging, maybe even perturbed, with the question of why anyone would want to use a satellite in a highly elliptical orbit (HEO).   After all, a HEO satellite requires a ground station or two with a moveable (steerable) antenna to speak to it (or the satellite’s antenna has to be gimbaled to allow continuous aiming at the ground station).  The satellite goes through the Van Allen belts four times a day.  And there are times in its orbit when it appears to hover, but other times when it’s moving very quickly around the Earth.

But it’s a very useful orbit if a country or organization uses it well.  The Russians, in particular, seem very fond of the HEO for their satellites.  Some of their satellites still use HEOs today.  Consider the location of Russia on the world’s face.  The country is primarily at very northern latitudes, with the bulk of the country between 50 and 70 degrees north latitude.  The country also spans two continents.


Cross-country communications were important to the Soviets–especially to its military (as it is with the US). One way to lower communications infrastructure costs and still deliver country-wide/global communications capability is through using communications satellites (satellites that could receive and transmit radio signals from and to the Earth).  Another factor for consideration is the Soviet Union’s huge coastline within the Arctic Circle.  The majority of the coastline is above 70 degrees north of the equator.  Why is this factor important in a satellite communications discussion?

During the Cold War, the Soviets had built up a tremendous submarine fleet, with a few ports well within the Arctic Circle.  The Soviet submarines routinely prowled those waters, but they would have been a less effective force with no communications link from headquarters.  There were also bomber bases in the Arctic “garden spot.”  Satellites were an obvious solution to the communications problem, but geosynchronous (GEO) communications satellites can’t see very well above 70 degrees latitude (read the “Curves and Angles” lesson for a refresher).  Radio signals also have a tough time going through all that atmosphere to and from GEO satellites—a very powerful radio transmitter would need to be used, meaning more weight would be added for batteries, solar panels, etc.

Could the Soviets have used GEO communications satellites?  Yes.  They have used, and the Russians still use, satellites out in that orbit.  But for the Soviets, there weren’t too many launch location options below 50 degrees latitude.  There are reasons why the United States uses the Kennedy Space Center to launch satellites into GEO.  There are reasons why the European Space Agency launches from French Guiana.  Both launch complexes are relatively close to the Earth’s equator.  Kennedy is a little over 28 degrees north of the equator, and Kourou, French Guiana is an even closer 5 degrees north of the equator.  These are great locations to launch a satellite into GEO, with Kourou the better of the two options.

Launch sites

The reason both are excellent launch sites has primarily to do with fuel and payload when trying to get a satellite out to GEO.  And of course there are barely any populated areas directly east of the sites, meaning no on gets hurt if something goes wrong during a launch.  The further a launch site is to the north or south of the equator, the more fuel it needs to get a satellite into GEO.  More fuel means more weight, affecting satellite payload weight requirements for launching to GEO.  Another option is building newer, more powerful rockets to put capable satellites into GEO.  But either option meant more money for getting satellites into GEO for the Soviets.

The HEO, though, was a relatively inexpensive orbit, fuel-wise, to launch Soviet communications satellites into.  The Soviets wouldn’t need as much fuel to get the satellite into a HEO inclination when compared to the fuel requirements for a GEO.  And the orbit’s Field of Regard (FOR) from apogee could also easily encompass the Earth’s North Pole.  Especially if they were using an orbit at a particular angle relative to the Earth’s equator (the orbit’s inclination) with a particular orbital period.

There’s a name for that orbit, to be talked about next lesson.