NextGen, GPS-style

No, not the FAA's NextGen, but the GPS system. A Delta IV rocket took the first of the "Block IIf" satellites into orbit today, after several aborts (including one atT-minus-6 seconds) and delays. The new satellite will transmit on the L5 frequency. This satellite is a completely different design from SVN49, and one hopes that there was more testing. According to the US Air Force, it will take 3 - 4 months before the satellite is marked "healthy."

There are more than enough birds on orbit, but as I mentioned last week they do have a finite lifetime.

SVN49 and Old Possum's Book of Practical Cats

I've been trying to piece together the story of SVN49. What's SVN49? Is it one of those unpronounceable high-altitude fixes that Center uses to steer you around uncharted military airspace (those of you who fly in the flight levels in the west know what I mean)? Or an oceanic fix? A proposed regulation? SVN49 won't affect me in my Cherokee Six or glider, right?

Wrong. SVN49 is a GPS satellite. Everyone in the world uses GPS, if not for navigation then for timing, so everyone should be worried.

Why haven't you heard of SVN49? A GPS satellite is like a cat. T. S. Eliot wrote

The Naming of Cats is a difficult matter, It isn't just one of your holiday games; You may think at first I'm as mad as a hatter When I tell you, a cat must have THREE DIFFERENT NAMES.

We can counter with

The Naming of Sats is a difficult matter, It just isn't one of those rocket nerd games; You may think that these geeks are as mad as a hatter When they claim a sat must have THREE DIFFERENT NAMES.

Obviously one of the names is SVN49; SVN stands for space vehicle number. The second name is NAVSTAR 63; NAVSTAR was the original name of the GPS program. And the final name, the one that belongs to "no other sat," is PRN01.

PRN01 should ring a bell; you've probably seen NOTAMs like

!GPS 12/064 GPS NAV PRN 25 OTS WEF 0912181500

Aviation GPS receivers usually refer to satellites by their PRN. PRN stands for Pseudo-Random Noise, and is one of the engineering marvels of the GPS system. The original GPS system had all of the satellites communicating simultaneously on two frequencies, called L1 (1575.42 MHz) and L2 (1227.60 MHz). You've heard the mess that results when two airplanes transmit on the same frequency: lots of noise followed by someone saying "Blocked." But that's the standard GPS communications environment.

The receiver gets the navigation data from one satellite at a time using CDMA (Code Division Multiple Access), which is also called spread spectrum encoding. Many cellphones use the same technique to allow simultaneous conversations on the same frequency. The technique was invented by, and patented by, the actress Hedy Lamarr during World War II. Her patent expired before the advent of GPS, so while her estate gets no royalties her name is revered in GPS circles. PRN01 refers to the specific binary code assigned to good old NAVSTAR 63.

SVN25, or PRN25, is out of service for a very good reason: it was launched in 1992, and has given its all for the cause. Much like the LGU VOR, which has been off the air for years and years, the satellite lives on in the NOTAM telling us not to use it. RIP. SVN49, however, is still begging at the door to be let in. It has been assigned PRN01, so we can tell its signals from all other signals, but its status is ominously unhealthy, so your receiver ignores it.

We all know that the FAA NOTAM system is a mess, but that's not the only NOTAM system involved. The US Coast Guard Navigation Center publishes NANU's. NANU sounds like something that Robin Williams said on Mork and Mindy, but in fact it is quite serious. NANU stands for Notice Advisory to Navstar (you remember Navstar, right?) Users, and this is where DUATS and Flight Service get their GPS NOTAMs. Here's the deal on SVN49:

!NOTICE ADVISORY TO NAVSTAR USERS (NANU) 2010068 NANU TYPE: GENERAL
*** GENERAL MESSAGE TO ALL GPS USERS ***
THE 50TH SPACE WING IN COOPERATION WITH THE GLOBAL POSITIONING SYSTEMS WING, WILL BE TESTING SVN49 (PRN01) SIGNAL CHARACTERIZATION OVER THE NEXT 6 MONTHS. SVN49 (PRN01) WILL REMAIN UNHEALTHY UNTIL FURTHER NOTICE, AND THE BROADCAST NAVIGATION MESSAGE WILL REMAIN IS-GPS-200 COMPLIANT. USERS CHOOSING TO TRACK AN UNHEALTHY SVN49 (PRN01) SHOULD CONTACT GPSOC (MILITARY) OR NAVCEN (CIVIL) IMMEDIATELY FOR ANY ISSUES THAT MAY BE ATTRIBUTED TO THESE ACTIVITIES.

How SVN49 got to be unhealthy for 15 months is a cautionary tale about engineering. The first thing to keep in mind about engineering is that at some point you have to freeze the design and start building: that's version 1. But even while you build version 1, you think of improvements, which eventually make their way into version 2. Etc.

One of the improvements to GPS is the addition of a third frequency, L5 (1176.45 MHz). This will give users improved correction for transmission errors, but the choice of this frequency is controversial.

In any event you have to test, so Lockheed-Martin engineers took a spare L5 transmitter and bolted it to a spare power bus on SVN49. Nobody has explained why a satellite has a spare bus, which is a lot more complex than having a spare USB port on your computer, but that is the case.

Now this was not a willy-nilly fly-by-night operation: I have no doubt that LMCO engineers did all of the requisite analysis, and that the proper drawings and other documentation were made. (It's very important to document every little detail of a satellite; imagine your embarrassment when the thing gets to orbit and doesn't work and you don't really know what you did when you built it.)

But despite this due diligence, the L5 signal interferes with the L1 and L2 signals, and the navigational data from the satellite is, so far, unusable.

Now there's more than one way to skin a cat, and lots of people are putting lots of work into figuring out how to make SVN49 useful. For the moment, though, it's still begging at the door, waiting to be let in. Let's hope that soon it will be PRNg.

Falcons

The Falcon jets from Dassault are beautiful airplanes, as I've mentioned before. Alas, I have yet to fly one.

People have mixed reactions, to them, though. The April issue of Professional Pilot, for example, poked some fun at them last month in their "Sid and Star" cartoon. Pro Pilot is a narrowly-aimed magazine with a focus on business aviation; it's free, but if you don't already get it you probably wouldn't enjoy it, because they send it to just about everyone who would. Sid and Star are a pair of hard-working pilots who fly a "Howler" for Lugnut Industries. Pro Pilot naturally has the point of view that business airplanes are far from luxuries, and while I generally agree with them, I have seen some abuses. In this case, a sales rep from "Dijon Aero" has come by to demonstrate the "Cameo 3X" and its luxurious appointments. In gratitude Lugnut takes the sales rep to his favorite local dive for a meatball sandwich. Aghast, the Dijon sales rep recommends against selling a Cameo to Lugnut. The strip is a nice concise argument against the idea that business jets are a luxury, at the expense of the French (it's easy to mock the French; just ask Disney).

Despite this, Dassault still has an ad for the Falcon 2000LX on the back cover.

By contrast, May's Business and Commercial Aviation's 20/Twenty column features the Falcon 900, praising its fuel efficiency and handling, and noting the continuous improvements over the aircraft's 24 year production run. They call the airplane a "well-defined work-a-day example of transport art and technology."

But whether the airplane is luxurious or work-a-day is an issue with the back of the airplane, and I'm more interested in the front. So let's turn to the May 3, 2010 issue of Aviation Week and Space Technology. The cover is a beautiful photograph of the 7X, with the familiar three engine configuration of the Falcon 900, flying away from the setting sun over the ocean. The airplane's elegant shape and smooth construction are highlighted by the swell in the ocean below.

AW&ST generally takes a neutral view, so their pilot report on the 7X is neutral in tone. The 7X's big innovation is its fly-by-wire control system, based on Dassault's success with the Rafale fighter.

The mathematician in me marvels at the progress that these systems have made, and while a little part of me whines about the need for perfect redundancy, Dassault is claiming 10^(-10) (yes, that's 9 zeroes between the decimal point and the one) reliability, so maybe I am beginning to soften a little. That's probably better than an Archer, and definitely better than a Seneca (Senecas came out of the sky in little pieces for a while due to an anomaly in the rudder trim system).

The glider pilot (yes, the glider pilot) in me admires how the sophisticated stability augmentation from the control system enabled Dassault to reduce the size of the empennage by 20%, cutting a ton of drag (approximately). I've flown draggy airplanes like King Airs and 182s, and sleek airplanes like Mooneys and gliders. The sleek ones are more fun!

The working pilot in me admires all of the labor-saving that fly-by-wire provides. Even more primitive flight control systems are a big help in this regard. I remember a busy early-morning arrival in Santa Monica in an EFIS King Air. Early morning arrivals in Santa Monica mean oh-dark-thirty departures from Idaho, and I was zonked and busy. Something distracted me and I was head-down for a little longer than I care to admit, and when I looked up, the airplane was turning final all by itself. I might get behind, but the Flight Management System stayed ahead.


The Falcon 7X's EFIS displays feature a Flight Path Symbol (FPS); we used to call it the velocity vector. These have been around in Heads Up Displays (HUDs) for a long time. I've never flown with one outside of simulations, but they make flying incredibly easy. You put the velocity vector (the circle with the little gull wings below) on the horizon and, by golly, you fly level. (The picture at the right is from the fabulous X-Plane App for the iPhone, which is well worth the $10 they charge.)

But the stick-and-rudder pilot in me is infuriated. Or worse! You never actually fly this airplane! Instead, the flight control system interprets sidestick inputs as requests to manipulate the flight path vector. Then the stability system takes over and keeps the FPS (and, with it, the flight path) where you put it. You never have to engage the autopilot, because in effect the autopilot is effectively ON as soon as the Built-In Tests are complete.

The sidestick is nothing more than an ergonomic and intuitive autopilot head. Sacré Bleu! I believe in autopilots but this has gone too far.

So I approach the airplane with mixed feelings. It's fast, it's efficient, it's beautiful, it's useful, and apparently its controls feel great. But if I ever win the lottery I think I'll opt for a nice 900 and a congenial copilot with good hands.

May 6

It's fun to think about what happened in aviation on any particular date, but I'm not sure it's fun enough to devote a whole blog to. So why is May 6 special? For me there are two reasons, one obviously personal and one becoming more so.

The personal reason is that I used to own Taylorcraft 9114 (N95814), which was built on this date in 1946. Taylorcraft was building 40 aircraft a day at that time, but went out of business by the end of the year. The T-cart was my vehicle for endless hours of fun, not all of them in the air. I sold it because I had to. They say that the average American family is one illness away from losing its house; in my case, I guess I was one illness away from losing my airplane. But I did sell at a substantial profit!

The emerging personal reason goes back to this post from September, 2008, when my daughter presented me with a gift of old postcards of Boston, where I grew up. One of them showed the airship LZ-129 Hindenburg over the city, and sense then I have spent a fair amount of time researching the great (and, frankly, not-so-great) airships. Someday I hope to write a book about them. The world needs an airship book that both underplays the Hindenburg accident and highlights the arrogance between the crash of the R-101.

Usually what I do is devote a day or so after the end of the semester to airship research. Sometimes this means going to libraries and studying newspaper microfilms, and sometimes it means surfing the 'net. And since I am giving my last final exam of the semester right now, I spent the usually pointless proctoring time (it's a Computer Science exam and it's open book, so really what am I protecting against?) surfing the 'net.

And May 6? May 6, 1937 is the date of the Hindenburg's crash at Lakehurst, an appropriate day to devote to its study. Especially since it is snowing here in Pocatello.

I will spare you any of the clichéd references to Herb Morrison of WLS and the iconic overused pictures of the fire. If you really want to watch what happened, see Howard Hughes' brilliant movie Hell's Angels. Not only will you get to hear Jean Harlow (a figure even more tragic than the Hindenburg) offer to change into something more comfortable, you'll see a harrowing scene of a Zeppelin fire that is eerily prescient of the Lakehurst accident.

---

The book I have in mind is really an engineering and transportation history of the era. I'm also very interested in the liner Queen Mary, which was formerly housed with Howard Hughes's Spruce Goose in Long Beach. It's maiden sailing bracketed the Hindenburg's "Millionaire's Flight" of October, 1936. And I suspect that, with her speed and easy access to Manhattan, the Queen Mary could beat the Hindenburg in a door-to-door race from Frankfurt to the Empire State Building. Of course neither could match the 777...

I would also discuss the decorative aspects of both ships; both featured fabulous Art Deco and International Style decor.

And of course I would also need to understand how they operate. Alas, the Queen Mary's boilers have been removed, but the bridge is intact, and I have spent enough time in the engine room to convince myself that I could get her moving. (Isn't fantasy fun?) But flying an airship is no fantasy: Airship Ventures has a Zeppelin on the West Coast of the US, and they offer training.

There are two obstacles, though: first, it's expensive, but I have been saving my pennies. (When the German government refused to support the construction of the Graf Zeppelin, lots of people made small contributions to fund the construction. Maybe I can get lots of small contributions to fund flying one of its successors?) Second: training requires a valid medical certificate. And since mine is "in line for review" according to the FAA, I am going to have to wait.

Maybe I can do it next year on May 6.

Jimmy on the SPOT

The more soaring I do the less it seems like flying. Now that's nonsense, because while you are soaring you are definitely surrounded by air. I have the same feeling about ag flying, too: yes, there is an airplane, but the flying seems secondary to the mission. Maybe the way to look at it is to that flying is such a large part of my outlook on the world that I spend more time looking at how things are different than how things are similar.

Or think of it this way. A couple of years ago I went to the Soaring Society of America convention. This was one of those typical soaring productions, involving dozens of phone calls and emails and several weeks of deciding the best way for all of us to get from Salt Lake City to Albuquerque. We're all pilots, and some of us are power pilots, so there was a lot of comparing my club's Cherokee Six to Lew's Bonanza and Tim's Mooney as far as comfort, performance, and cost. The Mooney lost on comfort. (Keep in mind that I am a former Mooney owner, but a couple of the guys are pretty big and it's hard to fit big and Mooney into the same sentence.) And in the end the Bonanza and the Six lost out to Southwest's inexpensive 737, which is certified for flight into known icing.

We arrived separately, but we all left on the same flight. So here we are, 6 or so pilots filing onto an airplane. I know a bunch of Southwest pilots and believe me, they are pilots just like we are. (If you doubt me, watch the crew exchange in the jetway: you'll see lots of hands in the air illustrating the finer points of landing on 7R at Las Vegas when the wind is out of the south.) But what they do, at least when they are at work, seems to have nothing in common with what we do. (And, again, this is nonsense, since lots of airline pilots are glider pilots, like Dave English from hikoudo.com, or Lew with the Bonanza, and even I am getting ready to do some King Air instruction later this summer.)

So maybe flying is flying.

But something is different about soaring. I was reminded of this yesterday as Tim (of the Mooney) set out to fly 1000km in his Ventus, a high performance single seater. He had been watching the weather for a few days (and, yes, this involved dozens of phone calls and emails; we are like a bunch of old ladies) and it looked good.

He launched at about 0800 local time, a time more typical of a King Air than of a glider, but the forecast was for strong west winds which would mean lots of ridge lift. He set his SPOT to track mode, and as soon as the first track message got out there was a flurry of emails.


School is still in session for me, so I was stuck in the office or, at best at the coffee shop. I checked Tim's progress through the morning, noting that he made his planned turn near Salt Lake City and was headed north. I told people about the attempt, and of course many of them looked at me funny. But I was excited for him. And jealous, of course.

Headed out for lunch I checked his progress. But now there was something different: instead of a "track" message, his SPOT was sending a "help" message. He had landed out. (SPOT has two help messages, the "I'm OK but need help" kind and the "Call 911!" kind. Tim's was the former.)

Or so it appeared. I tried to call him, and got no answer: the advantage of SPOT is that it works where cell phones won't. So I left a message and sent a text "saw your help msg what do you need?" Sometimes an SMS message gets through even when cell coverage is too weak for voice.

The old lady glider pilots started to light up the phone and T1 lines with talk and email. I was physically closest to Tim but nowhere near his trailer, but I started to head his way just in case. But before I got to my car, Tim called. He had hiked to get cell phone coverage, and as soon as he got it there was my text.

What a world! There you are, alone in a single-seat aircraft, in a sparsely settled valley, in a plowed field, almost as alone as Apollo XI astronaut Michael Collins on the back side of the Moon while Neil and Buzz explored the surface. But no, that's not right: your friends know where you are and before you can even ask for help it is on the way!

But that's one way soaring is like flying. We go out of our way to help each other out. I've had airliners relay messages to Center for me, and I have relayed messages to airliners, including whole IFR clearances. That's another story; or is it? The FO was a friend, we recognized each other's voices, and they couldn't reach ATC, and the next thing I knew I was saying "ATC clears Skywest blah-blah-blah to the ..."

I could have saved him from copying the clearance if I had thought to send him a text.