GPS aboard the world’s highest, fastest manned gliders

January 13, 2016  - By

Featuring an exclusive interview with Astronaut Scott Kelly from aboard the International Space Station

This month, we discuss sailplanes of all sorts and conduct a brief on-orbit interview with Astronaut Scott Kelly concerning his time piloting the space shuttle — actually a supersonic glider. We touch on the role GPS played in making it a safer rocket glider. Kelly also gives us an update on his time aboard the International Space Station (ISS), nine months and counting.

You can jump straight to U.S. space shuttles: The world’s highest flying and fastest manned gliders for the interview. For some background on gliders, read on.

Combat Gliders versus Sailplanes

When you think of gliders — or more accurately sailplanes — you probably think of long flexible wings, slow flight, bubble canopies, pristine white aircraft gleaming in the sunlight and tow requirements. For most aviators, the holiday picture of the beautiful Schleicher Model 32 sailplane below typically comes to mind.

AS (Schleicher) Model 32. (Courtesy of AS GMBH)

AS (Schleicher) Model 32. (Courtesy of AS GMBH)

However, there are certainly some World War II combat glider pilots living today, heroes all, although unfortunately fewer and fewer everyday, that think of gliders in a very different way. They think of and remember huge green, tan and camouflaged wooden and cloth flying machines that carried 10 or more troops, who — if they lived through the experience — were able to wear glider rather than paratroop badges.

Army General William C. Westmoreland said of the heroic combat glider aviators, “Every landing was a genuine do-or-die situation . . . it was their awesome responsibility to repeatedly risk their lives by landing in unfamiliar fields deep within enemy-held territory, often in total darkness. They were the only aviators during World War II who had no motors, no parachutes, and no second chances.”

The venerable wooden and cloth combat gliders of World War II were about as far removed from soaring sailplanes as a glider can be. Once released, they glided or, more accurately, careened to Earth. They were versatile and rugged enough to carry combat vehicles behind enemy lines and land in rugged terrain. but they most certainly did not soar.

The courageous flight crews did not have the luxury of GPS. Navigating for the short time after the tow vehicle — typically a transport, cargo (C-24) or bomber aircraft (like the B-24) — dropped them off at altitude, almost always below 10,000 feet, was a very hit or miss affair. There were only four very basic flight instruments on the glider’s rudimentary control panel, which most of the pilots completely mistrusted and ignored.

Glider flying in World War II was strictly VFR, or visual flight rules. Veteran glider pilots tell me that finding your landing zone (notice I did not say runway) was frequently haphazard. Often they had to make do with any decent-sized farmer’s field as a landing zone. Frequently, these landing were made in broad daylight, behind enemy lines, amid a hail of bullets, so they were fraught with danger in many ways, including not knowing their exact location when they finally landed. Glider infantrymen and glider pilot casualties reached 40 percent for some missions. What would they have given for a GPS?

The venerable WACO gliders were the most common versions. By war’s end, more than 13,900 CG-4A gliders had rolled off the production lines of several companies mass producing the same design for approximately $15,000 per copy — although one company charged as much as $50,000 per unit. It is estimated that less than one tenth of 1 percent of the gliders survived to fly after conflict ceased in 1945.

According to the Silver Wings National World War II Glider Pilots Association, “Over 6,000 individuals were trained as combat glider pilots and earned their silver wings with MOS (military operational specialty) 1026. Approximately 150 glider pilots and Troop Carrier Veterans still participate in the group’s activities, although their numbers are declining with ages in the 89- to 96-year group.

Author Michael MacRae, writing on the ASME (American Society of Mechanical Engineers) webpage in an article titled “The Flying Coffins of WWII,” describes the WACO CG-4A as America’s first stealth aircraft, but also as an aircraft expendable by design: “The CG-4A fuselage was 48 feet long and constructed of steel tubing and canvas skin. Its honeycombed plywood floor could support more than 4,000 pounds, approximately the glider’s own empty weight. It could carry two pilots and up to 13 troops, or a combination of heavy equipment and small crews to operate it. The nose section could swing up to create a 5 x 6-foot cargo door for Jeeps, 75-mm howitzers, or similarly sized vehicle. With a wingspan of 83.5 feet, the Waco maxed out at 150 mph when connected to its tow plane. Once the 300-foot length of 1-inch nylon rope was cut, typical gliding speed was 72 mph.”

Gliders first appeared in U.S. combat operations in the 1943 invasion of Sicily. They flew on D-Day into Normandy, June 6, 1944, and in other important airborne operations in Europe such as Operation Market Garden, the Battle of the Bulge, and crossing the Rhine, as well as in the China-Burma-India Theater.

After World War II, the gliders participated in U.S. military exercises in 1949, but glider operations were deleted from the U.S. Army’s capabilities on Jan. 1, 1953. Today, only special forces use gliders for silent, small-scale insertion.


In contrast, a modern-day open competition glider built by the world-famous Alexander Schleicher (AS) company, for example, can soar to more than 50,000 feet with a supplemental oxygen supply, cruise at 280 kph or 170+ mph with a glide ratio of up to 80:1, with flight durations lasting more than 50 hours. Most modern sailplanes today fully incorporate GPS into their avionics suite that rivals any powered aircraft cockpit.

Contrast this with the World War II combat gliders that careened Earthward with somewhere between a 16 to 30:1 glide ratio at 70+ mph on a trajectory that typically lasted 10-15 minutes max. Sad to say, most of the operational versus training flights during World War II were one-time affairs and one-way trips, but they delivered the goods, including some very expensive firewood once the gliders were abandoned. Certainly, the WACO CG-4A glider was the last of its genre. Mothballed at war’s end, fewer than a dozen restored gliders exist today.

Rocket Gliders

Now to the heart of the matter. Gliders have evolved in ways that are difficult to imagine. Many of the aircraft that have broken world altitude and speed records are actually gliders, although we don’t typically think of them as being among that genre.

Messerschmitt Me 163B at the National Museum of the United States Air Force. (U.S. Air Force photo)

Messerschmitt Me 163B at the National Museum of the United States Air Force. (U.S. Air Force photo)

Typically a rocket-powered glider consumes fuel at a rapid rate, so most glide in for a landing. Examples include the German Messerschmitt Me 163 rocket-powered interceptor seen above, as well as the American series of research aircraft starting with the Bell X-1, which first flew and glided in for an unpowered landing in 1946. Examples of the type include the North American X-15, which spent much more time flying unpowered than under power.
In the 1960s, research and development or test vehicles now known as unpowered lifting bodies such as the X-20 Dyna-Soar space project vehicle were all the rage, and even though the X20 was eventually cancelled, the R&D led directly to the development of the U.S. space shuttle.

U.S. space shuttles: The world’s highest flying and fastest manned gliders

NASA’s now-famous and retired space shuttle first flew on April 12, 1981. The shuttle, which was a powered rocket during liftoff and cruise, re-entered as the fastest glider known to man at Mach 25 at the end of each spaceflight, landing entirely as an unpowered glider that, ironically, created its own sonic boom when it re-entered the atmosphere.

The U.S. space shuttle and its Soviet equivalent, the seldom-seen Buran shuttle, were by far the fastest aircraft ever to fly and, by a wide margin, the fastest gliders ever to fly in space and in the atmosphere.

NASA astronaut Scott Kelly floats aboard the International Space Station after the hatch opening of the Soyuz spacecraft Mar. 28, 2015. (Photo: NASA)

NASA astronaut Scott Kelly floats aboard the International Space Station after the hatch opening of the Soyuz spacecraft Mar. 28, 2015. (Photo: NASA)

One of the more well known space shuttle command pilots is Commander Scott Kelly, who as I write this is well into his ninth month aboard the International Space Station (ISS). He has three more long months to go before he returns home to a hero’s welcome and a battery of medical tests to determine how longevity in space affects the human body by comparing him to his astronaut twin who remained Earth-side during the same 12-month period. You know Einstein’s general theory of relativity, divided by telomere length and all sorts of quantum mechanics and medical technology. Talk about being poked and prodded.

Scott Joseph Kelly (born February 21, 1964) is an American astronaut, engineer and a retired U.S. Navy Captain. A veteran of three previous missions, Kelly was selected in November 2012 for a special year-long mission to the International Space Station, which began in March 2015.

Scott Joseph Kelly (born Feb. 21, 1964) is an American astronaut, engineer and a retired U.S. Navy Captain. A veteran of three previous missions, Kelly was selected in November 2012 for a special year-long mission to the International Space Station, which began in March 2015.

Scott Kelly is interesting for one more record he created during his time as a shuttle commander and shuttle command pilot. He flew the first-ever space shuttle GPS approach on Aug. 21, 2007, on STS-118. When I first heard about this feat, I thought it would be interesting to talk with Scott about it, and I made plans to do so upon his return from the ISS in March 2016.

However, through the marvels of instant messaging and the good graces of my friend Joe Rolli at Harris Corporation (nee Exelis, nee ITT) I was put in touch with Scott Kelly.

We conducted our brief interview electronically with nary a glitch even though Scott is hurtling around the Earth in low Earth orbit at a speed of approximately 17,150 miles per hour (about 5 miles per second). This means that as Scott orbits the Earth, he experiences a sunrise once every 92 minutes for a total of 5,634 sunrise events during his year on orbit.

Relatively, however, compared with the speed of electrons or light, which travel at 670,616,629.4 mph in the vacuum of space, Scott and I — who are traveling at a differential of 17 orders of magnitude compared to electrons — are essentially standing still. So the seemingly huge speed differentials makes little or no difference. Again Einstein, Newton, Schroedinger and probably his cat, if alive, would beg to differ on a technicality, but for our intents and purposes, I stick by my statement.

Here’s how that interview went. I want to publicly thank Scott for taking the time out of an incredibly busy schedule to talk with us about the importance of GPS and the space shuttle. Scott currently serves as Commander of the ISS on the one-year mission. In October 2015, he set the record for the total amount of days spent in space by an American astronaut — 382. As this article goes to press, Scott has spent more than 445 days in space.

NASA astronaut Scott Kelly has been aboard the International Space Station since March as part of an endurance mission to test the effects of long-term exposure to space.

NASA astronaut Scott Kelly has been aboard the International Space Station since March as part of an endurance mission to test the effects of long-term exposure to space. In this July 12, 2015, photo he poses for a selfie in the “Cupola” of the ISS. (Photo: NASA)

(Don: Don Jewell, GPS World Defense Editor; Scott: Astronaut Scott Kelly)

Don: Scott, thanks for taking the time out of your busy schedule for our questions concerning GPS and the first space shuttle approach made using that technology, which you flew several years ago now.

Scott: This was eight years ago and I don’t have notes here, so this is my best quick effort.

Don: Why did NASA decide to approve GPS approaches for the space shuttle, and why were you chosen to fly the first one? I would assume that your experience, safety, approach options and flexibility would play a part here.

Kelly-patchScott: TACAN was going away. I wasn’t assigned to STS-118 because of this. This was a secondary DTO or Developmental Test Objective.

Don: Was a GPS approach after that first landing always an option?

Scott: GPS approach is kind of a misnomer. We incorporated GPS into the navigation state [for the space shuttle] from about Mach 5 [five times the speed of sound] until we transitioned to a microwave landing system on final.

Don: Were the certified and validated GPS approaches unique, or did they mimic current approaches such as ILS or VOR/DME?

Scott: Actually, Don, they have little to do with the GPS approaches aircraft fly.

Don: Were there both precision and non-precision GPS approaches? Do you remember the approach speeds and critical points in the approach? Can you discuss them? Since some of the alternates around the globe are in fairly primitive locations, did GPS make them more accessible and actually provide more alternates?

Scott: Again, GPS was used to update our navigation state. On an approach to a runway without an MLS (Microwave Landing System), GPS would have been our primary navigation source to the ground, but its not like we would be looking at an approach plate.

Don: What were the minimums for a GPS approach, before you could start a descent profile for a GPS (aided) approach and landing?

Scott: Actually, Don, our weather minimums were pretty restricted before we could start the de-orbit burn [while still in orbit]. Ceilings of 5,000 feet I think.

Don: At what point in your descent profile were you or NASA required to make a decision about your landing location and alternates? And, related to that, was there a typical point during the descent profile where you were committed to a landing location and could not choose an alternate? How far was that from your landing site nominally?

Scott: Legally you could re-designate after the de-orbit burn to an alternate [landing] site, but this would be in a very critical situation and was never done. Basically, when we did the de-orbit burn, we were essentially committed to landing at the chosen airfield.

Don: In an emergency, were you able or authorized to land at an alternate that did not have an advance NASA team in place, and were you able to fly the space shuttle totally manually or were computers always involved for stability?

Scott: Yes, and computers were always involved.

Don: Many modern fighters are inherently unstable. When the last computer fails, ejection is the only option. How did this apply to the space shuttle?

Scott: We were [essentially] fly by wire…the shuttle can’t fly without at least the backup flight control system (FCS) computer. Nominally, we have four FCS computers online.

Don: Since aerodynamically you were essentially flying the world’s fastest and highest flying glider, at what point were you committed to a landing site? What discretion as the Pilot in Command did you have, or was it all up to NASA headquarters?

Scott: When you did the de-orbit burn, you were committed to a landing attempt somewhere. If you had communications with the Mission Control Center (MCC), they decided where you would land. [With] no communications, it is up to the commander in an emergency.

Don: The space shuttle exceeded the speed of sound by a factor of 25 in the Earth’s atmosphere (Mach 25) on approach. What were the handling characteristics when this occurred? While there was obviously a sonic boom, where there any handling anomalies that required manual inputs from the pilot in command?

Scott: There was a little buffeting — sort of like running off the road in a pickup truck.

Don: Speaking of alternates, if your landing gear failed to deploy, or you had an indication that there was a gear malfunction, where you able to land on alternate surfaces such as grass or sand? Most importantly, in your opinion, would the shuttle and crew have survived a water (ocean or lake) landing? And were these alternate landing sites planned for or simulated to any high degree of fidelity?

Scott: The simple answer is you would try and bailout, but of course crash, if you had no choice.

Don: Finally, your comments. What was it like to pilot the space shuttle, and what did having a GPS approach available mean to you?

Scott: It was a privilege. GPS allowed us to continue to fly the space shuttle as legacy systems like TACAN were retired.

Don: Thank you so much for your time. If you have some comments concerning your current one-year experiment aboard the ISS, that would be great.

Scott: Sure, Don. I am currently a little over 270 days into my one-year flight aboard the ISS and going strong. Plus, to bring this all back to GPS, I can definitely say that GPS is working well on the International Space Station. We also have a Garmin GPS in the Soyuz, which we would break out in an emergency situation, and use a handheld satellite phone if we had an off-nominal landing, to tell people where we were.

The International Space Station. (Photo: NASA)

The International Space Station. (Photo: NASA)

Space Station and GPS

It is a good thing the GPS receivers on the ISS are working as well as they are. Since 2002, they have been the primary means for determining attitude, position, speed and universal coordinated time reference on the ISS. The GPS position of the ISS, which moves at five miles per second, is accurate to within 10 meters and is updated continuously.

Previously, according to NASA, the station’s position was determined using ground tracking and other techniques. That information was considered to be adequate if not overly accurate, as it was updated just once a day. Just before an update, the actual and propagated position of the station, the ephemeris, could differ by as much as 10,000 meters.

Specifically, the ISS uses the GPS position and velocity solution as the ISS navigation state. The ISS’s attitude determination filter combines the GPS receiver attitude information with ring laser gyro data available from the ISS rate gyro assembly (RGA) to produce the ISS attitude solution.

Today, continuous accurate knowledge of the space station’s location also keeps it safely out of the path of wayward space debris.

So now you know something about sailplanes, combat gliders, the U.S. space shuttle, the ISS, Astronaut Scott Kelly and how they are all affected by GPS. Even more importantly, I hope this column reinforces for you the ubiquity of the Global Positioning System.

GPS is the world’s time keeper and primary global time distribution system. GPS time synchronizes networks, computers, communications and any number of other devices, from Apple iWatches to undersea navigation, to systems used by private pilots, airlines, spacecraft and astronauts in deep space. You name it: If it uses time, chances are GPS time is the provider, with an incredible stability of 1E-14.

Indeed, you should think of GPS as an enabler. It enables so much of our technology today that it would be difficult to imagine living without it. Contrary to popular belief, even in the U.S. government, GPS is robust and reliable and becoming more so every day. Just think about it: GPS tells us when and where we are, how to get where we are going, and whether or not we are late. An amazing system, brought to you free of charge by the United States Air Force.

Until next time, happy navigating.


Featured photo: NASA

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About the Author: Don Jewell

Don Jewell served 30 years in the United States Air Force, as an aviator and a space subject-matter expert. Don’s involvement with GPS and other critical space systems began with their inception, either as a test system evaluator or user. He served two command assignments at Schriever AFB, the home of GPS, and retired as Deputy Chief Scientist for Air Force Space Command. Don also served as a Politico Military Affairs Officer during the Reagan administration, working with 32 foreign embassies and serving as a Foreign Disclosure Officer making critical export control decisions concerning sophisticated military hardware and software. After retiring from the USAF, Don served seven years as the senior space marketer and subject-matter expert for two of the largest government contractors dealing in space software and hardware. Don currently serves on two independent GPS review teams he helped found, and on three independent assessment teams at the Institute for Defense Analyses, dealing with critical issues for the U.S. government. Don has served on numerous Air Force and Defense Scientific Advisory Boards. He writes and speaks extensively on technical issues concerning the U.S. government. Don earned his Bachelor’s degree and MBA; the Ph.D. is in progress.