Aerospace Historical Engineering Analysis: The Boeing X-20 Dyna-Soar Hypersonic Vehicle. (2024)

Overview:

Among the Pantheon of Legendary Planes, two of the most commonly referenced are the SR-71 “Blackbird”, with a top speed of Mach 3.5, and to a lesser extent, the X-15, with a top speed of Mach 6.7:

Yet 60 years before any other nation, the United States was on its way to fielding an aircraft that would have SURPASSED both of these mythical aircraft: the X-20 Dyna-Soar:

An Amalgam of the words “Dynamic Soaring”, the Dyna-Soar hypersonic vehicle was designed to act as a bomber and hypersonic information, surveillance, and reconnaissance (ISR) asset, attaining speeds of Mach 20.

At Mach 20, the Dyna-Soar would have had GLOBAL RANGE, able to reach any location in the world within 30 minutes. Travel from New York to London would be 15 MINUTES, and a trip from Washington, D.C. to Moscow would be over in 20 minutes.

Yet despite all this promise, the “Dyna-Soar” project was cancelled.

What happened? Why was such a promising project that would have historical significance and implications cancelled before its time?

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In This Edition of The Engineer’s Perspective:

Could the mythical "Dyna-Soar" take to the skies today?

Overview:

Background:

Description and Specifications:

Calculations:

Thoughts and Conclusions:

References:

1. Background and History:

Technology constrains the future:

The X-20 Dyna-Soar started off on the background of World War II as the Silbervogel (Silver Bird) conceived by Eugen Sänger, a German rocket propulsion engineer, and his wife Irene Bredt, a mathematician.

According to Aerosociety.com:

[the Silbervogel] was designed as an unstoppable ultra long-range suborbital bomber, able to strike the US from Europe by ‘skipping’ in and out of the upper atmosphere. The Silbervogel would have been launched by rocket-powered sled, before engaging its own rockets to climb to an altitude of 90 miles and then using the upper atmosphere in a series of ‘skips’ to extend its range – reaching a top speed of Mach 17 during its flight. Once over its target, it would have dropped a 8,800lb bomb, before continuing on to land in Japanese Axis-held territory. Immune to countermeasures or interception, the Silbervogel would have had a staggering range of 19-24,000km. Fortunately for the Allies, this design for a spaceplane bomber was constrained by the technology of the day.

A. Post WWII Revival:

The Silbervogel, limited by the technology of the day, saw its revival after World War II in the early years of the Cold War and Space Age, when Eugen Sänger’s colleagues, familiar with the original Silbervogel, re-purposed the concept in 1952. The new project, modified for vertical rocket launch, was given the acronym of BoMi or “Bomber Missile”:

Initial studies proposed utilizing a delta-wing glider placed atop a rocket that would be boosted into sub-orbital speeds, and when separated from the booster, would travel vast distances by skipping into and out of the atmosphere. Eventually the proposal was modified to a Boost-Glide concept after a series of reports did not find much favor in the Skip-Glide technique, but the initial concept remained the same: An ultra-long-range rocket-boosted glider capable of extreme distance and speeds.

In 1957, three independent Hypersonic Vehicle research efforts:

• RoBo (Rocket Bomber)

• Brass Bell (Long Range Reconnaissance Vehicle)

• and Hywards (A Research and Development (R&D) program meant to develop the technologies for both RoBo and Brass Bell)

were consolidated into one overall project, creating a proposed system capable of both bombing and reconnaissance missions, and would act as successor to the X-15 research program:

Dyna-Soar.

B. The Program

Consisting of three Phases, the Dyna-Soar program consisted of:

Dyna-Soar I- A research vehicle

Dyna-Soar II - A reconnaissance vehicle (previously Brass Bell)

Dyna-Soar III - A Space Bomber (previously Robo).

A Dyna-Soar Promo film from 1962:

The development program according to the promo film consisted of Air-Dropping a manned piloted version from a host aircraft (a B-52), and then rocketing the Dyna-Soar into Space to test its aerodynamic characteristics and functional sub-systems:

The air-dropped launches would then be follows up with rocket-launched sub-orbital testing of unmanned vehicles with Titan boosters, followed by manned flights of the same mission profile:

The Orbital Missions would then follow, with the Manned vehicle being strapped to a Titan I Booster for a launch vehicle:

C. Dyna-Soar’s Extinction:

In 1963, the conflicting scope between this program (Air Force) and NASA’s realm of space flight, in particular the Mercury and Apollo program, combined with what Secretary McNamara decleared as a poor return on investment and the increasing cost and development with no clear product predicted until the mid-1960s, lead to the cancellation of Dyna-Soar on December 10 of 1963. Specifically from Popular Science:

By 1963, NASA’s Mercury program was taking great strides having put two men into orbit on increasingly lengthy missions that were also answering questions earmarked for Dyna-Soar, namely questions of aerodynamic heating and human response to being in orbit. And the agency was also by this point firmly committed to using capsules for the Apollo lunar landing program. There was no way a Dyna-Soar-type vehicle would supersede the ballistic-type Apollo spacecraft already under development.

Because Dyna-Soar didn’t factor into the nation’s success in the space race, it was subjected to yet another US Air Force mandated review in March of 1963 alongside a review of NASA’s Gemini program, comparing the military potential of both systems. Dyna-Soar just didn’t have a place, and in December of 1963, McNamara formally announced its cancellation. The decision, he said, boiled down to a poor return on investment. By that point, Dyna-Soar had cost close to $400 million (over $2.8 billion in 2010) and still didn’t have a firm mission or even a clear reason for being. In its stead, the Air Force would pursue a larger, militarized version of the Gemini spacecraft called Gemini B or the Manned Orbiting Laboratory.

2. Description and Specifications:

The actual Dyna-Soar Vehicle was a delta-winged glider vehicle that was 35.34 ft in length, 20.8 ft in width and 8.5 ft in height excluding the landing Skids.

It was meant to be boosted in its final configuration with Titan boosters for Stage I:

The Titan Stage I booster would then detach and Stage II would take the Rocket into its final flight path:

Successful testing would then to transition testing on Titan II and Titan III boosters to expand the X-20’s range over 25,000 miles:

3. Calculations:

NASA (Back then called NACA) has never revealed how it or its contractors created preliminary estimates regarding how far the Dyna-Soar could glide after release from its boosters.

One of the clearest predictions NASA did make however was in this illustration from its paper on Dyna-Soar’s aerodynamic performance:

Short of reaching out to the original engineers and scientists that calculated this, I looked into more contemporary research in the hypersonics field and identify a potential equation that would lead to accurate estimates of Dyna-Soar’s Capabilities.

A. Utilizing an unrelated paper to calculate Dyna-Soar’s Nominal Range:

To calculate whether the Dyna-Soar’s potential gliding range I identified a 2015 research paper from the Carnegie Endowment that derived modeling calculations for hypersonic glide weapons, 52 years after Dyna-Soar was proposed and cancelled:

In particular, paper author James Acton derived an equation for Hypersonic Boost Glide Weapons’ Length of Glide:

The equation is an open-source estimated Calculation of a Gliding Body’s range upon re-entering the atmosphere.

As Acton’s paper focused on hypersonic missiles, he never specifically focuses on Dyna-Soar, meaning his derived equation is ideal:

1. As his research never touched on Dyna-Soar, the derived calculation has no bias in estimating the distance Dyna-Soar could glide.

2. His derived equation is not specific about what kind of system is being modeled.

3. Finally, his equation is simple: there only a few terms that one needs to identify to "Plug and Play”

Acton’s calculation predicts a hypersonic vehicle’s (Boost-Glide Type) maximum range starting at the initiation of the glide. This glide occurs post-boost (when the glider separates from the boosting rocket/s) and is also called the “Pull-up”, as the Glider leaves space and starts to enter the atmosphere (Region between “t3” and “t4” in the section below taken from Acton’s paper):

A comparison between Acton’s screencap illustration to the screencap from NASA’s paper characterizing the Dyna-Soar’s aerodynamic profile reveals similarities between both flight profiles, revealing Acton’s glide length equation, which starts at the “Pull-up” maneuver for Hypersonic Glide Vehicles (HGVs), has an analog “Pull-up” maneuver in NASA’s Dyna-Soar mission profile at the “50” minute mark in the center of the illustration below:

B. Utilizing The Equation to predict the distance of Dyna-Soar’s Glide:

With this similarity between what Acton’s derived equation and notional trajectory and its similarity to NASA’s original predictions from the 1950s, we can implement Acton’s Equation to predict a notional Glide Length for Dyna-Soar at post-boost:

Key Terms from the equation are in gray box below:

lglide = length of glidere = Radius of earth (6,400,000 meters)L/D = Lift Over Drag ratio (identified from original NASA paper below)ln = Natural Logarithm vi = initial velocity (identified from original NASA paper below)ve = escape velocity (identified from original NASA paper below)

The method used to obtain the terms above have been listed below here:

Lift-to-Drag Ratio: the L/D for Lift-to-Drag Ratios, needs to be specified for the hypersonic vehicle. NASA pointed out a maximum Coefficient of lift (Cl) for Dyna-Soar in this paper: “Dyna-Soar Aerodynamic Performance by James S. Lesko”:

Assumption: Chosen L/D ratio is 2.18 to maximize glide distance

Initial Velocity (vi): The initial velocity we will use will come directly from a declassified document of Dyna-Soar’s estimated speed of 25,000 feet per second.

Converting 17,000 mph approximates to 7600 meters/second.

Assumption: The vi we will utilize is 7600 m/s.

Escape Velocity (ve): Acton argues that a hypersonic vehicle’s speed re-entering the atmosphere post-boost is always below the speed of low-earth orbit satellites.

This makes sense intuitively, for if the Hypersonic Vehicle moves faster, it then enters orbit and becomes a satellite.

Acton’s calculated speed of a low earth orbit satellite is:

The terms for the equation are listed below:

v = velocity, g = gravitational constant of 9.807ms2, re is the radius of the earth at 6,400,000 meters

Filling in this information we obtain the following:

The result is ~7920m/s

Assumption: The ve we will utilize is 7920 m/s.

Plug and Play:

Now we apply the example equation from Acton’s paper:

and fill in the blanks with what we learned from NASA’s original Dyna-Soar Paper:

The answer for lglide distance (The distance starting from on pull-up into atmosphere at ~300,0000 ft) is 17,692 km, which converts to approximately 9,553 Nautical Miles.

C. Comparing the Calculated glide length with NASA’s prediction from over 50 years ago:

Comparing this to the NASA estimation below , we see that at the 50 minute mark, the “Pull-up” occurs around 11,000 nautical miles (At approximately 300,000 feet), and the glide continues until approximately 20,000 miles:

We can cross reference this further with that second NASA paper, saying that the top speed of 25,000 feet per second would occur at approximately 300,000 feet:

Both documents indicate that at 300,000 ft around the 11,000 mile marker, the pull up occurs. As Acton’s calculation only applies to the “Pull-up” of the flight, we can identify NASA’s original estimation of a notional “Glide” for Dyna-Soar:

20,000-11,000 = ~9,000 Nautical Miles

With the reference NASA answer being 9000 Nautical miles. We are only 6% off the original NASA prediction in the 1960s utilizing an equation from an unrelated research paper!

Longest Distance the Dyna-Soar Could Travel?

Now the real fun begins!

In the 1950s, NASA predicted them maximum range of the Dyna-Soar would be over “20,000 miles by flying at (L/D)max”:

With Acton’s derived equation coming to less than 10% off of NASA’s original predictions, we can now estimate the potential maximum range of Dyna-Soar.

By bringing the initial speed of Dyna-Soar closer to orbital speed (7900m/s vs 7920m/s) as shown below:

we confirm that the distance traveled by the Dyna-Soar at full glide would be ~36,900km, or 22,878 miles, or 19,924 Nautical miles.

Combining this increased range (36,900km) with the standard boost range prior to gliding range shown below at range values 0 to 11:

We need to add 20,372km (converted from 11,000 nautical miles) to 36,900km for a total distance of 57,271 km.

Considering that the earth’s circumference is approximately 40,075 km the Dyna-Soar would have reached any part of the Globe!

Thoughts and Conclusions:

In the end, would Dyna-Soar have been feasible? Would today’s technology have enabled this system to take flight and join the legendary Pantheon of historical aircraft like the SR-71 and X-15?

Yes! Very much so!

Based on a derived calculation from an unrelated paper created 50+ years after Dyna-Soar, we were able to independently confirm the estimated performance that NASA Predicted for the Dyna-Soar over 60 years ago!

Even with a “nominal” performance, the Dyna-Soar would have been an incredible aircraft on the same level as the SR-71 Blackbird and the X-15, and if pushed, could have soared into a class by itself with Global Hypersonic range claims that would only be matched by the Space Shuttle decades later.

Unfortunately, due to Dyna-Soar’s abilities touching on the nascent Mercury and Apollo programs of the Space Race with Russia, the competition for budgeting forced a reckoning, and Dyna-Soar was halted as a result.

With the extinction of Dyna-Soar, the United States development of hypersonic-glide systems went into hibernation, and only resumed at full-speed in this last decade (2010s-2020s). It is only now (the 2020s), that Hypersonic Glide Vehicles similar in principle to Dyna-Soar’s functionality have started to become a reality.

Unrealized Implications:

The just-realized implication of this research (in my end at least), is that these rough calculations were only based on a nominal flight path for Dyna-Soar with only a smaller booster in partial-orbit. Dyna-Soar was planned for an expansion of its range with Dyna-Soar II and Dyna-Soar III. This implied that, we were only scratching the surface of what Dyna-Soar could have reached.

Should the United States have fully developed Dyna-Soar, it is clear that a fully matured system would have developed into a “Fractional Orbit” Bomber and Reconnaissance system similar in functional principle to China’s Hypersonic Glider test in August of 2021.

A bomber system of this range and speed, with the dynamic unpredictability of a human pilot at the helm, would have created a powerful nuclear deterrent early in the Cold War and changed history.

References:

• Godwin, Robert, ed. (2003). Dyna-Soar: Hypersonic Strategic Weapons System. Burlington, Ontario, Canada: Apogee Books. ISBN1-896522-95-5.

• Dyna-Soar Aerodynamic Performance (Nasa)

• Astronautix.com

• The space plane that wasn’t: everything you never needed to know about Dyna-Soar

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