Sprint: The Mach 10 Magic Missile That Wasn’t Magic Enough

Defending an area against incoming missiles is a difficult task. Missiles are incredibly fast and present a small target. Assuming you know they’re coming, you have to be able to track them accurately if you’re to have any hope of stopping them. Then, you need some kind of wonderous missile of your own that’s fast enough and maneuverable enough to take them out.

It’s a task that at times can seem overwhelmingly impossible. And yet, the devastating consequences of a potential nuclear attack are so great that the US military had a red hot go anyway. In the 1970s, America’s best attempt to thwart incoming Soviet ICBMs led to the development of the Sprint ABM—a missile made up entirely of improbable numbers.

Mach 10? You Betcha

A Sprint interceptor on a test stand, as pictured by the US DoD.

The Sprint anti-ballistic missile was an engineering effort in response to the nuclear threat posed by the Cold War. This missile, with its astonishing performance and parameters, was designed to intercept incoming ballistic missiles during their terminal phase in the moments before impact.

Despite its crucial task, and its impressive capabilities, the Sprint missile had a relatively short operational life, a reflection of the rapidly evolving strategic landscape of the time.

Developed in the late 1960s as part of the United States Army’s Safeguard Program, the Sprint was a key component of a layered missile defense system intended to protect against Soviet intercontinental ballistic missiles (ICBMs). It was intended to operate in tandem with the longer-range LIM-49 Spartan missile. The Spartan was designed to engage threats outside the atmosphere, with Sprint missiles addressing those that penetrated further inward.

The technical specifications of the Sprint missile were nothing short of remarkable. Powered by a solid-fuel rocket, it could accelerate to a speed of Mach 10 within 5 seconds of launch, covering an altitude of 30 kilometers in roughly 15 seconds. That’s 12,000 km/h for those of you playing along at home. This incredible acceleration of roughly 100 G was necessary to intercept ICBM warheads re-entering the Earth’s atmosphere at high velocities.

Sprint had to launch so quickly that there was no time to open hatches or silo doors. Instead, Sprint was designed to be ejected from its launch bay via an explosively-driven piston which punched the conical missile straight through the fiberglass cover on its silo. The first stage solid rocket fired for just 1.2 seconds, disintegrating shortly after due to the intense aerodynamic forces on the airframe. The second stage would fire shortly afterwards, boosting Sprint to an interception at altitudes between 1.5 to 30 km. Total flight and interception time was intended to be on the order of 15 seconds.

The immense speed of Sprint posed multiple engineering challenges. The missile’s skin was designed to withstand temperatures of up to 6,200 degrees Fahrenheit due to air friction at these speeds, with a special ablative coating to prevent it from burning up in flight.

The Sprint program apparently had some pretty rad overalls for technicians. Today’s public programs can’t claim the same. Credit: Ryan Crierie, CC BY-SA-2.0

One of the most notable features of the Sprint was its guidance system. It used a unique ground-based phased array radar system that could track incoming warheads and guide the missile to its target with phenomenal precision. This system allowed for mid-course corrections in the missile’s trajectory, a critical capability given the high speeds and short reaction times involved. However, the need for communication with the ground was a challenge, given Sprint’s intense speed. The friction with the air and the resulting intense heat tended to create a plasma around the missile, which made radio communication difficult. Incredibly powerful radio signals were required to penetrate the plasma and exhaust plume of the missile.

Sprint was not a hit-to-kill vehicle. With ICBMs incoming at even higher Mach numbers than Sprint itself, just getting close to an incoming missile was an engineering feat at the very edge of possibility with the prevailing technology. Sprint made up for this with the warhead it used to destroy incoming missiles—a nuclear one, in fact. Each Sprint missile mounted a 1-kiloton W-66 “enhanced radiation” warhead. These warheads were specially designed to not just destroy incoming missiles with blast effects, but with intense neutron flux from the nuclear fission reaction.

Detonating nuclear warheads over your own soil might seem reckless in the extreme, but it was the Cold War. It was deemed highly favorable to use small warheads high in the atmosphere for defence, versus having enemy weapons in the megaton-range destroying entire cities on the ground.

A Sprint nosecone, slightly separated from the body of the missile in its silo. Credit: Public domain

Despite its advanced capabilities, the Sprint missile was in service for a relatively short period, from 1975 to 1976, as part of the Safeguard Program. There were several reasons for this brief operational life. First, the strategic arms limitation talks (SALT) between the United States and the Soviet Union led to treaties that limited the development and deployment of anti-ballistic missile systems, including the Safeguard Program. These defensive systems were considered a threat to the delicate balance between the two superpowers. Without viable defences against ICBM attacks, each power could be reasonably assured of its own destruction if it chose to fire its own missiles. Having a working ABM system would allow one side the ability to strike without fearing retaliation, ruining the “safe” concept of mutually assured destruction (commonly referred to as MAD).

Additionally, the high cost of deployment and maintenance of such a complex system, combined with rapid technological advancements in offensive missile technology, made the Sprint system appear less cost-effective and strategically viable over time. Questions arose around whether a defence system based around Sprint could reasonably expect to counter Soviet missiles deploying multiple independent reentry vehicles, which could allow one missile to deliver up to 10 warheads on independent trajectories.

This image shows a Sprint missile launched from Meck Island. Note the debris from the destroyed silo cap at the base of the exhaust plume. Credit: US Army, public domain

The end of the Sprint missile’s service did not necessarily signify a failure, unless one considers huge expenditure for little end product a failure. Ultimately, it demonstrated the challenges of developing defensive systems in the nuclear age and the dynamic nature of military technology and strategy.

The Sprint missile demonstrated the technical feasibility of intercepting ICBMs during re-entry, a concept that has continued to influence missile defense strategies to this day. However, it couldn’t get around the ultimate concept that doomed many anti-ballistic missile defence schemes. While one can hope to intercept one ICBM, or even a handful, an attacker only needs to increase their number of missiles by a small amount to rapidly increase the numbers of intercepters required by a defender.

In retrospect, the Sprint anti-ballistic missile represents a fascinating moment in Cold War history; Fears around national security drove the development of a missile of truly wild performance. And yet, at the same time, it proved largely useless for its intended mission. The sheer scale of the potential conflict it was built for overwhelmed its very purpose.

74 thoughts on “Sprint: The Mach 10 Magic Missile That Wasn’t Magic Enough

  1. “you have to be able to track them accurately”
    Heh, we just had a discussion on the 1991 Patriot missile failure where 24-bit registers used for clock calculation lead to the system missing an incoming Scud missile by almost 500 meters.

      1. We are not talking about the same range here. The Sprint missile has a range of 40 km. The missiles which are being developed nowadays are hypersonic gliders with a much longer range (tens of thousands of km).
        Their goal is to replace ballistic missiles, which can already reach hypersonic speeds (Mach 25) but with a very predictable trajectory (which is the very reason for the existence of the Sprint antiballistic missile).

      2. There is no trouble building a rocket reaching Mach 10. It’s much harder to build an air breathing missile that can reach Mach 10. It’s a totally different engine which allows reaching much further.

        1. In addition to the engine, which is already tough enough, they are meant to have extreme maneuverability. Now what that means at those speeds, I can’t say, but yea as you said, the speed isn’t the problem. This sprint missile wouldn’t work if the target can be tens of kilometers away by the time it gets to where it was fired at.

          1. At hypersonic velocities, a 10 g turn can result in a radius larger than a state.

            Also, more to the point, you have to keep the actuators and control systems functional within a chassis that is totally soaking at temperatures above the melting point of almost every metal. Sprint only had to survive for a brief flight, so heat-soak wasn’t an issue, but as of right now, it’s an unsolved problem for that must be solved before long range hypersonic flights are useful.

            Things like Avangard are actually short-ranged (despite certain animations on the internet). A hypersonic flight of under 500 miles (which is spent largely in the upper atmosphere) is still manageable. A 19,000 mile flight spent at a pressure density sufficient to allow aerodynamic steering is sufficient to ensure that, even if you hypothetically made the vehicle out a single solid chunk of tungsten, you’d be risking melting it all the way to the core.

            Even the best actuators tend to have trouble with 300°C for 30 minutes.

            Finding airframe materials is challenging. Finding cooling systems to keep the active components functional is… hard. Hard enough that it’s an area of active research, and still mostly hypothetical.

  2. Interesting article. Thanks.

    I read that the LIM-49 Spartan had a five-megaton thermonuclear warhead… they weren’t messing about! It makes me wonder though, could any “standard” modern nuclear ICBM fill that role i.e. detonate in space to take out other ordinance, or was there something special/different about this Spartan design?

      1. Thanks. Do you think it’s a matter of circuitry, and presumably international agreements, or also the case that the missiles aren’t physically capable of doing the same job? It’s just an idle wondering really.

        1. Rog77, unfortunately there’s nothing about an ICBM’s design that makes it suitable for conversion into an ABM. A conversion would require adding an active seeker and/or receiver for target position messages from the ground. It would need a significantly more robust maneuvering system. The missile and its propulsion system is sized to loft warheads across the globe, whereas an optimal interceptor will be only as large as needed to get its smaller payload in a position to hit incoming. In the case of a US Minuteman III, the second and third stages would need to be completely gutted. There would be no cost savings and less capability compared to developing a purpose-built missile.

          1. There’s a photosensor with a little whirlygig in front that blocks and unblocks it at a steady rate, turning the signal from the photosensor into a sin wave that can be compared against a pre-recorded view of what it should see along its flight path.

            It sprang from some of the same research in the late 40s that also led to heatseekers and the TOW. Weirdly, the celestial navigation etc articles don’t give dates. Only reference I can find on short notice to the origins is in https://en.wikipedia.org/wiki/1948_Lake_Mead_Boeing_B-29_crash

      1. EMP is most certainly not worse than the incoming multi-megaton warhead heading for a dense city. My God. This risk calculation is mentioned in the article anyway, it was obviously taken seriously by the designers of the system.

        1. I would agree that I would prefer to lose a few modern conveniences than to either die in a giant fireball, of radiation poisoning, or of starvation following a successful enemy strike.

          1. @Ostracus Yeah, It would totally suck for anyone reliant on tech to stay alive in the moment, but I kind of think those people would not be much better off if a nuke actually hit their city. In fact, I would go as far as to say that would be bad for everyone all around.

            Whilst reasonable people can disagree on all sorts of things, I think most folk would agree they’d prefer not to be blown to smithereens, all things being even.

          2. Let’s not forget that in the late 1960s, there was a lot less consumer electronics, and most of that used vacuum tubes.
            IIRC, the Sprint silo cover was laced with det cord and disintegrated at launch. The pieces were still suspended in air as the missile flew through. Either the Sprint or Spartan left their silo at the muzzle velocity of a. 45 caliber bullet.
            I forgot which of the two received its targeting by radio as it cleared the silo.

      2. Starfish prime was a very large thermonuclear warhead. A 1 kt enhanced-neutron warhead is a very different thing, whether it be detonated at 3 miles, 30 miles or 300 miles. Among other things, it really can’t cause a sudden displacement of a significant portion of the earth’s magnetic field due to the growth of a large conductor (in the form of a miles-across plasma sphere).

        Also, part of the designated threat they were facing when this thing was designed is that the enemy would likely intentionally set off a few of the MIRVs in any salvo at extremely high altitude to help disrupt radar tracking of the remaining warheads.

        In other words, EMP if you do, EMP if you don’t…

        Speaking of EMP threats…

        While there are distinct consequences of high-altitude shots, the EMP isn’t an all-encompassing source of magical damage, and many of the hazards imputed to it are undermined by the actual testing that has occurred. It’s mostly limited to things connected to power distribution lines, as the long conductors can develop tens of thousands of volts and/or thousands of amps (starting fires as well as damaging equipment). Standalone equipment such as cars and laptops tends not to take significant permanent damage, according to tests in the US Navy’s EMP simulators. The repeated Soviet tests over Kazakhstan largely demonstrated the same thing: grid-connected equipment often burned, other things were either temporarily affected(radio propagation) or totally unaffected (battery-powered or generator-powered stuff, even a factory powered from an on-premises generator that was operating at the time of the detonation).

        Another thing that surprises some people is that the PRC-25 turned out to be more vulnerable to EMP damage than the PRC-77. They’re both VHF squad radios, with almost identical circuitry, except that when the PRC-25 was deployed, power transistors were still kind of failure-prone, so it used a single tube in the final rf power amplfier. Most of the line-replaceable modules in the two radios are not interchangeable due to improvements to the packaging and module-level testing, but the circuitry is largely identical except for the final amplifier.

        In the early 1980s, the Canadian military tested the PRC-25 and PRC-77 while they were setting up their EMP test facility, and unexpectedly found that the PRC-25’s tube would burn out when exposed to EMP, leaving the receiver functional but no ability to transmit. The PRC-77, on the other hand, would retain its ability to transmit. This was unexpected and led to some retesting…. They eventually found that the transistor was relatively undamaged by high voltages as present on the antenna during an EMP , while the fine grid in the vacuum tube was easily damaged by arcing due to the overvoltage.

        In general, anything that won’t fry due to a very nearby lightning strike will also survive any EMP that’s insufficient to kill the nearby humans. A human walking alongside a metal fence is more likely to die than the phone in the human’s pocket, or the bluetooth headset in the human’s ear (even if both are active at the time of the EMP)…

        Most of the EMP fear is due to “it *could* happen!” combined with “how do we know that it *doesn’t* happen, we can’t test it!” But, in both observation and practice, most of the EMP effects are similar to and not stronger than strong lightning, and only the parts of the *nuclear-generated* EMP pulse that affect large infrastructure, like copper-line telephone systems and the power grid, are all that unique.

        Grid and communications failure is a serious hazard, but EMP shouldn’t be extrapolated into a “magical threat”. Many of the hazards attributed to EMP require tens-to-hundreds of thousands of volts per meter of field strength. At those strengths, it doesn’t matter if your *phone* is still working, you’ll personally be dead. And, if the field strengths are lower, most of the hyped EMP threats fail to happen…

    1. Trying to nail something moving on the upward leg of a ballistic trajectory vs. trying to hit something stationary at the end of the trajectory.

      Missile interception is very hard, and (subtracting propaganda) we likely still can’t do it reliably outside of stuff like this (literally nuking the entire zone while it’s far away from people) or the iron dome (the inheritor of all this technology, can only handle missiles built by amateurs out of garbage)

      1. The modern version of the Patriot is doing a fine job in Ukraine, at least within the limited coverage area of the PAC-3 interceptors. Though if you intended “missiles built by amateurs out of garbage” to include Russia’s Iskanders and Kinzhals, well, you may have a point.

      2. And NASA did it on a planetary scale with the “kinetic impact” of a rocket or whatever into an asteroid.
        And also the same but returned samples. That’s so insanely hard I can’t believe we don’t have NASA day or something to commemorate it.

  3. “The missile’s skin was designed to withstand temperatures of up to 6,200 degrees Fahrenheit due to air friction at these speeds, with a special ablative coating to prevent it from burning up in flight.”

    quibbles : it’s not air friction, it’s compressive heating behind the shockwave. also, ablative coating protects BY burning up so the phrasing is misleading.

    anyway, nice article – it’s a mind-boggling engineering achievement

    1. A little quibble with our quibble :>

      Aerodynamic heating involves both compressive heating, as well as the viscous forces acting in the boundary layer that surrounds the missile (better known as air friction). The ratio between the
      two modes of heat generation varies along the missile or rocket in an atmospheric flight. Near the stagnation point, the heat generated by direct compression of the air will dominate while on the sides of the missile the conversion of velocity into heat by the viscous forces within the boundary layer will be dominant. Good article on the subject is here: https://www.abcm.org.br/anais/cobem/2009/pdf/COB09-0978.pdf

      As for the coating, the term ablative means by definition ablation through melting or evaporation. The original sentence wasn’t trying to describe preventing the coating from burning up, the ablative coating was to prevent the airframe missile from burning up in flight – made no mention of how it was going to do it, and for most people made perfect sense.

      1. Quibble with your quibble of their quibble…

        The Sprint is a cone.
        There are no “sides”.
        The entire surface (minus the engine) experiences mostly compressive heating.

        Also: Don’t make authoritative statements on what others do/don’t understand. You literally cannot know this.

  4. I love reading about these. It’s one of those ridiculous Cold War weapons that actually made it to production. I really doubt it would make economic sense to bring back … but I still want to see a kinetic warhead variation that peppers targets at Mach 10.

    1. The fact that they lost their stomach during this period for total war moral calculations, despite having just lived through two wars in which those calculations were embraced even for non-nuclear war, reveals that it happened not because they were unaware of the results but far too familiar with them

      1. I knew a guy…who, at least until he retired, had a job calculating nuclear “effects” for one of the military contractors in the area. Nice guy, but I don’t think I’d be interested in doing that kind of work.

      2. They never lost their stomachs for this. Reality changed, ICBMs replaced the idea of first strikes from bomber. Solid fuel ICBMs meant no long launch times, you could launch on warning. SLBMs meant a retaliatory force would be available. Better warning systems and satellites removed the idea of surprise attack. Trust me people are still making the uncomfortable calculations to this very day. I am a former member of Strategic Air Command Headquarters. Every human is fundamentally opposed to all out nuclear combat however there are professionals who have the job of planning for contingencies no matter how distasteful. The idea is to be strong enough and ready enough that no one considers it possible to take advantage of perceived weaknesses.

    2. You might be surprised how much protection ten kilometers of atmosphere can provide from a relatively small fission bomb. As long as they were employed as envisioned, against high-altitude bomber formations, the greatest hazard on the ground would have been from the crashing bombers and their payloads.

      It was hardly secret that they planned to fire nuclear warheads at incoming bombers. There were newspaper articles and press releases. They even pulled a publicity stunt with the AIR-2 Genie missile test: https://www.youtube.com/watch?v=x9kkKtpEVYM

      For other nuclear anti-aircraft weapons, also look up the BOMARC, Talos, Terrier, S-25 Berkut, and S-200 Vega/Dubna. There are probably more.

      1. yes, the M.1 “Ding Dong”, aka the AIR-2 Genie unguided air-to-air missile. They tested it during Plumbob John against 4 USAF officers and a photographer directly underneath the detonation at 25000 feet.

  5. I recommend looking for a video of a test of the device. The skin of the missile would heat up to such a degree that it would be a bright white dot on top of the exhaust plume. Very impressive.

  6. The only operational Safeguard base was at Nekoma, North Dakota. Shut down a week after it became operational. The Spartans were siloed at Nekoma, the Sprints were at 4 Remote Sprint Launch (RSL) sites approximately 25 miles from the Nekoma site, (4 different locations).
    The phased array radar that detected incoming missiles was not decommissioned, it still exists as Cavalier (North Dakota) Air Force Station. That radar was my first job out of Tech School.

    1. I remember writing a stupid article about the Hutterites reactivating SRMSC after it was sold by the air force, and briefly operating the only ABM capability in the west. However, being bound by the Schleitheim Confession, the Hutterite SIOP dictated that in the event of a nuclear attack they would have to detonate the missiles in their silos.

  7. There is a nice video about Safeguard on youtube:

    “AT&T Archives: A 20-Year History of the Anti-ballistic Missile (Bonus Edition)”

    It includes a lot of interesting information about the missiles, radars, and computer technology developed for the system. All set to the kind of special soundtrack you could expect from a 1976 industrial video. ….Progress!

    The Sprint part starts at 23:39

    My favorite missile failure video of all time is at 22:47

    31:16: 106 Wynn Drive, Huntsville, AL. The building is still there.

  8. Fun fact: the warhead, being a ‘neutron bomb’, wasn’t meant to physically damage the incoming missile (though that would be a bonus), but the idea was that the excess of neutrons would cause either a criticality in the incoming missile’s core, damaging it, or if it was about to explode at full strength cause a pre-detonation vastly reducing it’s power.

  9. That’s what the neutron bomb was developed for, not to deploy to Germany as it later was because, as one US military bigwig said, to paraphrase, “German villages are two kilotons apart,” pointing out that defending Germany with full-blast-yield nukes would destroy Germany.

    The exterior of the missile reached a temperature hotter than the missile’s combustion chamber. Rather than enhancing the power (specific impulse) of the propellant with powdered aluminum as is normally done, they used aluminum staples instead to add mechanical strength to the propellant grain so it could withstand the incredible acceleration forces. They had to be careful about the amount used to avoid disrupting communication with the missile through the aluminum oxide (causing the white smoke of the exhaust) exhaust plume.

    Bell Labs: Sprint Missile Subsystem (chapter 9)


      1. HIBEX


        The HIBEX (High-G Boost Experiment) research missile was built by Boeing for ARPA (Advanced Research Projects Agency) and the U.S. Army Missile Command as part of a project named Defender. It was designed to evaluate technology for very-high acceleration interceptor missiles, like the then planned Sprint short-range anti-ballistic missile.

        HIBEX had a short conical body and was powered by a solid-propellant rocket motor. Its design goal was the capability to intercept ICBM reentry vehicles at altitudes of less than 6100 m (20000 ft), where the RV would travel at about 3 km/s (10000 fps). The initial acceleration of HIBEX was almost 400 g. At least seven HIBEX rockets were fired at White Sands Missile Range (WSMR) between February 1965 and January 1966, and the test results were used in the development of the operational Sprint missile.

        1. McDonnell Douglas UpSTAGE Anti-Ballistic Missile


          In 2 more years, UPSTAGE, a maneuvering HIBEX second stage, demonstrated over 300 g lateral acceleration and a side-force specific impulse Isp > 1000 sec using external burning, jet flow control techniques and a laser gyro for guidance. The HIBEX technology furnished the basis for the Army’s LoADS short range interceptor program. UPSTAGE jet maneuvering control technology has been incorporated into the SDI’s HEDI missile.

  10. BTW, missile-based ABM systems are fundamentally incapable of protecting against anything other than accidental or very small scale attacks. It’s much easier and cheaper to overwhelm them with decoys and other countermeasures than it is to counter those countermeasures. Only incredibly powerful, rapid fire directed energy weapons with their many issues (currently not even remotely powerful enough to provide short linger time on target, blooming due to atmospheric heating along the beam, etc.) or tiny kinetic energy interceptors have any chance of being (mostly) effective against a large attack, but even if 99% effective (probably impossible), enough warheads will get through to do unacceptable damage to any country.

    ABM Countermeasures


    1. The Safeguard system was only intend to cover the missile fields of Grand Forks strategic missile squadrons. The idea was to preserve a retaliatory force and eliminate the advantage of a first strike strategy. As we went to Minuteman 3 missiles and improved warning systems it became possible to launch our missiles under an attack before the incoming warheads hit. Previous generations of our ICBMs required fueling and therefore more time to launch. This made the Safeguard system unnecessary. Under the ABM treaty the US and USSR were each allowed to maintain one system. The USSR established their ABM to defend Moscow and the US decided to defend the missile fields of North Dakota. Most people don’t understand that the point of ABM is really to ensure you can’t be disarmed in a first strike, not to cover a full on attack. The point is to prevent someone from even trying it.

  11. ABMs went out of style for many years since submarine platforms ensured survivability of the retaliatory forces. The rise of smaller potential nuclear powers such as Pakistan, India, and someday Iran revived the idea of possibly stopping a rogue launch or smaller attack using ABMs. They are also intended to defend point targets like carrier strike groups and major military imstallations.

    Also, in regards to comments on hypersonics above. It has been decisively been proven that MANUEVERING hypersonics are what matters. NASMS and Patriot have no problem calculating an intercept with anything on a straight line course. Inbound speed does not matter to them since they are only computing a point to meet you at head to head. Mach 10 is fast, RADAR is much faster. These systems give minute of warning time even at hypersonic speeds which is a long time for air defense systems.

    1. The problem is that friction-heating is a very difficult hurdle to overcome. A sprint missile had to function for 15 seconds, which is short enough for ablative heat dumping to still be effective.

      Any HGV operating at the altitudes and ranges that people hype is facing a thermal-soak problem that is sufficient to melt even refractory alloys. And guidance and steering systems tend to fail at only a few hundred degrees Celsius. There is a great deal of as-yet unsuccessful research into active cooling of the vehicle core, just to keep the maneuvering electronics alive.

      Additionally, the reported speeds are the *peak* speeds, achieved generally during the middle of the flight while they’re at the highest altitude they achieve.

      For steer-all-the-way-to-target designs, this is generally below 80,000 ft, which is still low enough for friction heating to be a serious issue; the much slower SR-71 had an average skin temperature of 500 to 600 degrees F, but local hot spots as high as 1200 degrees F. Also, the SR-71 kept its sensitive avionics deep in the airframe, and took great care to insulate them and prevent direct conductive heat transfer paths. A relatively small HGV cannot protect its electronics in this way.

      Now, once the vehicle gets near its target, it must descend into far denser air. Its velocity drops dramatically as it does so, and even so, its internal temperatures spike dramatically.

      Almost all of the engineering going into making a successful HGV is materials engineering rather than aerodynamics, and those problems are far from solved.

      There is another factor that sometimes gets brought up, that of the “anti-radar plasma sheath”. In practice, it’s not anti-radar (it actually reflects radar quite well). It’s simply that signals trying to pass THROUGH the plasma sheath, such as remote commands, onboard target radar, or voice comms (if it’s a manned vessel like Apollo) will be badly attenuated. For external hostile tracking, the plasma itself is an effective radar mirror, not to mention a serious IR emitter.

      Anyone who thinks otherwise should review any Shuttle reentry. For example, when Columbia disintegrated over Texas, the hypersonic debris was extremely visible on the weather radars even before the news channels realized there had been a problem.

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