hypersonics
“We’re able to
environmentally
control our flight
range in order to
reproduce an
acoustically and
chemically clean
flight environment”
unpowered launch on 8 June
1959. Its rocket powerplant was
ignited in the air for the first
time on 7 September, with Scott
Crossfield at the controls for both
missions. The program achieved
its greatest altitude – 354,200ft
– on 22 August 1963 and highest
speed – Mach 6.7 (4,520mph) –
on 3 October 1967. The 199th
and last X-15 flight was on 24
October 1968.
Designed as an experimental
vehicle in its own right, the X-15
could also be equipped to carry
test payloads, including cameras
and electro-optical sensors,
and to collect atmospheric
samples. The data gathered
over almost a decade of trials
added immeasurably to the
understanding of the hypersonic
environment and contributed
critical knowledge to the US
space program, particularly its
re-entry vehicles.
Royal United Services Institute says, “There’s arguably a
better investment case in hypersonics for China and
Russia when you consider the potential benefit of being
able to bypass high-end defensive systems, albeit with a
small number of very expensive missiles launched
against high-value targets.”
Such high-value targets could include aircraft
carriers or other defence systems. Bronk adds, “If the
cost per shot can be made low enough for it to be
practical at scale, the ability to strike mobile, long-range
defence systems – surface-to-air or anti-ship missiles –
from stand-off range before they can move, might also
have value.”
He also notes that hypersonic weapons are not new,
since all ballistic missiles are hypersonic, as are some
more recent defensive systems, including the latest
Russian S-400 SAM (surface to air missile) system.
“The Russian 3M22 Zircon anti-ship cruise missile,
which may have reached initial operating capability, has
a claimed maximum speed of between Mach 5 and
5
Mach 7. I’d say we’re very much in the era
of hypersonics already, but we aren’t in
the era of where they are replacing more
traditional systems on a large scale.
“They remain exotic, but both the US
and RAF have indicated that they are
looking to a future where hypersonic
weapons are part of core capability.”
GAS GUN ALTERNATIVE
With much hypersonic research therefore
still to be done, the Southwest Research
Institute (SwRI) at San Antonio, Texas,
offers a dramatic alternative to rocketpowered
trials – a two-stage light gas gun
system. Nicholas Mueschke, principal
engineer at the SwRI’s Mechanical
Engineering Division, explains, “It uses
conventional propellants to push a piston
down a barrel. The piston compresses a
AEROSPACETESTINGINTERNATIONAL.COM // MARCH 2020 33
5 // Major William J ‘Pete’
Knight with the X-15A-2 in
1965. In 1967, he took
the aircraft to Mach 6.7,
while a flight above 50
miles also qualified him
for astronaut wings
(Photo: NASA)
X-15
North American’s X-15
marked a step change in
aircraft performance. A 1952
National Advisory Committee
for Aeronautics requirement
calling for an aircraft capable
of investigating flight at speeds
between Mach 4 and 10 and
extreme high altitude, ultimately
resulted in a trio of rocketpowered
X-15s.
One machine was rebuilt as
the higher-performing X-15A-2
after an accident, while another
broke up at Mach 5.0, with the
loss of pilot Major Michael Adams.
Having achieved 266,000ft on the
15 November 1967 sortie, Adams
was posthumously awarded
astronaut wings. He was among
the X-15’s five military test pilots,
all of whom gained astronaut
wings, while three civilian pilots
received theirs only in 2005.
Always launched from an
NB-52, the X-15 achieved its first
Although Lockheed is unable to discuss HCSW and
its associated work in detail, a spokesperson said, “One of
the biggest hurdles is high temperature materials. An
incredible amount of heat is created at hypersonic
speeds. To manage this extreme heat, advanced materials
and composites are critical.
“From a hypersonic strike perspective intent is
critical, because our hypersonic strike programs serve
diverse mission sets. The ultimate goal is to engineer a
solution to enhance military effectiveness.
“Hypersonic capabilities will provide the US with the
ability to strike hardened or time sensitive targets with
conventional warheads.”
Meanwhile, in November 2019 two MiG-31K fighters
launched from Olenya, inside the Arctic Circle. One fired
a Kinzhal hypersonic missile at a ground target on a
range 800 miles (1,300km) distant, providing further
evidence that Russia has fielded an air-launched Mach 5+
weapon. Justin Bronk, research fellow for airpower and
military technology in the Military Sciences team at the
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