The Limits of Stealth and the F-35

Excerpt from Thunder without Lightning The High Costs and Limited Benefits
of the F-35 Program By Bill French with Daniel Edgren August 2015
[Bill French is a policy analyst at the National Security Network (NSN).
Daniel Edgren is a former researcher at NSN.]

Lacking maneuverability and payload, the survivability of the F-35 will
depend heavily on its stealth characteristics. In the context of modern
warfare, stealth is the suppression or camouflage of any signature that
could be used by the enemy to detect friendly platforms. With respect to
aircraft, this mostly refers to heat or infrared emissions, electromagnetic
emissions, and radar signature. Of these, stealth is usually most associated
with minimizing radar signature, an effect produced by a combination of
radar-deflecting shapes and absorbent materials.

Today’s stealth technology is an outgrowth of a broader “hider-seeker”
competitive dynamic for an information advantage fundamental to all warfare,
i.e., the evolving competition between the methods for finding an opponent
and the methods for hiding.42 The kind of stealth technology used in modern
aircraft has a development history dating back to World War II, when Germany
experimented with radar- deflecting shapes and radar-absorbing materials to
counter allied radars. During the Cold War, the United States attempted to
develop stealth technology in a series of projects, culminating in the
stealthy F-117A, B-2, and F-22. By the end of the Cold War, the United
States had invested heavily in stealth and adopted the technology as a part
of its efforts to maintain an airpower advantage. The F-35 is the latest
instance of this trend in the form of a multi-trillion dollar bet that the
kind of stealth technology that has worked in the past will continue to work
over the program’s five-decade-long service life.

The problem for the F-35 is that there is growing evidence that the program
is betting on the wrong side of the hider-seeker competition. Instead, it
seems that the seekers – not the hiders – are gaining the advantage. Chief
of Naval Operations Admiral Greenert wrote in 2012 that technological
innovations “make stealth and its advantages increasingly difficult to
maintain,” referring primarily to innovations in radar, computing, and
infrared sensors. “Those developments do not herald the end of stealth, but
they do show the limits of stealth design,” he concluded.43 Greenert more
recently characterized stealth as “over-rated.”44 As we detail below, the
limits of stealth are very real. In the case of the F-35, the limits of
stealth may be especially harsh because its radar-evading qualities are
built-in and difficult, if not impossible, to significantly alter once the
aircraft is produced.


1. Counter-Stealth Radar

The F-35 is reported to have a radar cross section (RCS) of 0.001 square
meters from a narrow frontal aspect. This is the size that the F-35 appears
on certain radars, despite its physical size, and is roughly equivalent to
the size of a small ball bearing or insect.45

However, the F-35’s low-observable radar signature has “some gaps in
coverage,”46 particularly when viewed from the sides, rear, bottom, or top
for which a ten-times larger RCS of 0.01 square meters or larger has been
reported.47 In other words, detection of the F-35 will be most difficult in
head-on engagements and less difficult from other angles. By comparison, the
F-22 is reported to have a smaller RCS of 0.0001 square meters from the same
narrow frontal aspect.48

But the returns on the kind of stealth technology employed by the F-35 are
being diminished by advances in radar technology. The low-observable
technology on the F-35, and to a lesser extent the F-22, is designed to be
effective against radar operating in the X-band range and at shorter
wavelengths. The rationale behind this decision was that X-band radars
detect aircraft with a high degree of accuracy and, as a result, are used to
provide fire-control information to anti-aircraft missiles to engage
targets. However, the same properties that make the F-35 stealthy against
X-band radars do not apply as effectively to lower-frequency radars that
operate on longer wavelengths. Lower-band radars are widely employed as
surveillance radars to provide early detection of incoming targets at ranges
that typically exceed those of X-band systems. Since lower-band radars
detect targets with less accuracy, they were traditionally considered
unsuitable for providing fire-control information to engage targets.49

But countries threatened by stealth aircraft have had decades of strong
incentives to refine anti-stealth radars. As a result, lower-band radar
technology has advanced considerably. So-called very high frequency (VHF)
and ultra-high frequency (ULF)‡ radars that operate on longer wavelengths
are now capable of providing usable targeting information, largely due to
more powerful computers that can process returning radar signals more
effectively to filter through clutter and more precisely locate targets.50
One former Navy official said plainly that because “Acquisition and fire
control radars are starting to creep down the frequency spectrum…I don’t see
how you long survive in the world of 2020 or 2030 when dealing with these
systems” using today’s stealth technology employed by fighter aircraft.51
This is not strictly new. The effectiveness of such radar systems to target
aircraft was demonstrated in 1999 when an American F-117A Nighthawk stealth
attack aircraft (RCS of 0.003 square meters)52 was shot down by Yugoslav
forces using a modified VHF radar model that was introduced in 1970.53

Foreign militaries are already deploying sophisticated counter-stealth radar
systems. Newer systems like the Russian-built Nebo SVU/M VHF mobile
ground-based radar are reportedly able to not only detect low-observable
aircraft but do so accurately enough to direct missiles toward intended
targets.54 The Chinese JY-26 VHF surveillance radar has reportedly been used
to track F-22 flights on the Korean Peninsula.55 But advances in technology
are also making even X-band radars on board fighters more capable of
detecting stealth targets. The IRBIS-E X-band radar developed for the
Russian Su-35 fighter can allegedly detect low-observable targets with a RCS
of 0.01 square meters – the same as or smaller than the F-35 from
non-frontal angles – at a distance of 50nm.56


2 Counter-Stealth Infrared Sensors

Perhaps more significant than counter-stealth radar is the F-35’s
vulnerability to detection by infrared sensors. Infrared search-and-track
(IRST) systems, which are widely deployed on foreign fighter aircraft, can
detect aircraft otherwise invisible to radar at significant distances
without emitting any signal of their own. Nodding to IRST technology’s
implications in bypassing radar stealth, Chief of Naval Operations Admiral
Jonathan Greenert stated, “Let's face it, if something moves fast through
the air, disrupts molecules and puts out heat—I don't care how cool the
engine can be, it's going to be detectable.”57 The F-35 will be particularly
vulnerable to IRST detection given its enormous engine that puts out 40,000
lbs. of thrust with no infrared shielding or suppression.

Already, the OLS-35 IRST featured on the Su-35 can detect aircraft from the
frontal aspect at nearly 30nm, from the rear at 50nm, and missile launches
at similar distances. The Eurofighter Typhoon and other Western fighters are
equipped with comparable or better technology. Moreover, IRST sensors are
poised for significant boosts in detection ranges in the near future. Some
analysts have predicted that IRST sensors will soon be able to detect
aircraft or missile launches at ranges of 70nm or greater.58
===================================
Notes:

‡ The VHF and UHF terminology is unfortunate because, despite their names,
VHF and UHF radars actually operate at lower frequencies than X-band radar,
a fact not captured by the nomenclature.

42 Watts, Barry. "The Maturing Revolution in Military Affairs." Center for
Strategic and Budgetary Assessments. Last modified June 2, 2011. Available
at:
http://csbaonline.org/publications/2011/06/the-maturing-revolution-in-military-affairs/
43 Greenert, Jonathan W., Adm. "Payloads over Platforms: Charting a New
Course." U.S. Naval Institute. Last modified July 2012. Available at:
http://www.usni.org/magazines/proceedings/2012-07/payloads-over-platforms-charting-new-course
44 Osborn, Kris. "CNO: Next-Generation Navy Fighter Might Not Need Stealth."
DefenseTech: Where Technology and Defense Interact. Last modified February 5
, 2015. Available
at:
http://defensetech.org/2015/02/05/cno-next-generation-navy-fighter-might-not-need-stealth/
45 Global Security. "Radar Cross Section (RCS)." Global Security. Last
modified November 7, 2011. Available at:
http://www.globalsecurity.org/military/world/stealth-aircraft- rcs.htm
46 Congressional Research Service. F-35 Joint Strike Fighter (JSF) Program.
By Jeremiah Gertler. Research report no. RL30563. Washington, DC:
Congressional Research Service,
2014. Available at: https://fas.org/sgp/crs/weapons/RL30563.pdf
47 Mills, Chris. "Air Combat: Russia's PAK-FA versus the F-22 and F-35." Air
Power Australia: Australia's Independent Defense Think Tank. Last modified
March 30, 2009. Available at:
http://www.ausairpower.net/APA-NOTAM-300309-1.html
48 Ibid.
49 For a summary of radar, stealth, and counter-stealth radar technical
considerations, see: Watts, “The Maturing Revolution in Military Affairs,”
available at:
http://csbaonline.org/publications/2011/06/the-maturing-revolution-in-military-affairs/
50 For a summary of some current and potential dynamics involving lower-band
radars, see: Kopp, Carlo. "Russian VHF Counter Stealth Radars Proliferate."
Defense Today, 2008, 32-36. Available at:
http://www.ausairpower.net/SP/DT-Rus-VHF-Radar-2008.pdf
51 Majumdar, Dave. "Chinese and Russian Radars On Track to See Through U.S.
Stealth." USNI News. Last modified July 29, 2014. Available at:
http://news.usni.org/2014/07/29/chinese-russian-radars-track-see-u-s-stealth
52 Global Security, “Radar Cross Section (RCS).” Available at:
http://www.globalsecurity.org/military/world/stealth-aircraft-rcs.htm
53 See Kopp, “Russian VHF Counter Stealth Radars Proliferate,” 32-36.
Available at: http://www.ausairpower.net/SP/DT-Rus-VHF-Radar-2008.pdf
54 Kopp, Carlo. "Russian / PLA Low Band Surveillance Radars." Air Power
Australia. Last modified April 2012. Available at:
http://www.ausairpower.net/APA-Rus-Low-Band- Radars.html: Kopp, Carlo.
"Assessing Joint Strike Fighter Defense Penetration Capabilities Annex A, B,
C." Air Power Australia. Last modified January 7, 2009. Available at:
http://www.ausairpower.net/APA-2009-01-Annex.html#mozTocId787784
55 Minnick, Wendell. "China's Anti-Stealth Radar Comes to Fruition." Defense
News. Last modified November 22, 2014. Available at:
http://archive.defensenews.com/article/20141122/DEFREG03/311220016/China-s-Anti-Stealth-Radar-Comes-Fruition
56 Kopp, Carlo. "Sukhoi Flankers: The Shifting Balance of Regional Air
Power." Air Power Australia. Last modified April 2012. Available at:
http://www.ausairpower.net/APA-
Flanker.html
57 Osborn, “CNO: Next-Generation Navy Fighter Might Not Need Stealth.”
Available at:
http://defensetech.org/2015/02/05/cno-next-generation-navy-fighter-might-not-need-
stealth/
58Quantum Well Imaging Photodetectors (QWIP) increase the sensitivity of
infrared sensors and allow the detection of heat signatures from greater
ranges and with greater accuracy. Mills, Chris. “Air Combat: Russia’s PAK-FA
versus the F-22 and F-35.” Air Power Australia. Last modified March 30,
2009. Available at: http://www.ausairpower.net/APA-NOTAM-300309-1.html