Saturday, September 8, 2012

"For the Snark was a Boojum, you see."

 I really enjoyed writing this piece. How often does one get to quote Lewis Carroll in the title? Plus Boojum is a really cool name to say.

This article was originally published in Airspace vol. 2 no. 11, September 2011. It is posted here with permission and has approved for public release case number 12-1433.

“For the Snark was a Boojum, you see.”*

By Tony Chong

Perhaps no two companion aerospace projects have had a more whimsical set of names given to them than the heritage Northrop Snark and Boojum.  Yet, like the fantastical creatures featured Lewis Carroll’s nonsensical poem, the Snark and Boojum were meant to be deadly as well.

In 1945 the U.S. Army Air Force’s Air Material Command issued a block of ten MX-designated research and study contracts to several companies for various advanced missile designs.  Half of them were allotted for subsonic and supersonic Surface-to-Surface Missiles, of which three were to be ultimately built as air-breathing cruise missiles.

Northrop was awarded one of these contracts, MX-775, in March of 1946.  MX-775A was for a subsonic intercontinental cruise missile, which eventually became the Snark.  The MX-775B was for a supersonic intercontinental cruise missile.  It was christened by the company as Boojum.

In December of 1946, the funding for Snark was deleted from the budget, but the more technically difficult Boojum survived.  After lobbying by Jack Northrop himself, Snark was reinstated in 1947 with the promise that it would only take two and one-half years to develop.  Boojum was retained as well, but now as the follow-on system to Snark.

1947 saw the formation of the U.S. Air Force as its own branch and the Snark was designated SSM-A-3 and the Boojum SSM-A-5.  “X” was added as a prefix to indicate the experimental nature of the programs at this stage.

The early version of the Boojum bears a distinct similarity to the early Snark.  Both had in-house N-25 designations, with N-25A for Snark and N-25B for Boojum (each would acquire new N-numbers later on, the Boojum in particular being noted as N-217 in some internal documents).  Both also carried thin, highly swept-wings on a long, semi-tailless fuselage.  A small vertical fin adorned each vehicle’s aft end.  However, Snark had a high-mounted wing with a flush belly inlet, while Boojum sported a mid-fuselage wing and an annular inlet. 

The final Boojum version would show a radical departure from the early configuration.  Ultimately the missile was to be a semi-tailless, delta-winged vehicle that would reach 85.33 feet in length and have a span of 50.85 feet.  

Missile construction was to feature a conventional semi-monocoque fuselage with aluminum alloy-faced, honeycomb core bulkheads.  The skin of the Boojum was to be made from a non-strategic magnesium alloy.

An “ultimate short-life” afterburning General Electric J47 turbojet was to be mounted near the tips of the wings, each providing 13,620 pounds of static thrust.  Engine life was estimated to be 25 hours, but the life of the continuous-use afterburners was only required to be 4.5 hours – the duration of a typical mission at Mach 1.8 with expendable drop tank. 

Estimated top speed was Mach 2.0 at 66,600 feet, with a range of nearly 3,400 miles clean and 4,980 miles with drop tank.  Maximum ceiling and range were 70,000 feet and 3,510 miles clean or 5,080 miles with tank at Mach 1.8.  All figures factored in the 3,000 lb. “special” (nuclear) warhead as the payload.

Alternate engines were available for use, with the primary one being the proposed General Electric XJ53.  Other types, including the General Electric/Allison J35 and Westinghouse J40 were considered as well, but more as a stop-gap measure if the J47 or XJ53 were unavailable for the test phase.

Like the Snark, the Boojum was to be guided to its target by the Northrop-designed Automated Celestial Navigation (ACN) system.  This system, which marked the start of Northrop’s Electronics “Nortronics” Division, utilized an automatic day/night star-tracking sextant and associated avionics that weighed nearly one ton. 

Boojum could be rail-launched in either a single or two-stage configuration.  The first stage component was a large 80.5 foot span straight-wing attachment with wingtip-mounted fuel tanks.  The wing mounted to the belly of Boojum via a massive pylon that remained with the first stage when it detached.

Boojum was also designed to be air launched from a large carrier aircraft.  Mounted on the top of the mothership because of its size, it resembled the recently retired 747/Space Shuttle combo.

Wind tunnel and rocket-boosted atmospheric models tests of the Boojum proceeded through the late 1940s, but by the start of the new decade customer confidence in the viability, accuracy and performance of the supersonic cruise missile waned.  The program was cancelled in 1951.

Snark would continue, but its path was long, difficult and marginally successful.  While the system did eventually attain operational status with the 702nd Strategic Missile Wing in February, 1961, its life was short.  The first U.S. intercontinental ballistic missile went operational months earlier in September 1959, rendering the in-coming Northrop vehicle obsolete.  The 702nd SMW was deactivated four months later.  Like the Baker in Carroll’s poem, Northrop’s aptly named cruise missiles softly and suddenly vanished away, never to be met with again.

Additional information about the Boojum can be found at the following links:

An interesting book called The Evolution of the Cruise Missile, by Kenneth P. Werrell, Air University Press, Maxwell AFB, 1985, can be found in pdf. format here:

Photo Captions
  1.      img779 – This scan of the N-25 3-view drawing comes from the in-house publication Northrop: An Aeronautical History, by Fred Anderson, Northrop Corp., 1976, (the “Brown Book”) and shows the early Snark configuration.  Note the flush inlet and high-mounted wings.  Tony Chong collection.
  2.     xssm-a-5 – A drawing of the early Boojum configuration shows the similarities with the early Snark.  The main external differences are with the mid-mounted wings and annular inlet.  Image credit USAF
  3.     100_0007_3 – Northrop issued a brochure in 1950 in an attempt to highlight the advantages of the Boojum to the customer.  This is a photo of the very dynamic cover art.  The artist is unknown, but it is very reminiscent of Jack Leynnwood, who occasionally worked for Northrop, but who also worked for the Revell and Aurora model kit companies, where he did a lot of their boxtop artwork.  Photo credit: Tony Chong
  4. img736 – The brochure contained this baseline 3-view drawing of the Boojum.  As noted in the text, the vehicle was over 85 feet long; a very impressive size even today.  While the engines are far apart, Northrop projected minimal control disruption with asymmetric thrust and was supposed to retain enough engine-out performance on take-off to direct the vehicle to a safe ditching point away from the base or populated areas.  Tony Chong collection.
  5.     img735 – This scan from the brochure shows the 3-view drawing of the Boojum and its large expendable fuel tank.  The tank slips over the bottom fuselage of the missile and extends beyond the nose and tail, increasing the length nearly 20 feet.  The sidebar art shows the tank being dropped in flight.  Tony Chong collection.
  6.    img734 – Another artist’s concept shows a larger image of the Boojum, two with tanks and one in the midst of dropping a tank.  In real life separation would have been an interesting issue at Mach 2 for an unmanned vehicle carrying a conformal tank longer than itself.  Tony Chong collection.
  7.   img771 – This plan-view drawing shows the Boojum with it straight-wing first stage.  Like the basic missile, the two-stage configuration was rail-launched.  Note the size of the wing and the tip tanks.  The sidebar shows the first stage dropping away from the missile.  Tony Chong collection.
  8.    img772 – The profile and front view of the two-stage configuration shows the massive size of the pylon attaching the vehicles together.  The acceleration stresses during rail launch are interesting to consider.  All of the thrust appears to come from the Boojum’s two J47 engines.  No mention is made anywhere in the brochure of expendable rocket or jet assisted devices.  Tony Chong collection.
  9. img773 – Another, larger artist’s concept showing a couple of Boojums in operation, one with its first stage attached and the other dropping its stage.  The art shows the drop taking place over land, which seems rather unlikely in real life.  In all probability Boojum basing would be near coastal areas and the drop points would be over water.  Tony Chong collection.
  10.   img777 – This image shows some of the interior structure of the first stage.  The inset art appears to highlight one of the pylon attach points.  What looks like wiring could be part of an explosive bolt triggering mechanism for first stage separation.  Unfortunately the various launch configuration drawings appear to be from a second brochure, not all of which was copied, so details are elusive.  Tony Chong collection.
  11. img778 – Ironically, one of the launch aircraft considered for the Boojum was the Convair B-36 Peacemaker.  This is a later version of the B-36 as it has the twin-engine jet pods outboard of the buried main piston engines.  The jets are non-afterburning General Electric J47-GE-19s, from the same family as the Boojum’s engines.  Tony Chong collection.
  12.       img776 – The final image is intriguing not just for the Boojum on the back of the mothership, but for the mothership itself.  It is a swept-wing, swept-tail, four engine turboprop version of the B-36 with counter-rotating blades.  This is likely an early concept for what eventually became the jet-powered, eight-engine YB-60.  Note the mushroom cloud in the background.  Since the aircraft are over land, and the two are still together, one can assume a strike has been made against the American homeland and a retaliatory launch is moments away.  Tony Chong collection

1 comment:

  1. Excellent article and beautiful artwork. I wasn't born then, but I miss those days anyway.