Michael

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Nuclear pulse propulsion battleship Michael from the novel Footfall by Larry Niven & Jerry Pournelle.

Image featured on Winchell Chung’s Atomic Rockets site, Michael Nuclear Pulse Propulsion Battleship. Scroll down at the link.

Featured on Realistic Spaceship Illustrations Blog, Link: here

“Michaels nose was a thick shield … armored in layers: steel armor, fiberglass matting, more steel armor, layer after layer of hard and nonresiliant soft.” —from Footfall, pg. 446 and 472

“Two great towers stood on the curve of the hemispherical shell, with cannon showing beneath the lip, aimed inward. Four smaller towers flanked them. A brick-shaped structure rose above them. The Brick was much less massive than the Shell, but its sides were covered with spacecraft: tiny gunships, and four Shuttles with tanks but no boosters. The bricks massive roof ran beyond the flanks to shield the Shuttles and gunships.”  —from Footfall, pg. 432

Michael is one of the Orion based concepts I knew I would have to take a run at sooner or later. I referenced the novel, extensively, and Scott Lowther condensed all the design bits he gleaned from Footfall into an Excel spreadsheet, available here, for a project he set aside. The spreadsheet is an excellent guide to all the passages describing Message Bearer, the digit ships, Michael, the stovepipes and Shuttles, and it proved invaluable in my effort.

Most people are probably familiar with Aldo Spadoni's visualization of the iconic warship from Niven and Pournelle’s novel, but for those who are not, Aldo’s drawings are available here.

What I’ve done is meet the Aldo Spadoni design half-way with my own interpretations. My intent was to complement Aldo’s design-thought without entirely rewriting it, keeping in mind what Aldo had to say about the process. One point Aldo raised in conversation on Scott Lowther’s blog is in regards to who is providing description in various scenes from the novel.

Aldo Spadoni: “Footfall is a novel of course, not an engineering proposal for a space battleship. You glean details regarding the various Footfall spacecraft from the conversations of characters in the story, many of which are not experts [with regard to] what they are describing. As Scott also pointed out, there are inconsistencies in the descriptions that are either intentional or simply mistakes on the part of the authors. Thus, the design of the Footfall spacecraft are open to interpretation.”

Aldo makes a good case for the distinctive angled shock absorbers of his design, and I’ll provide his commentary below, the sticking point for me, however, is the parabolic pusher plate Niven and Pournelle describe—early design work on Orion solidly ruled out a parabolic pusher. With shaped-charge nuclear pulse units the parabolic plate will only heat up while offering almost no thrust advantage. Heating and impact stress on the pusher would be of no small concern, the bombs necessary to loft something the scale and mass of Michael would not be the tame little devices used to propel a dinky NASA/USAF 10-meter Orion. Heating is the cost of even partially containing the ionized plasma resulting from nuclear detonation.

Orion works because the plasma is dynamically shaped (as the explosion happens) by the specially designed shaped charge nuclear explosive, X-rays are channeled by the radiation case in the instant before the weapon is vaporized, these exit a single aperture, striking and heating up a beryllium oxide channel filler and propellant disk (tungsten), resulting in a narrow conical jet of ionized tungsten plasma, traveling at high velocity (in excess of 1.5 × 10⁵ meters per second). This crashes into the pusher plate, accelerating the spacecraft. The jet is not physically contained by the pusher, and contact with the pusher is infinitesimally brief, so the pusher is not subject to extreme heating during thrust maneuvers. So, while offering very little performance difference compared to a flat pusher design, the parabolic plate would need regenerative cooling in the bargain, adding weight and complexity to the system. Engineering such a pusher plate would be fraught with difficulties, and conditions under which Michael is built, in my opinion, rule out any eccentric messing with the baseline system. A legion of Ted Taylors would already be kept busy night and day with the mere task of readying a conventional Orion designed under such circumstances—for delivery under a one year drop-rocks-from-orbit-dead deadline.

As Aldo points out, the text of Footfall leaves room for different interpretations and here is where I took some of Aldo’s design-thought and creatively merged it with my own toward the end of addressing the design as presented in the novel. (No, not the army of Ted Taylor clones inhabiting a maze of cubicles in some deep bunker somewhere—that’s just me.)

It occurred to me that what Aldo had done (following Niven and Pournelle’s description), was move the functions of the Orion standard propulsion module down, mounting them directly on the top of the plate, so really it’s a built up intermediate platform/propulsion module. What I’ve done is run with that thought: I chose to treat the entire pusher plate as an early large Orion: a dome sitting on flat pusher plate, concentric rows of toroidal shock absorbers surrounding a core array of gas-piston shock absorbers. There is no central hole-and-bomb-placement-gun-protection-tube in my design (but there is an anti-ablation oil spray system). Instead, pulse units are shot by bomb placement guns mounted to fire around the edge; exactly as in Aldo’s design (the early large Orion had rocket assisted bombs riding tracks on the exterior of the spacecraft—imagine the show that would make). The body of the “dome” in my design is stowage for tanked pressurization gas (for the shock absorbers), anti-ablation oil, and perhaps a reserve number of pulse units.

I’ve retained the scheme of duel pulse unit magazines. Niven & Pournelle called them “thrust bomb” towers. Four “spurt bomb” towers are also mounted to the base—the “spurt bomb” Niven and Pournelle describe is a type of bomb-pumped laser using gamma-radiation rather than X-rays. All of my towers are a good deal beefier than those on Aldo’s design. Narrative in the novel describes the “thrust bomb” towers as doing double duty, providing an extra layer of armor and shielding for the CIC/control room, the nerve center of the spacecraft, which is located in the lower portion of the Brick, wedged between two large water tanks (and two nuclear reactor containment vessels). The water tanks are frozen at lift-off, providing Michael with an ample heat-sink.  

As I mentioned above, Aldo makes an excellent case for the angled shock absorbers on his design, his description below:

Aldo Spadoni: “Most of the Orion designs were configured for non-military applications, whereas Michael is a maneuvering warship with massive nuclear pumped steam attitude thruster arrays. In addition to primary Orion thrusting, Michael will be subjected to multi-axial mechanical loads that are NOT along the longitudinal axis of the ship. … When Michael is thrusting under primary propulsion while engaging in combat maneuvers, an angled shock absorber array design is a good choice for handling the inevitable side loads and for stabilizing the shell [with regard to] the passenger/payload “brick.” Consider a high performance off road vehicle, which must provide chassis stability while the wheels and suspension are being subjected to loads from many directions. You don’t see any parallel straight up and down shock absorbers in the suspension system, do you?

If you look carefully at my design, you can see that that central shock absorber is longitudinal and more massive than the rest. This one is primarily responsible for handling the Orion propulsive loads. … The remaining angled shock absorbers handle some of that propulsive load while also providing multi-axial stability.”

Scott Lowther (of Aerospace Projects Review) offers this insight in regards to angled shock absorbers:

Scott Lowther: “I remain unconvinced at the off-axis "angled" shock absorbers, but they seem to be the popular approach. However, if you do go that route, you have to deal with the central piston in the same way... ball joints fore and aft. *All* the pistons must be free to swing from side to side. If one, even the central one, is locked, then either the pusher assembly cannot move sideways *thus negating the value of the angled shocks), or it'll simply get ripped off its mounts the first time there's an off-axis blast.

Given that the ship is clearly described as having nuclear steam rockets for attitude control, I don't see the value in off-axis blasts for steering. But... shrug.”

I spent a good deal of time reproducing Aldo’s shock absorber array because frankly I think it is brilliant, going back and forth between Aldo’s drawings and my file … in the end the detail would be invisible, so I created a cutaway render with two of the “spurt bomb” towers removed to reveal the system.

True to the novel Michael’s main guns are the 16"/50 caliber Mark 7 gun and turret taken directly off the New Jersey. There is a good deal of discussion (on Scott’s blog and elsewhere) on the suitability of the guns and turrets—the mounting is rotated ninety degrees to vertical relative to the orientation turret, guns, and loading mechanisms were designed for—however, Aldo is quite clear that mounting the full turrets “as is” reflects the author’s intention, and so I’ve kept to their vision in this regard.

In the novel the guns are described firing a nuclear artillery round, this would be a modern version of the W23 15-20 kiloton nuclear round. The Mark 23 was a further development of the Army's Mk-9 & Mk-19 280mm artillery shell. This was a 15-20 kiloton nuclear warhead adapted to a 16 in naval shell used on the 4 Iowa Class Battleships¹. 50 of these weapons were produced starting in 1956 but shortly after their introduction the four Iowa's were mothballed. The weapon stayed in the nuclear inventory until October 1962. Presumably under war conditions a new production run would produce the numbers necessary for Michael’s assault on Message Bearer.

Secondary batteries: a generic turret roughly based on the secondary turrets of the Iowa class.

Missile launchers based on the MK-41 Vertical Launching System (VLS).

The “Battle Management Array” is a set of phased-array radars and tight-beam communications antenna for passing targeting information to Michaels secondary spacecraft, all mounted to a pair of shock-isolated cab, each riding its own set of shock absorbers, one mounted atop each “thrust bomb” tower.  A fall-back set of communications antenna and radar are mounted beneath the overhang of the forward shield atop the Brick.

I’ve gone with the dimensions Scott arrived at, which Aldo confirmed in his comments on Scott’s blog: Length:742’ Diameter: 371’.

Different opinions have been offered in regards to Michael’s mass, between 35,000 and 50,000 tons have been opinioned on Scott Lowther’s blog. Pournelle was quoted as saying 2 million tons on one occasion, and 7 million tons on another.

Michaels launch, in the novel, is shortened for reasons of narrative brevity; one character wonders if there were perhaps 30 or more nuclear detonations. Putting Michael in orbit would require 8 minutes of powered flight and about 480 bombs lit off at one bomb per second.

The novel is clear that Michael carries four Space Shuttles mounted to their external tanks sans their SRBs. The number of Gunships is less clear. Nine Gunships are described as destroyed in combat, an unspecified number survive to confront Message Bearer in the final scene. Designing the most compact spacecraft necessary to fill the role, my Gunship measures 100 feet in length, 25 feet in diameter. At these dimensions, 14 Gunships total can be comfortably mounted to Michaels flanks.

For detail on my Gunship design see my following post, Gunship.

Update Note 1/25/2014: A miscalculation on my part gave the vehicle a longer stroke-length than the vehicle could absorb. Scott Lowther, of Aerospace Projects Review, identified the error and provided a set of solutions to address the issue.

I’ve rebuilt the second-stage gas-piston shock absorbers to provide proper stroke-length and added a ball joint to the top and bottom of the central second-stage shock absorber in order to permit lateral motion of the pusher during off-axis thrust maneuvers. In addition to these changes I’ve shortened the “Thrust Bomb Towers” rebuilding the base of each and lowering the upper sections, moving all of the towers outward, closer to the rim of the pusher, opening up the central space around the base of “the Brick” in order to provide better clearance for motion of the pusher and towers during off-axis thrust maneuvers. As an additional effect the changes provide better clearance for the main guns when firing aft.

¹ W23