This is from material from the Fourth Symposium on Advanced Propulsion Concepts parts i, iii, iii and from Aerospace Project Review Issue Volume 1, Number 5. As always, in the datablocks you see in on the edges of this page the values in black are from the source documents but the values in yellow are not. Yellow values are ones that I have personally calculated, sometimes using questionable assumptions. Yellow values are not guaranteed to be accurate, use at your own risk.

In March of 1965 the Orion program was pretty much over. Nobody was interested in a spacecraft powered by hundreds of atom bombs. In a frantic attempt to keep it alive, General Atomic released a report describing several potential military applications. Hey, Pentagon, here are some great serving suggestions for an Orion! Please don't let the program die.

It didn't work but you can't blame them for trying.

STANDARD ORION ENGINES

D = pusher plate diameter (meters)

L = engine length (meters)

F = thrust (pounds force)

I sp = specific impulse (seconds)

WT = engine weight (pounds)

Note how sensitive I sp is to pusher plate diameter.

NASA found the 10-meter engine was optimal for a wide range of lunar and planetary missions.

Reference Orion Configurations Pusher Diameter (m) 8 10 12 Length (m) 22.1 25.7 29.7 Thrust (N) 2,360,000 3,470,000 4,320,000 I sp (sec) 2,720 3,300 3,670 Exhaust Velocity (m/s) 26,700 32,400 36,000 Weight (kg) 81,700 109,000 172,000

The applications used all three of the standard Orion engines: eight, ten, and twelve meter pusher plate sizes. Since a nuclear launch was pretty much out of the question, each proposal used a stage of quick-and-dirty solid rocket clusters to loft the Orion to an altitude of 76,200 meters before the nukes started. The liftoff thrust-to-weight (T/W) ratio was 1.8 for all three Orion sizes. The solid rockets got the spacecraft up to 76,200 meters and 2,900 m/sec, the Orion drive kicked it the rest of the way into a 370 km orbit. The back of my envelope says the Orion has to expend 8,300 m/s of delta-V, some of that is aerodynamic drag and gravity drag.

8-meter Orion spacecraft would be lofted by a cluster of seven 120-inch solid rocket boosters, developed from the strap-on solid rockets used on the Titan III launch vehicle. They would have been more powerful than the Space Shuttle solid rocket boosters.

10-meter Orion spacecraft would be lofted by a cluster of four 156-inch solid rocket boosters. These were studied in the 1960s as possible strap-ons for the Saturn V, and as a cluster to replace the first stage of the Saturn Ib.

12-meter Orion spacecraft would be lofted by a cluster of seven 156-inch solid rocket boosters.

When the Orion drive started up at 76,000 m, its T/W was only 0.55. This meant a very ugly gravity tax, but the total payload delivered to orbit was maximized. Who cares about gravity tax, the Orion has delta-V to spare.

From a military standpoint, the Orion drive is attractive not only because of its high thrust and specific impulse. The drive is also resistant to damage. Fussy delicate chemical engines can be disabled with a handgun. Orion drives are built to be tough enough to withstand hundreds of impacts by nuclear explosions at close proximity. A handgun bullet will just bounce off. The enemy will have to use massive weapons in order to dent one of those babies. This is not as big a selling point for NASA, who generally does not have to worry about enemy spacecraft taking pot-shots at them.

For the same reason such drives are very easy to maintain and repair. You don't need needle-nosed pliers and micro-screwdrivers. A sledge hammer and a cold chisel will do. It helps that the engine is made of good ol' simple to fix steel, instead of cantankerous titanium or aluminum.

And unlike nuclear thermal rockets, Orions have very low residual radioactivity. It is safe to go out and work on an Orion drive only a few minutes after the last nuke exploded. Nuclear thermal rockets on the other hand will be unsafe to go near for a few thousand years.

Amount of gross mass deliverable to 200 nautical mile circular orbit by various engines

8-meter = 750,000 lbs gross

10-meter = 1,160,000 lbs gross

12-meter = 1,470,000 lbs gross

Subtract engine mass to get maximum payload in orbit (i.e., fuel tanks empty)

Graph assumes a first stage of solid rocket motors with a launch-to-thrust-weight ratio of 1.8 and a stage propellant fraction of 0.76. Staging altitude is 250,000 feet and 9,600 ft/sec. Orion drive second stage starts with thrust-to-weight ratio of 0.55

Engine performance beyond 200 nautical mile circular orbit by various engines

You select the desired excess delta-V, chart shows the maximum payload allowed. You are trading payload for extra nuclear pulse units. The larger engines have better payload fractions because of higher specific impulse.

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Some of the applications had the Orion spacecraft stationed in space, others had them based on the ground. The former was basically using the Orion drive to loft an outrageously huge military space station into permanent orbit, in one piece. Applications stationed in space could be launched at leisure. Applications stationed on the ground on the other hand were a reaction force. The Orions would sit in their silos "on alert", ready to launch at a moment's notice. For space based system the primary concern is maneuverability and survivability. For ground based systems the primary concern is readiness.

The minor drawback of the Orion spacecraft's titanic mass is there was no practical way to land them back on Terra (short of lithobraking). Once they were launched into space, they stayed there. The crew was rotated by space shuttles or small reentry vehicles. Trying to land under Orion drive power is a very bad idea, especially on a planet with an atmosphere. The ship will be entering the center of each raging nuclear fireball with lamentable results.

STATIONED IN SPACE

Command/Control

Strategic Weapon Delivery ("Bomber")

("Bomber") Surveillance-reconnaissance

Space Defense

Orbit Logistics

Lunar Base Support

Space Rescue and Recovery

Satellite Support

R&D Laboratory

STATIONED ON TERRA SURFACE

Emergency Command/Control

Space Interceptor

Damage Assessment

Space Rescue and Recovery

Satellite Support

Recreations of the military Orion types by Scott Lowther

He estimates the 8-meter plate diameter Orion spacecraft at 45 meters tall (with pusher plate in the neutral position), the 10-meter plate at 57 meters tall, and the 12-meter plate at 51 meters tall.

Details can be found in Aerospace Project Review Issue Volume 1, Number 5

EMERGENCY COMMAND/CONTROL (ECCS)

ECCS Orion Stage 2 Orion Engine Pusher dia 8 m I sp 2,720 sec Exhaust Vel 26,700 m/s Thrust 2,400,000 N Stage 2 Payload Mass 91,000 kg Orion Engine Mass 82,000 kg Dry Mass 172,700 kg Pulse Units Mass 290,300 kg Wet Mass 463,000 kg Mass Ratio 2.678 Total ΔV 26,300 m/s Reserve ΔV in LEO 18,000 m/s Stage 1 Chemical Engine Type Solid-chem I sp ? Exhaust Vel ? Stage 1 Payload Mass 463,000 kg Engine Mass ? Dry Mass ? Propellant Mass ? Wet Mass 2,540,000 kg Total ΔV 3,100 m/s Misc Stack Height 64 m Stack Max Dia 9.1 m

Emergency Command/Control System launching from its secret silo

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In case NORAD gets taken out by a dastardly nuclear first strike on the United States, the ECCS Orion was designed to survive in its secret armored launch silo. It would boost into orbit and take over NORAD's functions, coordinating the nuclear retaliation.

Actually the plan was to launch before the enemy bombs actually hit the ground. NORAD can probably predict it will be unlikely to survive an incoming nuclear strike long before the bombs actually arrive.

The ECCS was housed in an 8-meter Orion. The surface geometry was smooth to avoid creating shot-traps, since an enemy would target an ECCS with lots of hostile weapons fire. After expending all those extra nukes to obliterate NORAD the enemy will be obligated to destroy all the ECCS NORAD-back-ups, otherwise they will have wasted all those warheads and have nothing to show for it.

Since the ECCS would operate beyond Terra's magnetosphere, the crew would need radiation shielding from galactic cosmic rays. Not to mention enemy nuclear warheads, possibly including enhanced radiation weapons.

The wet mass was 2,540,000 kg (5,600,000 lbs), of which 91,000 kg (200,000 lbs) was payload (apparently "payload" is the dry mass of the Orion spacecraft, without any nuclear pulse units. At least that's what my calculation suggest). Stack height with solid rocket boosters was 64 m (210 ft) (cluster of seven 120-inch solid rockets) and a maximum diameter of 9.1 m (30 ft). The boosters loft the Orion to an altitude of 76.2 km (250,000 ft). Then the 8-meter Orion engine uses its 2,400,000 N (530,000 lb f ) of thrust and 2,750 seconds of I sp to get the rest of the way to a 370 km (200 nautical mile) circular orbit. At this point it would still have a delta-V reserve of 18,000 m/sec (60,000 ft/sec) for further maneuvers. The reserve can be used to provide orbit altitude and plane changes to provide the most effective surveillance coverage and to evade hostile weapon interceptions.

The ECCS will require a silo only slightly larger than a standard ATLAS or TITAN ICBM silo.

The ECCS would carry a crew of from ten to twenty, with lots of advanced surveillance and communication equipment. Average mission was 30 days, with provisions for up to 60 days. Radiation shielding on the order of 244 kg/m2 (50 lb/ft2) would be around all command/control and crew operating station, to protect against galactic cosmic rays and possible hostile enhanced radiation weapons. The structure, life support systems, and attitude jet fuel will provide an additional 244 kg/m2 for a total of 488 kg/m2 (100 lb/ft2). By way of comparison, a storm cellar protecting the crew from a significant solar storm should have at least 5,000 kg/m2.

Several ECCS would be on constant standby in their silos. If nuclear war was immanent one would be launched as a show of force, demonstrating that the US was "not unprepared to defend itself." Along with a diplomatic reminder that there are more ECCS where that came from.

One would NOT be launched if it was only a time of crisis instead of immanent war. That would be provocative, and could precipitate matters. It is difficult to convince the enemy to stand down from DEFCON 2 when you are massing troops on their boarder, so to speak.

Deployed in low orbit allows immediate surveillance coverage of enemy territory and maximum image resolution. Deployed in remote orbits provides broader coverage of the planet's surface and also allows early warning of incoming hostile weapons fire aimed at the ECCS.

COMMAND/CONTROL (SSCCS)

SSCCS Orion Stage 2 Orion Engine Pusher dia 10 m I sp 3,300 sec Exhaust Vel 32,900 m/s Thrust 3,500,000 N Stage 2 Payload Mass 136,000 kg Orion Engine Mass 110,000 kg Dry Mass 246,000 kg Pulse Units Mass 354,000 kg Wet Mass 600,000 kg Mass Ratio 2.439 Total ΔV 29,300 m/s Reserve ΔV in LEO 21,000 m/s Stage 1 Chemical Engine Type Solid-chem I sp 294 sec Exhaust Vel 2,880 m/s Stage 1 Payload Mass 600,000 kg Engine Mass 936,000 kg Dry Mass 1,536,000 kg Propellant Mass 2,964,000 kg Wet Mass 4,500,000 kg Mass Ratio 2.930 Total ΔV 3,100 m/s Misc Stack Height 96 m Stack Max Dia 10 m

Location of space-based command/control ships

This is similar to the ECCS but with important differences. It is stationed in space. It is intended for permanent operations, not just for 30 days. It is larger, requiring a 10-meter Orion engine.

Three of these would be placed in geosynchronous orbit to provide constant global surveillance. They would augment their coverage via inter-ship relay. This will allow the ships to randomly change their positions and frustrate enemy weapons interceptions, yet still maintain coverage. One ship will be the "flagship" but others could take over if the flagship is disabled.

The wet mass was 4,500,000 kg (10,000,000 lbs), of which 136,000 kg (300,000 lb) was payload. Stack height with the stage 1 solid rocket boosters was 320 feet (cluster of four 156-inch solid rockets) and a maximum diameter of 96 m (33 ft). The solid rocket booster has a mass of 3,900,000 kg (8,500,000 lbs). At an altitude of 76.2 km (250,000 ft) the 10-meter Orion engine uses its 3,500,000 N (780,000 lb f ) of thrust and 3,300 seconds of I sp to get the rest of the way to a 42,162 km (22,766 nautical mile) geosynchronous orbit. At this point it would still have a delta-V reserve of 21,000 m/s (70,000 ft/sec) for further maneuvers, though in theory it is in its forever home.

Actually, since the SSCCS will be launched in leisurely times of peace instead of under the urgent pressures of impending nuclear armageddon, solid rocket boosters are not needed. Instead the more sophisticated (but more time consuming) liquid-fueled Saturn V's S-IC stage could be used. Especially if NASA ever manged to make the S-IC recoverable, which as SpaceX has demonstrated drastically lowers the launch cost. Such a stack would have a wet mass of 3,300,000 kg (7,200,000 lbs).

The SSCCS will require about 3 megawatts with a peak of 9 MW or so for the surveillance and communication systems. This can be provided with RTG or other advanced power source. The crew will number from 20 to 30, with six-month tours of duty. The SSCCS will stay on location for their operational lifetimes, 15 to 20 years. The long lifetimes are due to the fact that upgrading obsolete surveillance and comm systems is a snap when you are using Orion drive cargo ships. No matter how much the replacements weigh. The communication/surveillance section is basically a chassis accepting plug-in replaceable modules.

STRATEGIC WEAPON DELIVERY (SSSWD or "Bomber")

SSSWD Orion Stage 2 Orion Engine Pusher dia 12 m I sp 3,670 sec Exhaust Vel 36,000 m/s Thrust 4,300,000 N Stage 2 Payload Mass 136,000 kg Orion Engine Mass 170,000 kg Dry Mass 306,000 kg Pulse Units Mass 424,000 kg Wet Mass 730,000 kg Mass Ratio 2.386 Total ΔV 31,300 m/s Reserve ΔV in LEO 23,000 m/s Stage 1 Chemical Engine Type Solid-chem I sp ? Exhaust Vel ? Stage 1 Payload Mass 730,000 kg Engine Mass ? Dry Mass ? Propellant Mass ? Wet Mass 6,800,000 kg Mass Ratio ? Total ΔV 3,100 m/s Misc Stack Height 88 m Stack Max Dia 12 m

Orion Bomber

Strategic Weapon Delivery AKA raining nuclear warheads onto the nation that attacks us.

This would require a full blown 12-meter Orion engine, because nuclear missiles are very heavy. And because you want to carry as many as you possibly can.

The wet mass was 6,800,000 kg (15,000,000 lbs), of which 136,000 kg (300,000 lbs) was payload. Stack height with the solid rocket boosters was 88 m (290 ft) (cluster of seven 156-inch solid rockets). At an altitude of 76.2 km (250,000 ft) and a speed of 3,100 m/s (10,000 ft/sec) the 12-meter Orion engine uses its 4,300,000 N (970,000 lb f ) of thrust and 3,670 seconds of I sp to get the rest of the way to its patrol orbit. At this point it would still have a delta-V reserve of 23,000 m/s (75,000 ft/sec) for further maneuvers.

Terra is small dark sphere. Outer edge of yellow circle is geosynchronous orbit

At A the SSSWD boosts into LEO (370 km) with solid rockets and Orion drive. The crew does a systems checkout.

the SSSWD boosts into LEO (370 km) with solid rockets and Orion drive. The crew does a systems checkout. At B burns into a Hohmann transfer (blue arc)

burns into a Hohmann transfer (blue arc) At transfer apogee C it burns to circularize the orbit. SSSWD is now in a 190,000 km circular orbit (green circle)

it burns to circularize the orbit. SSSWD is now in a 190,000 km circular orbit (green circle) At D burns to enter Patrol orbit (red ellipse). Orbit has a perigee of 190,000 km and apogee of 410,000 km (a 190,000-410,000 km Terran orbit). The orbital period is 18.9 days

The crew will number 20 or more. A semi-closed ecological system will be used to permit a six-month tour of duty, with an emergency capacity of one year. It would require about 1 megawatt of onboard power for ship systems.

The interesting details about the weapons loadout are either not defined or classified. They are not in the report at any rate. Drat!

Defensive weapons include decoys and antimissile weapons. Defensive weapons are carried because bombers are the enemy's prime targets. The enemy knows that every single strategic weapon a SSSWD carries is a mushroom cloud with their name on it.

The strategic nuclear weapons were to be carried internally to allow easy access for maintenance. That way the technician wouldn't have to wear a space suit. The weapons are probably either megaton-range "city-killer" nukes, or MIRVs of deci-megaton-range. For reference, the original Minuteman-II ICBM carried a 1.2 megaton W56 thermonuclear warhead. The Minuteman-III had a MIRV bus carrying three 0.17 megaton W62 thermonuclear warheads (170 kilotons). Scott Lowther's recreation of the SSSWD carries 25 MIRVs, each with three warheads.

The nukes could be launched in either of two ways. [1] warheads could be mounted on missiles, launched from deep space, and guided to their targets. [2] the Orion bomber could use its 23,000 m/s of delta-V to enter a close hyperbolic flyby of Terra and release the warheads when near Terra.

On the one hand, the first option means the Orion does not have to get close to the target and be exposed to hostile weapons fire. On the other hand the missiles will have very limited delta-V because you cannot cram a full sized ICBM into the Orion bomber. True, the missiles will start with the Orion's orbital velocity but still. Since the paper cites enemy interceptor missiles requiring a day or two to reach the Orion bomber, presumably any missile the SSSWD launched will require a similar amount of time to reach the enemy cities.

The second option means the Orion bomber has to go into harms way. The up side is it can use its awesome amount of delta-V to deliver the MIRVs ballistically. And it probably can deliver the warheads to the target much quicker than any missile. One can just imagine the enemy generals freaking out at the sight of a three-hundred-ton spacegoing ICBM-farm dive-bombing you at hyperbolic speeds on a trail of freaking nuclear explosions while machine-gunning your continent with city-killer nukes.

According to the paper, a fleet of about 20 spacecraft would be deployed. Presumably this will ensure that there will always be several bombers close enough so that the MIRVs travel time will be short enough to give the enemy a major strategic problem. If my slide-rule is not lying to me, a 190,000 km-410,000 km orbit has an orbital period of 1,635,282 seconds or 18.9 days. With 20 SSSWD evenly spaced, that would have a bomber passing through perigee every 81,764 seconds or every 22.7 hours. I picked 410,000 km as a nice round value "beyond Luna" since the report did not give a precise figure. They might have selected an apogree figure to make a bomber pass through perigee once a day.

Siteing strategic nuclear weapons in deep space would be a major escalation of the nuclear arms race. Such Orion bombers are much more difficult to attack, compared to ICBMs in silos or nuclear submarines. It would require entirely new strategic planning and weapons systems. The high orbits mean that enemy weapons would require a day or more to reach the orbiting Orion bombers. If the enemy wishes to take out the Orion bombers simultaneously with the US ICBM silos and nuclear missle submarines, they will be forced to give the US a day or more of warning time. This sort of spoils the surprise of a first strike. In addition the long warning gives the Orion bombers ample time to take evasive action and/or deploy decoys and antimissile weapons.

On the minus side, such a drastic escalation may panic the enemy into starting a nuclear war before the Orion Bomber network was fully established. If the enemy is only half-panicked, they will probably start a crash-priority project to make their own Orion bomber network.

Orion bomber launching strategic thermonuclear weapons (1)

Orion bomber launching strategic thermonuclear weapons (2)

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Model made by Convair workshop for General Atomic

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