— By /u/HephaestusAetnaean 2015.
I am by no means a subject-matter expert. However I find myself in the curious position of being better informed overall than nearly all the commentators I’ve seen on reddit. I’m quite interested in these systems, but it’s very difficult to find good analysis or primary sources. So I’m writing this FAQ piece hoping to raise the standard of discourse and advance the starting point of our discussions… so that I myself may learn something NEW.
On accuracy: I haven’t kept up with new developments for some months, and some numbers are from memory.
If anyone has more experience with any of these subsystems, please make yourself known. I’d love to hear your input.
(All albums used in this FAQ. Many of these pics/albums were converted from pdfs. If you’d like the original pdf, just pm me.)
Feel free to ask questions. I’ll try to answer as time permits.
Q: What is a railgun?
This is the notional 64 MJ railgun (w/pics), the first gun to likely leave testing and enter service [in 2030?]:
(Estimated specs for a 64 MJ railgun : 155 mm x 10 m barrel, 20 kg projectile, peak 46,000 g’s, 256 MJ CPA, 64 MJ muzzle energy, Mach 7.35 muzzle velocity, 13.5 MWe recharge for 6 rounds/min, 4,000 gal/min cooling water.)
On the USS Zumwalt, capacitors/flywheels store electricity that shoot a 20 kg, 155 mm diameter, saboted projectile at ≤60,000 g’s through a 10 m long electrified barrel, reaching Mach 7+, curving out of the atmosphere and then back down to land 250 mi away at Mach 5, guided by GPS/INS, releasing a cloud of hypersonic tungsten shrapnel.
Possible upgrades include a multi-mode seeker (semi-active laser, millimeter wave radar, imaging IR), or even semi+active radar, 2-way datalink, a unitary payload for anti-armor, and more range (longer/heavier barrels and beefier power supply). Then it could hit point targets and moving targets (like tanks and ships and… even missiles).
Correction: the first gun slated to enter service is a 32 MJ version firing 20 kg, GPS/INS-guided rounds at Mach 5+ out to 100 mi. ~30,000 g’s at launch. [Article 1].
- Video 1 . Chief of Naval Research interview. ($25k aerodynamic prototype round, test footage, truck+”warhead” impacts)
- Video 2 . Compiled ONR footage. (test footage, launch, in-fight, dispense, on-target effects)
- Video 3 . via DoD. (test footage, similar to Video 1 B-roll, 1 additional launch closeup)
- Video 4. General Atomics Blitzer interview #1, May 2010. (explains how rails work, shows off their round)
- Video 5. General Atomics Blitzer interview #2, April 2011. (shows off their round; ‘at sea demo in 2015, IOC in 2018’)
- Video 6 . BAE interview, April 2014. (shows off the 30 MJ gun, the HVP round, and rails replacing Burke’s 5-inch mount—that cap bank is tiny!)
- Video 7 . (armatures, earlier test footage)
- Video 8 . IEEE Spectrum, ONR interview. (100 MJ caps, 32 MJ gun; shrunk the caps; next gen integration/RoF) [comments]
- Article 1. USNI 4/2015. Railgun news/updates, and performance hints.
- Article 2. USNI 1/2015. RFI for railgun guidance kit for ballistic and supersonic missiles.
- Article 3. USNI 6/2015. HVP fired from Mk 45 or larger.
- General Atomics railguns .
- BAE railguns .
- Other railgun pics .
Q: Are the rounds solid slugs?
The shells can carry different payloads, just like other artillery shells: high explosives, shrapnel, or unitary “solid slugs.” (Possibly even EO/IR for battle damage assessment). “Slugs” like APFSDS’s are better for destroying tanks; shrapnel is better for hitting small, fast missiles.
HVP (Hypervelocity Projectile, by BAE) is the current round. It carries a payload of either HE or shrapnel [Video 2 ]. It’s command-guided; a GPS/INS package will be added later. It can also be fired from normal 5″ naval guns (albeit only to Mach 3)[Article 3], so Burkes/Ticos can soon also launch GPS shells. [longer comment].
The rounds also shed some pieces after launch: the armature (conductive bit touching the rails that actually pushes the round down the barrel) and sabot (like an AFPSDS).
Q: Are the rounds guided?
You NEED guidance to hit anything at 200+ mi.
First rounds will be GPS/INS guided (like other GPS guided artillery shells), accurate enough to hit fixed targets. A 2-way datalink will be added soon thereafter, so that you can (eg) change targets in flight.
Later rounds might have laser, radar, and/or IR homing to hit tanks, IFV’s, artillery, and other moving targets.
G-hardened, gun-launched multimode seekers (SALH, IIR, MW radar) have been demonstrated! For $20k-$50k +inflation. GPS/INS already developed for guided artillery shells, like the Excalibur and the Zumwalt’s AGS/LRLAP.
- [see “high-g” sections below for examples].
Heat-resistant IR and radar seekers for supersonic (not hypersonic) missiles are in service. Additionally, the DF-21 ASBM allegedly uses IIR guidance to hit moving ships after re-entry (not demonstrated).
Maneuvering is done with fins. Strakes (like on the ESSM and SM-6 ) and attitude control motors (ACM) (like on the hit-to-kill PAC-3 and CUDA) may be added later to help intercept missiles, increasing agility during the terminal phase .
Q: How many g’s does the round endure at launch?
38,000 g’s to 46,000 g’s for a 64 MJ railgun, partially depends how uniformly the power supply can form its pulse. Lower g’s are better (lower stress, lower material requirements): use longer barrels or a smoother/cleaner pulse .
Varies with gun/manufacturer. For same muzzle velocity, lower is better. General Atomics quotes 60,000 g’s for a 3 MJ (4-5 m) prototype.
Doing the math, you find you require only 30,000 g’s to reach Mach 7+ in 10 m. But acceleration is not totally uniform down the length of the barrel. (IIRC it increases toward the muzzle, but don’t quote me.) I think peak:min acceleration ratio is just <1.5, which is very good compared to conventional guns. But peak g’s are still higher than average g’s.
Using flywheels, SAIC estimated 46,000 peak g’s (64 MJ, Mach 7+).
Capacitors might output a smoother power pulse, yielding a flatter acceleration profile and lower peak g’s (lower stress). This relaxes the material requirements somewhat for both the barrel and round… thus cheaper/easier/sooner to mature. Maybe that’s why the navy went with caps. (I’ve seen literally NO ONE advocate for caps over flywheels in ANY publication ANYWHERE—flywheels were a foregone conclusion—so I’m still bewildered why the Navy chose capacitors.)
40,000 g’s might be enough for the 64 MJ gun [Article 2].
Q: Doesn’t the high-g launch destroy delicate electronics (guidance)?
G-hardened guidance kits are proven, improving, and surprisingly affordable.
- Mk 110 57mm fires radar-fuzed shells at 60,000 g’s [@3:00 ].
- Command-guided rounds (radio controlled) work fine at Mach 7 and <60,000 g’s [see Video 1 and 2].
- GPS/INS guidance kits for artillery shells have been tested up to 28,000 g’s without signs of failure. They weren’t tested to higher loads because they was no need at the time. The Navy is currently running a program to g-harden a GPS/INS+datalink kit to 40,000 g’s; it’s expected to be ready by the mid-2020s when the first railgun becomes operational [Article 1].
… guidance, navigation, and control functions (including … (INS)/GPS with anti-jamming…) and [a 110-200 nmi 2-way datalink at 5-10 Mbps]. … GPS positions with accuracy better than +/- 5 meters, 6DOF projectile orientation, … at speeds in excess of Mach 8. [ed: compatible with a later, more powerful 64 MJ gun] … anti-jamming, GPS up-finding, safe/arm functionality, and height of burst sensors.
The package must fit within the mass (< 2 kg), diameter (< 40 mm outer diameter), and volume (200 cm3) … survive accelerations of at least 20,000 g (threshold) / 40,000 g (objective) in all axes, high electromagnetic fields (E > 5,000 V/m, B > 2 T), and surface temperatures of > 800 deg C. …operate in the presence of any plasma … radiation hardened [for spaceflight]. … less than 8 watts (threshold) / 5 watts (objective) and the battery life must be at least 5 minutes …. In order to be affordable… a goal of less than $1,000 per unit.
[NB: 40,000 g’s is apparently enough for a Mach 7+, 230 mi railgun]
- LRLAP – 155 mm guided (GPS/INS) shell for Zumwalt’s AGS, rocket-assisted, 100 mi range.
- M982 Excalibur – 155 mm guided artillery shell. CEP≪6m. [Vid. ] ≫7,000 g’s. $50k.
- XM1156 Precision Guidance Kit – 155 mm artillery shell guidance (GPS) kit. Screws in like a fuse. Fielded 2013. Analogous to JDAM guidance kit).Screws in like a fuse. CEP≪30m. Fielded 2013. [Global Security][Google Img][album ]. ≫7,000 g’s. $3k.
- XM395 PGMM – 120 mm guided (GPS) mortar guidance kit. CEP<10m. Fielded 2011. $10k.
- Uncooled IIR, MWR, and SALH multimode seekers have been fired from tank cannons, survived, and then hit targets 12 km (iirc) away. Launch acceleration was 15,000 to 30,000 g’s (iirc).
- XM1111 MRM – 120 mm guided (MWR/SALH or uIIR/SALH multimode seekers) tank-cannon launched anti-tank round. By far the most impressive weapon on these lists, in my view. [album ]
- Two competing designs: MRM-KE by ATK, and MRM-CE by Raytheon. Both could be fired beyond line of sight, fire-and-forget, autonomously.
- The MRM-CE variant (Chemical Energy, with shaped charge): muzzle velocity of Mach 5; range of 12km; guided by uncooled IIR and SALH, which survived ≫30,000 g’s at launch. In 2006, it struck a moving T-72 at 8.6 km. [DID article]. Anticipated: $30k.
- M712 Copperhead – 155 mm guided (SALH) artillery shell. Can hit point and moving targets, like tanks. Developed ca 1970s? Still in service. [Video 2:07 ]. $30k.
- XM1111 MRM – 120 mm guided (MWR/SALH or uIIR/SALH multimode seekers) tank-cannon launched anti-tank round. By far the most impressive weapon on these lists, in my view. [album ]
Note: Not all seekers are made equal. Quality/power/resolution will vary for different applications. Eg, a Hellfire’s radar is far cheaper than a SM-6’s [relatively] massive radar.
Q: How much will it cost?
Myth: “$2.50 per shot!”
$25k to $250k per round, depending on guidance package. [See: previous section.]
- Command guided – Current prototype is $25k (tungsten pellet payload, limited production).
- GPS/INS – (land attack) – $25k to $50k projected. Comparison: M982 Excalibur, 155 mm artillery shell, GPS/INS guided, $50k. Comparison: JDAM, GPS/INS, $25k.
- Multimode seeker – (anti-ship, anti-armor) – ≤$250k? (wag). Comparison: SDB-II, tri-mode seeker, $125k (low-rate production).
The barrel? No idea. Add capacitor banks or flywheels, power management, autoloader, control software.
Energy is cheap: ~3.5 gallons of diesel (450 MJ) per 64 MJ shot (energy losses from converting diesel to electricity to kinetic energy).
Q: Doesn’t the launch destroy the barrel? The gun only lasts a few shots?
Rail durability like that hasn’t been a problem for years [ed: 2004 ]. Rails can handle shot counts in the low hundreds [ed: 400 shots according to FY14 HASC testimony]. The only problem is the Navy wants 1000 shots for the finished product. [comment link]
[The rail material is] a copper alloy with a metal coating that can resist friction. Anything more specific is classified. [comment link]
- Download: materials selection for EM launch rails, PDF .
Early barrels were just test rigs, fired infrequently, not built for high rates of fire. An operational barrel must at least enough shots to empty its magazines… unless you want to carry spare barrels. Swapping a 15 tonne barrel while underway… that’ll be fun.
My pet favorite partial remedy is injecting pressurized inert gas (like N2) behind the round, accelerating it to, say, 100 mph as it enters the breach; since it’s already moving when it touches the electrified rails, the barrels will last longer (no spot welding), and the inert gas will both cool the rails a tad and reduce oxidation immediately after firing.
[see: Table 1] — barrel life compared to other guns (below)
Too heavy: 64 MJ barrels weigh only 15 tonnes. Iowa’s barrel+breech weighed 120 tonnes.
[see: Table 1] — gun system comparison (below)
The rails needn’t be aimed exactly because the shells are guided and can maneuver.
Q: Are railguns special?
It’s much like any other precision guided projectile.
Two ways to think about it (simplified!):
Gestalt #1: railguns are like really long range artillery. Or cannon. It’s about as powerful as a 200 mi Hellfire/LRLAP/Excalibur/APFSDS/SDB-II.
Gestalt #1b: railguns fire really small SRBM payloads.
Gestalt #2: rails replace a missile’s rocket motor. Missile rocket motors often only burn for seconds to less than a minute (eg A2A missiles), after which they coast, slowly bleeding speed, steering with just canards/strakes/fins. The motor just adds speed. So if you launch a missile from a railgun, you don’t need the motor. Imagine launching an ESSM’s nose/guidance-section from rails. At 20 kg, a railgun round is roughly the size/weight of the guidance section of the AIM-9X/Hellfire/SDB-II.
Table 1: Gun systems compared
|Ship||Gun||System weight||Barrel length||Barrel life (shots)||Rounds per gun||Shell weight||Muzzle Energy||Muzzle velocity||Range|
|Zumwalt||64 MJ railgun||67 mt||10 m||???(1000+ goal)||?||20 kg||64 MJ||Mach 7+||200+ mi|
|Zumwalt, Burke, Tico||32 MJ railgun||<67 mt||?||400 (1000+ goal)||?||20 kg||32 MJ||Mach 5+||100+ mi|
|Zumwalt||155 mm AGS/LRLAP||106 mt||9.6 m||?||335||100 kg||36 MJ||Mach 2.5||100 mi|
|Burke, Tico||Mk 45 5″/62||29 mt||7.8 m||7,000||<700||30 kg||10 MJ||Mach 2.4||23 mi|
|Iowa||Mk 7 16″/50||≫120 mt||20 m||300 (1500 post-WWII)||130||1,200 kg||360 MJ||Mach 2.2||24 mi|
|M777 howitzer||155 mm||3.5 mt||5 m||2,650||?||45 kg||16 MJ||Mach 2.5||15-24 mi|
- Note that the HVP is 1/4 the size of the LRLAP , so many more rounds can fit in the same magazine.
- Zumwalt carries 300+ rounds/gun. Note on barrel life: the LRLAP burns hotter than other 155 mm propellants, so barrel life is likely shorter than, say, a Mk 45.
The railgun’s proportions are largely similar to other guns, neither terribly heavy nor large. But the rounds are smaller, traveling much farther and faster.
Q: What roles will a naval railgun play?
- Seeker/guidance options: GPS/INS, mm-wave radar, semi-active laser, uncooled IIR, or multimode. +datalink. (1st gen rounds will have at least GPS/INS+datalink)
- This is the most obvious role: hitting fixed targets, like C3, bridges, fuel depots, power stations, ammo dumps, SAM sites, artillery. Railguns would hit many of the same targets as traditional artillery, and some of the targets usually assigned to cruise missiles and other standoff weapons, ie high value targets and defended areas usually inaccessible to ground/air forces except for stealth fighters/bombers. This will become more true if future railguns can reach out to, say, 500+ mi. 1000 mi would rival the range of carrier aircraft armed with AShM’s.
- Seeker/guidance options: likely GPS/INS, mm-wave radar, active+passive radar, IIR. +datalink. (Options similar to other AShM’s).
Hitting missiles/aircraft is hard because the rounds are small. The seeker and control surfaces are shrunk to fit inside a narrow 6″ barrel (ie poorer sensor + less maneuverable = lower Pk). Also, targets are hard to hit—small, fast, maneuverable, and likely stealthy in the future.
It’s hard enough for an SM-2/6, which is massive in comparison (and not g-hardened). An ESSM is 10″ in diameter; even an AMRAAM is 7″; an AIM-9X is 5″. You’d also have to defeat a fighter’s IR countermeasures and EW suite to hit it.
HOWEVER, the USN recently issued a Request for Information for railgun fire control systems for LO targets, airborne and surface targets, and ballistic missiles. Prototype desired in 2018; IOC desired for early 2020s. [See: Article 2](includes further links).
Also, the Navy says the kill probabilities are quite good, comparable to other weapons [Article 1].
- Seeker/guidance options:
- None. Command guided only. Easiest option. Least accurate. Lowest SSPK.
- SARH. Challenging b/c high closing speeds and smaller sensor aperture.
- IIR. Challenging b/c high closing speeds and smaller sensor aperture. Thermal challenge.
- Multimode (some combination of the above) +datalink
- At these ranges (200 nmi), you’re probably firing on aircraft, not small/nimble missiles. You may need to use discreet onboard guidance or passive/LPI/LPR off-board targeting (eg an F-35) to avoid alerting targets, who’ll gently fly out of the way before the rounds arrive (6 min flight time)… since you can’t do mid-course corrections (no atmosphere for the control surfaces).
- While difficult (read: $$), rail-launched AA rounds are still conceivable. If technically feasible, they could augment ESSM’s or supplant CIWS/SeaRAM against super/hyper-sonic sea-skimmers. Lasers might be more suitable in some cases… but that’s for another FAQ.
- Rate of fire is ~8 rpm/gun/20 MWe. Can be saturated.
I’m not well-versed enough to provide insight here. 100-200 mi artillery might count for something, though the power supply is large. The Navy plans to make a modular, land-based version [Article 1]. General Atomics unsuccessfully pitched a mobile, land-based version of their Blitzer 32 MJ railgun for air defense.
Conceivably, you could rain shells from 10,000 miles away from a very powerful gun safely sitting in Colorado. You just need a 160 m gun with a 250 mt barrel (1024 MJ muzzle energy, Mach 28-ish muzzle velocity) fed by 2400 MJ flywheels weighing 300 mt. Don’t forget the other 600 mt for the switching, recharging system, and cooling. Minimum. (I work for cost+10%. Cash or check is fine.)
More seriously, it’s comparable to Iowa’s 1,700 mt turrets with her 3x 100 mt barrels. Better electronics and materials might shorten the barrel to 40-80 m, which isn’t totally unheard of.
Conceivably, you could hit satellites in LEO. You’d have to shrink a fairly sizable IIR seeker, divert/attitude thrusters, and propellant tanks into a very small round ($). Then g-harden it ($). The upside is simplicity—the round is basically just a kill vehicle (cheaper(?) without the massive rocket booster, and small enough to store dozens). But the result is still less capable and less accurate than other options, just because the round must be smaller. However, if the round is cheap enough (say, $500k to $1m), it doesn’t matter [as much] if the SSPk is only 5-10%—just shoot 10 or 20 of them.
But current rounds (Mach 7+ muzzle velocity) wouldn’t fly high enough, even if launched straight up (225-275 km). Most LEO sats won’t dip below 300 km, avoiding atmospheric drag. Maybe wait two generations.
I’ve never seen ASAT rails mentioned officially. Perhaps no one talks because of treaty limitations(?) or because it highlights the vulnerability of our own LEO sats (which doesn’t include many, many sats in higher orbits that won’t be vulnerable even to missiles for quite some time)… but I’m not convinced. After all, ASAT warfare isn’t new.
Honestly, I don’t think we need ASAT railgun rounds. We won’t shoot down that many sats (not that many targets). It’d be cheaper to keep launching SM-3’s ($12 million each) than spending $1 billion designing a small, g-hardened, rail-launched ASAT round. At least for now…
Q: How are railguns powered? / Capacitors vs. flywheels
A 64 MJ shot is equivalent in energy to just a few gallons of marine diesel (accounting for inefficiencies when converting to electricity and then to kinetic energy). About 300 laptop batteries. But batteries put out too little power.
When firing, the [30 MJ prototype] draws an average ~12.5 GW (3% of the US grid). They need a hefty power supply to store and then release that energy.
CPA’s (aka flywheels with generators, aka Compensated Pulsed Alternators, aka compulsators) used to be the favorite way to store energy for railguns. In the 90s, the Army tried to develop a railgun for an armored fighting vehicle. They created very compact CPA’s, by far small enough for the Navy. The Army project was cancelled, but the Navy leveraged some of their work .
CPA’s were more compact (higher energy/power densities), lighter overall , and degraded predictably. In fact, the Ford’s new EMALS catapult is powered byCPA’s (designed by UTexas?) storing 484 MJ, delivering 122 MJ to aircraft.
Here depicts Zumwalt refitted with a railgun and CPA’s .
Capacitors: However, capacitor tech improved over the last 25 years, apparently now favored over CPA’s because I haven’t heard anyone talk about developing CPA’s for railguns for a long time. Capacitors banks (not individual cells) also degrade gracefully and are modular. Conceivably, you could even design the modules to fit within the ammo handling scheme of the Zumwalt, easily(?) swapping tired cells for fresh ones. But you probably can’t replace a CPA without cutting a hole in the hull or removing the turret; it’s too big.
[insert cap vs. cpa slides] [insert][file: railguns > power system > high energy density capacitors; a GA ppt on caps . long life (20-40 years), low maintenance, plenty of shots, good energy density, simpler (DC, not AC+rectifier).]
Again, caps might output a smoother pulse, lowering peak g’s, thus lowering stress on the rails and projectile, thus lowering material requirements.
Myth: Railguns require nuclear powerplants.
No, gas turbines are fine.
Short comment: Even without nukes, Zumwalt could empty her [notional railgun] magazines in 1 hour at 100% power.
I’ll say it again: [Including CVN/CG/DDG/LCS/LHA/LPD’s], Every single major surface combatant in the USN produces enough raw power for a relevant railgun. Even a 4x larger railgun with a 1000 mi range wouldn’t need a nuclear reactor. But you need generators (and a new power grid) to [convert the shp into MWe].
Nuclear reactors [are energy dense, but not very power dense]. Turbines have great power densities. This is 27000 hp (20 MW), almost enough to power an early LA class submarine. A reactor’s shielding alone is much larger and heavier.
Q: How to defend against railguns:
- Break the kill chain.
- Hide (technical and operational stealth).
- Destroy their long-range targeting aircraft/satellites/submarines. Air superiority.
- Jam/spoof the targeting assets and the round.
- Threaten the railgun platform (A2/AD, mines, subs, AShM, ASBM’s/MaRV’s).
- DIRCM–directed IR countermeasures,
- EW: Jamming, spoofing
- Hard kill
- SAM’s (eg, SM-2/6, ESSM, S-300, THAAD, Patriot)… and yes, this will get expensive. And the volume of incoming railgun rounds could saturate defenses.
- Note: railgun shells aren’t rock-solid slugs: seeker windows, the guidance section (electronics, battery, antenna), and control surfaces (fins/strakes) are all vulnerable to blast-frag warheads… just like any other “missile.”
- Lasers. (I’m on the fence about this one. Lasers can certainly engage hypersonic rounds… but a round designed to briefly withstand Mach 7 at sea-level (~Mach 6 re-entry) is pretty heat-tolerant.)
- Active-protection system (for tanks). (Debatable.) Even if the APS hits the incoming round, 16 MJ of KE still slams into the tank’s weak roof armor; requires larger impactor/EFP.
A railgun round is much like any other guided ballistic projectile. In fact, the terminal velocity is similar to SRBMs with similar ranges… and is actually slowerthan MRBMs (though faster than Mach 3 tank-launched APFSDS). Theatre BMD SAM’s can intercept railgun rounds.
- SAM’s (eg, SM-2/6, ESSM, S-300, THAAD, Patriot)… and yes, this will get expensive. And the volume of incoming railgun rounds could saturate defenses.
- CIWS. Pk too low.
- ERA (for ships),
- Armor. You cannot armor a ship against rounds that cut through 1000 mm of RHA steel. Except for critical areas.
Q: What ships will be armed with railguns? / When will it be ready?
- 2016: A 32 MJ prototype will be tested at sea .
- ~2025: 32 MJ rails will replace some 5″ guns on Burkes/Ticos, according to tentative Navy plans in this [Article 1].
- Zumwalt is perfect. She supplies plenty of power (all-electric ship), has the magazine space, and already has mounts. A 64 MJ railgun will double her range. The Navy might decide later this year to install rails on Zumwalt [Article 1].
- Burke/Tico will receive 32 MJ rails… giving them the same range as Zumwalt’s AGS!!! That’s even farther than ERGM (cancelled), a rocket-boosted, GPS/INS guided, 5″ shell.
- Zumwalt #3 is likely the first to field one. It produces far more electrical power and has far more space to accommodate the power supply and a larger magazine.
- Burkes only produce ~8MWe, but a 32 MJ gun at 8 rounds/min draws 10 MWe. I’m guessing they’ll add more gensets or upgrade from the current ones.
- The 32 MJ gun will be fielded mid-2020! Apparently they’re no longer waiting for a 64 MJ version, though they’re going ahead with the larger 20 kg round (current prototype is 10kg/23lb).
- They must expect that barrel life will be long enough, that the power supply is small enough, and that the guidance system will mature soon. aka, they think they’re almost ready.
Q: What are its advantages/benefits?
- Long range. 32 MJ rails on Burkes will match Zumwalt’s AGS range.
- Rounds are small; deep magazines. Engage more targets. Prototype/planned round is 1/4th the size of LRLAP rounds fired from Zumwalt’s AGS. Ergo, up to 4x the magazine (minus space for the power systems).
- Rounds are affordable. (But not “cheap”.) See: Cost/Seekers/Guidance sections.
- Rounds are inert. Except for a small charge to disperse it’s payload (if applicable), railgun rounds are solid metal and electronics. Safer than storing tons of explosive warheads, rocket motors, or propellant charges. May change.
- Velocity/power is dial-able. Eg, 100% power (full-sized, long-range, land-attack rounds) or 50% power and 4x rate-of-fire (half-sized CIWS rounds).
- Rounds/shrapnel fall near-vertically (especially at less than max range) like other artillery—hard to avoid well-targeted rounds (can’t hide behind walls). Exposes thin top armor of tanks.
- Rounds/shrapnel is dial-able. Eg, for a payload of shrapnel, you can vary burst distance for different effects: wide dispersion for anti-personnel and volume; moderate dispersion for anti-air; limited or no dispersion for… penetrating a ship from deck to keel.
- Rounds can carry different payloads and sensor packages — same as other artillery shells and missiles.
- Multiple-rounds simultaneous impact (MRSI) capability — same as other artillery (vary gun elevation and power).
Q: What are its limits?
- It needs long-range, networked targeting to hit moving objects. Can’t emphasize this enough!
- It’s power-hungry. The notional 64 MJ gun draws 20 MWe. Few ships generate that much electricity, just Zumwalt and CVN’s. A Burke-successor may have larger gensets, or even go all-electric. Also requires cooling water.
- Counter-battery radar – each shot reveals ownship location to within 8-32 mi (wag), even if both the ship and round maneuver after firing.
Q: What does the future bring? (wip)
In order of futures…:
- 32 MJ operational.
- 64 MJ operational.
- Range: AGS/LRLAP equivalent and better
- Off-board magazine, eg for F-35 or other VLO OTH targeting assets.
- Multimode seekers for attacking point/moving targets.
- Range: exceed carrier aircraft based weapons.
- Range: intercontinental??? Gun based in CONUS or regional allies.
Myth: Railguns can only shoot line-of-sight. Only flat trajectories.
Railgun rounds fly ballistically, just like ballistic missiles and other artillery shells. Launched at Mach 7+, they’re faster than artillery and small/medium SAM’s, but…
They’re not even particularly fast compared to large SAM’s and medium to large ballistic missiles. THAAD reaches Mach 8+; SM-3 reaches Mach 15+… acceleratingup the entire way. MRBM’s, IRBM’s, and ICBM’s re-enter at Mach 10 to Mach 20.
Myth: Railguns launch 1 tonne hypersonic 16″ shells!
Pushing just 20 kg to Mach 5 takes a lot of power. The system barely fits in the Burke. Hurtling a hypersonic, 1,200 kg, 16″ shell would take 1,000 tonnes of flywheels.
While larger bores are more efficient , they also weigh disproportionately more.
- Myth: Time of flight to target it too long
- It’s the same 6 minutes as ERGM and LRLAP .
Opinion and other comments
- FY14 HASC testimony.
- 400 shot life. 1000 program target. for barrel life.
- “current research is focused on a rep-rate capability of multiple rounds per minute which entails development of a tactical prototype gun barrel and pulsed power systems incorporating advanced cooling techniques
- Opinion: by focusing on rate of fire and ship integration, (and not as heavily on power/energy density and barrel life, which I’m sure they’ll continue to develop), the USN seems to be making good progress. A mid-2020s IOC sounds very plausible.
To Do List / Minor comments / Notes to self:
- Actually 17 MJ on target, but 16 MJ is close enough for a rule of thumb.
- caps/cpa’s only store 1 shot’s worth of energy (equal to 2-3x the muzzle energy)… plus buffer so cpa’s don’t spin down completely (less efficient at lower speeds).
- A railgun is NOT a coilgun. It doesn’t use coils. Also, it’s not EMALS.
- At Mach 12, 1 kg of mass is equal to its weight in PBXN (8 MJ/kg). Although near-future rail guns won’t reach those velocities. Comment.
- 01 [delete later]
- 02 Yes, range estimates already account for drag.
- 04 Mounting railguns and lasers on LCS… for fun.
- Reiterate how CIWS doesn’t always save you from debris. radars not armored. CIWS limitations. mission kill. here.
- could fill gap between essm and sm-2/6… but essm+booster could do that
- keywords: payload, G/C, SAM, army EMRG, army gun/cannon launched PGM’s, size/power/cooling reqs, why flames (see prior posts), refit in zumwalt… electricity and ammo handling, water cooling.
- Q: How are railguns different? (wip)
- vs. traditional artillery: faster than traditional artillery shells, but smaller.
- vs. gun-CIWS or SeaRAM/RAM: much higher muzzle velocity for intercepting supersonic AShM
- Rear-facing GPS in tail, jam resistant: http://imgur.com/a/BvLi4#rpTODVY
- $10,000/round, HVP derived from barrage round program, shock testing, components up to 35 KG, flight at 25 KG: http://imgur.com/a/BvLi4#dbD55tz
- bae gun models. http://www.modeledhorizons.com/index.php/portfolio/military-models/rail-gun/
- 60,000 g’s is highest number i’ve seen anyway. Once on ga.com, and possibly a second time for an early army gun.
- Video 8 quotes 100 MJ caps (higher than 75 MJ expected for CPA’s) for 32 MJ rails. Why? Newer/better numbers? Is “100 MJ” rounded up from 75?
- HVP armature clearly visible in test footage.
- ship stresses: in-bore time comparable with other naval round. recoil force moderate.
- Why is the 32 MJ so long?: they sized the 32 MJ barrel for 10m and 10kg… to test physics on a larger 64 MJ 10 m 20kg gun… So the 64 MJ gun will likely still be 10 m, as planned.
Table 2: Railgun scaling
- Range ∝ V2/g … (for ranges ≤1,000 miles)
- range ∝ [muzzle velocity]2 , [muzzle energy]1 , [projectile mass]-1
|Muzzle Energy||32 MJ||64 MJ||128 MJ||256 MJ|
|Range||125 mi||250 mi||500 mi||1000 mi|
|Muzzle velocity||Mach 5.3||Mach 7.5||Mach 10.4||Mach 14.7|
|Terminal velocity||–||Mach 5||–||–|
|Energy on target||8 MJ||16 MJ||32 MJ||64 MJ|
|Energy @”breach” (stored) low est||64 MJ||128 MJ||256 MJ||512 MJ|
|Energy @”breach” (stored) med est||75 MJ||150 MJ||300 MJ||600 MJ|
|Energy @”breach” (stored) hi est||96 MJ||192 MJ||384 MJ||768 MJ|
|Power (8 rnd/min) low est.||8 MWe||16 MWe||32 MWe||64 MWe|
|Power (8 rnd/min) med est.||10 MWe||20 MWe||40 MWe||80 MWe|
|Power (8 rnd/min) hi est.||12 MWe||24 MWe||48 MWe||96 MWe|
|on-target energy equiv:||–||–||–||–|
|5.56×45 mm (1.8 kJ)||x4,500||x9,000||x18,000||x36,000|
|7.62×51 mm (3.5 kJ)||x2,500||x5,000||x10,000||x20,000|
|20×102 mm (56 kJ)||x150||x300||x600||x700|
^ Assuming 20 kg complete round, including sabot and armature; 155 mm.
^ Alternate spec estimate for 64 MJ, SAIC 2002: [slide ]
8 MJ = 1 kg PBXN explosive 6 MJ = M829A1 APFSDS fired from Abrams tank (@muzzle) 12 MJ = M829E4 APFSDS fired from Abrams tank (@muzzle) 340 MJ = 16" shell from Iowa class battleship (@muzzle), KE only 95 MJ = Nimitz steam catapult (delivered energy) 122 MJ = Ford EMALS catapult (delivered energy) 484 MJ = Ford EMALS catapult (stored energy) 80 MW = shaft power of Zumwalt DDG, Burke DDG, LCS-1 and -2. 8 MW = electrical generation of Burke 80 MW = electrical generation of Zumwalt 480 MW = electrical generation of Ford CVN???
- General Atomics – Railguns – pics and descriptions
- UTexas CEM.
- NavWeaps.com (naval weapons/systems info)
- NDIA.org (more great technical pdfs)
- DTIC.mil (great technical pdfs)
- Office of Naval Research
- Naval Research Laboratory
- USNI.org, including news.USNI.org.
- National Academies Naval Studies Board – not much on rails, but great publications (click on “Published Reports”)
- wiki (the railgun article is a good primer, but sprinkled with innaccuracies and dated info)
- google (eg: “railgun site:dtic.mil filetype:pdf”)
- ACM – attitude control motor
- HTK – hit-to-kill – see SM-3, PAC-3
- IIR – imaging infrared – basically an IR camera. Older seekers could only sense IR intensity/direction, but couldn’t form an image (like finding a campfire blindfolded, getting hotter/colder). They often use nitrogen/argon bottles to cool the sensor. Uncooled IIR sensors don’t use argon/nitrogen; they’re less sensitive, but cheaper and easier to maintain.
- mmWR/MWR/MW radar – millimeter-wave radar – a very short wavelength radar often used by small anti-surface/air-to-ground weapons, like the Hellfire-II, JAGM (Hellfire/Maverick-successor), and SDB-II. Can form “images” of the target, harder to fool.
- OTH – over the horizon (targeting)
- Pk – Probability of kill
- SALH – semi-active lasing homing
- SARH – semi-active radar homing
- SSPK – Single-shot probability of kill – probability a single shot hits its target [see: Pk]
- ABM – anti-ballistic missile
- AGS – advanced gun system – 155 mm, 100 mi range naval gun for the Zumwalt destroyers
- APFSDS – armor-piercing, fin stabilized, discarding sabot – cannon-fired anti-tank round
- ASBM – anti-ship ballistic missile – eg, DF-21
- BMD – ballistic missile defense
- CPA – compensated pulsed alternator, aka compulsator, aka flywheel with generator
- DF-21 – DF-21 – a Chinese ASBM w/MaRV, often touted for supposedly making carriers obsolete
- EMRG – electromagnetic railgun
- ERGM – extended range guided munition – 155 mm GPS/INS guided naval artillery shell. Would have extended naval 5″/62 gun range to 70 mi. Failed. Cancelled. 1994-2008.
- Hellfire – air-to-ground anti-armor missile – can defeat any MBT
- HOBS – high off-boresight [missile/seeker] – a seeker that needn’t look directly at a target to see it; harder to fool/outmaneuver; a staple of modern A2A missiles
- HVP – hypervelocity projectile –
- LRLAP – long range land-attack projectile – 155 mm rocket-assisted shell for the AGS, GPS/INS guided.
- M712 Copperhead – 155 mm guided (SALH) artillery shell. Can hit point and moving targets, like tanks. Developed ca 1970s? Still in service. $30k.
- M829 APFSDS – primary anti-tank round for the M1 Abrams tank
- M982 Excalibur – GPS/INS guided 155 mm artillery shell
- MaRV – maneuverable re-entry vehicle – increases MIRV accuracy; may allow ASBM to hit moving targets, like ships. Examples: DF-21 and Pershing II
- SDB-II – small diameter bomb – 250 lb guided (IIR/SALH/MWR) bomb – can defeat any MBT
- SRBM/MRBM/IRBM/ICBM – short-, medium-, intermediate-range ballistic missile – shorter ranged systems are slower and typically smaller
- XM1111 MRM – mid range munition – 120 mm, guided (uIIR/SALH or MWR/SALH) cannon-launched (high-g) anti-tank weapon. ~$50k. Longer range than APFSDS. Cancelled.
- APS – active protection system – protects tanks, fires explosively-formed projectiles to destroy incoming rounds.
- ASuW – anti-surface(ship) warfare
- BDA – bomb damage assessment
- EO – electro-optical – fancy camera
- ERA – explosive reactive armor
- IOC – initial operating capability – when a system is first fielded, but not yet fully operational
- RDT&E – research, development, testing, and evaluation –
- VLO/LO – (very) low observability – “stealthy” / reduced signature