Longshot multistage gun launch

[StraumliBlight]

The Bay Area startup with a 'bats—t' plan to take on Elon Musk's SpaceX [Feb 27]

Into the Nevada desert

For Longshot’s desert base, the team chose a milelong strip of land near the airport in 3,000-person Tonopah, Nevada, about halfway between Reno and Las Vegas. Since the airport is still in use and Longshot’s land is nearby, the company needs Federal Aviation Administration approval to start building its next guns. Nathan Saichek, Longshot’s chief technology officer and a longtime aerospace engineer, said the team plans to test subsections of its next, bigger pipe on private land nearby while they wait.

First, Longshot plans to build what Grace called a “minigun,” measuring 30 inches in outside diameter. Once they build two smallish segments, making sure that pressure-firing works and the rig inside the tube speeds up right, they plan to expand it to about 1,800 feet long, or longer. Their hope, Saichek said, is that the 1,800-footer will propel a 220-pound object — closer to the weight of an average satellite than the Oakland gun’s 300-gram payloads — to Mach 5 and work as a hypersonic tester.

Saichek called the next Nevada gun an “intermediate stepping stone,” necessary for testing and proof-of-concept before the company would procure the vast amounts of money needed to build a version long enough — likely more than 10 kilometers — to actually send something to space.

[catdlr]

[edzieba]

Looks like Building 29 at Alameda.

[StraumliBlight]

Join us for a live-streamed demonstration of Longshot’s revolutionary space launch technology. We’ll be firing our very own gas gun (at low pressure) followed by a live Q&A with the team behind the tech.

[0:35:40] Low energy test shot occurs using Nitrogen gas.
[1:35:00] Talks about building a 10-20 km long Mach 15-25 space gun in Australia.
[1:40:10] Possibly launch large payloads into space within 6 years.

Time	Space Gun‎ Name	Length (km)	Diameter (m)	Projectile Mass (kg)	Cost ($/kg)	Acceleration (G)
[1:53:10]	Baby Bear	15	2	~3,000	300-400 (100-150 with H2 recapture)	200-300
[1:53:10]	Mama Bear	~20	5	~40,000	>50	N/A
[1:54:20]	Papa Bear	~35	10	~800,000	>10	<200

[1:56:40] 100 m/s delta-v needed to circularise payload's orbit, could use a cold gas thruster/solid motor.

Payload: Longshot is Gunning For Kinetic Space Launch [Jun 23]

Progress report: At an investor day last week, the team showed off a 70-ft long prototype that accelerates payloads to just past Mach 4. Now, they are building a 180-ft version suited for military hypersonics, with testing at speeds above Mach 5. Weapons researchers today might pay $6M to $8M to put materials or components in that environment, according to Grace, who said his company could do it for $150,000.

If that works, the big leap is a 12-mile gun to send 100-kg payloads into orbit.

[TrevorMonty]

Probably better suited to launching materials into space from moon. Only need DV of Mach5-6 and payloads like water in metal canistor don't care about high Gs so barrel can be short.

[edzieba]

Probably better suited to launching materials into space from moon. Only need DV of Mach5-6 and payloads like water in metal canistor don't care about high Gs so barrel can be short.

On the Moon (or any other vacuum environment) they can omit the barrel entirely and just use guide rails for the projectile. Longshot's accelerator is not a pressure-based multi-chamber gun.

[Robotbeat]

Probably better suited to launching materials into space from moon. Only need DV of Mach5-6 and payloads like water in metal canistor don't care about high Gs so barrel can be short.

On the Moon (or any other vacuum environment) they can omit the barrel entirely and just use guide rails for the projectile. Longshot's accelerator is not a pressure-based multi-chamber gun.

But it is pressure-based and they would face the problem of not having a lot of volatiles to work with. I think for the higher velocity they’re going to end up needing to use hydrogen, and the moon is very hydrogen poor. Even on earth, you probably would have to recycle the hydrogen in order for it to be economical. I don’t buy that they’ll be able to get by with just compressed air at Mach 25. Then again, the moon is much lower launch velocity, so perhaps they could get by with using oxygen gas. But honestly just use a rocket if you’re gonna do that. Or something like spin launch. Spin launch faces major scaling issues on earth related to the vacuum pressure vessel, which linear launch improves on dramatically, but that is not a factor on the moon. So I kind of doubt you would use a compressed gas based accelerator for the moon at all.

[edzieba]

Probably better suited to launching materials into space from moon. Only need DV of Mach5-6 and payloads like water in metal canistor don't care about high Gs so barrel can be short.

On the Moon (or any other vacuum environment) they can omit the barrel entirely and just use guide rails for the projectile. Longshot's accelerator is not a pressure-based multi-chamber gun.

But it is pressure-based

See post 2: not pressure based, but impingement based. Inert gas pressure discharge is a nice easy way to implement it for testing, but you can produce your jets in other ways (e.g. as very short duration rocket exhaust plumes*).
For ISRU, it depends on whether it's easier to gather some manner of propellant or other pressurisable gas (you only care about exhaust/discharge velocity, not composition) or whether it is easier to build an electrical generation and distribution system to run your spinner. Both have their pros and cons when it comes to upfront cost/mass reuqired vs. ongoing cost/mass required.

\* an interesting boostrapping method would be to land structural elements using landers with a lot of small descent engines rather than one or two large ones, then unmount those and line them up to form the launcher. Probably not worth it, by the time any sort of fixed lunar launch infrastructure is needed (or even viable) you probably have a regular reusable shuttle surface to/from the surface so don't need to mess about with disassembling dedicated landers in the first place.

[Robotbeat]

Impingement of what? Pressure. I’m aware of the pinching mechanism. It’s still pressure, force over an area. A way to try to exceed the usual limits. But it is most certainly pressure.

[Twark_Main]

Impingement of what? Pressure. I’m aware of the pinching mechanism. It’s still pressure, force over an area. A way to try to exceed the usual limits. But it is most certainly pressure.

I think we all understood that, but what terminology should we use to distinguish between the two types?  For practical usability it needs to be something that isn't an entire paragraph.

"Pinch-type gun" vs "piston-type gun" seems to capture it, and isn't egregiously long. Any objections?

[redneck]

Probably better suited to launching materials into space from moon. Only need DV of Mach5-6 and payloads like water in metal canistor don't care about high Gs so barrel can be short.

Within the velocity of tank guns on Earth at 5,000 fps or so. The barrel of a Lunar gun could be fairly low quality ISRU as it could be arbitrarily thick. Sintered iron? One of the advantages is vacuum in the tube which allows bore diameter to be quite large. 10 ton projectile in an 8 foot diameter at 1,000 psi gets around 350 gees acceleration for about a half second boost to orbital velocity. 2,000 feet long allows the last quarter of the barrel to do gas recovery with secondary chambers and fast acting muzzle cap.

[edzieba]

Impingement of what? Pressure. I’m aware of the pinching mechanism. It’s still pressure, force over an area. A way to try to exceed the usual limits. But it is most certainly pressure.

Well, at the rawest level its particle impact based. Using particles in a gas just makes handling much easier (and minimises erosion), but you could be firing small metallic pellets to the same effect.

The key part is it's not propelled by a pressurised gas in an enclosure pushing a slug. No enclosure is required if your external environment is already a vacuum - the gas only needs to be directed from a nozzle to the passing projectile (which with correct nozzle design can be done through free space, as with every rocket with a de Laval nozzle), and once it impinges you don't care where it ends up afterwards, beyond preferring it to remain behind the projectile to minimise drag.

This means you do not need a barrel to contain the gas, because gas containment is not a factor in the accelerator's operation. It also means you are not limited to the speed of sound in that gas, so you don't need to mess about with hot Hydrogen as in light-gas-guns.

[catdlr]

A series of three short videos published today:

Big Iron Demo: Highlights




Nano Gun: Where We Were




Mini Gun: Where We're Going

[Asteroza]

Impingement of what? Pressure. I’m aware of the pinching mechanism. It’s still pressure, force over an area. A way to try to exceed the usual limits. But it is most certainly pressure.

Well, at the rawest level its particle impact based. Using particles in a gas just makes handling much easier (and minimises erosion), but you could be firing small metallic pellets to the same effect.

The key part is it's not propelled by a pressurised gas in an enclosure pushing a slug. No enclosure is required if your external environment is already a vacuum - the gas only needs to be directed from a nozzle to the passing projectile (which with correct nozzle design can be done through free space, as with every rocket with a de Laval nozzle), and once it impinges you don't care where it ends up afterwards, beyond preferring it to remain behind the projectile to minimise drag.

This means you do not need a barrel to contain the gas, because gas containment is not a factor in the accelerator's operation. It also means you are not limited to the speed of sound in that gas, so you don't need to mess about with hot Hydrogen as in light-gas-guns.

Would mini-macron guns be potentially suitable for the impingment process?

[edzieba]

Impingement of what? Pressure. I’m aware of the pinching mechanism. It’s still pressure, force over an area. A way to try to exceed the usual limits. But it is most certainly pressure.

Well, at the rawest level its particle impact based. Using particles in a gas just makes handling much easier (and minimises erosion), but you could be firing small metallic pellets to the same effect.

The key part is it's not propelled by a pressurised gas in an enclosure pushing a slug. No enclosure is required if your external environment is already a vacuum - the gas only needs to be directed from a nozzle to the passing projectile (which with correct nozzle design can be done through free space, as with every rocket with a de Laval nozzle), and once it impinges you don't care where it ends up afterwards, beyond preferring it to remain behind the projectile to minimise drag.

This means you do not need a barrel to contain the gas, because gas containment is not a factor in the accelerator's operation. It also means you are not limited to the speed of sound in that gas, so you don't need to mess about with hot Hydrogen as in light-gas-guns.

Would mini-macron guns be potentially suitable for the impingment process?

Since the end-goal of macron beams is generally destructively ablating the target, that sounds like making a rod for your own back. Gasses are easier to handle and cause less erosion of the projectile, so I can't think of a good reason not to use gasses. Inert gasses are nice because they are... inert (won't oxidise your projectile, storage and handling is simplified), but combustion products may be easier above a certain velocity because they are self-accelerate and has be stored as solids or liquids rather than as pressurised gasses, and do not need pumping infrastructure to pressurise between shots.

[Robotbeat]

I just don’t get the advantage over rockets. If you’re not recovering the gases, why not just use a rocket?

[Paul451]

I just don’t get the advantage over rockets. If you’re not recovering the gases, why not just use a rocket?

If the "first stage" is on the ground, it breaks the exponent of rocket equation. You don't have to carry propellant to carry the propellant that carries the propellant... Additionally, you can overbuild it, since mass fraction isn't a thing. And you can store the "first stage" propellants away from the launcher, so there's less "kablooey" risk.

That said, I'm not sure there's a market for enough many-small-things to pay for a gas-gun launch system. (Except maybe a military application. Throw a bunch of expendable micro-sats up during a conflict where the enemy is shooting at your big sats.) It feels like we're moving to cheap-big-things launching many-small-things-at-once. However, it ain't costing me anything, and multi-stage impingement acceleration is one of my "why don't they just..." whenever the problems with gas guns comes up, so it's fun to watch.

[Robotbeat]

It just doesn’t matter that much that the gun is on the ground. There’s something analogous to the rocket equation for gun launch, and the rocket equation actually doesn’t bite for low delta-v. At low delta-v, the exponential is close to a linear relationship (remember conservation of energy is quadratic!).

If you actually run the numbers, I don’t think you’d end up being any more efficient (in terms of volatiles mass and energy) with gun launch than rocket launch when discussing the low delta-v of the Moon, particularly if you’re not using a tube and therefore not recovering the volatiles.

[edzieba]

It just doesn’t matter that much that the gun is on the ground. There’s something analogous to the rocket equation for gun launch, and the rocket equation actually doesn’t bite for low delta-v. At low delta-v, the exponential is close to a linear relationship (remember conservation of energy is quadratic!).

If you actually run the numbers, I don’t think you’d end up being any more efficient (in terms of volatiles mass and energy) with gun launch than rocket launch when discussing the low delta-v of the Moon, particularly if you’re not using a tube and therefore not recovering the volatiles.

The "at low delta-V" is the kicker there. The neat think about Longshot's accelerator vs. a light-gas-gun or multi-stage pressure gun (or regular big-ol-gun a'la HARP) is that they do not hit the speed-of-sound-in-driving-gas limit. You are playing in the coilgun or railgun range, but without the payload requirements of those accelerators (i.e. your payload is not limited to conductive or ferrous metals).

There are other limitations like requiring a kick motor to achieve orbit (the higher the velocity the smaller the motor, as you reach a greater apogee before it needs to fire), heating during ascent through the lower atmosphere, and limited range of target orbits (effectively fixed inclination but variable eccentricity). The payoff is that even with those, at sufficient repetition rate you can get a whole lot of bulk mass to a specific orbit for very cheap, since the majority of your launcher mass does not need to RTLS, it is the launch site.

The question then becomes the economic one (same as for Spinlaunch): does anyone actually want a lot of bulk mass in one particular orbit? The irony is that the front-runner for being that customer is a propellant depot, as that payload is near infinitely divisible (it is liquid in both senses) and to the same orbital location.

[Robotbeat]

It just doesn’t matter that much. If you look at the actual energy for gun launch and rocket launch, there’s no clear advantage to gun launch. Megajoules to Megajoules. And LOTS of drawbacks.