Why Physics Favors a Mass Driver Over Heavy Lift Rockets

As a land surveyor i do stare out the window in awe of the scale of interstate infrastructure as a whole and in a localized manner

The difference between this and the infrastructure projects you cite is that this doesn't do anything until its finished. Power grids and data cables have been built out by lots of different groups piece by piece. The demand for them is also enormous.

Next video: Why 5-year VC horizons, 4-year election cycles, zoning laws and airspace management DO NOT favour a mass driver over heavy lift rockets

Thing I noticed was, there as no mention of the total size of this thing. Their website shows a model. It needs Google Earth to display it. It's a ring. One side is east of Lake Tahoe. The other side is west of … Brisbane. Australia. They want to build a continuous track that circles the whole Pacific Ocean. Kiiinda guessing maintenance inspections on that, probably going to cost more than the launches save.

Planetary LEO is cursed. Should be LPO because LEO is specific to Earth.

This seemed to have skipped over quite a few significant engineering details. The usefulness of a mass driver depends on A) How much Δv you can get out of it. B) How much of a payload it can launch. Lets look at point A for a moment, due to the nature of how a mass driver works, the velocity of a payload exiting the driver is equal to the Δv the mass driver would provide, since a mass driver can't exert force on an object that's already been fired after all. It takes about 9km/s to get from the surface to LEO, some of that is lost to air resistance, but most of it goes towards actual orbital velocity. If we look at the Space X starship as an example, the lower stage has about 3.6km/s of Δv and the upper stage has about 6.5 km/s, if we assume the mass driver provides only the Δv of the first stage, that means the payload would have to be traveling at 3.6km/s (almost Mach 11) in 1 atm, whihlch would cause serious heating issues, and the payload would still need to have 6km/s on-board just to get to LEO, and increasing the Δv should only amplify the heating problem. Now, you mention building the driver at high altitudes in your lecture, which would reduce your atmospheric pressure, and therefor reduce heating concerns, but the highest point on earth, Mt.Everest still has about .35 atm and very little significant change to Δv required to get to orbit, and considering spacecraft have to deal with reentry heating at pressures significantly lower than that, it likely still won't be nearly enough, and you would have to build significantly higher before you can get any practical amount of Δv out of the mass driver without heating issues, but as you build higher and higher, you start to run into the same issues a space elevator would have with material science being unable to keep up. Along side this, you also need to consider the maximum size and weight a mass driver would be able to sling, if we assume the above problems are somehow solved and we theoretically have a mass driver that can give a 6km/s Δv boost to a payload with minimal interference from the atmosphere, that payload would then need about 3km/s of its own Δv to orbit, and another 4km/s if it wants to go to another body with aerobraking and no return trip. Just getting that much Δv into a payload small and light enough to fire out of a mass driver would be an undertaking in itself, even with these liberties, the mass driver would be extremely impractical for anything but small probes run on highly efficient engines. By the time we get to the point where we can get significant practical use out of a mass driver on an atmospheric body, we would probably already have better options anyway, and it would make far more sense to relegate mass drivers to non-atmospheric bodies like the moon.

"support it with drones" - hahahahahhahahahaa I almost sprayed my breakfast all over the screen

Good luck pulling a vacuum in that tube and not having any issues when when the vehicle leaves the end of it

I find it quite hard to believe that a mechanical system like screws would be better than plain ol linear motors - electronics is fast and cheap. Dynamic structures are all but a pipe dream for now - supporting launch tube using drones? Oh come on. Building it on the ground or side of a mountain - thats a more realistic proposition. I'd like to see a launch loop based system built someday.

Inertially supported structures are ridiculous. The chance of the drive system failing and the whole thing collapsing makes it a risk no sane person would ever take. Even ignoring that, is the cost of generating that much inertia included in the estimate of the mass driver? Propelling a hose into upper earth atmosphere large enough to hold the screws and magnets needed would require a constant baseline supply of power onto which you would add the cost of launching each payload into space. For that matter, the variable pitch screw idea also seems ridiculous. There's only one animation of how it would work in the whole presentation. Going by that animation, the payload is supported by a series of small magnets on the ends of moveable arms that adjust the orientation of the magnets to match the pitch of the screw. The problem with this is that propelling an object forward to reach escape velocity requires very large forces, and assuming magnets strong enough to hold onto the screws are able to fit in such a small space, there would still be enough force on each arm to make robotics a struggle. Now consider the fact that to adjust to the pitch of the screw, the arms need to occasionally pick up their magnet and move it to the other side of the screw. To do this, the arm would need to be able to pull the magnet away from the screw it's holding on to, so the arm would be subjected to even more force! The design in the presentation at least is ridiculous. Maybe a completely different design could utilize a variable pitch screw, but not this one. Despite the exponential costs of sending rockets round-trip to mars and other places, I don't see any other method becoming viable in my lifetime. But please, do your best to prove me wrong.

Undersea cables were first laid in 1988? Huh? Surely they've been around since shortly after the first telegraph networks.

I always thought the "halfway there" quote was referring to technological challenges.

I note a conspicuous absence of any cost estimates for the mass driver system itself. Yes, it might scale better, but what actually is the baseline cost? If it adds up to thousands of times more than a conventional rocket design, then that’s a huge up-front cost hurdle, which would only be economically viable if the system were used thousands of times. Doing only a few launches a year would obviously not satisfy that requirement. Therefore, the main thesis of this project - that of cost reduction - is untenable.

Fascinating concept, I would love to see a full feasibility study on this concept given the amount of trouble military contractors have had trying to make pulsed magnet railguns work. Seems like this could be trialled first on the moon to get cargo back off of the lunar surface, all aspects on the moon are better - lower escape velocity, no environmental concerns in terms of affecting the environment or the environment damaging the equipment (severe storms, earthquakes etc), no atmospheric pressure to deal with so no tube needed etc. This concept also means not blasting hundreds of tons of nasty regolith off of the lunar surface to settle on other space infrastructure like habitats. Biggest issue I can foresee is the amount of electrical energy needed in a short time, that infrastructure doesn’t exist on the moon today. Minor concerns of asteroid impacts damaging the system, but that’s extremely unlikely. However, it’d definitely be more of a concern if it were the only way (single point of failure) to get humans off of the lunar surface.

This proposal is like a Hyper-Loop on steroids....X 1,000,000. So far...the people who have tried to build even a short length of tube...then evacuate it have found it to be VERY hard to do. The velocity proposed for this 'Mass Driver' is many times greater and would require a near perfect vacuum which achieving in such a long tube would be nearly impossible. It's great to dream of 'what if's'...but when they can't be built regardless of the cost....we're stuck with the old 'Rocket Equation' as our only way to space.

I must have missed something. What was the cost of the proposed mass driver? (then, of course, multiply that number by 50 to get the real "built" cost). And what is the proposed cargo capacity? (cost of the mass driver will increase by the cube for more mass) I believe you proposed only a few launches a year, shouldn't you include this "cost per flight" as part of the analysis?

Re: Mass stream or dynamic support infrastructure; I have seen plenty of theoretical design work, but outside of (comparatively trivial) things like mass dampers for skyscraper stabilization I have not seen any real implementations of dynamic structural engineering. It would seem that smaller scale design implementations would be a necessary precursor to any practical space infrastructure. Are there any examples of such, planed or working, dynamic support engineering?

The different powers of the launch mass cost and velocity curve are great. I never saw that basic concept.

I had never heard of a plasma window before this, incredible invention

I didn't follow entirely but costs need to be divided clearly into development, construction and operational cost. For a mass driver it's also a huge difference if its cargo/fuel only or man rated. As an amateur I believe first step is a hybrid cargo and fuel launcher. It will accelerate at lots of Gs, be only some kilometers long, fire through a simple membrane at modest altitude. Also the cost of delta V is different. Once in orbit ion thrusters or nuclear can be used. Only crew to orbit will need the conventional rockets but we do that already.