[ralphington]

They mention in the article of being able to launch objects at 3,000 MPH. That's a tad short of the typical 17,500 MPH used for low earth orbit, and that's not counting the extra Delta-V required to resist atmospheric drag.

I'm very glad that this company exists, but this article doesn't help its case very much other than "Hey look, they got a load of funding".

[pesmhey]

Just a wild guess here, maybe they’re using a variant of a ramjet, skipping the inefficient speeds, and then propelling it to LEO speed once it’s launched.

[jcims]

Ramjet would still require atmosphere. If you look at the Japanese SS-520 or the RocketLab's Electron, you don't need a giant rocket to get a small payload to orbit from a standing start. If you give your payload a Mach 5 kick you can eliminate a lot of the propellant mass and get by with smaller rocket motors optimized for high altitude operation.

Elon Musk wants to put 12,000 satellites into orbit. It would be very strange to me if he doesn't have someone looking into the feasibility of a giant subterranean launch tube to do something similar. Get the payload up to Mach 10 on terrestrial power and complete the orbit with a small single stage.

[bboreham]

> Elon Musk ... giant subterranean launch tube

Hyperloop?

[manigandham]

The Hyperloop is a rehashed vacuum-train idea originally from the 1800s (reduce air and rolling resistance as the primary forces counteracting speed). [1]

A launch tube would be very different, if for no other reason then the fact that you need to actually jettison the payload at one end at high speed.

1. https://en.wikipedia.org/wiki/Vactrain

[skookumchuck]

We should just rename him Tom Swift:

"Tom Swift and his Subterranean Launch Tube"

[Taniwha]

so to put something in orbit you have to do 2 things:

- get it high out of the atmosphere - give it a sideways kick so that it's going fast enough as it falls back that it misses the earth

Going straight up minimises the velocity lost by drag, but means you have to pull a right angled turn, going straight sideways grossly increases drag but makes the energy for insertion less

A railgun can only put one velocity vector on a launch, you still need a rocket of some sort to pull that turn

[whatshisface]

All unthrusted orbits eventually return to their starting points - so without a rocket on the payload there would be absolutely no way for a railgun to orbit anything. (Even if the railgun was on a tower on the moon, the satellite would eventually hit the back of the railgun.)

[toomanybeersies]

Unless you gain enough velocity that your projectile is trapped in the gravity well of another planet.

[throwaway99OO]

Agreed the articles leaves technical information to be desired.

On the point of 3,000 MPH. One of the comments on the TechCrunch article maybe provides some insight on why they aren't targeting 17,500 MPH.

"even if they need to supplement with rocket propulsion (after exiting the rotational acceleration phase), the amount of rocket energy needed will be way less. could see a huge increase in payload mass fraction as a result. maybe closer to 20 or 30% instead of 1 or 2%"

IF they are flying beyond Mach 1, drag coefficient will actually drop as Mach number increases. [1] Gravity loss will play an interesting roll as well for a system launching with a high initial velocity. There will be a balance between aerodynamic drag and gravity drag losses. The lower the angle launched, the higher the aerodynamic drag but the low the gravity drag loss. [2] Typically launch vehicles actually need more than 9.5 km/s of delta-v even though the orbital velocity for low earth orbit is only 7.8 km/s. This is due to predominantly to account for the large drag forces the velocity experiences during the vertical portion of ascent at sub, trans, and lower super sonic speeds prior to exiting the atmosphere. Some allocation will need to be made for drag loss, but I suspect it is less than a traditional launch vehicle. I would also suspect there is a balance between launch speed, fuel fraction reduction, and difficulty of implementation. The sweet spot between those three things will be important to hone in on.

[1] https://en.wikipedia.org/wiki/Drag_(physics)#/media/File:Qua... [2] https://en.wikipedia.org/wiki/Gravity_drag

[neaanopri]

$30 million is NOT a load of funding, especially for something like this!

[loeg]

It is a ton of funding considering the physics seems nonsensical.

[hartator]

Hawaii giving away tax payer money is not funding.