Giant catapult sends satellites into space • Hacker News Board

Re: Giant catapult sends satellites into space

#21

Post by dudinax » Sat, Feb 01, 2025, 7:59 PM UTC

Manuel_D wrote: post #13

inexcf wrote: post #11

I remember this being a horrible idea for many reasons. One reason being the speed needed at the start which probably meant most loads burning up in the thick atmosphere immediately. Another reason being that if you would use it to start a rocket which will only use the spin launch as a booster replacement, you would run into the problem of the fuel being pressed towards the front of the rocket as it is constantly de…

The Excalibur 155mm artillery shell is supposedly subject to twice as much acceleration as the spin launcher, and it has a solid rocket motor. So it's probably possible. But solid rocket motors are less efficient than liquid fuel.

Maybe a small solid booster to keep it accelerating immediately after launch before the liquid fuel kicks in.

Re: Giant catapult sends satellites into space

#22

Post by ortusdux » Sat, Feb 01, 2025, 8:00 PM UTC

Manuel_D wrote: post #8

There's some pretty fundamental problems with spin launch. Atmospheric drag is greatest at sea level, and drops as altitude increases. A traditional lift vehicle is traveling slowest during the early parts of its ascent, and starts reaching high velocity once it's cleared the thicker parts of the atmosphere. In contrast, spin launch is at its highest velocity (before the rocket engine ignites) right after it's releas…

I could see it being a great option for getting bulk goods into space. Fuel, water, food, spools of wire or powders for additive manufacturing, structural components, etc. Depends on what is cost effective. The difficult part would be catching the payloads.

It would probably be an even better option on lower gravity lower atmosphere celestial bodies.

Re: Giant catapult sends satellites into space

#23

Post by inexcf » Sat, Feb 01, 2025, 8:02 PM UTC

vpribish wrote: post #16

Manuel_D wrote: post #8

There's some pretty fundamental problems with spin launch. Atmospheric drag is greatest at sea level, and drops as altitude increases. A traditional lift vehicle is traveling slowest during the early parts of its ascent, and starts reaching high velocity once it's cleared the thicker parts of the atmosphere. In contrast, spin launch is at its highest velocity (before the rocket engine ignites) right after it's releas…

You got the basic physics, but don't you think they have considered these issues? It's why this is interesting at all : despite the very obvious difficulties they think this has a case.

First time i saw this i thought it must be people who do actually know their stuff. But then they realized it can not be done and decided to have fun while scamming investors.

Re: Giant catapult sends satellites into space

#24

Post by echoangle » Sat, Feb 01, 2025, 8:03 PM UTC

londons_explore wrote: post #18

Manuel_D wrote: post #8

There's some pretty fundamental problems with spin launch. Atmospheric drag is greatest at sea level, and drops as altitude increases. A traditional lift vehicle is traveling slowest during the early parts of its ascent, and starts reaching high velocity once it's cleared the thicker parts of the atmosphere. In contrast, spin launch is at its highest velocity (before the rocket engine ignites) right after it's releas…

> spin launch is going to have to withstand both lateral and vertical Gs. I wonder if there is a trick to rotate the craft between disconnection and hitting the atmosphere so that the forces are in the same direction for both?

You would have to do the rotation in the short straight section in the vacuum chamber after it is released from the centrifuge. The craft is traveling extremely fast at this point and you only have maybe 50m or less to do the rotation. I think doing a 90 degree rotation in this timespan (25ms or so, because you’re traveling at 2km/s) would need extreme rotational acceleration which wouldn’t be much gentler on the craft, and you would need some system that can actually achieve this rotation in this short time.

Re: Giant catapult sends satellites into space

#25

Post by derektank » Sat, Feb 01, 2025, 8:05 PM UTC

Manuel_D wrote: post #8

There's some pretty fundamental problems with spin launch. Atmospheric drag is greatest at sea level, and drops as altitude increases. A traditional lift vehicle is traveling slowest during the early parts of its ascent, and starts reaching high velocity once it's cleared the thicker parts of the atmosphere. In contrast, spin launch is at its highest velocity (before the rocket engine ignites) right after it's releas…

SpacePort America, SpinLaunch's New Mexico test flight facility, is at ~5000' above sea level. If drag is a serious limitation, they could potentially see additional gains by relocating their launch facilities to a city in e.g. Peru. My understanding is the atmospheric density is about 25% lower above 12K feet compared to sea level and about 15% lower than at 5K feet and there are a handful of places with road networks that go that high

Re: Giant catapult sends satellites into space

#26

Post by matthewdgreen » Sat, Feb 01, 2025, 8:06 PM UTC

There seem to be a lot of businesses like this one: well-funded by VC money, but trying to do things that are scientifically questionable. This reminds me a bit of Helion Fusion, which is supposed to produce commercial power by (I think) 2029? Something seems a bit wrong with our VC markets if stuff like this is getting funded.

Re: Giant catapult sends satellites into space

#27

Post by petee » Sat, Feb 01, 2025, 8:07 PM UTC

ARandomerDude wrote: post #19

From what I can tell looking at SpinLaunch's website and web search, they were founded in 2014, "launched" a couple projectiles in atmosphere, had a leadership change in 2022, and have been pretty quiet since then. Unless I've missed something, the headline "Giant catapult sends satellites into space" is not true. To date, they have not put anything into orbit and the company appears to be on life support.

From what I could find they have only reached 1/10th of the Karman line.

I also think its a red flag that they do not have actual press releases or data, just a list of any random website that wrote a story about them.

Re: Giant catapult sends satellites into space

#28

Post by gmueckl » Sat, Feb 01, 2025, 8:09 PM UTC

patwolf wrote: post #15

readams wrote: post #7

Earlier quoted context omitted.

They'd be great for the Moon though.

Makes me think of "The Moon Is a Harsh Mistress", where the moon went to war with earth by catapulting rocks.

A military moon base could lay waste to any area on earth that way. There will definitely be a new moon race once a permanent moon base becomes sustainable. I don't see how the existing space treaties can survive past that point.

Re: Giant catapult sends satellites into space

#29

Post by isoprophlex » Sat, Feb 01, 2025, 8:14 PM UTC

isoprophlex wrote: post #14

I have so many questions..! (And maybe the answers are somewhere on the page, but its navigational paradigm is too atrocious for me to handle) - how fast do you have to push something through the atmosphere to have it reach space? - and, how fast is the lever spinning to reach that velocity? how precise do you have to time the release? - after release, your lever is going to be pretty unbalanced. having seen what hap…

Okay so say 15.000 km/h, escape velocity + compensate for drag.

At a 100 meter radius, that's a radial velocity of 41 radians per second (4100 meter/second) => 6.5 Hz spinning rate, or one full circle every 0.15 sec

To hit the exit at an angle that's within 1 degree of target, that requires you to launch with 0.15/360=0.4 millisecond precision.

Which seems... not entirely unhinged?

Those 1000s of g-forces though...

Re: Giant catapult sends satellites into space

#30

Post by MadnessASAP » Sat, Feb 01, 2025, 8:14 PM UTC

bloopernova wrote: post #17

Accelerating in a huge vacuum chamber seems pretty difficult to achieve, and wouldn't there be a huge shock to the vehicle as it hits a wall of dense air? How much of a difference would a low pressure chamber make, I wonder? Maybe you could build the circular accelerator then a much longer exit pipe that runs up the side of a mountain. Although that sounds way, way easier said than done! But if your exit air pressure…

Well actually....

Even if you place the exit at higher altitude with lower pressure, without a seal you'll still end up with higher pressure at the base. Just like you do in open air, the weight of the air column pushing down increases the pressure.