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Catapult to Orbit - SpinLaunch


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Once Breaking Ground has seen the light, people start building real-life space catapults...

 

30 minutes ago, natsirt721 said:

SpinLaunch employs a rotational acceleration method, harnessing angular momentum to gradually accelerate the vehicle to hypersonic speeds. This approach employs a dramatically lower cost architecture with much lower power.”

They prefer proven technologies.
 

Spoiler

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Definitely a dubious prospect. The engineering challenges are a huge hurdle and even after you solve them, the things it could launch force them into a pretty small niche. It does have one advantage over a lot of other non-rocket space launch systems: you can conceivably change your launch azimuth. A gun or linear accelerator approach would almost certainly be a fixed installation, but this one could change the release point or even rotate the whole launch system into the proper orientation (since it must be movable). Still like most non-rocket space launch systems it probably makes a lot more sense on an airless moon where you don't have an atmosphere in the way and you can scale down the system to something you can practically build because the orbital velocities are lower.

Scott Manley did a video on them about a year ago. No huge surprise that a lot of the potential problems mentioned earlier in the thread were brought up, but he added few more and threw in a little bit of interesting history relevant to the topic.

 

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Oh, these guys again!

A problem not yet covered is that they plan to instantly go from “vacuum” to “high Mach at sea level”.

That’s not particularly survivable.

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  • 11 months later...

1700 m/s isn't much, but it should be enough to loft it above the thickest part of the atmosphere. You could then start off with an upper stage engine and a whole lot lighter rocket.

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The vehicle and its payload—up to 200 pounds’ worth of satellite—will experience forces that, at their peak, will be ten thousand times stronger than gravity. Once it’s spinning at launch speed, the centrifuge will release the rocket and send it screaming into the stratosphere. At the threshold of the cosmos, it will fire its engine for a final nudge into orbit.

I have difficulty believing the structural reinforcement to handle 10,000g of lateral force will be worth it for what, roughly 1/5 of the orbital dv requirement?

According to Wiki, 1.3-1.8km/s roughly cancels out the gravitational and drag losses from a launch, so you still need the ~8km/s dv to get to orbital velocity.

(and you can get away with a lower thrust engine if you start your horizontal thrust as soon as you are out of the launch tube as opposed to waiting until you are near the peak of your arc.)

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Actually a 1/5 dV orbital requirement reduction is massive. Literally. The rocket equation causes mass to snowball very quickly once your dV exceeds your exhaust velocity. If you cut out 1.8km/s, this will pretty much reduce your LV to its upper stage. SSTO with such assistance will be a practical proposition, also because you could use a lower TWR, altitude (likely not vacuum, for optimum performance it'd likely be something like a 2nd stage engine) optimized engine.

Structural issues can be handled by a support structure that would be left with the centrifuge. However, securing the payload against such forces will be a challenge. This may have limited applications, due to additional requirements it will place on payload design.

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Even if they do get it working, you aren't going to be able to launch any old satellite on this. 10,000 gee is well beyond the acceleration rating for many sensitive electronics e.g. IMUs.  The payloads are all going to have to be incredibly over-engineered just to withstand launch, which is going to cut into their stated cost reduction fraction quite a bit. Not to mention the fact that maybe we should consider the consequences of flinging thousands of satellites into a low orbit every year (I'm looking at you, starlink).

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So we have some new data to work with:

10 000 g
4 000 - 5 000 mph
200 pounds payload
counterweight detaches at the same time as the rocket
1 minute coast after detachment from the centrifuge
1 minute booster burn starting at 200 000 ft
10 seconds orbit insertion burn

What I'm interested in is how are they going to catch the counterweight, without exploding the facility.

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6 hours ago, Shpaget said:

So we have some new data to work with:

10 000 g
4 000 - 5 000 mph
200 pounds payload
counterweight detaches at the same time as the rocket
1 minute coast after detachment from the centrifuge
1 minute booster burn starting at 200 000 ft
10 seconds orbit insertion burn

What I'm interested in is how are they going to catch the counterweight, without exploding the facility.

You could probably use water or sand as counterweight. 

I think this would be more realistic on the moon once we start to mine it, requirements would be far lower. but on it they would have to think far harder on counterweight handling. 

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This system is still in the conceptual development phase, but it can potentially launch a payload to 9 km/s. It is complex and massive, but it requires less electrical power than the railgun or the coilgun. However, it suffers from a number of air drag and mechanical friction problems. The estimated minimum system mass required to launch a 1-ton payload is 104 tons. The engineering-physics for this concept is still not mature enough for one to be confident in its performance characteristics and promise as an innovative advanced concept. It is the author’s opinion that further design studies and experimental work needs to be done to compile detailed performance data before this concept can be seriously considered.

Source: Davis, E. W. (2004). Advanced Propulsion Study.

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What's the countdown like for one of these? "3... 2... 1... YEET!"

But yeah, keep in mind that the rocket needs to be built to survive the g-forces, not just the payload. Engines, plumbing, tanks... Tanks alone are going to have to be made way thicker and heavier to prevent immense weight of the fuel under high acceleration from buckling and rupturing them. Building a rocket that can survive 10g sustained is a challenge. To get to 1km/s with 100m arm is 1000g. And they're talking about higher speeds with smaller arm? Yeah, I don't buy it.

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2 hours ago, K^2 said:

What's the countdown like for one of these? "3... 2... 1... YEET!"

But yeah, keep in mind that the rocket needs to be built to survive the g-forces, not just the payload. Engines, plumbing, tanks... Tanks alone are going to have to be made way thicker and heavier to prevent immense weight of the fuel under high acceleration from buckling and rupturing them. Building a rocket that can survive 10g sustained is a challenge. To get to 1km/s with 100m arm is 1000g. And they're talking about higher speeds with smaller arm? Yeah, I don't buy it.

I could see a rocket sleeve which reinforces on the arm and is discarded in the launch tube as part of the plan, but I don't see a way to discard such a sleeve without tearing off the skin of the rocket unless said rocket was floating in a pool of liquid mercury(which would require good insulation from any cryogenic fuels)

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4 hours ago, K^2 said:

What's the countdown like for one of these? "3... 2... 1... YEET!"

Not gonna lie, most of the non-rocket space launch methods can be pretty much reduced to yeeting something into orbit instead of carrying it

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The “arm” doesn’t need to be an arm but could be a wire made from carbon fire. You’ll need something to spin it up initially but once it’s going it’ll do the job.

The counterweight could be massive but  mounted very close to the axis. When it’s released it’s linear velocity  will be relatively low, which means catching it should be not be as hard as imagined. Relatively. Maybe if it’s water it just splashes around? If you can maintain the vacuum it might have boiled off most of the mass before hitting the wall.

I still wonder how the spin chamber reacts to all that air rushing in when you launch. Heat shouldn’t be that much of an issue at 1 km/s — we launch artillery shells with  such  velocity all the time after all.

It’s an insane idea. It will never work. Clearly these people don’t know anything about rockets or spaceflight. Then again, we’ve heard that before, too.

 

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On 6/10/2020 at 12:41 PM, SOXBLOX said:

It might be a little more dramatic than that :lol:

Well, the full sequence might go something like this. Whichever tank fails first, the loss of structural integrity compromises the other as well, causing both fuel and oxidizer to almost simultaneously slosh onto the wall of the chamber, giving it just enough time to mix a bit from impact before a stray spark sets it ablaze. Combustion almost instantly turns into detonation of the mixture and blows out the wall of the chamber, setting off an implosion of the entire complex. Heap of twisted metal and concrete in a crater. Shrapnel continuing to rain down long enough for you to start wondering if it shouldn't have stopped already. Then a couple more large pieces make a late landing, leaving only dust and deafening silence to fill the air. SpinLaunch execs watching all of this from a bunker in shock. After a few long seconds CTO turns to CEO and says, "I honestly don't know what else you were expecting."

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8 hours ago, K^2 said:

Well, the full sequence might go something like this. Whichever tank fails first, the loss of structural integrity compromises the other as well, causing both fuel and oxidizer to almost simultaneously slosh onto the wall of the chamber, giving it just enough time to mix a bit from impact before a stray spark sets it ablaze. Combustion almost instantly turns into detonation of the mixture and blows out the wall of the chamber, setting off an implosion of the entire complex. Heap of twisted metal and concrete in a crater. Shrapnel continuing to rain down long enough for you to start wondering if it shouldn't have stopped already. Then a couple more large pieces make a late landing, leaving only dust and deafening silence to fill the air. SpinLaunch execs watching all of this from a bunker in shock. After a few long seconds CTO turns to CEO and says, "I honestly don't know what else you were expecting."

Think the kinetc energies here is larger than the chemical ones. 
And in the water counterweight idea I forgot this was inside an vacuum chamber. 

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