Crossbow To Orbit

[Spacescifi]

Just curious whether or not such could compete or be viable. Two staging is a given.

I mean if catapult to orbit is considered we may as well consider crossbows as well!

I think the main limit is material strength, and you would need a long and massive vacuum launch chamber to get the most thrust from the launch.

 

Is this mechanically viable? Just scale it up and use strong materials?

At least the bow string is resuable!

 

Edited December 4, 2021 by Spacescifi

[JoeSchmuckatelli]

From Oamuamua, yes a crossbow should work 

[DDE]

3 hours ago, Spacescifi said:

Just curious whether or not such could compete or be viable. Two staging is a given.

I mean if catapult to orbit is considered we may as well consider crossbows as well!

A centrifugal gun can achieve far greater speed than a spring. A ballista might have a higher limit, but I'm still doubtful.

[Gargamel]

Honestly, I don’t see this being a thing.    It’s a kinetic launcher, in the same vein as a Spinlaunch or cannon.    You’d have to overcome the same flight issues as those.  
 

And those options are drastically more practical than a giant crossbow.   If you have mastered the engineering challenges that a giant crossbow presents, of launching something to orbit using tension and elasticity of materials........ then it would be far more efficient to build a space elevator with those same technologies.   

[Spacescifi]

7 minutes ago, Gargamel said:

Honestly, I don’t see this being a thing.    It’s a kinetic launcher, in the same vein as a Spinlaunch or cannon.    You’d have to overcome the same flight issues as those.  
 

And those options are drastically more practical than a giant crossbow.   If you have mastered the engineering challenges that a giant crossbow presents, of launching something to orbit using tension and elasticity of materials........ then it would be far more efficient to build a space elevator with those same technologies.   

 

What about a ballista instead?

[Gargamel]

5 minutes ago, Spacescifi said:

What about a ballista instead?

A ballista is merely a large crossbow.

[Spacescifi]

30 minutes ago, Gargamel said:

A ballista is merely a large crossbow.

 

True... at least we don't have the high gees over an hour of time problem we have with the catapult though.

 

And perhaps it's an easier to fix or modify to work than spin launch?

[RCgothic]

No, I don't think it would be easier.

Compared to spin launch the vacuum chamber would have to be a lot larger - probably  400mx100m across instead of 100m diameter. The tension members need to be in vacuum or they'd contribute very significant drag.

The acceleration would probably be similar to Spin Launch around 5000G falling to 0G, averaging 2500G.

The tension element would have to hold enough force to accelerate a multiple ton rocket at 5000G. See how thick the rotor is on Spin Launch? Except a crossbow needs flexible elements. Worse, the angle means the tension is a multiple of the force needed for acceleration. Very implausible.

Also when the tension elements reach the end of their travel 2000m/s is very close to being a hypervelocity impact where materials behave like liquids.

Significant issues.

[Gargamel]

41 minutes ago, Spacescifi said:

True... at least we don't have the high gees over an hour of time problem we have with the catapult though.

Catapults do not build up g's over time.   The g's are over a very short span of time when the arm is released.   For any catapult ever built, it would be a second or two at most. The structure is under very high stress as the spring is loaded though.    But those aren't the issues with a catapult capable of launching to orbit.     A catapult launches it payload when the arm comes to a very abrupt stop.    In order to have the velocity required to reach orbit (or altitudes high enough to fire the second stage), you either need to move the arm very very fast, or make it very very long.  

The problem with very fast is stopping it.   The forces involved with stopping an arm going this fast would be catastrophic at best.   If we make the arm longer, we now encounter a couple more problems.  First off, keeping an arm this long rigid is problematic.   If we can design an arm rigid enough to survive the initial acceleration, then we also have to stop it.   The traditional design has it hitting a single point to arrest the movement.   In this case, that would mean we have this immense momentum hitting a single point, and the arm would snap.  So perhaps we build a gigantic structure to distribute the load of stopping.   Very impractical.    So let's switch the launch mechanism to like one on a trebuchet, where it is released at a certain angle.   We still have to arrest the arm eventually.   Letting it hit the ground would be as catastrophic as hitting a stop.   

So.... why don't we just elevate the axle of the arm so that after launching, it can just spin freely?   Then why do we need the instant acceleration, when it is has unlimited room to spin up to speed?   Let's just attach it to a motor to gradually speed it up and then slow it down.    And....... we have SpinLaunch.     SpinLaunch is a catapult, just a few design iterations along. 

The same thought process can be applied to a trebuchet.   There's a reason trebuchets are more efficient than a catapult, mainly because they throw farther and are less self destructive, but they tend to be far more massive.   Instead of building a massive structure, we can just simplify it down to another SpinLaunch. 

5 minutes ago, RCgothic said:

Compared to spin launch the vacuum chamber would have to be a lot larger - probably  400mx100m across instead of 100m diameter. The tension members need to be in vacuum or they'd contribute very significant drag.

I think that size estimate is quite low, by a couple orders of magnitude at best.  

As you mention, the projectile has to reach hypersonic speeds, and as you mention, to get within even sci-fi based materials, the width of our crossbow would probably need to be several dozen kilometers across. 

[insert_name]

I seriously doubt that there is any material that is capable of contracting at hypersonic speeds while remaining intact. Furthermore, steps must be taken to stop the "bowstring" from shooting out with the projectile and then getting pulled back into the "bow",  because hypersonic collisions are not something you want to have happen to your launch infrastructure.

[sevenperforce]

It has already been expressed by everyone else here, but for the record -- no, none of this would work in any way, shape, or form.

Medieval ballistae didn't even actually work on spring-constant-force cords; rather, they worked on tension via torsion. You design a ballista such that pulling back on the projectile twists the ropes holding it all together. The energy is stored in the twisted ropes which want to untwist, which is easier than trying to store energy in something stretchy.

[kerbiloid]

It's all we need.

(As a Plan B to the Malstrom-Iceland launch tunnel.)

1 hour ago, insert_name said:

I seriously doubt that there is any material that is capable of contracting at hypersonic speeds while remaining intact.

No problem. A multistage trebuchet.

The large trebuchet throws a smaller trebuchet, that one launches in flight the next one, and so on.

I've already suggested this in the game section of the forum.

[Scotius]

And how, pray tell, would you make those flying trebuchets to work in flight? Where would they deposit the "reaction" part of "action and..." equation?

I have a better idea. Let's genetically engineer a Baron Munchausen, sit him on top of the payload, then make him pull up the entire contraption by his own hair

[kerbiloid]

2 hours ago, Scotius said:

Where would they deposit the "reaction" part of "action and..." equation?

They should be shooting without a pause, so the weight of the next one should be under reaction from the shot of the previous one.

I just worry about the scale factor. Can we get enough sequoias?

[DDE]

3 hours ago, Scotius said:

And how, pray tell, would you make those flying trebuchets to work in flight? Where would they deposit the "reaction" part of "action and..." equation?

I have a better idea. Let's genetically engineer a Baron Munchausen, sit him on top of the payload, then make him pull up the entire contraption by his own hair

Ah, yes, the anti-gravity drive.

Anyway, what if we propelled the trebuchet using Project Orion?

[kerbiloid]

1 hour ago, DDE said:

Anyway, what if we propelled the trebuchet using Project Orion?

Like if Medusa was something more reasonable.

[kerbiloid]

Quote

Crossbow To Orbit

They did it.

 

[sevenperforce]

12 hours ago, Scotius said:

And how, pray tell, would you make those flying trebuchets to work in flight? Where would they deposit the "reaction" part of "action and..." equation?

I have a better idea. Let's genetically engineer a Baron Munchausen, sit him on top of the payload, then make him pull up the entire contraption by his own hair

Any of these ideas are, in principle, the attempt to use the Earth as part of the remass.

Just like an airbreather is an attempt to use the atmosphere as part of the remass.

[JoeSchmuckatelli]

12 hours ago, NFUN said:

made a small modification for easy copy-pasting in his future threads

Don't forget that the dreamers do, occasionally, stumble upon something brilliant that no one else did.  

[KSK]

I'm not sure about brilliant but the catapult to space idea is just gloriously out there. It's almost a shame that it's not practical.

"And yet, even with the Acme Space Catapult, the Roadrunner eluded my grasp."

[JoeSchmuckatelli]

In the sense of "if we can use a catapult, why not a crossbow" it is fantastic satire.  Spinlaunch is one of those 'are you cereal' kind of things.

[Vanamonde]

Some content removed. Please don't make fun of people for asking questions. We're all born knowing nothing and asking questions is how we learn. Answering the questions gives the rest of us something to do, and you might even learn something new as you think over a subject in the process of answering a question for someone else. That's happened to me. 

[Rakaydos]

Fundamentally, this is the difference between a linear accelerator and a circular one. It doesnt matter if we're talking bows vs slingstaffs or rail launcers vs spinlaunch

A circular accelerator trades having to deal with (the illusion of) Centripetal Force (which isnt a force but is an artifact of a rotating frame of reference blablabla) in exchange for only needing to build one loop, and not hundreds of kilomoters of track. The circular launcher still needs the equivilant of hundreds of KM of track to get up to speed, but it uses the same track over and over.