Space Elevators and Mass Driver Runways

[Drakenred65]

This sums up the response the idea of building a man rated rail gun to LOE USUALY gets over at clear lake...

 

BwSts2s4b

The main problem being that the shuttle did a constant burn at around 3 gs   to a altitude of 104 miles. And that design would not survive the atmospheric preasure at that velocity below 90 miles. So you need a much more solid design if you launch it at a lower altitude.....because it has to punch through the atmosphere and gravety....so higher velocity so longer acceleration time because 3g is also the practical limmit given the length of time.

If you build it Any lower and you need a longer acceleration on a vehicle that needs to survive a higher maximum pressure at point of launch, which partly negates any savings from not building it as high...

 

And unfortunately building anything like carriers catapult but scaled up for space launched a runs into a severe diminishing returns problem.

 

[KerikBalm]

Im more interested in a mun mass driver than a kerbin one.

As long as I can do air launch to orbit, and recover the launcher, I'll do that.

Besides, where are they gonna go from Rapiers? Scramjets?

A metallic hydrogen based rapier?

Any higher tech airbreathing/atmosphere engine is going to make getting to orbit trivial enough already

[DunaManiac]

The problem with a space elevator in-game is that when you leave the top, your velocity is at 0 relative to kerbin. So you need to waste fuel achieving orbit with  rockets, while with a LKO space station, you don't need to use that fuel. To me, I think it is a bit too unrealistic to me, because, while I think this would be cool, it would be boring.

[DStaal]

2 minutes ago, DunaManiac said:

The problem with a space elevator in-game is that when you leave the top, your velocity is at 0 relative to kerbin. So you need to waste fuel achieving orbit with  rockets, while with a LKO space station, you don't need to use that fuel. To me, I think it is a bit too unrealistic to me, because, while I think this would be cool, it would be boring.

This is not true at all, at least if the space elevator is realistic.  A realistic space elevator gets you off at geosync - at orbital velocity.

[nejc]

2 hours ago, DunaManiac said:

The problem with a space elevator in-game is that when you leave the top, your velocity is at 0 relative to kerbin ...

On top of what was just said above, space elevator does not end at GEO since it needs counterweight. If it went only to GEO it would fall down. By going further than GEO you can be on an interplanetary trajectory by just releasing the cable.

Edited September 9, 2019 by nejc

[GoldForest]

8 hours ago, Brikoleur said:

Then what would be the point of having it at all? If you're in the late game with the kind of tech a mass driver would need, you will already have designed all the lifters you need, the tedious bit will be the routine flying, and the mass driver wouldn't even help with that.

Again, I'm all for having the parts to build one, but having one pre-built for as a building upgrade would be silly -- that would be the gameplay analogue of having a ready-made one-part lifter stage, and I don't think anyone is asking for those.

To help the player launch shuttles and rockets easier. The mass driver would only take your craft up to mach 3 to 5, which is about half way to escape velocity. Then the shuttle boosts itself up to space. 

5 hours ago, [email protected] said:

This sums up the response the idea of building a man rated rail gun to LOE USUALY gets over at clear lake...

BwSts2s4b

The main problem being that the shuttle did a constant burn at around 3 gs   to a altitude of 104 miles. And that design would not survive the atmospheric preasure at that velocity below 90 miles. So you need a much more solid design if you launch it at a lower altitude.....because it has to punch through the atmosphere and gravety....so higher velocity so longer acceleration time because 3g is also the practical limmit given the length of time.

If you build it Any lower and you need a longer acceleration on a vehicle that needs to survive a higher maximum pressure at point of launch, which partly negates any savings from not building it as high...

 

And unfortunately building anything like carriers catapult but scaled up for space launched a runs into a severe diminishing returns problem.

 

The space shuttle did 3gs constantly upon launch and it made it into space. Besides, I think you think the mass driver is for getting things to orbital speeds, it is not. Mach 3 to 5 at launch, maybe even a little faster. The shuttle then has the boost itself to orbital height and then circlerize. SSTOs dont go vertical, they launch to orbit horizontally and gain speed as they climb. It's a concept that is sound as most SSTO airplanes will use that method. Even the new mach 5 boeing airplane will use this method. It will fly relatively parallel with the ground until it got enough height to go into space. 

3 hours ago, KerikBalm said:

Im more interested in a mun mass driver than a kerbin one.

As long as I can do air launch to orbit, and recover the launcher, I'll do that.

Besides, where are they gonna go from Rapiers? Scramjets?

A metallic hydrogen based rapier?

Any higher tech airbreathing/atmosphere engine is going to make getting to orbit trivial enough already

Scramjets would be used for the SSTO in atmosphere, and once the air ran out they would switch to traditional rockets, possibly and aerospike. Rappers are also another method.

3 hours ago, DunaManiac said:

The problem with a space elevator in-game is that when you leave the top, your velocity is at 0 relative to kerbin. So you need to waste fuel achieving orbit with  rockets, while with a LKO space station, you don't need to use that fuel. To me, I think it is a bit too unrealistic to me, because, while I think this would be cool, it would be boring.

Wrong. If you release the payload at any height along the elevator, the payload is going the same speed as the elevator, so it already has orbital speed. Tou can literally push the satellite off the pad and it will orbit Earth, or kerbin in this case, fine.

1 hour ago, nejc said:

On top of what was just said above, space elevator does not end at GEO since it needs counterweight. If it went only to GEO it would fall down. By going further than GEO you can be on an interplanetary trajectory by just releasing the cable.

The weight would be about 1/4th to 1/3rd the way to the Moon/Mun. Hardly interplanetary speed. 

[KerikBalm]

5 hours ago, GoldForest said:

Scramjets would be used for the SSTO in atmosphere, and once the air ran out they would switch to traditional rockets, possibly and aerospike. Rappers are also another method.

...

Wrong. If you release the payload at any height along the elevator, the payload is going the same speed as the elevator, so it already has orbital speed. Tou can literally push the satellite off the pad and it will orbit Earth, or kerbin in this case, fine.

The weight would be about 1/4th to 1/3rd the way to the Moon/Mun. Hardly interplanetary speed. 

1) do you have a point about the ecramjets/airbreathets, or are you just stating the obvious?

2) not any height... Realease below GSO, and the payload falls relative to the elevator, realease above it, and it climbs.

Depending on how high / how massive the counterweight is, releasing near the counter weight can give you interplanetary velocity

[GoldForest]

6 minutes ago, KerikBalm said:

1) do you have a point about the ecramjets/airbreathets, or are you just stating the obvious?

2) not any height... Realease below GSO, and the payload falls relative to the elevator, realease above it, and it climbs.

Depending on how high / how massive the counterweight is, releasing near the counter weight can give you interplanetary velocity

1) I don't know why I do that. Bad habit. 

2) I just realized your right. The whole station is going at GSO speed. The only place you could release satellites without boosting or slowing them is in fact the GSO station. Okay, I admit I was wrong. Though, boosting or braking a satellite in space is a lot easier than launching from Earth. Less fuel and power too. The Satellite's station keeping thrusters could do the work close to GSO orbit and anything else could just use kick motors. 

[Rejected Spawn]

Surprised nobody has mentioned the elephant in the room yet, or did I miss a post somewhere? Some propulsion tech can't be used anywhere near a base if you want to keep the base. Rather than bog such a fragile and destructive craft down with additional tiny stages to get it away from a ground colony it would be nice to just give it a good "push" of enough magnitude that it can fire up after a couple of seconds and go on its merry way. Not sure I'd specifically choose a rail for this purpose but a truly Kerbal insanity would be a spring loaded launch platform, if they can build an Orion they can surely boing a sizeable ship 200 meters straight up from a tall equatorial spot on Minmus? Would be far less tedious to assemble fragile ships in a low gravity colony than fly load after load of materials to orbit and still need to push it away from the builder with something other than the main engine.

Obviously the launch mechanism would have its structural limits (not too sure about being able to catapult an entire stellar exodus ship high enough to fire up safely) but it would certainly be in the Kerbal spirit of things to put an Orion on a catapult and call it a "safety measure". Launch clamps would probably have to be possible to autorelease at the end point though, getting the timing wrong there would still mean going to space but in many more directions at once.

Oh for the record I'm against space elevators in all forms for numerous reasons that others already stated, in addition to several other gripes I won't even bother listing because the odds of space elevator nonsense being in KSP2 is so close to zero it's not even worth debating.

[Incarnation of Chaos]

32 minutes ago, Rejected Spawn said:

Some propulsion tech can't be used anywhere near a base if you want to keep the base.

Orbital Assembelly+ a kick stage=problem solved.

[Rejected Spawn]

1 hour ago, Incarnation of Chaos said:

Orbital Assembelly+ a kick stage=problem solved.

1 hour ago, Rejected Spawn said:

-- Would be far less tedious to assemble fragile ships in a low gravity colony than fly load after load of materials to orbit and still need to push it away from the builder with something other than the main engine.--

-- I'm against space elevators --

I was in fact very clear with every aspect of my reasoning, the highlights don't mean you can just not bother reading anything else I've said - I use them to put emphasis on an important point so that a skimming reader can get a good idea of what my post is about and read the rest if the topic is of interest.

[nejc]

10 hours ago, GoldForest said:

The weight would be about 1/4th to 1/3rd the way to the Moon/Mun. Hardly interplanetary speed. 

Altitude alone is not indicative of the speed. It's 1/3rd the way to the moon at 24 hour period. This gives it a speed of 9.8 km/s. Sea level escape velocity is 11.2 km/s, and at 1/3rd the way to the moon the escape velocity is ~2.5 km/s. So quite interplanetary assuming I did the math right.

Furthermore, if the cable alone is used as the counterweight by just extending it beyond GEO without using dedicated weight structure, higher altitudes can be achieved. 

Edited September 10, 2019 by nejc

[GoldForest]

3 minutes ago, nejc said:

Altitude alone is not indicative of the speed. It's 1/3rd the way to the moon at 24 hour period. This gives it a speed of 9.8 km/s. Sea level escape velocity is 11.2 km/s, and at 1/3rd the way to the moon the escape velocity is ~2.5 km/s. So quite interplanetary assuming I did the math right.

Furthermore, if the cable alone is used as the counterweight by just extending it beyond GEO without using dedicated weight structure, higher altitudes can be achieved. 

Well, considering everything is moving at GSO speeds along the space elevator, relatively of course, it's not that hard to assume the counter weight is going fast enough that if it snapped it would hurl off into space. 3.07 km/s is the speed that the GSO station would be going on Earth. So the father from Earth you are from the GSO station, the higher the speed the higher stations would need to go to keep up. I'm not going to do the math, but the high orbit station and counter weight will be doing more than double or even triple the speed of the GSO station. 

[Incarnation of Chaos]

19 hours ago, Rejected Spawn said:

I was in fact very clear with every aspect of my reasoning, the highlights don't mean you can just not bother reading anything else I've said - I use them to put emphasis on an important point so that a skimming reader can get a good idea of what my post is about and read the rest if the topic is of interest.

Assuming I didn't read all of it was your mistake; I did and I highlighted the important portion to respond to. 

But if you want me to address all the points presented then here we go.

#1- the ship is too fragile and or the drive system too weak/dangerous to use on a base. 

If it's too fragile to sit on a pad then the sudden acceleration from a spring system like you described would completely obliterate it. 

#2- it would be easier to assemble it on the ground than in space.

This one I do have to give you; space is hard and requires adapting both the workers and equipment to it. But a facility dedicated to fabricating large vessels could mitigate this; and resupply largely automated.

 

 

[Rejected Spawn]

33 minutes ago, Incarnation of Chaos said:

-- If it's too fragile to sit on a pad then the sudden acceleration from a spring system like you described would completely obliterate it. --

Well if that was what you meant I can't agree with you regardless, the "spring system" works as a replacement for firing the main engine for about 2 seconds to get clear of the base in an extremely low gravity environment. The key here is that if you tried building the same craft on Kerbin it would possibly topple over and explode on its own; you can't put it on just any launch pad but by fragile I clearly don't mean it would explode from a force equivalent of using its own engine. The surface gravity on Minmus that I stated as a specific example due to its ease of access from Kerbin (and instead of the Mun that has a much higher surface gravity) is just under 0.5m/s2. Now let's say we need 200m distance to the base to fire the main engine safely, reaching this height requires launching with the final speed an object would have when dropped from the same height. This speed comes out to about 14m/s if I did the math right, at 0.8G that's less than 2 seconds of acceleration and a distance less than 15m and should be a tolerable stress for anything that can just barely survive actually using something like the Orion. Honestly this is the first time I did the math on it properly and it's even more realistic than I expected, my first "guesstimate" was a little over 1G for 2-3 seconds which is still within a reasonable Kerbal "spring launch" territory.

In practice it's probably no better than using a 3 second booster stage when it comes to getting clear but it's very Kerbal and doesn't leave a bunch of debris raining down on top of the precious colony full of loveable Kerbals. Heh, looks like I just convinced myself to actually vote for this spring launcher for more than just the comedy, hadn't even thought of the debris aspect until now...

[tseitsei89]

Mass drivers would be much more feasible on atmosphereless bodies. But that would be a nice idea. Space elevator, if implemented should be insanely expensive to build. I mean, it is HUGE!

[Guest]

On 9/8/2019 at 12:49 AM, GoldForest said:

A static space elevator on Earth is actually doable right now. 

A group of space elevator scientists calculated it would take, right now, $120 Billion Dollars to set up an elevator.

It would have two space stations, low earth orbit and high earth orbit, then there would be a weight in Geostationary orbit to keep the station from speeding up or slowing down. 

Source? Pretty sure it's not doable.

[tseitsei89]

1 hour ago, Aperture Science said:

Source? Pretty sure it's not doable.

Yep. I dont think we have materials that could handle the forces the elevator needs to endure...