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Circular Runways [video]

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Re: Circular Runways [video]

#21

Post by nkoren »

nthcolumn wrote: post #8

Okay only slightly related, I had an idea a long while ago for putting satellites into orbit where you just fling them? I didn't think it good for humans because of the G but for stuff. The win being that the power required is all on earth and you don't have to carry fuel with the payload. You could spin them up on a centrifuge and then let go at just the right time (and angle). I was going to mention it to Elon one…

Start by researching this: http://www.nextbigfuture.com/2013/07/250000-slingatron-kicks...

Re: Circular Runways [video]

#22

Post by derekp7 »

mrfusion wrote: post #18
tdb7893 wrote: post #17

Earlier quoted context omitted.

Wouldn't the problem be air resistance? I thought you generally need to bring fuel with you because if you don't the air will brake you too much

Air resistance hurts you for sure. but the prospect of not bringing your fuel with you (see the rocket equation) really saves the most. In my design I have the ship tethered by a cable and a pipe that's delivering the fuel.

Orbital velocity is about Mach 25. You would need to be going much faster than that, if your only power is applied in the atmosphere (you'd need enough additional speed to get above the atmosphere, and enough to overcome air resistance. And after the cable lets go, the the orbit will be elliptical, which means that at the end of one orbit you come right back to the launch site. So you need to bring enough fuel with you to flatten out the orbit once you are at the highest altitude. Oh, and then you have the weight and tensile strength of the cable, so similar issues to that faced by building a space elevator.

A better idea is the launch loop, but again you have to deal with cable weight and tensile strength.

Re: Circular Runways [video]

#23

Post by pjc50 »

nthcolumn wrote: post #8

Okay only slightly related, I had an idea a long while ago for putting satellites into orbit where you just fling them? I didn't think it good for humans because of the G but for stuff. The win being that the power required is all on earth and you don't have to carry fuel with the payload. You could spin them up on a centrifuge and then let go at just the right time (and angle). I was going to mention it to Elon one…

This sounds related to "railgun launch": http://physics.stackexchange.com/questions/35139/what-is-the... and http://physics.stackexchange.com/questions/35921/could-we-ma...

The main limitations are surviving the hypersonic launch and short trip through the atmosphere, and you still need a second stage to get into a stable orbit. Your launch vehicle would basically be an upwards-travelling meteor.

Considerably more viable on the moon; lunar escape velocity is "only" 2.38km/s and there's no atmosphere. There's lots of 70s moonbase concept art depicting the use of rail launchers to return mined material to earth. Although I'm not sure it would be economically viable even if the moon were made of solid platinum.

Re: Circular Runways [video]

#24

Post by binarymax »

nthcolumn wrote: post #8

Okay only slightly related, I had an idea a long while ago for putting satellites into orbit where you just fling them? I didn't think it good for humans because of the G but for stuff. The win being that the power required is all on earth and you don't have to carry fuel with the payload. You could spin them up on a centrifuge and then let go at just the right time (and angle). I was going to mention it to Elon one…

There was a kickstarter for this idea that I posted several years ago: https://news.ycombinator.com/item?id=6092668

https://www.kickstarter.com/projects/391496725/the-slingatro...

It didn't get backing but was a fun idea!

Re: Circular Runways [video]

#25

Post by SteveNuts »

nkoren wrote: post #20
Nrsolis wrote: post #4

Yeah. Not so much. http://www.airliners.net/forum/viewtopic.php?t=1357935#p1941...

A lot of idiots on that forum. "Hey, in just two minutes of casual thinking about this, I've identified a flaw which a professional working on this for years has been unable to see!" Um, yeah, not so much. The concept may have problems, but that's not how it'll be debunked.

That sounds a lot like a lot of comments on HN honestly.

Re: Circular Runways [video]

#27

Post by Applejinx »

Nrsolis wrote: post #4

Yeah. Not so much. http://www.airliners.net/forum/viewtopic.php?t=1357935#p1941...

Well that's interesting. They seem to be arguing that the bank angle is super high, causing the planes to pull massive Gs just to land or take off, and that's terrible.

Even if it's true all that means is,

(a) planes achieving takeoff instantly have better than stall speed in the open air and can safely get up and away from the city,

(b) planes landing can come in at any angle, have infinite space to negotiate a decent landing and no specific window to hit as far as retaining enough runway, plus the landing speed is significantly higher than stall speed in free air. That directly improves the controllability of the aircraft.

The guy's right, this would work just fine. Even without a bank and increased G forces, it's not a bad idea, but when you include the reality of the banking increasing takeoff/landing speed over normal stall speed, it becomes a slam dunk. Very good idea anywhere you can afford to build three or more runways in your airport.

Re: Circular Runways [video]

#28

Post by mrfusion »

derekp7 wrote: post #22
mrfusion wrote: post #18

Earlier quoted context omitted.

Air resistance hurts you for sure. but the prospect of not bringing your fuel with you (see the rocket equation) really saves the most. In my design I have the ship tethered by a cable and a pipe that's delivering the fuel.

Orbital velocity is about Mach 25. You would need to be going much faster than that, if your only power is applied in the atmosphere (you'd need enough additional speed to get above the atmosphere, and enough to overcome air resistance. And after the cable lets go, the the orbit will be elliptical, which means that at the end of one orbit you come right back to the launch site. So you need to bring enough fuel with y…

Yes good points. I envisioned it more as a first stage and partial 2nd stage replacement. You'd still need to bring some fuel like you said.

In my design the vehicle would feed its rockets from an onboard fuel tank which would be constantly replenished from the pipe/tether. At detachment time it would still have a full tank to manage drag, getting up to final speed, and circularizing the orbit.

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