[nthcolumn]

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 day...

[pjc50]

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.

[avian]

You still need to carry some fuel to achieve an orbit that does not intersect with the launch site. It's quite an old idea.

https://en.wikipedia.org/wiki/Space_gun

[binarymax]

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!

[ChuckMcM]

that works well on the moon because there isn't an atmosphere to speak of but on the earth trying to accellerate to 26km/hr at sea level is both very energy intensive, and the vehicle experiences intense heating due to the atmosphere. Atmospheric drag makes this idea impractical for pretty much anything.

[ChuckMcM]

as was pointed out offline, that is 26000 km/hr

[nthcolumn]

Yeow. Only good for rocks then.

[mrfusion]

You know I've been researching the very same idea. And guess what none of the math I've tried so far rules it out!

You do need a very big cable though. Think miles.

There are actually many promising technologies to get mass into space with much lower marginal cost. I think the problem is that they all have high capital costs and no one wants to take the risk on a new technology.

[tdb7893]

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

[mrfusion]

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.

[derekp7]

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.

[mrfusion]

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.

[vanattab]

I don't think you could build a cable that has the tensile strength to hold a payload spinning at 27+ km/s. Even if it was made of carbon fiber I think it would have to be crazy thick and massive. Probably orders of magnitude heavier then the payload itself.

[mrfusion]

Interesting thought. I was thinking just 1.6km/s for use as a first stage replacement. With a 60km tether that works out to only 4Gs. [1]

(1) http://www.calctool.org/CALC/phys/newtonian/centrifugal

[vanattab]

I don't think you could build a cable that has the tensile strength to hold a payload spinning at 27+ km/s. Even if it was made of carbon fiber I think it would have to be crazy thick and massive. Probably orders of magnitude heavier then the payload itself.

[nkoren]

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

[atonse]

Wouldn't the force required push the satellite so far towards the edge that it would get crushed?