# The Naked Scientists Forum

### Author Topic: Multi Ground Stage Space Launch Vehicle. Would it work?  (Read 7014 times)

#### CliffordK

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #25 on: 22/09/2012 23:59:25 »
Note the change of units for the calculated mag gun above at 36,000 kph, and the escape velocity of 11,190 kps.  [xx(]

With the U above, using gravity alone, one would get high speed at the bottom of the U, but not at the top, so it would be ineffective of aiding the launch.

However, the level, then curve up might be effective as it would be easier to create a long path allowing slow acceleration, and the elevation change from start to release might be less than a a vertical acceleration pathway.

#### wolfekeeper

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #26 on: 23/09/2012 15:52:26 »
A pure gravity U shaped track would essentially give no significant benefit over a static launch.
That's actually wrong. There's a (somewhat) significant advantage.

When you turn a rocket engine on, pointing downwards, you gain speed from the gravity and the rocket.

And then when you're moving, the rocket engine acts over the distance; generating work, so the faster you're moving the more energy you make.

The net upshot is that the rocket gains speed from turning on at the top of the U, going downwards and back up again.

#### CliffordK

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #27 on: 23/09/2012 19:39:31 »
Ok,
So, if you drilled a hole 5 miles deep for the launch, then you would have 5 miles of extra gravity to contend with, reducing the velocity by 9.8 m/s2 for every second until one gets back up to ground level.

If you launched horizontally, then turned up, you would not have to contend with the extra gravity during the initial acceleration phase.

Interesting thinking about the U-shaped launch.
So, if the time is greater for the downward path, and shorter for the upward path.
Then the effect of gravity may not in fact be symmetrical, and one may get and extra boost from the gravity.

The same would be true if you bored a hole through the center of the moon for some kind of a magnetic accelerator.  One would spend more time travelling towards the center of moon than away from the center of the moon.  And, thus would get an extra boost from the moon's gravity, albeit weak.

This time effect of gravity may also explain why there is a benefit of a nearly vertical launch of a wingless rocket vs launching at an angle, say 45 degrees.  One wants a launch that gets to as high of an altitude as possible, as quickly as possible.

#### wolfekeeper

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #28 on: 23/09/2012 19:57:53 »
The same would be true if you bored a hole through the center of the moon for some kind of a magnetic accelerator.  One would spend more time travelling towards the center of moon than away from the center of the moon.  And, thus would get an extra boost from the moon's gravity, albeit weak.
Oh, no, not weak at all, that would be a MASSIVE win!

You would wait till you reached very nearly the middle before turning on the rocket engine. You should always use rockets when you're going as fast as possible.

edit: Mmm come to think of it, you should light the rocket at the bottom of the U for the same reason.
Quote
This time effect of gravity may also explain why there is a benefit of a nearly vertical launch of a wingless rocket vs launching at an angle, say 45 degrees.  One wants a launch that gets to as high of an altitude as possible, as quickly as possible.
I think that that's just the Earth's atmosphere. In the absence of atmosphere you would launch very nearly horizontally, with the rocket angled to support its own weight, and to give as much sideways thrust as possible, although that would vary somewhat if you are trying to achieve a particular orbit, then you would launch more steeply upwards and then lean over.

The "time effect of gravity" is more normally called 'gravity losses' and are a thing though.
« Last Edit: 23/09/2012 20:01:10 by wolfekeeper »

#### Airthumbs

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #29 on: 08/01/2013 05:06:49 »
Did anyone see the successful test of the British inventors space rocket recently?  I did refer to him earlier on in the discussion and am very excited about it's development.  It uses air drawn into the rocket externally to power combustion.  I may have heard that it makes a 50% weight loss for the same performance as a normal rocket.  Interesting prospect for a combo Airthumbs solution :P

http://www.bbc.co.uk/news/science-environment-20510112
« Last Edit: 08/01/2013 05:10:41 by Airthumbs »

#### CliffordK

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #30 on: 08/01/2013 19:42:56 »
I'm glad to see work on Jet/rocket hybrids.

Do they count the extra weight for carrying liquid helium coolant?  Or, would the liquid hydrogen used for fuel be enough for the precooling?

Of course, helium has a much lower density than hydrogen.

#### Airthumbs

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #31 on: 14/01/2013 23:07:17 »
Hi Clifford K, I think the information you might be interested in can be found here... http://www.reactionengines.co.uk/sabre.html

The engine is called Sabre.

If this was used in conjunction with a ground launch system as discussed then I do not see how it would not work.  I have not seen any of the people at NASA, ESA or any of the private space companies give this a good look over yet but I hope they do as it would be great to get some feedback from the people who have all the experience.

I have e-mailed the company and asked them for some input into my idea so watch this space........ exciting times.
« Last Edit: 14/01/2013 23:11:10 by Airthumbs »

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##### Re: Multi Ground Stage Space Launch Vehicle. Would it work?
« Reply #31 on: 14/01/2013 23:07:17 »