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#226 2020-02-29 19:29:44

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,348

Re: Un- conventional ways to LEO

If we use electromagnetic acceleration for the first stage, then we can reasonably (no invocation of launch methods that impart extreme acceleration forces or use materials that aren't already commercial commodity products) and affordably (less energy / time / effort than conventional pad-based vertical rocket launches) accelerate an upper stage to booster burnout velocity before it ever leaves the ground for very little energy in comparison to the energy contained in a liquid chemical bi-propellant rocket.  The electrical energy required to achieve orbital velocity is roughly 28kWh/kg.  That said, if we only supplied the dV increment that a liquid chemical rocket booster provides, or perhaps a little extra to overcome the aerodynamic drag associated with a sea level Mach 5 to Mach 7 acceleration (the vehicle is only at sea level for a matter of seconds), then we have immediately thrown away 2/3rds of the propellant requirement to achieve orbital velocity and 2/3rds of the associated rocketry hardware.  This is not a final solution to the space launch problem so much as something that replaces propellant with electricity.  For a place like the Mars or the moon or asteroids with thin to non-existent atmospheres, it'd be an orbital or escape velocity solution.

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#227 2020-03-01 08:51:06

tahanson43206
Member
Registered: 2018-04-27
Posts: 2,202

Re: Un- conventional ways to LEO

For kbd512 re #226

The time may be right for another look at this concept.  The US Navy achievement you've noted in another topic may (may) indicate the technology is ready for real-world development for space launch.

For SpaceNut ... if it appears there might be interest in turning this specific technology into a focus for the NewMars forum, then it would seen potentially appropriate to create a unique topic for "Electronmagnet Boost First Stage" or something similar.  This topic, if created, would be undertaken with the objective of attracting and retaining volunteer contributors who would bring actual real-world experience to bear on the design problem.

As a reminder ... any project undertaken in this forum would be understood to be of an Open Source nature, and no patents or other claims of Intellectual Property can be asserted by any individual or group for ideas, methods or insights published here.

(th)

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#228 2020-03-01 09:08:02

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 351

Re: Un- conventional ways to LEO

kbd512 wrote:

If we use electromagnetic acceleration for the first stage, then we can reasonably (no invocation of launch methods that impart extreme acceleration forces or use materials that aren't already commercial commodity products) and affordably (less energy / time / effort than conventional pad-based vertical rocket launches) accelerate an upper stage to booster burnout velocity before it ever leaves the ground for very little energy in comparison to the energy contained in a liquid chemical bi-propellant rocket.  The electrical energy required to achieve orbital velocity is roughly 28kWh/kg.  That said, if we only supplied the dV increment that a liquid chemical rocket booster provides, or perhaps a little extra to overcome the aerodynamic drag associated with a sea level Mach 5 to Mach 7 acceleration (the vehicle is only at sea level for a matter of seconds), then we have immediately thrown away 2/3rds of the propellant requirement to achieve orbital velocity and 2/3rds of the associated rocketry hardware.  This is not a final solution to the space launch problem so much as something that replaces propellant with electricity.  For a place like the Mars or the moon or asteroids with thin to non-existent atmospheres, it'd be an orbital or escape velocity solution.

I think the basic limitation is the height of the barrel.  The tallest structures built to date are a little under 1km high and the Saudis plan on building a structure a little over 1km high.  The link below indicates that a building 2 miles (3.2km) high is feasible using existing technology with a few new innovations.
https://www.citylab.com/design/2012/08/ … -get/2963/

The base of the structure would need to be much wider than the top and hollow, not unlike the Eiffel Tower.  Of course, what we are planning is very different to an inhabited building.  We merely want a tube about 10m in diameter with conductor rails and electromagnets running up the inside.  Maybe that would be easier?  Maybe we could stabilise the structure using extended bracing cables that are attached to concrete piles anchored to the ground.

With a 3km tower, muzzle velocity at acceleration of 5, 10 and 15g, will be 550, 775 and 950m/s, respectively.  If we could build a 10km tower, a 15g acceleration (about the limit that people can withstand without passing out) would yield muzzle velocity of 1700m/s.  The final figure would be enough to replace the lower stage altogether, especially when you consider that 10km is 33,000' and two-thirds of Earth's atmosphere would be beneath you at that height.  Rail guns with muzzle velocities exceeding 2km/s already existing.  And it is theoretically possible at least to build a launch tower that high without enormous technological stretches.  The big question is how much will it cost?  And will there be enough launch traffic going into orbit to justify that cost?  My guess is that Musks starships would need to be launching dozens of times a day before the enormous cost of the electromagnetic launcher had any real chance of amortization.  None the less, if Musk makes good on his plan for a million person colony on Mars, the traffic volumes would appear to be sufficient to justify the capital cost.  It may make sense to build the 10km launcher by mid century.

In the meantime, a smaller and technologically simpler launcher, with muzzle velocity just beneath Mach 1, would be a useful tool for boosting the payload of the existing 2-stage Starship configuration.  A 1km long barrel, accelerating the Starship at 50m/s_2, would have muzzle velocity of 316m/s - just shy of Mach 1.  This would boost the propulsive efficiency of the lower stage and would reduce gravity losses.  The gain in payload should be substantial and the device is small enough and technologically simple enough that development and build costs should be modest.  There are lots of ways of propelling a projectile to sub sonic speeds.  Rail gun, coil gun, chemical propellant, steam and maybe even compressed air.  I think it is a promising concept, because it could operate very profitably in the short term.  We can build the tower out of structural steels, which are cheap to buy and easy to work with.  And at least part of the height is within the reach of conventional cranes, which makes fabrication easier.  We could construct the tower as a flanged tube with individual sections maybe 10m in length, which can then be bolted together.  Each section would have eyes attached to the flange to which bracing cables would be attached.

Last edited by Calliban (2020-03-01 09:19:53)


Interested in space science, engineering and technology.

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#229 2020-03-01 10:46:22

tahanson43206
Member
Registered: 2018-04-27
Posts: 2,202

Re: Un- conventional ways to LEO

For Calliban re #228

It is encouraging seeing you engaging with kbd512!

FYI ... The height of the tower reference (and barrel) reminded me that kbd512 is talking about an open top track, not a gun with a barrel.

I ** thought ** you were talking about what kbd512 was talking about, when you spoke of a launch track on the Moon.

However, communications in a text environment like this one can often reveal lags as individual contributors catch up with posts by others.

The previous launch proposals I have seen (as revealed by Google) seem to presume the launch will be at an angle, along a sturdy foundation such as a mountain.   Dr. Hunter's proposal for a sea based system was unique in that it could be pointed in both azimuth and elevation.

A mountain mounted launcher would be a fixed asset, but for customers who could live with the orbital plane that would be established, the launcher could be quite cost effective.

(th)

Last edited by tahanson43206 (2020-03-01 10:46:42)

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