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

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,205

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
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Registered: 2018-04-27
Posts: 11,960

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: 2,210

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)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

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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#230 2020-04-30 18:01:25

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

This topic has been quiet for a while, so here is an item to (try to) give it a boost ...

Somewhere in this topic (I could not find it) I ** think ** I recall kbd512 considering using microwave power to help with acceleration of a vehicle to space.

The patent I just found, while looking for microwave power transfer to moving vehicles, appears to be designed for use in a permanent location in the sky, which is pretty much what is needed for WiFi access for rural communities in the US (and other countries).

The patent may never have been given a chance at real world "life", but the current stay-at-home time is an example of how useful such a capability would be.

https://patents.google.com/patent/WO1995011828A1

(th)

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#231 2020-04-30 18:36:08

kbd512
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Registered: 2015-01-02
Posts: 6,205

Re: Un- conventional ways to LEO

tahanson43206,

Yes, you can direct a high-frequency microwave beam generated by a series of MW-class gyrotrons onto a heat exchange plate on the underside of the powered vehicle, basically the entirety of that surface, whereupon it superheats a monopropellant gas (such as H2) to produce solid core NTR-like specific impulse values without resorting to GW-class nuclear thermal rocket engines.  Some combination of EMALS and beamed power propulsion would provide the total dV increment required to attain orbital velocity and circularize the orbit- unless your goal is direct transfer orbit injection, in which case you just keep accelerating until you achieve escape velocity.

My "grand plan" was to have electromagnetic launchers on the moon / Earth / Mars used in conjunction with solar power stations in orbit that provide additional power to circularize low orbits or to achieve escape velocity.  There's more infrastructure to set up, but vastly less propellant to ship back and forth.  What comparatively little propellant is required could also be some kind of monopropellant gas that's otherwise required by humans, such as O2 and N2.  An electric propulsion system then takes over for cruise and you have 100% powered flight, coming and going.  We would also utilize on-orbit propellant depots filled with gases collected from the upper atmospheres of planets to avoid trucking any more propellant out of a gravity well than is absolutely necessary to achieve orbit.  We can sustain that model into functional perpetuity.  The various alternatives require far too much fuel for the ordinary person, typically of modest monetary means, to ever pay for their transportation.

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#232 2020-04-30 18:37:20

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

Here is an article from 2015 showing a proposal for a microwave powered spacecraft.

The key concept that i found interesting is the microwave absorbing heat exchanger.

https://www.visiontimes.com/2015/07/22/ … craft.html

This technology does not exist on the scale proposed, although the article implies some small tests have been done to show it might work.

Never-the-less, it ** is ** similar to what I understood to be kbd512's concept for delivering microwave power to a space going vehicle.

I am interested in the microwave absorbing heat exchanger for Void's moon launch steam rocket, which needs to be able to absorb enough energy from trackside suppliers to deliver 51.5 kilograms of water to the nozzle of the boiler at sufficient pressure to provide 245,000 Newtons of thrust.

This post is in Un-conventional ways to LEO, so I'll point out that a vehicle launched with sufficient velocity to escape the Moon ** could ** end up in LEO, with a bit of touchup retro-propulsion upon arrival at the Earth. 

Edit#1: Void is now disclaiming his having brought up the steam rocket idea (by accident) while posting about work done on steam rockets for asteroid exploration.

(th)

Last edited by tahanson43206 (2020-04-30 18:39:06)

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#233 2020-05-11 14:13:51

elderflower
Member
Registered: 2016-06-19
Posts: 1,262

Re: Un- conventional ways to LEO

Why would you convert the microwaves to heat and use it to drive a thermal rocket? Microwaves could be converted directly to electrical power and this can be used to accelerate ions, with a huge gain in specific impulse.

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#234 2020-05-11 17:13:01

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

For elderflower re #233

The objective under discussion is delivery of 10 tons of mass to Lunar escape velocity (using electromagnetic launcher) or 5 tons to Lunar escape using steam.

It would be interesting to learn that ion engines have progressed to the point they can deliver 245,000 Newtons of thrust.

As a reminder for forum readers who have just come across this discussion, a link to a paper about design of a nuclear fission rocket for Lunar escape is posted in the forum archives.  It should not be difficult to find, if anyone is interested.

It was that paper that convinced me that Void's original idea/question about the validity of steam as a propellant is feasible.

(th)

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#235 2020-05-11 19:04:08

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 26,733

Re: Un- conventional ways to LEO

Engine thrust is a summation game for ion and chemical engines...not just power and fuel/oxidizer types.

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#236 2020-07-14 14:10:57

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Un- conventional ways to LEO

Resurrecting the idea of a launch cannon.  The basis of the idea is to fire existing launch vehicles out of a large smooth bore gun, providing them with an initial boost of several hundred metres per second.  This should substantially increase the payload capability to orbit, by eliminating the fuel needed by the first stage in accelerating the rocket to the initial 300-700m/s and the gravity losses up to that point.  It also allows the lower stage to achieve better propulsive efficiency, as the burn does not begin until an initial velocity of several hundred metres per second is reached.  The most fuel intensive part of a rocket launch is the initial acceleration from zero to low sonic speeds, because the rocket experiences high gravity losses (which are a function of time spent in the gravity field) and poor propulsive efficiency during this period.

The goal is to develop a technologically simple cannon with low development and build costs.  Limitations of the device are as follows:

1. It is expected that the rocket vehicle will be a pre-existing design, with minimal design modifications and will be seated on a sabot during the acceleration phase.  The acceleration of the sabot is limited by the structural withstand of the rocket, payload and physiology of the passengers.  A tentative limit is 5g (50m/s2).

2. The assumption is made that the gun will fire the sabot straight up, thus minimizing gravity losses and allowing a more rapid transit into the stratosphere, where lower stage engines achieve better expansion ratio and are more efficient.

3. The tentative practical limit to the height of the cannon is taken to be 2km, roughly twice the height of the world's tallest buildings.  The cannon is assumed to be a steel tube, with lateral stability provided by bracing cables that are anchored to the ground using deep piles.

Assuming constant acceleration within the barrel, gives a muzzle velocity of 447m/s at a height of 2km.  The lower stage rocket engines would be throttled up following exit from the barrel and the vehicle would detach from the sabot.

As the intention is to use the gun literally thousands of times over its operational lifetime, the key costs involved are capital cost of building the gun and operational costs (energy, labour, maintenance, etc).  The benefits are increased payload capacity to orbit for existing rockets.  For example, the Falcon Heavy has a payload capacity of 63,800kg to LEO at a cost of $90million in reusable mode.  If we could increase that payload capacity by 30% say, at an additional cost of just a few million dollars per shot, then we have not only increased the mission capability of the rocket vehicle, but also reduced the per kg cost of reaching orbit by some 25%.

Last edited by Calliban (2020-07-14 14:44:20)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#237 2020-07-14 14:30:29

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

For Calliban re #236

Bravo! Best wishes for success with this new subtopic.

Something this ambitious would be a multi-person project in the real world.  In the virtual world here it might putter along as a one person inquiry, but considering the level of talent in the active membership, let alone the ** inactive ** membership, it may be possible to assemble helpful insights from a number of disciplines.

My assessment at this early stage is that the design of a slow burning chemical system to fill the piston at precisely the rate needed to sustain the pressures and temperatures that will be needed would fall into the purview of a chemical engineer.

However, I ** also ** suspect that the rate of delivery of fuel and oxidizer to a launch system of this nature is critical, and for that the services of someone comfortable with mechanical engineering would (I presume) be helpful.

Computer modeling would help at every stage of the development process.

To start things off, please consider setting a goal for the project team.

You've hinted at the scale of the  capability you would like to see, and you've (most recently) suggested a range of performance.

My recommendation is that you settle upon very specific goals to be achieved.  Ambiguity is a destroyer of momentum. Ambiguity is a destroyer of motivation.

The mass of the vehicle you would like to launch, plus a margin for confidence, seems to me like a good starting point.

A range of 300-700 m/s seems to me too wide ... you started out with a figure of precisely 500 m/s, and I'm hoping you'll be willing to consider returning to that.

Bravo (again) !!!

(th)

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#238 2020-07-14 15:09:58

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Un- conventional ways to LEO

Agreed, regarding the need to set specific design requirements.  It is difficult to know where to pin these.  A start would be to understand the structural design limits for acceleration for a candidate launch vehicle, the ITS being the most sensible at this point.  Once that is known, simplistically, the limit to muzzle velocity is set by the practical limits of how high we can build the barrel.  Ordinary cordite can propel rifle bullets to speeds of up to 4500 feet per second, so I think it unlikely that we will be limited by the speed of propellant gas molecules, which for an H2/O2 reaction is 4500m/s.

One thing that might be problematic is accelerating the sabot to supersonic speeds inside of the barrel.  At these speeds, air becomes incompressible,  and the forces exerted on the sabot will be extreme.  I previously toyed with the idea of either evacuating the barrel or filling it with hydrogen (which has a much higher speed of sound) to get away from this limitation.  But it may be that it isn't the problem I imagine it to be.  This is where CFD modelling is needed.

This is an interesting discovery:

'The booster return flights were expected to encounter loads lower than those experienced on the Falcon 9 reentries, principally because the ITS would have both a lower mass ratio and a lower density than Falcon 9.[25] The booster was to be designed for 20 g nominal loads, and possibly as high as 30–40 gs without breaking up.[25]'
https://en.m.wikipedia.org/wiki/Starshi … ort_System

A 20g acceleration through a 2km long barrel, would allow a muzzle velocity of nearly 900m/s.  That is nearly Mach 3.

Last edited by Calliban (2020-07-14 15:24:10)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#239 2020-07-14 15:21:37

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

For Calliban re #238

May I offer a suggestion here?

Dropping the barrel into the ground will have many advantages.

Chief among these is persuading a customer whose expensive (and delicate) rocket would be entrusted to your care, that the investment will not be lost due to failure of a hoist to get it to the top of a two kilometer lift.

Dropping the velocity to be imparted to the vehicle to under the speed of sound will help to alleviate the speed of sound problem.

300 m/s was in the bottom of the range you mentioned, and a customer whose rocket will be travelling that fast before it is released should be happy.

However, I cannot imagine ** any ** customer agreeing to ignite engines ** after ** the boost your system would provide.

Please consider that ** every ** liquid fuel rocket I know of fires the engines and insures they are at full thrust before the vehicle is released from the lockdown clamps.

In the case of the massive boost your system would provide, the piston would contain the massive lockdown mechanism to hold the vehicle.

I am definitely looking forward to seeing your sketch.  The image I have built up in my mind is (most likely) very far from what you have in mind.

Your mention of a sabot was the tip off .... I am imagining a piston engine configuration inside an automobile cylinder, and if you are thinking of a sabot then you are "seeing" something very different.

(th)

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#240 2020-07-14 15:39:54

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Un- conventional ways to LEO

The gun would need to be breach loaded I think.  You assemble the rocket on a pad built on top of the sabot, at ground level.  Whether we assemble it inside the gun breach or transfer it there using some kind of tractor, is a design detail that will need to be figured out.  After the rocket is safely clamped onto the sabot, you then seal a robust steel door before firing.

Not sure how the need to run the engines at full power before firing would work out.  But if we are accelerating the rocket and sabot at 20g, then I don't imagine it would be much of a problem.  We could actually vary acceleration for different launch vehicles.

One problem does come to mind.  If the rocket explodes, as they unfortunately do all too often, then it would likely take our billion dollar cannon with it.  That would be a very bad (and expensive) day.  It has a bearing on the design of the cannon.  It cannot be so expensive that we cannot afford to replace it.  We want something that is no more than a few times as costly as a new lower stage.  That suggests to me that the cannon should probably be tailored towards low cost, rather than high performance.  There are a lot of design options in terms of how we propel the sabot with the rocket seated on it.  Steam generated within the barrel; a chemical reaction releasing a propellant gas, or maybe even compressed air.  The ultimate limit to projectile velocity is the speed of the propellant gas, which is a function of temperature and molecular weight.  Linear electric motors are a possible option, although the power requirements are enormous and they must be generated by a generator that only operates for the few seconds it takes for the shot to clear the barrel.  One reason why I thought non-electrical propulsion was a more economical option.

Last edited by Calliban (2020-07-14 15:51:08)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#241 2020-07-14 17:51:54

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

For Caliban re #240

While we await your sketches, I am reminded of Jules Verne and his invention of a launcher ...

From the Earth to the Moon: A Direct Route in 97 Hours, 20 Minutes (French: De la Terre à la Lune, trajet direct en 97 heures 20 minutes) is an 1865 novel by Jules Verne. ... The character of Michel Ardan, the French member of the party in the novel, was inspired by the real-life photographer Félix Nadar.

From the Earth to the Moon - Wikipedia

Edit#1 ... I note your most recent post elevates acceleration from 5 G's to 20.

I'd have been happier if you'd stayed at 5. 

The Falcon 9 Manual says that full-weight payloads will take a maximum of 6g axial acceleration. so the peak of the blue line should be something under that, probably in the ballpark of 5g.Apr 12, 2016

Falcon 9 g-level/acceleration profile - Space Exploration Stack ...

Regarding an explosion of a rocket inside the launch tube .... My expectation is that if you analyze the process you may find that the forces generated by the chemical combination of fuel and oxidizer from the vehicle will contribute to the ejection of material from the barrel, and will not injure the barrel at all, since the entire mass (vehicle, fuel and oxidizer) will be under acceleration.

The difference between ignition of a shell travelling up a howitzer tube and this scenario, is that the shell contains powder that is designed and formulated to burn quickly.  A rocket filled with oxidizer and liquid fuel is NOT designed to burn quickly, although I'll admit that a sufficient quantity allowed to combine in a small volume may exert significant pressure on the walls.

Those walls will have been designed to withstand the pressure of a gaseous mixture of sufficient vigor to lift a multi-ton rocket at 5 G's.

Those will be sturdy walls.

Edit#1: There is a range of possibilities for a fixed location non-rocket boost system.

Calliban has opened the current initiative with a vision of a large structure able to post a fully loaded Falcon 9 rocket to 500 m/s in a run of 2 kilometers.

I am hoping the engineering details for a system of that capability will flow from the current discussion.

However, at the lower end of what is possible, there is the option to boost a one-passenger vehicle to LEO/ISS orbit.

In that case, the acceleration could be more than 3 G's, but because of precedent, I'd like to invite design of a system that can deliver a SSTO single passenger vehicle to orbit while staying at 3 G's for the entire trip.

The deepest mines on Earth are now in excess of 4 kilometers, so it is feasible to drop a boost system that far, as an outer bound.

The ideal solution would be an single passenger vehicle able to return safely to Earth, as the X-37b is doing today, with the additional touch that the second stage would also return safely to Earth after releasing the passenger capsule.

(th)

Last edited by tahanson43206 (2020-07-15 07:58:19)

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#242 2020-10-02 08:20:04

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Un- conventional ways to LEO

A link to a Wikipedia article that I hadn't read before: topic = Rocket Sled Launch.
https://en.m.wikipedia.org/wiki/Rocket_sled_launch

A few interesting quotes:

'The Space Shuttle used more than a third of its fuel just to reach 1,000 mph (1,600 km/h).'

'Due to factors including the exponential nature of the rocket equation and higher propulsive efficiency than if a rocket takes off stationary, a NASA Maglifter study estimated that a 270 m/s (600 mph) launch of an ELV rocket from a 3000-meter altitude mountain peak could increase payload to LEO by 80% compared to the same rocket from a conventional launch pad.'

'Rocket sleds at China Lake testing ground have reached Mach 4 while carrying 60,000 kg masses.[citation needed] A sled track that gave a Mach 2 or greater launch assist could reduce the fuel to orbit by 40% or more, while helping counter the weight penalty when aiming to make a fully reusable launch vehicle. Angled at 55° to vertical, a track on a tall mountain could allow a single stage to orbit reusable vehicle with no new technology.'

This would appear to indicate that even a modest propulsive boost from a sled or steam cannon, would result in large increases in rocket payload capability.  A 270m/s boost is still subsonic.  There are many propulsive technologies available for providing a rocket with an initial 270m/s takeoff velocity.  This is within the achievable velocity change of some very simple technologies like gas turbines, ram jets, steam cannons, steam rockets and even compressed air.  It seems to me that such options present no real technological challenges, it is just a question as to whether the reduced capital and operational costs of the launch vehicle outweigh the capital and operational costs of the cannon or sled.  This would depend on launch frequency more than anything else.

If a sled or cannon can be produced that reduces the fuel mass required to reach orbit by 40%, this would appear to be as much as is needed to allow the rocket vehicle to function as a single stage to orbit.  Mach 2 is 686m/s.  This is an achievable dV for a sled vehicle, mounted on a conventional rail track, propelled by gas turbines or ramjets.  A carbon steel tank full of supercritical water discharged through a delavelle nozzle would be even simpler, though substantially heavier.

One idea that comes to mind is to use a steam catapult to accelerate a sled to 500mph, before igniting ramjet engines on the sled.  This would appear to me to be a simple design that makes use of existing technology and is easily reusable, without adding too much weight to the sled.  High acceleration would appear to be an important consideration in minimising capital costs.  If acceleration of 10g can be achieved and tolerated, then track length would be 2.4km (1.5 miles) for a Mach 2 final velocity from standstill.  How we would decelerate the sled after payload separation is as an important consideration.  A smaller solid fuel rocket perhaps?

Last edited by Calliban (2020-10-02 09:46:07)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#243 2020-10-02 09:42:40

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,306

Re: Un- conventional ways to LEO

There was a 1950's movie--"When Worlds Collide"--which was produced by George Pal, utilized a rocket sled to assist a takeoff of the Earth escape ship. He also produced "Destination Moon." I was only a preteenager at the time of seeing these but they were a fun watch.

Last edited by Oldfart1939 (2020-10-02 09:43:44)

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#244 2020-10-02 10:16:55

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,306

Re: Un- conventional ways to LEO

A feature I DO remember from the film was the track carrying the rocket sled was initially DOWNHILL, and utilized gravity assist to get the whole works in motion. After reaching a dip, the sled engines took over and boosted the whole works uphill with the vessel's main engines firing only on the uphill portion of the flight.
Building such a launch system would be an enormous engineering undertaking, but would certainly be reusable many times. God only knows where the sled would land!

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#245 2020-10-02 14:40:17

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Un- conventional ways to LEO

Evel Knievel's Skycycle X-2 used for the Snake River Canyon jump used a steam rocket designed by Robert Truax.  Could we drive the sled to Mach 2 using a steam rocket?  This would be a tank of water heated to about 300C, with the water escaping through a nozzle to produce thrust.  The simplest and cheapest rocket imaginable, but the achievable velocity change is limited by the low effective exhaust velocity.  Could we get Mach 2 out of a steam rocket with an acceptable mass ratio?

NIST provide an excellent online resource for fluid properties under a huge range of conditions.
https://webbook.nist.gov/chemistry/fluid/

Water at 600K is liquid at 10MPa. Its internal energy is 1.322MJ/kg.  If the water expands through a nozzle to atmospheric pressure, what emerges will be a two phase flow of water vapour and liquid droplets at 100C.  The residual internal energy in the water droplets at 100C, is 417.4KJ/kg.  The difference in internal energy is 0.905MJ/kg, which is the kinetic energy of the droplets and vapour.  This equates to an exhaust velocity of 1.345km/s.  The rocket nozzle equation can be solved for an exhaust pressure of 1atm.
https://en.m.wikipedia.org/wiki/Rocket_engine_nozzle

This gives an exhaust velocity of 1.153km/s, which is remarkably similar to the estimate based on internal energy.  I could have gotten a closer answer by taking entropy into account, but I am lazy.  Mach 2 is about 700m/s.  Solving the Tsiolkovsky rocket equation for an exhaust velocity of 1153m/s and dV of 700m/s, gives a mass ratio of 1.83.  That means empty mass of the sled plus payload would be 55% of starting mass.  Looks feasible, so long as the pressure vessel doesn't weigh more than the water it contains.

Last edited by Calliban (2020-10-02 15:06:43)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#246 2020-10-02 15:51:43

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,733

Re: Un- conventional ways to LEO

This is similar to the flight deck catapults and eml on board the newest of carriers topic that kbd512 generated.

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#247 2020-11-27 23:26:16

kbd512
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Registered: 2015-01-02
Posts: 6,205

Re: Un- conventional ways to LEO

I'm putting this here because it's an interesting advanced concept under active development:

JP Aerospace - Airship To Orbit

A thorough "back-of-the-envelope" analysis of all the pertinent design concepts by someone who can do basic math:

Can JP Aerospace's Future Giant Airships Slowly Accelerate To Orbit? Looking At The Numbers by Robert Walker for Science 2.0

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#248 2020-11-28 07:46:29

tahanson43206
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Registered: 2018-04-27
Posts: 11,960

Re: Un- conventional ways to LEO

For kbd512 .... re #247

Thanks for bringing JP Aerospace back into view, and for doing so in a topic that is a better match for their initiative.

No doubt SpaceNut will find other references, but here is one: http://newmars.com/forums/viewtopic.php … 29#p163729

John Powell was interviewed multiple times on www.thespaceshow.com, if anyone is interested in hearing his personal recollections.

Broadcast 2882 John Powell of JP Aerospace Tuesday 14 Mar 2017

Broadcast 2402 Tuesday 27 Jan 2015 John Powell

Broadcast 2229 Tuesday 15 April 2014 John Powell

Broadcast 1864 Tuesday 02 Oct 2012 John Powell

Broadcast 1723 Tuesday 28 Feb 2012 John Powell

Broadcast 1297 Tuesday 26 Jan 2010 John Powell

Broadcast  972  Monday 30 Jun 2008 John Powell

Broadcast  667 Thursday 08 Feb 2007 John Powell

Broadcast  167 Tuesday 04 Nov 2003 John Powell

Edit: I note with some concern that the pace of appearances dropped off completely in 2017.

Edit#2: The most recent update to a company website (that I found) is from 2007:

http://www.jpaerospace.com/whatsnewjune-july07.html

Edit#3: I had forgotten that John Powell had begun to explore submarine technology ...

http://jpaerospace.com/blog/?p=7159 "Status of Bellavia" 

This entry was posted on Tuesday, June 26th, 2018 at 7:12 pm

The web page for the company was last updated September 2, 2020

http://www.jpaerospace.com/

I would imagine the  Covid pandemic has brought work at the company to a halt since is is entirely volunteer based.

Edit #4: I was not aware there is a book about the company:

https://dark-sky-market.myshopify.com/c … g-to-space

(th)

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#249 2020-11-28 08:46:37

kbd512
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Registered: 2015-01-02
Posts: 6,205

Re: Un- conventional ways to LEO

Edit: Content of post moved here, per request from SpaceNut.

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#250 2020-11-28 12:00:06

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,733

Re: Un- conventional ways to LEO

Please start a new topic on "develop micro capsules and micro space planes for both commercial and military purposes" KBD512, as its worth exploring in terms of what we have for the launchers which are in that arena.
Currently the large end of the plane would be the  x37 or DreamChaser but I think you are looking even smaller....

Good to see that JPAeroSpace is still plodding along with the launcher even if its slow progress.

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