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#176 2019-07-20 18:10:16

GW Johnson
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From: McGregor, Texas USA
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Re: Un- conventional ways to LEO

200 kg to LEO is within the capability of the final version of the old "Scout" satellite launcher of the 1960's through the 1980's.  It was a 4-stage solid that was utterly reliable and quite inexpensive for the times.  I got to work on it as a graduate student summer hire at LTV Aerospace in 1974.  They lost 1 in the 4-flight flight test program, then not another failure in over 3 decades' service launching satellites.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#177 2019-08-08 16:35:19

Terraformer
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Re: Un- conventional ways to LEO

How about an air-augmented rocket airship for the lower stage? Use the large frontal area as a funnel to collect the thin atmosphere, and use it as additional remass to achieve a far higher effect Isp than you'd otherwise have.

Lower down and subsonic, perhaps such funnels would allow very efficient propeller driven airships to be constructed.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#178 2020-02-20 17:42:19

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 530

Re: Un- conventional ways to LEO

Terraformer wrote:

How about an air-augmented rocket airship for the lower stage? Use the large frontal area as a funnel to collect the thin atmosphere, and use it as additional remass to achieve a far higher effect Isp than you'd otherwise have.

Lower down and subsonic, perhaps such funnels would allow very efficient propeller driven airships to be constructed.

The idea of a sub sonic lower stage is interesting.  It would be less efficient in one way, because it would suffer high gravity losses.  However, given that oxygen is about 80% of the mass of rocket propellant, a fully air breathing stage would still appear to have a significant advantage.  The link below provides details on the thrust-weight ratio of jet engines.

https://www.grc.nasa.gov/www/k-12/BGP/D … nswers.htm

The Boeing 747-400 engine has thrust-weight ratio of 6.  This raises an interesting question: could we build a lower stage using turbofan jet engines, mounted in a ring around the circumference of the stage?  Could it achieve vertical takeoff?

If we could ride a stage like that up to 40,000 feet, say, and launch the upper stage at 600mph, then you have provided upwards of 1km/s of delta-v when gravity losses and air resistance are accounted for.

I can remember Musk saying that the BFR upper stage could have functioned as an SSTO, but would have had close to zero payload capacity in this mode.  I wonder what the payload capacity would be with an air breathing lower stage if it could provide, say, 2km/s total dV?  Could the jet engines slow the stage down from landing using some kind of reverse thrust mode?

Last edited by Calliban (2020-02-20 17:46:36)


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#179 2020-02-20 17:49:55

SpaceNut
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Re: Un- conventional ways to LEO

The entry of the oxygen is gasseous and it needs to be in a liquid form for the system to use it. The liquidation is possible but to get the rocket moving you still need a starter level of oxygen to gain speed. Once you reach that edge of space at the 24 mile mark you need all remaining air onboard and the ramjet inlet closed for the remaining part of the journey as you are traveling above mach 5.
The saber rocket and a few others come to mind for the use there in for scam thrust all the way off from this rock called earth.

hypersonic

Russia tests SCRAMJET - Working on thir spaceplane

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#180 2020-02-20 18:14:55

Calliban
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Posts: 530

Re: Un- conventional ways to LEO

A steam cannon would be an interesting way of eliminating the need for a lower stage.  Imagine a long vertically mounted steel tube, with a starship upper stage mounted on a sabot within it.  The sabot would sit on top of a cage at the bottom of the barrel, containing super heated rocks with a temperature of a 1000C.  To launch the rocket, we would pump water into the rock bed, probably using a centrifugal pump.  The steam would be heated to several hundred degrees centigrade.  At that temperature, the average speed of the water molecules will be 1km/s and pressure would build up beneath the sabot, accelerating it and the starship stage sitting on top of it.  We would continue pumping more water into the rock bed to maintain steam pressure behind the sabot as it accelerates vertically up the barrel.

If the starship and sabot accelerate at 5g and the barrel is 2km high, then the starship will leave the barrel at a speed of 450m/s.  The actual contribution to delta-v would be more impressive, because the propulsive efficiency of rocket engines is very low when accelerating from zero off of the launch pad and gravity losses are very high.  The idea would be to fire straight up to allow the upper stage engines to switch on at a height of 10,000 feet and a speed around Mach 1.

It would be interesting to understand what sort of performance would be needed from a steam cannon to eliminate the need for a lower stage altogether and still allow for good payload capacity.  Is a muzzle velocity of 450m/s at 6500 feet enough to allow the upper stage to reach orbit with good payload fraction?

The thing I do like about this idea is that everything about it is low tech.  The steel barrel would be a 2km tall tower, stabilised by bracing cables.  The tower could be formed from segments that are flanged or welded together.  The rock bed at the base of the barrel, could be heated slowly using excess electricity from the grid.  Intermittent energy would do, as the heat capacity of the rock would be huge and thermal losses to the surroundings would be prevented by many metres of rock, sand and gravel, which would provide both thermal inertia and insulation.

The rock bed would probably be heated either by heating elements, with heat transferred to the rock using a fan.  It would be even more efficient if the heating were accomplished using the exhaust gases from an open cycle gas turbine.

On the moon, a cannon could be powered by burning a rich mixture of magnesium and oxygen.  The flame would reach temperatures of 3000C, at which the mean molecular speed of magnesium atoms would reach 1500m/s.  A plasma arc generated in magnesium vapour would be more energy efficient, but would require a lot of electric power.

Last edited by Calliban (2020-02-20 18:55:18)


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#181 2020-02-20 18:41:27

tahanson43206
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Re: Un- conventional ways to LEO

For Calliban re #180

Interesting concept!

For SpaceNut ... is this the first time someone has come up with a positive use of steam for launches? 

My recollection is that steam has been discounted as a propellant, but I can't remember now if that was in this forum or elsewhere.

In any case, Calliban's ideas seems new and quite plausible to me, and NOT subject to the criticisms of proposals of carrying water along in the vehicle to make steam along the way.

Finally ... the main engines of the Space Shuttle ** were ** steam engines, and very effective ones.  The difference was they MADE steam, and did not just use it as throw mass.

(th)

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#182 2020-02-20 18:59:44

SpaceNut
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Re: Un- conventional ways to LEO

simple search on steam for 6 topic areas returned 13 pages of 30 topics a page for the word being used.

I do remember thrusters and microwave energy to make a satelite move in a topic with the use of water but not a barrel gun approach to a massive stage to be fired from it.

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#183 2020-02-20 21:41:33

kbd512
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Re: Un- conventional ways to LEO

I still think an electromagnetic launch followed by microwave propulsion is the most economical way to get to orbit.  The first 4 km/s to 5 km/s of the dV increment would be provided by the launch loop, eliminating the need for a booster entirely, and the upper stage would have an Isp equivalent to a nuclear thermal rocket using microwave heating of Hydrogen propellant.  The propellant mass fraction then becomes very similar to what a fighter jet consumes over the hour or so that it can remain airborne on internal fuel per ton of delivered payload.  We could launch once per hour with minimal resource expenditure using a small fleet of robotic payload delivery vehicles.  During the course of any given year, a single electromagnetic launch system would deliver more tonnage to orbit than all of humanity has sent into space during the entire history of human space flight.

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#184 2020-02-21 05:14:27

tahanson43206
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Re: Un- conventional ways to LEO

For kbd512 re #183

I like the idea you've described, and would be interested to read a sequence you've written about it.  You've written at such length on so many topics it would help if you would add a search tag to the sequence you've written on THIS topic.  GW Johnson provided an example of how that would work, with his sequence using the tag "EducationDoneRight".  The tag you choose is up to you, but once you've chosen the tag, just edit the posts you want to include and Voila! any forum reader can study the entire sequence in a single sitting.

(th)

Last edited by tahanson43206 (2020-02-21 05:15:03)

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#185 2020-02-21 05:29:55

tahanson43206
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Re: Un- conventional ways to LEO

For Calliban re #180 ... continuing ...

By any chance are you familiar with the work of Dr. John Hunter?  Your vision of a gas pump for a large payload reminded me of Hunter's ballistic launcher concept.  The key difference is the working fluid.  Your choice is water, which has a higher molecular weight.  Hunter is proposing Hydrogen, with the lowest possible molecular weight.  As I understand Hunter's concept, the physics is such that the hydrogen lifting fluid is capable of accelerating a payload to near escape velocity.  Hunter plans (as you do) a rocket motor finishing stage to round out the ellipse into a circle.

Another example, this time from the military, is use of (I think) compressed air to pop ballistic missiles out of submarines under the surface of the ocean, proving that modern engineering can solve the many problems that come with lifting a heavy mass out of a tube with a velocity sufficient to clear the water and allow for ignition above the surface.

Your suggestion of a length of the launch tube of two kilometers is similar to Hunter's design.  He proposed a 1 kilometer launch tube for a payload mass of (as I recall) of a metric ton or less.  Hunter's design could be mounted permanently on a mountain side, but the more interesting implementation would be a tube floating in the ocean which could be positioned to meet a customer's requirements.  I expect the change in orientation of the tube would take a number of hours, depending upon how great the change might be, but once pointed it should be possible to hold position relatively easily.

However, the aspect of your post that ** really ** caught my attention was your interesting solution to the rapid heating problem for a system of this type. Dr. Hunter has been (probably deliberately) vague about how he would heat the liquid hydrogen he'd use for propulsion.  I've been wondering about that, and your solution is so simple I'm wondering if a variation of the long heat soak idea might be what Hunter has in mind.  If he heated up a mass of metal to a sufficient temperature, and then introduced a flood of hydrogen gas, he could (presumably) feed the acceleration tube at a rate sufficient to boost the payload over the one kilometer run.

You can find video and text about Dr. Hunter's project, and he has contributed several interviews on TheSpaceShow.com.  I'd like to see both your ideas come to pass.

(th)

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#186 2020-02-21 06:18:01

Calliban
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From: Northern England, UK
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Re: Un- conventional ways to LEO

tahanson43206 wrote:

For Calliban re #180 ... continuing ...

By any chance are you familiar with the work of Dr. John Hunter?  Your vision of a gas pump for a large payload reminded me of Hunter's ballistic launcher concept.  The key difference is the working fluid.  Your choice is water, which has a higher molecular weight.  Hunter is proposing Hydrogen, with the lowest possible molecular weight.  As I understand Hunter's concept, the physics is such that the hydrogen lifting fluid is capable of accelerating a payload to near escape velocity.  Hunter plans (as you do) a rocket motor finishing stage to round out the ellipse into a circle.

Another example, this time from the military, is use of (I think) compressed air to pop ballistic missiles out of submarines under the surface of the ocean, proving that modern engineering can solve the many problems that come with lifting a heavy mass out of a tube with a velocity sufficient to clear the water and allow for ignition above the surface.

Your suggestion of a length of the launch tube of two kilometers is similar to Hunter's design.  He proposed a 1 kilometer launch tube for a payload mass of (as I recall) of a metric ton or less.  Hunter's design could be mounted permanently on a mountain side, but the more interesting implementation would be a tube floating in the ocean which could be positioned to meet a customer's requirements.  I expect the change in orientation of the tube would take a number of hours, depending upon how great the change might be, but once pointed it should be possible to hold position relatively easily.

However, the aspect of your post that ** really ** caught my attention was your interesting solution to the rapid heating problem for a system of this type. Dr. Hunter has been (probably deliberately) vague about how he would heat the liquid hydrogen he'd use for propulsion.  I've been wondering about that, and your solution is so simple I'm wondering if a variation of the long heat soak idea might be what Hunter has in mind.  If he heated up a mass of metal to a sufficient temperature, and then introduced a flood of hydrogen gas, he could (presumably) feed the acceleration tube at a rate sufficient to boost the payload over the one kilometer run.

You can find video and text about Dr. Hunter's project, and he has contributed several interviews on TheSpaceShow.com.  I'd like to see both your ideas come to pass.

(th)

Tahanson, hydrogen is most efficient as a propellant gas as it has the lowest possible molecular weight and therefore the highest molecular speed.  But the best propellant gas depends upon the anticipated muzzle velocity of the gun.  For a gun launching a projectile, the speed of the projectile obviously cannot outpace the speed of the propellant gas.  The speed of molecules in a gas follows the Boltzmann distribution, with the most probable speed being:

V=sqrt(RT/mm)

Where V is velocity in m/s; R is the gas constant (8.31); T is temperature in K; mm is molar mass in kg/mol.  As the velocity of the projectile increases beyond the most probable speed, the expanding gas becomes less and less efficient in accelerating the projectile.  Hydrogen at 2000K has a most probable speed of 2.88km/s.  If we aren't worried about acceleration, then a gas gun using hydrogen propellant could accelerate projectiles to muzzle velocity of 3km/s with good efficiency.

I suggested water/steam as propellant because: (1) the acceleration of the Starship upper stage in flight reaches a peak of 5g.  I do not know how close this is to the design limit, so I assumed it could not be exceeded.  Dubai is planning to build a tower 1km high, so I assumed that 2km would be achievable for the cannon.  Put these two constraints together and maximum muzzle velocity comes out at 447m/s.  If acceleration could hit 7g, then muzzle velocity could reach 529m/s.  At 600C (873K) the most probable speed of a water molecule is 635m/s; so steam at superheat temperatures is adequate to accelerate the starship upper stage, given the design constraints.  (2) Water is a room temperature liquid: it is very cheap, non-hazardous and can be pumped very easily.  We could even use hydrostatic pressure to transfer water into the gun barrel and just open a valve into the chamber.

Using hydrogen, we could accelerate the starship to 3km/s.  But if the acceleration limit is 5g, the tower would need to be 90km high.  If 7g, it would be 64km.  Either way, it is probably not achievable.  If the payload is a dumb projectile, the acceleration could exceed 1000g and the gun barrel could be as short as 450m.  The projectile may reach a height of a few hundred km, though it would have no tangential velocity required to achieve orbit.


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#187 2020-02-21 17:08:31

SpaceNut
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Re: Un- conventional ways to LEO

Of course with a gun like cannon firing the barrel is made to allow for very little lose around the round that is being fired in the chamber. So the exit velocity is compensated in a delta equation that gives the average velocity for time spent from start to exit.

Mad Mike is a flat lander that is building a steam powered rocket to see if its flat https://www.space.com/mad-mike-steam-ro … -show.html

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#188 2020-02-21 20:47:56

tahanson43206
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Re: Un- conventional ways to LEO

For Calliban re #186

Using hydrogen, we could accelerate the starship to 3km/s.

I have quoted your theoretical prediction above, because I found that your prediction matched actual research results.

Thus, my assessment of your capability is increased.

https://en.wikipedia.org/wiki/Super_Hig … ch_Project

Tests and cancellation
Headed by John Hunter, the SHARP gun fired projectiles using expanding hydrogen and achieved velocities of 3 km/s (6,700 mph) or Mach 8.8 for 5 kg (11 lb) projectiles. Had the project continued, there were plans to elevate the tube and begin space launch trials potentially reaching speeds of up to 7 km/s (16,000 mph), or about Mach 21.[1]

(th)

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#189 2020-02-22 08:24:40

elderflower
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Re: Un- conventional ways to LEO

A slight issue with these designs is that the tube is filled with air that must also be accelerated out of the end. It isn't much of an issue with a regular gun barrel but we are talking about kilometre lengths.
Ideally we would evacuate the tube before firing and this might be done by purging it with anhydrous ammonia and fitting a burstable membrane over the end. A water spray would absorb the ammonia (it is very strongly absorbed by cold water) and deliver a partial vacuum in the tube. Pump the ammonia solution out and recover the gas for the next shot. The higher the outlet end of the tube is the lower the atmospheric pressure will be at the top and the lighter the cover can be.  There may be other combinations of gas and solvent which would produce a better vacuum, or purging with steam and allowing it to condense after fitting a cover, might be considered. This would need a temperature regulated  barrel to avoid formation of ice frost.
When the projectile exits the end of the tube in a cloud of hydrogen and ignites its engines, there might be some interesting pyrotechnic effects.  This may well happen without the projectile igniting it as you may expect large static discharges, so I would suggest that we don't use hydrogen. Steam used as a propellant will require the barrel to be heated but there will be less of a fire/explosion risk.
In the gold mines on South Africa's rand there are shafts of large diameter with depths of  three thousand metres and more. Obviously if you installed your system in one of these it is going to be simply vertical and not steerable. The floating tube may have recoil issues that would prevent accurate directional launching of the projectile.

Last edited by elderflower (2020-02-22 08:28:32)

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#190 2020-02-22 14:43:17

Calliban
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From: Northern England, UK
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Re: Un- conventional ways to LEO

Elderflower,

The tube will probably need to be purged, because the muzzle velocity is supersonic.  At this speed, the air ahead of the projectile behaves like an incompressible fluid and will exert a back pressure on the projectile, reducing efficiency and requiring higher driving pressure.  Purging is sensible but will complicate design, as prior to firing the tube will be under vacuum.  Ammonia is an option as a purging gas and has the advantage that it can be condensed to liquid on a cold surface.  Another possibility is to fill the tube with steam.  This will push out the air and as it cools, it will condense into liquid which can be pumped out of the chamber.  At 20C, the residual pressure in the tube will be down to 23mbar.

I like the idea of launching from a vertical well.  Elon Musk is putting money into boring machines.  So maybe this is an option that has crossed his mind.  If we could build a 5km tube, with the bottom 3km beneath the ground; and accelerate at 7g, then muzzle velocity could be increased to 820m/s and delta-v would be 840m/s.  This should be enough to push the upper stage to around 80,000 feet (assuming that around 1/3rd of kinetic energy is lost to air resistance).  This shaves almost 1km/s off of the total dV needed to reach orbit and allows the upper stage engines to fire in a vacuum.

Last edited by Calliban (2020-02-22 15:00:11)


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#191 2020-02-22 16:00:21

SpaceNut
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Re: Un- conventional ways to LEO

What ever is holding the vaccumn before launch must move out of the way before it gets to close to the top of the barrel. That means it will have only that distance for the 1 atm to refill the tube in front of the rockets ever drawing close to the tops distance for back pressure that will reduce the speed of exit.

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#192 2020-02-22 17:10:56

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 530

Re: Un- conventional ways to LEO

SpaceNut wrote:

What ever is holding the vaccumn before launch must move out of the way before it gets to close to the top of the barrel. That means it will have only that distance for the 1 atm to refill the tube in front of the rockets ever drawing close to the tops distance for back pressure that will reduce the speed of exit.

Ideally, the barrel would be evacuated.  If it isn't, the driving pressure of the charge would need to be greater in order to clear the gas in front of the projectile.  The barrel would need to be thicker and heavier to accommodate the increased driving pressure, which would push up cost.  Perhaps we could blow open a hatch on top of the tube with compressed air, a second before the upper stage reaches it?  The problem with evacuating the tube, is that thin vessels are vulnerable to buckling when they are subject to compressive forces.  This makes vacuum vessels much heavier than one would expect for the forces involved.

An alternative would be to fill the tube with a gas with a greater speed of sound than ordinary air.  If the speed of sound is greater than the peak velocity of the projectile, then the gas can compress ahead of the projectile and the back pressure will be much lower.  The speed of sound in a gas is approximately equal to sqrt(pressure/density).  You will note that if temperature is constant and you halve the pressure of a gas, you also halve density, so the speed of sound is unaffected.  To increase the speed of sound, you must maintain pressure whilst reducing density.  This implies either heating the gas, or using a gas with lower molecular weight.  Gases with lower molecular weight than air, are hydrogen, helium, methane and steam.

Last edited by Calliban (2020-02-22 17:21:11)


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#193 2020-02-22 18:15:37

SpaceNut
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Re: Un- conventional ways to LEO

Its the rate of inlet pressure for the steam that is also with issue for acceleration as the start and flow must keep ahead of the drop in pressure caused by the object moving upward in the barrel length.
The wider diameter will hurt performance as in a Dragon vs a starship for ability to launch the rocket.
https://www.grc.nasa.gov/WWW/K-12/rocket/rktstomp.html
rktstomp.gif

slaunch.gif

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#194 2020-02-23 07:56:45

elderflower
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Re: Un- conventional ways to LEO

Ammonia is also a light molecule, Caliban. MW =17. However, I believe a vacuum is a better solution.
Admission of more propellant to the tube at higher elevations as the projectile passes  injection points, is a possibility to improve performance. It has been tried in very large artillery pieces.
The cap can be a simple bursting disc. These are widely used in chemical and petroleum industries The outward dome pattern enables it to be made from friable material which is kept in compression by the external pressure. As the projectile shoots up the tube the residual gas will build up in front of it and blow the bursting disk away before it arrives at the  tube exit.
I did consider such a boost device a long time ago, but mine was to have been supported by toroidal helium balloons. I decided it was unlikely to be practical due to atmospheric movement.

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#195 2020-02-23 12:38:26

tahanson43206
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Re: Un- conventional ways to LEO

For Calliban re #186

This is a continuation of discussion of your clarification of computation of the velocity that might be obtained from a ballistic launcher using Hydrogen as the working fluid.

Because Dr. John Hunter is predicting a velocity at the muzzle for his design, I worked my way through understanding your presentation, and then computed the temperature T that would (presumably) have to exist in the barrel of the launcher for the payload to reach 6 Km/second.

I'll paste my work here and invite your review:

https://www.engineeringtoolbox.com/indi … d_588.html

Individual gas constant for hydrogen (from table)

I succeeded in replicating Calliban's results …

The Universal Gas Constant appeared later in the table as 8.31

V=sqrt(RT/mm)

R equals 8.31

T = 2000

mm = 2.016 grams per mole or .002016 Kg/mole

The result is given in meters per second: 2871 so converting to km/s gives 2.87 which is close enough for this analysis.

Now proceeding to Dr. John Hunter's plan for a hydrogen launcher:

From Wikipedia we have:

For Dr. John Hunter (Quicklaunch)

The proposed launcher was designed to give projectiles an initial speed of 6 km/s (3.7 mi/s) while the Earth orbital speed is 6.9 to 7.8 km/s. The projectile design therefore included a one-stage rocket which ignites some time after launch. The designed payloads could include spacecraft, satellites, consumable, water or fuel to supply a propellant depot in orbit.

Formula: V= sqrt(RT/mm)

For 2000 T and 8.31 R divided by .002016 Kg/mole, V = 2871 meters per second

V**2 = RT/mm

V**2*mm = RT

V**2*mm/R = T

So: 6000 meters per second * .002016 / 8.31 should reveal temperature

8,733 T

This number is substantially higher than 2000.  I'm not sure if it is meaningful in the context of a "real world" design.

It would be 8459.85 degrees Celsius.

This temperature would have to persist (I would assume) for the duration of the flight of the payload along a 1 km launch tube.

(th)

Last edited by tahanson43206 (2020-02-23 12:43:23)

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#196 2020-02-23 13:23:55

Calliban
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Posts: 530

Re: Un- conventional ways to LEO

Tahanson, at temperatures greater than 2000K, diatomic hydrogen starts to break down into atomic hydrogen.  By 3000K, about 2/3rds of the hydrogen has broken down and at 4000K, the transition is complete.  So at 3000K,  the molecular mass of hydrogen is 1.33 and at 4000K it is close to 1.
http://capturedlightning.com/Papers/Mon … drogen.jpg

So the gas would not need to be 8000K to reach 6kms.  Just a tad over 4000K.  And remember the speed of the gas follows a distribution curve and 6kms is merely the average.  Still, you would need microwaves or an electrical discharge to get the gas that hot.

Last edited by Calliban (2020-02-23 13:29:08)


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#197 2020-02-23 15:28:48

SpaceNut
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Re: Un- conventional ways to LEO

All the while feeding the gas to the location under the rocket shell that we are firing at an accelerated rate keeping that pressure from dropping while we keep the gas hot.
Hydrogen is very explosive when even just a little oxygen gets ignited so the risk of its use is high additionally with the exit since the gas will become very flamable.
Helium is quite limited for supply that we can not replentish at hugh costs which is the sane for all noble class gasses.

Of course this is the wrong way to use steam as "Mad" Mike Hughes was an American limo driver, daredevil, and flat Earth conspiracy theorist known for flying in self-built rockets. Daredevil 'Mad' Mike Hughes has died after launching himself into the air on a homemade rocket that later crash landed, possibly due to a parachute malfunction.

RIP...

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#198 2020-02-23 19:13:32

tahanson43206
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Re: Un- conventional ways to LEO

For Calliban re #196 ... thank you for this additional help with the concept!  I've captured and will study it.

For SpaceNut ... thanks for mentioning the sad loss of Mike Hughes .... I caught a cell phone video of the flight.  He was in the air for a lengthy period, or so it felt to me as I watched.  Details of the failure are likely to emerge in coming days, but a preliminary suggestion is that the parachute system failed.

As a point of clarification ... Hydrogen is NOT explosive.  That story seems to emanate from the Hindenburg disaster, but ** that ** was found to have been caused by the use of an extremely fire prone covering for the fabric of the dirigible.

None of the articles I have read about actual research instruments used during the Cold War, nor plans for hydrogen ballistic launchers have ever included any mention at all of the risk you've identified.  That said, I appreciate the reminder that hydrogen gas needs to be captured efficiently after a payload boost operation.

Edit#1 ... for Calliban ... while starting to follow up on #196, I found a Thesis dating back to 2008 (apparently).

http://www.wag.caltech.edu/home/jsu/Thesis/node31.html

In 1912, Langmuir [39] immersed a hot tungsten wire in a hydrogen atmosphere, and found that above 3000 K, heat was carried away from the wire at a rate much higher than would be expected by convection alone. The abnormally high conductivity appears because hydrogen molecules dissociate into atoms at that temperature, absorbing heat which is later released when the atoms recombine. At higher temperatures ($ \sim$10000 K), hydrogen atoms separate into protons and electrons. Heavier atoms ionize at even higher temperatures, and Saha [40] proposed in 1920 that one could infer the temperature of stars from their relative concentration of ions.

What I'd like to point out to readers of this topic is the observation that heat is consumed by the disassociation of Hydrogen as Calliban has described.

My interest in pointing this out is that the energy stored in the Hydrogen to give it the capability to launch a payload must be accounted for after the launch.

Part of the accounting would be the energy invested in disassociation, which is recovered as the monatomic Hydrogen cools and returns to to molecular form.

Work is done lifting the payload, and the gas will cool as it expands into the barrel of the launch tube, but it will release heat as the atoms recombine into molecules.  Simulation of the behavior of the Hydrogen under these conditions will require sophisticated software.  Fortunately, commercially available software exists which may be capable of solving this challenge.   There exists free software able to perform similar calculations, but it's been a while since I checked on its status.  When I tried to get it to work several years ago I found myself baffled, both by the physics involved, and the nature of the software itself.

For Calliban ... as a reminder ... Your original proposal to generate large quantities of high energy steam by heating rocks and then forcing water through them is the impetus for our current discussion.  I have puzzled over what method Dr. Hunter could have had in mind for his Quicklaunch system, because he was appropriately sparing in details shared with the public.

While I am no closer to knowing what Dr. Hunter ** actually ** had/has in mind, I ** am ** able to imagine that a heat soaked metal gridwork of some kind could serve as a rapid heating environment for the hydrogen to be fed into the barrel of a ballistic launcher.

There would (I presume) be a large piston behind the cold gas before it is delivered to the hot metal gridwork.

Going forward from here, I am thinking about trying to calculate the energy that would be needed to propel a 1 metric ton capsule (payload, rounding rocket and sabot) over a distance of 1 km to a velocity of 6 km/seconds.   That energy value would then show the amount of heating needed for the metal gridwork through which the hydrogen would be forced.   

In his Star Wars research, Dr. Hunter used a two stage process, in which the first stage was a massive ram.  The ram delivered the compression (and heating) needed to accelerate the 1 kg (as I recall) payload to 3 km/second velocity.

Perhaps a ram is needed in addition to the heated gridwork, because the total temperature needed would presumably be on the order of the 4000 K you suggested.

(th)

Last edited by tahanson43206 (2020-02-23 20:57:11)

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#199 2020-02-24 04:40:11

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 3,304
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Re: Un- conventional ways to LEO

We have to bear in mind that bulk commodities are far less fragile than human beings. If we can launch fuel, food, water etc into space for $10/kg, then it doesn't actually matter that much that humans and electronics have to go up on significantly more expensive rockets. Almost all of the mass we need to do stuff is in the former group. Though we might need orbital tugs to capture it on-orbit, if it's launched dumb.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#200 2020-02-24 06:45:42

tahanson43206
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Registered: 2018-04-27
Posts: 3,496

Re: Un- conventional ways to LEO

For Terraformer re #199

Thank you for your support of the ballistic launch concept.  In the current instance, I am focusing on Dr. Hunter's vision of a system that would use hydrogen as a working fluid.  In planning for charging for launch, the operator would have to pay off the bill for construction of a large piece of equipment, as well as ongoing expenses of staffing, licensing, protection services of various kinds, sales support and business support, as well as the cost of energy supply.

Shortly, I hope we will have available here in the topic, a post showing the amount of energy to be invested in launch of a 1 metric ton capsule.  That should be knowable from the work to be done, plus charges for losses of various kinds.

A factor mentioned often is expected losses due to drag on the capsule as it ascends.  The mass of air above a launch tube can be estimated from air pressure. I estimate the mass of air above a launch tube at sea level as about 36 tons for a tube with a two meter diameter.  I find that to be a sobering number, considering that the capsule under discussion here would mass only one ton.  According to Dr. Hunter, a slim taper shape for the capsule can reduce losses due to having to move all those air molecules aside during ascent, but the losses for the first few seconds would be considerable.

The launch rate is a factor in how charges must be set for the customer.  It will take time to accumulate all the energy needed for a launch, regardless of the source.  One launch a day seems like a target rate worth pursuing.

In that case, 500 kg would be delivered to LEO once a day, supported by the plant and equipment listed here, and probably more I've not thought of.

It seems possible to me, as I think about all those costs, that the advances made by Elon Musk to reduce costs would explain Dr. Hunter's decision to suspend development of Quicklaunch.  Indeed, the Wikimedia article about Quicklaunch includes words to that effect.

(th)

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