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#276 2013-11-05 01:09:02

RGClark
Member
From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
Website

Re: Reusable Rockets to Orbit

GW Johnson wrote:

For a different reason,  I had to rough out essentially the same plane circa 1985.  Mine was turbojet/ramjet parallel-burn propulsion,  a similar layout,  and designed for M5 at 100-150 kft.  I did it from all open sources. 
It was so close "to reality" the FBI confiscated all my design notes,  but not my sources or my slide rule,  because I did not possess the clearances "to know about such a craft".  I have often wondered if such a thing ever got built. 
It appears in hindsight apparently not.  Although it could have been.  The delta-wing pulse detonation experimental craft (seen above Groom Lake) of about 1995 apparently led nowhere. 

GW


If the ramjet would work to Mach 5, makes you wonder if it is worthwhile to develop the scramjet just to get to Mach 6.
In either case, this is why I'm optimistic about getting a combined cycle SSTO, with the rocket sharing the same combustion chamber as the ramjet.

  Bob Clark


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#277 2013-11-05 14:39:47

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reusable Rockets to Orbit

Hi Bob:

One of the ramjet missiles I worked on was a low drag wingless finned "dart" that accidentally went M6 at 20 kft,  setting the record for airbreathing flight.  The ramjet worked fine,  and the bird was still slightly accelerating when it ran out of fuel.  It's skin was beginning to melt,  too,  especially since it was supposed to cruise at only M4,  with a terminal dive speed near M5. 

This was a throttle runaway incident on a first test that was supposed to fly sedately at its takeover M2.5.  Getting the M6 speed depends on the vehicle drag more than anything else.  That speed record stood from 1980 until NASA broke it with their X-43 in 2004. 

You do not need scramjet to fly between M4 and M6.  You need it to fly M7+.  But,  scramjet min takeover is M4!  Ramjet can be in the M1.5 to 2.5 range. 

Vehicle aero heating gets really,  really difficult above M6,  which is why M5 to 6 is what these pipe dream programs are all about.  You can tell a gravy train technology program from a real flight development,  simply because the gravy train guys want to fly scramjet at M5 to 6,  when it isn't necessary. 

Ramjet features relatively lower chamber pressures compared to rocket (50-100 psi typical vs 1000-2000 psi).  Ramjet nozzles have throat areas that need to be as large as possible,  right up to 65% of the combustor area (a flame stability limitation).  The max exit expansion area ratio is the pretty close to 1/0.65= 1.53. 

Those geometries are very,  very,  very far from what works with a rocket nozzle.  Compromising nozzle geometry "kills" (quite thoroughly) the performance potential of both rockets and ramjets.  That's why most designs feature an ejectable booster nozzle with suitable rocket proportions,  nested within a ramjet nozzle sized to work well.  It's a one-shot geometry change,  you cannot go back-and-forth.  Boost,  then sustain.  Period. 

There are ways to close off the inlets during rocket boost:  frangible or moveable or ejectable port covers.  Their best location is at the point where the inlet enters the combustor.

Most of the missile designs have you cast a solid propellant rocket inside the ramjet chamber.  As it burns out,  you open the inlets,  start the kerosene flow,  eject the booster nozzle assembly,  and light-off an ignition charge,  all at once.  The bird I spoke of transitioned from full rocket thrust to full ramjet thrust in 100 milliseconds.  You do need a very sharp booster tailoff to make that work,  which means a very careful interior ballistic design for almost no sliver. 

Some designs I worked on accepted a big loss in booster performance to avoid the ejectable nozzle.  There is a design called "nozzleless booster" for that.  The interior ballistics are very tricky,  there's more than one layer of propellant each with a different burn rate,  and the aft-end propellant shape is the nozzle.  It's a difficult art. 

There's no reason ejectable nozzles could not be used with liquid propellant rocketry,  using the ramjet chamber as the rocket chamber.  Nobody has ever done it,  but it could be done.  So could a hybrid booster. 

Solids came from missile work,  where they are preferred for a variety of very good,  practical reasons.  I even worked on some designs with fuel-rich solid propellant gas generators supplying combustible effluent as fuel,  instead of pumped liquid kerosene.  I actually know two really good ways to throttle a solid generator fuel supply,  too,  one of them with no moving parts at all. 

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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#278 2013-11-06 21:13:59

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
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Re: Reusable Rockets to Orbit

Hi Guys:

I did another ramjet-assist launch to LEO study,  this one horizontal takeoff and horizontal landing.  It's not exactly 2-stage,  nor is it 3-stage,  it's a little different.  I had to get very creative to solve all the thrust and drag and hypersonic aeroheating problems,  and still make every component credibly reusable.  But I did use all LOX-CH4 rockets and a CH4-fueled ramjet.  It's posted as of today (11-6-13) over at "exrocketman".  Enjoy.

Midoshi:

You should be about a week or so from launch with MAVEN.  How's it going?

GW
http://exrocketman.blogspot.com


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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#279 2013-11-10 23:13:48

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
Website

Re: Reusable Rockets to Orbit

SpaceX has given the propellant amounts for both the first and second stages in the required Environmental Impact report for the Falcon 9 v1.1. These propellant amounts have been much speculated about on the internet. The amount for the first stage is about what has been estimated. However, the propellant load for the second stage is about 50% higher than the estimates.

Given this and the propellant fraction for the first stage given by Elon in the Royal Aeronautical Society lecture, you can calculate the dry mass at least for the first stage. Plugging these values into the rocket equation you see it can carry quite a significant amount of payload as an SSTO.

However, an SSTO achieves its best performance when altitude compensation such as aerospike is used. Then the payload in fact becomes surprisingly high. So high in fact that the cost per kilo of the expendable SSTO F9 is better than that of the standard expendable two stage without altitude compensation.

In other words by investing in altitude compensation, the F9 first stage SSTO is a more efficient launcher than the standard two stage F9 if you don't invest in altitude compensation. Surprisingly, this superiority of the SSTO on the cost per kilo metric, is still true for the reusable launcher case, even when you make an apples-to-apples comparison of also giving the two stage an altitude compensating first stage.

Discussion here:

The Coming SSTO's: Falcon 9 v1.1 first stage as SSTO, Page 2.
http://exoscientist.blogspot.com/2013/1 … first.html


  Bob Clark


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#280 2013-11-16 19:32:43

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
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Re: Reusable Rockets to Orbit

DARPA has released a request for proposals for its reusable spaceplane program:

DARPA issues first-phase solicitation for XS-1 hypersonic space plane for deploying satellites.
November 15, 2013
By John Keller , Editor
http://www.militaryaerospace.com/articl … plane.html

Several links to reports describing the program here:

Experimental Spaceplane (XS-1).
Solicitation Number: DARPA-BAA-14-01.
Agency: Other Defense Agencies
Office: Defense Advanced Research Projects Agency
Location: Contracts Management Office
https://www.fbo.gov/index?s=opportunity … e&_cview=1

I found this one the most informative:

Experimental Spaceplane (XS-1).
A First Step Toward Reducing the Cost of Space Access by Orders of Magnitude.
Mr. Jess Sponable, TTO Program Manager
https://www.fbo.gov/utils/view?id=66259 … 5ac956cd9f

Bob Clark


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#281 2013-11-17 14:53:09

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
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Re: Reusable Rockets to Orbit

Hi Bob:

If you haven't seen it yet,  I posted some payload fraction comparisons on "exrocketman",  in one of two articles posted today (11-17-13). 

The DARPA spaceplane thing looks relatively undefined,  which may be a good thing,  as most federal government new-item development projects are way-over-specified.  It appears they want a hypersonic winged stage that can reach about 3 km/s just outside the atmosphere,  so it can land horizontally.  Vertical vs horizontal launch seems to be wide open. 

Based on the numbers I have been playing with,  that sort of thing is possible only with hydrogen-powered rocketry,  whether or not any airbreathing propulsion is used.  It's a nice wide-open solicitation,  often typical of DARPA.  I have very real doubts about getting anything flying in 5 years,  though. 

Looks to me like they are begging both XCOR and Spacex to respond.  I have good contacts at XCOR.  Do you know anybody at Spacex? 

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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#282 2013-11-17 15:48:19

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 3,293
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Re: Reusable Rockets to Orbit

Hmm, they want to be able to launch a few tonnes. I can see why you need hydrogen for that...

Could we launch payloads of 0.5-1 tonne with a lower stage that has those general characteristics (3km/s outside atmosphere) that uses methlox, though, using a ramjet?


"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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#283 2013-11-26 21:10:32

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
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Re: Reusable Rockets to Orbit

RGClark wrote:

GW's presentation at the 2013 Mars Society convention on a lightweight thermal protection ceramic material is available on Youtube:

Reusable Ceramic Heat Shields - GW Johnson - 16th Mars Society Convention.
http://www.youtube.com/watch?v=3MXYY3jnNr0

This ceramic material is quite light at .03 specific gravity. However, it is tougher than the shuttle ceramic tiles. The shuttle tiles were quite fragile and maintenance intensive. GW's tiles would cut down on this maintenance cost and would have much reduced turnaround time due to thermal protection system maintenance.
I'm thinking it could also be used on the X-33. The X-33's TPS consisted of metallic shingles. There were tougher than the shuttle's silica tiles thus requiring minimal maintenance but they were rather heavy. GW's ceramics would also be more damage resistant than the shuttle tiles, but would be much lighter than the X-33's metallic shingles.

GW, the ceramic aerogel tiles on the shuttle have a specific gravity of  .144. Are you sure of that .03 number for your tiles, equivalent to a density of only 30 kg/m^3?

  Bob Clark


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#284 2013-11-27 10:39:37

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
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Re: Reusable Rockets to Orbit

Hi Bob:

Not as sure as I'd like to be. 

My stuff simply "felt like" styrofoam,  and middle-of-the-range for commercial styrofoam is near .03.  My stuff could be as dense as shuttle tile,  I suppose,  and still feel like commercial styrofoam.  I just don't know.  It is far more damage resistant,  as the unreinforced stuff (like NASA's stuff) shattered to pieces almost instantly when I drove that little combustor into rich instability. 

The reinforced stuff survived dozens of instabilities and hours of burn at the hairy edge of meltpoint.  I had shrinkage cracking post-burn,  but in that application,  cracking was not objectionable.  It didn't go all the way through.  I suppose without proof you could ride it through entry with surface cracking,  but I don't like the notion of hypersonic fluid shear tearing at the edges of cracks like that.  Flow speeds were very subsonic inside that little combustor. 

I think the density depends critically upon the curing process.  The maker lists a much higher density for the material,  but my molding process was quite different from what most folks do.  I had a lot of metallic confinement,  and I cured above the boiling point of the water vehicle in the potting compound,  instead of below.  I think the steam wormholing its way out is how I achieved low density in what is otherwise just a slather-on ceramic pipe insulation potting compound. 

Metal shingles would be a lot stronger,  but would have a conduction path "open" into the interior of the vehicle.  That would require backside cooling or heat-sinking to go through re-entry.  That's how they were going to do it on the old X-20 with Inconel skins.  I suspect the X-33 would have functioned similarly.  The advantage of the low-density ceramic (mine or NASA's) is that you cut off that conduction path.  The backside can be uncooled aluminum. 

The advantage of mine over NASA's is actually threefold:  (1) larger panels that are way easier to install,  (2) redundant retention (bondline plus mechanical retention of the reinforcing fabric),  and (3) non-exotic commercial materials in common use for decades now.  You do have to install it integral with the hull plating panels,  as simple bolt-up items to the framing. 

The biggest question would be process controls during panel cure to ensure an acceptable low density.  I hit on that by accident when I did this back in 1984.  I don't forsee a problem with that,  but a spec does have to be defined. 

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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#285 2013-11-28 08:45:40

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
Website

Re: Reusable Rockets to Orbit

GW, that DARPA spaceplane initiative would be an ideal place to get funding to develop your heat shield material further. I was interested to see in your Mars Society lecture that you were also able to use it make nozzles. This would have great importance for making lightweight nozzles. For instance adding the nozzle extension to the RL-10 engine doubles the mass from 150 kg to 300 kg. If your material is as lightweight as it appears then you could reduce that to a fraction of the added weight.

   Bob Clark

Last edited by RGClark (2013-11-28 08:46:20)


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#286 2013-11-28 10:30:59

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reusable Rockets to Orbit

Hi Bob:

I had considered external airframe insulation,  and I have used it inside a burner to include a low-pressure gradient nozzle.  It would do what fiberglass wool does at temperatures higher than glass can stand.  Had never considered rocket nozzle bell extensions,  but it might work. 

Proposing to the government is a difficult process at best.  Do you know someone in DARPA we can approach with this,  someone who can guide us through the proposal minefield?  And,  the small business minefield is different from the big corporate minefield for sure,  but just as lethal.  That's why we need a contact inside DARPA.

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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#287 2014-02-24 21:24:51

Hop
Member
From: Ajo
Registered: 2004-04-19
Posts: 146
Website

Re: Reusable Rockets to Orbit

Rune wrote:

I know how to figure out hyperbolas since I was 17.

I've never seen the slightest evidence from either you or Josh that you can figure the speed of a hyperbola. In spite of the fact I've shown you how many times.

Hyperbolic orbits are necessary for departing earth for other planets. I will try again to teach this very simple device:

What the heck is Vinf

What about Mr. Oberth?

and

The most common delta V error

Rune plays a role in each of these.


Hop's Orbital Mechanics Coloring Book - For kids from kindergarten to college.

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#288 2014-03-07 10:35:15

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
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Re: Reusable Rockets to Orbit

Did you really feel that it was necessary or worth your time to necropost a discussion from twenty-seven months ago in order to condescend to myself and a user who is not even active on these forums anymore? 

Far be it from me to say that I often think that I am wrong; But at the least I am not still sore about any discussion on the Internet that happened 27 months ago.  To be honest, I barely remember any internet discussions I had 27 months ago.  Since Rune posted that there have been 220 posts in this thread.

I can't (and wouldn't ever think of trying) to tell you what to say on your own blog, but off topic rules do apply here.


-Josh

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#289 2014-03-07 10:46:43

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
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Re: Reusable Rockets to Orbit

Hi Josh:

I looked at Spacex's site yesterday.  It appears that the next Falcon-9/Dragon shot to ISS will be rigged with a working set of landing legs.  I got the impression that they plan to try the legs out.  They didn't hold out much hope for success,  but at least it's a trial. 

Not sure what landing legs get you,  with an ocean landing,  but the test is planned.  Has anybody heard of which island they might eventually land these reusable stages upon?

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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#290 2014-03-07 11:07:48

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
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Re: Reusable Rockets to Orbit

I read somewhere on Space.com or spacedaily.com that the next flight will have landing legs. The last attempt at a water landing failed because the vehicle got in a spin and that centrifuged the propellant away from the drainpipe, so the engines went out. After that, Musk said that even a pair of landing legs would be sufficient to reduce the spin, allowing the control rockets to control the spin. So that may be the purpose of the legs, even if the water landing will do no good.

My understanding is that the plan is to return the stage to the spaceport, not to land it at a remote location. Rather ambitious.

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#291 2014-03-08 10:03:36

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reusable Rockets to Orbit

We'll soon see.  I think the launch is scheduled for March 16.

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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#292 2014-11-30 09:29:43

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
Website

Re: Reusable Rockets to Orbit

GW Johnson wrote:

Hi Bob:
One of the ramjet missiles I worked on was a low drag wingless finned "dart" that accidentally went M6 at 20 kft,  setting the record for airbreathing flight.  The ramjet worked fine,  and the bird was still slightly accelerating when it ran out of fuel.  It's skin was beginning to melt,  too,  especially since it was supposed to cruise at only M4,  with a terminal dive speed near M5. 
This was a throttle runaway incident on a first test that was supposed to fly sedately at its takeover M2.5.  Getting the M6 speed depends on the vehicle drag more than anything else.  That speed record stood from 1980 until NASA broke it with their X-43 in 2004. 
You do not need scramjet to fly between M4 and M6.  You need it to fly M7+.  But,  scramjet min takeover is M4!  Ramjet can be in the M1.5 to 2.5 range. 
...
GW


Weird Crystal Can Absorb All The Oxygen In A Room -- And Then Release It Later.
Popular Science
This could potentially make fuel cells, space travel, and scuba diving a lot more efficient.
http://www.popsci.com/article/science/w … e-it-later

Could this be used for air breathing propulsion?

   Bob Clark


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#293 2014-11-30 11:48:28

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,180

Re: Reusable Rockets to Orbit

chemical name of the salt is written out as {(bpbp)Co2II(NO3)}2(NH2bdc)2 * 2H2O, where “bpbp” stands for 2,6-bis(N,N-bis(2-pyridylmethyl)-aminomethyl)-4-tert-butylphenolato, and “NH2bdc2” stands for 2-amino-1,4-benzenedicarboxylato).

Cobalt=Co
Cabon monoxide= Co
confusing...

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#294 2014-11-30 12:19:30

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,026
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Re: Reusable Rockets to Orbit

In chemistry, a single capital letter followed by a lower case letter designates an element. All caps means different elements. So...
Cobalt=Co
Carbon monoxide=CO
Only difference is the "O" is capitalized.

This gets messed up when they use shortened nic-names for large complex chemicals with long names. For example, I had to look up what "bis" means. It's a chemical prefix meaning two of something. But I'm used to the prefix "di" meaning two, so why use "bis"? I think part of the confusion comes from chemists using different languages. Latin used "bi" or "duo" for 2, while Greek uses "di" or "dy".

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#295 2014-11-30 18:58:06

Impaler
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From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Reusable Rockets to Orbit

The oxygen absorber didn't need to be double posted in two different threads, that said it would be a very valuable addition to life-support systems, it may solve the excess oxygen problem of the Mars One greenhouse at low cost and high reliability.

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#296 2014-11-30 20:03:15

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 509
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Re: Reusable Rockets to Orbit

Two completely different applications. It would hardly be relevant to discuss its use making scuba dives that last forever in this thread.

  Bob Clark


Nanotechnology now can produce the space elevator and private orbital launchers. It now also makes possible the long desired 'flying cars'. This crowdfunding campaign is to prove it:
Nanotech: from air to space.
https://www.indiegogo.com/projects/nano … 13319568#/

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#297 2014-11-30 20:42:56

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,180

Re: Reusable Rockets to Orbit

Also with Oxygen being stored there might also mean we would want a means to store hydrogen as well...
http://hydrogenmaterialssearch.govtools.us/

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#298 2014-11-30 21:59:57

Impaler
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From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Reusable Rockets to Orbit

If were assuming propellent is the ultimate use for hydrogen or oxygen then I don't see any any option but to store them as cryogenic liquids, the absorbent is far too heavy to actually bring with the rocket (heck the hydrogen ones are too heavy to use on a ground vehicle on Earth), and the time and wattage needed to flush the stuff out and liquify it would be horrible.

The only propellent application I can see is in the ISRU processing of Mars atmosphere (in an ice processing system you get oxygen separation for free from your electrolysis so no point to this specific O2 absorber).  Current ISRU designs from Zubrin are batch processes but with a set of absorbents for the target gases it may be possible to make a continuous flow process which would be massively massively simpler and more reliable as it would have just a single intake fan rather then numerous pumps valves and compressors and all the attendant energy consumption thouse things entail.  The final step of cryocooling you can't get around cause you need the propellent at that density to feel to the rocket and that's still a big energy cost so were talking modest energy reduction and high reliability improvement.

I'm imagining a CO/O2 bi propellent system, your raw Martian atmosphere get turned into a CO/O2 mix and the O2 and CO are each absorbed away by their own VERY selective absorbents (maybe running past one absorber first can mitigate an absorber that is non-selective, but at least one needs to be very selective so it can go first).  Each absorbent is in some kind of honey-comb/exchanger so it can vent to the opposite side and the pure gas can be drawn off.  The apparatus consists of two systems that simply alternate absorbing and venting (or more if the absorb/vent times are not equal) and are fed by a single intake that just switches a valve to send air down a different absorber throat.  All CO2 that isn't converted to CO or O2 and all the trace gasses just blow right out the rear of the machine and we don't have to worry about them.

Last edited by Impaler (2014-11-30 22:17:07)

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#299 2014-12-01 00:53:07

RobertDyck
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From: Winnipeg, Canada
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Re: Reusable Rockets to Orbit

NASA had looked at converting Mars atmosphere in to CO & O2 bi-propellant for fuel. The problem is burning liquid CO with liquid O2 is very poor fuel. Specific impulse is very low. To use a rude expression: it sucks.

It was after NASA did that study that Dr. Robert Zubrin and Dr. David Baker came up with their idea for Mars Direct: bring hydrogen from Earth, use a Sabatier reactor to convert Mars CO2 + H2 into methane and water. Run water through electrolysis to convert to H2 and O2, store O2, recycle H2. Paul Sabatier invented the Sabatier reactor; it was used in the 1910s to generate methane for natural gas lighting. It was this idea from Mars Direct that brought the Sabatier reactor to NASA's attention; they have already used it to improve life support. But for In-Situ Propellant Production, the described system is not complete. The ratio of methane to oxygen is not correct for a rocket engine, more oxygen is needed. So Mars Direct includes a system that uses a thin wall tube that is a catalyst to convert CO2 into CO and O2. The O2 passes through the thin wall, CO2 and CO do not. It's carbon dioxide electrolysis. This only converts 80% of CO2 into CO and O2, but there's lots of CO2 on Mars. So this can generate the extra O2 for balanced rocket fuel.

The point is going back to CO & O2 is a major step backward. And it was already looked at.

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#300 2014-12-01 03:14:01

Impaler
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From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Reusable Rockets to Orbit

The numbers I've seen say 290 for a pump-fed CO/O2 engine which is poor compared to Hydro-Lox but ball park with Metho-Lox 360 which is the real comparison.  Assuming assent DeltaV of 4.1kms That means a mass fraction of 77% for CO/O2 and 69% with Metho-Lox.  A grand total of just 8% more (for dry fractions of 23% and 31% respectively) and well withing the range of a plausible assent vehicle.  The Delta-V is just not high enough to create the kind of fraction differences that we would assume come from taking that kind of specific impulse hit because were usually thinking about Earth's high gravity well which is where specific impulse is so heavy.

If you push the into reusable range and need another 1.4kms for a decent and you had to bring that with you on the assent for a total 5.5kms (or alternatively direct Earth return from Martian surface) then indeed the CO/O2 propellent mass fraction starts to get mean at 86% vs the Metho-Lox still plausible 80%.  So I'd agree that CO/O2 looks very weak for say Elon Musk, but it is perfectly plausible for Zubrin and NASA who are looking at expendable architectures, and a Mars orbital rendezvous.

CO/O2 is expected to have advantages in simpler equipment and lower energy input per unit of fuel.  Also the potential to use a hybrid engine which initially burns Metho-Lox for decent and then CO/O2 on assent has been explored, as your decent propellent has to come from Earth (at least once) their is every reason to use that higher impulse for that stage, the tank doesn't even need to be purged as CO and Methane will mix fine.  The fact that this rocket can land COMPLETELY empty of fuel without even a H2 feed-stock must be considered too, that reduced landing mass is a multiplied backwards through decent propellent and all the mess of heat-shields, parachutes, landing legs etc, the Delta-V may be less then assent but it is full of parasitic mass budget and it currently one of the big technical barriers.

Last edited by Impaler (2014-12-01 05:07:41)

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