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#26 2017-06-30 09:39:23

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,829
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Re: Space X launch

What Kbd512 calls a "fubar" is an inherent part of rocketry,  both solid and liquid (and hybrids).  It is also a part of other propulsion approaches like ramjet,  and to some extent,  still with gas turbine.  You simply have to plan on being able to handle "unscheduled rapid disassembly in multiple directions simultaneously". 

I cannot tell you how many chigger bites I got walking in the pasture picking up pieces after one of these events.  We would put it back to together for the forensics,  eventually being able to tell what came loose early versus what came loose later.  You actually want them during early phases of development.  That's when it is still relatively cheap.  Identifying unknown failure modes late in development,  or in early production,  is very expensive. 

That effect is why I want to put atomic propulsion efforts on the moon,  where there are no neighbors to annoy,  and no air and water to pollute.  "Fubars" with these things are likely to make really dangerous messes.  But they inevitably will occur.  Can't do this in space,  where every test is a flight test.  You simply have to have a stable unmoving thrust stand for your early development testing. 

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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#27 2017-06-30 14:35:32

kbd512
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Registered: 2015-01-02
Posts: 3,337

Re: Space X launch

GW,

Actually, Oldfart1939 called it "FUBAR".  I simply stated that from my own very limited experience with rocketry, these things just happen during testing.  We've already done preliminary testing on NTR's, including exploding one, just to see what would happen.  I agree that nuclear reactors in rocket engines can get messy if things go wrong, but we can limit where "things go wrong" to an orbital environment.  The current generation of reusable rockets are fine for getting payloads into orbit.  From there, we still need a high-thrust, very high-Isp engine to get humans to other planets.  Whether the propulsion solution is fission (NTR), fusion (FDR), or even EMDrive, it involves radioactivity in operation.  There's no way around that.  If EMDrive works as well as initial indications have demonstrated, then thrust is a little bit better than SEP at the same power levels, which means a small fission power source is required to provide 1MW+ of output in a manageable package.

The goal with all three systems should be 90 day transits to Mars.  If you can get there faster without sacrificing significant payload mass, fine, but if not then 90 days is quite reasonable and cut's the consumables masses for transits in half.  If the transit to Mars was only 90 days, then a pair of Falcon Heavy rockets and a Falcon 9 with a Dragon can deliver six astronauts to Mars in a vehicle roughly equivalent in size and shape to an ISS lab module.

A confluence of technologies makes this mission possible, but propulsion plays a big part.  There is no single piece of tech that makes the mission more feasible.  Right now, we have lower mass and power consumption avionics and life support equipment, better software and hardware for systems control, better solar arrays and batteries for power, lighter materials for astronaut protection, and better propulsion in the form of reusable and thus far more affordable chemical rockets.

Completion of testing of the life support equipment and completion of development of any of the three named propulsion technologies would provide the "critical mass" required to make the mission affordable, efficient, safe, and productive.

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#28 2017-06-30 16:05:41

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Space X launch

Kbd512, Zubrin's nuclear salt water rocket would seem to represent the best of all worlds.  No one in official NASA circles appears to take it seriously.  To my knowledge, it has never been subjected to serious modelling.  Yet it would appear to allow unlimited access to the solar system within timescales of weeks or months.  What is your opinion on its plausibility?

I have been working on a lower performance concept for a nuclear thermal engine that uses natural uranium as fuel.  Whilst this is much more bulky than NERVA, it could be constructed on Mars using local materials.  The engine is only really workable in space, as it's T/W ratio is too low to achieve take-off from a planetary body.  However, T/W would be substantially greater than any electric propulsion system and ISP would be 800-1000.  It should therefore be possible for a freight carrying vessel to traverse from low Mars orbit to high Earth Orbit and back again with a single tank of hydrogen propellant.

There are two ways that the engine could be built.  The most technically easy option for a mars colony would be a pebble bed reactor with natural uranium carbide slugs embedded within graphite spheres.  However, the low  moderating power of carbon would result in an excessively large core.  The second option would be a hybrid, hydrogen cooled, heavy water moderated core.  This would have higher power density, but requires a more complex design.  Uranium carbide fuel must be housed in graphite sleeves within magnesium alloy tubes running through a tank of D2O.  The graphite is in place to insulate the D2O from the hot hydrogen gas used to cool the fuel.  Because the moderator remains cool, the neutrons remain fully thermalised even as the uranium reaches temperatures of >2000C.

An obvious problem with a hydrogen cooled, deuterium moderated rocket is that the propellant has a 641x higher neutron absorption cross-section than the moderator.  This could both dampen the reaction and could make core physics unstable.  However, the propellant atom density at 10bar and 2500K is still 1000 times lower than that of the moderator.  Also, because phase-change does not occur in the propellant, any power transients will be relatively slow and should be dampened by the Doppler effect and active control systems.

Because the burn-up of natural uranium is limited to ~500GJ/kg, the fuel must be replaced after about 2 round trips.     This would presumably be carried out in Mars orbit at the same time as hydrogen propellant refilling.

The purpose of the core would be to power large volume freight transport (1000s of tonnes) between Earth and Mars orbits.  Freight must travel in both directions cheaply, because beyond a certain point, a Mars colony must be capable of paying for its imports using exports.

Last edited by Antius (2017-06-30 17:10:17)

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#29 2017-07-01 02:42:46

kbd512
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Re: Space X launch

Antius,

A NSWR may or may not be technically feasible, but the second neutron moderation of the fuel is lost the fuel becomes a very powerful and dirty nuclear bomb.  Assuming the neutronics associated with this concept functions as intended (major assumption alert since I'm not aware of this ever having been modeled, let alone tested), then the NSWR is essentially a continuous very low yield nuclear explosion (which still provides a stupendous amount of thrust).  Irrespective of what the thrust chamber is made of, the thermal damage would be absolutely fantastic absent an incredibly efficient cooling solution to inhibit ablation.  The neutron environment there doesn't help, either.  I would have to see a neutronics model for the NSWR and the cooling solution for the thrust chamber before rendering a final opinion about feasibility.  It's about as close to the edge of what's technically feasible as the old nuclear pulse detonation rockets were and are.  As expensive as fissile materials are, I'm not too keen on throwing hundreds of tons of those materials out the back of the rocket.

I've become more interested in the Dusty Plasma Fission Fragment Reactors (DPFFR's) as of late.  There's enough experimental results-based basic science behind the concepts backing what Clark / Sheldon / Chapline have proposed to say with a relatively high degree of certainty that the basic design will work as intended.  The devices require relatively low fissile inventory to achieve serious power levels because it's not limited by Carnot efficiency (since it's not a heat engine).  The quantities of radioactive exhaust products required to provide a given level of thrust are also relatively limited compared to NSWR and NPDR technologies.  Isp is high enough that operational design life becomes a function of material degradation limitations and fissile inventory burn up.  The core is relatively large, but total mass remains relatively low because it directly converts fissile material into thrust or electrical power using relatively low mass means (electrostatic and/or electromagnetic).  Confinement of the fissile material to the core and thermal dissipation are not particularly problematic, either, even though it's essentially an open cycle nuclear rocket.

All the extreme performance solutions (high-thrust and high-Isp) seem to run into extreme engineering issues.  The Fusion Driven Rocket is the only program with serious funding from NASA that combines high-thrust and high-Isp.  The Nuclear Thermal Rocket program is still working on the design of the fuel elements and that's likely to be as far as that concept is ever taken again.  I have no idea what the developmental state of the EMDrive is, but FDR or EMDrive combined with a small DPFFR to provide electrical power would provide a lot more general utility than NTR's.

I'm a little skeptical about the general utility of high-thrust and high-Isp engines for cargo delivery.  If nobody's hair is on fire, then why can't the cargo take the proverbial slow boat to its destination?  Reaction mass is hard to come by on these long interplanetary trips as a function of what chemical rockets can deliver to orbit, but energy from fission or fusion is and always will be abundant.  The less reaction mass required for planet hopping, the better.

In any event, I'd still be interested to know the details of your propulsion concept once you have it worked out.  Cheap is good when it comes to cargo delivery.

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#30 2017-07-01 14:59:17

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,829
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Re: Space X launch

A wee bit of history.  "FUBAR" is an acronym dating to WW2-vintage US Navy carrier forces.  Aircraft might actually make it onto the flight deck,  but be so damaged as not to be repairable.  These were pushed overboard,  and the records reflected their status as "f***ed up beyond all repair".  The short form was the acronym "FUBAR". 

There was a similar acronym reflecting an expression summarizing whatever state of affairs was under discussion.  This was common in the US Army of that same WW2 time.  The expression was "situation normal,  all f***ed p",  for which the acronym was "SNAFU".

The US Army Air Corps of that same time (later USAF) had their own version of this same state-of-affairs expression:  "totally and royally f***ed up".  That acronym is "TARFU".

Thought you all might like to know.  Sometime ask me where the expression "cold enough to freeze the balls off a brass monkey" came from.

GW

Last edited by GW Johnson (2017-07-01 15:00:56)


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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#31 2017-07-01 17:18:18

louis
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From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Space X launch

Thanks for the acronym history, GW!

FUBAR is definitely part of rocketry but the good thing about rockets (unlike human society - please note Elon) is that rocket launches are in fact fairly stable causal networks (the machinery, atmosphere and ground conditions don't vary much) , as long as you don't do stupid things like launching in hurricanes or frosts. In other words, it is quite easy to learn from your mistakes and improve. That seems to be what Space X have been doing by having a very focussed approach, that avoids complexity wherever possible.


GW Johnson wrote:

A wee bit of history.  "FUBAR" is an acronym dating to WW2-vintage US Navy carrier forces.  Aircraft might actually make it onto the flight deck,  but be so damaged as not to be repairable.  These were pushed overboard,  and the records reflected their status as "f***ed up beyond all repair".  The short form was the acronym "FUBAR". 

There was a similar acronym reflecting an expression summarizing whatever state of affairs was under discussion.  This was common in the US Army of that same WW2 time.  The expression was "situation normal,  all f***ed p",  for which the acronym was "SNAFU".

The US Army Air Corps of that same time (later USAF) had their own version of this same state-of-affairs expression:  "totally and royally f***ed up".  That acronym is "TARFU".

Thought you all might like to know.  Sometime ask me where the expression "cold enough to freeze the balls off a brass monkey" came from.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#32 2017-07-02 21:13:36

SpaceNut
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Posts: 18,340

Re: Space X launch

There have been a few more firsts by space x for making use of pieces that have been recovered from flights.
First Falcon 9 Re-Flight Achieves Successful Launch, Landing & Payload Fairing Recovery

the two fairing halves fell away from the rocket four minutes into the mission and were set to deploy auto-steering parachutes for a pin-point landing in the ocean. Elon Musk said the recovery was a success after seeing a photo of an intact fairing half floating in the Atlantic.

I have suggested for unpressuring cargo that the fairings or payload shroud is tough enough to be used for mars landing and Space x seems to have proven that they are. Plus they are construction shells for anything that we can once they are on the surface of mars as well.

The grid fins seem to be taking a beating on reentry...
33678823692_706c887f32_q.jpg

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#33 2017-07-03 09:07:53

Oldfart1939
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Registered: 2016-11-26
Posts: 1,805

Re: Space X launch

The grid fins have been upgraded from Aluminum to Titanium on the latest iteration of Falcon 9--so-called Block 4 of production.

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#34 2017-07-03 09:21:46

SpaceNut
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Posts: 18,340

Re: Space X launch

Aluminum to Titanium trade off seems to be correct... google terms of difference for links since I am not a genius....
http://www.differencebetween.net/object … -titanium/

http://www.aerospacemetals.com/all-about-titanium.html

Titanium is 30% stronger than steel, but is nearly 50% lighter. Titanium is 60% heavier than aluminum, but twice as strong. Titanium has excellent strength retention to 1,000 degrees Fahrenheit. Titanium is alloyed with aluminum, manganese, iron, molybdenum and other metals to increase strength, to withstand high temperatures, and to lighten the resultant alloy.

would have been another step
https://www.americanelements.com/alumin … nium-alloy

Seems the trade is in the correct direction....

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#35 2017-07-03 09:23:34

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,829
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Re: Space X launch

That should help.  Most duralumin alloys are junk at only 300 F material temperature.  6-4 titanium becomes junk structurally at about 750 F material temperature.  It's heavier than aluminum,  but lighter than steel. 

Just FYI, the grid fin idea has been flying in the R-77 / AA-12 "Adder" Russian air-to-air missile for many years now. 

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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#36 2017-07-03 10:22:28

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,829
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Re: Space X launch

I saw something on the internet about an automatic Falcon-9 launch abort over some sort of guidance problem.  Perhaps try again tomorrow?

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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#37 2017-07-03 10:36:50

Oldfart1939
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Registered: 2016-11-26
Posts: 1,805

Re: Space X launch

I saw a re-launch is possible today; the major problem is the 3 week shutdown of the range for maintenance is looming later this week.

Scheduled for today at 19:37 EDT.

Last edited by Oldfart1939 (2017-07-03 10:43:06)

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#38 2017-07-03 12:05:22

RobertDyck
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From: Winnipeg, Canada
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Posts: 5,898
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Re: Space X launch

Intelsat 35e Mission

Following scrub for a guidance abort on the first attempt, SpaceX is now targeting launch of Intelsat 35e from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center in Florida on Monday, July 3, at 7:37 p.m. EDT, or 23:37 UTC. The launch window will remain open for 58 minutes and the satellite will be deployed approximately 32 minutes after launch.

SpaceX will not attempt to land Falcon 9’s first stage after launch due to mission requirements.

You can find more information about the mission in our press kit.

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#39 2017-07-03 14:53:35

SpaceNut
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Re: Space X launch

SpaceX launch scrubbed at T-minus 10 seconds

SpaceX will make another attempt to launch the Falcon 9 and its communications satellite payload on Monday. CloseSpaceX

Forecasters predicted a 60 percent chance of acceptable weather Monday for a planned launch at 7:37 p.m. ET.

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#40 2017-07-03 17:46:20

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,340

Re: Space X launch

Another first has occured as the same Dragon capsule has now been flown twice to the station and back home.

SpaceX Dragon Becomes First Re-Flown Commercial Spacecraft To Successfully Return To Earth

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#41 2017-07-03 18:38:47

Excelsior
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From: Excelsior, USA
Registered: 2014-02-22
Posts: 120

Re: Space X launch

SpaceNut wrote:

SpaceX launch scrubbed at T-minus 10 seconds

SpaceX will make another attempt to launch the Falcon 9 and its communications satellite payload on Monday. CloseSpaceX

Forecasters predicted a 60 percent chance of acceptable weather Monday for a planned launch at 7:37 p.m. ET.

Weather was good, but the launch was scrubbed again. No apparent cause.


The Former Commodore

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#42 2017-07-05 02:22:10

louis
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From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Space X launch

Space X is always in the news now!


http://www.dailymail.co.uk/news/article … Ocean.html

Another first - use of spacecraft that's been recycled...if I've followed that right. The costometer of space flight must be falling as I write.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#43 2017-07-05 07:04:52

SpaceNut
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Re: Space X launch

The link Louis provided contains ISS experiment information that Nasa is looking at to aid man's trip to mars.
SpaceX’s Dragon spaceship made space history today as being the first capsule used twice in two different missions that has never been done before.
Was surprised that it takes capsule a 5½-hour journey back to Earth.

Sure looks well done...
4209223100000578-4666402-Pictures_of_the_SpaceX_Dragon_capsule_that_made_history_by_becom-a-6_1499237534551.jpg

18 images http://photos.dailynews.com/2017/07/pho … history/#1

Previously, the Dragon carried supplies and equipment to the orbiting module in 2014 on SpaceX's fourth resupply mission. It delivered nearly 2.5 tons of cargo to the orbiting laboratory.

SpaceX carrying more than 4,100 pounds of cargo and research specimens, descended to a predawn splashdown Monday in the Pacific Ocean southwest of Los Angeles, completing the first re-flight of one of SpaceX’s unpiloted supply ships to the International Space Station.

SpaceX's 11th cargo resupply trip to the ISS to be carried out under a $1.6 billion contract with NASA.

SpaceX refurbished it for the planned launch, providing a new heat shield and fresh parachutes for re-entry at mission's end along with a new truck with fresh fuel and its ready to go?

We have question what else is done:

There were so many X-rays and inspections that savings, if any, were minimal this time, said Hans Koenigsmann, vice president of flight reliability for SpaceX.

The vast majority of this Dragon has already been to space, including the hull, thrusters and tanks.

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#44 2017-07-05 18:57:34

Excelsior
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From: Excelsior, USA
Registered: 2014-02-22
Posts: 120

Re: Space X launch

Excelsior wrote:
SpaceNut wrote:

SpaceX launch scrubbed at T-minus 10 seconds

SpaceX will make another attempt to launch the Falcon 9 and its communications satellite payload on Monday. CloseSpaceX

Forecasters predicted a 60 percent chance of acceptable weather Monday for a planned launch at 7:37 p.m. ET.

Weather was good, but the launch was scrubbed again. No apparent cause.

Third times the charm.


The Former Commodore

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#45 2017-07-06 09:08:08

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,829
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Re: Space X launch

Looks like 3rd time was the charm.  15,000 lb Intelsat sent to geosynch transfer orbit by Falcon-9 successfully.  No attempt made to recover booster as all propellant on both stages was needed to send heavy payload to that energy. 

The first scrub seems to have had something to do with guidance software.  No one seems to be talking about the cause of the second scrub.  The third attempt,  after a day spent going through the telemetry, seems to have had no problems. 

One report has it there will be a supply launch to ISS scheduled for Aug 10. 

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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#46 2017-07-07 15:21:16

kbd512
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Re: Space X launch

The "well done" capsule is why I say that nothing that's reentered is reusable without significant refurbishment.  There's no telling what's damaged until it has been thoroughly inspected.  Educated guesses won't cut it.  You have to know with certainty that the thermal protection is intact before you reenter.  The same applies on Mars, which is why I think multiple uses are a pipe dream before someone invents the test equipment, inspection methods, and repair methods that work outside of a near clean room environment.  After someone does that, then multiple reuses prior to significant refurbishment become a possibility.  In time, SpaceX may add that "first" to their growing list of "firsts", but until they do ITS remains a paper concept, even after the hardware has been built.

NASA did some work to determine the feasibility of on-orbit repair of the Space Shuttle's TPS, but that was never actually tested in the orbital environment.

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#47 2017-07-07 19:10:09

SpaceNut
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Re: Space X launch

The test gear would be of the same application as what is used in the build process but its that cost to which is being hidden at this point under the low pricing. How through the test are on the refurbishment is a time factor of costs and of how much risk he is willing to take as that is what insurance is all about. I do agree that the repair kits need to be built and tested as shuttle proved that they would have been of great value.

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#48 2017-07-07 20:59:17

kbd512
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Re: Space X launch

SpaceNut,

The point is that it must be a functional solution on the surface of another planet if anything is to be reusable after it reenters on Mars, as ITS is supposed to be.  Someone actually has to test this in space and on Mars to know with certainty that it works well enough in practice.  NASA should probably front the money for this.  They have more at stake than anyone else right now, and most certainly in years past, in ensuring that this technology works.

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#49 2017-07-08 08:57:23

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,340

Re: Space X launch

Sort of like how the Mav would land versus its reuse to be part of the ascent vehicle and not so much orbit to orbit.. Which is only if its a single stage unit that would be the case but most options of a lander for mars are usually thought of as being 2 stage.
The ITS would be in that single stage category and ya that would want some deep inspections if it lands back on earth before reuse. With the same if only refueled in orbit of earth for another landing on mars. Thats just more gear for mars or in orbit for that inpection but its gear for infrastructure building in the first case just needed sooner rather than after insitu use.

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#50 2017-07-08 09:55:10

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,829
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Re: Space X launch

Odd how this thread has morphed into capsule heat shield reusability.  Oh,  well...

Most folks no longer remember that one old Gemini capsule was re-flown back about 1969.  It was from an early unmanned test,  and was reflown as a pathfinder test for the Gemini-B configuration intended for the USAF's Manned Orbiting Laboratory (MOL) program.  The one and only test in MOL put a mass model laboratory and a reflown Gemini in orbit.

I don't know if they replaced the heat shield or not for the reflight.  Gemini-B had the seats angled further apart,  with an off-center hatch between them,  cut right through the heat shield.  That was how the astronauts were to enter the station without going outside.  That reflown Gemini with the hatch in the heat shield made it back fine,  and is now in a museum somewhere. 

If your heat shield is an ablative,  then each reentry removes a certain amount of material.  Theoretically,  you should be able to take reentry after reentry until the remaining virgin material is too thin to survive.  If your heat shield is a monolithic part,  then all you need look for is the presence of cracks.  You should be able to determine how much material has been lost by the change in the exterior dimensions. 

If your heat shield is made up of pieces,  then the sealing between those pieces becomes an issue,  because of the risk of hot plasma infiltration between and behind the pieces.  That's going to require some sort of imaging to probe those joints,  perhaps ultrasound or x-ray?  I don't know. 

Dragon has an ablative heat shield made up of pieces sealed together.  It was designed for 17 km/s entry coming back from Mars,  which theoretically means it could survive 2 returns from the moon at 11 km/s,  and multiple (4+) reentries from LEO,  or so I read about it.  There is plenty of material thickness to do that. 

The problem is the joints.  I doubt Spacex has an inspection system for joint sealing in place,  that they trust well enough,  to risk reflying a used heat shield.  But eventually they will have such inspection,  and they will start reflying used heat shields.  Otherwise,  why build them that thick?  Makes no sense. 

We already know you can refly low-density ceramic non-ablative heat shield materials.  They are not supposed to lose material,  and if they do,  you can see it.  The problems are two-fold:  (1) joint sealing between the pieces,  and (2) positive retention of those pieces (the bond joint).  Those are the issues that made the shuttle so expensive to refly.  They make X-37 a bit expensive,  too. 

I made such a material out of pipe insulation paste and fire curtain cloth more than 3 decades ago.  Because it was a fiber-reinforced ceramic-ceramic composite,  it was a lot more structurally robust than NASA shuttle tile,  although still fragile in a stress properties sense.  You could let the fire curtain fabric extend outside the edges of the panel,  wrap it around behind,  and "glom" onto it there for positive retention of a metal-backed structure you can bolt down.  And a fiber reinforced material can be of larger dimension (by far) than the few inches of a shuttle tile. 

There really are ways to build heat shields that you can refly with some confidence.  It wouldn't take that much of an effort to try them out and demonstrate suitability. 

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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