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#1 2018-12-23 15:12:56

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,068

Starship is Go...

https://www.youtube.com/watch?v=VoegqRJKGE8

Sneak look at the shiny new stainless steel Spaceship!

Looks like this is really going to happen!! smile 

Very interesting video...


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#2 2018-12-23 16:56:00

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,985

Re: Starship is Go...

Louis,

1. Lockheed-Martin investigated the use of reusable high-temperature metallic TPS in the 1990's, but of course, never followed through with it in the Venture Star program.

2. Lockheed-Martin determined through tests that a metallic TPS would be vastly cheaper to manufacture and maintain than the then state-of-the-art aerospace composites and ceramics, as used on the Space Shuttle.  Strangely, it didn't increase mass that much due to the layer cake of both structure and thermal protection technologies.  Composites and Aluminum are indeed lighter than steel, but once you start adding all the TPS layers the mass starts to resemble the mass of a thin super grade of stainless steel.

It's interesting that he didn't mention the use of 300 series stainless steel in the Centaur upper stages.  Stainless was used in Centaur because it could be made very thin and thus light, it's fast and easy to weld or repair if damaged, and has less thermal conductivity than Aluminum so thermal transfer into the LH2 from ascent heating was less of a problem.  Today, even high grades of stainless are cheap and plentiful.

3. A metallic TPS either limits reentry velocities or requires active cooling.  In recent times, aircraft have been equipped with Titanium leading edges that use micropores to emit heated liquid anti-icing agents to prevent icing.  There's no reason the same technology couldn't emit cryogenic propellants to cool the skin during reentry, given that the heating happens over a period of a couple minutes at most.

The new nanoparticle-infused ceramic metal matrix composites, such as the Aluminum I've been working with for an engine fastener application, have 3 to 4 times the strength of a piece of conventional Aluminum of the same volume or dimensions and that's without any heat treatment at all.  They also have greatly increased resistance to oxidation and loss of strength at elevated temperatures.

There are also special high-temperature nanotechnology processes, such as RF-85 (as the name might hint at, it reduces friction by 85%), that alter the surface structure of a metal rather than coat it with an oxide layer, to provide extreme oxidation and friction resistance by deforming to protect the coated surface.  The results of that work was validated / tested by ORNL and later Sandia Labs about a decade ago.

4. The added weight of the stainless steel will inevitably further reduce the payload since it will be a bit heavier than TPS-covered composites.  My wild guess is about 100t or so.  As long as it's fully reusable and not merely refurbishable, as the Space Shuttle was, then I don't see that as a major problem.  After initial fabrication costs, the major costs of any reusable vehicle are maintenance.  If that is minimized, then this system could be vastly cheaper than any other launch system we've ever seen.

5. Glad to see real hardware taking shape there.  I'm starting to believe that this will happen.  My fingers are crossed.

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#3 2018-12-24 11:18:45

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,694
Website

Re: Starship is Go...

Four points:

1. Spacex is going to build and fly a heavyweight test vehicle made of stainless steel to check out the guidance and all the logistics for BFR/BFS.  This thing will bear the same relation to BFR/BFS that the "Dragonfly" (?? name ??) flying test article did to Falcon-9.  Stainless steel can be made into leakproof cryogenic tanks that are thinner and easier to repair than any other known material.  It can also take more surface heating (rocket plume exposure !!!) than the aluminum-lithium alloy,  or any known organic-matrix composite.  Why would they NOT build this test vehicle from stainless steel?

2. During entry,  which is a ~3 minute transient,  you have to account for all the energy.  There is convective heating to the external surface,  and above 10 km/s speeds,  radiative heating to the surface becomes significant and quickly dominates.  There is conduction (and maybe convection) into the interior,  and re-radiation from the surface back to the surroundings,  as energy lost from the surface material.  The shortfall of heat added minus heat lost is heat that is "sinked" into the surface material,  which raises its temperature.  That's just physics,  it cannot be ignored or bypassed.

3. Practical material technology:  the very highest-temperature epoxy I ever heard of was junk (debris) by 290 F.  Most are junk at 212 F.  These are the basis of all carbon-epoxy composite materials.  Aircraft-grade aluminum alloys are mostly junk at about 350 F.  Carbon steel (and titanium !!!) is junk at about 750 F.  There are alloy steels and many stainless grades that have max service temperatures of about 1000 F.  There are 2 or 3 stainless grades good to 1600 F or thereabouts.  Non-steel superalloys like Inconel X and the afterburner-part alloys are good to ~ 2000 F.  But they are expensive and very difficult to work.  If you need significant hot strength out of any of these materials (more than about 1-2 ksi),  you cannot operate even that hot. 

4. Practical cryo-tank technology:  LOX leaks through composite walls unless there is some sort of impervious liner.   Metals retain it,  but embrittle badly in the cold,  except 300-series stainless,  which is why it is preferred for Earthly LOX tanks.  Liners are usually cold-tolerant polymers,  but these are junk at about 212 F.  With LCH4 and especially LH2,  the leakage through porosity is far worse.  And LH2 will slowly leak right through a metal wall (compressed gaseous H2 leaks through metal much faster).  If you build a carbon composite tank with a polymer liner,  nothing about any of those materials can exceed 212 F during entry.  If it does,  you have no choice whatsoever but the stainless steel tank.

Substantive Conclusions:  if aerothermal analyses of BFS entry show higher-than-212 F material temperatures even with thicker PICA-X,  then carbon composite construction is infeasible.  Period.  Then stainless can operate hotter with thinner PICA-X.  Thinner PICA-X is lighter,  so the metallic construction may not really be the weight penalty so many think it is. 

SS-316/-316L can endure repeated exposures to 1600 F without scaling.   It's common,  and not that expensive. It's easily formed and quite weldable,  especially the -316L form.  SS-309/310 will go to 1900 F,  but are hard to get and quite expensive.  I'd go 316L stainless steel myself,  faced with such a conundrum.  Leading edges and nose caps might require an Inconel,  but that's localized. Everything is covered in PICA-X,  to a max steel temperature of 1000 F.  Black-surfaced on the windward side for higher re-radiation,  white-surfaced elsewhere. 

GW

Last edited by GW Johnson (2018-12-24 11:23:17)


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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#4 2018-12-24 11:57:46

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,068

Re: Starship is Go...

Interesting stuff.  You think they are going to give up on the carbon fibre tanks after all that effort?  Maybe!

I think the hop thing leading to the Falcon 9 was called the Grasshopper.

GW Johnson wrote:

Four points:

1. Spacex is going to build and fly a heavyweight test vehicle made of stainless steel to check out the guidance and all the logistics for BFR/BFS.  This thing will bear the same relation to BFR/BFS that the "Dragonfly" (?? name ??) flying test article did to Falcon-9.  Stainless steel can be made into leakproof cryogenic tanks that are thinner and easier to repair than any other known material.  It can also take more surface heating (rocket plume exposure !!!) than the aluminum-lithium alloy,  or any known organic-matrix composite.  Why would they NOT build this test vehicle from stainless steel?

2. During entry,  which is a ~3 minute transient,  you have to account for all the energy.  There is convective heating to the external surface,  and above 10 km/s speeds,  radiative heating to the surface becomes significant and quickly dominates.  There is conduction (and maybe convection) into the interior,  and re-radiation from the surface back to the surroundings,  as energy lost from the surface material.  The shortfall of heat added minus heat lost is heat that is "sinked" into the surface material,  which raises its temperature.  That's just physics,  it cannot be ignored or bypassed.

3. Practical material technology:  the very highest-temperature epoxy I ever heard of was junk (debris) by 290 F.  Most are junk at 212 F.  These are the basis of all carbon-epoxy composite materials.  Aircraft-grade aluminum alloys are mostly junk at about 350 F.  Carbon steel (and titanium !!!) is junk at about 750 F.  There are alloy steels and many stainless grades that have max service temperatures of about 1000 F.  There are 2 or 3 stainless grades good to 1600 F or thereabouts.  Non-steel superalloys like Inconel X and the afterburner-part alloys are good to ~ 2000 F.  But they are expensive and very difficult to work.  If you need significant hot strength out of any of these materials (more than about 1-2 ksi),  you cannot operate even that hot. 

4. Practical cryo-tank technology:  LOX leaks through composite walls unless there is some sort of impervious liner.   Metals retain it,  but embrittle badly in the cold,  except 300-series stainless,  which is why it is preferred for Earthly LOX tanks.  Liners are usually cold-tolerant polymers,  but these are junk at about 212 F.  With LCH4 and especially LH2,  the leakage through porosity is far worse.  And LH2 will slowly leak right through a metal wall (compressed gaseous H2 leaks through metal much faster).  If you build a carbon composite tank with a polymer liner,  nothing about any of those materials can exceed 212 F during entry.  If it does,  you have no choice whatsoever but the stainless steel tank.

Substantive Conclusions:  if aerothermal analyses of BFS entry show higher-than-212 F material temperatures even with thicker PICA-X,  then carbon composite construction is infeasible.  Period.  Then stainless can operate hotter with thinner PICA-X.  Thinner PICA-X is lighter,  so the metallic construction may not really be the weight penalty so many think it is. 

SS-316/-316L can endure repeated exposures to 1600 F without scaling.   It's common,  and not that expensive. It's easily formed and quite weldable,  especially the -316L form.  SS-309/310 will go to 1900 F,  but are hard to get and quite expensive.  I'd go 316L stainless steel myself,  faced with such a conundrum.  Leading edges and nose caps might require an Inconel,  but that's localized. Everything is covered in PICA-X,  to a max steel temperature of 1000 F.  Black-surfaced on the windward side for higher re-radiation,  white-surfaced elsewhere. 

GW


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#5 2018-12-24 12:05:52

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,068

Re: Starship is Go...

Thanks for the technical input!

kbd512 wrote:

Louis,

1. Lockheed-Martin investigated the use of reusable high-temperature metallic TPS in the 1990's, but of course, never followed through with it in the Venture Star program.

2. Lockheed-Martin determined through tests that a metallic TPS would be vastly cheaper to manufacture and maintain than the then state-of-the-art aerospace composites and ceramics, as used on the Space Shuttle.  Strangely, it didn't increase mass that much due to the layer cake of both structure and thermal protection technologies.  Composites and Aluminum are indeed lighter than steel, but once you start adding all the TPS layers the mass starts to resemble the mass of a thin super grade of stainless steel.

It's interesting that he didn't mention the use of 300 series stainless steel in the Centaur upper stages.  Stainless was used in Centaur because it could be made very thin and thus light, it's fast and easy to weld or repair if damaged, and has less thermal conductivity than Aluminum so thermal transfer into the LH2 from ascent heating was less of a problem.  Today, even high grades of stainless are cheap and plentiful.

3. A metallic TPS either limits reentry velocities or requires active cooling.  In recent times, aircraft have been equipped with Titanium leading edges that use micropores to emit heated liquid anti-icing agents to prevent icing.  There's no reason the same technology couldn't emit cryogenic propellants to cool the skin during reentry, given that the heating happens over a period of a couple minutes at most.

The new nanoparticle-infused ceramic metal matrix composites, such as the Aluminum I've been working with for an engine fastener application, have 3 to 4 times the strength of a piece of conventional Aluminum of the same volume or dimensions and that's without any heat treatment at all.  They also have greatly increased resistance to oxidation and loss of strength at elevated temperatures.

There are also special high-temperature nanotechnology processes, such as RF-85 (as the name might hint at, it reduces friction by 85%), that alter the surface structure of a metal rather than coat it with an oxide layer, to provide extreme oxidation and friction resistance by deforming to protect the coated surface.  The results of that work was validated / tested by ORNL and later Sandia Labs about a decade ago.

4. The added weight of the stainless steel will inevitably further reduce the payload since it will be a bit heavier than TPS-covered composites.  My wild guess is about 100t or so.  As long as it's fully reusable and not merely refurbishable, as the Space Shuttle was, then I don't see that as a major problem.  After initial fabrication costs, the major costs of any reusable vehicle are maintenance.  If that is minimized, then this system could be vastly cheaper than any other launch system we've ever seen.

5. Glad to see real hardware taking shape there.  I'm starting to believe that this will happen.  My fingers are crossed.


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#6 2018-12-24 13:04:16

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,694
Website

Re: Starship is Go...

Grasshopper,  that's right!  Thanks,  Louis,  I could not remember that name. 

The FAA limits at the McGregor facility where they flew Grasshopper were within-the-property-boundary,  and under 2500 feet-above-ground-level.  I think they only had one Grasshopper vehicle,  and were nearly done with it when it was lost. 

It was a range-safety self-destruct.  They lost control of it in flight.  It was threatening to fly outside the FAA limits,  out of control.  Over populated areas.  Very loud "bang" that day,  instead of the usual continuous roar. 

Those are very familiar sounds,  to me,  from my years testing similar such things.

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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#7 2018-12-24 15:32:18

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,756

Re: Starship is Go...

To All-

Just a few words from the resident organic (and polymer) chemist. All of theses "composite" structures are carbon based polymers. As GW has already stated, most of them are toast at ~ 300 degrees C. Even with some type of fiber reinforcement, (carbon filament), they will melt, lose strength and ultimately burn up. Type 316 Stainless is the best answer.

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#8 2018-12-24 16:31:38

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

The already did a scaled version of a first stage and unless they are making it with different fuels and engines there is nothing more to learn from one.
BFR relies on the technology of it second stage refueling from a reuseable first stage capable of mass payload delivery.
Flying a composite tank its only good for show if its to size and filled for repeat use.

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#9 2018-12-25 04:54:19

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,985

Re: Starship is Go...

Louis,

Lightweight carbon composites have fantastic material properties for relatively low-speed aircraft, but if a vehicle's design Mach number goes up substantially or the thermal environment for the structure deviates substantially from Earth sea level ambient atmospheric conditions, as it always does in cryogenic propellant storage tanks used in hypersonic vehicles, the problems with using those lightweight composites quickly become insurmountable when using presently available aerospace technology.  Lockheed-Martin's F-35 has to use onboard fuel and a complex pumping system as a heat sink to keep all the composite airframe structures within design limits.  That's also part of the suite of stealth technologies, since it lowers the vehicle's IR signature, but it's incredibly complicated and expensive to maintain.

Passive techniques, which is mostly re-radiation of absorbed thermal energy into the surrounding atmosphere, are an important part of the overall TPS solution.  Various types of steels work well enough for most applications.  Inconel may be very difficult to properly weld, but it's routinely done for aircraft engine exhaust systems.  Apart from Inconel's weight, which is considerable, it's a very good thermal protection material for structures that don't become as hot as the leading edges do during reentry.  The leading edges could be RCC or TUFROC or UHTC since they'll see the greatest thermal flux during reentry.  Starship's control surface leading edges are comparatively sharp, rather than blunt like the leading edges of the Space Shuttle, so UHTC's are probably their best bet.  However, UHTC's require heat sinking the absorbed thermal flux into the rest of the vehicle structure to do what they do.  I've provided a cursory sampling of passive TPS technologies, but I believe one or more of the documents mentions active techniques for UHTC thermal management as well.

I found that document on metallic reusable TPS developed by BF Goodrich's Aerostructures Group for LM's VentureStar vehicle:

Reusable Metallic Thermal Protection System Development

CMC's:

Ceramic Matrix Composite (CMC) Thermal Protection Systems (TPS) and Hot Structures for Hypersonic Vehicles

UHTC's:

Ultra High Temperature Ceramics UHTCs

However, there are various methods to address thermal protection and some more creative and mass-efficient than others.  An active TPS that injects water or gaseous propellant through laser-formed micro pores in Starship's skin could make the entire vehicle substantially lighter, if no other form of passive TPS is required, since residual propellant has to be carried for reentry and landing burns.

Laser formed micro pores in Titanium alloy are used in the leading edges of aircraft in lieu of complicated and expensive-to-maintain anti-icing boots.  A heated anti-icing fluid is expelled through the pores and the result is a much faster and more complete ice removal from wings and empennage than inflatable rubberized anti-icing boots permit.  The flow rate is so low that there system can simply be turned on in known icing conditions to inhibit the formation of icing.  That's an example of transpiration heating, but it works quite well.

Modern jet engines run so hot to achieve desired fuel economy and emissions that the blades in the hot section of gas turbines already use transpiration or film cooling.  That also works quite well, else there'd be numerous airliners experiencing catastrophic engine failures.

If you do a bit of "googling", there are lots of other papers from NASA, ESA, CAAA, and various public-private university research projects.  Most use H2O, but many have also tested air / He / O2 / N2 / Ar / whatever else they could get their hands on.  The consensus is consistently that H2O works best and requires very little water since its vaporization energy is so high.  High flow rates and pressures are not required since the metals / ceramics / composites tested use capillary action to expel the water.

Concept Design of an Enhanced Radiation Cooling Thermal Protection System

Here's another paper on the topic:

Platelet based Active Thermal Protection System (ATPS)

The papers from various university student theses and European space programs are quite detailed and include experimental results.  There are a series of papers about combining UHTC's for sharp leading edges and transpiration cooling mechanism for DLR's orbital space plane concept, for example.

A thin 300 series Stainless would be ideal for the propellant tanks for all the reasons GW and Oldfart1939 alluded to.  Here on Earth, Stainless Steel is the material of choice for transportation of cryogenic liquids that include LOX / LH2 / LN2 / LCH4 and others.

Masteel UK - 9% Nickel Steel for LNG and Cryogenic Applications

There are a wide variety of different materials that could possibly work for Starship's skin if the thermal energy from reentry is dumped into water and/or residual propellant in order to carry away excess thermal energy.

Starship's booster could probably get by with Aluminum CMC alloy, given the strength of the material at elevated temperatures.  The higher grades of this stuff (more nano powder added to the composite) are only ~0.1g/cm^3 heavier than traditional Aluminum alloys and weld just as easily as ordinary Aluminum alloys.  Cutting and drilling are a different story (better have carbide cutting tools or something even harder if you want your tools to last any reasonable amount of time).  Some of the Aluminum CMC's (7000 series replacements) are roughly as strong as 4130 (a type of alloy steel commonly used in aircraft engine mounts) at room temperature.

The most important part of their manufacture is that cost is equivalent to a moderate cost 300 series Stainless Steel and unlike conventional Aluminum alloys that level of strength is achieved without a heat treatment process of any kind, which is just one more thing that increases raw material cost and can also be easily screwed up if it's not tightly controlled.  When you see something like 6061-T6 or 7075-T6, the "-T6" part is the heat treatment specification.  It adds manufacturing time and expense.  A heat treatment can make the Aluminum CMC's even stronger, but at 3X to 4X the strength of conventional Aluminum and at elevated temperatures, why bother with another manufacturing step that can be screwed up?

Anyway, it's not a perfect solution but it's still a lot better than composite delamination causing rapid unscheduled deconstruction.

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#10 2018-12-25 08:07:06

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

Transpiring heat shield was talked about in quite a few tpics in the past when the direction of the shuttle was being canned and a new ship was to be born from the COTS materials to form a capsule baed system.

TPS and RLV
VentureStar is it possible now
Russian Klipper or US CEV - why can we not get it done sooner
Space Launch System
Space Initive Launch Vehicle
Spaceplane

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#11 2018-12-25 12:01:57

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

While fixing Christmas dinner and fixing the topic that needed to be... I got thinking about what could we use for a working fluid for a mars landing ship and the answer is in the recycling of the waste stream from life support and other activities during the 6 plus month journey to mars.
Yes using co2 and the Amines that are spent or the Li solutions which was used to scrub the cabin air and waste water filtering . We could also super heat in a chamber to breakdown the plastic and paper waste to bulk up the amounts that would be required to land.

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#12 2018-12-25 17:39:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,068

Re: Starship is Go...

Seems to be even more confirmation of rapid progress on pilot BFR Super-Heavy/Starship...

https://www.youtube.com/watch?v=l6dCkI0eCag

The steel plated nose looks v. basic! Presumably it's covered in something eventually? What would the something be?

Seems like Musk is planning a full Starship presentation in March/April after initial hop flight. So we can expect (if we are of an optimistic disposition) that the first hop flight will take place in the first quarter of 2019, which is earlier than I was expecting...

Last edited by louis (2018-12-25 17:41:57)


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#13 2018-12-25 18:18:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

This is what documents are

lower engines and legs
Starship-hopper-construction-bocachicagal-NASASpaceflight-5c-573x346.jpg]

Assembling the nose
Boca-Chica-Starship-Alpha-progress-122318-Maria-Pointer-bocachicagal-1c-656x331.jpg


https://www.teslarati.com/spacex-licens … -campaign/

https://www.teslarati.com/spacex-raptor … p-testing/

Raptor-throttling-2018-SpaceX-gif-small.gif

https://spaceflightnow.com/2018/09/18/j … th-spacex/

Promising to take a half-dozen or more artists with him on the journey, Japanese fashion magnate Yusaku Maezawa said Monday he has paid a deposit for a ride around the moon aboard SpaceX’s planned BFR rocket as soon as 2023, a financial infusion that will help bankroll development of the company’s futuristic interplanetary transporter.

https://www.teslarati.com/spacex-elon-m … or-finish/

While the suggestion that Raptor’s turbopumps (basically fuel pumps) would need at least 100,000 HP per engine seems to indicate that the flight design’s thrust has been appreciably uprated, a past figure of ~2000 kN (450,000 lbf) per engine suggests that Starship V0.1 could weigh as much as an entire Falcon 9 Block 5 rocket (~1.2 million pounds, 550,000 kg) and still having a solid 80-100% of Falcon 9’s liftoff thrust.

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#14 2018-12-25 18:45:02

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,068

Re: Starship is Go...

Seems like everyone is now on board with the reality that Space X are making significant progress with the BFR Starship project...

Great news for 2019. 

For me this is the all-important project. Crew Dragon and Falcon 9 Heavy are interesting, inspiring exciting,  but this is the project that really matters! If we see a first hop flight in the first quarter of 2019 that will be fantastic.

SpaceNut wrote:

This is what documents are

lower engines and legs
https://www.teslarati.com/wp-content/up … 3x346.jpg]

Assembling the nose
https://www.teslarati.com/wp-content/up … 56x331.jpg


https://www.teslarati.com/spacex-licens … -campaign/

https://www.teslarati.com/spacex-raptor … p-testing/

https://www.teslarati.com/wp-content/up … -small.gif

https://spaceflightnow.com/2018/09/18/j … th-spacex/

Promising to take a half-dozen or more artists with him on the journey, Japanese fashion magnate Yusaku Maezawa said Monday he has paid a deposit for a ride around the moon aboard SpaceX’s planned BFR rocket as soon as 2023, a financial infusion that will help bankroll development of the company’s futuristic interplanetary transporter.

https://www.teslarati.com/spacex-elon-m … or-finish/

While the suggestion that Raptor’s turbopumps (basically fuel pumps) would need at least 100,000 HP per engine seems to indicate that the flight design’s thrust has been appreciably uprated, a past figure of ~2000 kN (450,000 lbf) per engine suggests that Starship V0.1 could weigh as much as an entire Falcon 9 Block 5 rocket (~1.2 million pounds, 550,000 kg) and still having a solid 80-100% of Falcon 9’s liftoff thrust.

Last edited by louis (2018-12-25 18:45:27)


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#15 2018-12-25 21:17:02

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

newest of the topic 1 for a not so scaled version of the shape but not quite what we will build so its not even going to prove much...

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#16 2018-12-26 04:49:45

Sinn
Member
Registered: 2018-12-26
Posts: 2

Re: Starship is Go...

GW Johnson wrote:

Everything is covered in PICA-X,  to a max steel temperature of 1000 F.  Black-surfaced on the windward side for higher re-radiation,  white-surfaced elsewhere. 
GW

Hello there!
But Elon eliminated of PICA-X heat-shielding recently.
Or I just misunderstand the twit - "windward side will be activity cooled with residual (cryo) liquid methane, so will appear liquid silver even on hot side"?

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#17 2018-12-26 09:47:45

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

Welcome to Newmars Sinn

This appears to be a Pica panelled side of the ship.
aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzA4MS85MDAvb3JpZ2luYWwvc3BhY2V4LXN0YXJzaGlwLWVsb24tbXVzay1kZWNlbWJlci0yMDE4LmpwZw==

I think that there is an issue with any holes in the cooled shiny side of the ship as the heat would cause a fire to occur once in earth oxygen and even if the tanks are partially empty the amount of heat exspansion pressure would be to great to direct the heated gas back into the fuel tank as its stilll needed to land the ship on its tail.

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#18 2018-12-26 09:52:45

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,694
Website

Re: Starship is Go...

Myself,  I put little stock in tweets.  Believe it only when hardware flies. 

The stainless steel vehicle under construction is not a prototype BFS,  despite all the sincere beliefs and wishes otherwise.  It is a full diameter,  short-length,  heavy-construction-but-right-takeoff-mass test vehicle for proving-out the controls of a BFS with a full complement of Raptor engines.  It will never fly fast or far,  and never experience re-entry conditions.  But it is a very necessary step along the way to a flying BFS.

Stainless steel exposed to re-entry aeroheating would only survive with massive amounts of liquid cooling.  SS covered in some PICA-X would require only minimal liquid cooling,  even steady state.  If too thin to be a heat sink,  it might require that minimal liquid cooling during the short re-entry transient. 

GW

Last edited by GW Johnson (2018-12-26 09:58:20)


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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#19 2018-12-26 10:01:57

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

That is also why I hunted down something other than a utube video also and while it could be a recording its not going to give details of what will be done. Of course if you peice together the video and the twitter you might end up with points that could be put together to form something.
It does get the general nose shape and mass for landing tests if you load it for what would be remaining fo the ship on earth atmospheric entry but thats a big if.

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#20 2018-12-26 11:32:09

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,756

Re: Starship is Go...

In spite of all Elon's enthusiasm, I suspect his thoughts of a carbon fiber composite met the barriers of reality. When high temperatures are encountered, carbon based polymers simply go out the window. Now we see some "bait" photos, but not much else. Everything we've heard on YouTube and through Tweets is highly speculative--which gets many members here--highly agitated! I suspect what we're seeing is a new "grasshopper," being built in order to test fly the new uprated Raptor engines and test software control systems. Not discouraging, since these, and more, still need some hardware for testing. I consider what we've learned to be highly positive signs that SpaceX knows what needs done.

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#21 2018-12-26 12:57:09

Sinn
Member
Registered: 2018-12-26
Posts: 2

Re: Starship is Go...

SpaceNut wrote:

Welcome to Newmars Sinn
This appears to be a Pica panelled side of the ship.

Thank you!
To me it's just the same structure with bare SS sheets with contre-jour effect smile

GW Johnson wrote:

I put little stock in tweets.

Yes, sure. "We wanted the best, you know the rest".

GW Johnson wrote:

The stainless steel vehicle under construction is not a prototype BFS,  despite all the sincere beliefs and wishes otherwise.

Fully agree! The thing is more like a mockup for me.

GW Johnson wrote:

Stainless steel exposed to re-entry aeroheating would only survive with massive amounts of liquid cooling.

Massive amounts but not with "residual liquid methane"? The residual amount is smth like 10t or more?

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#22 2018-12-26 14:01:45

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,694
Website

Re: Starship is Go...

The quantities of methane and oxygen still in the tanks at entry have nothing to do with skin cooling,  until you direct them in the correct amount and speed,  fully wetted to the skin you are trying to cool.  You do NOT do that with a single thin skin.  It takes a double shell,  or tubes welded to the skin,  or some of both.  Free convection to the skin from the static cold vapor in the tank will not do the job.

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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#23 2018-12-26 14:20:25

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,473

Re: Starship is Go...

Using a transpiring shell and water that is used for radiation protection and not methane or oxygen as the working fuild would work as you pump it into the capivity of a double shell and monitor the heat and internal pressure on the way down pumping in more to keep it cooling and venting.

I agree Oldfart1939 that its a good test bed for the Raptor engines and fuel use with a smigde of aerodynamics thrown in for its shape. Other than that we are just redoing the grasshopper tests for Falcon 1....

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#24 2018-12-26 17:31:51

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,985

Re: Starship is Go...

GW,

Capillary action alone was sufficient to force water through a porous metal skin with pores of the correct size.  That was proven through testing in one of the documents I linked to regarding a biconic reentry vehicle ("Concept Design of an Enhanced Radiation Cooling Thermal Protection System") from Post #9.  However, ESA and affiliates have a variety of documents where similar tests were performed to characterize the ability of water-based active TPS to negate an additional 300t worth of launch vehicle to accommodate mass increase associated with pure passive TPS for DLR's proposed space plane.

Transpiration Cooling to Handle the Aerothermodynamic Challenges of the SpaceLiner Concept

Anyway, the biconic's water tank was located in the nose of the test article / reentry vehicle.  The water tank had to be pressurized to about 5atm to prevent the water from boiling in a vacuum.  Their flow rate was ~0.2g/s, which proved to be a bit too much.  I've seen multiple documents from multiple sources that reference that figure as the maximum flow rate, beyond which you start heating up the vehicle instead of cooling it.  Anyway, testing indicated that even .2g/s was too much.  Finally, DLR's intent was to cool the leading edges and part of the vehicle's skin using water to reduce the mass of passive TPS that would mandate a 300t launch vehicle mass increase.

The leading edges of DLR's space plane are expected to experience aerodynamic heating near 1.9MW/m^2, as compared to Space Shuttle's .5MW/m^2.  Scaling from their experimental results indicated that their vehicle would have to carry 9.1t of water to cool a surface area of approximately 955m^2 to achieve surface temperatures of 500K / 440F / 227C.  The 500K surface temp was far below what they were shooting for

Q: Is there any way to do this using passive metallic TPS for the skin and UHTC's (Hafnium-based CMC's) for the leading edges?

The UHTC's require structure that permits thermal transfer away from the leading edges, but Stainless and Inconel have poor thermal conductivity compared to Aluminum, so this is sub-optimal from a mass perspective but works anyway in actual testing of hypersonic test vehicles like X-43.  There was no institutional knowledge of how to use UHTC's at NASA until they recently brought that capability in-house.

Q: Is there any way to trap a substantial portion of the water vapor in the hypersonic flow to reduce water consumption and spread heat from the leading edges over most of the vehicle, a sort of thermal soak system that reduces the thermal gradients across the vehicle?

Q: If the skin was made from Inconel, is a skin temperature of 500K sufficient to prevent significant oxidation or loss of strength?

Starship's total surface area should be around 1,700m^2.  Nobody knows exactly what it will be at this point, but that's a pretty reasonable guesstimate based upon the surface area of a cylinder with the diameter and length they provided, but the nose is a paraboloid and I don't have numbers for their fins.

Q: What's the maximum temperature that a monocoque Inconel airframe could withstand without unacceptable thermal expansion or deformation under load if the reentry flight profile mimics that of the Space Shuttle?

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#25 2018-12-26 17:33:28

Void
Member
Registered: 2011-12-29
Posts: 3,011

Re: Starship is Go...

Yes, I show up I will give you unrocketwise!

The thing I am looking at that just sort of fascinates me, is that if you could use propellants to cool.  Those are after all supposed to be supercooled, to the point that they are almost frozen.  If that is still their condition upon re-entry, then they occupy a reduced volume, and are obviously colder.

But....See what I am looking at is do you have a chance to recycle some of the energy inertia of the vehicle in such a process?

So, they say shiny special stainless steel to reflect off a lot of that energy.  But if you are going to cool it with supercooled fluids that will be propellants, what are the energy results for landing? 

Like a cat with a mouse I have some interest in it.  That is could you cool your stainless steel while moving from supercooled propellants to condensed propellants? 

In other words can you recapture some of the energy of aerocapture into the propellant fluids?  You would make them vibrate more, so you do add vibrational molecular energy.  But of course then the fluids are expanded not to a vapor we hope but they are expanded.  Still can you cycle them through the engines for your landing and recapture a fraction of your momentum of arrival to Earth (Or Mars)?

I just like looking that over.  It would be cool to do so.


Done.


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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