Starship is Go...

louis · 2018-12-27 19:37:52

Thanks for the instructive analysis kbd. The thing that surprised me from the photos was that it looked like some 19th century ship hull being welded together with obvious rivet points! They surely must have to coat it in something for it to operate efficiently in a thick atmosphere? That said, having seen some original space craft from the early 60s in museums it is amazing how basic they look, so maybe I shouldn't be looking for that "fine finish"!

kbd512 wrote:

SpaceX has to decide whether or not they'd rather have a vehicle that's lightweight and thus high performance, durable, or cost effective to operate. The way I see it, they can build a launch vehicle that has 2 of those 3 characteristics, but not all 3 at the same time. All historical evidence says that's not possible. If it were me, I'd choose durability and operational cost-effectiveness. A vehicle that costs a bit less to construct using cheaper materials is virtually meaningless when you throw the entire vehicle away after its first use and I completely agree with SpaceX's thought process on that matter. If the materials cost a bit more, but used to construct a durable and dependable vehicle, then I judge the trade in absolute payload performance to be worth it.
Stainless Steel retains adequate ductility and strength at the cryogenic temperatures of LOX and LCH4, making it the material of choice for cryogen transport here on Earth. The additional benefits are that it's easy to bend and weld, has moderate cost thanks to the increasing variety of uses for the material, and retains strength at temperatures that turn all Aluminum alloys, even CMC's, into silly putty. A high grade Stainless Steel will eventually fail, as all materials do, but Aluminum and Carbon Composites will fail much faster. There will never be a time in the life of this vehicle when it's acceptable to have no propellants left in the tanks, and both are cryogens so autogenous pressurization is practical. Every LOX/LH2 Centaur stage from about the late 1950's onwards proved that monocoque Stainless Steel construction works.
If some geniuses working for NASA or their contractors come up with a composite that can take the abuse, then great. SpaceX can capitalize on that technology advancement after it's proven to work acceptably well with adequate flight heritage. For those in doubt, that's what we really need NASA for. The government can afford to take a loss on a high-risk / high-payoff technology that doesn't pan out. A corporation could easily bankrupt itself trying to make something work that's just not ready for prime time. That's how I feel about composite cryogen tanks. There's no reason to stop working on the technology, but it needs to be done on Uncle Sam's dime as part of public-private partnerships so that the contractors who provide bread and butter launch services to the government can continue to butter the government's bread with functional and affordable launch services.
I think Sylramic and Super Sylramic could provide a durable surface insulation solution for most of Starship. NASA has completed 9,000 hours of testing in jet engine combustion liners at 2,200F without fatigue failure and it's now a commercial material that SpaceX could simply purchase. GE's plant in Huntsville could mass manufacture the stuff. This material is more than 30+ years in the making and GE only started fabrication for commercial aircraft engines in 2018 after qualifying the materials and components.
Silicon Carbide (SiC) Fiber-Reinforced SiC Matrix Composites
Ultra High Temperature (UHT) SiC Fiber
Creep and Cyclic Fatigue Durability of 3D Woven SiC/SiC Composites with (CVI+PIP) Hybrid Matrix
COI Ceramics Inc - Sylramic SiC Fibers
The 600 and 700 series Inconels also do relatively well at cryogenic temperatures and better at higher temperatures than Stainless Steel, but they're a little heavier than the Stainless alloys I'm familiar with. So... Perhaps some of this new 3D woven fabric over Stainless or Inconel could get the job done, provided that the leading edges use ZrB2 or HfB2 with appropriate thermal sinks. There are also developmental synergies between Sylramic fiber and ZrB2 since it can strengthen that particular UHTC by reducing grain size.
Critically, Snecma Propulsion Solide's SEPCARBINOX A500 SiC CMC's inhibit delimitation of the bound carbon fibers from oxidation through self-sealing of the matrix that prevents chemical vapor infiltration. I believe the F414 turbofans' "turkey feathers" used by the US Navy's Super Hornets tested A500 in their exhaust nozzle divergent flaps and seals and some hot section components. I think the F100 turbofans in the US Air Force's Falcons were some of the first technology testbeds, though. I'm pretty sure some of this new tech has been incorporated into the F135 engines, too.
Ceramic Matrix Composites taking flight at GE Aviation
In case someone missed that concept, that means a small hole or imperfection in your heat shield fabric shouldn't create the dreaded "zipper effect" that Space Shuttle HRSI tiles were thought to be susceptible to. That's kinda important for vehicle durability and survivability. That said, few other materials top HRSI tiles for re-radiation of absorbed thermal flux.
Here's a nice little Science Direct article on Cobalt Super Alloys that kinda explains why CMC's are desirable where usable:
Cobalt-Based Superalloys
A very good article on CMC's from a book published in 1998 called "Ceramic Fibers and Coatings: Advanced Materials for the Twenty-First Century":
Current and Future Needs
There are also Aluminum fiber composites that can withstand LOX and LH2 that do not micro-crack after 100+ cycles from -450F to +250F. These materials retain 85% of their strength to 700F. They have half the CTE of conventional Aluminum alloy, less expansion than certain types of Titanium alloys in some cases, double the stiffness and strength of 7075-T6, are lighter than pure Aluminum, and are compatible with LOX / LH2 / LN2 / LHe2 (no idea about LCH4). In terms of strength compared to a low alloy steel, the strength-to-weight ratio for two parts of identical mass would be approximately 5.3 times higher for this material. If mass is a consideration, as it always is in aerospace applications, there are no steel alloys I'm aware of that have that kind of strength-to-weight. The critical design figures of merit are thermal transfer rates and peak heating if using the structure as a cryogen tank the pulls double duty as a heat sink during reentry.
MetPreg Datasheet for Aluminum Matrix Composite
For good measure, here's another report from DLR that explains 3 different methods or approaches for carbon composite tank fabrication (from Boeing, Lockheed-Martin, and Northrop-Grumman):
Final Results of Advanced Cryo-Tanks Research Project CHATT
If someone here has a social media account, please ask Elon Musk if he's considered the use of SiC and thermal soaking the airframe to use the entirety of Starship's structures and propellant load for thermal control / protection. It works in modern stealth fighters like the F-35 and it has a dramatic effect on thermal control as IR videos of hovering F-35B's have clearly demonstrated (the only way you get to a usable thermal signature to lock onto is if you're directly behind the F-135's exhaust nozzle), and it can also work for spacecraft made from appropriate materials designed to take the heat. The only reason that the composites in the F-35 don't melt and delaminate is application of that design principle of using jet fuel to absorb the heat from aerodynamic heating and the engine and running it through a thermal exchanger to the atmosphere (won't work the exact same way for a reentry vehicle, but it still works). There's just too much heat to use composites without aggressive active thermal control, but a combination of refractory alloys, CMC's, and cryogenic propellants should be able to get the job done.

kbd512 · 2018-12-27 21:03:11

For those who haven't put two and two together, let me explain how these new metal matrix materials work to SpaceX's advantage:

1. Aluminum composite with roughly twice the useful thermal range on the high side makes using the tankage and propellant as a heat sink a practical proposition.

2. Right now SpaceX wants to put miniature descent propellant tanks inside the primary propellant tanks to prevent propellant sloshing. That's not a good idea from a mass-utility perspective. It mandates support structure that serves no other purpose than to keep the descent tanks secured to the primary tanks and that increases the mass of the primary tanks because it provides no structural reinforcement to the primary tanks. You could obviously keep them secured to the top or bottom of the tanks, but that just changes where the load is distributed and there's still no side wall reinforcement. The alternative is giant slosh baffles, but at least in some formats that provided some side wall reinforcement. Neither are optimal and the propellant still requires re-pressurization for EDL. The alternative is a double wall tank.

How would a double side wall tank be better since it increases mass?

A. In some way, form, or fashion, you have to prevent propellant sloshing. There's no way around that problem. The vehicle is dangerously unstable when tens of tons of propellant are freely moving around inside the tanks. The tremendous acceleration force and attitude control keeps the propellant in the bottom of the tanks during ascent, but reentry is an entirely different problem due to rapid changes in vehicle attitude and very little forward acceleration to keep the propellants transfixed within the tanks.

B. The side wall structure of the propellant tank can be structurally reinforced to eliminate the need for constant pressurization.

C. The vast volumetric difference between the side wall propellant tanks and the primary tanks means that excess pressure from thermal soak during reentry can be vented into the primary tank and then used to maintain pressurization of the side wall tanks during the landing burns. That also means that main tank pressurization can be used to assist with on-orbit propellant transfer if the two vehicles are oriented correctly towards the Earth so that microgravity draws the propellants to the bottom of the tanker's tanks and accumulated pressure from the refueled vehicle's tanks works to forces propellant into its own tanks.

D. For long duration propellant storage, the side wall tanks act as a partial vacuum jacket that greatly limits thermal transfer, so propellant can be pumped out of the side wall tanks and into the main tanks. Any residual gaseous propellant can be consumed by gaseous O2/CH4 thrusters for attitude control and course correction.

E. The use of multi-cell side wall tanks, combined with pressurization control, can be used as a CG-shift mechanism to assist with attitude control during reentry. That doesn't eliminate the need for thrusters and aerodynamic control surfaces, but it should provide enough control authority to enable the use of smaller surfaces. Recall that JPL's Mars missions since Curiosity use ballast to control the reentry vehicle's angle-of-attack during reentry. Tens of tons of propellant could also be used as an attitude control mechanism that is more useful than dead weight. Perhaps a few high precision electromagnetically or pneumatically movable side wall tanks could entirely negate any requirement for aerodynamic control surfaces for vehicle attitude control.

There are engineers on this forum who are a lot smarter than I am who could take these ideas and determine how to best utilize the mass and thermal control characteristics to construct a functional vehicle with minimal dead mass. All I know is that every bit of mass on a spacecraft is at a premium and the more uses you can get from the mass that you're forced to carry with you, the better.

SpaceNut · 2018-12-27 21:28:11

The difference for a second stage fuel slosh and that of the reuseable first stage seem to be the same functional problem as when we get to the top of the flight for recovering the first stage its flopping around to change direction and gets a 0 g moment before changing direction. A second stage is already at 0 g on orbit so its already under pressure.

Void · 2018-12-28 14:44:34

I very much enjoyed the teachings here, and say that you have saved yourselves from tolerating my next set of speculations elsewhere.

Good job, I think.

louis · 2018-12-28 19:29:41

Just in case anyone missed it... I really think this live, atmospheric video of the "Bighopper" construction site is rather brilliant!

https://www.youtube.com/watch?v=UHGlw9H_OaI

SpaceNut · 2018-12-29 14:39:04

The question belows here as well for the active cooling of the heatshield:

Void wrote:

https://en.wikipedia.org/wiki/Methane
I am speculating here that the needed cold to keep Methane liquid is attainable by sunshades and radiative cooling of a tank, perhaps even near Earth. I am thinking that to turn it into a slush, may not be beyond bounds.
So, as may be necessary, for a actively cooled heat shield, perhaps Methane would have to be used to cool through pores. But I like to at least have a shot at something more.
Water ice is, I believe relatively unique, in that it becomes lighter than the liquid phase.
I do not know about Methane Ice. I will need to be told.
But suppose a simple tank of Methane slush, perhaps stainless steel, is doing an aero capture. If the ice of slush of Methane is heavier than the liquid of Methane, then we might hope that the very strong g forces of aero capture will press the slush crystals against the inside of the tank on the windward side. How many g's quite a lot perhaps. So, you would have a phase change on the inside of the tank, and of course massive heat on the outside of the tank.
For the ship, I would have a separate tank for liquid Methane fuel to be burned with Oxygen to produce thrust as may be useful during the trip.
So just perhaps by such a method you can minimize the venting of Methane in order to survive Aero Capture.
But this will be dependent on being able to produce an appropriate slush, and that the ice of Methane is heavier than the liquid of Methane.
This I do not know so far.
If this is true, then the nature of the slush must be fluid for best effects in a 'g' force.
But you still may have a backup should a void appear , I think, where if ice crystals are not proximate enough to a part of the heat shield, perhaps liquid Methane would boil at that point and still cool the heat shield. To bubbles of boiling would travel "Upward" in the 'g' force field, and would encounter slush or liquid and should be containable as to build up of tank pressure.
I just prefer to avoid boiling as it might damage the interior of the heat shield. Still in that case the cargo ship might survive.
Lots to discover here.
Done.

So does slush of any fuel exhibit the solid being lighter than the liquid?

louis · 2018-12-29 19:13:41

News report on Space X activity at Boca Chica

https://www.youtube.com/watch?v=KQ1dNxjRqh4

SpaceNut · 2018-12-29 20:29:31

Not a video but here is a news story on the site... In 2008, the company’s Falcon 1 was the first privately developed liquid rocket to reach orbit. SpaceX now plans for Boca Chica to be operational before the end of 2018. Work on SpaceX’s Boca Chica launch site continues as it had to back fill the property to make it ready to build on.

SpaceX still doing site prep for Boca Chica launch pad east of Brownsville, to stabilize the ground there before construction of the launch site itself can begin.

https://en.wikipedia.org/wiki/SpaceX_So … aunch_Site

https://futurism.com/spacex-is-on-track … g-by-2018/

Once the facility is completed, people nearby will be able to watch rocket launches from a 4000-person amphitheater from the county’s planned rocket launch parties.

louis · 2018-12-29 20:32:13

Good to see Space X thinking commercially and also getting local people onside through job creation.

SpaceNut wrote:

Not a video but here is a news story on the site... In 2008, the company’s Falcon 1 was the first privately developed liquid rocket to reach orbit. SpaceX now plans for Boca Chica to be operational before the end of 2018. Work on SpaceX’s Boca Chica launch site continues as it had to back fill the property to make it ready to build on.
SpaceX still doing site prep for Boca Chica launch pad east of Brownsville, to stabilize the ground there before construction of the launch site itself can begin.
https://en.wikipedia.org/wiki/SpaceX_So … aunch_Site
https://futurism.com/spacex-is-on-track … g-by-2018/
Once the facility is completed, people nearby will be able to watch rocket launches from a 4000-person amphitheater from the county’s planned rocket launch parties.

louis · 2018-12-30 11:42:57

Another interesting video from Mic of Orion (ignore the superfluous intro about Robert "Zurbin" - there's no evidence Musk has ever been a "disciple" of Zubrin's).

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

louis · 2018-12-31 04:46:34

Interesting video about Gwynne Shotwell's key role at Space X...

https://www.youtube.com/watch?v=E3UmHzbT8fw

Probably underplays Musk's importance in order to shine a brighter light on Shotwell, but nevertheless, a v. interesting profile.

louis · 2019-01-01 06:35:10

Some nice close up shots of the Big Hopper as I am calling it.

https://www.youtube.com/watch?v=zv1FhhEY5L0

louis · 2019-01-01 12:58:05

And some nice aerial footage of the Boca Chica site...

https://www.facebook.com/CBS4RGV/videos … 322789105/

Void · 2019-01-01 20:34:00

Very exciting Louis.

https://www.youtube.com/watch?v=8smyzbepCD4

They are not kidding around it would seem.

Done.

louis · 2019-01-02 19:28:30

Exactly - I think they are really going for it. Whether they succeed is another matter but they are definitely going for it. This isn't NASA shadow-boxing.

A lot of this will relate to how much money Musk can throw at it. He seems v. confident. I am wondering whether there are already a lot of sponsorship deals in place but they are covered by NDAs, so we know nothing about them, but the money might already be flowing.

Void wrote:

Very exciting Louis.
https://www.youtube.com/watch?v=8smyzbepCD4
They are not kidding around it would seem.
Done.

louis · 2019-01-04 16:25:00

Another interesting vid from Scott Manley...

https://www.youtube.com/watch?v=XVgEKBwE2RM

Compromise rocket nozzle shape to get good performance at different altitudes...

It's interesting he says it doesn't look flightworthy! My impression also...

SpaceNut · 2019-01-04 19:40:22

Sorry gang but my junk computer can not do the videos so I am going to need something different..

Variable nozzles are nothing new and some are planned on being of the inflateable type as well but what they typically can not do without some real modifications is use a different fuel oxidizer type...

louis · 2019-01-04 20:48:01

What do you mean by "a different fuel oxidizer type"? Do you mean different from a standard oxidizer type? If so, what are we talking about here?

SpaceNut wrote:

Sorry gang but my junk computer can not do the videos so I am going to need something different..
Variable nozzles are nothing new and some are planned on being of the inflateable type as well but what they typically can not do without some real modifications is use a different fuel oxidizer type...

Oldfart1939 · 2019-01-04 21:41:27

I too, watched the Scott Manley video on YouTube. I gather what's being built is something to fly as a test bed only, so it doesn't need the sleek cosmetics of a Falcon 9 or Falcon Heavy. 3 engines, fuel tanks, avionics, and landing legs. So we must ask ourselves "what can this accomplish?" In reality, a lot. As far as we know, no Raptor has yet flown, and the throttle controls will be tested, in addition to the gimbaling for directional control. Of course, the control avionics will get a real workout. This will also be a major step forward using the methylox propulsion couple. If it's crude and still works--it's not that crude!

Oldfart1939 · 2019-01-06 15:39:34

Some other speculation appeared on Reddit--that the Starship we see may be just a prototype. It certainly looks pretty crude with slightly buckled panels and hurried looking construction. The motors may also be mockups. Could just be studying the assembly protocols for the real thing?

louis · 2019-01-06 16:27:34

Musk publishes pic of what the Big Hopper will look like....

https://twitter.com/elonmusk/status/1081576707365064704

1950s Sci-Fi mags rule!!!

SpaceNut · 2019-01-06 18:12:31

Shiny silver or charcoal grey rocket having no written values for its hieght, diameter, mass, fuel types needed for the many engines and thrusters, is just that art....

louis · 2019-01-06 18:50:06

You're saying Elon is scamming you with a bit of CGI art? I don't believe it. In Musk I trust.

SpaceNut wrote:

Shiny silver or charcoal grey rocket having no written values for its hieght, diameter, mass, fuel types needed for the many engines and thrusters, is just that art....

louis · 2019-01-06 19:17:22

Mic of Orion has his latest say on the Big Hopper...

https://www.youtube.com/watch?v=HnHwVog0UNA

RobertDyck · 2019-01-07 02:43:12

GW Johnson has posted on this forum that 300 series stainless has long been demonstrated with cryogenic temperatures. Stainless is established, durable and rugged. GW has pointed out aluminum alloy experiences metal fatigue, so can't handle as many pressurize/depressurize cycles. Aircraft handle a pressure cycle with every flight; how many flights per day? How many flights total before too much metal fatigue? Cryogenic cycling may accelerate fatigue. And I have no idea about composites. They're obviously lighter and can handle cryogenics, but I don't have any idea about fatigue. Using stainless may just be to take that variable out of the equation for testing the hopper.

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