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#751 2020-06-24 21:59:37

Oldfart1939
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Registered: 2016-11-26
Posts: 1,872

Re: Starship is Go...

I seem to recall Elon making a comment (on Reddit?) about the Lunar Starships being a one way mission for freight hauling? Then could be used as habitats for the astronauts. These could be cheaper to build since they would be one way transport systems carrying heavy load of supplies.

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#752 2020-06-25 09:21:45

Void
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Registered: 2011-12-29
Posts: 3,474

Re: Starship is Go...

I like that O.F.
You stimulated some thinking....I am very unsure what a tanker starship might need for propellants for a one way trip.  Maybe someone better could figure that out.

The reason I am going that direction is the need for pressurized living space on the cheep on the Moon.  The more the better, as far as I am concerned.  The Moon being more hostile than Mars, I presume that extra treated volume would be preferred.

GW has rightly told me that an empty shell in LEO would have serious value problems.  You would have to do a lot of additional expensive work to make it worth anything.  For LEO, it probably makes the most sense to prefab it on Earth, and pay the propellant costs of a Super Heavy.  I appreciate having my mind adjusted that way, so I don't have foundations of "Stupid".

But an empty shell of metal on the Moon could be a much better situation, I think, because of the materials of the Moon which could be converted into a resource.  I learn from Dr. Zubrin also.

So you send a propellant ship to the Moon to land.  You can take your choices. 

1) You only fill it enough for the one way trip with it itself being its only payload.
2) You attach large landing feet/cargo holds to the thing in LEO.  Of course those must be sent up with other Starships.  You totally fill the beast, and put cargo into the external cargo holds which are also landing legs/feet.

For #1, it lands, and we hope it does not topple in an unplanned way.

For #2, it lands, and you secure it from an unplanned topple.  You remove the cargo from the external cargo holds.  You might then remove the cargo holds themselves.  Possibly they would then be repurposed.  Perhaps they could become landing pads for future ships to arrive.

So you have vertical shells pointing up from the surface.  It is possible you might want to leave some of them that way for some purpose.  It is conceivable that solar panels would be already attached to the surfaces of them, or could be prefabbed so that they would be attachable.  This might suit a south polar base, as the sun should usually be not too far from the horizon.  To make it more sensible though there could be a bearing on the top of the shell, and the solar panels could sun follow in a slow rotation as the Lunar day progressed.

But to create real useful pressurized and/or radiation protected volume, it would be desired to lay them on their side.  That sounds like a lot of work if you have to do EVA's and have heavy equipment.  But, what if you could do it with rocket engines?

The small landing engines, if they are indeed part way up the ship as seems to be depicted in the illustrations I have seen, might be able to do it.  So, you could lay them on their sides, if that is indeed what and where they are.  Some other people have interpreted them as landing lights.  I guess I don't know why you would want to land in the dark, if at the South Pole most of the time there is sunlight.

Once on their sides, it may even be possible to "Roll" them in position.  Of course for that you will need heavy machinery.

Probably landscaping, that is to contour the lunar surface appropriately is needed first.

Then lay them down, perhaps roll and skid them where you want them.  Perhaps connect them together with modifications, involving cutting tools, and welding.

Then cover them with regolith.

I think that could go a long way towards making empty stainless steel shells useful on the Moon.

Radiation protection, protection from impactors, and thermal insulation.

That then suggests that some that are used in the upright mode may serve as thermal radiators, should your collection of shells, have an overheating problem.

Done.

Not done smile

If my interpretation of the small engines being engines up the body of the ship, and not landing lights, another trick might be available.

Do something a bit like the Vulcan.  Detach the engine section in LEO, and take it back down in a Starship.  A returned Raptor engines section should be valuable, I would think.

Then the Lunar bound tanker, would be lighter, and the little engines should be able to navigate the thing to the Moon and land it.  Only complication is if they are not Methane and Oxygen fed.  Then it gets a little different, but not impossible.

Done.

Not Done smile

Rather than rolling and skidding the things, perhaps a Tesla electric truck could be attached to the nose of the shell, and then jack up the tail end and put temporary wheels on it.  Drive it like a Semi.
https://www.bing.com/search?q=tesla+sem … lang=en-US

Done.

Last edited by Void (2020-06-25 10:18:30)


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

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#753 2020-06-25 16:08:35

Void
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Registered: 2011-12-29
Posts: 3,474

Re: Starship is Go...

I have an amendment for post #752.

And then my computer locks up, can't find the page when I try to save it, I have to shut down, and then clean things up.  Just love it.

Anyway, it makes no sense to put landing legs on case #1 and then later topple it horizontal.  Might as well land strait onto the engine skirt.  The raptor engine section having been removed in LEO, get rid of the legs for a further weight reduction.  Thump down just a bit, and initiate a controlled topple to horizontal.

Previously, it would be wise to rid of large rocks that might damage the hull.

The bring the Semi, and attachable wheels, and away it goes.

Done.

Last edited by Void (2020-06-25 16:23:30)


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

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#754 2020-07-03 19:55:10

louis
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From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Starship is Go...

Looks like it's 3 steps forwards after the recent 2 steps back.

https://www.youtube.com/watch?v=XbuxRJni5XY


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

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#755 2020-07-04 13:16:26

Oldfart1939
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Registered: 2016-11-26
Posts: 1,872

Re: Starship is Go...

It appears that SN 5 is being readied for a static test firing with Raptor SN 27. Probably as early as the 8th of July.

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#756 2020-07-09 05:48:04

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Starship is Go...

As always, Felix gives a very helpful update on where we are with Starship development.

https://www.youtube.com/watch?v=7fP8ZiOi10w


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

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#757 2020-07-09 13:40:38

Oldfart1939
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Registered: 2016-11-26
Posts: 1,872

Re: Starship is Go...

Starship SN 5 is being readied for a static firing. Possibly on the 10th of July, if road closures mean anything.

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#758 2020-07-13 21:35:50

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
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Re: Starship is Go...

In post 751,  Oldfart1939 said:

"I seem to recall Elon making a comment (on Reddit?) about the Lunar Starships being a one way mission for freight hauling? Then could be used as habitats for the astronauts. These could be cheaper to build since they would be one way transport systems carrying heavy load of supplies."

I think I understand why Musk said that.  In the last few weeks I have used my reverse-engineering results for Starship / Superheavy to quantify expected performance for lunar missions.  Despite the growth from 1100 tons to 1200 tons of propellant,  the growth from 85 to 120 tons of inert structure has just killed direct moon landings with Starship,  except for one-way strandings there.  Growth in inerts affects mass ratio far more strongly than growth in propellant. That affects delta-vee capability,  and quite adversely.

I'm still showing two-way trip capability to Mars,  using local refilling on Mars to come home.  But the payloads aren't as large as I found in 2019 and earlier. I'm still showing very respectable performance to LEO,  but again,  for 2020,  payloads are smaller. 

But for the moon,  two-way unrefilled travel is infeasible with the 2020 data,  and there is just no way around that conclusion.  I did find a couple of ways to send big payloads to the moon with the 2020 characteristics,  but these require send tankers to LLO and refilling the cargo Starship in LLO,  either before or after making the landing.

All this is posted over at my "exrocketman" blog site,  under the title "Non-Direct to the Moon with 2020 Starship" dated 7-13-2020 (looking at the refueling-in-LLO scenarios),  and "2020 Estimates for Spacex's Starship to the Moon" dated 7-5-2020 (examining the direct unrefueled landing scenario).

Beyond that,  I am now entering official geezer status tomorrow,  when I officially turn 70.

GW

Last edited by GW Johnson (2020-07-13 21:37:15)


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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#759 2020-07-13 21:42:14

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,196

Re: Starship is Go...

That's not sounding all that promising for the moon missions.

So how much fuel must be made on the moon to get one back home with the bare minimal of payload coming home.
Then again where is the carbon to make the methane with.....

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#760 2020-07-14 07:25:17

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

Re: Starship is Go...

The water,  if it really is there,  is at the south pole,  which is very hard to reach,  no matter what vehicle.  And the carbon simply is not there.  Refilling vehicles that use methane and lox seems unlikely on the moon,  at least to me.  Even lox-hydrogen doesn't look good,  because the resource is so limited.

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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#761 2020-07-14 13:57:46

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 478

Re: Starship is Go...

The moon may have some surprises in store for us when it comes to volatile elements.
https://www.sciencealert.com/the-moon-i … o-question

The surface is routinely baked at 100C temperatures in a hard vacuum.  It isn't surprising to find that a few billion years of that treatment has dried it out.  But drill a few metres beneath the surface and the story could be different.

But we can only plan for what we know now of course.

Last edited by Calliban (2020-07-14 13:58:40)


Interested in space science, engineering and technology.

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#762 2020-07-14 19:06:39

Void
Member
Registered: 2011-12-29
Posts: 3,474

Re: Starship is Go...

A very interesting post Calaban.  By the way, I did apologize for my activity on Alternate BFR.  I am going to borrow your info from this post.


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

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#763 2020-07-15 01:42:25

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 478

Re: Starship is Go...

No worries Void.  The giant impact hypothesis is plausible enough in my opinion.  But when modelling a scenario like that, a lot of assumptions tend to be made which are little more than educated guesses.  This happened very early in the solar system's history, whilst all of the planets were still embedded in the proto planetary disc.  How precise is our information on other inputs, like the luminosity of the sun at that time?

There is also the possibility that the Earth already had a fully formed satellite at the time of the giant impact with Thea.  The moon could be a hybrid of the material ejected from the impact and the original satellite.  Again an assumption.  Unless someone builds a time machine, we will forever be speculating on the exact conditions that preceded the creation of the moon.


Interested in space science, engineering and technology.

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#764 2020-07-18 14:58:36

Oldfart1939
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Registered: 2016-11-26
Posts: 1,872

Re: Starship is Go...

I will note here that I am in complete agreement with GW regards the availability of water on the lunar surface. If it IS there and IS scarce, then it's too valuable to be used in propellant production. Human habitation requires water for drinking and sanitation, and conversion to breathable Oxygen through electrolytic separation of water into it's constituent elements. Another possibility for using Lunar Landing Starships would be as tankers on the surface, avoiding orbital rendezvous for refueling. Once depleted, use them as construction elements for habitat modules.

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#765 2020-07-18 18:25:38

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,196

Re: Starship is Go...

What we are building in Texas is not even a scale model of the starship.

There aren’t many facts about the BFR available, but we do know that it’s designed to be around 350 feet tall, with an incredible 10.8 million pounds of thrust, which is a lot more than any rocket NASA has created.

Dammed mixed units of English and metrics....

350 ft is approximately 107 meters

What is being built is starhopper….
dims?thumbnail=640%2C&quality=95&image_uri=https%3A%2F%2Fs.yimg.com%2Fuu%2Fapi%2Fres%2F1.2%2FqoLd.jR3ie02a19YU64HqA--%7EB%2FaD0xMzY0O3c9MjA0ODthcHBpZD15dGFjaHlvbg--%2Fhttps%3A%2F%2Fo.aolcdn.com%2Fimages%2Fdims%3Fresize%3D2000%252C2000%252Cshrink%26image_uri%3Dhttps%253A%252F%252Fs.yimg.com%252Fos%252Fcreatr-uploaded-images%252F2019-09%252F5622d6d0-e15e-11e9-afff-c51aa4a0317a%26client%3Da1acac3e1b3290917d92%26signature%3Dd1cf2c64a25849da51b475eb65702528a2bab439&client=amp-blogside-v2&signature=5086bb97973bde4bb9b40ade030251251e7b9e91

50 meters long and powered by three Raptor engines, creating a whopping 12,000 kN of thrust.

Since this one has not been blown up it may get a chance to fly A new SpaceX filing with the FCC suggests Starship rocket prototypes may fly more than 12 miles above Texas within the next 7 months

So we are looking at a first stage that is roughly just 60 meters in height.

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#766 2020-07-19 17:46:07

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
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Re: Starship is Go...

Spacenut:

That's not "Superheavy",  that's the "Starship" second stage spacecraft.  It has an inert structural mass in the vicinity of 120 metric tons,  according to Mr. Musk's presentation at Boca Chica.  The Spacex website claims its propellant capacity is 1200 metric tons,  although I doubt this prototype has tanks that large.  It is supposed to be 50 m long,  and it is.  And it is the claimed 9 m diameter. 

The "Starship" design has a max of 6 engines,  3 sea level Raptors,  and 3 vacuum Raptors.  The vacuum Raptors cannot be used at sea level,  only the sea level Raptors,  which are supposedly rated at 2 MN sea level thrust each.  This prototype has 1,  maybe 2,  at most 3 sea level Raptors in it.  For a max 6 MN sea level thrust.  You cannot count the vacuum Raptors at sea level because they will self-destruct thermally if run there. And they probably are not in this prototype at all.

6 MN sea level thrust,  and Mr. Musk's Boca Chica value of sea level launch thrust/weight = about 1.5,  lead very quickly to a max launch mass of 271 metric tons for prototypes powered this way.  At 120 tons inert,  that leaves 151 metric tons for the sum of loaded propellant and payload.  Including any crew.  You can fly these second-stage prototypes by themselves for flight test purposes,  but you cannot load them anywhere near full propellant capacity if you do. At zero payload,  151 metric tons of propellant is only 12.58% of the max propellant capacity.

The first stage is the "Superheavy",  which Spacex has not yet built at all.  It is 9 m dia and well over 50 m long,  and according to Musk at Boca Chica,  has 37 sea level Raptor engines,  for some 74 MN sea level thrust.  Anything more than an abbreviated hop for a test,  will therefore require use of the "Superheavy" booster.  There is no way around those physics. 

What makes this work at all is that only the "Superheavy" first stage must fly vertically upward (and at initial thrust/weight 1.5 at that).  The trajectory bends over nearly horizontal,  and the air has greatly thinned to almost-but-not-quite-insignificant drag,  by the time it stages off and the "Starship" second stage ignites,  on its vacuum Raptor engines,  3 of them,  at about 4.5 MN thrust each.  It burns nearly (but not all) its propellant load getting to LEO. 

It has to keep a deorbit burn allowance and a landing burn allowance in order to survive the return.  That's somewhere between 5 and 20 tons,  depending upon the payload carried.  The deorbit burn can be vacuum Raptors,  but the landing MUST BE the sea level Raptors. 

Meanwhile,  the "Superheavy" has a 3300 or 3400 metric ton propellant capacity per Spacex's website (memory does not serve,  but it is in that ballpark).  It uses about half of that to reach the stagepoint,  which my estimates say is 1.8 km/s at around 50-60 km altitude. My estimates also say that it uses the other half to kill that forward velocity,  and add enough reverse velocity and velocity upward,  to parabolic-arc back to the vicinity of its launch point.  That's the reverse-course burn.  Then it does an entry burn to kill the gravitationally-accelerated velocity downward,  and then it does a final landing burn. 

It is pretty-much a hugely scaled-up Falcon-9 core,  but they say it will be made of stainless,  not lithium-aluminum (which has NO fatigue life). They want a lot more than 5-10 flights out of every "Superheavy". 

What Spacex is outlining for its testing program is pretty much the same as was presented by Von Braun in the 1950's Disney features about going into space.  You can do very limited suborbital flights with the upper stage all by itself,  then you have to add the lower stage to fly any further up and any faster. It really is that simple.

And even if there were 6 sea level Raptors in the tail of a "Starship",  there would only be 12 MN sea level thrust. For thrust/weight = 1.5,  that puts max launch mass at 542 metric tons.  120 tons inert plus 1200 tons propellant capacity plus a nominal 100 tons of payload is a design ignition mass of 1420 tons.  Vs 572 max for vertical self-launch of the second stage "Starship".  Which is why I laugh at the notion of ever using this vehicle as an SSTO. Not with these engines. There's no room for any more.

GW

Last edited by GW Johnson (2020-07-19 18:06:05)


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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#767 2020-07-19 17:57:24

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Starship is Go...

Great clarification GW!

GW Johnson wrote:

Spacenut:

That's not "Superheavy",  that's the "Starship" second stage spacecraft.  It has an inert structural mass in the vicinity of 120 metric tons,  according to Mr. Musk's presentation at Boca Chica.  The Spacex website claims its propellant capacity is 1200 metric tons,  although I doubt this prototype has tanks that large.  It is supposed to be 50 m long,  and it is.  And it is the claimed 9 m diameter. 

The Starship design has a max of 6 engines,  3 sea level Raptors,  and 3 vacuum Raptors.  The vacuum Raptors cannot be used at sea level,  only the sea level Raptors,  which are supposedly rated at 2 MN sea level thrust each.  This prototype has 1,  maybe 2,  at most 3 sea level Raptors in it.  For a max 6 MN sea level thrust.  You cannot count the vacuum Raptors at sea level because they will self-destruct thermally if run there. And they probably are not in this prototype at all.

6 MN sea level thrust,  and Mr. Musk's Boca Chica value of sea level launch thrust/weight = about 1.5,  lead very quickly to a max launch mass of 271 metric tons for prototypes powered this way.  At 120 tons inert,  that leaves 151 metric tons for the sum of loaded propellant and payload.  Including any crew.  You can fly these second-stage prototypes by themselves for flight test purposes,  but you cannot load them anywhere near full propellant capacity if you do. At zero payload,  151 metric tons of propellant is only 12.58% of the max propellant capacity.

The first stage is the "Superheavy",  which Spacex has not yet built at all.  It is 9 m dia and well over 50 m long,  and according to Musk at Boca Chica,  has 37 sea level Raptor engines,  for some 74 MN sea level thrust.  Anything more than an abbreviated hop for a test,  will therefore require use of the "Superheavy" booster.  There is no way around those physics. 

What makes this work at all is that only the "Superheavy" first stage must fly vertically upward (and at initial thrust/weight 1.5 at that).  The trajectory bends over nearly horizontal,  and the air has greatly thinned to almost-but-not-quite-insignificant drag,  by the time it stages off and the "Starship" second stage ignites,  on its vacuum Raptor engines,  3 of them,  at about 4.5 MN thrust each.  It burns nearly (but not all) its propellant load getting to LEO. 

It has to keep a deorbit burn allowance and a landing burn allowance in order to survive the return.  That's somewhere between 5 and 20 tons,  depending upon the payload carried.  The deorbit burn can be vacuum Raptors,  but the landing MUST BE the sea level Raptors. 

Meanwhile,  the Superheavy has a 3300 metric ton propellant capacity per Spacex's website.  It uses about half of that to reach the stagepoint,  which my estimates say is 1.8 km/s at around 50-60 km altitude. My estimates say that it uses the other half to kill that forward velocity,  and add enough reverse velocity and velocity upward,  to parabolic-arc back to the vicinity of its launch point.  Then it does an entry burn to kill gravitationally-accelerated velocity downward,  and then a final landing burn. 

It is pretty-much a hugely scaled-up Falcon-9 core,  but they say it will be made of stainless,  not lithium-aluminum (which has NO fatigue life).

What Spacex is outlining for its testing program is pretty much thesame as was presented by Von Braun in the 1950's Disney features about going into space.  You can do very limited suborbital flights with the upper stage all by itself,  then you have to add the lower stage to fly further up and faster. It really is that simple.

GW


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

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#768 2020-07-19 20:03:53

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,196

Re: Starship is Go...

I would say that based on the image that 30 meters is about what the tanks will be taking up for the ships fuel area. So twice the fuel could be at best with in the first stage for use based on it being nearly 60 meters....which ball parks the figure GW is quoting...

https://space.stackexchange.com/questio … the-raptor

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#769 2020-07-19 20:47:09

kbd512
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Registered: 2015-01-02
Posts: 3,561

Re: Starship is Go...

I still want to know if 2 solid rocket boosters could be added to the first stage and Raptors swapped with RS-25's in the second stage to improve the payload performance.

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#770 2020-07-20 07:49:10

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

Re: Starship is Go...

I am not at all sure that tanks designed to hold methane can be used to hold hydrogen without serious modification,  beyond just the wildly different volume ratios of fuel to oxidizer. But if they can,  and the volume ratios can be satisfied,  then I see no fundamental reason why RS-25's could not be installed in place of Raptors. 

Having the space and the fitments available to mount those RS-25's is quite another matter.  I do not know how many could fit.  And there is the demonstrated-in-test vulnerability of the conical aft tank dome to point thrust loads,  since they use that dome as a "thrust puck",  when they should not. The proper place to take those loads is the aft skirt ring where dome and cylinder join,  which their design does not have.  But if you use constant-thickness sheet metal instead of a forged and welded part,  you simply can't do that job right.  And they didn't.

Adding solid boosters to the Superheavy opens the same structural can of worms that going to a triple core opened with Falcon-Heavy.  The center core had to be completely redesigned to handle the side-booster loads.  So far,  no Superheavy hardware has been built;  it is easier to change a design at the paper stage.  That process proved quite costly with the already-flying Falcon-9.

However,  I rather doubt Spacex would consider these mods to the Starship/Superheavy design.  Their business model has always been to minimize outside vendors,  to do as much as possible in-house.  Somehow,  I doubt that will change. 

Plus,  if they can ever get the inert structure down closer to 100 tons instead of the current 120 tons,  the design just as it is,  will deliver more payload to LEO than SLS Block 2B,  and for 10-100 times lower price per launch.  Why should they change it?

GW

Last edited by GW Johnson (2020-07-20 07:53:59)


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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#771 2020-07-20 10:37:25

Oldfart1939
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Registered: 2016-11-26
Posts: 1,872

Re: Starship is Go...

The SpaceX business model and planning is superb. I don't disagree that maybe some strap-on boosters could benefit the payload to LEO for each flight, but with a multiplicity of launch vehicles, why bother? I too, expressed interest in some solid core strap-ons, but those would be throwaways, which violates the basic premise of reusablity being important for cost control per kilogram to orbit.

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#772 2020-07-20 13:30:09

kbd512
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Registered: 2015-01-02
Posts: 3,561

Re: Starship is Go...

GW,

I want to take the working parts of SLS and transfer them to Starship so we can finally shut down the SLS program since it can't provide the payload performance or marginal cost required.  All that development work could be transferred to Starship to allow SpaceX to recover the time and money squandered by Congress and their favored contractors.  Starship Super Heavy is still in the design iteration stage and that's pretty clear.  I want NASA to fully fund SLS development.  Let a company that's serious about producing results take a crack at the problem.  Congress and Boeing and Lockheed had their chance, but they didn't deliver.  I want results, not excuses.

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#773 2020-07-20 16:13:51

Oldfart1939
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Registered: 2016-11-26
Posts: 1,872

Re: Starship is Go...

kbd512=
There's just too much "cultural bias," built in to the space program for such a thing to happen. It's the "Old Space" crew, and the "old way of doing things," that you're battling. A mix and match space vehicle would be fun to build from all the best parts, but "ain't gonna happen."

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#774 2020-07-20 17:27:45

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,196

Re: Starship is Go...

https://en.wikipedia.org/wiki/Rocket_propellant
http://braeunig.us/space/thermo.htm
https://www.brighthubengineering.com/ma … uel-ratio/

Even if you have a 6:1 mass ratio of LOX to LH2, the volume ratio is 6:16 or 1/2.7, ie the hydrogen tank is 2.7 times as big as the oxygen tank. The ideal mass ratio in rocket engines is 1kg of methane for every 3.6 kg of oxygen.

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#775 2020-07-20 19:34:58

kbd512
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Registered: 2015-01-02
Posts: 3,561

Re: Starship is Go...

Oldfart1939,

A pair of SLS SRB's, the Starship Super Heavy booster, and the RS-25 powered Starship (3X RS-25D's) with its 9m diameter tank and a length of ~15m provides enough LOX/LH2 in the upper stage to mirror Starship performance, assuming a prototypical launch from KSC to LEO and that the inert stage masses for Starship Super Heavy remain unchanged (highly unlikely).  The upper stage wet mass, less payload, is around 420t.  The payload performance estimate is 152t and ranges between 111t and 204t.

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