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#101 2019-01-12 18:06:05

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 15,823

Re: Starship is Go...

A test article is a final design full size not a scaled version not a functional subset still trying out features, to make sure that there are no more design bugs within the design, that it is capable of performing all functions unaltered.

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#102 2019-01-12 19:06:36

louis
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From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

Interesting video again from CloudLicker

https://www.youtube.com/watch?v=KA8IiBPxRXU

Takeaway points:

1. They are already building the bulkheads for tanks for the Starhopper (as it seems people are now calling it).

2. The whole of the Starship/Super Heavy rocket will be shiny silvery steel.


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

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#103 2019-01-17 12:16:16

louis
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From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

Great new update from Curious Elephant.


https://www.youtube.com/watch?v=2i91ugBKjUA

According to CE, BFR is still the name for the whole rocket system Superheavy Plus Starship.


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

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#104 2019-01-18 05:12:50

elderflower
Member
Registered: 2016-06-19
Posts: 1,096

Re: Starship is Go...

So, Spacenut,since the spacex hopper is not full size and therefore not a test article, what shall we call it? How about, since it is a bit shorter than a test article would be, we shorten the description "test article" by deleting the bit in the middle thus "test----icle"?

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#105 2019-01-18 13:30:30

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,565
Website

Re: Starship is Go...

I do see a recurring failure of some to distinguish between a flying test article and a real spacecraft.  There is no way in hell the real BFS is going to re-enter with a bare stainless steel skin.  Or any other metal.   It WILL be covered by some sort of thermal protection layers. 

At peak heating about halfway through re-entry,  the flight speed is about 4000 m/s,  for a driving temperature of ~4000 K!  Yep,  I said 4000 K!!!  And I mean it.  There is convective heating to the surface,  and radiation to the surface from the incandescent plasma that is the slipstream.  Under 10,000 m/s,  convection dominates. The only saving grace is the air is SO thin ~60 km up. That lowers film coefficients.

Conservation of energy requires that the rate of heat built up in the materials equals the input heating,  minus the heat lost.  Heat lost includes re-radiation to the environment,  heat conduction into the interior,  and heat lost to active fluid cooling,  if any. 

Radiative cooling works best at high surface temperatures,  beyond red-hot!  You can forget aluminum and titanium.  Some stainless alloys might work,  but they are butter structurally at such temperatures.  Inconel-X (Inconel X-750) works better but is very heavy and expensive.  There are a tiny handful of others. 

That is why most TPS systems are exotic metallics-over-insulation,  ceramic insulation tiles or blankets,  or slow ablatives like carbon-carbon or PICA-X.  And those last require special insulated designs to slow heat flow into the interior.

And don't point at aluminum Falcon first stages "re-entering".  They do NOT come back that fast!  First stage entry is nearer 900-1000 m/s,  where heating is far,  far,  far less.  They do deceleration and entry burns to enforce that. 

A test article flight made subsonic at low altitude can be bare steel or even bare aluminum,  or even organic-matrix composites.

Don't read so much into the new "grasshopper" in south Texas.  It is what it is,  and nothing more.

GW

Last edited by GW Johnson (2019-01-18 13:43:33)


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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#106 2019-01-18 13:42:29

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

Hi GW,

Elon seems to disagree with you:

https://twitter.com/elonmusk/status/107 … 76?lang=en

He seems to set great store by mirror-like reflectivity of radiation.

Any thoughts on what Musk says?



GW Johnson wrote:

I do see a recurring failure of some to distinguish between a flying test article and a real spacecraft.  There is no way in hell the real BFS is going to re-enter with a bare stainless steel skin.  Or any other metal.   It WILL be covered by some sort of thermal protection layers. 

At peak heating about halfway through re-entry,  the flight speed is about 4000 m/s,  for a driving temperature of ~4000 K.  These is convective heating to the surface,  and radiation to the surface from the incandescent plasma that is the slipstream.  Under 10,000 m/s,  convection dominates.

Conservation of energy requires that the rate of heat built up in the materials equals the input heating,  minus the heat lost.  Heat lost includes re-radiation to the environment,  heat conduction into the interior,  and heat lost to active fluid cooling,  if any.  Radiative cooling works best at high surface teperatures,  beyond red-hot.  You can forget aluminum and titanium.  Some stainless might work,  but is butter structurally at such temperatures.  Inconel-X (Inconel X-750) works better. 

That is why most TPS systems are exotic metallics,  ceramic tiles or blankets,  or slow ablatives like carbon-carbon or PICA-X. 

And don't point at aluminum Falcon first stages "re-entering".  They do NOT come back that fast!  Entry is nearer 900 m/s,  were heating is far less.  They do deceleration and entry burns to enforce that. 

A test article flight made subsonic at low altitude can be bare steel or even bare aluminum,  or even organic-matrix composites.

Don't read so much into the new "grasshopper" in south Texas. 

GW


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

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#107 2019-01-18 13:47:56

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,565
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Re: Starship is Go...

Lois:

Look in your high school physics book.  It is non-reflective "black" surfaces that radiate efficiently.  Reflective "shiny" or "white" surfaces must be very much higher temperature to radiate the same energy. 

The phrase "mirror-like reflectivity of radiation" is utter nonsense. 

All this does is show "for sure" that Elon is not the technical "brains" behind the BFR/BFS design. 

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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#108 2019-01-18 15:29:52

louis
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From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

You've TG'd me from Louis to Lois!

I'm not saying you're wrong but I'd be surprised if Musk wasn't repeating something's he's heard from his technical staff unless perhaps this is a subtle sort of disinformation campaign aimed at his rivals!

I presume from the other discussions about materials that "stainless steel" is a shorthand and we aren't literally talking about ordinary stainless steel.

GW Johnson wrote:

Lois:

Look in your high school physics book.  It is non-reflective "black" surfaces that radiate efficiently.  Reflective "shiny" or "white" surfaces must be very much higher temperature to radiate the same energy. 

The phrase "mirror-like reflectivity of radiation" is utter nonsense. 

All this does is show "for sure" that Elon is not the technical "brains" behind the BFR/BFS design. 

GW


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

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#109 2019-01-18 16:47:56

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,565
Website

Re: Starship is Go...

Sorry,  Louis.  Think of it as more typo than TG.  My keyboard is failing.  The u-key is one of several that is very difficult to get anything from.

Whether "shiny radiation" is deliberate or uneducated misinformation from Musk doesn't matter.  He has people who know these things,  even if he doesn't.  Although by now,  he should. 

My guess is is new "grasshopper is probably 304L stainless.  Good for cryogenics,  good structurally to ~900-1000 F,  nonscaling (but weak as butter) to ~1200 F. 

A real flight vehicle,  if really made of stainless for the cryogenics,  would be better as 316L.  Free of scale to 1600 F,  but still weak above 1000 F.  Still quite readily available.  347L is another,  similar candidate,  not quite as cheap. You need the L-suffix grades for welds that don't crack.

I know of a black ceramic paint that might stay on in high-speed air.  I don't know of any metallurgical black coatings for 300-series stainless. 

Actually,  I'd just glue PICA-X all over the stainless hull,  if it was my design.

GW

Last edited by GW Johnson (2019-01-18 16:49:24)


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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#110 2019-01-18 18:24:19

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,823

Re: Starship is Go...

The shiny principle that Louis is refuring to is how How Does a Thermal Blanket Work? The thermal blanket is more than 80 percent reflective in that the body heat of its wearer is sent back to the person under it. The issue is the heat is coming from the air friction against the metal surface and no matter how much polishing the air will always heat up the metal on atmospheric entry.

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#111 2019-01-18 18:26:19

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

I wouldn't presume to claim I follow all the technical info but Space X's CGI  versions of the Starship imply a stainless steel body, no black paint or glued-on ceramics.  Hopefully we shall see before too long what the reality is. smile


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

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#112 2019-01-18 18:34:37

louis
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From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

New Mic of Orion video (good stuff).

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

He references Elon's tweet suggesting the orbital Starship will be available June 2019.  smile  Let's hope so.  That would mean a 2022 cargo flight would definitely be feasible.

BTW - I note the number of YT vids covering the Starship is growing at a huge rate.  I see this as the beginning of  "hockey stick" graph - interest is going to build and build. In my view sponsorship opportunities for Space X will grow and grow as interest develops. By this time next year we could really be in the grip of a "Mars fever" if orbital Starships have already flown. smile


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

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#113 2019-01-18 20:09:03

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,823

Re: Starship is Go...

Falcon 9’s Grasshopper and F9R (Reusable) hop test articles, this ungainly Starship hopper – standing an impressive 9m (29.5 ft) wide and ~40m (131 ft) tall. The Grasshopper runs, which helped SpaceX get ready to land and re-fly Falcon 9 rocket first stages, reached a maximum altitude of about 2,500 feet (700 meters).

SpaceX said it planned a combination of low-altitude flights, going no higher than 500 meters, and high-altitude ones, going as high as 5,000 meters, from the Texas site. Which it will not see anything real to a reentry temperature for oing only up and down to that altitude.


SpaceX had developed a “superalloy” for Raptor, called SX500, designed to handle hot oxygen-rich gas at pressures of up to 12,000 pounds per square inch.

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#114 2019-01-19 07:29:47

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

Latest from Cloudlicker...

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

Lots happening at Boca Chica.


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

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#115 2019-01-20 19:39:48

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,823

Re: Starship is Go...

?url=https%3A%2F%2Fg.foolcdn.com%2Feditorial%2Fimages%2F507155%2Fbfr-is-spacex.jpg&w=700&op=resize

Elon Musk's New SpaceX Starship: Here's Everything We Know So Far

Time is running out for Boeing, Lockheed Martin -- and NASA's Space Launch System

Musk now puts the chances of Starship Mark I reaching orbit by 2020 at "60% and rising rapidly."

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#116 2019-01-23 18:13:54

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

Star Hopper is Gone...blown over by high winds! From Mic of Orion:

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

I did wonder about that - hurricanes being the obvious danger in South Texas. I never expected "high winds" to topple it!!

Not good news.


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

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#117 2019-01-23 19:34:28

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,823

Re: Starship is Go...

Thats almost comical to not secure it when vertical....Now you know why Nasa moved the shuttle on the crawler locked in...

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#118 2019-01-23 20:33:13

Oldfart1939
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Registered: 2016-11-26
Posts: 1,647

Re: Starship is Go...

The problem: large side area--little weight to keep it standing. They built the original in about 2 weeks; suspect it can be replaced faster than repaired.

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#119 2019-01-23 20:36:47

kbd512
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Registered: 2015-01-02
Posts: 2,889

Re: Starship is Go...

I see that SpaceX has just discovered why the landing gear track needs to be significantly wider.  It's almost as if GW knew what he was talking about when it came to landing gear requirements for rough field performance.  However, that was a much shorter version sitting on a concrete slab without 100 tons of cargo suspended 75m+ in the air.  At least nobody was hurt.

SpaceX welds the landing gear pads to the deck of the recovery drone ship immediately after touchdown, so it's not like they're unaware of what can happen.  This incident seems like poor supervision.  Oh well.  I'm sure a new one can be built in another few months.

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#120 2019-01-23 21:48:56

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 501
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Re: Starship is Go...

On the SpaceX forum on Reddit is being discussed that the plan is to use transpiration cooling on the BFS for thermal protection:

Elon Musk: Why I'm Building the Starship out of Stainless Steel.
Musk tweeted in January that the rocket formerly known as BFR would be built of stainless rather than carbon fiber. In this exclusive interview, he tells PM Editor in Chief Ryan D'Agostino why.
As Told To Ryan D'Agostino
Jan 22, 2019
https://www.reddit.com/r/spacex/comment … h=f985179a

Bob Clark

Last edited by RGClark (2019-01-24 05:33:12)


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

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#121 2019-01-24 03:54:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

I can't see it toppling over on Mars due to wind.  And I can't see it toppling over in anything less than a 5% gradient. But non-stable ground or poor cargo-loading/unloading could do it.


kbd512 wrote:

I see that SpaceX has just discovered why the landing gear track needs to be significantly wider.  It's almost as if GW knew what he was talking about when it came to landing gear requirements for rough field performance.  However, that was a much shorter version sitting on a concrete slab without 100 tons of cargo suspended 75m+ in the air.  At least nobody was hurt.

SpaceX welds the landing gear pads to the deck of the recovery drone ship immediately after touchdown, so it's not like they're unaware of what can happen.  This incident seems like poor supervision.  Oh well.  I'm sure a new one can be built in another few months.


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

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#122 2019-01-24 04:58:42

elderflower
Member
Registered: 2016-06-19
Posts: 1,096

Re: Starship is Go...

A hold down arrangement with bolts or clips that would melt as soon as the engines ignite would do the job for the empty vehicle on a pad. It wont work on Mars though. Maybe tin/lead/silver soldering?

Last edited by elderflower (2019-01-24 05:04:59)

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#123 2019-01-24 11:17:49

Oldfart1939
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Registered: 2016-11-26
Posts: 1,647

Re: Starship is Go...

kbd512 wrote:

I see that SpaceX has just discovered why the landing gear track needs to be significantly wider.  It's almost as if GW knew what he was talking about when it came to landing gear requirements for rough field performance.

Stability of lightweight structures need for the center of gravity to remain within the footprint of the supporting structures. The center of aerodynamic pressure put a force vector outside that footprint and exceeded the downward vector holding it to the ground.
Blows over. QED. The wider the footprint, the better the inherent stability of the vehicle against tipover. This was an unintended consequence of building the vehicle in a windy environment, but probably resulted in an excellent demonstration--better than any planned stability experiments.

Last edited by Oldfart1939 (2019-01-24 11:18:46)

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#124 2019-01-24 11:43:53

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,565
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Re: Starship is Go...

High winds during storms in Texas is not unexpected for residents.  Out here on this farm on top of a hill that acts like a wind tunnel,  my local wind speeds are nearly always 40-50% higher than officially reported at Waco airport a few miles away. 

In 30-some years,  I've been through 7 straight-line wind storms out here at 100+ mph,  and hundreds at 70+ mph.  The worst was 122 mph.  Straight-line gust fronts,  not tornadoes.  (Been through those,  too.)

Decades ago I was driving home from work to the farm in an old VW camper bus,  when such a gust front overtook me from the rear. The speedometer pegged,  but from the tach I figured 80-85 mph,  far faster than that vehicle's top speed.  I also noticed a nearly-closed throttle.  Rolled the window down and stuck my arm out into dead air (an 80-85 mph tailwind).  Such are common out here.

Out-of-staters not familiar with life on the great plains are unaware of high wind dangers.  That includes Californians.  It's usually not so bad in far south Texas,  but it can be.

Landing leg spacing is not the only difficulty the Spacex design faces.  There is also surface bearing strength.  They have ONLY ever landed on concrete pads or solid steel barge decks.  Natural "dirts" are very much weaker.  The soil bearing capacity needs to be at least twice the applied bearing load,  to keep the legs from digging-in during the landing transient. 

The applied bearing load is vehicle weight divided by the sum total of the landing pad areas able to contact the ground.  Spacex's landing pads are way too small to function adequately,  even on tight-packed sand-and-gravel-with-rocks that requires a pick to remove. I explored this in the BFS evaluation I posted over at "exrocketman" some months ago.

SLIGHTLY-inadequate soil bearing strength for the applied building weight is precisely why the Leaning Tower of Pisa leans. Even if you might land successfully at near-burnout weight,  it gets a lot heavier when you reload propellant.  That refuelling may topple your spaceship. Even at 0.38 gee.

GW

Last edited by GW Johnson (2019-01-24 11:49:32)


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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#125 2019-01-24 12:00:45

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,709

Re: Starship is Go...

It's very odd they failed to address the high wind problem. Someone has fouled up big time. Some form of protection would not have been that costly to build or put in place (e.g. three diggers supporting the sides).

We get major gusts in the UK which regularly blow over high sided trucks.  This was a foreseeable hazard for sure.

I too am concerned about the small size of the footprint of the fin-pads.


GW Johnson wrote:

High winds during storms in Texas is not unexpected for residents.  Out here on this farm on top of a hill that acts like a wind tunnel,  my local wind speeds are nearly always 40-50% higher than officially reported at Waco airport a few miles away. 

In 30-some years,  I've been through 7 straight-line wind storms out here at 100+ mph,  and hundreds at 70+ mph.  The worst was 122 mph.  Straight-line gust fronts,  not tornadoes.  (Been through those,  too.)

Decades ago I was driving home from work to the farm in an old VW camper bus,  when such a gust front overtook me from the rear. The speedometer pegged,  but from the tach I figured 80-85 mph,  far faster than that vehicle's top speed.  I also noticed a nearly-closed throttle.  Rolled the window down and stuck my arm out into dead air (an 80-85 mph tailwind).  Such are common out here.

Out-of-staters not familiar with life on the great plains are unaware of high wind dangers.  That includes Californians.  It's usually not so bad in far south Texas,  but it can be.

Landing leg spacing is not the only difficulty the Spacex design faces.  There is also surface bearing strength.  They have ONLY ever landed on concrete pads or solid steel barge decks.  Natural "dirts" are very much weaker.  The soil bearing capacity needs to be at least twice the applied bearing load,  to keep the legs from digging-in during the landing transient. 

The applied bearing load is vehicle weight divided by the sum total of the landing pad areas able to contact the ground.  Spacex's landing pads are way too small to function adequately,  even on tight-packed sand-and-gravel-with-rocks that requires a pick to remove. I explored this in the BFS evaluation I posted over at "exrocketman" some months ago.

SLIGHTLY-inadequate soil bearing strength for the applied building weight is precisely why the Leaning Tower of Pisa leans. Even if you might land successfully at near-burnout weight,  it gets a lot heavier when you reload propellant.  That refuelling may topple your spaceship. Even at 0.38 gee.

GW


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