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#76 2023-10-05 11:47:54

Steve Stewart
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From: Kansas (USA)
Registered: 2019-09-21
Posts: 161
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

fN5AikY.jpg


SpaceX's mega-rocket has a 'decent chance' of making orbit

This time, Musk said Starship's engines will be lit while it's essentially still connected to its booster.

...

"Of course, it's the first time we're doing it. And I'd say that's the riskiest part of flight two," Musk said during a livestreamed interview at the International Astronautical Federation annual conference on Thursday.

"If the engines light and the ship doesn't blow itself up during stage stuff, then I think we've got a decent chance to reach orbit," he added.

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#77 2023-10-05 12:35:05

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,464
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Well,  I hope they succeed. 

Hot staging has been done for decades,  but never with items intended to be reusable.  One has to add some blast and heat protection to the forwardmost surfaces of the lower stage,  lest the rocket blast rip it apart locally.  The Russians did this with an open truss between stages. 

And,  there is a risk to the engines and rear surfaces of the upper stage,  even if you use the open truss.  But much more so if your interstage won't let massive quantities of hot gas go freely through.  The Starship./Superheavy interstage is,  or at least was,  a solid ring.

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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#78 2023-10-05 13:05:15

tahanson43206
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Registered: 2018-04-27
Posts: 17,301

Re: SpaceX should withdraw Starship as an Artemis lunar lander.

If someone has really sharp eyes, it might be possible to see what SpaceX has put in place for the interstage fitting, because the rocket is stacked and various news media have been looking at it for some time now.

(th)

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#79 2023-10-07 09:56:44

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

kbd512 wrote:

RGClark,

Boeing's proposal more is more of the same exceedingly expensive non-reusable hardware intended to be another reprise of the unsustainably expensive Apollo missions.  It does nothing to advance the state-of-the-art, nor does it achieve anything from a scientific understanding that will be useful for long term human habitation of space or colonization of other planets.

Refueling your ship, even if you have to do it 8 times to completely fill its tanks, is the least absurd proposal I've seen, if cost and general utility are at all important.  SpaceX has already demonstrated the launch cadence to make that happen.  Eventually we'll require on-orbit refueling to send people and cargo to other planets with any regularity.  If we develop this technology now, then it doesn't need to be developed later.  They're advancing the art of aerospace engineering, drastically improving our capabilities to land serious tonnage on other planets, and returning them home, all using the same basic launch vehicle design with 3 variants- crewed, cargo, and tanker.
150t of payload to the moon is enough to do lots of useful long-term science and exploration missions.  It's a Space Shuttle that can go to other planets with 5X more payload than the Space Shuttle, land on those "other planets", which the orbiter was never designed to do, and then return to Earth.  Why settle for reduced capability that can never do what we want it to?
The Boeing proposal requires 2 SLS launches at $2B each, 2 new rocket stages for their lunar lander, and a new aerospace vehicle design.  It took Lockheed-Martin and Boeing more than 10 years to develop new vehicles.  As of 2023, the first crewed flight has yet to occur.  The Apollo Program lasted from about 1965 to 1975, from start to finish.
If Boeing said "we're going to spend $3B to deliver a working lunar lander in 2 to 3 years", I'd be onboard with that, but Boeing's ability to accurately estimate cost and timeline is nonexistent.  This is essentially the same as delivering a B-2 stealth bomber.  We're spending a known quantity of money to deliver a known quantity result.  That is not what Lockheed-Martin and Boeing actually do.

The Starship HLS lander is overly large. It’s literally a hundred times larger than it needs to be for a lunar lander, assuming the Starship fully-fueled at 1,200 tons propellant and a 120 ton dry mass so 1,300 tons gross mass. But an Apollo style lander could be done at ca. 13 tons gross mass:

Thursday, November 10, 2022
A low cost, lightweight lunar lander.
https://exoscientist.blogspot.com/2022/ … ander.html

The argument is made that it could carry more cargo to the Moon. But remember by their plan each launch must be accompanied by a SLS launch. But the SLS is far too expensive to use for cargo launches, at ca. $2 billion per launch. For cargo instead use commercial launches. For instance the Falcon Heavy could get ca. 15 tons to the lunar surface one way by using cryogenic in-space/lander stages.


  Bob Clark

Last edited by RGClark (2023-10-07 09:57:42)


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#80 2023-10-07 10:31:25

RobertDyck
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

index.php?action=dlattach;topic=59110.0;attach=2202450;image

images?q=tbn:ANd9GcTvYmmz0S4bf199zA4JnYt7apM6NZMUi9Ly-pyA7RmdeopVXY0&s

The hot stage vent ring has a dome to protect the first stage tank dome from hot exhaust.

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#81 2023-10-19 09:47:00

Steve Stewart
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From: Kansas (USA)
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Posts: 161
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

From space.com

SpaceX stacks Starship to gear up for launch rehearsal (photos)
Posted 2 days ago



VVO9Thi.jpg

The work — which took place at Starbase, the company's facility on South Texas' Gulf Coast — is part of the leadup to Starship's second-ever test flight, which SpaceX hopes to launch soon.

...

The FAA is the U.S. Federal Aviation Administration, which recently wrapped up its investigation of Starship's first-ever test flight, which occurred on April 20.

...

Elon Musk has said that the latest Starship vehicle is ready to go from a technical standpoint; SpaceX has successfully test-fired the Raptor engines on both of its stages, for example.

But, as the above post on X notes, the company is still waiting for a launch license from the FAA.


YouTube Video
Starship Stacked and then Destacked - SpaceX Boca Chica
8m 53s
(Skip the first 2 minutes. Fast forward to 2m)
Video shows time-lapse video of the stacking and unstacking of Starship
Posted 1 day ago

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#82 2023-12-19 07:37:45

RGClark
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From: Philadelphia, PA
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Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Two separate, independent methods suggest SpaceX throttled down the booster engines < 75%, while the Starship engines fired at ~90% thrust.

This is important to know because if the engines need to operate at < 75% to be reliable, then I estimate the reusable payload would be lowered from 150 tons to ~100 tons. Then instead of needing perhaps 16 refueling flights for the Artemis landing missions there would need to be perhaps 24.

Did SpaceX throttle down the booster engines on the IFT-2 test launch to prevent engine failures?
http://exoscientist.blogspot.com/2023/1 … oster.html

  Robert Clark


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#83 2023-12-19 10:51:53

GW Johnson
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

If the deliverable propellant payload to low-inclination eastward LEO with Starship/Superheavy is 100 metric tons,  the propellant tank capacity of a Starship on orbit is 1200 metric tons,  the ship is there with essentially dry tanks,  and all we are delivering is propellant,  then the number of tanker flights is 1200 m.tons / 100 m.tons per tanker = 12 tanker flights. 

On the other hand,  if deliverable propellant payload to LEO is nearer 150 m.tons,  then the number of tanker flights is 1200/150 = 8.  Which is pretty near what I was saying a couple of years ago,  when others were saying 4 to 6,  for the same claimed payload capacity.  You can do my idiotically-simple little calculation any time you want,  to see who is lying and who is not.

As for tanker designs,  they have some concepts on paper,  but that's all.  Supposedly,  the initial "tanker" is just a cargo Starship without any payload in its cargo bay,  yet flown with full tanks so that there is significant unused propellant aboard upon reaching LEO.  You cannot deliver all of that,  unless you sacrifice the vehicle. 

To re-use the vehicle,  you must retain aboard it enough propellant to do a deorbit burn,  any entry burns,  and the landing burn.  That might be around 20-50 tons or so.  The operative word here is "might".  The rest of the unused propellant can be transferred on-orbit,  in the "tanker" role.  What that number really is,  who knows?  Not even anybody at SpaceX yet knows "for sure". 

However,  no one can yet testify as to the accuracy of the payload delivery numbers projected.  They are only projections,  after all.  This design has yet to reach orbit and return successfully for the very first time.  And the Starship test vehicles still bear very little resemblance to any of the design concepts.  If trends follow everyone else's experience,  the inert mass is going to grow by the time this design is finalized. That really cuts into performance projections,  more than any other factor. 

To the best of my knowledge,  Raptor-2 is what they are flying,  with a shorter bell for sea level,  and a longer bell for vacuum.  It does better than Raptor-1 did,  because they were never able to even reach the design Pc with Raptor-1.  Its turbopump design was not good enough.  They did reach full Pc with Raptor-2,  but the question is,  can they routinely operate there?  Is something else standing in the way?  SpaceX has been close-mouthed about that.

There is supposedly a Raptor-3 design with even more thrust capability.  I would hazard the guess that these are still in experimental test on the ground.  Some may get flown,  but they still have a stockpile of Raptor-2's to fly.  And I would find it very unsurprising if they have run into something unexpected that has forced them to reduce thrust setting to avoid catastrophic failures.  The experience of others is full of exactly such examples. 

The title of this thread says SpaceX should withdraw Starship as an Artemis lunar lander.  I'm not sure that should be done.  NASA has no landers that are anywhere near ready,  from anyone.  Not Blue Origin,  not anybody else.  There are concepts and paper designs,  but nothing ready.  And,  bear in mind that any of these concepts will see the very same kind of mistakes-and-failures history being made ready. 

NASA had no business telling the world a few years ago that they were going to put people on the moon in 2024.  Their old hands probably knew that,  back when those announcements were made.  But the older hands were probably muzzled.  The main mismanagement problem that ultimately caused the Apollo-1 fire,  the loss of Challenger,  and the loss of Columbia,  has NEVER been fixed: managers do NOT want to listen to their senior engineers,  the ones actually experienced enough to know better.  They never have wanted to listen to facts they didn't want to hear. 

Sometimes NASA management gets away with this misbehavior,  sometimes not.  And when they do not,  people die.  Which is the most expensive outcome of all.

When you combine that kind of management with Congressional micromanagement of budgets and objectives (incompetently,  I might add),  you get exactly what we have seen for decades now:  $billions spent in LEO without any people ever going outside LEO,  and without addressing the long-known needs for spin gravity and solar flare radiation protection.

I am not surprised at all that no single component of Gateway has yet been launched,  when that is supposedly "the" way to go back to the moon and on to Mars.  And yet that supposed "enabling station" does NOT address spin gravity or solar flare radiation protection. 

Does anyone else see what I see:  there is no intention at NASA management (or the Congress that controls it) of doing anything but what they have been doing since the end of Apollo? (update 12-20-23:  Which is only corporate welfare for outfits sited in the districts of powerful members of Congress.) 

I think they know that at SpaceX.  The "old space" outfits certainly know it.

We will see how this plays out;  whether SpaceX can milk some more funds from the government to get Starship/Superheavy working right.

GW

Last edited by GW Johnson (2023-12-20 10:17:48)


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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#84 2023-12-21 12:19:53

RGClark
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From: Philadelphia, PA
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Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

SpaceX @SpaceX
Flight 3 Starship completed a full-duration static fire with all six of its Raptor engines.
Embedded video
0:11 5:40 PM · Dec 20, 2023·1.3M Views
https://twitter.com/SpaceX/status/17376 … 33181?s=20

I really dislike this phrasing of SpaceX of calling a burn “full duration” to mean it lasted the planned time of the burn, even if it was only 5 seconds. It used to be the term “full duration” meant the length of an actual flight burn, which will be several minutes long.

If you want to say the burn lasted the planned length just say it lasted the planned length.

It’s hard to believe that both the FAA and NASA would be effected by this “Jedi mind trick”: just call it “full duration” and that means the engines have been fully flight qualified for a full burn time in flight.

  Bob Clark

Last edited by RGClark (2023-12-21 23:35:21)


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#85 2023-12-21 15:16:04

tahanson43206
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Posts: 17,301

Re: SpaceX should withdraw Starship as an Artemis lunar lander.

For RGClark re #84

Thanks for the link to the test video!

Regarding the length of a test .... I don't know the answer to this question, but I'm assuming/hoping the SpaceX folks do ...

How long is it appropriate to run engines to be confident the systems are working, before increasing risks overwhelm the benefit of the test?

If all the hardware has a fixed life before it has to be rebuilt, then it seems to me reasonable to avoid unnecessary exercise.

These engines are intended to be used over and over again, with maintenance.

I'd definitely be interested in the opinions/suggestions/recommendations of more knowledgeable members.

(th)

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#86 2023-12-21 17:15:34

SpaceNut
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From: New Hampshire
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Posts: 28,958

Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Watch: Starship’s third flight on track after successful engine test]AA1lPPWt.img?w=768&h=512&m=6

static fire test of its Starship upper-stage prototype, Ship 28, at its Starbase facility in South Texas on December 20

SpaceX is confident that it can overcome these challenges and launch Starship again soon, as evidenced by the rapid testing of Ship 28 and its companion, Booster 10. However, the company still needs to obtain a launch license from the Federal Aviation Administration (FAA) to investigate the cause of the November mishap. The FAA will issue a license once it is satisfied that SpaceX has taken the necessary corrective actions to ensure safety and compliance.

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#87 2023-12-21 17:54:40

RobertDyck
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From: Winnipeg, Canada
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Did you notice the flame appeared as a triangle, then the triangle inverted? That means they fired 3 engines, then the other 3. If they fired all 6 at once, there was danger of the rocket launching. Yes, the test stand has hold-down clamps, but still. And yes, engines have a specific life of hot fire time. Firing full duration is done for development of a new engine design only, not testing flight hardware. A full duration test would reduce the life of the engine, making it less reliable.

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#88 2023-12-21 23:43:41

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

RobertDyck wrote:

Did you notice the flame appeared as a triangle, then the triangle inverted? That means they fired 3 engines, then the other 3. If they fired all 6 at once, there was danger of the rocket launching. Yes, the test stand has hold-down clamps, but still. And yes, engines have a specific life of hot fire time. Firing full duration is done for development of a new engine design only, not testing flight hardware. A full duration test would reduce the life of the engine, making it less reliable.

Good catch. I hadn’t noticed that.

The key point of the matter is the Raptor is still not flight qualified. SpaceX has still not successfully tested the Raptor on the booster or Starship at full thrust and full flight burn times. Not on the test stand, not in flight.

THIS is a full duration static test as the rest of the industry other than SpaceX uses the term:

Rocket Factory Augsburg
@rfa_space
280 seconds of glorious hot fire! ? We are incredibly proud to be the 1st private company in #Europe (?) to hot fire a staged-combustion upper stage for its full duration. This qualifies our upper stage and Helix engine for flight ? Enjoy the video and read more in our press release ➡️ https://bit.ly/3WJY2G4
https://x.com/rfa_space/status/1664683388928655374

Robert Clark

Last edited by RGClark (2023-12-21 23:44:22)


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#89 2023-12-22 00:03:59

RobertDyck
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Not what I meant. This video shows several tests, including 300 seconds (5 minutes) of Raptor vacuum. That's orbital insertion full duration. At an engine test stand in McGregor Texas. Uploaded to YouTube November 13, 2022.
Raptor Vacuum Performs Orbital Insertion Length Test

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#90 2023-12-27 21:13:12

RGClark
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From: Philadelphia, PA
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Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

GW, you commented on my blog:

What I hear from the ground testing at the McGregor site (6 miles from my front porch) is no more Raptor starts at full power. I suspect they may have learned the hard way not to do that.

Do you mean by that the static tests sound like they are no longer doing full power tests or someone connected to SpaceX said they won’t?

  Bob Clark


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#91 2023-12-28 15:36:01

RGClark
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From: Philadelphia, PA
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Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

The SLS has public reliability estimates for each of its components. For the Merlins engines on the Falcon 9's we can estimate it as better than 99.9% based on the over 100 successful launches and 10 Merlins on each rocket.

But for the Raptor engine no such estimate has been publicly provided. Based on the number of engine failures or explosions on actual test flights, for the Starship during landing tests or the SuperHeavy/Starship orbital test launches, we can estimate it as quite low.

SpaceX should withdraw its application for the Starship as an Artemis lunar lander, Page 2: The Raptor is an unreliable engine.
https://exoscientist.blogspot.com/2023/ … ation.html

  Bob Clark


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#92 2023-12-28 17:43:51

SpaceNut
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Thinking towards the future where a starship will land on the moon.

NASA astronauts test SpaceX Starship elevator for future moon landingsAA1mazJT.img?w=768&h=432&m=6&x=862&y=457&s=200&d=146

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#93 2023-12-29 10:04:36

GW Johnson
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From: McGregor, Texas USA
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

I'm not so sure the Raptor-2 can be characterized as "unreliable".  I have noticed a change in how they operate it when they test-fire at McGregor:  they no longer light them at 100% thrust,  which is something I thought was a bad idea anyway,  especially for 3-D-printed metals that often lack the elongation-to-failure of wrought alloys. 

Yes,  there were a lot of engine fires seen during the Starship-only test flights.  But were these due to flaws in the engine design,  or in how they were mounted in the vehicle?  Or maybe some of both?  Hard to say. 

But with exposed plumbing and wiring to the turbopump feeds and controls,  in an engine bay seeing hot gas backwind,  while doing a landing burn,  and at full sea level pressure where heat transfer coefficients are highest,  maybe that's another prime cause of the failures seen. 

If so,  simply covering that plumbing and wiring up should stop most of those fires.  Anything still occurring would likely be insufficiently robust plumbing or plumbing fittings.  Which was greatly simplified in Raptor-2 over Raptor-1. 

Don't forget,  also,  that most of the engines flown in the Starship-only flights were Raptor-1's.  Raptor-2 is different:  simplified plumbing,  plus a better turbopump design actually capable of reaching or exceeding Pc = 300 bar. 

Just things to think about.

GW

Last edited by GW Johnson (2023-12-29 10:08:54)


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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#94 2023-12-30 02:26:36

RGClark
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From: Philadelphia, PA
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Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

For every other rocket intended for orbital flight they do full up(all engines together), full thrust, full flight duration(several minutes long) static tests. But for both stages of the Superheavy/Staship all they do are these 50% thrust burns of only a few seconds duration.

Why? For the SuperHeavy booster with its 33 engines an explanation that has been offered is it’s “too big”. But that explanation doesn’t make sense for just the 6 Raptors on the Starship. So why hasn’t SpaceX done such flight simulation static burns, which are just standard industry procedure, even for the Starship?

The most obvious reason is SpaceX believes it would cause a RUD.

   Bob Clark


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#95 2023-12-30 10:22:14

tahanson43206
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Registered: 2018-04-27
Posts: 17,301

Re: SpaceX should withdraw Starship as an Artemis lunar lander.

For RGClark re interesting question in Post #94

I hope you and other members will attempt to answer the question you have posed.

It seems to me that traditional companies have failed to perform well in the open competitive market.  Perhaps part of the reason is inability to stop doing old, useless procedures.  SpaceX has shown that such tests as you have described are not necessary.  Yet traditional companies persist (or so you have reported).

No wonder they are falling behind.

(th)

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#96 2023-12-30 10:33:45

SpaceNut
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

The military still control the old school businesses and they require it be traceable in paper as to what was done and with what so as to find root cause to failures.
It's that auditable trail that is what causes cost to rise not to mention standing around charging for non-work.

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#97 2023-12-30 11:07:17

GW Johnson
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From: McGregor, Texas USA
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Don't forget that every single engine that flies (Raptors and Merlins) gets static-tested at McGregor before they are installed in the flight vehicles.  Those static tests in McGregor are full duration,  a few to several minutes long.  It's hard to tell exactly which is what,  because their experimental engine testing is also conducted at McGregor,  and those are quite often short burns.  So I hear all sorts of tests. 

As I noted elsewhere on these forums,  I have heard a change in the way they test the new Raptors.  Until recently,  there was a loud boom like a massive explosion followed by the rumble and roar of a successful burn,  usually for 3 minutes-plus.  The water deluge steam cloud seen 6 miles away had almost zero soot,  so I knew these were the methane Raptors.  Those "explosion" sounds started with Raptor-2.  They never ignited Raptor-1's at full power. 

That was them igniting those engines at full thrust (really meaning full propellant flow rate),  which no other company does (historically,  for good reason:  that's a really good way to blow your chamber to smithereens).  The safer procedure is lighting at lower flow rate (lower thrust),  immediately throttling up to full power. That's what they do now.  I never hear the "explosions" anymore,  only the loud roar and rumble of a test.

The longer ones (3+ minutes) I suspect are Raptor-2's,  the current model being flown.  They no longer test or fly the earlier,  less capable Raptor-1's.  The shorter tests I suspect are the Raptor-3 models still in engineering development.  But as that matures,  they will be flown,  and eventually supersede the Raptor-2.  Rumor has it thrust is higher than in Raptor-2.  And testing in the open constrains the expansion ratio for "vacuum" designs (no separation).

GW

PS -- as you know,  there is no such thing as a "vacuum-optimized" design.  There are only nozzle bells that fit the allowable space at the rear of the stage,  and there are only nozzle bells that do not quite separate from backpressure,  so as to be testable in the open air.  Otherwise you must test in a giant vacuum tank,  which is horribly expensive.

PPS -- there is a "roughness" to the sound of some Raptor tests.  I would hazard the guess that comes from testing a "vacuum" Raptor with the bigger bell that is operating right on the hairy edge of flow separation,  due to ambient backpressure at about 600 feet above sea level (just about 0.99 bar at about 14.4 psia).  There would be a localized,  moving unsteadiness to the shock/boundary layer behavior right at the exit lip.  That unsteadiness would impart a roughness to the emitted sound.

Last edited by GW Johnson (2023-12-30 11:22:21)


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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#98 2023-12-30 17:39:28

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 711
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

tahanson43206 wrote:

For RGClark re interesting question in Post #94

I hope you and other members will attempt to answer the question you have posed.

It seems to me that traditional companies have failed to perform well in the open competitive market.  Perhaps part of the reason is inability to stop doing old, useless procedures.  SpaceX has shown that such tests as you have described are not necessary.  Yet traditional companies persist (or so you have reported).

No wonder they are falling behind.

(th)

I don’t agree.  My opinion for why the Raptors explode in flight is because they don’t do all up, full thrust, full flight duration static burns.

  Bob Clark


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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#99 2023-12-31 10:54:54

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,464
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Re: SpaceX should withdraw Starship as an Artemis lunar lander.

Everybody is entitled to their opinion.  Bob and I disagree a bit on this one.  That's OK.

I did point out in the first paragraph of post #97 that every single engine that flies is tested full duration at McGregor.  However,  this is before installation into the stage.  It's just the engine,  on a thrust stand. 

They have 3 such test stands fitted for the big flight engines,  two on the surface with flame pits and water deluge,  and the original tower stand inherited from Andy Beal's operation.  That tower stand is the really noisy one,  being way up in the air like that.  Even the Merlins really rattle windows when fired on it.

What this gets down to is whether one believes a short burn test post-installation & just pre-launch,  is enough verification that things are OK for launch.  That is the question,  for which you have to consider that history of a full-duration demo burn statically,  before the engine is installed.  SpaceX thinks it is,  Bob does not.  Personally,  I have no opinion.

The in-flight and landing fires we have seen could have any of a number of different causes,  including a possible shortfall in the engine design itself,  which is what Bob is suggesting.  Complicating that picture is the fact that most (but not all) of the Starship-only flights involved Raptor-1's,  while both of the Starship/Superheavy flights have used Raptor-2's (I don't believe the Raptor-3 is quite ready to fly yet,  although I could be wrong,  there is nothing publicly available either way). 

There is a big difference between Raptor-1 and Raptor-2:  the turbopump and plumbing/wiring.  Raptor-1's turbopump proved to have insufficient flow capacity to deliver enough propellant to reach the full design chamber pressure of 300 bar.  The Raptor-2 turbopump is a new design that does have the flow capacity to reach or even slightly exceed 300 bar.  The plumbing/wiring is a lot simpler and cleaner,  which would make it easier to cover up and protect from hot gases.  I do not yet know what they did with the Raptor-3 design,  although I did hear 1 rumor that it reaches even higher thrust than Raptor-2 does. 

Hot gases in the engine bay do not need to just come from plumbing or chamber leaks that inevitably cause fires.  Don't kid yourself:  when the stage or vehicle is flying sideways-to-tail-first,  there is significant hot plume gas backwinding into the engine bay.  And that hot gas is only reduced from full chamber temperature (!!!) by whatever extent it has gotten mixed with the surrounding cool air before backwinding into the bay.  That mixing effect is actually very low once you are fully tail-first.

Just food for thought.  There are a lot of things going on in such engine bays,  more than usual,  just because of the ways these things are flown for recovery.  Most folks don't know,  or if they do,  they don't want to think about that,  because it is so complicated.

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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#100 2024-01-03 11:00:02

RGClark
Member
From: Philadelphia, PA
Registered: 2006-07-05
Posts: 711
Website

Re: SpaceX should withdraw Starship as an Artemis lunar lander.

This video attempts to argue the Raptor is reliable by looking at static fire tests:

1000 Starship Engine Tests (on a graph).
https://www.youtube.com/watch?v=I6GJVvwUEGk

A key question in the video is how many of the test fires fall short of the expected length, suggesting a test failure or for whatever reason the engine had to be shutdown. The video host suggests it is small number. I suggest it is more than it should be for an engine at this stage in its development. Someone may want to count the percentage themselves where it is displayed graphically at about the 5:55 point in the video.

Also I don’t like the lengths of the engine tests. The video host says most are about 2 minutes, 120 seconds, suggesting that is where SpaceX thinks that is what the flight burning time should be. But judging from the test flights for the booster that should be in the 2 minutes 40 seconds range, 160 seconds, https://en.m.wikipedia.org/wiki/SpaceX_ … ht_profile, which means even for static fires of individual engines SpaceX is not doing realistic static fires.

Additionally, SpaceX needs to be open about how many of these static fires are done at full power.

  Bob Clark

Last edited by RGClark (2024-01-03 12:06:36)


Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):

      “Anything worth doing is worth doing for a billion dollars.”

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