SpaceX should withdraw Starship as an Artemis lunar lander.

GW Johnson · 2024-01-03 16:48:23

Bob:

I finally saw Spacex's own video of that test flight. It is clear something was going wrong in the engine bay of the Starship a couple of minutes before the end of its ascent burn. I saw the same kinds of laterally-directed thin-but-bright gas plumes that preceded the booster explosion. Ullage problems cannot be the excuse, because the vehicle was under significant accelerating thrust right up until contact was lost.

Whether that rates withdrawal as an Artemis lander remans to be seen, especially since the GAO cites SpaceX's delayed Starship as only one of several compelling reasons why NASA cannot land people on the moon before about 2028 or later. But it certainly rates investigation and correction of whatever actually went wrong. That much is for sure.

GW

RGClark · 2024-01-08 11:53:31

I have been accused of being anti-SpaceX because of my criticism of the Starship. Actually, after a calculation I'm convinced the Starship can be operational, like, tomorrow, with relatively small design changes:

Towards advancing the SpaceX Starship to operational flight: SpaceX should lower the Raptor chamber pressure and thrust level.
https://exoscientist.blogspot.com/2024/ … ip-to.html

The Raptor engine has shown continued failures on all of test stands, Starship low altitude landing test flights, and the two orbital test flights. But the Raptors on the booster on the last test flight were able to complete the ascent part of the flight without failures. They failed only after the attempted to relight.

Multiple-lines of evidence suggest that on that last test flight SpaceX throttled down the Raptors on the booster to less than 75% while those on the Starship were run at ~90%. I've suggested this is why the booster engines were able to fire reliably during the ascent and those on the upper stage were not.

If this is the case, then it suggests a method to get Raptor reliability: run them at ~75% throttle on both stages. But if keeping the same stage dry masses this would result in the payload of the reusable version being reduced to approximately in the range of 100 tons from 150 tons.

Instead, I advise first start with reducing the dry masses by optimally lightweighting the expendable versions of both stages. Surprisingly this gives a greater expendable payload than the expendable payload of the current version. Secondly, I suggest using winged, horizontal approach to reusability gives a much reduced payload loss due to reusability. Thirdly, basic orbital mechanics shows high delta-v missions to the Moon or Mars are done more efficiently by using more stages. Then a third stage is suggested for the Superheavy/Starship, a mini-Starship as called by Robert Zubrin.

This allows single launch and fully reusable missions to the Moon or Mars. No refueling flights required.

Robert Clark

RobertDyck · 2024-01-08 12:20:58

You can't reduce thrust to 75%, and just reduce payload to 75%. It doesn't work that way. SuperHeavy has an empty mass of 200 metric tonnes, propellant 3,400 tonnes. Starship has dry mass 100 t, propellant 1,200 t. Total launch mass before including payload is 4,900 t. With 100 t payload, total mass is 5,000 t. I'm amazed, rockets usually have much lower payload fraction than that. It's listed as payload between 100 t and 150 t, because design is still ongoing. Reducing payload from 150 to 100 may allow you to reduce propellant mass a bit, so total launch mass is reduced, but it won't be enough to reduce thrust to 75%. Most of the propellant is expended lifting the mass of propellant. I know that's ironic, but that's the rocket equation. Ain't physics a bitch.

RGClark · 2024-01-08 15:13:19

RobertDyck wrote:

You can't reduce thrust to 75%, and just reduce payload to 75%. It doesn't work that way. SuperHeavy has an empty mass of 200 metric tonnes, propellant 3,400 tonnes. Starship has dry mass 100 t, propellant 1,200 t. Total launch mass before including payload is 4,900 t. With 100 t payload, total mass is 5,000 t. I'm amazed, rockets usually have much lower payload fraction than that. It's listed as payload between 100 t and 150 t, because design is still ongoing. Reducing payload from 150 to 100 may allow you to reduce propellant mass a bit, so total launch mass is reduced, but it won't be enough to reduce thrust to 75%. Most of the propellant is expended lifting the mass of propellant. I know that's ironic, but that's the rocket equation. Ain't physics a bitch.

I’m aware of that. My suggestion that the expendable payload size could be maintained even at 75% reduced thrust is coming from the idea the expendable stage dry mass can be greatly reduced from the dry mass of the stages now in the reusable versions.

It’s all dependent on this statement by Elon Musk:

Elon Musk @elonmusk
Probably no fairing either & just 3 Raptor Vacuum engines. Mass ratio of ~30 (1200 tons full, 40 tons empty) with Isp of 380. Then drop a few dozen modified Starlink satellites from empty engine bays with ~1600 Isp, MR 2. Spread out, see what’s there. Not impossible.
9:14 PM · Mar 29, 2019
https://x.com/elonmusk/status/1111798912141017089?s=20

That 40 ton dry mass Elon suggested there for the expendable Starship is 80 tons less than the cited reusable dry mass of 120 tons. 80 tons is a *huge* difference in dry mass, especially for an upper stage where every extra kilo subtracts directly from the payload that can be carried.

Presuming you also get a greatly reduced dry mass for the SuperHeavy results in such a high expendable payload even for Raptors running at 75% thrust.

Bob Clark

RGClark · 2024-01-13 16:17:10

GW, Elon Musk gave an update on the status of SpaceX where he said the upper stage on IFT-2 exploded because of a fire after an intentional lox dump:

Gav Cornwell @SpaceOffshore
Elon on Starship Flight 2: "Flight 2 actually almost made it to orbit (...) The reason it didn't quite make it to orbit is we vented the liquid oxygen (...) ultimately led to a fire and explosion (...) we wanted to vent the (LOX) because we normally wouldn't have had that (LOX) if we had a payload. Ironically if it had a payload it would have reached orbit"
https://x.com/spaceoffshore/status/1745 … 83273?s=61

Have you ever heard of a rocket being made to dump propellant while in flight either for a test flight or an operational flight? Why couldn’t they just use a partial propellant load?

Robert Clark

Last edited by RGClark (2024-01-13 16:18:08)

GW Johnson · 2024-01-14 11:27:46

They should have flown with only the propellant they needed. But they do need a dumping capability, and that requires a demonstration, too. Venting used stages dry has long been done, to prevent their exploding from evaporation of residuals over-pressuring the tanks.

The real question here is why did dumping LOX cause a fire?

It should not have, unless there were a also massive presence of co-located methane. The engine plumes are fuel-rich, but they leave the open bay at very high speed.

About the only way I can see to ignite with a fuel-rich engine plume inside the bay would have to do with about 94 degrees of Prandtl-Meyer expansion at the nozzle exit lip causing plume gas to strike the aft edge of the bay wall. If that were happening, it should be leaving very serious damage on the struck zones.

They might not have seen this effect in the Starship-only tests, which apogeed within the atmosphere, not out in vacuum.

You avoid it by making sure the nozzle exits protrude past the aft edge of the engine bay. I'm not sure the Starship design as it currently exists does that. Their Falcons did.

An "old hand" would have known better than to submerge exit lips within a bay exposed to vacuum. But they have none. They hire no one old enough to have learned better, because older hands like that cannot put up with chronic 70-80-hour weeks.

The other possibility is a massive leak in the methane delivery plumbing. Which should absolutely NOT be happening in something considered worthy of flight test.

GW

Last edited by GW Johnson (2024-01-14 11:38:57)

RGClark · 2024-01-14 17:22:41

GW Johnson wrote:

They should have flown with only the propellant they needed. But they do need a dumping capability, and that requires a demonstration, too. Venting used stages dry has long been done, to prevent their exploding from evaporation of residuals over-pressuring the tanks.
…
GW

Thanks for that. That sounds like it’s done after the mission is completed. Has it been done while the engines are still firing where the stage has not completed its portion of the flight?

Bob Clark

RobertDyck · 2024-01-14 17:41:24

The first rocket to land on its tail was the Delta-Clippper-eXperimental (DC-X). That was upgraded to "advanced", DC-XA. After that was SpaceX Falcon 9, and Blue Origin New Shepard. A few startups are trying it now, but these were the first. That means all the work described by GW Johnson are with rockets that didn't even try to land. Venting was done in flight.

GW Johnson · 2024-01-15 11:13:31

What I described was previous experiences with rocket stages left in space with some propellant residuals, after the mission. These were vented to prevent forming scattered space junk by over-pressured tanks bursting. You do NOT vent the oxidizer and the fuel simultaneously!

The same technology could apply for the same or similar reasons to the rockets flying and landing today. It's actually the analog to dumping fuel from an airplane to enable a safer landing at a lower weight. With an airplane, the risk of ignition with oxygen-bearing air means the fuel dump ports are NEVER near the engines, which are a source of ignition stimulus.

The problem here with LOX dumped from Starship in flight with the engines running, is that of fuel and oxidizer in the same place at the same time with sources of ignition also present! Rocket oxidizers, even if not hypergolic, are really, really easy to ignite with any combustible material: it does not take much of an ignition stimulus at all. SpaceX has already seen this risk venting tank vapors from Starship post landing after the Starship-only flight tests: post landing fires around the vehicle sitting on the ground.

It's less about rocket technology and more about fire prevention thinking. If you dump LOX from anywhere on a rocket under thrust, it will move toward the rear of the vehicle at the vehicle's acceleration rate. There is a wake zone behind the vehicle into which LOX or oxygen vapor can be captured. The exact same thing is true of any fuel dumped from anywhere on the thrusting vehicle. The rear is the engine bay, and those running (or still hot just shut down) engines are sources of ignition for a mixture that needs very little in the way of ignition stimulus.

Which in turn is why you turn off the venting completely for one propellant while you dump the other, and you wait several seconds after turning off that dump before you dump the other. This is very, very true in the atmosphere, but it is still true as you fly out into vacuum. The atmosphere has no sharp edge. You have to wait until the vapors from one propellant have cleared out from around the engines before you allow the vapors of the other propellant in that space. The merest little spark or hot spot will set off fires with LOX.

Hypergolics are even worse: you cannot vent them until you are no longer under thrust, and then you wait for a time between venting the one before venting the other.

It's all about the fire triangle plus a bit of smarts about flameholding.

GW

PS -- yes, I have done fire protection engineering professionally.

Last edited by GW Johnson (2024-01-15 11:17:23)

SpaceNut · 2024-01-15 11:18:55

Temperature of the engines running can cause the atmosphere that enters to break down and give fuel to the Lox dump, as air has moisture, nitrogen that can burn.

GW Johnson · 2024-01-18 14:46:11

I thought most of the oxides of nitrogen formed endothermically, not exothermically. But I'm no proper chemist, I might be wrong. Just a fuel-air combustion "chemist-and-more".

GW

SpaceNut · 2024-01-18 19:15:48

Here are the Artemis designs slide show. That include the halo unit as well as the lunar landing.

https://www.nasa.gov/specials/artemis/

https://en.wikipedia.org/wiki/Artemis_p … dmark).svg

It still shows the other much to heavy LEM that was under constellation.

2020 NASA’s Lunar Exploration Program Overview

GW Johnson · 2024-01-19 10:25:44

Sacenut:

I rather doubt all this will go through, not with far-right GOP trying every trick in the book to thwart everything their opposition (including half the GOP) wants to do. Congress has not passed a proper budget in 2 decades, and the chaos is only getting worse.

Meanwhile, Artemis as planned is "old space's" last gasp to do giant corporate welfare. SpaceX is participating only to get some income, and I suspect Bezos's bunch is doing the same. Meanwhile, NASA is trying to figure out which "new space" outfits might actually be able to do the things NASA cannot do (and never could do, with that history of buying everything from "old space").

In a world on fire from multiple (!!!) wars in the middle east, and one in Ukraine, plus with China threatening one in the Pacific, none of this space boondoggle (and expensive boondoggle it is !!!) is going to get done according to those plans.

The money is NOT going to be there. Especially at $4+B per SLS launch.

GW

Last edited by GW Johnson (2024-01-19 10:27:26)

SpaceNut · 2024-01-20 08:10:16

The money comes from the shifting of funds from the ISS to this program. But it's a long time off to that point and it does rely on Axiom space and others to create the next replacement in orbit for continued presence other than the Chinese station.
The srb went up in costs due to the new electronics and altered. design, the same happened with the orange ET and shuttle engines that all got upgrades with a new brain and changes to how the tank was made. These both made the ship continue to inflate for each launch.
The upper stage and even the capsule had a ton of funds poured into design under constellation and in the end, they are much too costly.

'Just A Worse Version Of Apollo:' Elon Musk Baffled By NASA Veteran's Push To Ditch SpaceX, Blue Origin And Use Existing Tech For Artemis Moon Mission

ya, let's just hit reset again.

NASA's $93 Billion Moon Landing Program is Riddled With Safety and Technical Issues through the end of 2025.

Houston’s Axiom Space has been recruited to develop the astronauts’ suits. With yet another commercial outsourcing, it is possible NASA may encounter another setback with Axiom Space, though all parties remain hopeful.

GW Johnson · 2024-01-20 16:54:38

I am a fan of SpaceX, but I find Musk himself not very admirable. SpaceX gets into trouble with the government every time he over-rules what Shotwell and her staff come up with. I don't put a lot of stock in what he has to say.

That being said, today's NASA is absolutely NOT the NASA of the 1960's. I don't put much stock in what they say or do, because their top management has evolved into corporate revolving-door politicians who value only money and schedule, and that killed 2 shuttle crews. (The very same problem now afflicts Boeing, as we have seen.)

Something that exacerbates this problem is the emphasis in engineering schools upon proficiency in running software packages, almost to the exclusion of being able to run ballpark numbers pencil-and-paper, by-hand. As a result, nobody is capable recognizing GIGO anymore. And that is killing people (and causing needless space mission failures).

Couple that with top dogs who don't give a damn about anything but money and schedule, and you get idiocies like the B-737 MAX debacles. Such as an MCAS that was not in the flight manual, and how to turn it off was also not in the flight manual. Both are egregious violations of the FAR's. And the "talent" at FAA was unable to see this crap as it unfolded.

Let's just say I have almost zero confidence in most things going on out there, and leave it at that. To make my complaint more specific, would require obscenities that not tolerable in this venue.

GW

SpaceNut · 2024-01-21 10:49:54

Going to mar

https://youtu.be/tujL0xrQ2Os?si=G6I_utmStjIicVA0

RGClark · 2024-01-23 12:47:40

If you assume an Apollo-sized lunar lander there are multiple ways to do single launch Artemis lander missions. No Starship HLS, or multiple refueling flights required:

Possibilities for a single launch architecture of the Artemis missions, Page 4: lightweight landers from NRHO to the lunar surface.
http://exoscientist.blogspot.com/2024/0 … aunch.html

Bob Clark

Last edited by RGClark (2024-01-23 12:48:34)

GW Johnson · 2024-01-24 11:58:01

The SLS/Orion could reprise Apollo if the service module were as large in proportion to Orion as the one on Apollo. That could enter a low retrograde orbit about the moon, making near equatorial landing sites feasible, just like Apollo. But not polar sites, Apollo could not reach them. That requires entering a low polar orbit, something that was out of reach even for the Apollo service module.

The mission drives the vehicle designs, when done properly. Initially Apollo was not. Von Braun's Saturn-5 was not originally designed as a moon rocket. It was a paper design, done for the Army, as a giant two stage booster to send a sub-orbital payload one way to Russia. That payload was 100 soldiers plus a jeep and small artillery piece.

His Saturn-1 was a two-stage ICBM intended to carry the gigantic thermonuclear weapons of the late 1950's. It was also a paper design done for the Army. He was working for them at Huntsville, AL, in the 1950's before NASA was ever formed.

Once Von Braun went to NASA, he took those paper designs with him, and lot of his old crew of Germans from Operation Paperclip. NASA realized that the Saturn-1 with very little change would be useful for LEO Apollo missions, and that the Saturn-5 with a third stage could potentially be the moon rocket they needed. That third stage was the second stage of the Saturn-1 design, conveniently enough.

Now, by about 1961-1963, NASA had a design for Apollo that landed the entire capsule and propulsion unit directly on the moon. That concept required two Saturn-5 launches per moon mission, with on-orbit refilling from a Saturn tanker to the moon mission Saturn. They did not have the schedule time to learn how to do the propellant transfers and still meet Kennedy's deadline. So they were forced to accept a concept from an outsider to NASA for lunar orbit rendezvous. That so substantially reduced the size of the Apollo cluster that they could do each mission with only one Saturn 5 launch and no refilling on-orbit.

As I already said, the mission normally drives the vehicle designs, but in Apollo's case, the reverse was true.

SLS is a reprise of Saturn-5 capability with Shuttle-derived hardware. The Orion and service module that it flings was not designed to do an Apollo mission. It was designed only to reach a point in circumlunar space, and not necessarily around the moon at all. That much-lower delta-vee is why the Orion service module is so undersized that it cannot reprise Apollo 8, much less Apollo 11.

Picking that mission to size hardware instead of a real lunar landing mission is the actual design mistake here, and it is less of an engineering mistake and more of a program management mistake. The engineers here and in Europe built and supplied exactly what they were asked to supply, with one exception: Orion's heat shield (and that too is a program management mistake).

The whole Gateway boondoggle (and soon-to-be debacle) is the only way NASA could figure out how to do lunar landings with the not-up-to-capability launcher and spacecraft that they had, when the landings they wanted to do, were beyond even what Apollo did, being polar. It has the look of a real screwed-up composite of various band-aids, because that is exactly what it is.

And even then, they could not get it "right", because Block 1 SLS/Orion is almost incapable of reaching an elongated halo orbit about the moon.

The halo orbit that SLS/Orion can reach has an apoapsis outside the moon's hill sphere: it is dynamically unstable! They cannot quite reach a stable one! Which instability means you have to burn repeatedly to stay in it, or else wander off into a distant orbit about the Earth instead of the moon! THAT is why there is the significant propulsion included in Gateway's "propulsion and power" module! And that propulsion WILL require repeated and continuing tanker flights over the life of the station, lest the station be lost!

Landing on the moon from one of these things is way more expensive in terms of delta-vee than Apollo ever saw. The periapsis speed is near lunar escape at that altitude, which in turn is way farther more delta-vee than from the low orbit Apollo used. That means the transfer orbit to the surface is way more energetic than the one Apollo used. By the time you account for rendezvous budgets, your delta-vee is well beyond surface escape at 2.6-2.7+ km/s one-way, versus the 1.6-something one-way km/s Apollo had to deal with. And if you are to make your lander reusable, you have to do this 2-way unrefilled single-stage!

So in order to meet a more-demanding lunar mission than Apollo, with a launcher/spacecraft that was less capable than the Apollo CSM, they had to band-aid the whole concept with a multi-$billion-boondoggle distant lunar space station, and look for a lander with way to hell and gone more than double the capability of an Apollo LM. THAT is why the SpaceX and Bezos lander designs look so big! They have to be big!

AND they are going to be flying tanker flights to that distant lunar station for its entire lifetime, even if they never refill another lander, and THAT tanker stuff that far out ain't easy!

THOSE choices are the real design mistake here! And not much is going to be able to fix it. The distant station boondoggle is too far along now to cancel, and return to a low-orbit type of mission more similar to Apollo. Which they could do with a larger service module and/or adding some Centaurs and/or relying on the more capable Block 1B "exploration upper stage".

But, when the $2-4 billion per launch costs start to accumulate, my money is on the EUS being cancelled, if not the whole program. Such is Congress these days.

GW

PS -- the heat shield mistake was switching from the gunned hex fab approach to a tiled approach with no hex, to save money building heat shields. The result was much higher ablative erosion that was erratic and fundamentally unpredictable, with charred material sloughing off because there was no embedded hex to reinforce it. The Artemis-2 flight was delayed because they're still trying to figure out how to get around this, without going back to the original heat shield design that was on the unmanned Artemis-1 shot. That's because the Artemis-3 craft already has the Artemis-2 faulty heat shield design on it. But to replace it with the proven design not only raises costs, but more importantly means a NASA manager somewhere has to admit making a bad mistake. And we saw how reluctant they are to do that, with the Challenger and Columbia investigations.

Last edited by GW Johnson (2024-01-24 12:54:30)

kbd512 · 2024-01-25 11:12:59

GW,

If the face of the heat shield material is subject to severe erratic erosion, altering the outer mold line and thus the aerodynamics of the vehicle in the process, does that also mean there's no way to guarantee a precision splashdown after reentry?

Assuming the heat shield still does its job protecting the vehicle, even if some minor damage occurs, how far off-course could the capsule be when it lands?

The Navy normally has an amphibious dock ship (a helicopter / amphibious armored vehicle carrier normally used to land Marines), a boarding party in a pair of small boat to tow the capsule back to the amphibious ship, and a rescue helicopter awaiting the capsule's arrival. How far away do they have to be to ensure they're not accidentally in the error ellipse of the flight path of this now-slightly-unstable vehicle?

GW Johnson · 2024-01-25 12:38:54

An asymmetrically-roughened heat shield face might well affect landing accuracy with an unguided entry. But with controlled lift at angle-of-attack and controlled roll angles, this can be compensated on the way down. It should not be a problem with Orion capsule recoveries. Or not much of one.

The real risk is two slough-offs in the same location leading to a heat shield burn-through. That would be a loss of capsule and crew. It's a low probability, but it is NOT zero. Doing the heat shield "right" with the gunned hex would zero that probability. But it would cost schedule and money.

And we have already seen them value schedule and money over the risk of a lost crew, twice now.

GW

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

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

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

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

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

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

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

#109 2024-01-15 11:13:31

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

#110 2024-01-15 11:18:55

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

#111 2024-01-18 14:46:11

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

#112 2024-01-18 19:15:48

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

#113 2024-01-19 10:25:44

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

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

#116 2024-01-21 10:49:54

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

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#119 2024-01-25 11:12:59

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