Starship is Go...

Oldfart1939 · 2021-08-22 11:05:42

GW-

Here's the Elon Musk interview part #1. https://www.youtube.com/watch?v=t705r8ICkRw

Go to 33:59 minutes to pick up the conversation about the Raptor design and where it's headed.

GW Johnson · 2021-08-23 08:02:47

OF:

The reverse engineering I did on the Raptor is documented on "exrocketman" as the article titled "Reverse-Engineered Raptor Engine Performance", dated 26 September 2019. This was before they ever reached full thrust at full pressure in their testing. I used the data they once posted about Raptor on their website, and duplicated the performance they then projected for it.

I used 4400 psia Pc = 299 atm = 303 bar as max Pc, and 20% of that = 880 psia as min Pc throttled fully down, per their website back then. What I found was that sea level turndown hit backpressure limits on-the-deck at about factor 2.5:1 throttle-back, but that above 20kft altitude you could throttle-back the full 5:1 turndown ratio.

Max thrust at sea level was 440,000 lb = 1.958 MN. I got 331 s Isp at sea level, vs the 330 they then projected. I pretty much duplicated the vacuum Raptor, too. And projected altitude performance of the vacuum Raptor, including duplicating its projected vacuum performance. My exit diameters pretty much matched theirs, allowing for them rounding to 2 significant figures.

I'm not sure what I heard from Musk in the video, but I didn't hear anything over 300 bar Pc. It sounds like they did change the expansion ratio a tad from the 40:1 area ratio that I used (which is what was on their website back then). The vacuum engine used 100:1.

I suspect they no longer publish details like that on their site, precisely because of what people like me can do with it.

GW

Last edited by GW Johnson (2021-08-23 08:06:51)

louis · 2021-08-24 13:50:27

Felix's latest video:

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

Very good overview.

Void · 2021-08-25 19:26:22

Since nothing is happening here I will dare.

I have seen hints that Elon Musk will hope to revise raptor engines to be able to throttle them down enough to use for a Moon landing without a landing pad.
I am not saying anything about landing legs.

Other things I am thinking are true, are that the Super Heavy and Starship will
be able to hover, unlike the Falcon 9. So, I guess I though I saw an article that
indicated that Elon Musk would dream to catch the Super Heavy and Starship
without a landing burn at all. The tower is supposed to have significant shock
absorbers. However, I think that is a wish. I think he intends to hover the ships
into the catchers.

But who knows maybe very far down the line, they can get away with a lesser
landing burn.

I don't know. I am not speculating. I am just saying things I have come across.
Talk is cheep

Done.

Last edited by Void (2021-08-25 19:29:47)

GW Johnson · 2021-08-31 10:44:52

I have seen nothing substantive about the upcoming orbital launch. I presume they are still waiting on regulatory approval, per what I said several days ago in post 1445 above.

I do see progress being made toward the orbital tank farm, and putting the swing arms for fueling on the launch tower. I am also presuming that those things need to be in place for any orbital launch. I'm unsure whether the launch stand is ready. One can interpret those pictures in multiple ways. But I'm also presuming it needs to be ready for a live-fire launch as well.

Since those things would seem to be necessary, yet unready for a live-fire launch, it would appear that more than just regulatory approvals are holding up this test. My conclusions in post 1445 above need to be modified to include that the necessary infrastructure was not in place for a launch, either.

I haven't heard a peep out of anybody regarding the regulatory approvals.

It would appear that the necessary infrastructure items will be in place within weeks, perhaps.

Then we shall see.

GW

Oldfart1939 · 2021-08-31 10:57:39

I heard on one of the websites (cannot recall which one) that there's a possibility that SpaceX might be able to get a temporary, or one shot approval of launch. That would skirt the Environmental Impact Study that would give a blanket authorization...

SpaceNut · 2021-08-31 20:23:02

If monitoring of said launch was to occur then the resulting information would be used to pave the way for the future as its reporting would be part of the impact that could occur with more launchings form the site.

GW Johnson · 2021-09-12 15:16:58

Looks to me like the regulatory hurdle is still unsurmounted. I told y'all that would be a tough one. Not a peep out of anybody in some weeks now.

Plus, there is a tropical storm headed for the vicinity of Brownsville. Spacex is going to have to put all its "precious" indoors till the storm passes.

GW

louis · 2021-09-12 17:52:55

I told y'all this administration will use regulatory obstruction to try and halt what will be a huge ideological defeat for a stunted unimaginative statist space policy.

That said, my current view is Musk is several moves ahead in this game, as always. Seems like they were nowhere near orbital launch capability a few weeks ago. A lot still remains to be done. But Space X have been applying the pressure early I think in the hope that any regulatory hurdles can be overcome before he achieves orbital launch capability. Felix has some good update info:

https://www.youtube.com/watch?v=ljXq-TbjdFA&t=825s

So much going on and needing to go on... I think we can rule out a September launch.

GW Johnson wrote:

Looks to me like the regulatory hurdle is still unsurmounted. I told y'all that would be a tough one. Not a peep out of anybody in some weeks now.
Plus, there is a tropical storm headed for the vicinity of Brownsville. Spacex is going to have to put all its "precious" indoors till the storm passes.
GW

SpaceNut · 2021-09-12 21:03:03

GW's forecast Tropical Storm Nicholas forms in Gulf of Mexico

Nicholas is forecast to approach the middle Texas coast and strengthen to a strong tropical storm on Monday. There is a chance it could achieve hurricane-force winds if it moves right of the forecast track and stays over water longer than expected.

of course I continued to check for other tropical storms and the one which crossed Florida is now heading up the east coast bringing more rain to area that are still recovering from IDA and Larry still.

GW Johnson · 2021-09-13 08:58:03

Today, they seem to think its more headed toward Beaumont to Morgan City, than Brownsville. Musk's "precious" is off the hook for storm damage, apparently.

GW

GW Johnson · 2021-09-14 13:50:24

The silly thing defied all the predictions I saw. At least it's ashore. -- GW

kbd512 · 2021-09-15 13:32:31

Louis,

I'm beginning to believe that you're correct, regarding your point about using regulatory agencies to halt progress. Both parties love boondoggles, though, and here comes this upstart who's getting things done 10 times faster than NASA's bureaucracy would ever allow for, so perhaps Starship truly is getting put on the back-burner until SLS flies. Thus far, there's zero explanation for the hold-up, which usually means that hold-up is a manufactured event.

GW Johnson · 2021-09-15 14:58:57

It is hard to tell the deliberate misuse of a bureaucracy to impede something, from the usual bureaucratic ineptitude and glacial slowness. In either case, nothing gets done in a timely fashion.

One could make a case that the FAA is being used to destroy Boeing over the problems it has had building airliners of late. But I don't currently believe that. Instead, it appears to me FAA may be overreacting a bit, after getting caught with its pants down not regulating Boeing adequately in the first place. It's the in-house DER problem: supposed to work for FAA, but getting paid by Boeing.

Those DER's have been complaining (1) that Boeing corporate is forcing them not to do the legally-prescribed job of an in-house DER, and (2) that FAA has not been listening to them. Apparently it has begun to listen now. There is clearly still far more for FAA to correct at Boeing Commercial Airplane Company.

If Spacex's "environmental impact" problem is getting an impact statement modified or updated with the EPA, as I suspect that it is, I find it entirely unsurprising that the delay is getting to be quite long. That particular agency is utterly notorious for such foot-dragging, and has been for multiple decades now. Especially as in recent decades, the most numerous type of worker on the EPA payroll has become lawyers, not scientists. Lawyers: infamous for straining at gnats while swallowing camels whole.

Assuming that I am right about that agency and the nature of Spacex's problem, then why would you ever expect anything but interminable delay? You don't need deliberate political misuse to get those effects.

GW

Last edited by GW Johnson (2021-09-15 15:06:06)

SpaceNut · 2021-09-15 18:42:00

They did not do any tests with the first stage to show how its going to go up or return and that is part of the issue for the stage getting the green light to fly. SpaceX and others are doing the its just like the other stuff so why should it be any different. Well space x up did blow up many test units while on the pad as well as coming back down. Thats something that is never done by other space contractors, now is there?
You give no data to show differently at this point.

tahanson43206 · 2021-09-18 19:19:00

https://www.yahoo.com/news/draft-review … 00962.html

The draft PEA is available online at faa.gov/space/stakeholder_engagement/spacex_starship/.
Hard copies of the draft PEA are on display at the Brownsville Public Library Main Branch, 2600 Central Blvd, Brownsville Public Library Southmost Branch, 4320 Southmost Rd., and the Cameron County judge's office in the Dancy Building, 1100 E. Monroe St., Brownsville.
After the public-comment period is closed, the FAA will revise the draft PEA as appropriate in preparation of a final Programmatic Environmental Assessment, according to the agency.
"The final PEA will reflect the FAA's consideration of comments and will provide responses to substantive comments," the FAA said. "Following review of the final PEA, the FAA will either issue a Finding of No Significant Impact (FONSI), Mitigated FONSI, or issue a Notice of Intent to prepare an Environmental Impact Statement."

The FAA appears (to me at least) to be trying as hard as it can to smooth the way for SpaceX tests of Starship.

The risks to the environment and to people and living creatures are real, but my interpretation of the language is to discount the risks.

(th)

SpaceNut · 2021-09-18 21:11:47

The article states that SpaceX proposes 20 Starship suborbital flights and full 5 orbital launches next year.

There is a permit process that needs a 30-day window for public review and comment and public hearings scheduled for next month.

This is where abutters usually can stop a project cold....

More than 320 comments were submitted as part of the scoping phase of the PEA. The commenters expressed concerns over the potential impacts of SpaceX's plans on protected species and habitat, cumulative effects on other development projects in the Rio Grande Valley, closure of public areas, namely S.H. 4 and Boca Chica Beach, and appropriateness of an environmental assessment versus the more rigorous environmental impact statement.
Commenters likewise expressed concerns about potential impacts on airspace, minority and low-income residents, and land of cultural importance; safety of launch operations with as-yet-to-be-constructed liquefied natural gas facilities nearby at the Port of Brownsville, and environmental degradation.

This is not going to be orbital with the stage dropping off that soon.

The Super Heavy (first stage) boosters would separate from the Starship (second stage) at roughly 40 miles altitude and land either at the Boca Chica launch site or downrange in the Gulf, either on a floating platform or in the water itself, according to the draft PEA.

tahanson43206 · 2021-09-18 21:56:43

For SpaceNut re #1467 ....

The quote you provided shows ** altitude ** .... 40 miles altitude means many more miles downrange.

Here is a report from SpaceX (per Google) on Falcon 9 staging:

Approximately 158 seconds into flight, the first-stage engines are shut down, an event known as main-engine cutoff, or MECO. At this point, Falcon 9 is 80 kilometers (50 miles) high, traveling at 10 times the speed of sound. Three seconds after MECO, the first and second stages will separate.

I hope that a ** real ** rocket engineer will comment and help us understand the tradeoffs at work here....

I am ** guessing ** that Starship is more capable than the Falcon 9 upper stage, so it can do more of the work of reaching orbit.

The Super Heavy has it's work cut out just to put a fully loaded Starship at 40 miles up going some significant velocity.

(th)

GW Johnson · 2021-09-19 09:59:18

What I think you will find is that for a two-stage vehicle, most of the gravity turn is made during the first stage burn, as it climbs out of the atmosphere. Most, but not entirely all of the gravity turn. Once the turn is mostly made, your distance downrange is very much larger than your altitude. That's just the nature of a gravity turn. On an altitude-range plot, it resembles one branch of a parabola laying on its side, with vertex at launch point.

Thus the first stage incurs all the effective drag loss, and most (but not all) the gravity loss. It must have enough thrust to accelerate the vehicle upward against gravity and drag initially (an ignition thrust/weight in the 1.3 to 1.5 range is the "rule of thumb" for this), and still maintain a net positive vehicle acceleration against drag without "overdoing it", all the way to burnout, as the vehicle rapidly burns off mass. Somewhere about Mach 1-ish at about 20,000-feet-ish while still moving pretty much vertically upward is "max dynamic pressure", where the drag force is the highest, before the air can thin out enough to reduce it.

The second stage is much less constrained by thrust/weight, flying almost horizontally during its burn. The gravity losses are not zero, but they are quite small compared to those incurred by the first stage. The drag losses really are essentially zero. You can pretty much use a vacuum bell on your second stage engines, no matter what. The stage point is effectively outside the atmosphere, at 80+ km altitude. If you use low thrust, you must burn longer, incurring more gravity loss. In the limit, you burn continuously all the way to orbital insertion.

On the other hand, if you burn at high thrust onto a transfer ellipse to your orbit altitude, you incur less gravity loss, but you must burn again at apogee for orbital insertion, after coasting much of the way to that point. That's a vacuum engine re-ignition, plus a solution to the propellant ullage problem, if you are using cryogenic propellants in a free-surface tank. If you are using storables from bladdered tanks, ullage is not a problem.

There is no "speed of sound" outside the atmosphere, although at all altitudes within the atmosphere it is a value somewhere between about 900 to 1100 ft/sec. One can use as a nominal figure 1000 ft/sec ~ 300 m/s for speed of sound, to express your velocity as a "Mach number", if you wish. Especially for reentry, most of the aerodynamic calculations are made using Mach number and atmospheric pressure, instead of velocity and atmospheric density. That is because the drag and lift coefficients correlate with Mach number, not velocity.

As near as I can tell from the reverse-engineering I have done, the stagepoint velocity is lower for Starship/Superheavy than it is for Falcon-9 or -Heavy. That is because they always want to fly Superheavy all the way back to launchpoint, rather than recover it at sea, the way they most often do with Falcon cores. I show just under 2 km/s stagepoint velocity for Starship/Superheavy, and over 2.5 km/s (almost 3 km/s) for Falcon-9. I might be wrong, of course, because I don't have access to all the "real" numbers, but I'm pretty sure that's in the ballpark.

Having the lower stagepoint velocity puts the onus on Starship to shoulder more of the delta-vee to orbit, which is right at 7.9 km/s for most low orbit altitudes of interest (around 300 km). That increases the mass ratio requirement, which for a large desired payload capability, sets a very low target for inert mass of the vehicle, a high target for its fueled-up mass, and a high target for vacuum engine performance. For otherwise-similar engine bell hardware, LOX-LCH4 has significantly-higher vacuum Isp than LOX-RP1. LOX-LH2 is much higher performance by far, as we all know.

Now you know why they went that way with the Raptor engine configurations. The kind of payload-carrying vehicle they wanted was pretty-much out-of-reach with kerosene, but they did not need to incur the low-density/high-volume problems to get all the way to LOX-LH2 performance. What they needed was only a little beyond what they could do with kerosene.

GW

Last edited by GW Johnson (2021-09-19 10:08:57)

tahanson43206 · 2021-09-19 10:16:12

For SpaceNut ... thank you for setting up such a terrific post by GW Johnson!

The detail that really caught my eye was the need to be able to return the Super Heavy to launch point. It appears that my intuition was close, that Starship bears more of the responsibility to reach orbit, in order to give Super Heavy a chance to return home safely.

SearchTerm:Orbit Two Stage Analysis (Super Heavy and Starship)
SearchTerm:Launch planning with return of booster to launch site

If anyone would like additional tags to find this post by GW Johnson easily, please add them.

(th)

GW Johnson · 2021-09-19 10:24:41

Three-stage vehicles have a lower 1-2 stagepoint, and a higher 2-3 stagepoint, than a 2-stage vehicle. The thrust/weight requirements for the second stage are nontrivial, although not as stringent as those on the first stage. The third stage has little thrust/weight requirement, and may burn continuously at lower thrust to orbit insertion, or it can make two burns separated by coasting on a transfer ellipse.

Now you understand why the Saturn-5 did what it did, and had the engines on the stages that it had. The second stage had 5 engines, just not as high a thrust as the 5 first stage engines. The third stage usually burned at low thrust to orbit insertion. And in the stage separation films, you can see the 3 little solid ullage motor plumes just a couple of seconds before the stage engines light. Those were all free-surface tanks, with LOX and RP-1 in the first 2 stages, and LOX-LH2 in the third stage. The “Minuteman” family of ICBM’s was a 3 stage solid, although its payloads included a hydrazine-fueled “bus” for precise trajectory control, before finally releasing the warheads.

The old “Scout” launcher I worked on at LTV Aerospace was a 4-stage solid. The way it was usually used for low orbits, the first 3 stages got you onto a transfer ellipse, and the 4th stage burned for orbit insertion. Geosynch was different, by tradition, back then (1960’s-1970’s). All 4 stages got used for reaching the much-higher energy transfer ellipse orbit. The payload itself was responsible for its own orbit insertion burn. In those days, hydrazine or hydrazine-NTO was used for that.

GW

SpaceNut · 2021-09-19 17:45:08

Still getting the ship ready for flight...
Moment of Proof for Ship 20 and Booster 4

With Booster 4 and Ship 20 reunited at the launch site, both vehicles will undergo proof testing and Static Fire tests before becoming an integrated stack for the second time.
Currently awaiting its re-stacking with Booster 4 to become an integrated stack once more, workers have been busy replacing Thermal Protection System (TPS) tiles on the nosecone area of the vehicle.
This process has seen technicians replace several hundred tiles, denoted by the various colored stickers placed on the areas of interest.
However, the three Raptors for Ship 20 (SN73, 78, and 69) rolled down Highway 4 last week

louis · 2021-09-22 19:21:36

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

Sounds like progress on FAA approval/environmental assessment.

My view: Musk is always several steps ahead of the game. He will probably have a back-up plan e.g. launching from somewhere like Brazil maybe.

Interesting that the video says FAA has dragged out the environmental assessment.

Last edited by louis (2021-09-22 19:22:25)

louis · 2021-09-23 18:19:07

Sounds like this guy has been reading some of my posts! lol

https://www.youtube.com/watch?v=mH70dmEu2EI

louis · 2021-09-24 13:20:28

Felix still sounds quietly confident about Space X's Starship programme despite the small number of orbital launches scheduled for the next year.

https://www.youtube.com/watch?v=g-ThNeIGtBY

One possibility is that there could be launches from Cape Canaveral, he notes.

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#1451 2021-08-22 11:05:42

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#1452 2021-08-23 08:02:47

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