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Commercial Space Flight General / Re: Stoke Space Technologies: General Company and Development Updates and Discussions

« Last post by Action on Today at 09:27 pm »

I have designed zero-length plugs off and on for forty years, but based on original P&W experimental results from the late 1960s, I always used a Prandtl angle of at least 10-12° to achieve the plug nozzle effect (also a function of base pressure).  I've been confused by Stoke's "straight down" combusted exhaust approach since I first saw it.  Presumably they have tested it a subscale or analyzed by CFD before they built the full scale version.

That's an interesting comment, and indeed that's what a lot of schematics I've seen show.

How well understood are the dynamics of the gas bubble?  What variables drive that?

Complex subject.  Mainly, what is required is "closed wake."

Mmm.  It's going to be interesting to see how those spaced out thrusters work out.

Maybe they're just thinking it will be better to figure this out in hardware as they iterate.  All the theorizing in the world doesn't seem to have convinced people.

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Space Policy Discussion / Re: Jared Isaacman nominated as NASA Administrator

« Last post by meekGee on Today at 09:22 pm »

Hmmm.

Musk is great at building companies from scratch.

But it's a lot harder to turn companies around once they're on the wrong path.  And when you try, it involves by necessity getting rid of most of the people that define what is wrong with the company - which is all of the people that thrived in that wrong path.

Tough enough with a private company that it's really often easier to start a competing company from scratch.

With a government agency, neither of these things is possible, and I'm sure Musk knows that.

It'll get interesting to see what he has in mind.

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Commercial Space Flight General / Re: Stoke Space Technologies: General Company and Development Updates and Discussions

« Last post by HMXHMX on Today at 09:17 pm »

I have designed zero-length plugs off and on for forty years, but based on original P&W experimental results from the late 1960s, I always used a Prandtl angle of at least 10-12° to achieve the plug nozzle effect (also a function of base pressure).  I've been confused by Stoke's "straight down" combusted exhaust approach since I first saw it.  Presumably they have tested it a subscale or analyzed by CFD before they built the full scale version.

That's an interesting comment, and indeed that's what a lot of schematics I've seen show.

How well understood are the dynamics of the gas bubble?  What variables drive that?

Complex subject.  Mainly, what is required is "closed wake." 

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Missions To The Moon (HSF) / Re: NASA's Artemis Program Updates and Discussion Thread 5

« Last post by clongton on Today at 08:56 pm »

From the same Eric Berger article:

So how would NASA astronauts get to the Moon without the SLS rocket? Nothing is final, and the trade space is open. One possible scenario being discussed for future Artemis missions is to launch the Orion spacecraft on a New Glenn rocket into low-Earth orbit. There, it could dock with a Centaur upper stage that would launch on a Vulcan rocket. This Centaur stage would then boost Orion toward lunar orbit.

https://arstechnica.com/space/2024/12/how-did-the-ceo-of-an-online-payments-firm-become-the-nominee-to-lead-nasa/

Another possible scenario for future Artemis missions is to launch the Orion spacecraft on a Falcon Heavy into low-Earth orbit. There, it could dock with a Falcon upper stage that would launch on another Falcon Heavy rocket. This Falcon stage would then boost Orion toward lunar orbit.

This provides the dual redundancy that NASA wants for launch services, while still retaining the Orion spacecraft with its ESA Service Module.

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ESA Launchers - Ariane/Vega / Re: Vega C VV25 - Sentinel-1C - 5 December 2024 (21:20 UTC)

« Last post by jcm on Today at 08:55 pm »

Anyone got NOTAMs for Stage 3 and 4 entry areas?

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Heavy Lift Launch Vehicle (HLV/SLS) / Re: Jupiter DIRECT - Livestream Discussion - Sat 11/11/2023

« Last post by sdsds on Today at 08:54 pm »

For the Jupiter design the key aspect of SRB thrust oscillation was that NASA knew the STS hardware solved it somehow. By retaining ET design and manufacturing techniques, and staying at least initially with four-segment boosters, Jupiter-130 could conceivably have flown while Shuttle was still in service. Or at least with no slip in the launch cadence. That seems like a good thing, right? Consider though the implications:

STS-134: May 16, 2011
STS-135: July 21, 2011
Jupiter 1: September 26, 2011
                 ↕
Orion EFT-1: 5 December 2014

The Orion capsule was only ready for an uncrewed LEO test flight (on DIVH) 3 years after what would have been the Jupiter program's "need by" date. Look at that from the perspective of Lockheed-Martin. Doesn't allowing Boeing to muck around with the SLS core design and manufacturing guarantee you the schedule buffer you need? And aren't you willing to trade the low margin External Tank and Jupiter core business for the high margin capsule business?

Specifically on how the Shuttle stack dealt with SRB thrust oscillation, the intertank structures (including the thrust beam) carried the SRB loads into the mass of the propellants. For the SLWT, wiki says the LOX load was ~629 tons and the LH2 load was ~106 tons, so pretty clearly the LOX dynamics dominated. (Details at https://en.wikipedia.org/wiki/Space_Shuttle_external_tank#Intertank for those interested.)

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Mars Rovers and Spacecraft / Re: Possible cost-reduction possibilities for the NASA portions of MSR

« Last post by VSECOTSPE on Today at 08:45 pm »

Well in that case what this paper showed is that scientists have no trouble distinguishing Earth microbes that come from contamination and potential alien microbes, so this refuted whole argument that "if sample is contaminated there would be no way to know if the microbes are alien lifeforms".

Like deadman pointed out, that’s not the issue.

Either way it makes planetary protection looks unnecessary just as Robert Zubrin predicted.

Zubrin hasn’t been a practicing engineer for decades and never had expertise in planetary protection or most other things (Mars radiation, etc.) he comments on.  His one claim to fame is popularizing propellant production from the Martian atmosphere and how that could change human Mars architectures.  Folks in the business agree about the impact, but think the masses and margins in Zubrin’s architectures are wildly optimistic, unworkable, and/or would result in dead astronauts.

Anyway this whole discussion is likely moot as I said in the other thread, even more so with the appointment of Isaacman as new NASA administrator. Once he's on the job I see only two possibilities left for MSR: Starship or cancellation.

The program has given public presentations on a solution that closes for half the $11B cap using Perseverance EDL systems.  There seem to be lots of MAV options that would additionally buttress the margins. Zuber’s (not Zubrin’s) independent expert committee is reviewing until/through the holidays.  Unless they endorse something else, it’s hard to see any incoming Administrator singlehandedly going against expert committee advice or not taking the bird-in-the-hand that the program is presenting.

Isaacman himself will have bigger battles on the human space flight side of the house.  And to preserve his independence and authority as Administrator, his answer to everything can’t be Starship.  If he has half a brain for strategic thought, he’ll save that card for something in Artemis or human space flight.

And then there’s still the forward contamination issues... etc, etc.  Anything could happen, but while Starship is a distinct possibility for MSR, it remains a long shot, at best.

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SpaceX General Section / Re: SpaceX progress towards a 144 launch year in 2024

« Last post by meekGee on Today at 08:42 pm »

Keep an eye on the median turnaround stats¹ over the rest of 2024! On Oct 15 it was 51.4 days, now still very close 48.5 days, but it should start trending, slowly at first, but then picking up speed.

^{¹ - I forget which member [EDIT Shiro] maintains these stats, but credit!}

Now comes the part where the trend accelerates. Currently 42.7 days, after Starlink 9-14 it will drop, and soon [EDIT later this month] be under 28 days.

The current record is 34.1 days, set in June

The turnaround time is not indicative.

For example, for a given launch rate, if they manufacture a new booster, the turnaround time will actually increase.

And they have - they have more boosters then are necessary, to take care of scheduling edge cases and for redundancy in case they lose one on landing.

And they'll add a pad, so the launch rate will increase, but again w/o a change to the turnaround time.

It's an interesting but rather meaningless metric.

Refurbishment time may be a useful metric as a proxy for refurbishment cost. Time from launch to "available to launch" may also be a useful metric. Unfortunately, these both require inside information, so we are left with launch-to-launch turnaround time and number of boosters in the fleet as our two (more or less) public metrics.

It's the old and false mantra that any data is better than none.

The launch-to-launch time for a booster is almost solely an indication for fleet size and total launch rate.  It's just not a good proxy for anything else.  (Except for being a very far lower bound to refurbishment time)

And besides, as you say, what we really want to know is the cost / number of man-hours, and that's even more divorced from that metric.

Someone should simply ask Musk in a future AMA...  I bet it's a lot less secret nowadays.

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ESA Launchers - Ariane/Vega / Re: Vega C VV25 - Sentinel-1C - 5 December 2024 (21:20 UTC)

« Last post by jcm on Today at 08:39 pm »

AVUM first burn shutdown at T+16:45, altitude 253 km.

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SpaceX General Section / Re: Starlink direct to cell (was SpaceX & T-mobile event 25 Aug 2022)

« Last post by Twark_Main on Today at 08:36 pm »

On orbit Snapshot of Nov. 18 DtC launch Group 9-12

Again close proximity "pairs" testing as we have seen in Groups 10 and Groups 11.

Potentially a MIMO implementation?

Doubtful. I expect this is just an artifact of these satellites phasing into their final orbital slots.

It's a shame we don't get the Starlink builout animations anymore. The latest update was over 3 years ago.