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Posts posted by RyanRising

  1. thanks johnnyothan! this is a lot of fun to play with and as a mod it's come so much farther and gotten so much more polished than I could have imagined it would be. It must be an incredible amount of work to make this happen.

  2. On 9/14/2023 at 2:36 PM, AckSed said:

    I mean I sort of expected the flaring about the base. that's where the hydrogen vents from the expander cycle, but the flares from the side were a surprise.

    I think those are roll control thrusters! 

    On 9/9/2023 at 6:15 AM, magnemoe said:

    Shuttle and SLS is insulated on the outside, could you insulate the inside instead? Benefit is that you have no risk of damaging the fragile insulation while handling. But then you needed to make it pretty hydrogen tight. should be doable I think. It will be a bit heavier than on outside like on the shuttle tank but if would be reusable. 

    Yep! Saturn’s S-IVB was a notable use of internal insulation, so it’s definitely doable.

  3. On 9/7/2023 at 6:09 AM, sevenperforce said:

    That's how they are cooling the heat shield, but insulation is a different issue entirely -- keeping the propellant from boiling off due to ambient heat transferred through the skin.

    To @RyanRising's question -- my guess is that these early hopper prototypes have simply dispensed with insulation altogether. The low fineness of the stage minimizes surface area, anyway. For short hops and even suborbital hops, the amount of propellant lost to boiloff is going to be relatively negligible.

    Once they have an actual orbital vehicle under construction, we'll see whether they do some sort of insulation. It may be that the additional weight of insulation would be greater than the weight of propellant lost to boiloff anyway, and so eschewing insulation entirely is the best approach.

    I'm not sure that's plausible. For one, we can see that in the pic they showed of a WDR that there isn't ice on the tank when that happens with things much less cold than liquid hydrogen on uninsulated tanks. Secondly, because of its unique properties - not just freezing water but often liquefying air through a tank wall if not insulated - I don't believe even for short hops or static fires that the boiloff losses would be negligible. Even with insulated tanks, remember that some hydrogen rockets have pour twice their fuel capacity into a tank before it fills.

  4. The approach outlined here seems to be lacking a temperature-dependent heat generation or rejection property? Without that feedback, won’t systems either cool to the temperature of their environment, heat until something explodes, or remain constant at whatever temperature they happen to be? This is fine if that temperature happens to be what you want to operate at, but if parts are to have different behaviour based on their temp doesn’t the lack of any feedback loops make getting a part to a desired temperature frustrating at best?

  5. 34 minutes ago, tater said:

    Marketing implies sales. Who would be buying trips to Mars exactly?

    Who would invest in Mars—what's the RoI on that? Do they hope to get their payout while they are still alive as part owner in some city on Mars?

    Investors in? People with the large quantities of money to participate in SpaceX funding rounds are capable of doing the research of business models. The launch market is pretty well established, and it's chump change. To the extent they are investing they are throwing money at space because they think it's cool—not because they expect a meaningful return.

    The whole point is Mars. Again, "marketing" for what? Selling Nuke Mars t-shirts as their primary source of revenue?

    Kinda contrary to what Pthigrivi said, I think big investors have shown pretty well that they're not necessarily the smartest people around, and are very impressionable. If that "big vision" is persuasive enough, you can get people to funnel money into it without necessarily having a clear path to profitability.

    At any rate, SpaceX's Mars plans seem to be more aligned with stroking Musk's ego rather than making technologies for a practical mission architecture. The really important, development-heavy parts of a Mars mission: "how do we keep people alive and healthy for so long in such unforgiving environments," "what can we do there to best make use of human presence," while extremely criticial, aren't sexy. Making the biggest rocket ever made? That's sexy, put our money and effort into that. The payloads aren't just going to magically be there to launch once Starship starts working, but what plans SpaceX has put out almost unviversally glosses over that part, instead focusing on the evocative images of domes already there, big towers touching down on the red planet, people stepping out from the lander in a SpaceX Dragon IVA suit, etc. It's not serious as a Mars plan, but what it does do is make the people who are putting money into it - one person in particular, but no doubt the others too - think they're contributing to some great higher purpose, and feel motivated to continue fudning the project.

    In the meantime, they're making a really big rocket that has the potential to be very useful in a much more general sense, so that's cool and I'm rooting for them there. But when they say "making humanity multiplanetary," given the information of what they're actually doing, it reads to me as either very naive about what really needs doing, or just a platitude to tell those with infludence "hey that money is definitely well spent here, don't take it elsewhere."

  6. 1 hour ago, tater said:

    FWIW, the 17th is still on various NASA schedules.


    01:28:43          Starship is Transonic
    01:30:00          Starship Splashdown


    The booster mentions landing burn... so not even gonna try and flip SS?

    Nope, evidently not.

  7. 3 hours ago, sevenperforce said:

    I think you're making an assumption here about what the "regime of typical LEO spacecraft entries" constitutes. It's not an either/or distinction between radiative and convective heating. Rather, re-entries start with radiative heating as the dominant factor, and then the radiative heating decreases while the convective heating increases.

    You're correct that certain vehicles are designed to accept convective heat and then radiate it away. However, the image you provided above (Figure 10) isn't applicable to LEO entries generally. The source you cite says they "apply only to single-pass, nonlifting, parabolic-velocity entries." The real numbers are more complicated.

    The actual numbers can be found in this presentation, which explains the relationship between convective heating and radiative heating based on multiple factors. Importantly, one of the factors is the effective radius of the vehicle:

    Qconv ∝ v3(ρ/R)0.5 but Qrad v8ρ1.2R0.5

    As the effective vehicle radius increases, convective heating decreases, but radiation heating increases. For something like the Shuttle, which had a very deep atmospheric entry (to allow a lifting entry) and a very high effective radius, it would make sense that radiative heating was a major component.

    It is true that I’m making several assumptions about “what the typical LEO entry is.” Those assumptions are relatively high altitude, >~30km, and speeds of less than 8 km/s. Anything above those speeds wouldn’t be a low earth orbit and anything reaching those speeds at lower altitudes is… well it isn’t a crewed spacecraft like any we’ve seen before. I think these are reasonable assumptions.

    The paper you reference does not support your claim that LEO entires are dominated by radiative heating at first and then convective heating as they slow down. It does show that this is the case for higher-velocity entires, and the paper is clearly concerned more with those than LEO ones. These graphs start from 10 km/s and only go up from there.


    However, even in the larger 5m radius case the heat fluxes at 10 km/s are roughly equal, and it’s reasonable to extrapolate that it becomes very much lower at LEO entry speeds of 8km/s. (edit: to be clear, this doesn’t mean there is no radiative heating whatsoever in these regimes, only that it is significantly lower i than the convective heating)

    The equations you show are proportional, and describe the growth of each. However, this still leaves room for constant scale factors, and the examples they give show that for the size of entry vehicle they consider, those scale factors work out so that convective heating will dominate radiative heating at lower entry speeds near 8 km/s. The presentation says as much: reflective TPS is applicable for high-velocity, interplanetary missions. It doesn’t claim it’s very useful for LEO missions.

    The scales that this presentation considers include crewed space capsules that have been fielded. For those, it’s pretty clear that convective heating is higher than radiative at speeds < 8 km/s. However, it’s still possible that the flatter areas of the Space Shuttle experienced much more significant radiative than convective heating. I don’t have data on the type of heat flux experienced in those areas, but maybe I just need to look a little more.

  8. Radiative heat transfer from the vehicle is indeed very significant during shallow entries, though. That is indeed why the high-temp shuttle tiles were black, and wouldn’t have worked well at all if the majority of the heat coming into them was radiative. 

  9. On 3/14/2023 at 5:13 PM, sevenperforce said:

    It does, in fact, appear to be the case in LEO. And it is, in fact, the case in LEO.

    The actual area of plasma producing that amount of radiation is very large. That's why you can see shooting stars

    I think you’ve got things mixed around. It’s worth noting that while you see silver reflective back shells on Orion and Apollo, you do not see those on LEO spacecraft, which should tell you about the different types of heating they experience.

    But if we just make numbers up and only look ant the visible features of spacecraft, even if we do math on those made-up numbers, we’d be here all day. Instead, let’s look at some actual material on the topic. Here’s what Mr. H. Julian Allen of NASA Ames has to say about the topic:

    on ballistic missiles entering from near-orbital velocity: 


    Now, the heating rate for these vehicles is very large compared to the rate at which heat can be reradiated from the surface, and the driving temperature potential promoting the convective transfer of heat is determined essentially by the air temperature (i.e., the wall temperature can be ignored by comparison to the air temperature).

    Of manned space vehicles at orbital velocity:


    In contrast, for manned vehicles which must employ shallow-angled
    trajectories to avoid excessive accelerations, the heating rate is more modest but lasts for a considerable period. The conductivity problem is so severe that insulation is required to prevent overheating of the substructure.

    Also for large heavy vehicles the flight Reynolds number is lower so that a laminar flow can be maintained where otherwise turbulent flow would occur - hence, the heating rate is lessened.

    This implies that convective effects make up a significant amount of the heat transfer for atmospheric entry vehicles. However, what really seals the deal is this little transition:


    Up  to this point the tacit assumption has been made that convective
    heating constitutes the total. For speeds up t o nearly parabolic speed
    for Earth, this is essentially the case.

    He outright says that the heating is still essentially convective at speeds even exceeding that of LEO. At this point, the Mercury orbital flights had already been performed, so if NASA had designed its TPS, and that of Gemini, assuming this to be true when in reality radiative heating dominated the entry environment, they would have cooked their astronauts. 
    Mr. Allen then goes on to describe the radiative heating effects that occur with the higher-energy plasmas associated with super orbital velocities, and yes, this was clearly important enough that a reflective backshell had to be incorporated onto Apollo where the previous spacecrafts‘ leeward sides were designed to essentially be black bodies.


    And from another report, https://ntrs.nasa.gov/api/citations/19980227977/downloads/19980227977.pdf, here’s a handy graph (though in imperial units, bleh) of the rough relationship of convective and radiative heating. As you can see, in the regime of typical LEO spacecraft entries the convective heating is greater than the radiative by some orders of magnitude.image0.jpg

  10. On 3/13/2023 at 8:29 AM, RCgothic said:

    NASA has dropped an updated timeline:



    Now, they can’t possibly think Artemis III can still happen in 2025. That was earlier predicted in a timeline that also had starship launching its orbital test flight in early 2022. But since the people putting together those schedules should know that better than anyone, why put this out?

    Maybe they were moving stuff over to make room for it but ran out of time before they could slide Artemis iii to the right. :wacko:

  11. I appreciate the post, as much as it seems like damage control. I’m very disappointed to hear there are issues with scaling the fuel flow, however. This was a known and problematic issue with large scale crafts in KSP1, and I would have expected the development of KSP2’s system to specifically avoid that, since very large crafts are supposed to be common in this game.

    but, whatever. I’m not gonna fix it by complaining. I hope you guys can work that out satisfactorily, and if you do I’ll be happy to buy the game.  

  12. 23 hours ago, StrandedonEarth said:

    A few factoids about todays launch, courtesy of teslarati:

    200th Falcon 9 launch, of which 199 were successful.
    177 consecutive successful launches.
    138th launch of flight-proven boosters.
    93rd consecutive successful landing of booster.

    "Launches" instead of "missions" is doing a lot of lifting there huh? I suppose I shouldn't expect much from a source called Teslarati, but man, 199 out of 200 is not I feel an honest description of a rocket that has twice exploded losing customer payloads. I'm not trying to claim that F9's record is not impressive, of course, only that this source misrepresents the data.

    I wonder where 177 consecutive successful launches comes from? CRS-7 was the 19th launch, meaning there have been 181 launches since then, so they don't mean that, but AMOS-6 happened before the 29th flight, meaning there have been 172 successful launches since then. Maybe they're using the AMOS-6 as a failure there, but including the 5 Falcon Heavy flights as well as Falcon 9? Sneaky. 

  13. 1 hour ago, Ultimate Steve said:

    Unfortunately might mess with the thermals if it's on anything other than the fairing but cool idea!

    darn things are already flying when black with soot, so I’m not sure that’d be a dealbreaker 

  14. 21 hours ago, RealKerbal3x said:

    New video (it's a recruitment ad, but lots of nice new footage):


    I’m by far not the first to come up with this comparison, but I do think it’s rather sinister they appear to be pitching to employees the prospect of a company town. Live on company land, eat at company restaurants, have fun at company sanctioned events, send your kids to the company school, etc.

    Really cool footage of the operations, though! 

  15. 2 hours ago, intelliCom said:

    But anyway, back to the main subject of this post: the technicalities of a full-flow hydrolox engine. Just how possible is it, and if it is possible, is it worth doing over conventional methods? To my own not-an-engineer knowledge, it might be possible but not particularly useful over a less complex, more conventional system.

    The powerhead of the rocket engine is the part that differs with FFSC, all the other parts of the engine have no important differences because of it. And the powerhead of a full-flow staged combustion engine as the IPD was brought up to full power operation and otherwise succesffuly tested (https://spaceref.com/press-release/new-rocket-engine-of-the-future-goes-to-mainstage/). So it's very possible, just as much as with methane. In fact, it might be less complex to make a FFSC hydrolox engine than a dual-shaft fuel-rich staged combustion engine like the SSME because it eliminates the need for a complicated seal between a hydrogen-rich preburner turbine and the pump it drives, full of oxygen.

  16. 11 hours ago, AVaughan said:

    Are you saying companies should tell their competitors all their secrets?  Give away their competitive advantages?

    Yes, exactly. That’d be great - no more holding back technical knowledge for the purpose of profits. Patents I can support, trade secrets I cannot. 

    However, even failing this utopian ideal, it’s absolutely reasonable to require companies to share more internal detail about the progress of publicly funded projects like HLS than they have. We should not, for example, be asking if SpaceX even knows how many tanker flights will be required - whether they do or do not have the required details to finalise that number, they should be communicating that. Same with their plans for the demo, or the video of Crew Dragon exploding - the public absolutely should not be required to search for unsanctioned leaks to find this kind of information on programs with any public funding.

    11 hours ago, AVaughan said:

    Ah so they are still in competition with other companies for the the NextSteps lander(s), so it would be unfair to expect them to divulge anything to those companies at this point in time. 

    Quite the contrary - divulging that info would allow each competitor to improve their design based on what the others are doing.

  17. On 10/28/2022 at 3:14 PM, cubinator said:

    I mean...the public has visible and infrared cameras trained on the rocket and factory at basically all times, do you want the chamber pressure .csv's to go with that?

    That'd be nice, but they could start with actually talking to the public about what their HLS plans are or not firing people for sharing video of anomalies.
    Lemme just be clear here, I know they won't suddenly start being transparent - they've chosen to do their business with trade secrets and that and PR stuff means they won't give the public any more info than they have to. However, simply because this is the way things are doesn't mean it's how things should be, and I don't believe companies should be allowed to keep secrets to preserve company interests.

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