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Posts posted by sevenperforce

  1. 6 minutes ago, cubinator said:

    That is called power armor.


    However, it's my understanding that even without servo assist, mechanically constrained joints can solve the ballooning problem all on their own.

    The possibility to later add servos is surely not lost on Musk.


  2. One of the wildest things ever done with an SR-71 (which brings this thread back from its brief derailment) was to flight-test one of NASA's aerospike engine designs.

    Here's the hydrolox linear aerospike on the ground:


    And here's what it looked like when it was mounted to the back of the SR-71:


    Sadly there are no images of it being fired in flight.

  3. 6 minutes ago, tater said:

    I recall reading that it leaked like a sieve on the ground until it heated up in flight. (unless I am misremembering)

    Yes, in order to keep the tanks from buckling under thermal expansion during flight, there were big gaps that left it leaking on the ground.

    It also had to refuel immediately after takeoff, but this was not because of leaks; the volume of leaked fuel was negligible. Rather, it could not take off with a full fuel load at all, even with both afterburners. So it would take off with a partial fuel load and rendezvous with a specially modified tanker for top-off. Even then, it would eventually become too heavy to sustain level flight and would need to fire up a single off-axis afterburner to hold altitude and complete the fuel transfer.

    Most tanker refueling runs are performed at or around cruising speed but the tanker had to get all the way up to its max speed of ~500 knots to keep pace with the Blackbird.

  4. 4 minutes ago, tater said:

    Yeah, I was thinking later, with "rapid reuse." In general it seems like it could be moved onto the transporter using the hardpoints. The trick is getting it to the test stand then.

    I don't think anything other than the chopsticks can utilize the hardpoints. You end up with too many degrees of freedom.

  5. 7 minutes ago, mikegarrison said:

    The interesting thing is that as the airplane refueled it got heavier, and toward the end of refueling they didn't have enough thrust to stay in level cruise. But two engines on afterburner would have been too much thrust. So they would would put one engine on afterburner and deal with the asymmetric thrust by side-slipping.

    Was literally typing this out.

    The SR-71 could not achieve supersonic flight on its engines alone without afterburners, but once through the transonic regime, it could shut off the afterburners and cruise just fine at around Mach 1.2 with military power.

    However it was actually more efficient in ramjet mode with full afterburner at Mach 2++. The ramjet inlets were designed for Mach 3.24 so that's where they flew the "cleanest" and that was usually the target "top speed" for sorties.

    Purportedly it got to over Mach 3.5 on a few occasions.

  6. 2 minutes ago, tater said:

    I have to wonder what the ultimate solution is for the crane attachments on the nose.

    I think they keep the crane attachments in place until they are ready to actually launch, and then they remove them and put on the tile cover sections before final stacking.

    Until they are ready to actually launch, those crane hooks remain the only way of lifting other than the chopsticks.

  7. 1 hour ago, tater said:

    Wonder how tight they can get the launch date once they actually get ready? I need about a 15 hour warning (more if I want to stop for a meal).

    Least if I take my son out of school for it, he can do half the driving.

    My oldest son is just under 10 so I'll have to do it all myself.

  8. 22 hours ago, tater said:

    That's just a shockingly huge change in period.

    Prior to the impact, the period was 11.9216 hours with an eccentricity of 0.03. The periapsis velocity and distance would have been 0.1777 m/s and 1.1427 km while the apoapsis velocity and distance would have been 0.1674 m/s and 1.2134 km.

    Assuming an impact near apoapsis, the dV change required to decrease the period to 11.38 hours would have been 0.00285 m/s or 2.85 cm/s.

    Assuming an impact near periapsis, the dV change required to decrease the period to 11.38 hours would have been 0.00229 m/s or 2.29 cm/s.

    Using the 5e9 kg mass estimate for Dimorphous, that's a change in kinetic energy of at least 13.11 kJ and a change in momentum of at least 11.45 million kg*m/s. DART itself, at 500 kg and a relative speed of 6.6 km/s, had a kinetic energy of 10,890,000 kJ and a momentum of 3.3 million kg*m/s.

    So we are looking at a momentum gain factor of about 347% for an impact with a rubble pile. Extraordinarily good news. 

  9. 32 minutes ago, Beccab said:

    Interesting, why is the nozzle not truncated? From what I know, it's very rarely worth it to keep the full spike

    I don't know. Possible that since it is an expander cycle, they want to maximize the surface area to maximize the power output of the cycle. The more heat they can acquire, the higher chamber pressure they can achieve. That's particularly important with methalox, after all, since methane has a lower heat capacity than hydrogen. It's a 3D-printed engine, I believe, so that makes designing the cooling channels for maximum heat takeup a little easier than it otherwise would be.

    I'm guessing it's a pure dual closed expander cycle without a split. But who can tell for sure?

    Interestingly enough one of their patents contemplates first-stage recovery using ducted lift fans located perpendicularly up the sides of the first stage.

  10. 6 minutes ago, wumpus said:

    Are dilithium crystals trademarked?  If not, use them.  You don't want anything that would actually work (we've had this argument 100 times) so just use dilithium crystals.

    Dilithium crystals don't provide enough lithiums to counteract flux capacitor depression.

    The only true solution is the trilithium crystal. 50% more lithium and 100% as much crystal.


  11. I didn't see a thread yet for this, so I figured why not go ahead and talk about it?

    Spanish smallsat launch startup with a dual-regeneratively-cooled methalox aerospike engine. Or, more accurate, a "spike" engine; there's no truncation of the nozzle.

    Here's one of the hot fires:


    Some of their corporate material suggests a two-stage reusable rocket:


    This cutaway seems to confirm an annular chamber:

    I do love a dual-expander cycle methalox design, if that's what they're doing here. Won't have a TWR ratio as good as staged combustion but there's still something very pure about it.

  12. 2 hours ago, JoeSchmuckatelli said:

    I was hoping for something that could basically be sent out to scoop/flatten an area and poop out 3D printed bricks behind it, laying a 'pad' for something to land on.  Probably nothing that easy would work...

    One of the issues with a prepared landing surface is that you can end up making the problem worse if you’re not careful. As long as your landing site is sufficiently flat, your landing engine plume is **probably** only going to spew dust everywhere; there’s a risk of excavating larger pieces of debris but there’s also no guarantee there are any such pieces of debris to be excavated.

    In preparing a pad, you’ve gotta be 100% certain that your preparation will result in a surface that’s truly impermeable to an exhaust plume, because otherwise you have basically just created a giant layer of potential shrapnel. 

  13. Interesting that they're using TEA-TEB for a hydrolox engine. Ordinarily you can just use an augmented spark igniter because hydrogen ignites so easily. I wonder if they're going with a hypergolic starter because it ends up being simply lighter for a bunch of different engines, or if they're doing a hypergolic start now but something else in the future.

    It was interesting to me that the Ars Technica article didn't talk about it being an aerospike. It may not be exactly an aerospike after all.


    "Because all parts of a rocket are designed to be as light as possible, such extended nozzles are often fairly fragile because they're only exposed above Earth's atmosphere. So one problem with getting an upper stage back from Earth [orbit] . . . is protecting this large nozzle. One way to do that is to bury the engine nozzle in a large heat shield, but that would require more structure and mass. . . . [D]uring reentry, with a smaller number of smaller thrusters firing, it's easier to protect the nozzles.

    "What you're seeing in the photos of the test is a high-performance upper-stage engine that can operate within atmosphere at deep throttle to support vertical landing but then also perform at a higher ISP than some variants of the RL 10 engine in space."

    Higher than some RL-10 variants -- that's quite the boast!

    It sounds less like a proper aerospike and more like a bimodal engine that operates as an aerospike at low throttle but as a fully-expanded vacuum engine at high throttle.

    The patent may prove instructive:



    In the patent disclosures: "Referring to FIGS. 7 and 8, the augmented aerospike nozzle 10 includes at least one initial nozzle portion 60 through which exhaust gas initially exits at least one high pressure chamber 36, and a secondary nozzle portion 62 downstream relative to the initial nozzle portion 60. . . . The secondary nozzle portion 62 also includes an outer expansion surface 30 outboard of the inner expansion surface 26, and an expansion cavity 32 defined between the inner expansion surface 26 and the outer expansion surface 30. Referring to FIG. 7, in some embodiments . . . [a]n inflection point 68 is defined where the outer diverging surface 66 of the initial nozzle portion 60 meets the outer expansion surface 30 of the secondary nozzle portion 62."

    In other words: at low throttle for landing, there is induced flow separation at the inflection point 68, making the entire engine act as a conventional aerospike. However, at high throttle, the inflection point 68 acts like a secondary throat and is the origination point for the bulk of expansion, allowing the entire cavity to serve as an expansion nozzle without any aerospike effects required. As envisioned by FIG. 8, it is even possible that no outer expansion surface 66 is required at all, allowing the inflection point and the nozzle throat to be one and the same.

    It also appears that the inflection point 68 may also be the gas bellows seal at the gimbal joint.

  14. On 10/9/2022 at 4:52 AM, SunlitZelkova said:
    On 10/8/2022 at 6:23 PM, Rutabaga22 said:

    Would the best orbit for an International space station(Not the real one) be polar? It would make it so every country can launch to it.

    Dunno. That would require higher performance rockets probably as you don’t have the Earth’s turn to assist you on the way up.

    Proton and Shuttle did just fine launching ISS modules into inclined equatorial LEO, not sure if they have the same payload capability to any polar orbits.

    As others have pointed out, there are really no countries with launch sites at higher latitudes than Baikonur, so there's really no need for a higher inclination.

    Also keep in mind that for everyone else, a higher inclination means a shorter launch window. A perfectly polar orbit means an instantaneous launch window for everywhere other than the poles. So that's annoying.

    On 10/9/2022 at 10:04 PM, JoeSchmuckatelli said:

    I'm wondering what the binding agent is.  Guessing since cured with light, its some kind of resin based composite, like they use in teeth.  Question is; could we dump a dedicated rover on the moon and have it build anything with 3d printing tech?  Like a landing pad?  I'm guessing the binder is no small part of the whole; the payload would have to be full of the stuff.

    I've seen research that shows sintered regolith construction to be pretty promising. No binder needed.

  15. On 10/9/2022 at 10:04 PM, Spacescifi said:

    I was thinking of a linear acceleration scifi drive that relies on main rocket engine acceleration to start it, but after you shut the rocket engine down the scifi drive will continue accelerating in a linear manner at the same rate as the rocket engine was before it shut off.

    Obviously it needs enough thrust to get off the ground... but after that you can just turn on the scifi linear acceleration and let it do the rest as the SSTO takes off.

    So, magic.

    The answer, FWIW, is that you can give a chemical rocket engine almost arbitrarily high T/W.

    A Merlin 1D at full thrust pushes a T/W ratio of around 180 which is certainly more than you'd need for any conceivable application.

    On 10/9/2022 at 10:04 PM, Spacescifi said:

    Overall it is less overpowered thsn other ideas I have had but still utilizes rocketry that is not a fantasy torch or a radioactive nightmare.

    It's actually one of the most overpowered possible designs. It will be a relativistic projectile within a few hours.

    On 10/9/2022 at 11:06 PM, Spacescifi said:

    Solid rockets can be throttled or turned on and off... so there is no reason to think such an engine could not exist.

    And solids have better TWR than chemical rockets due to the fact that they have denser fuel so it requires less fuel to get the same amount of thrust you would get with a chemical rocket.

    Solid-propellant rockets are chemical rockets.

    17 hours ago, MatterBeam said:

    A flat disk.
    A layer of explosives.
    ... stacked

    TWR should be in the millions.

    Yep, this should work.

    You can have explosives in a semiliquid form that are pumped into a very wide cylindrical chamber, then have the doors open. Ignite it as you switch the linear accelerator on. T/W ratio is arbitrarily high.

  16. On 10/6/2022 at 5:51 AM, RCgothic said:

    2) Non-propulsive landing. Substantially safer than relying on engines 

    True. However, there are situations where engines are more fault-tolerant than wings; for example, fewer weather constraints. There were numerous shuttle missions where re-entry and landing had to be delayed due to inclement weather at the landing site. In contrast, propulsive landings (at least of the SpaceX variety) couldn’t care less what the weather is like.

    If Shuttle had possessed the ability to abort or divert landings via onboard jet engines as originally imagined, this would have been ameliorated a little.

    On 10/6/2022 at 5:51 AM, RCgothic said:

    3) Use of existing landing infrastructure (airports). Land almost anywhere if necessary.

    Yeah, the propulsively-landed horizontally-flown spaceship of science fiction is super cool but it is really only needed on an undeveloped world. 

    On 10/6/2022 at 5:51 AM, RCgothic said:

    So if you want to bring a lot of mass back to earth, don't care too much about where you land, and want the vehicle to be rapidly reusable, a spaceplane is a fair design bet.

    The Space Shuttle never really brought down anything particularly heavy, in practice only ever landed at three facilities, and other design decisions compromised points 2 and 4.

    So far we have not really had reasons to bring significant downmass. If we had a colony on another planet with an atmosphere similar to Earth’s, that would be a meaningful consideration, but that doesn’t appear to be on the horizon in this solar system. 

    On 10/6/2022 at 5:51 AM, RCgothic said:

    If you don't mind landing propulsively at the launch site, wings are pretty superfluous.

    Even Shuttle had oversized wings for ordinary landing because of crossrange reqs. The Air Force wanted to be able to do polar dogleg launches with a landing at the launch site after a single orbit, so it needed insane amounts of glide. Without those requirements I believe the Shuttle would have been closer to a pure lifting body design. 

  17. 41 minutes ago, Exoscientist said:

    The point I’m making is that in reading the proposal to NASA the ~16 launches per mission were built into the contract. Suppose instead that in the original contract they said it would only take ~4 launches per mission using the stripped down 40 ton mass of the lander.

    Well we could also suppose that rockets are powered by unicorn farts, but that wouldn't be any closer to reality than whatever this is. ~16 were most certainly not built into the contract from the beginning. The "~16 launches" bit was part of an attack ad from Blue Origin. Rather, as Elon points out in the tweet you quote, the total tank capacity of Starship is 1200 tonnes, so with 150 tonnes of propellant delivered per fully-reusable launch, that's a max of 8 launches.

    Elon further notes that they may be able to lighten the lander vehicle enough that it could make the trip to the moon on as little as half a tank, necessitating fewer prop launches. However, these would still be fully-reusable launches. NONE of this has anything to do with Starship tankers flying expendable.

    But even if it did, it still wouldn't be a reason to suggest that there was something amiss about the contract price. NASA is paying for a service, not a series of launches. If SpaceX decides to reconfigure its launch system to include expendable tankers in order to do the whole thing in fewer launches, that's up to them to pay for (or reap the benefits of); NASA doesn't care. NASA only cares about the whole system meeting certain safety requirements.

    26 minutes ago, Exoscientist said:

    Actually, the mass of the Starship as an expendable is the entire point of the matter.

    Which is why it's so puzzling that you keep trying to estimate the mass of an expendable Starship, when Elon already stated it.

    26 minutes ago, Exoscientist said:

    From that you see you can get quite high payload as an expendable rocket.

    By this I suppose you mean an SSTO expendable Starship. If that's the case, then no, not so much once you add sea level engines. And SpaceX doesn't want to operationally throw away engines.

    26 minutes ago, Exoscientist said:

    In fact, it’s in the same percentage of gross mass range of other currently in use expendable rockets.

    Gross mass is all well and good, but the bottom line is money.

    SpaceX wants to deliver a certain amount of payload (usually propellant) to orbit. They will endeavor to do so at the lowest possible cost. Throwing away engines to save on propellant only makes sense if propellant is very expensive or upper-stage recovery is too long a pole.

    30 minutes ago, Exoscientist said:

    it is an extremely important thing to know if NASA, the U.S. tax payers, are getting jobbed if the original ~$3 billion price was based on ~16 flights per mission

    It was not, and even if it had been, that wouldn't be meaningful. If SpaceX can do it cheaper than expected, more power to them.

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