CBase

They are currently on the ridge of wasting millions because the leaked hydrogen kills several certified limits. And you are afraid of loosing a fan ? I mean with 2 billion per launch and only a handful of launches I am not sure that building pipes would ever pay off. This is the very difference between SpaceX and the rest: Good enough let's you focus on the next challenge. Optimise later.

The problem is not leaked hydrogen, but increased concentration in the air around the rocket and associated fire risk. Wouldn't a constant airflow around the valve prevent the fire risk ? So just putting something like this near the leakage ?

The problem ist really more about slow turn around: failing is painfully slow until they are ready for another attempt. WDR or ground problems pushed the schedule by months. And because they do, they try to skip some only to later learn that it was needed. pushing it even further. I mean the WDR tests did not any alignment with launch windows if they were planned as it. Being on schedule on any innovative project is really a lot about failing softly.

Did I missed something or had SX sent out 3 static fire warnings in a row without any testing taking place, substantial action around the test points or comments ?

Develop by Airbus: For sure ! Contract by JSAT with delivery in 2024 at a time when not any of them had even a prototype ? I doubt it. JSAT is not a venture founded silicon valley company where it is normal to bet millions on optimistic proposals. I wouldn't even be surprised if SX used FH as insurance to meet the customers timeline if starship is not yet ready.

I could not find any specifications for the Superbird-9 regarding mass or size, but according to Ars Technica: Com sats are pretty big, but it seems unlikely that JSAT and Airbus contracted something in 2021 that could not be transported by any commercial rocket.

Are there any serious numbers out there how much mass you actually save from any high altitude launch (20km+) ?

If you read the article above SpaceX has the habbit of actually changing flight parameters constantly to find the optimal ones. Having engines max thrust increase certainly gives them more room to experiment with. Although quite likely it doesn't mean they will use the maximum thrust or duration of maximum thrust might be more limited than for falcon 9. Actually starship has already a pretty decent TWR, so efficency gains from using more thrust will propably be weighted against wear and tear.

Maybe rather vice versa: attach the door to the payload rack like kitchen appliances. With a 30° - 45° opening it should be open enough to let the payload slide out. Anyway stress on the door is mainly on ascend when it can be manually closed after loading. On return from orbit even some small gaps on backside shouldn't matter - the pez dispenser door could propably even stay open -, which does simplify whatever construction they will head for.

I do think it depends what your nominal AoA is during the landing phase without corrections on target. If you are using a very low (0-5°) AoA slightly raising it should improve range as L/D improves. Actually I could not find what the AoA for shuttle was after thermal braking was done and heat shield not required. Choosing the nominal AoA will depend on other mission requirements: longer glide allows for bigger latitude changes (not that important if spaceplane and Kerbal SC is on equator), shorter glide for more spontaneus player decisions to land after doing some stuff in orbit. The shuttle final approach was in manual control, so maybe even visual view might influence the decision.

Actually for real spacecrafts the AoA is defined by thermal protection. That's why the space shuttle did S shaped approach: AoA stays constant but rolling the lift vector sideways let you control range. For kerbal parts without too much realism added, I think 2 different AoA should be considered during reentry: 1. Low Drag phase: 60-90 degree AoA inspired by starship. Lift is completely neglectable and reduced AoA results in slightly increased range for the control loop. 2. Lift phase: 30 degree AoA is about maximum lift from wings and body. Since I enter with low PE to quickly cross first part, the lift turns the ballistic trajectory enough to not hit the ground before speed is shed off. Increase AoA and range is reduced since L/D is reduced. Decrease AoA and range increases as speed stays higher and trajectory more turned into flight. L/D is pretty constant from 10 to 30 degree if I remember charts correctly. But I never tried to bring this different approaches into a single mathematical optimisation as various effects dominate each other. I used trajectories mod to get downrange predictions and added a mechjeb control loop with above logic: Decrease AoA to get further, increase to shorten.

Actually I am more worried about using graphite moderation. This is considered an outdated design, because the moderator allows for thermal runaways unlike water moderated designs, where reaction stops if you fail to provide fresh water.

Actually I watched last 5 month starlink launches and there have been several before >8000km/h at start of entry burn and ~2200km/h dV for entry burn. Due to high drag at end of burn it is visually not easy to spot 50km/h differences, but if they actually reduced the burn duration, they did it incrementally.

Does this all really matter ? I mean we all started in KSP with suborbital expierences. They did it with a complete new design. Why not just applaud and hope they manage to improve their stages to get higher and faster ? I do so !

Recently was in the news a report about a peer reviewed paper from UCF about some interesting breakthrough for jet engines: https://newatlas.com/aircraft/oblique-wave-detonation-engine-hypersonic-ucf/ The precessor aka rotating detonation engine was only slightly discussed here before: There is still for sure a lot of works ahead as currently they used oxygen and not air, but hey they actually benefitted from a supersonic reaction mixture flow and it looks promising to scale up to hypersonic speeds for a spaceplane. And in some other article there was a statement about the Navy being interested, they would upgrade their turbines as the Isp of this is expected to be higher and therefore a lot of fuel to be saved. But if this really can be applied to ship turbines, any jet turbine could be upgraded for increased efficiency. And unlike scramjet engines this might be enough for jet engines to be useful at a broad range of air speed

High altitude wind was just mentioned as reason for delay, so might be a scrub, although they still hope for conditions to get better

Actually you are solving the problem that NASA always did: How to get a single rocket up there. That was never the intention of Elon Musk: He wants a Mars colony with hundreds of rockets flying, so his vision is a rocket and a factory. He takes a lot of expierence from automotive engineering where a lot of test vehicles are built while building up the factory. Although these prototypes are work intensive and do cost more than final versions, their cost is less than it seems because you need to build them anyway to master the production process. And even if they are not perfect for orbital flight and landing, they might be good enough for some hop tests. So build them early and they are useful to engineering. Build them later and they are just scrap.

True a minimal raise on PE will happen, however shifting around argument of PE is probably always more expensive. what ? How low is the TWR if you can do a couple hunded long duration burns without escaping SOI ? Gravitional losses must be huge once you finally do the escape

As others mentioned already: Going prograde is most efficient as it turns all thrust into kinetic energy. I do think you are messing things up: If you always do prograde burns at PE you are rising only AP, not PE. The main problem with longer prograde burns is timing and planing: The true curve of any prograde burn is a spiral not an ellipse. The instantanoues change abstraction from in game planning will fail as well as symmetric burn timing. Fixing wrong orbital orientation at the end is way more expensive on delta v than loosing small amounts for not burning prograde, thats why following the burn indicator is a good advice for most burns. For burns longer than a 6th of my orbital period I am using an old tool that I found here some time ago, which helps to calculate the asymmetric burn start offset, but you still want to break down very large burns into several to keep most from Oberth effect: Another nice information from the tool is how much gravitional delta v loss you have, which increases when burn duration increases.

If you check the thermal cam from LabPadre, it is visible that there was a lot of chilled gas around the rocket after it had landed: it is all black until the unscheduled ignition. Maybe some small wind or wind machines could help on next try by simply reducing gas concentration. I mean even too much oxigen can get very dangerous even without methane leaks.

Actually I did combine Trajectories for better prediction with MechJeb for this in a personal test build. However even Trajectories is not precise enough to really pinpoint the launchpad as good as SpaceX does. With enough aero control surfaces my atmospheric MechJeb landing can compensate for most of it. But the final landing is still too tricky: You would need to fine tune a couple of PID controllers for your booster design to land with thrust alone within few meters of your target. Since I am playing with various boosters this was a killer for me, so I stopped pursuing this idea. SpaceX did this for Falcon 9, but are you really willing stay with a single booster after you took 10-20 landings to tune all parameters ? Adding a drogue chute helped equally: Easy to control, the booster descends at a rate slow enough to have time for corrections and yet fast enough for aero surfaces to generate enough sideway lift. But now it is not a Falcon 9 style landing anymore.

Can you open up AeroGui (Alt-F12 -> Physics -> Aerodynamics -> Check Display Aero Data GUI) during ascent and try to get a screenshot right when it starts to tip ? Note altitude, repeat with vessel that works and get a screenshot at same altitude. If I am right dynamic pressure is really high and quite a lot higher for failing one. My Guess is that you tip close to MaxQ. You have quite decent TWR, but draggy shape: Dynamic pressure might be just little bit too high for gimbal and reaction wheel to cope with small sideway aero forces due to vibrations and suddenly the vessel starts to tip over. The normal counter measure is to throttle down around 300m/s to limit MaxQ ("dynamic pressure" in Aero GUI) until air gets thinner and you can throttle back up. You probably want 50-75% throttle.

It isn't that simple, at least if you want to land somewhere beyond earth: Your legs need to extend in order to land and after take off the doors need to close well enough for reentry back at earth. If you want to extend the legs outwards, then you should bulge the hull around the extension path to give room.

I do have Breaking Ground DLC for the robotic parts, just not Making History. It didn't appeal me somehow. Actually what is recovery friendly on Twin-Boar ? I would always consider a Main Sail engine with 2 Jumbo tanks and small control wings more recovery friendly as the performance across all altitudes is better. Personally I added fixed and recovered 1.25m tank and engines to scale performance until I unlocked bigger diameters.

Unfortunately I do not have Making History to check this specific design. I did rebuild it closely with some SpaceY boosters and a weight at top, but at this small dV differences even small build changes make too much difference. But on the topic of this thread about optimal TWR it is a nice example that the answer is not purely to look at TWR and indeed the added hammer booster only barely help to achieve orbit: TWR ~2 is high enough so you are not loosing a lot of efficiency to gravity and going more shallow with the extra thrust is eaten by increased drag, therefore your solution to throttle the main stage early on makes sense. However it might be more sensible to look at your vacuum Isp during ascent beyond 15km altitude: The twin boar engine is sub optimal compared to a main sail or pure vacuum engines. The major dV proportion for gaining orbit is mostly at low pressure. So the second stage or SSTO stage should always have an engine with okay to good vacuum Isp. Then you add either a first stage or boosters to get high enough TWR at launch pad. For SSTO you add engines until you reach at least 1.3 TWR. A true two staged designed will propably aim for higher TWR at launchpad and lower TWR with the vacuum stage, like RizzoTheRat posted.