sevenperforce

Fascinating -- it looks like they plan to test vibration impact for two different mounting approaches: At left you have the familiar three-stud attachment. You can tell this is being used because of the adjacent stud-holes. At right you have some sort of metal frame that they fit into. Or they may use both -- framed in the high-heat regions, bolted in the medium-heat regions. Not sure why Tim is confused, but Elon already answered this before. They are lightweight, ruggedized siilica tiles that do not ablate. Their purpose is to hold the highest-heat interface away from the steel so the steel survives uninjured. They are a what the Shuttle tiles were supposed to be, but couldn't. The Shuttle tiles were quite lightweight -- basically glass foam -- but had to be very thick because they were protecting an aluminum skin. They were also bespoke. Virtually every tile was a different shape due to the shape of the STS Orbiter. They were glued on to save weight, which was a time-consuming and faulty process. Because Starship is a near-perfect cylinder, all the tiles are the same shape, and they can be bolted on easily. Failsafe redundancy because they have three bolts. They are also vastly thinner (lighter, less bulky) because the steel substrate can take much more heat on the back end than aluminum. That's the whole idea. These flaps are permanently stalled; that's what gives them their control function. More like airbrakes than traditional flaps or elevators or other control surfaces. The only lift is compressive body lift.

A LOX-afterburning methane-based nuclear-thermal rocket would be hella thrusty. Jump off the pad like an SRB; burn to orbit with an efficiency exceeding an RL-10.

No need to add redundant small reactors. Just pump in heavier propellant. Nuclear engines have constant temperature so all you have to do is change the mixture. Pump water through the engine for high thrust and low(er) specific impulse; mix in liquid hydrogen to increase specific impulse at the cost of lower thrust, go to pure hydrogen to maximize specific impulse. A LOX-afterburning nuclear thermal rocket (LANTR) is a very good design. Your main engine is a pure-hydrogen NTR, but you have LOX injectors downstream that you can use to add mass and energy. The LOX burns with the hot hydrogen, raising temperature even hotter than in the chamber and adding reaction mass to boost thrust tremendously. It would be fairly easy to build a LANTR-based SSTO, if the normal hurdles could be overcome. A 1994 study looked at a LOX/LH2 variable-mixture nuclear thermal rocket. It found that a pure-hydrogen rocket gets 941 s with a T/W ratio of 3. Inject an equal mass of LOX downstream, and your T/W jumps to 5 while only reducing your specific impulse to around 770 s. You can raise the LOX/LH2 mixture ratio as high as 7 for a specific impulse of 514 seconds and a T/W ratio of more than 13. https://space.nss.org/lunar-base-studies-1994-lantr-and-lunox/

Tricky proposition. I admit we don't know much about the pumping mechanism or approach to begin with. They are using autogenous pressurization for the tanks -- is that how they're pumping props around already? Is there enough piping to move the CoM around that way? We just don't know.

It was pointed out to me on another forum that I had confused the LoX and CH4 tanks, so pumping between those tanks is a non-starter. But perhaps pumping LOX between the nose header and the main would do the same thing.

IIRC, the 1.25-m service bay works well for this. With the doors open its collision box is larger and so it displaces more liquid. With the right choice of internal ballast it can provide positive or negative buoyancy on an action group.

Not a bad idea. I am unsure of whether it would have enough control authority to provide fine adjustments. More importantly it would have little or no roll authority. So I think we will still see flappy fins. How many, and where, is up in the air. But broadly similar. The Apollo CM positioned heavier equipment on one side, producing a positive-lift aero stability design: The CM could then use a handful of roll thrusters to turn the lift vector left or right without having to push against the airstream; they were rotating around a passively-stable axis. This was super important. SpaceX will presumably draw on prior experience, right? And while Dragon 1 used the same approach as the Apollo CM, Dragon 2 uses a ballast sled which can translate on rails between the capsule and the heat shield, thus changing the CoM in real-time. I wonder. What if Starship uses its landing props, pumped forward or aft between discrete header tanks, to change the CoM in real time and control pitch? Then the forward fins could be smaller, and fixed, and roll control would be achieved by feathering smaller flaps on large, fixed rear fins. We know what the header tank in the nose looks like. Could the new structure in the aft tank be the corresponding balance tank?

This was the original BFR design, actually.

Note: if you like this idea and want Elon to comment on it, retweet it to him here:

Ah, shoot. Looks like @Superfluous J beat me to it. Notwithstanding I will re-christen this El Barato.

Here's what I'm thinking Fixed forward fins parallel to the midline. Rear wings offset ventrally from the midline but tilted back in a dihedral; fixed but with actuating control surfaces in the center. Freeze the two control surfaces, and the whole thing falls like a skydiver with passive aerodynamic stability and a small amount of body lift. Pull both of the control surfaces back (dorsal) and pitch up; push both forward to pitch down. Differential rotation rolls left or right. You have a little bit of yaw control by using pitch and roll together, but RCS provides primary reaction control. If one of the control surfaces fails, lock the other one in the same position and use RCS to compensate until you are low enough to perform the kick-flip. Nominally, the kick-flip is initiated by folding both control surfaces back and firing RCS hard. If you lose RCS, you can use the control surfaces + engine gimbal to do the same thing; if you lose control surfaces, you can use RCS + engine gimbal to do the same thing.

"The best part is no part, the best process is no process, the best system is no system." Even though the four-flap approach approximates the four limbs of a skydiver well, I've always thought it seemed failure-prone. Curious to see what exactly they can eliminate. If they lose the nose flap actuators altogether and make the forward fins smaller, will they save enough weight to reserve propellant for heavy RCS use during descent? "Static aero" sounds like passive aerodynamic stability. I wonder if we see smaller, fixed forward fins and dihedral rear fins with the medial region fixed and the lateral region actuated. Half as many failure points. Add a bunch of the hot-gas thrusters and you might have something workable. Presumably the idea is that if the rear flaps were to lock up, you might go into a slow tailspin and miss the center of your landing zone, but you could control the spin with hot-gas thrusters and use engine gimbal to correct before landing nearby.

I've been toying around with different ways to get that coveted Ruby Star from the beginning. I had some very promising designs involving fairings and command chairs, but then they were outlawed. I had an SSTO with a solid first stage at around 2400 kerbucks, but then @bayesian_acolyte got a cheaper version first. But I plugged along anyway, and I'm finally proud to present El Cheapo, coming in at a launch cost of just 1,823 kerbucks. Full album: https://imgur.com/a/qlajob4 It turns out that the smallest 1.25-m tank with only a couple of units of propellant is actually cheaper than a decoupler, and works just as well. Who knew? Plus, the game's aero engine doesn't realize that my ship has a "front" and so the drag is very low, allowing me to squeeze all the value I can out of the solid booster. Launch cost: 1,823 Mission cost after recovery: 874 I've now claimed Ruby Star, hopefully for a while. @bayesian_acolyte still holds Sapphire Cluster and the Gold Florettes, though. I believe this qualifies for Zircon Chevron and Onyx Eyes but sadly I have one part too many for Amber Leaves. Those Oscar-B tanks have so little drag for the amount of propellant they contain that they were essential...though perhaps I could squeak by with lower margins if I swapped two of them for another FLT-100 placed between the pod and the engine. Would give a better crumple zone, too.

"Static aero" suggests that the baseline configuration is changing. We should start speculating. Unfurled dragon wings? Fixed wings with dihedral and edge flaps? Something that would make it controllable via engine gimbal even if the actuators seized up?

It may or may not be cumulative, I don't know. But I think @kspnerd122 was basing it off the Apollo missions where two SEPs were deployed at the landing site and four were deployed at a distance from it.

I've flown many spaceplanes but never actually submitted for the K-Prize. I figured this Saturn V SSTO created for Apollo Style Redux 3 and documented below would be a good first entry: Sneak peek:

After a long wait, I've finally wrapped up my Apollo Redux and gotten all the photos organized. If you'll recall upthread, I initially commented on this challenge, saying "Tempted to try and hit every point item with a rocket that looks as little like the Saturn V as possible." After some reflection, I decided to tweak this a bit, and instead use a rocket that looks as much like the Saturn V as possible but is nothing like it. Here's the full imgur album in all its glory (I strongly suggest reading through this before you click the spoilers below). Nothing on the pad...is this Saturn V horizontally integrated?? Ah, there's the familiar shape. I didn't earn all possible points, but I earned most of them. Scoring below:

Except gimbal the engine a bit, to compensate for the off center trust. The reason for three engines in the center is to give engine out capability. One option is to land on two engines or only one, last who would give it low enough trust to hover. Downside with this is engine out as it takes some time to start another engine and if you are 5 meter up you might not have enough time. Gimbal can compensate torque if the thrust vector points to the center of gravity. But it causes lateral force, which makes killing of lateral velocity impossible, if the rocket is not tilted so that working engine is under center of gravity. Landing will be asymmetric and cause excessive load to lander legs. Probably they can save the rocket in emergency situation, but it is hard to believe that they could use asymmetric landing as normal operation and reuse the rocket after that. I don't recall if it was Twitter or elsewhere, but Elon said that they would typically hoverslam for this reason. They can use asymmetric landing for emergencies but that's it. EDIT:

My first submission was just a test flight of a design intended to reach orbit three times. It did reach orbit twice (and made it over 90% of the way to orbit on a third attempt), so it qualifies for the challenge, but I didn't document everything by photo yet so I am not sure if it counts.

Right. Pressure-fed rockets are hella simple. Helium at super-high pressure pushes against fuel in a tank at lower (but still very high) pressure, which is thus pushed into a combustion chamber at lower pressure. The pressure in the tank must be greater than the pressure in the combustion chamber in order to maintain positive flow. Unfortunately, this means the tanks must be very strong -- stronger (in an absolute sense, not for their size) than the combustion chamber itself! This means a low chamber pressure (which is inefficient) or a very heavy tank (which hurts mass ratio) or both. For low dV burns (or for stuff where inefficiency is okay, like RCS), this extra weight is not too big a problem, but when you need to squeeze out lots of dV, it hurts you. According to this Rochester Institute of Technology whitepaper which I completely have not vetted, moving from a pressure-fed cycle to a pump-fed cycle can save 90% of tankage weight for burns lasting longer than a minute. So if the weight of a turbopump is less than 90% of your tank weight, you should switch. On to the maths (or at least back of the envelope maths) for @Cunjo Carl's idea. My suspicion is that the available work-energy in the pressurized helium is going to be the same regardless of whether it is used to run a turbopump or is used to pressurize the entire tank. There might be some inefficiencies on either side that I'm not thinking of, but it's probably going to be roughly the same amount of work-energy at the end of the day. But localizing the high-pressure region to the turbopump can still have major benefits. If you can reduce the head pressure in the tanks (let's say to halfway between a typical pressure-fed cycle and a typical pump-fed cycle) by putting the helium through a simple turbopump first, you can cut the weight of the tanks to around 55% what they would otherwise be. And since your turbopump has no combustor and is operating on inert helium, it doesn't have to be extraordinarily heavy and it doesn't need to be made of ridiculous corrosion-proof metals. So you should probably come out on top.

I've been wanting to try my hand at a true SSTA now that we can have easy props on Eve.

Mine is still above but I haven't actually submitted more than a photo in the hangar yet. I am going for three orbits. You have the lighter craft by far -- mine started around 60 tonnes and is now up at 100 tonnes.

Water tower was able to hover because it had a single engine. SN4 and all the rest of its line have three engines in a triad configuration so there's no way to hover on just one central engine.

It doesn't necessarily need to be more efficient if you can save a lot of weight by reducing the pressure in the tanks and thus reducing the weight of the tanks. Could also be used to adapt existing pressure-fed engines to work with larger stages (and correspondingly better mass ratios) than would otherwise be possible.

Ventilators are already known to be pretty harmful, generally.