sevenperforce

It's a valid problem. We don't know for sure that distant 1a supernovae and local 1a supernovae have exactly the same brightness. There could be any number of reasons why they wouldn't be, and some observations suggest they aren't. But consistency remains the best hypothesis at this time.

See how many times you can go to orbit and back in a vehicle that weighs under 100 tonnes. Staging encouraged, of course -- just don't refuel.

I see that you too found a need to fire the Thuds on the runway. Do you think you could have used the Goliaths without them to get more altitude and speed once airborne? Very nice, clean planform. You've got me beat on mass barely but I think I have a touch more dV. I didn't know until I did it that the Goliath has a shroud on the front if you attach a 2.5-m part. Very interesting design! I think you definitely saved on weight by doing it this way, but less payload for sure.

Perhaps that is why I said that S-turns were required to control descent rate and not something to do with stability. It was more than re-entry accuracy. If it was just a matter of landing in the right spot, the Shuttle simply could have begun re-entry earlier. The Shuttle had to maintain a strict 40-degree angle of attack to shield vulnerable portions of the airframe from direct re-entry heat. However, at this airspeed and angle of attack, the Shuttle had a tremendous amount of hypersonic compressive body lift due to its high wing plan area (necessary in order to allow a reasonable, somewhere-better-than-brick subsonic glide ratio). It had so much lift that if the 40-degree AoA was maintained through the re-entry interface, the orbiter would have actually begun to climb, trading velocity for altitude. This would have been bad, because both speed and atmospheric pressure would be decreasing, leading to less control authority on aerodynamic surfaces. The only way to maintain control authority while losing airspeed is to descend into thicker air, but the Shuttle couldn't descend with a 40-degree AoA. The way to maintain descent rate without decreasing AoA was to turn the lift vector sideways with a bank/roll maneuver. This pulled the Shuttle off-track, but induced cosine loss in the lift vector that allowed a better descent rate. The craft would then need to bank in the opposite direction to stay on track, and repeat through the re-entry interface. Indeed they do. However, a loss of roll authority (as happened in TMA-10 and TMA-11) or a steeper-than-planned entry trajectory (as with MS-10) resulting in a ballistic re-entry is still aerodynamically stable. It's just very unpleasant. TMA-10 actually re-entered nose-first, with the orbital module still attached, and it melted off and then the craft tumbled into its aerodynamically-stable re-entry orientation. The crew was banged up but the chutes deployed properly and they survived. That is what I mean by passive aerodynamic stability. Yes, Dream Chaser and the MiG-105 (as well as the X-37B to a lesser extent) have better passive aerodynamic stability. With that sort of shape, a failed control surface may result in an off-target entry but you will at least survive to an altitude where you could conceivably bail out. Yep. That's where "what if you lose tank pressure" comes in. Some things like major structural failure are never going to be recoverable. Crew Dragon can obviously save the crew if there is a major structural failure of the F9 booster, but if there is a major structural failure of Dragon itself there's simply nothing you can do.

A passenger airliner has multi-fault tolerance and multiple landing modes (runway landing, belly landing, splashdown). If the rudder becomes stuck, for example, the pilot can use differential engine thrust to counteract it. If an aileron locks up, the pilot can use leading edge flaps, slats, and elevators to balance and provide supplementary control. If the landing gear locks up they can belly land. If they lose both engines on ascent they have an aux power unit to provide enough power to operate the control surfaces, and on and on. There are contingency modes for practically any set of failures. Starship can ONLY land safely if all of its flaps work with sufficient precision to successfully execute the tail-flip AND if the tanks have sufficient pressure AND if the legs all lock out. There are no other options. It cannot glide. It cannot splash down. If a flaperon gets locked, it might be able to feather the others and survive re-entry but the tail-flip is going to be extra dicey.

The Shuttle was more passively stable than Starship will be, but less passively stable than the X-37, which is much less passively stable than a capsule. The Shuttle really was NOT that passively stable, all things considered, because it needed S-turns to control its descent rate.

Doesn't mean it needs to land passively, just that it doesn't tumble or enter an unrecoverable attitude without active stabilization.

Not rapidly reusable, mebbe.

The trouble is that even in KSP's simplified universe, I really can't come up with a good reusable crewed upper stage design that hits all the design requirements. Ideally, a 21st-century spaceship/shuttle would have the following attributes: Required Auxiliary, 0-0 abort system from launch to landing Contingency landing modes Two-system fault tolerance Passive aerodynamic stability from re-entry to touchdown Preferred Parallel-staged Horizontal-attitude touchdown Drop-in cargo variant You would think that it would be possible to design Starship such that the wings/flaps could be "locked" in a position on orbit, such that you'd gradually transition from a lifting re-entry to a tail-first orientation as your airspeed and the air density changed. Then you'd just need to feather the wing position to different places depending on your entry angle, entry speed, and the world you were landing on.

The placement of the forward LOX tank makes this complicated, and I understand why they want the same vehicle configuration for every variant (if nothing else, it adds to reliability when you are flying the same design over and over). But yeah, it would be a good thing. The problem is that this doesn't allow for P2P, which is something they seem to desperately want. Not enough margins for P2P LES. You mean not very costly? I like giving a vehicle enough wing space (preferably wet wings) to safely belly-glide to a landing, but also giving it retropropulsive horizontal landing. That way you don't have to deal with the weight of wheels but you have a backup in the event of a propulsion system problem.

True, but the chutes in KSP never foul, never tangle, and never have trouble opening.

Depends on the rocket-plane. Shuttle didn't have a great record. X-15 did slightly better (similar number of missions and only one loss of life/crew and vehicle), but the sample sizes are too small to be significant. It might well be easier to improve retropropulsive landing than increase the safety of a spaceplane. I'd be much happier riding a passively-stable capsule. Although chutes are a harder problem than KSP would lead us to believe. When it comes to passive aerodynamic stability, a broad truncated cone (Apollo CM, Orion) is more stable than a narrow truncated cone (Crew Dragon), which is more stable than a blunted hemisphere (Soyuz), which is more stable than a blended lifting body (X-37), which is more stable than a spaceplane (Orbiter), which is more stable than whatever Starship is. SpaceX has demonstrated that they can do retropropulsive landing, so I am not worried about that. I am worried about passive stability from re-entry interface until landing burn ignition. Just look at CRS-16. The booster had enough passive aerodynamic stability to survive entry and to maintain roughly consistent pointing up to landing burn ignition, and the engine burn successfully dropped it into the drink intact (although its subsequent, unavoidable tipover was not pretty). But Starship does not have enough passive stability to do this. A stuck hinge could mean Starship goes nose-down, tail-first, or tailspins...all of which are unrecoverable.

I always align my landing gear correctly, but I will try the friction control changes and see if that makes a difference. Usually I just end up adding more vertical stabilizers but that's a painful way of doing it. And my large nose gear was unsteerable so that might have contributed too.

That appears to be their plan.

I wonder if it would be possible to reinforce and/or daisy-chain in-game parts to create this spin effect. If you put the whole thing inside a maximally-expanded 5m fairing it might not register air resistance.

Here's my entry -- the Goliathud X. Weighs in at 60.8 tonnes. You'll notice that I made use of the attachment node on the front of the Goliath. Having a bare 2.5-m face was going to produce ridiculous levels of drag, so I utilized four air intakes instead. The shock cone intakes don't have enough static suction, so I added two basic air intakes at the rear of the main rocketfuel tanks. They are just slightly heavier than a small nose cone but have less drag, so it was worth it. I also had to use large landing gear due to the significant weight of the vehicle, which I didn't like, but oh well.

I made it to LKO easily enough once I was able to get off the runway in one piece, but the Goliath was useless. Basically I just made a Thud-based SSTO that carries a Goliath along for the ride. Engine gimbal with the Thuds was the only way I was able to get off the ground at all.

I have so much trouble with yaw authority on the runway, on almost all of my designs.

There's actually a huge difference. A leak in a metal tank results either from weld bead displacement or from plastic deformation. Note that I'm not talking about polymer plastics here, but rather the permanent deformation of a solid material when its yield strength is exceeded. A rupture, on the other hand, is different. It can be initiated by plastic deformation or the loss of weld material, but the big "boom" takes place when a fracture propagates within the crystalline structure of the metal, pouring the pressurant energy directly into the metal matrix. If your tank won't leak before it ruptures, then its failure characteristics are nonlinear. You can pressure-test, but you cannot be sure that your pressure test didn't introduce small cracks that weakened the vessel. You also won't be able to know whether the tank will still hold pressure under transient loads. On the other hand, if you can design a tank that leaks before it ruptures, then you know EXACTLY how much pressure the tank can take. You can determine the level of plastic deformation that will result from a particular pressure load. You can calculate how the tank will perform under transient loads. You can pressure-test to a specific safety factor without increasing the risk of subsequent rupture. Both are equally bad when they happen on a rocket, but leak-before-burst is vastly better for being able to figure out what your rocket is capable of.

Jeff Bezos spends $1,000,000,000 per year on Blue Origin. Jeff Bezos earned $2,264,400,000.00 last night. Well this was a scheduled disassembly. They were intentionally testing to failure. That burn...like fuel-rich oxyhydrogen staged combustion. I don't like it either. Ostensibly they want to avoid seams in the heat shield. But it does seem messy.

I didn't see any indication that a fairing was disallowed. If a Kerbal has a helmet and is exposed to the air he can handle up to 800K at over 1 km/s . However, sans helmet his resistance is much lower -- in level flight at 400 meters I got "Jebediah Kerman died without a helmet, too hot" at just under 400 m/s. Tucked behind a heat shield, but still exposed to the elements, Jeb died at a slightly higher speed (but also at a slightly higher altitude) so I don't think it makes any difference.

Got up to 1,179 m/s at around 6 km with a kickback as the first stage and two Whiplashes and an aerospike for the second stage. No problems. Recovered successfully. Looks like being helmetless doesn't hurt Kerbals at all under 10 km.

A Kerbal's altitude limit is roughly 10 km ASL before they run out of oxygen. If you put one in a fairing then they can go pretty much as fast as you want. So this is just a speed test under 10 km.

First attempt with a half-full Kickback got me to 724 m/s trivially. Higher is clearly possible. Didn't slap chutes on this but obviously recovery is trivial.

Any word on fairings? The entry burn view, with the terminator afterward, was amazing. Was it just me or did the post-landing fire seem moreso than typical on Block 5 landings?