sevenperforce

And if that doesn't give us enough thrust, we can maybe push some more fuel into the exhaust so that it burns after the main burn. Like an after burn.

Starship needs to fly to Mars, enter and land, refuel, fly back to Earth, and enter and land. So they had to design something that would be able to do controlled EDL on both worlds.

That was my point, originally. I was initially saying we should have the capsule with no onboard propellant tanks and feed it during transit from an external drop tank. That requires development of a high-flow bipropellant coupling but does not require the development of micro-g propellant and pressurant transfer. If we are putting tanks in the capsule and transferring in propellant and pressurant, then it will return to LOP-G with nearly dry tanks and nothing that needs disposal.

Resupply is definitely necessary, and it would be great to be able to do each lunar sortie and resupply with a single TLI, but provisions for sending Cygnus resupply to TLI independently is fine too. How much dV does Cygnus have? I assume it's more than enough to get from TLI to LOP-G. I'm confused about the hypergolic propellant tank. If it is only there to transfer propellant into the onboard tanks of the capsule, then why not drop it when you drop the ascent module? For that matter, just do the propellant transfer directly from the ascent tank...or even directly from the drop tanks.

Sometimes solids are more reliable. To date, the only engine-related human fatalities have been the result of a solid rocket motor failure. Small nitpick here, but the distinction you're drawing (complex, pump-fed, non-hypergol vs simple, pressure-fed hypergol) is inaccurate. You can have pressure-fed cryo engines (Kestrel, Xodiac, Tronador T10, Aerospike Annular J-2, RS-17, RM-1500) and you can have pump-fed hypergol engines (RD-253, LR-87-11, YF-20, RD-215, Gamma-8, and many others). We often see pressure-fed cycles combined with hypergolic propellants because hypergols need no ignition system, which makes them more reliable. Pressure-fed cycles are favored when either high reliability or low propellant volume is involved. It is not enough, not for abort and certainly not for landing. We can do that in KSP, because all solid motors have identical firing characteristics and can be perfectly aligned, but clustering solids in real life is not a good idea. Rockets with solid boosters strapped to the first stage (Atlas V, Vulcan, Delta IV Medium) use nozzle deflection, where the nozzles are canted away from the rocket body to fire through the center of mass: This is used regardless of whether even or odd numbers of boosters are installed. As I said before, the STS used the largest TVC system ever built to solve this problem of inconsistent thrust on the Shuttle SRBs. The only time I know of when a great number of solid motors have been clustered in parallel (like Sepratrons) was in the second stage of the Jupiter-C: This rocket used eleven scaled-down Sergeant missile motors which fired simultaneously for six seconds, after which the core popped out and fired its own internal motor. These motors did not have canted nozzles, but instead used an electric gyrostabilizer inside the payload spinning between 450 and 750 rpm to accommodate for thrust variations. If land without chutes and start ignite at 2 km altitude. No astronaut in her right mind would ever climb aboard a capsule with a solid landing motor and no chutes. A hyrid motor, maybe. But never, ever a solid. Using a solid motor for landing really puts the "suicide" in suicide burn. Nothing wrong with using solids to brake at chuted-landing touchdown. That's how Soyuz does it and that's how New Shepard does it. Starliner uses airbags to perform the same function. Service module. Two heat shields? No, no, definitely no. And the trunk is not "heavier" by any stretch. It is very lightweight, and it allows both Dragon vehicles to co-manifest unpressurized cargo.

I like the increased stability. Multidirectional thrusters on the lower stage are necessary, I believe, for the purposes of docking at LOP-G. Docking while connected to FHe upper stage is a non-starter; NASA would not entertain having an upper stage, even a safed one, meaningfully close to LOP-G. I think we can obtain much better performance and more downmass if we skip the Cygnus resupply module.

But of course if you have ZBO for non-storables, you can use distributed launch and you don't need SLS in the first place. "Ground rules" is a term of art referring to basic principles or starting points; it has nothing to do with GSE. Those boil off numbers are for tanks in transit from Earth to the moon, assuming barrel roll or other mitigation. Fair, but that quote was from February, before any Starlink flight flew. I suspect, as I've said before, that the Starlink stack is braced against the fairing for stability during ascent.

Cool to see the engine covers popping off!!! I noticed that! I'm not so sure. We do not know exactly how to make reusable, lightweight pressure vessels that can go to orbit and come back and don't blow up when in use. I agree. I have done a significant amount of work in the past with steel pipeline pressurization and there is NOTHING that gives you as much good data as a burst test.

NASA's current Ground Rules and Assumptions for cislunar activities presume total propellant mass boiloff, per day, as follows: 0.35% for hydrolox 0.20% for methalox 0.20% for kerolox We know kerolox does not boil off at all -- rather, it is more likely to freeze -- and so the LOX is the limiting factor for both kerolox and methalox. O/F ratio is higher for methalox than kerolox, anyway.

The requirements for an abort motor and deorbit motor may reflect similar dV, but they otherwise could not be more dissimilar. An abort motor needs high thrust and low precision; a deorbit motor needs low thrust and high precision. While it is theoretically possible to design a solid motor which would have both high-thrust and low-thrust modes, such complexity would not be ideal for something mission-critical as an abort engine. If this were KSP, one could imagine an array of small solid motors which would fire concurrently on abort but sequentially on deorbit; however, real-life solid motors have thrust fluctuations which make this infeasible. Strap-on SRBs typically need inclined nozzles for this specific reason, despite the cosine losses they incur; the STS SRBs used the largest TVC ever designed to accommodate this. Unless a solid motor is used to brake just before touchdown under parachutes, as with Soyuz or New Shepard, it is wholly unsuitable for soft landing. Computers may be very good at suicide burns but they still must throttle. Moreover, the need for propellant inside the capsule comes from the need for the capsule to maneuver on orbit. Cargo Dragon has already been reusing its propellant tanks and Draco thrusters for OMS, rendezvous with the ISS, and so forth for ages.

Even in the original conception, where Crew Dragon was to use the engines nominally for landing with chutes as backup, Crew Dragon would never have used its SuperDracos more than once per flight. Firing the SuperDracos for abort would expend so much propellant that the chutes would be required for post-abort splashdown. It is my understanding that once the burst disc is ruptured, the engines will only fire once, after which the burst disc must be replaced. The engines can of course be throttled and even turned off after that point. The engines are hot-fired before each launch anyway, with the burst disc being replaced between hot-fire and launch.

The engines themselves are not single use, but the engines can only be used once per flight. Once brought back, the engines are certainly still good for use on a subsequent flight. The fuel tank and propellants double for RCS/OMS so it's not a waste. The engines are not terribly heavy.

It's my understanding that once you fire the SuperDracos once, you can't fire anything else until you replace the check valves. But I could be wrong.

At one point, after propulsive landing was canceled but before the capsule failure, I believe Hans or someone said that the programming for propulsive landing was still in there and could be activated in the event of a chute failure. But given the burst disc changes that seems unlikely to remain.

Not any more. After the capsule explosion, the SuperDraco valves were replaced with burst discs, so they are now single-use. Although I suppose they could still be used for chute failure in a nominal landing situation, though not post-abort.

The probability of LOCV is the reciprocal sum of failure probabilities for all landing modes. So adding any backup mode decreases the probability of LOCV as long as that mode's existence doesn't increase the risk of abort conditions being met.

Inner hydrogen balloon, outer helium balloon, run the helium balloon's contents through an ICE to maintain low hydrogen levels?

With all the problems with these parachutes, I can see why SpaceX wanted to land on SuperDracos.....

That's a good start...but I want to try to make the lower module launch vertical and mate horizontal too.

The problem with this argument is that Artemis 1 is not an all-up test. I agree that a manned vehicle should launch first without crew; that only makes sense. But Artemis 2 is a different vehicle than Artemis 1. The EUS is brand new and never-flown, and it will not fly until it has people on it. It would be like launching Dragon 1 on Falcon 9v1.0, calling that a "test launch," and then flying crew on Dragon 2 on Falcon 9 Block 5 on the next flight. If the point is to have an all-up test flight before launching crew, then they should have an all-up test flight before launching crew. If they are okay with launching crew on the first all-up test, then they should have just put humans on Artemis 1.

In theory you could spam thrusters around the skirt and use them for hover, translation, and landing with the ascent engine off. That would obviate the need for a frag shield on the main engine or deep throttling. Then maybe go with a Superdraco or a generally thrustier engine. This would absolutely require multiple launches. The drop tanks would fall very low.

The failed O-ring caused a pressure drop that decreased the thrust on that booster, requiring the TVC on both the boosters and the SSMEs to gimbal hard to keep the stack flying straight. Only a few seconds longer, and the thrust shortfall would have exceeded TVC correction capability and pinwheel-yawed out of the flight path, causing the same catastrophic breakup. There was a structure failure in the external tank, likely due primarily to transverse loads, before the crippled SRB fully separated, rotated, and impacted it. The SRB impact to the intertank caused tank failure earlier than it otherwise would have, but only by seconds. You are correct that the SRBs did not rupture, other than the failed one that transected at the failed o-ring. One of the SRBs may have bounced off one of the orbiter's wings, but it was immaterial; the aerodynamic loads shredded the orbiter instantly. The thrust shortfall still would have eventually caused uncontrollable yaw. Also, the hole was widening every moment, so the entire SRB would have eventually separated at the O-ring.

Plus, let's not forget that the 37-tonne Boeing lander places no less than 3,030 m/s in dV requirements on the descent stage, whereas going straight to LLO would be only 2,770 m/s. Then again, the descent stage would need to brake Crew Dragon into LLO. Then again, the ascent module would only need to provide 1,870 m/s to meet Crew Dragon rather than the 2,600 required to get back to LOP-G, so I think direct to LLO still wins out.

Yikes.

I know @tater and I feel like broken records, but damn, failing to upgrade Orion's capabilities after Constellation was canceled just simply makes no sense.