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Everything posted by sevenperforce
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25x reuse? FLEX.
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totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
Well, they don't necessarily need to be stacked by inline docking; they can also be stacked by tangential/perpendicular couplings, if the couplings allow for high-volume flow and structural linkage. My thought is to use EOR; launch the lander/ascender on one Falcon Heavy, then launch the expendable tanks on another, couple the two, and use the second FHUS for the TLI. Then the lander/ascender serves as the transit vehicle. Is there an engine under there? If it is supposed to be reusable then presumably they are planning for propellant transfer through the forward docking port. What's the bit with the golden tanks? Is that supposed to be a transfer vehicle? It wouldn't need landing legs. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
I wanna see more about that first one. Are those radiators on the front? -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
You know, I was looking at this over on a thread by @Spacescifi, and I was reminded of the parallels we all like to draw between Tony Stark and Elon Musk. I was also reminded of the various EVA designs that have been proposed over the years, and the most recent one unveiled for Artemis. Also remember this hideous (but surprisingly mobile) one: The Artemis suit has a soft exterior with hard internal joints to preserve mobility. What if SpaceX used its existing IVA suit and went with a hard exterior, like the Iron Man suit? The Iron Man suit built by Adam Savage is 3D printed from titanium, is literally bulletproof, and is light enough to walk around in. If SpaceX astronauts on the moon or Mars could don a plate-armor overwrap, it would prevent ballooning of their IVA suit and guarantee joint mobility. Range of motion is a problem in soft suits because of dynamic volume change. When a soft suit is pressurized, the pressure pushes all joints to the "open" position; any motion within those joints will decrease the total volume in the suit, which increases internal pressure (PV=nRT). Thus, every single motion is essentially compressing a piston, making any activity physically exhausting. Hard suits and hybrid suits have bearings and couplings that allow the joint to change shape without changing total volume. With plate-armor overwrap, however, the IVA suit would be unable to expand as far as it ordinarily would in a capsule depressurization event. The armor itself would not need to be airtight, of course; it merely provides mechanical backpressure to the IVA suit, as well as providing superior impact, puncture, and radiation protection. The joints would be designed for constant-volume movement. If dynamic volume change remained a challenge, the joints could even be equipped with sensors that would trigger air to be pumped out of the suit when the joint is being compressed and pumped back in when it was extended. In the future, the joints might even have braking mechanisms, to enable a user to "lock" certain joints in position. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
This is the ideal, I agree. Single launch, replaceable if it wears out but otherwise reusable. There are a lot of elements to optimize for, not all of which are straightforward or even compatible. Ingress and egress is the obvious one. Do you depressurize the entire cabin or use an airlock? Is the airlock hard or expandable, reusable or jettisoned? Do you use ladders or do you leverage the structure to get down to the surface directly? Cargo delivery and access is another critical question. If you can fold up a rover and slap it on the side of the descent module, like they did in Apollo, then good for you. But if you can drop cargo from directly underneath, like the Starship concepts, that's even better. And to top it all off, you want a lander stack that is modular (so you can build on it), assembleable on orbit, capable of jettisoning unnecessary mass as fast as possible, AND has the lowest possible complexity. It would be far easier, I think, to replace drop tanks manually using a Canadarm than to master multi-tonne hypergolic propellant transfer. More mass-efficient, too. If they didn't want to do an all-up test, they could do a rerun of Apollo 10, but with a descent stage carrying side-slung or under-slung cargo that would land autonomously while the crew vehicle returned. That way you don't waste the launch. -
Late to the party, but yeah, Ares I was intended to toss Orion into LEO to rendezvous with Altair and its EDS launched on Ares V. That's one of the reasons they never bothered to give Orion meaningful props, which is why we are stuck with LOP-G, since Orion has insufficient capacity to enter LLO from TLI and return.
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totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
One pair of sepratrons to boost out of the bay; one pair to cancel horizontal velocity, and some cubic octagonal struts for sacrificial lithobraking. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
A methalox FHUS would either need to be stretched (which would push fineness ratio too high) or swollen (which would mess with aero loading on the side boosters) to be optimal. You'd have more thrust and less weight. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
You know, I was going to say that there is not enough volume to fit sufficient propellant into the trunk, but after doing a little digging it looks like there is a shocking amount of volume. Even if only half the quoted volume of the Dragon 2 trunk (37 cubic meters) was utilized, due to tank wall volume, helium COPVs, and potential added thrusters (it is easier to add additional Dracos than redesign the dragon claw to allow propellant transfer; right now it only provides electrical power and coolant), the high bulk density of NTO/MMH would permit 22 tonnes of added propellant. Assume 4 tonnes of additional dry mass for tankage, etc., and you end up with a whopping 2100 m/s of dV in the "service module" tanks alone. Of course T/W would be lousy. With four forward Dracos, Dragon 2 had something like a fifteen-minute deorbit burn. You would need a vacuum-expanded SuperDraco, which would bump you up to 2200 m/s and get you to a T/W ratio of at least 0.25 gees (more as prop is expended; less if you downthrottle). That's more than enough dV to deliver significant cargo to the Gateway and return; not enough to enter and leave lunar orbit, though. And with a wet mass of 43 tonnes, you would need an expended-center-core Falcon Heavy just to get to LEO. You could, however, expend a Falcon Heavy with a small orbital module a la Soyuz, dock it to the Dragon 2 with the FHUS still attached, then fire the FHUS once more for TLI. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
If you do both then you have two different dockings, which is unpleasant in a sense but I suppose not fatal. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
If you want the mission to DO anything other than just being in what is essentially a really really high elliptical orbit, you'd need it to be able to dock at the destination. You'd either have to have the cabin feature a docking port on the other end (requiring inline thrusters) or dispense with the cabin entirely and use a service module that docks inside the Dragon's trunk. -
[New] Space Launch System / Orion Discussion Thread
sevenperforce replied to ZooNamedGames's topic in Science & Spaceflight
Constellation actually did a test launch. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
Arguably even more efficient to give Dragon a 10-tonne service module (maybe docked to an IDA inside the trunk?) and use FHUS residuals to do the TLI. Dragon 2 is not really great for lunar ops though. Not enough space or capability to really do anything other than go and return. Would be fine if you had LOP-G though. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
Abort works almost exactly the same way (higher MaxQ probably isn't an issue) so it would be a question of abort odds rather than abort risk. Abort is not a low-risk scenario; even in an abort, there are potential problems. If we suppose that 95% of aborts will be successful, then the booster needs to be 93% reliable in order to put LOCV risk at better than 1/270. If 98% of aborts will be successful, then the booster needs to be 82% reliable to meet the same standard. Man-rating Falcon Heavy would require a showing that it is at least as reliable as Falcon 9, or in any event close enough that LOCV risk remains acceptable. -
Matter Transmutation Made Easy... What If?
sevenperforce replied to Spacescifi's topic in Science & Spaceflight
[snip] But anyway, if such a thing existed, any competent physicist would be able to tell you how much minimum energy would be required to operate it and how much waste heat it would produce. -
totm nov 2023 SpaceX Discussion Thread
sevenperforce replied to Skylon's topic in Science & Spaceflight
The Artemis program does not require launching humans on commercial LVs. Duties for commercial vehicles in Artemis are limited to component lift only. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
Good catch. Not flow separation so much as combustion instabilities. Flow separation and combustion instabilities can both happen if you downthrottle too low, but outside of atmo it is only combustion instabilities. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
It just occurred to me -- another advantage here is that you can give the central engine a shorter nozzle if needed to allow downthrottling without flow separation combustion instabilities, since you can use the other two engines for the high-efficiency burns. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
Placing them inline was my thought as well. Great redundancy, and with sufficient gimbal even a single surviving outer engine could thrust through the CoM. However, it clashes with the need for an airlock that is jettisoned on the surface. I'm not sure about sizing the engines, though. The sea level SuperDracos barely have any nozzle at all so they will be underexpanded and easily downthrottled. I wonder how big a proper nozzle would be. Calculations suggest that the SuperDracos have an expansion ratio of 4.2 and an exit pressure of around three atmospheres, for a vacuum thrust of 73 kN and a sea level Isp of 235 s. Vacuum Isp is 242 s. With a chamber pressure of 1000 psi, SuperDraco should be good for up to 330 s if it had a proper engine bell (compare the RD-843, pressure-fed at 300 psi with a vacuum Isp of 315.5 s; AJ10, pressure-fed at up to 131 psi with a vacuum Isp of up to 319 s; peak theoretical propellant Isp of 341 s). Increasing Mach number by 37% with a propellant specific heat ratio of 1.225 requires a nozzle with just 10.9% greater area or an exit diameter of about 8.4 inches. Not nearly as large as I would have expected...I guess the ridiculously high chamber pressure helps with that. With 15 degrees of gimbal, the engine cluster would fit in a 1.07 m x 0.43 m x 0.5 m box (L x W x H). Way more compact than I would have predicted. Just trying to think, now, of an architecture where the airlock and landing legs can be jettisoned on the surface. Then again, if the airlock is sufficiently lightweight it's not a terrible burden. I agree on using Dracos to circularize in LLO, but I would say to drop the entire descent/ascent stage as a monolith (think dropping the external tank off the Shuttle). Replacing thrusters via Canadarm is not feasible, however. Any problems with the crew capsule would result in needing a new crew capsule. Orion also has a thermal backshell with a titanium honeycomb body, fiber tiles, and aluminum plating. No idea how much that weighs. Dragon 2 is lighter and is already plumbed with Dracos...just saying. It is very telling that LM's reusable lander design assumes the creation of a solar-electric hydrolox-electrolysis depot to make their lander feasible. But yes. Replaceable drop tanks are the only real reuse enabler at this point. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
Yes, but the SuperDraco is rather thrusty. SuperDraco's 100% thrust is 71 kN, but that's highly underexpanded. With a proper engine bell, which is essential for efficiency, the SuperDraco would push at least 95 kN if not substantially higher. You probably can't downthrottle as far if the engine is properly expanded, but even if you could, SuperDraco's 20% minimum throttle would still be 18 kN. If you have just a single SuperDraco directly under your CoM, then you can hover if you are landing above 11 tonnes, which is easy enough. But if you are doing balanced engines on the sides, you need to be landing at least 22 tonnes, which may be a bit much (remember that the landing stage is empty at touchdown). Hover is essential for hazard avoidance on landing. I wish we had a good idea about the mass of the thermal backshell and the main heat shield on Orion. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
Sure am. Can't swing that though, unfortunately -- prior engagement. This is why I propose using a reusable crew module that makes the trip from LLO to Gateway under RCS, and having a single-stage lander/ascender with drop tanks for the landing itself. I think I can get it down to one SLS launch and two commercial launches. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
This veers OT but I think there is still a societal expectation for a female displaying a suit to "model" it in a way that wouldn't be expected of a man. Not a NASA-specific thing or even something specific to Kristine; just how society functions. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
It deeply annoys me that in 2019, women are still expected to maintain a frozen smile in public like that. Kristine's face looked like it hurt. Compare to Jim -- he's not forcing a smile the entire time they are evaluating the suit. They said she will be at 8 psi 100% oxygen, but the suit drops pressure to 4 psi gradually to add mobility. Presumably the suit was pressed to around 22 at 60% oxygen in the demonstration, based on what Jim said. Though Jim's technical knowledge is not necessarily trustworthy. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
No reason it shouldn't have been, I suppose. -
totm dec 2023 Artemis Discussion Thread
sevenperforce replied to Nightside's topic in Science & Spaceflight
Some other clips show the ability to bend and pick up a rock from the ground with both hands. I wonder what kind of pierce protection it has.