AckSed

Hm. Deep-space monitoring of probes might be a service a future Lunar base could offer.

Summary (from here): They didn't want to give updates before now because information was changing too quickly as they were working through the issues There were three issues: the Centaur O2 leak, the Starliner helium leak, and a deorbit burn scenario that they found when considering the helium leak. For the Centaur leak, they find that the valve had exceeded its rated number of cycles. It was a complicated activity to change the valve, as Centaur is only stable under pressure or under tension, and they needed to depressurize it to change the valve To put it under tension, they attached a crane to Starliner, which is how they install it so not an issue, but since, in addition to its own weight, it also had to apply tension to Centaur to stabilize it, they had to confirm it was capable of handling the extra strain. For the helium flange, it sounds like it's a defective rubber seal (but they're not sure). After a few cycles, the leak rate got worse, but then stabilized. The flange is part of an assembly that is exposed to NTO, so they can't replace the seal without destacking Starliner and moving it to a place where that hazard can be neutralized. The leak rate is low enough and stable enough that they are comfortable launching; even if the seal failed completely, they would still be comfortable with the leak rate. No other seals are leaking. They had no way of noticing the leak during launch; they only noticed it during post-scrub operations. If they had launched, the mission would still have been safe and successful. Nonetheless, they will fix it for Starliner-1. The de-orbit scenario that they discovered is a rare one (0.7% of failure modes). They have two pairs of OMAC thrusters and would need to lose one of each pair, so that they had to deorbit using only RCS thrusters. On top of that, they would need to lose two helium manifolds immediately adjacent to each other. They did not have a plan for if this scenario occurred; now they do (instead of an 8-RCS-thruster burn, this scenario would require two 4-RCS-thruster burns). Part of the delay until the next launch opportunity is so that the team, who have been working long hours and seven day weeks the past two weeks, get the long weekend off. Nothing on the rocket or Starliner should expire until late June at the earliest (at which point the FTS pyrotechnics would need to be changed out). They're good to remain stacked until then. The changes have impacted Starliner's interim human rating for CFT, so they're holding a Delta Flight Readiness Review to make sure that it still qualifies for human rating with the changes. The FRR will be Wednesday, May 29.

Digging it out of here: https://en.wikipedia.org/wiki/Spacecraft_attitude_control The geometry reason is that "Attitude and position fully describe how an object is placed in space." The practical reason is there is no 'down' in space, and once you leave the orbit of a planet, no real orientation unless your instruments take that planet as your frame of reference. Attitude is determined through some frame of reference e.g. how far it is from the Sun. You may say your probe is pointing north in space, but relative to what? The plane of the Solar System is not quite flat, especially when you take into account orbits of the gas giants. Linguistically, "orientation" generally means where it is with a taste of which way it's pointing. "Attitude" only refers to which way it's pointing. It's more precise language.

That was going well until it wasn't.

A while back I posted about new alloys of magnesium, including one using 0.15% calcium to make "stainless magnesium". Well, Lenovo has made a shell for a new laptop out of it.

Totally missed this earlier, but EA has a new video comparing and contrasting RFA and ISAR, another startup. Tl;dw RFA takes advantage of automotive suppliers and a cost-optimising expert system to have components tweaked and supplied for a tenth of the cost from aerospace supplier, while ISAR is a near-full-integration vertical: https://www.youtube.com/watch?v=LRFnGnJzRJQ Honestly, RFA seems to have this: they build cheaply, build cleverly and outright state that they have to be profitable or they'll die. Edit: However, as a rocket propellant nerd, I like that ISAR is not only using propalox, but also cooling the chamber and throat with the LOX, with the propane cooling the nozzle.

Dogs in Roman frescoes and mosaics were symbols of fidelity, and were sometimes painted/inlaid looking straight at the viewer as if to say "This won't end well": https://livyarrow.org/2024/04/12/new-pompeii-images/

Pulsing... wouldn't be a good idea either. The inventor, Dr. Robert Zubrin, the one who came up with Project Orion in the first place, said that this concept depends upon a steady stream of constantly-fissioning propellant, and water to shield the reaction chamber/nozzle. For the why, read on. From what I have read, a lot of the engineering and startup/shutdown processes in any rocket engine are attempts to mitigate/eliminate transient events. Transient events, or transients for short, are the bane of any system in spacecraft, most often fluid-carrying systems. They happen when you turn something on and things are in the process of starting, or the opposite, when things are in the process of stopping. Sometimes it's when you have almost reached full power, but have to literally wait for the pumps to catch up. We find this on Earth with normal plumbing. Closing or opening a tap/valve suddenly will cause a bang as the speed of a mass of an incompressible liquid (water) is reduced to zero, and the energy is dissipated at shockwaves ringing through your pipes. This is hydraulic shock AKA "water hammer". If the system isn't engineered to mitigate it, such shockwaves can cause pipes to crack from the strain and bubbles of vacuum or vapour to form. That's like a couple kilograms per minute in a good water system. In a rocket engine pumping hundreds of kilograms of propellant per second, suddenly closing a valve that's feeding the propellant from the tanks is Bad. And explodey. Citation: "Treatment of Transient Pressure Events in Space Flight Pressurized Systems" It gets worse, though. "Hard starts" are generally caused by fuel or oxidiser left in the engine or pipes meeting up with new oxidiser or fuel being fed in when you restart the engine. Certain mixture ratios or allotropes or frozen/semi-frozen mixtures of fuels explode. You must run the engine lop-sidedly by feeding in one part of the propellant to wash away any trace of the other, and in the case of cryogenic fuel/oxidiser, do not boil when entering the pumps, causing vapour bubbles that the pumps will ingest, overspeed and then tear themselves to shreds. (This is what "engine chilldown" is prior to a Falcon 9 second stage engine igniting.) See here: https://space.stackexchange.com/questions/41473/how-does-lox-lead-startup-prevent-hard-starts A NSWR, when the propellant is dissolved nuclear salts of a certain concentration that can boil off the water and become more concentrated, will need to be really, really, absolutely certain it is not leaving a crust of uranium tetrabromide on the reaction chamber walls that will not detonate when more nuclear fuel is fed in. Because water (which we are using to cool the chamber walls) is a good way to slow down highly energetic neutrons so that they can split fissile uranium i.e. it is a moderator. So if a restart doesn't feed multiple swimming pools of water into it beforehand, it's going to suddenly produce much more radiation and then blow up in a very dirty explosion.

So help me, I am now imagining a bit where Kathy is the grizzled Starbase manager, Musk is the dorky rebel come to throw their weight around and Gwynne the loyal right-hand woman. "Elon, we can't deal with Leuders. She shot you." "Just a little bit."

Also, the welders are scrapping one of the stainless steel tanks next to the launch site right now.

Local news reporting Kathy Leuders' statements on the extensive building they're doing in Boca Chica to support "a workhorse area": https://www.youtube.com/watch?v=diMvd2n7_6c

Someone's been watching For All Mankind... Okay, "plasma" is characterised by the presence of a significant portion of charged particles in any combination of ions or electrons. A NSWR rides a continuous nuclear explosion held at bay by the flow rate, but the peak neutron flux should happen outside the craft and in the nozzle. Should. A nuclear explosion contains some charged particles due to how hot it is, and maybe some alpha and beta particles. The magnetic nozzle will be able to corral them. So the advantage is that the ISP will rise. Slightly. But now you are stuck designing a superconducting nozzle that will withstand a constant barrage of neutrons, gamma rays and heat. I wouldn't want that challenge.

Okay, so. Six NIAC projects have been selected to enter Phase II. One of them is about constructing lenses and mirrors in zero-G from suspended ionic liquids. That's not the important part for the purposes of this thread. What is important is that it cites a mission on the ISS, which turned out to be run by Axiom-1 in 2022 to make perfect, solid polymer lenses in microgravity, and I somehow tracked down the video of the entire experiment: My observations: You have to build up a bead on the nozzle of the syringe that also sticks to the rim of the frame, then trace a line around the outside before the blob gloms together. Tricky in a glovebox. You really have to keep it still, and bubbles are a problem. Not a major problem, as he simply used a pipette to suck them out, and you can just wait for the jiggling to subside before curing. I can easily see this being automated. Controlling the curve depends upon controlling the volume of resin. First syringe used less than 9.5 ml to make an estimated 5-6cm lens. Used a literal egg-timer to time the UV curing (4 minutes). Mission control had to ask everyone to stand still while it cured. First lens looked almost perfect. Taping the cap to the side of the next syringe is a trial. Mission control asked him to just take the major bubbles out of the next thicker one, as time was ticking. Couldn't see very well to judge the position of the bubbles to take out.

I'm sorry, we saw "Space" and immediately climbed over ourselves to explain. But this is also the Science part of this forum, so this amateur librarian will take a stab. As for actually doing it on the ground, cryocooling is used, but for things that you have to keep cold like cryopreserved people. Even then, it is actually cheaper to either accept bulk delivery and any boil-off, or (according to manufacturers of nitrogen condensers) generate it yourself on-site. Here's a leaflet outlining how liquid nitrogen is utilised in an IVF lab. It's quite involved. And here's someone who built his own LN2 generator from - yes - a cryocooler: https://benkrasnow.blogspot.com/2008/08/diy-liquid-nitrogen-generator.html

With Gateway and Starship HLS on the way, NASA has been forced to swim, when previously they were testing the waters with the tip of their big toe and cringing. Let's hope something comes of it.

Less maths, more practicality and some inertia. MMH/Hydrazine, and Hydrazine as mono-propellant, have the advantage of reliability and simplicity. They can take severe swings in temperature with just insulation protecting them. Building on research done for ICBMs, they can be stored for years to decades in tanks before being mixed in the engine, and not do anything exciting. Bladders and/or pistons in the tanks can pressurise the propellants in zero gravity. The engines are often pressure-fed, either combining the two fuels or feeding one over a catalyst bed, which makes them, again, simple and reliable. Specific impulse is not the main priority here. Cryogenic propellants are trickier. Orbital propellant depots must deal with the same issues as a deep-space probe, and this paper outlines the somewhat truncated state of the art: https://www.nature.com/articles/s41526-024-00377-5.pdf In short, keeping heat out isn't simple because keeping cryogenic liquids floating around in zero-G from boiling isn't simple either. To reliably cool a zero-G liquid, it must be touching the cooler. Materials for bladders/pistons that can stay flexible in such temperatures aren't common. Or researched. Further, most of the research was conducted on the ground. However, Intuitive Machines' Nova-C probe was methalox and used cryogenic propellants. When it landed on the Moon in February, it broke a leg and tipped over, but through no fault of the engines or fuel. So it has been done. If you want to use cryogenic, methane is not a bad bet. When shaded and insulated with MLI, it can remain at a reasonable temperature for months. ...The real issue is that orbital propellant depots, and thus long-term cryogenic propellant storage, were either paid lip-service or downright ignored by certain elements of NASA. Here's an article from 2008: https://www.thespacereview.com/article/1127/1 Edit: Then a little later, when SLS was in its infancy: https://arstechnica.com/science/2019/08/rocket-scientist-says-that-boeing-squelched-work-on-propellant-depots/

A sample of printed cardiac tissue for Redwire, and 11 kilometres of ZBLAN optical fibres (sold by the company Flawless Photonics at standard going rate of $1000/m), were returned from the ISS on a Cargo Dragon the other day. Are we approaching a level of It's Happening?

Idle thought: would the stacking arm count as the largest industrial pick-and-place robot?

So when I was searching for how high a high-altitude balloon can go, I found that the Pongsats had their own Wikipedia page: https://en.wikipedia.org/wiki/PongSat Buried in the references is a 2020 roundtable by Weekly Space Hangout where they interview John Powell (segment starts 10:34, ends 20:31) and he lays out the whole rationale behind the Airship To Orbit program: Condensed transcript (to read the transcript for yourself instead of watching the video - and this works on all subtitled YT vids - go to the page, expand the description and click on "Show Transcript"): JP Aerospace is a volunteer aerospace company with a small paid staff and about 70 volunteers. The airship-to-orbit thing is their patented(!) idea, and the Pongsat was a side thing about 15 years ago of taking student payloads to orbit for free, that's kinda grown to this "giant, unwieldy monster" that's now about half of what they do. Airship-to-orbit is a new way to get to space that doesn't use rockets. Not until the end, at least. Unlike Orbital Sciences and Pegasus' 50,000 feet, they want to start at mach ten and about 300,000 feet (91,440m) and go from there. Starting with the predecessors to Echo 1 in 1959 and onwards to something called the ROBIN program, almost to the present day people have been firing off sounding rockets and deploying balloons at very high altitudes and at Mach 10. (The latest reference I found on a cursory search is of a 1991 paper, "The inflatable sphere: A technique for the accurate measurement of middle atmosphere temperatures." Fire rocket up to 85km, deploy balloon, track with radar as it sinks, gain accurate density and thus temperature data on the middle atmosphere.) There's actually been a dozen of these balloons, and they're all about the same: getting balloons to cruise at Mach 10 for atmospheric research, measuring drag, consistency, and after a while they started putting solar panels, radio, instruments on them. They also dovetailed into using them as nuclear weapon decoys which ended up as big sources of funding of such work; the science ended up being a rider of the decoy program. When an ICBM comes in it deploys quite a few decoys, and these are reentry vehicles at hypersonic speeds, but they're also balloons. (Found under "Penetration aid" *snrk* on Wikipedia, where mylar balloons are indeed mentioned. For pictures, see also: https://www.globalsecurity.org/space/systems/decoys.htm. I love the dummy nuclear warhead.) Their thinking was: what if you made it more aerodynamic? What if you went faster? What could you do with 60 years of advances in technology: Mach 14? 500,000 feet (152,400m)? Mach 18? 800,000 feet (243,840m, which is above the final 224km VLEO of ESA's GOCE, which had xenon ion thrusters)? That's the question they're trying to answer: can you take it all the way to orbit? He has no idea! V-shape of high-altitude-to-orbit vehicle is because it ended up being statically stable in all three regimes: subsonic, supersonic and hypersonic. Craziest part is this has to be so big: you end up as a gossamer structure that goes at hypersonic speeds. An airship like that doesn't survive in the lower atmosphere. With a 5MPH crosswind you suddenly have 800,000 tons (assuming US imp. tons, that's 725,600 metric tons) acting on the side, and then you have confetti. It basically cannot fly any lower than the edge of space. So they have three stages: the blunt, minimally-aerodynamic v-shaped bulk load-lifter that goes to 140,000 feet (42.6 km) and no higher, the Dark Sky Platform high-altitude station and the high-altitude-to-orbit launch vehicle that docks and lives there. They tested their 100-foot (30m) long Ascender 9 prototype [in 2019] and their DS is made of 5 of them connected together, which makes a stable platform. The giant things they launch are completely silent as they streak away. They had some nasty official outs from that as it kinda freaks out the authorities - which they enjoy. Orbital vehicle, as mentioned, has to live on the platform, and has to be assembled - well, inflated - there. It's buoyant to 180,000 feet (54.8km) then slowly starts to move forward. Not even breaking Mach (presumably Mach 1) till they get to 200,000 feet (61km). Engines are plasma engines. Had 200 test firings and literally 800-900 more test firings to go, probably 5-6 more years (from 2020. Most recent Dec. 2023 update they had just started on the magnetohydrodynamic tests, where they added energy by making a spark gap in a magnetic field, and turned on the propellant). Ion engines are too low thrust, chemical rockets would rip the ship apart. Their solution is essentially 'dirty' ion engines: the mixed gas coming out of the combustion chamber is the plasma to be ionised (Editor's note: sounds like a magnetically-contained arcjet-boosted rocket). The engines they're running right now (in 2020) could be thought of as the world's worst ion engines: instead of about 60,000 ISP, theirs are about 1200 ISP. Which is actually good for chemical. It's a stupid engine that only has one use: it's "a steamship engine that goes putt-putt-putt for days". (Propellant is paraffin seeded with potassium. No note on oxidiser.) Once they get to the altitude of the rocket-launched weather balloons, they have a little more structure and aero and hopefully they can go faster. Once clear of the atmosphere, they turn off the electrical stage to have a final chemical-only orbital insertion burn. On the way down they fly at mach 1. Sounds impressive for a structure made out of foam and carbon fibre, but at 100,000 feet (30km) they've kinda pulled the teeth out of that; it's really not impressive. Efficiency-wise it's not very efficient; a more instantaneous release of propellant is the most efficient. What you gain is thinking time for emergencies: he cites the narrow windows of escape in the space shuttle; a loss of an engine is a loss of crew. With this, say you're Mach 15, you're only three quarters of the way through the entire process and you have a big engine failure. Well you go back and you take a look at it. You sit down and have a meeting while you're drifting back down to try to get it to work. If you do, you continue on. If you don't you can float back down and rejoin the station. You really don't have that in rocketry. (I will note that their focus in 2024 has shifted to bulk cargo transport, with a humongous 30-metre payload bay that'd let them capture Hubble intact.) Pongsat has become so overwhelming with 80,000 ping-pong balls flown and 3-4 missions a year, it's being spun off into its own non-profit. They get so much flat-earth hate mail.

They plan on using a plasma leading-edge to reduce drag (that's the purple edge on the render) and cite several papers where the general concept was proved in the lab, but admit it's another thing entirely to scale it up. One of the papers they cite is really quite interesting: "Lines of Energy Deposition for Supersonic/Hypersonic Temperature/Drag- Reduction and Vehicle Control" Not only do you gain something like a 40-90% reduction in drag and skin temperature by firing frickin' lasers ahead, it is also possible to use the reduction in drag to control a fixed wing by moving the plasma-induced low-pressure area off-centre. Note this is at normal altitudes. At their proposed altitude for the first stage high-altitude balloon (42 km or so), air-pressure is less than 1/20th of normal or ~5 kPa, almost as low as some neon tubes (3 kPa), and the power requirements to strike a plasma are lower. Bonus: check the infographic for the Airship To Orbit: Mad. But I'm glad they're doing it.

Is it possible for a space program to be endearing? I say to you that JP Aerospace is that space program. This is Grandad's garden shed hobby run on a shoestring, with a notable focus on practical testing and taking small steps towards a big goal. So far they've sustained themselves by launching 'Pongsats' and other payloads on high-altitude balloons, slowly working out their weird magnetic/electric/chemical engines that they are going to fit to a *deep breath* mile-wide, solar-powered, inflatable VLEO -> LEO launch vehicle that they propose to launch from a honest to goodness high-atmosphere aerostat station: Instead of saying, "Ohh, this won't work," I take a different tack. Someone has been trying to build this for 40 years, using prototyping and design changes where needed. I don't care how realistic it might be, I just absorb the sense of wonder at seeing someone dream big and actually trying in a reasoned manner.

Well now. I look forward to its career with great interest. Let's hope for 2024.

On one hand it is cool stuff. On the other hand I spent the entire day watching his other videos! Shame on you. :p

Looking over that paper, I don't see any show-stoppers on the new block-by-block placement. In fact it was made to be more easily checked. I note that the rectangles, edge pieces and curved parts have been replaced with curved parts and edge pieces on the Artemis 1 HS. I wonder if LOFTID could be adapted? Edit: I have been told that Apollo 4 used an elliptical trajectory and the Saturn upper stage to simulate lunar re-entry speeds. The velocity was 11,168 m/s, close to the proposed 11,111 m/s of Artemis 1. Of course Orion's heavier, so it's striking the atmosphere with greater energy, but we've seen that the shield is thicker.

Excellent "Vwoomph" at the end. For the force, 268,000lb is about 1,192.12 kN or 121.56 metric tons, which is more powerful than Rocket Lab's Archimedes.