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.