AckSed

Who wants to know how full the urine tank aboard the ISS is? Or would like to know the station's exact mass to 5 decimal places? Live ISS Telemetry

Did you, prospective satellite builder, like the video of Starlink broadcasting live from inside re-entry? Do you want your own link? SpaceX is selling! https://www.reuters.com/technology/space/spacex-says-plans-sell-satellite-laser-links-commercially-2024-03-19/ Yet another way to make money with their satellite internet.

Don't know if you've ever played a 3DS, but the top screen had this parallax 3D system: https://www.cnet.com/tech/gaming/how-good-is-the-3d-on-the-nintendo-3ds-and-how-does-it-work/ It had a low viewing angle, though.

Okay, okay, you win, I'll call SpaceX and tell them someone wants a proper mass simulator on the next flight. Except they're not accepting my calls for some reason.

Ever since the Industrial revolution, humans have been searching for more ways to boil water into steam for industrial processes. Coal boilers. Gas boilers. Concentrated solar. Nuclear reactors. Now someone is proposing heatpumps, which is more viable on industrial scale than you might think. And the government seems to agree, awarding them up to 145 million dollars to develop their drop-in heat-pump boilers to convert low-grade heat into industrial steam. The specs seem right, because at minimum, it uses water as a refrigerant, can work on heat sources as low as 29 deg. C and operate at a Coefficent of Performance of 2.1. It's even capable of leaving the gas boilers in place as a backup.

On a tangent: is anyone else pursuing the mass-production of satellites and, more importantly, satellite sensors suitable for using on probes? Starlink and its sister project Starshield seems like it's not only a turnkey solution for communication and surveillance, but a full satellite bus for any customer to place their satellite/probe on. Project Kuiper is 'just' a Starlink competitor, but it could be turned to the same ends. OneWeb is... lagging behind. If you can figure out how to mass-produce a generic suite of planetary science (like narrow and wide-field cameras with multiple filters, spectrographs and radar) that fits onto a cheap satellite, you'll have a product. Now I think about it, the real thing stopping a swarm of sats being placed around Mars, Venus or the outer planets is now not hardware, it's the lack of ground-support: receiving signals, upkeep, debugging, interpreting data. SpaceX is already doing that with over 6,000 sats and rising. If someone could figure out how to run a planetary science sat swarm (P3S for short) on minimal personnel, such that it could be sustained with throughput over 5 years for half the current cost, then you have an attractive product.

The first Z-pinch machine was ZETA, in 1957. It did not end up working, but the British government thought it had: https://www.iter.org/newsline/-/2905 The Centauri Dreams blog has multiple articles on fusion drive: https://www.centauri-dreams.org/?s=fusion That led me to this Popular Mechanics article from 2012 on pulsed fusion drive (which is what a Z-pinch essentially does - pulses of fusion explosions): https://www.popularmechanics.com/space/rockets/a7715/the-big-machine-that-could-lead-to-fusion-powered-spaceships-9450996/ With regards to an alternate history, fusion is a dense subject that is filled with failures and lessons learned. You would need steady funding, a willingness to take risks with almost certain knowledge you aren't going to get it right the first or fifth time, perhaps a nuclear reactor for power and, ideally, a reasonably-affordable heavy-lift launch system to test it in space.

As I've heard, in a two-stage reusable rocket, going up on a flatter trajectory is a lofted trajectory, and it's indeed an advantage for reusable boosters if you can push the work of getting to orbit on to the second stage. Because if the fuel burn rate is constant, the booster uses less energy to punch through the thick lower atmosphere, and to boost back to cancel its sideways momentum so it can return to the launch site. In the first instance, though, boosting till you leave the SOI is a tad trickier to do from Earth. If this cheat-sheet is correct, the amount of delta-V to escape Kerbin and into an elliptical orbit (3400 + 930 = 4330 m/s) is slightly less than that of escaping the SOI of Mars (3800 + 1440 = 5240 m/s): An equivalent manoeuvre to leave Earth and reach its escape velocity requires 9400 + 3210 = 12,610 m/s. So the bar is set nearly three times lower for Kerbin.

Propellant density is important with SSTO, yes, but I've seen other proposals say that it can work with normal propellants. And I would reluctantly decline developing horizontal-takeoff SSTO spaceplanes, no matter how cool they are. Skylon's air-breathing rocket engines currently aren't getting the funding to turn them into reality. Perhaps you heard that hydrogen doesn't have the density for SSTO. It doesn't, not until you make it very big like the ROOST proposal. Second/third stage rocket engines working in vacuum need lower pressures, and hydrolox's high specific impulse is an advantage for for orbital manoeuvring, so it's more common there. Check this table of bulk densities for different fuels. That's the combination of LOX and a fuel in the optimal ratio. Any air-breathing rocket proposes not taking the LOX along for most of the trip to save mass. Methalox is middle-of-the-road in performance, and was passed over for the longest time, except when talking about colonising Mars. Even now, it's the propellant of choice for Raptor because of SpaceX's Mars ambitions AND engineering talents AND the amount of money coming in from launch services and Starlink AND their tolerance of risk are pushing it to its limit. Its ratio of 3 parts oxygen to one part methane means that the majority of propellant is dense LOX, increasing its bulk density to 8/10ths kerelox. Methane's handling is manageable and it is cheap.

If metallic hydrogen could be a thing in multi-ton lots, it wouldn't need it. MH changing phase and decomposing back to regular hydrogen would release incredible amounts of energy (216 megajoules/kg) that makes hydrolox (10 MJ/kg) and TNT (4.2 MJ/kg) seem wimpy. Melting carbon and such to make methalox is gilding the lily, so to speak. The decomposition is at a ferocious 6000+ deg. C, so you're stuck taking hydrogen or some other fluid anyway to cool the reaction chamber. Water might work, though the heavier exhaust products would halve the specific impulse, but increase the thrust.

The plasma will hit the sides and burn some shielding. The inductor's field would drop rapidly and be expressed as heat in the coil; it'd probably burn out. The plasma's temperature might be impossibly high, but the total thermal energy is relatively low. Part of the reason they are so damn difficult to build is that you have a very slippery snake of plasma and you're containing it with, essentially, magnetic rubber bands. Soon as you lose containment, it squirts out the gaps. If you're thinking Z-pinch = short in coils = fault will crunch/heat tokomak plasma so much it will explode, no. You have to design this ability to compress to fusion temps/pressures in. It's also not trivial. We are learning that we can make coils that can survive a quench with minimal violence, too. I'll repost what I posted in Science News: https://news.mit.edu/2024/tests-show-high-temperature-superconducting-magnets-fusion-ready-0304

Helion is developing its reactor that uses field-reversed confinement with magneto-hydrodynamic pickup, and iterating on engineered prototypes with realistic expectations, which is a huge win. I think it's the closest to true fusion right now. But it and its banks of capacitors are the size of a building. Here's the thing. A superconducting magnetic coil is an energy storage device, or SMES. It's not great on volume, it's kind of heavy, but the energy it stores and the current is amazing. Further, it's being used today, mainly in smoothing out power delivery in chip fab plants. Hand-in-hand with most developed fusion reactors are... superconducting magnetic coils. We already have comparatively lighter and smaller coils from MIT's SPARC project. I say 'comparatively', but the test magnet is 9.6 metric tons. Even if Helion or the other reactors coming out don't work out as a reaction drive, what if they were combined in some near-future ship? FRC reactor charges the coils, coils discharge into a Z-pinch drive. It'd be an absolute pig, but we have a reusable heavy-lift vehicle coming online in a few years. There'd be advantages to a charged superconducting magnetic coil as well, like maintaining an active storm shelter.

That'd be the Pulsed Magneto-Inertial Fusion: https://www.scientia.global/dr-john-slough-fuelling-the-next-generation-of-rockets-with-nuclear-fusion/ I remembered this because the D-D Fusion Magneto-Inertial Reactor is a key card in High Frontier 4 All, and a favoured way to build a rocket. (If you're a rocket nerd, you need to play this boardgame.) The Appendix helpfully listed the specs (0.1 Hz firing rate, Q of 200, 510MWth and the person responsible, John Slough, though its version uses a "350kW solar-powered initiator".

Tests show high-temperature superconducting magnets are ready for fusion tl;dr New superconducting REBCO magnets tested that run at 20 Kelvin and made a steady field strength of 20 Tesla. Unique, no-insulation design that allows you to lower the voltage, which leaves more room for more cooling or stronger structures. Deliberately quenched a full-scale coil to see what broke and where the models failed, so they could update their models: one corner melted, most of the rest of the coil survived with no damage. Led to revisions in design that are supposed to prevent the failure mode.

A read of xkcd's What if? on Fire By Moonlight gives a reasonable explanation of how optics and light-gathering by a lens works in explaining why you can't set fire to anything with moonlight, no matter how large a lens: for one, you can't exceed the surface temperature of a heat/light-emitting black body, and the Moon's is ~100 deg. C; for another: So the diagrams are simplifying for illustration because you can't show every beam of light entering, but also lying in the process. Lenses do gather light from as many directions as possible to project an image. The "point of sharp focus" is where the smallest image gathered by the main lens is. Focal length is how far behind the point of sharp focus the lens (or group of lenses) projects the now-inverted image. More on focal length, field of view. The double lenses are for reducing chromatic aberration (the rainbow at the edge of images), as different wavelengths of light are refracted differently to a greater or lesser degree by the same material, so (at least in the earliest achromatic doublet lenses) two different types of glass that form a single lens were used, the second type with a different refractive index to bend the light back.

Gravitics is developing gaseous methalox RCS for their space-station modules, with a throttle range from 5N pulsed to 40N continuous. If they wanted (nearly) off-the-shelf, it's there.

Gravitics is the one that makes methalox vernier thrusters! I knew I hadn't imagined them. They have a product that Starship could use, I think.

Ooof, that ending. From that I'd conclude that it does need dedicated RCS to keep it pointed the correct attitude upon reentry, or Bad Things Happen. Maybe dig up the idea of gaseous methalox once more.

This is true. However, I pessimistically imagine how a hard start, pump cavitation or fluid hammer might go, and I shudder.

Does the Superheavy take a lofted trajectory, and would that make a difference to any added tonnage from safety features? Because Eager Space makes the argument that F9 already pushes the bulk of the work onto the second stage, and if you're designing reuse from the start, then optimising for a lofted trajectory decreases the energy needed for the boostback burn in RTLS: https://www.youtube.com/watch?v=zQp9UdppD-4

Awesome picture. Given the Shuttle comparison, it makes me wonder how they're going to configure the payload bay on Starship. Clamshell doors, sliding hatches?

They could go Aperture Science and test this test by asking 'are the argon thrusters enough to raise their orbit from a near-orbit parabola?' These will not be small satellites, and perhaps they have space to add extra argon or thrusters.

There's an interesting comment about how Starlink could/should have transmitted all through the descent: So 1: when it cut out would have been when the airframe couldn't take it any more; 2: next test we should see it stream its reentry all the way to the ground. Ocean.

If they don't crack relight soon, 150 tons leaves room for a hell of a boost stage. In fact, the F9 second stage would be perfect.