AckSed

Relevant: Jatan's Space has begun collating happenings in India's space program in a dedicated Indian Space Progress newsletter. Click through "Latest and all posts" to find it in the future, as linking directly brings up an annoying "subscribe" box.

Ugly, and looks like it was welded in a couple of days. I love it.

I was wondering about the proportions of LOX to CH4, but it'd need the mass to hold it down.

There are grippers/litter pickers that let you pick up rubbish without bending. They could just as easily pick up your yardstick. Might have to find or modify one that'd let you keep the stick straight. https://www.gardentoolbox.co.uk/garden-hand-tools/gardeners-tidying-tools/litter-picker/

The way this heatshield/aerospike operates is elegant. First off, the upper-stage rocket itself is powered by an expander bleed cycle: liquid H2 flows through the combustion chambers and nozzles to cool them, absorbing heat and expanding along the way. Some of it is tapped to run through the O2 and H2 turbopumps, but instead of returning the lower-pressure gaseous H2 to the chambers, it's dumped overboard. In this design, the vent for this is in the centre of the heatshield. Truncated aerospikes need what's called base-bleed to maintain the 'spike'... and what a coincidence, here's some waste gas that feeds through the centre to do so. Once it's up above atmosphere, the bleed gas also provides something for the exhaust from the combustion chamber to push against. If you've seen this video from inside a SpaceX F9 fairing, note that the rocket exhaust of the second stage exits the nozzle in a sideways sheet (really a half-sphere, but). I may be wrong, but intuition says the bleed gas also expands sideways, crashes into the expanded gas from the aerospike combustion, and half the collision would impact the heatshield and give it a bit of extra push. In reentry mode, the bleed gas might even push the shockwave a bit further out, reducing the heat load. Of course if it ever increases, the heat will just push the LH2 around the heatshield faster, expelling more relatively cool gas in front and reducing the heat load once more. And the heatshield is canted to give the same lift and control authority as a ballistic capsule without moving the centre of gravity too far from the central axis. *shakes head* Genius. Though you have to make triply sure you don't run out of hydrogen. But LH2's heat capacity makes it the finest method of cooling bar none, so it works out. Barely a single wasted part. They're even packing the avionics and turbomachinery behind the heatshield. Now this gives me pause: cryogenic LH2 has a habit of condensing out liquid oxygen from the atmosphere, and if that drips straight onto your electronics or insulation, you have Problems. I didn't gather whether the LO2 tank was on the bottom or on the top. However it does make for a bottom-heavy design - ideal for a stable ballistic reentry. Best part was, they didn't even plan to make an aerospike. Edit: Full-flow staged combustion on their first stage engines. They don't lack for ambition! However, knowing something can be done does make it easier to attract investment and talent, and if you have the metallurgy to withstand it, the stress on the turbopumps is lessened. I do note that Rocket Lab has switched to ox-rich staged combustion for Neutron for this very reason. Finally, I have to ask: does it scale? Could this make a Falcon 9 or Neutron-class launcher?

Huh, it turns out I was accidentally right: increasing magnetic field strength is key to making smaller, more powerful Hall thrusters. It's just a comment, but this student of UMich's Plasmadynamics and Electric Propulsion Laboratory says they hope to achieve power densities that reach 10N of thrust within a device a square foot across.

Other recent technology that might make this better: The iROSA recently fitted to the ISS and the former DART are lightweight, high-efficiency roll-out solar panels. Each one fitted to the ISS masses 325kg and generates 20 kilowatts of electricity in Earth orbit. A hypothetical spacecraft would have to massively overbuild (8 panels, about 3 tonnes) to have a reasonable power supply out to Mars, but it could be done today. MIT is building the miniaturised SPARC tokomak, using electromagnets wound with superconducting tape that works at liquid nitrogen temperatures. The tape is capable of carrying kiloamps of current and creating 10 tesla of magnetic containment. The relatively modest electromagnets and cathode/anode in a HET would be much easier. Imagine the electron density inside a superconducting HET: it'd be the size of a dinner plate but rated at *pulls numbers out of air* 300kw and 50 N of thrust; VASIMR would be proud. Now, you're exchanging one form of cooling with another, but I think in space it's simpler to keep something at 77K than shedding kilowatts of waste heat - something like the JWST's layered mylar infra-red shield plus a helium/neon heat-pump?

*nods* Somewhat related, I've been following Momentus Space purely because they have microwave electro-thermal thrusters on their satellite tugs. Rotten specific impulse for electrical thrusters - something like 10kw of solar panels creating 900s for their largest proposed tug - but the propellant is simple water that's cracked into hydrogen and oxygen by microwave-induced plasma. It recombines in the nozzle to give 10s to 100N of thrust, and it's electrically neutral so you could cluster them to push a larger vehicle. Plus the actual engines aren't much more complex than a microwave. It could be the basis of a very cheap inflatable spacecraft that uses water-walls as radiation shielding, fuel tank, life-support and structure, mining fuel from asteroids and comets as it goes. This finding, though it needs cooling (which is a big, heavy can of worms by itself) could also be a basis for the same concept, since it seems to work better with lighter, more available noble gases. Mars' atmosphere is about 2% argon.

I recommend digging into these archives of the Usenet group sci.space.tech. There are some real gems gleaned from moderately famous rocket scientists (including people involved in the DC-X and Roton) and general all-round smart geeks. It's not at all up to date, with few of the posts dated after 2000, but I learned things I'd never have found out otherwise: Propargyl alcohol (H-C-C-CH2-OH) is a room-temperature liquid fuel that is denser than kerosene and produces slightly better performance than it when burned with liquid oxygen, and is even better with high-test hydrogen peroxide, a room-temperature liquid oxidiser. The latter combination is nothing you'd want to splash around, but it's not half as bad as hydrazine and its pals. Propane (C3H8)/liquid oxygen has one or two nice tricks that make it a bit better than methane. Like methane, it can be used for combustion chamber or nozzle cooling, converting it into a warm gas to feed into the injectors, improving mixing. It also boils off into the atmosphere once testing is finished, making reusability easier. Unlike methane, once it's chilled down to LOX temperatures it has similar density to kerosene, and its melting point overlaps with the boiling point of oxygen, allowing it to share a common bulkhead with the LOX tank, saving weight. Carbon Monoxide (CO)/LOX could be a cheap, simple rocket fuel to produce on Mars or in the atmosphere of Venus, as while performance is poor, it needs no hydrogen and can be made directly from their CO2 atmospheres. Ethyl alcohol/ozone (O3) was tried, but the ozone was not only more oxidising than fluorine, it was too damn unstable. Diluting O3 in liquid oxygen made it marginally safer, but it had a higher boiling point than O2, so once testing was finished evaporation would concentrate it out into high-concentration O3, and then explode. Violently. Furfuryl alcohol/white fuming nitric acid (HNO3) has a bit of history as the first practical hypergolic liquid bipropellant. Performance wasn't that good, though, and making the nitric acid storable involved adding nitrogen tetroxide. It's still available in bulk and is cheap, though. Polyamide plastic/Nitrous oxide (N2O) is the basis of one of the few hybrid solid/liquid rocket engines actually flying (or flown) - on Virgin Galactic's SpaceShipTwo. It's cheap and relatively safe, and allows throttleability by restricting the nitrous as needed. Propane/N2O, or NOP for short, was test-fired enough to gain a patent, because N2O can be catalytically decomposed like peroxide, but is self-pressurising, providing pressurisation for its own tank and for the propane tank, stores as a dense liquid but injects as a gas and is less finicky than peroxide. It can even be used as a monopropellant for attitude control and ullage thrusters. Propane's advantages are already known, but the combination is low-risk, easy to handle and both are available in bulk. Kerosene/peroxide is one of the might-have-been-greats. Both liquid at room temp., both safe to moderately safe, and with clever design the peroxide not only cools the engine, the heat (and/or a catalyst) decomposes it into oxygen and steam hot enough that it automatically lights the kerosene. It launched a satellite. It's even clean-burning. But US rocketry is really skittish about peroxide, and chemical suppliers won't sell it in the higher concentrations needed.

I am told ion engines tend to have the highest efficiencies when all the ions have the same mass/charge ratio. According to Messer, who supplied the xenon for the Dawn probe, propulsion-grade xenon is 99.9995% pure; the largest impurity allowed is krypton, at a 'generous' 5 parts-per-million. Prices were not given, but if you have to ask, you can probably afford it. How much a mix of different-sized buckyballs would affect efficiency for the already over-amped, lower-efficiency ion thruster is something you could only discover through experimentation. There might be knock-on effects or it could be fine. If 98% pure C60 still works, it goes down to a more reasonable £182 ($223) per gram. If it would cause a 10% decrease in specific impulse but still retains the increase in thrust, people might begin to take interest. I can think of a further advantage to buckyballs as a propellant - no need for cryogenic storage. That'd save a fair bit of mass, even if the transfer of an atomically fine powder in zero gravity is by no means a solved problem, and the buckyballs might be less dense than LH2. It'd essentially be a big plastic bag of soot.

Idea: I did hear of one proposal in the 90s to use buckyballs (C60) as ion engine propellant. Apparently they are not only tough enough to survive impacts with metal surfaces at 15,000mph, they also have a lower ionisation energy than xenon and more than five times its molecular mass (Xe - 131.3; C60 - 720.3). Theoretically, it could have 1.5 times the thrust to power ratio of xenon. Now combine that with this finding and we might see something special. ...though now I look further, the price might make one pause: high-purity 99.9% fullerene is available from Merck at an eye-watering £538 ($660) per gram. The Deep Space 1 probe carried 82 kilograms of xenon; the Dawn probe 425kg. Xenon prices are considered high but this would make them seem reasonable. Ironically, producing the buckyballs is simple, it's purifying them that's expensive... and ion engines tend to need pure propellants. Someone did discover a process to purify them with silica gel, heat and dienes, but so far as I know nothing's come of it.

Wow. That's a small-scale data centre's worth. Ask the Internet Archive? https://archive.org/about/contact.php For example, they helped with (partial) digitisation of the Prelinger Archives, a 60,000-strong collection of film ephemera. And of course I'm interested. I just don't have the storage space!

Rockwell's 80s concept for a jet-sled-assisted Trans-Atmospheric Vehicle is so presciently Kerbal it's amazing: It does make a bit of sense, though. Why build an expensive, one-off launch track that's fixed to one location when you could build an expensive, one-off aircraft that can launch from a normal airfield? (Stratolaunch says hi.)

It's what was predicted way back when: once nuclear fusion happened and the price of energy plummeted, no need to drill for hydrocarbons when you can take it out of the air and the sea. It's just that this is happening with wind power. Another small company, Terraform Industries, is proposing to use cheap solar power to make methane to be sold as a further chemical feedstock. When I look at how many processes a crude oil refinery employs to clean the salt and sulphur out of crude & make lighter compounds, this backwards, inefficient pathway that produces light hydrocarbons from the start seems elegant in comparison. The heavier hydrocarbons used in asphalt and diesel may be a problem, but polymerisation and desaturation are already an established business.

There is another option for lifting gas: carbon monoxide. About the same lifting power as nitrogen, a product of multiple industrial processes including the extraction of oxygen from CO2, and an intermediary in extraction of carbon for all the graphene you'll need... and quite toxic, but you can't have everything. It can also be burned with O2 as a mediocre rocket fuel. (Or in a turboprop, for the control needed to travel between habitats and factory complexes.)

If I don't miss my guess, Helion's fusion reactor is using a magnetohydrodynamic generator to gather energy, which makes sense. You already have the magnetic coils to compress the fusion plasma, so once the fuel fuses, they allow it to expand, pushing against the magnetic field & generating electricity directly. It's not like the concept's unknown or unused, as the lack of moving parts is highly appealing, and Wikipedia says that it's been trialed on several coal or gas power plants around the world. (I have also seen it proposed in a kooky 70s design document plugged into a Saturn V 1st stage as a one-time megawatt power source.) But it lost out to fission, the Brayton cycle and boiling water. Its key advantage is compact size.

I can think of a survival sense, if not an economic sense, for there to be mining of the Venusian surface. Say an aerostat colony has been cut off from resupply missions. They typically sustain themselves by airmining noble gases, making advanced plastics, carbon nanotube composites and fusing deuterium into He3, but they do not have the resources to transmute certain trace elements like phosphorous for enriching their soil. In that case, they could make a pressure vessel and mine the peak of Maxwell Montes. At a 'chilly' 380 deg. C and 41 atmospheres it's... within sight of sanity. It makes me wonder how much cooling could be had with a kite-lofted radiator or similar, though,

Sled-assisted launcher concepts. "So what," they ask, "if the first stage was not thrown away but stuck to the ground?" It's fairly attractive: what's oft-quoted is that the Space Shuttle used a third to 40% of its fuel just to get up to 1000MPH. Cutting out that mass either leads to a lighter, cheaper vehicle that can lift the same payload or lift an increased payload. It makes a SSTO much less massy. Rocket-sleds are a classic, proposed for Bono's Hyperion among many, many others: Maglifter (magnetic levitation) was seriously studied by NASA before the turn of the 21st century: http://www.projectrho.com/public_html/rocket/images/surfaceorbit/rocketSled11.jpg They are usually struck down by the massive infrastructure costs and/or the challenges of finding a suitable slope. But I think the study that was low-tech enough to actually work today was the Closed End Launch Tube. Spurred by the proposed development time of 25 years for the Maglifter, it was essentially a sled stuck to a pneumatic train. It wasn't as beefy, but it would have been much simpler, requiring little more than low-pressure steel vessels, concrete, valves and compressed air. The chamber wouldn't be evacuated much either. Acceleration for a combined 700 metric ton sled and craft was calculated at a modest 20 m/s per second (or 2 G), release velocity around 260 m/s or 936 km/h and along a 6km track. It was meant to supplement a ramjet vehicle.