wumpus

Mostly confined to amature rockets (for when you want to go well past the pre-made Estes stuff). While parafin+N20 is said to have the highest Isp for this type of thing HTPB tends to be far more popular (presumably thanks to burn rates, it sounds even easier to fabricate). It gives you many of the advantages of liquid rockets with a much easier design, although pressure fed rockets (the limit of most amature designs) will of course have more dry mass leftovers. For the big boys, hybrid rockets are non-cryogenic (N20 is non-cryogenic). You could presumably use a turbopump (or use LOX if you were using a hybrid design for other reasons, such as a single carbon-fiber tank for a pressure-fed oxidizer). - note that in the US, N20 is commonly available in large quantities spiked with "forum friendly" additives, typically for welding and drag racing/other car mods.

There appears to be some folks at NASA willing to throw money at SSTOs on the basis that the logistics and integration benefits outweigh the tiny payload capacity (DC-X is my best example). I wouldn't be surprised if some of the smaller new space companies scarf up some money to produce powerpoint decks of their boosters being used for SSTO. Probably not worth it to Spacex to lose focus on something as critical as Superheavy to teach expensive lessons on how stupid SSTO is.

The point is that naval dogfights occur when large capital ships launch tiny "fighter" craft to do battle. On Earth, that is done because the large capital ships are trapped on a 2d ocean, but the tiny fighters can fly in 3d airspace, often with great speed advantages. In space, it isn't clear what advantage a fully 3d space fighter has over the fully 3d capital ship that launched it. That is why I limited my examples to sea vessels launching other sea vessels (whaling ships). If fighters are launched in space, I'd assume that they'd be unmanned (if only for the acceleration benefits). That might be sufficient reason to launch them vs. crewed capital ships. I'm not sure another generation of manned fighter aircraft will be built on Earth for that matter.

Traveler had an interesting set of rules that allowed for Newtonian physics (well, in 2D) for your tabletop starship maneuvers. You'd have three tokens per ship. Where you were last turn, where you are now, and where you plan on being next turn. The "where you will be" starts opposite of "where you were" (thanks to your current velocity) and you are then allowed to move the "where you will be" one hex (or square, whichever it was) for each "count" of acceleration your ship had. Made it easy. But it wasn't anything like a dogfight. That would make sense only for ages that you would launch tiny boats from a main ship. Only case I can think of that happening is whale hunting. So maybe zerglings or pirates? But I'm blanking on why pirates would want small attack boats.

Hint: if you have a magic engine (especially one capable of >=1g thrust), there's your SSTO. Use magic instead of bad science. Traveler used a lot of guns (weapons that fired bits of metal propelled by chemical reactions) in addition to proper "sci-fi" weapons. There was no reason to believe that they would be rendered completely obsolete, and even included bladed weapons for similar reasons. (4. ... As a result, people are more careful with their lives) you mentioned this together with "usenet". My edition (from the 80s, I think the first one) had an amazing character death rate just rolling up the characters. No only that, but it came in a box set and if you wanted to play the "included adventure" (just a bare framework for exploring the galaxy) you needed to roll up and kill off a lot of characters just to get the guy to survive the scout service with enough decorations to get the starship reward (even then you didn't get it outright, just the downpayment and were on the hook for the mortgage). It is my favorite tale of "you youngin's have no idea how lethal old school rpgs were. Back in traveller, your characters often died while being rolled up".

How exactly is a low-mass piston & plate supposed to work? The whole point is to absorb the momentum from the shock wave and slowly transfer the momentum to the ship. It entirely relies on mass for that.

This only quenches the combustion if you are in a significant atmosphere. You could also arrange to have net-zero thrust by careful selection of blowout panels in front in vacuum. https://what-if.xkcd.com/24/ And the payload small enough. And even the answer given assumes multiple stages and presumably no structural mass other than the container for the estes rocket engine (which would certainly be more than the payload even if you were just gluing the motors together, thus requiring an even bigger rocket...).

Look up the Isp (pretty sure its less), and plug those numbers into the rocket equation and see how far you get. Make sure include all the mass for your nuclear pulse propulsion.

Have to be a much more powerful than typical ion engine. SMART-1 took 4 months to get to the Moon (~4000m/s delta-v? Don't know where to find requirements for circular orbits). You'll need more than twice that in 4-5 days. But at least it isn't an SSTO.

Shuttle SRBs (also 1970s design) had an Isp of 275s. But if launched from air, you can probably start with vacuum numbers. Vega stage 3 (presumably close to vacuum) gets 295s. Figure your crew, passengers, cargo, and non-fuel bits of the spacecraft and plug it into the rocket equation to see how big a monster it will be. Don't forget that the entire length of the rocket surrounding the solid rocket fuel will need to withstand the pressure of the combustion chamber and be fairly massive even if carbon fiber. Refuel? If you somehow manage to get a single stage to orbit with a Isp of 300ish it isn't going to be reused. There won't be any cargo space to speak of, let alone heatshields and landing gear. Anyone bringing up the SSTO fantasy (with current rocket engines, or worse airospikes) merely shows that they can't handle simple equations like Δv=Isp*g*ln(mo/mf). Equation one of rocket science. Δv=9400m/s g=9.8m/s2 Isp=300s (generous) mo=total mass of rocket (fueled) mf=final mass of rocket (crew, passengers, cargo, and non-fuel bits of the spacecraft) Plug away and try to come up with some viable rocket that even gets to orbit and I'll be impressed. Don't even think of safely landing it.

Mostly, but most engines get hot regardless of the exhaust. I'd expect it to require cooling after you land, and if all that cooling air is directly down it will scatter at the ground and cook the legs of anyone nearby.

Unless your efficiency is perfect, there will be vast amounts of waste heat. Of course, the atmosphere provides an ideal heatsink, but there will always be an issue of which way the heat is vented and whether or not you can be near anyone else (not wearing such a suit) while wearing the suit. Would be quite sad if you turned and walked away and incinerated your companion in the vented heat (flowing out behind you). Perhaps you'd have to practice backing away from people before turning around, like a courtier leaving a king.

India spends half of what France (just France*) spends on space. ESA seems to have all the pork of issues "old space". Granted, India hasn't stepped up to crewed flight, but I wouldn't be surprised if they do before the ESA isn't still having to buy flights from others. * source, one the the graphics in this sub-forum. Possibly the Chinese thread.

Except that you can get better performance the smaller and quicker the pulses get until you have a steady stream of antimatter. Pulses are kludges for when you can't get power any other way. The V-1 "flying bomb" used a pulse-jet for propulsion, because it gave them the ability to make an early jet and also make it cheap enough to be expendable. I don't think anyone has made a production pulse-jet since. There have been (I think it rose and fell in the 1990s) some experiments with pulsed detonation rockets. The idea is to build an air-breathing rocket that detonates the fuel instead of combusting it. Mostly I think the goal was to get an air breathing rocket however they could, but also to raise Isp by having supersonic exhaust velocity (detonation implies the reaction moves supersonic and produces a shock wave, not sure if the exhaust gases move any faster). Pulses are a "last choice" to use a fuel. Not something to find a fuel that will provide a pulse.

They probably figure that they'll be enough stops and aborts on the first attempt so they really don't want to use up the finite number of times they can refuel the tank. Just take it down to T-21 and fix it then.

In other words, what you want is a solar sail (directly absorbing the momentum of the solar energy). Using the solar energy to pump a laser makes no sense. Even the laser bit makes no sense, you'd be better off with high efficiency blue(ish) LEDs. You want the momentum, and coherence doesn't buy you any. And as far as "light powered rockets" the two possible uses are: lifting off a planet with abundant energy (so the rocket doesn't carry its engine and fuel) and interstellar travel (because the Isp of light is near infinity). The energy efficiency is so bad you'd never use it to travel between planets.

I suspect it would be easier to get 4 AJ-260s (roughly equal thrust) all firing at once vs. 16 F1s. Don't ask about the next stage.

Didn't we discuss something about NASA switching to "success-based-planning" and how that was technically the dumbest possible way to run a project (it might be smart with dealing with Congress, and it might maximize revenues for the prime, but it isn't likely to get anywhere near on time or on budget). Something about planning a schedule such that all your tests work the first time? Sounds like taking this further so it can break the mission as well as the budget.

The shuttle boosters weighed at 91tons while falling to Earth under parachute for recovery and refurbishment. I wonder if you could do a "parachutes plus bouncy landing gear" for an engine compartment. Sure, the whole thing might weigh more than an electron booster, but hopefully it has the thrust to eat the rather large mass of the parachute compartment and bouncy house gear. Granted, the STS boosters hit hard (>100mph from memory) and no idea how much parachute it would take to cut down 16 tons + other stuff + parachute itself + landing gear to the point the landing gear would work. Postscript: How does this thread last this long? We've seen what a reusable SLS looks like, it had 100+ flights to orbit. Something called the "space shuttle". SLS is the "single use" version of the thing (just with even more costs added on). There were some "two stage shuttles" on the drawing board in the 1970s, but I can't see them working if you are adding the solid boosters from the shuttle.

I'm still trying to figure out what kind of definition of "efficiency" spacescifi is using. Not energy. Probably not even mass (the ship itself needs to be massive, unless you are stuffing the pusher plate with cargo as well. But building an expendable Orion is certainly not efficient). Cost is unlikely, because the Orion only goes to LEO *once*. While it might be able to bring unbelievable massive cargoes along, that will come at a huge cost, and will only be used for that one flight up (you can go as far as you want in space, but you aren't going to land that thing). I'd be shocked if a few hundred Starship flights wouldn't be cheaper. Even Falcon can probably beat it, even if it takes the whole fleet launching 1000 flights during the time it takes to construct an Orion. The only thing that is perfectly clear is that in the 20th century it was the only way to lift an ultra-giga-heavy-spacecraft to orbit (Saturn V was a "heavy lift rocket"). This probably remains the case as I'm not aware of any replacement nuclear rockets being capable of going from the Earth's surface to LEO (most are great once you get them to LEO (or further depending on exhaust evilness).

It is fairly significant. As far as I know, keeping combustion chambers from melting has a small limit on the Isp of chemical rockets (true at least for shuttle engines, and they have amazing Isp). Of course, the real problem is always mass. And bringing along a power supply that might cause the ship to melt is going to be heavy, too heavy to bring to space (although the kilopower project might give us hope for a somewhat lighter and less solar dependent power supply). But there is also a known solution: radiators. The ISS has a set of radiators that are about 1/10th the size of the solar panels, but they are there and needed. For any reasonable power needs, you just scale them up. I once calculated (for one of spacescifi's space battle threads) that the upper limit for an ISS-sized array was 60MW, an that you would have to scale up from that (and that said radiator would make an ideal target in a space battle). But in reality, you'd just keep building bigger radiators. Melting is a huge issue for re-entry, and the entire reason we lost the Columbia. On the other hand, the larger the vehicle landing, the less of an issue this is (although you'll pay later with a higher terminal velocity). I'd assume that any "commercial trips to orbit" would have sliding "wings" that would increase the surface area of the returning ships by a significant multiple, and that this would make it much easier to return from orbit. See also inflatable heat shields (no idea how to reuse such a shield). But looking at all the examples, the only reason "melting" is an issue is that the real question is "what is the least amount of mass we can spend to avoid melting". The real issue is always mass.

Didn't NASA get into the SLS trap by trying to play KSP with existing rockets? edit: maybe they could get Orbital as the prime for this new rocket. Orbital has been remarkably successful in putting together rockets out of surplus parts and existing rockets.

Old space (and the entire military industrial complex typically operates this way) create new rockets as a government funded project. If they tried to build a rocket for some "fairly short time horizon", they'd be "new space" (like Orbital long before Spacex). Things like Atlas, Delta, and SLS simply aren't designed with the "old space" contractors paying the bills and hoping to make money with in the future. Much of the reason is that you can never know which way NASA is going to go: every 2 years a "new" Congress gets elected (with almost always the same faces), and the committee's that control NASA's (and DoD launches) budget changes. So they might want a completely different rocket, and be willing to pay a competitor to design one. So while the Pegasus might be the type of rocket that could fit this "return on investment in a short horizon", it wasn't "old space" Even the Falcon 9's design budget was paid for by NASA . Although, considering what a shoestring budget it was, it probably never occurred to NASA that they were going to design a medium lift orbital rocket with just those funds. Pretty sure spacex is far too big to do it again, although I'd be curious to see what the design costs of the Neutron are. Disclosure: I currently work for a military industrial complex company who oddly enough, *does* design products on its own budget. I was fairly shocked at the concept, but it allows for modular products that can be reconfigured to sell for multiple roles instead of forced into a narrow role to meet an entire committee's requirements. It helps that they are relatively small: don't try this with a plane, ship, or tank.

The "extended stay missons" (with LM hab) lasted 3 days maximum ("J missions, Apollo 14 & Apollo 15). I suspect that docking in Earth orbit and flying the entire contraption to the Moon would make more sense. The real issue is exactly when they could pull resources off Apollo 11 (just getting the boots and flag to the Moon before the USSR) and start building a new hab. No way they will complete the hab and integration before Apollo gets canceled (regardless of how they plan to deliver the new hab to the Moon. As far as I know, Saturn 1B was a cheaper and more efficient means to orbit than the Space Shuttle (and Saturn V would have been far superior in assisting the building of ISS, although if it wasn't launched from 1975 to 1985 it would have been effectively impossible to launch at all, thanks to some of those sustainability issues. No idea how long you could go between launches but it was far less than 10 years). The sins of sustainability and efficiency were largely political (being easier to cancel than the sunk costs of the Shuttle). Rushing the job meant that they didn't have the time to add the bloat in costs and inefficiency of the SLS. Old space (and the rest of the US military industrial complex) has very weak links between performance and funding. Expecting rational project goals from them doesn't make sense, and the rush to build turns out to be a strength of Apollo and not a weakness (NASA had no reason to listen to every senator's pet requirement).

I know that had *an* orbit, but did they specifically fly over a place that NASA had specified as a possible landing site? Even on the Moon, inclination changes require a ton of delta-v. Mariners 4,6, and 7 did reasonably close flybys of Mars in 1964, 1969, and 1969, so maybe they were sufficiently accurate. While I might play KSP with an "any orbit will do, just kill your orbit and find someplace to land", NASA has far more exacting requirements. Also a reason I prefer Minmus: randomly landing on random patches of Mun (and presumably the Moon) is dangerous.