wumpus

Good question. I'd assume it would take a long time to detect such a thing. Detecting planets seems to require observing minute occultations of stars via said planets, so I can't image how we would see an Orion. Perhaps we could detect a fission-based Orion, as any fusion reaction would be lost in the noise of the fusion from the nearby star. Why aliens would be using fission during the timeframe where we were just able to observe them would come down to "because the plot required it" regardless of how statistically unlikely.

I've always heard of things like "max delta-v = 30Mm/s (.1c), but never heard of anybody explaining how that would fit into the rocket equation. Granted, a lot of that is because pusher plates don't really use the rocket equation at all: they use the blast to transfer the energy into momentum on the pusher plate, and that is what drives the ship (surprisingly efficiently, and scales up with the mass of the plate). Still, 30Mm/s is a *lot* of delta-v (and presumably means you will be doing .05c if you want to slow down when you get there. Of course, .05c means you need a lot less shielding from all the interstellar spacedust hitting you at relativistic speeds). For intra-solar system travel, the Orion is pretty extreme but doable. Whatever "the aliens" used to get here would require some pretty extreme technology. Even if their tech was anything we could possibly create (such as the Orion), they would be likely be operating on timescales of thousands or millions of years. Such an alien "invasion" might not contain any members of the species/culture/whatever who built it but would be just a delivery pod for the "de-terraforming" equipment and lifeforms (assuming the "equipment" is some sort of self-replicating nanotech, the differences would be academic). Perhaps the plot may involve tripping some sort of 'don't wipeout inhabited planets' code in the pod, or maybe it sees Earth as "extra vermin infested" and attacks harder. Remember, sending Earth's human population back to the dark ages requires somewhere between 1950s to 1960s tech. And it could be done well under an hour once you reach Earth orbit. Making a starfaring alien enemy that wouldn't simply crush humanity (presumably the same way we've been wiping out most of Earth's various species*) while happily modifying Earth (as well as Venus and Mars) to meet their needs is fairly tricky. Space warfare has been possible for over 50 years, with much of that time largely assuming it would escalate into "global thermonuclear war". Starting a spacewar has always been the province of 007-type villains, not something a rational type would do (the rationality of starting a terrestrial-based war is beyond the scope of this forum, but no "modern" war has been "necessary" thanks to "insufficient technology" (while this might require some circular definitions, I'm sure there are recent examples that fit, and involve nations with higher available tech than most counterexamples)).

I've never thought of (nor heard of) Orion dropping booster stages. Generally speaking, extreme mass is a bonus for pusher-plate designs, especially if using nuclear explosions (and moreso if using fusion explosions). You take something the size of a battleship and not only blast it into orbit, but zip around the solar system with the whole battleship. Smaller "boom-boom" craft using nukes would likely have to be unmanned, as the acceleration and pulses would be too high for a crew (or use extremely inefficient nukes). Even if you built one out of "belter steel", you'd probably scale the thing up to handle roughly 1g acceleration for crew comfort and efficiency. At that point neither the individual output of your nukes nor the mass of the craft would be a limiting factor (unless you want to scale it to nukes >>10Megatons or something like that).

But even the spaceless parent company isn't the beer company. How disappointing. They are a "American, privately held aerospace and national security contractor specializing in aircraft modification and integration, space components and systems, and related technology products for cybersecurity and Health", according to the infallible wiki.

When you set up a redundant bidding system (which is especially smart as one of the original commercial resupply contract winners failed and dropped out), you tend to get an oversupply. Which is kind of the opposite of letting NASA/Congress micromanage a launch project.

Elsewhere I posted this (thus the fission/fusion notes. It was in a fusion thread): In other news, NASA is paying BWXT ~$9.4M for one year's development of a nuclear thermal rocket. Granted, I'm sure they are using fission, but it seems more likely than some powerpoint slides will progress quickly towards fusion. https://arstechnica.com/science/2021/04/rocket-report-spacex-abandons-catching-fairings-ula-bets-on-upper-stages/ It appears to be a separate contract.

This basically assumes that Falcon Heavy can lift considerably more to LEO than Falcon 9 expendable. Which in turn assumes that Block 5 was designed with that in mind and provided the support for ~150 ton loads to orbit (as the infallible wiki claims). I'm a big fan of Falcon Heavy, and have seen no evidence implying that at all. But the bigger problem for SLS is that any timescale for NASA planning for Mars would be far more than a decade away. So any plan to include SLS would have to provide for the thing to survive Shelby's 2022 retirement. And a commitment to keep the ISS going for well over a decade or provide some other means to assemble such a beast (I'd assume that ISS and the CanadaARM would be invaluable, even with the problematic attitude). If you are budgeting for Mars, most of the reasons for the Gateway won't be needed anyway. They'll just roll up the Gateway pork into the Mars budget.

In other news, NASA is paying BWXT ~$9.4M for one year's development of a nuclear thermal rocket. Granted, I'm sure they are using fission, but it seems more likely than some powerpoint slides will progress quickly towards fusion. https://arstechnica.com/science/2021/04/rocket-report-spacex-abandons-catching-fairings-ula-bets-on-upper-stages/

In other news, SpaceX has given up on catching fairings in nets, showing that they realize that the wind is just to variable to control. Then there's the issue of "do you just release the parachutes and make them disposable", which might rub Elon the wrong way. When I first joined this forum I was convinced that parachutes were the way to go (something KSP teaches badly), but now I'm highly skeptical of combining parachutes with landing in exact locations (one or the other is fine).

Nearly all the work directed at that involved looking for another planet inside Mercury. Einstein's motivation was to extend his Theory of Relativity (then only Special Relativity) to show that the laws of physics held in accelerated fields of reference, instead of just at arbitrary fixed velocity. Explaining Mercury precession just helped justify acceptance of a pretty extreme theory.

I'd have to assume the whole scaling issue would be a bigger problem than the wind. The shuttle SRBs splashed down over 44 m/s (I remember reading >100mph), although it is possible that Starship will be lighter. If you are planning on falling through the upper atmosphere, I'd still think you could use drogue chutes to cut your delta-v. You'd still need retro-rockets, but far less fuel (and thus more mass going up, assuming the parachutes were lighter than the propellant mass. Which isn't a guaranteed thing).

The real question is what happens when they don't sell him a nuke. What does he come up with? Is it safer for the US or Chinese just to sell him a nuke?

A U2 managed to glide from Tennessee to Arizona (or vice versa. Call it 2500km if you aren't familiar with American geography). Of course you could claim that a U2 was a glider with a jet engine. Then there's the Pelan/Perlan 2. How does it soar? How about higher than said U2. U2 (I think the story involves a SR-71) to flight control: "request clearance for FL600" (60,000 ft, call it 18km) Air Traffic Control: "(joking) it is yours if you can get that high" U2: "descending to FL600" Probably mythical, as I don't think 60,000 ft is controlled airspace (modulo notice to airmen around rocket launch sites).

Well, the real ratio of Dawn ion thrust vs Em drive is infinite. On the other hand, a blue* LED will do exactly what the Em drive claimed to do: put energy in and get momentum out, without using any propellant outside of the energy you put in your device. Just don't expect to get within a factor of 30 of Dawn. If you wanted to scale Dawn up, consider accelerating the ions in something more like a cyclotron. Thanks to relativity, your "delta momentum" is just the force of thrust (F=dp/dt): this doesn't really change as you approach c. * blue chosen because I think the equations scale better with more momentum per Joule of light with shorter wavelength. In practice you would pick whatever put out the most light per Watt. Don't forget to make your heat sinks direct most of the black body radiation in the same direction as your propulsive light source, as they will produce a significant percentage of your momentum.

Most shots fired during war are to force the enemy to take cover in place, or at least be more careful while moving (and considering the number of bullets fired to the casualties, this has to be an understatement). My guess is that such indirect fire simply didn't have the psychological effect as direct fire as the troops wouldn't see/hear the shots and they didn't make enough noise when they landed for the soldiers to be aware they were being shot at. Not to mention that you would have to land in the trench to do any good. I'd be shocked if any side during WWI could even make enough bullets to be effective (not to mention that in less active areas, soldiers tended to try to keep informal truces with the "enemy". Don't count on them even thinking about putting the rounds in the opposing trench. From the infantryman's point of view, it was the officer corps* trying to get him killed, not the guys in the opposing trench). * Probably less true about junior officers. They died in greater numbers than even the enlisted men, and likely felt like the senior officers didn't want any competition coming up the ranks. If you drop a bullet or penny off a building and it hits someone, there is a good chance that it will hit the head. A direct hit on the flattish part of the skull is going to be dangerous (even if not lethal) for anything even that light approaching terminal velocity. Also, long before the penny hits terminal velocity it will be completely vertical (pushed vertical by air resistance) so it will be relatively aerodynamic. A soldier in the field would be wearing a helmet, and wouldn't have nearly the danger of the odd headshot.

"Unscheduled" presumably means just that. It wasn't on the flight plan, but happened when it veered off course and the range officer (human or software) pushed the big red button and the rapid disassembly happened. I suspect you also have to push it early enough that the debris falls in the allowed area. Sorry. All sufficiently large vehicles are anthropomorphized. Probably predates Homer.

If you put the tank on top of the booster, made it smaller and a vacuum engine (J-2X), you'd have an Ares rocket (one prototype made in 2009).

According to the infallible wiki, in 2005 each mission was budgeted ~$300 million for "flight hardware". This includes the entire fuel tank, refilling and stacking the SRBs, retilling the orbiter (I'm sure Columbia cost more to retile. Not sure if she flew in 2005), as well as rebuilding the RS-25s. The RS-25s are staged combustion, so presumably extremely expensive to make. I wouldn't be surprised if a few were quietly retired during the shuttle program as too hard to rebuild, but I doubt they were ready to build more of them (this certainly helped profits during the SLS program). There were always cheaper engines that had higher performance for less money (for the cheaper engine vs. refurbishing the RS-25s), but there was never an engine that could fit into the shuttle program quite the way the RS-25 did. It was a full staged combustion engine, so that had to be costly. A J-2 engine might make more sense, and was considered early in the Shuttle program. It wouldn't start at sea level (but didn't have a problem starting in the Apollo program), and would require slightly more powerful boosters. Unfortunately I can't find a cost for the J-2 engine, but it had to be cheaper than the RS-25 (and as a gas generator, it should be relatively cheap).

The first zero-g movie did remarkably well for a Hollywood product (I'm assuming Apollo-13 counts).

Seriously planned? The Orion (for some values of seriousness. They were serious, but the people who needed to sign the big checks had to have been laughing). Ever launched? Saturn V. Currently launching? I'm a big fan of Falcon Heavy and think it is greatly unappreciated. Then again, it might help if they ever managed to bring all three boosters home.

$.47B Filled. While the SLS appears overpriced everywhere, I doubt they are paying hundreds of millions of dollars for a steel tube. Filling them is the tricky part. One more important detail might include not stacking them until the green run is complete (although I don't want to know how much extra that would cost, presumably all the guys hired to stack the things being paid to not do any stacking). Now the SLS is on a specific deadline, one which nobody knows if it is really ready to meet. One of my biggest disappointments in "things KSP lied to me" was that SRBs are not that cheap (and also tend to explode). They do have pretty good Isp, especially from sea level, unlike their kerbal counterparts. I have spent a lot of time building rockets that primarily used SRBs and they are extremely price-effective in KSP (unless you are using the bigger lie of airbreathers).

Considering the shuttle landed the sustainers without the need to throttle this seems a bit odd. It would certainly help if you could throttle the boosters and vertically land them*. It would also help a lot if you could return the fuel tank. Thanks to the density of the fuel tank, I have to wonder if spacex's various tricks could return the fuel tank (not applicable to designs signed off in the 1970s). * sure, the shuttle recovered the boosters via parachutes and reused them. But they were basically extremely strong steel pipes which hit the Atlantic at >100mph. All the tricky bits involved making the aluminum perchlorite and mixing it in those steel pipes without air bubbles or flaws.

There aren't many good reasons to use sustainers. Particularly sustainers that go from launch (sea level) to orbit. I think mostly they have been used when there wasn't enough confidence in lighting the engines during flight (expect to see it more often in lower budget rockets, but even then more often as a 2.5 stage instead of a 1.5 stage).

That must be it. Sound isn't working and youtube-cc must have lopped off some of Scott Manley's accent. I googled it and it existed, but didn't check closely enough.

Thrustiest boomsticks that ever launched. AJ-260 [edited] and its 2.6 MN thrust weeps on Earth. [further edit: 2.6MN needed a nozzle which was blown off during the test].