wumpus

While this sounds well and good, I'd expect some real science with a name like that (especially considering just how much rocket science we all learned with KSP). That is a hard act to follow. Also, wasn't this (Making History) announced April 2013? We may have a bit of a wait for the next one (although considering just how deep in early access KSP was in 2013, a DLC was a particularly stupid thing to announce). Maybe they needed to impress investors or something.

XKCD. With occasional forum mentions elsewhere.

Because Rovers! That's pretty much the whole point (although an automated crawler up an Eve mountain is another story). I can't recommend trying to use a rover to get to different biomes even on KSP's 1/10th toy scale. This doesn't include landing near Easter eggs and driving over to them.

Which is the crux of the issue. Isp of an air-breather is a non-issue, but thrust is the real problem. For maintaining LEO, "all" you need are sufficient batteries to maintain constant operation. For GTO (and presumably escape velocity, it isn't much more) you need to accelerate from ~7km/s to ~10km/s or ~11km/s respectively. You also have to do so only at your Pe (because that is where the air is). Smart-1 took about a year to go from ~10km/s to ~11km/s (GTO to LTO) so a multi-year plan is not out of order. Any design trying to do this would have to be built to handle two different modes: circular and elliptical travels. In circular mode, all power would have to be generated with the solar panels at roughly zero angle of attack (flat to the wind). You would also need to charge the batteries enough to provide enough power to maintain your Pe in space. Assuming the solar panels can supply the motors with full power (and the batteries can't supply full power for circular operations) you have 3 months to get your Ap out of the atmosphere (and preferably away from the shadow of Earth). I can't imagine the power supply being lighter than simply bringing along ~3km/s worth of Xe (or even Ar) and avoiding the atmospheric drag while using your solar panels more efficiently. Also note that you are going through both the inner and outer Van Allen belts with every orbit. When Smart 1 did this they avoided the inner belts (nearly all the radiation) and all other deep space probes have gone straight to escape velocity (even though using chemicals is vastly more expensive than their onboard ions).

I've seen documentation from high-powered model rocket manufacturers state that you need TWR>6 for stability with their motors. Even Orbital solid boosters (that resupply ISS) have some pretty high TWR. According to the above, this was higher than that.

Even worse is that two reasonably influential and extremely kerbal designs have proposed this: Jules Verne's means to travel "From the Earth to the Moon" (a classic cannon). Project Orion (the real one by Freeman Dyson), which not only exploded a nuke to launch a carrier sized spaceship, it kept exploding nukes to get it to starfaring* speed. * the popularizations I've read claim ".1C", but I really have to wonder how many kg of nukes that would take. Isp might be in the thousands, but 30,000,000m/s is a *lot* of delta-v. Presumably you would need highly efficient neutron bombs using mostly hydrogen (or be able to cheaply provide thousands of tons of deuterium.

My understanding was that if one guy opened the missile hatch, pretty much any other submariner could launch the missiles. Not that the warhead would be armed, but it would fire the missile. The idea of a nuclear-armed country (with early submarine warming RADAR) would wait until a full broadside from an Ohio-class boomer explodes to launch a retaliatory strike seems unlikely. - While this story seemed quite true, I have no idea if it was Ohio class or earlier. I doubt they could/would change the issue, and the earlier boomers certainly had plenty of firepower. The old joke was the "third most powerful man in the world was the captain of a US boomer".

Or while flying around Icarus style. Just lose the seeker, it only made sense as a Macguffin. From yet another RAH lunar story (involving a boy trying to a Earth triple Earth-Moon-Mars* Eagle scout. Q: What's the first aid for a broken visor (or other bits of the helmet)? A: You bury them - Not sure if Mars was the "other Eagle" or not. Might have been Venus (presumably from before 1967). - Don't remember any RAH in Boy's Life (US boy scout publication) in the 1980s. Plenty of Asimov, even though RAH wrote great scouting stuff. Presumably his weird sex stuff got him censored.

While spreadsheets certainly work (and are feasible for players with wimpy notebooks they can move near consoles), I really like my solid boosters. I really question my ability to compute delta-v while solid and liquid rockets are simultaneously firing (I know, the answer is putting drop tanks on top of your SRBs. More efficient and easier to calculate).

It would have to be more like indoor (6+ player teams). Jumping, blocking, spiking, and serving would all be great (forget flat [knuckleball] serves and go with high-topspin jump serves). Defense would have to dig the way I used to: be where the ball is coming and let it bounce off of you. Nobody is making fast moves to dig a volleyball: that uN friction limit will stop you (even if they replaced the regolith with a high friction surface).

Robert Heinlein published a story called "The Red Menace from Earth" (title menace is an Earthling redhead starlet hanging around the narrator's boyfriend). Most of the story centered around recreational Lunar flying (Icarus style, presumably possible under low gravity). No idea how the math works: I'm sure a gymnast could do it but larger types might not. Lunar golf has been tried, and it appears that the 1km/s needed to get the ball into orbit is impossible even with a perfect (non-restricting) spacesuit.

It's amazing that any gas with a half life of 3.8 days is detectable at all in someone's house (although anything so unstable it falls apart in 3.8 days is *nasty*. I imagine venting the homes must be more serious than I thought and must do wonders for any insulation. Presumably you could create a source from depleted uranium, but there's no way you have any sort of Isp carrying enough uranium to source radon. There's always argon. We can't run out of argon (we can't "run out" of xenon either. Just run out of any xenon made as byproducts of making liquid oxygen and/or liquid nitrogen. Liquifying the entire atmosphere is a bit expensive to squeeze out the last Xe).

I missed why mercury would make a good propellant at all, but judging by the mN of force generated by throwing these substances at multiple times orbital velocity, I don't think Radon pollution would be a problem. Depending on the location doing the research, it might not be measurable over the background Radon emitted from the ground. Ion engines can't possibly emit all that much propellant. I'm less sure about having a tank of radon around, but it certainly beats having LH2, LO, LCH4, etc. (not to mention hypergolics and many of the stars of Ignition!).

Any idea why Radon isn't used for ion engines? While I suspect that Radon might be excessively rare in the atmosphere (Xenon certainly is), there is an unbelievable amount of data in the US on areas where Xenon leaks out of the Earth in much higher quantities than normal (in much of the US basements are a popular form of foundation, and when Ra leaks into them, it stays put and poisons/irradiates the residents). My best guess is that it comes down to two issues: the high percentage of Ra is a slow thing, and once the air is liquified once it the Ra level drops to basically zero for the next month or so, and that the rock formations in question (granite, from memory) doesn't form the type of cave systems needed to really supply enough "new radon" for such a collection scheme. But I still have to wonder if there is anywhere to scoop up some Radon. Note that I'm not certain that doubling the efficiency of ion engines is worth it (Isp is "good enough", power efficiency could use some help), but it might help ion drives scale better than limiting them to the Xe supply (there is more Argon in the atmosphere than CO2, but I you might need to make up the Isp losses if you use Ar).

Except that Hayabusa didn't stick around using its ion engines to escape the Van Allen belts, but simply blasted through them on its delta rocket. It seems rather odd that they would use expensive hydrolox fuel (instead of adding more instruments) to blast out quickly if the on board ion engines could do the job just as well? All the ion-powered spacecraft I've heard of have been chemically placed in either escape trajectories or at least GTO. There's a big difference between spending a few hours in the Van Allen belts and spending several months. Deep Space 1: "At 13:01 UT the third stage burn put DS1 into its solar orbit trajectory" https://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1998-061A Hayabusa: "As with the NEAR Shoemaker mission, it was decided that the launch vehicle would provide an initial heliocentric orbit. This is achievable via a multi-staged Delta class rocket" https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140004799.pdf OSIRIS-REx: "Its hyperbolic escape speed from Earth was about 5.41 km/s (3.36 mi/s)" (from the infallible wiki) DAWN: "reaching escape velocity with the help of a spin-stabilized solid-fueled third stage" (wiki, again) The one exception I could find was SMART-1. As mentioned above, it was left in GTO. However, unlike GSO, that is elliptical and *does* imply going through at least some of the Van Allen belts. In this case it appeared to avoid the inner belts (thanks to launch position) and only had to deal with the outer belt (it started in an extremely elliptical orbit). It *did* spend about a year working its perigee out of the outer belt. It is possible that an "inter-belt" area might be a staging ground for moving fuel/cargo beyond Earth (as most of the Van Allen issues happen when crossing the inner belts). Note that NASA doesn't seem involved at all in this one (ESA mission, Ariane rocket) and had no way to enforce its "rockets must be big" turf mantra.

One catch is that between LEO and GTO lie the Van Allen belts. These are not kind to spacecraft, especially to solar panels. The other catch is that ion drives are slow, and time is money. That said, fix this issue (and as you can see, billions of dollars are spent lobbing these things all the way to GTO: funding shouldn't be a problem) and suddenly travel beyond LEO is a solved problem. Just send fuel and cargo via ions, wait (quite a long time in some cases), and then leave LEO, dock with fuel tanker, hit escape velocity to Mars (or wherever), fire a two month ion capture burn (likely then combined with aerobraking and maybe retrorockets), dock with your trusty cargo ship, land ... There isn't much data on this problem. I was convinced that ion craft to the Moon and Mars were the answer, until somebody on this forum pointed out the problem. The only paper I could find was from the Apollo era, but NASA simply sends ion missions into escape velocity by booster and then turns on the ions (note that NASA thinks they are in the "big rocket" business and politics may have been involved). I thought there was a British ion mission to the Moon (which would presumably give some data to the issue), but either I missed it or it was cut.

I think Tesla has only made money during one quarter [i.e. 3 months] over its entire life. On the other hand I expect Musk's [Tesla] stock portfolio has wildly inflated (and I'm hoping both he and Tesla managed to diversify. That price isn't really sustainable). Once capitalism starts happening, "profits" and "wealth" don't always have any discoverable correlation. Solar City is structured for high startup costs and long term profits, which might be some kind of way to diversify Telsa stock sales. It can only be seen as profitable by counting the long term revenue it has basically already locked in (the electricity it is selling for a profit to people with Solar City panels on their homes).

From Ment18's picture, there appears to be significant aerodynamic issues as well. It looks like they keep the cross-section constant-ish, which is critical in transonic and supersonic flight. - not sure why they boosters keep tapering after the sustainer stops. Could be for manufacturing, or it could be that a too sharp bend was worse than violating the cross section.

A SSTO shuttle isn't just expensive, it may well be on the wrong side of physical limits. If you don't drop the fuel tank (and stop being "fully reusable"), it almost *certainly* is on the wrong side. Staging is simply required for the Isp used in currently available fuels, and there is no reason to believe Allen has anything up his sleeve beyond a whole lot of money. A two stage shuttle (presumably both landing like planes/gliders) still has problems, but might be considered easier/cooler/less "me-to" than a vertical landing. I don't know Stratolaunch's cost/schedule, but building a rocket for it would presumably be a project of similar scope. I'd expect a rocket sized for stratolaunch would be a more complex project, but presumably Stratolaunch already knows from working with Scaler (who built both the White Knight and Space Ship 1). BFR is well along the way in design. Presumably New Glen is also coming along. I'd assume at least one of them will be flying while Stratolaunch is grounded/reduced to ferrying Pegasus regardless of how fast Allen spends money. There's also the issue that the Electron can already send more payload to orbit than any SSTO light enough for Stratolaunch to carry. If any work starts on the design, that "nearly SSTO" will drop down to "just getting out into space".

My point was that even if they effectively remove the cost of the booster (which would come anyway with a Falcon 9 and 10 launches), I don't expect that payroll costs will go down all that much (launch/logistics people would replace manufacturing, but the costs will be still significant per launch). On the other hand, the subsidies necessary to compete with Spacex would just keep getting harder and harder to justify, and also get harder to keep quiet about (except for Bezos, who just writes another billion dollar check. And is equally committed to reuse).

Those costs aren't going to be paid (except by Paul Allen and co). There are basically four paths: mothball the thing (presumably not happening. It seems to be complete) sell and take whatever money they can (then the buyer doesn't need *quite* the return on investment bankruptcy (and a situation similar to the above, although Stratolaunch people are more likely to wind up with the plane) eat the loss and try to launch things None of "the big boys" seem all that interested in building a rocket for them (apparently Orbital does a bit of consulting, but isn't under contract to build a rocket). On the other hand, I'd assume that Rutherford Labs (the Electron rocket people) and any competitors building small rockets would be interested. Most of the reasons to avoid this type of thing would be deep uncertainty of the plane flying (a few test flights might make investors willing to at least ink deals) and fear of tying themselves to the small rocket market (which isn't that profitable, look at how often Pegasus flies).

The best data from Spacex seems to indicate that the cost of a booster is less than a third of the cost to launch a Falcon 9. The whole idea of getting it down to the pro-rata cost of the vehicle (assuming Musk's wild "1000 launches" scheme) is not going to happen. From Southwest Airlines 2016 annual report (page 45): http://investors.southwest.com/~/media/Files/S/Southwest-IR/Annual Reports/2016_AnnualReport_LUV.PDF Payroll : 40% of expenses Fuel : 22% of expenses (which is historically low: in 2003 it was 16% [listed twice under 20%] and in 2011 it was 37% [part of a 7 year run over 30%] see page 4) Vehicle pro-rata costs (rentals and depreciation): 8.6% Maintenance and repairs: 6.2% Landing fees (presumably whatever they pay the airports): 7.3% Everything else: 15% Even if you get the pro-rata vehicle costs down to the fuel costs (somewhere between 100-1000 flights) you can expect that the rest of the spacex payroll to be pretty steep (and when launch/landings become commonplace he won't be able to work geniuses like slaves, they will go elsewhere or expect more pay and more time off). Obviously an airline is more of a "asymptotic goal" and won't match up all that well, but it is the best data we have for an ideal situation. There is a *long* way to go to get here, but certainly removing booster costs gets you 1/3 of the way there (or more likely 1/2, I'd expect a lot of costs can't be avoided). I'd assume that a post-BFR rocket would involve something other than chemical rockets (assuming fuel costs began to dominate) but would be designed on "Elon time" taken to a whole new level (because there wouldn't be a hurry to replace the BFR). There are quite a few ways to get into orbit (or at least get enough delta-v to save a ton of fuel) but they require a lot of research that will take a very long time (and aren't getting the funding for much more than powerpoint slides).

I'd still prefer just docking and firing if my life was on the line. On the other hand, I'm pretty sure the ISS takes fuel to keep itself in orbit, so this appears to have been solved for at least some situations (I was expecting this to go the way of asparagus staging).

By "refuel" I suspect you mean "dock with a complete rocket stage, ready to fire and be discarded", at least until this type of thing becomes commonplace. The other catch is that such fuel pretty much needs to be non-cryogenic, and probably hypergolic as well, I'd strongly look into hybrid rockets (presumably pressure fed for the crew-rating, but I'd look into using turbopumped NO2 as well) as they shouldn't need to vent. Presumably this is how a two Falcon Heavy trip to the lunar surface would work. Each docking would be "dock or die" which might scuttle the mission right there.

This is called "the rule of cool" and is vastly more important to movies (in all genres, not just sci-fi) than any law in any science book. History gets at least as good a beating as science (que complaints about overstated American war presence in films to increase American gate returns), and the role phones play in daily life is finally being adapted (I wonder how long phones were still used as a murder weapon long after AT&T stopped renting [not selling] those old clunky black phones). There's a good chance that the guy buying the props really doesn't know what either the gun described by the script is supposed to be, nor the gun he is buying/renting/building a model of is, just as long as it looks cool he has done his job well.