Steel

Well the paper's abstract gives us the headline figure of 1.2 (+/- 0.1) mN/kW, so 1 MW (assuming a perfectly linear relationship) would give 1.2 N of thrust. Interesting to note that the authors, in their own conclusion, cede that the effects of thermal expansion were only "addressed to a degree" and that further testing would need to be performed to completely rule out thermal expansion having an impact on reported results. EDIT: Reading a little further, even the units of the headline figure are a little odd, considering it quotes a figure in mN/kW, when in fact their tests only go up to 80W. It's a fair bit of extrapolation to go from 80W to 1000W... EDIT #2: also can we please talk about how these guys have assumed a straight line fit over a range of input power in the kilowatts, based on a data set of three points over range of 40W...

Broadly speaking: Turbofan: will stop working efficiently somewhere in the transonic region (0.8<M<1.2) due to shock wave build up on the turbine blades. Turbojets: somewhere above Mach 1 they'll start becoming inefficient due again to the fact they rely mainly on blades for compression. Ramjet: dependent almost entirely on intake geometry. Will stop working efficiently once intake can no longer slow the air to subsonic speeds, or compresses the air so much by doing so that it becomes too hot to use efficiently. Scramjet: again, dependent almost entirely on intake geometry. A scram jet designed to go at Mach 5 will no longer be efficient once it goes a reasonable amount faster or slower than that. Morale of the story: Max speed is dependent on individual engine design. Actual engine failure is highly unlikely, rather the engine will become so inefficient and so produce so little thrust that it will just slow back down to a more efficient speed.

Ah but he's actually only tackled dropping food from orbital height, not from orbital velocities. The extra 6 km s-1 or so will do wonders for your crispy base!

I would argue that far more ridiculous things have been suggested in these forums. Early re-entry vehicles for warheads often used a big conducting block (copper or similar) to store and then radiate re-entry heat. The only technical difficulty you're going to have (for the sake of argument we'll ignore the obvious, massive danger to the lives of everyone on Earth) is getting the landing site accurate enough. All re-entires work within a corridor of accuracy, so your pizza could well be delivered completely on time, just in the next town 50 miles down the road

This is where radar is good, out to around 10AU. Once you go further out you really get bitten hard by the fact that radar range has a fourth-root dependence, which is why there are very few radar studies beyond the orbit of Saturn. Hence radar is probably not ideal for an initial survey, rather a detailed study of bodies that are already reasonably well known (and you are within roughly 10AU of)

I actually got curious and started to play around with some numbers. Using a 30 MHz signal with a 1 TW transmitter and assuming you can detect a minimum signal on 1 nW on the way back, you'd need roughly a 100m diameter parabolic dish to make out an Earth size object at 30AU... assuming you could track it for the 4 and a bit hours it would take for the signal to do the round trip

I would have two main issues with radar: 1. Your power to resolve objects is very much limited by the size of your ship. If you were out at Neptune distance you might need a dish in the 100s of metres in diameter to resolve an earth-like object that is almost 30AU away. 2. Accurate radar astronomy today relies heavily on already knowing where things are in the sky. To get good information about the various bodies you would likely need some other detection system first of all. Other than that it would be ideal for getting information about spacial position, velocity and all sorts of other things like ice concentrations

From the wikipedia article: Main hazards Skin and metal corrosion; serious eye damage; toxic (oral, dermal, pulmonary); severe burns and the mandatory John D. Clark recollection from Ignition!: "the acid couldn't be kept indefinitely in a missile tank — or there wouldn't be any tank left. It had to be loaded just before firing, which meant handling it in the field. This is emphatically not fun. RFNA attacks skin and flesh with the avidity of a school of piranhas. (One drop of it on my arm gave me a scar which I still bear more than fifteen years later.) And when it is poured, it gives off dense clouds of NO2, which is a remarkably toxic gas. A man gets a good breath of it, and coughs a few minutes, and then insists that he's all right. And the next day, walking about, he's just as likely as not to drop dead. So the propellant handlers had to wear protective suits (which are infernally hot and so awkward that they probably cause more accidents than they prevent) and face shields, and frequently gas masks or self-contained breathing apparatus" Not sure it sounds like great fun to me...

I would say it's a fairly significant result. If this sort of thing can be applied and held true across past and future supernova measurements it could very well mean changing or superceding the ΛCDM model, which is not necessarily bad thing. At the end of the day this is a model that currently requires inflation (or any of your other your favorite, similar mechanisms) and possibly a quintessence mechanism (still debatable) added into it to explain many observational phenomena. While this definitely does not disprove acceleration, it may mean that our cosmology needs to be a little more nuanced which may bring about some exciting changes. On the other hand it could be statistics playing its wonderful games with us.

I though this may interest the more Physics & Astronomy inclined among you. I read a phys.org article that I found interesting today, so I dug around a little. Believe it or not, the classical black hole is far from the only suggested object that satisfies the Schwartzchild solutions of general relativity, so while black holes are perhaps the most known (and perhaps having the most observational evidence supporting them) there are a host of other suggestions, including the Gravastar (Wikipedia link here if you want a quick overview). A quick Gravastar summary: From the bits I've read today, gravastars are an attempt to re-write a lot of black hole theory using elements of quantum mechanics, including the idea of smallest possible lengths, times e.t.c (for instance, respecting the Planck length as the smallest possible quantum of length, not something that is traditionally stuck to when talking about black holes). The result of this is that - in the Gravastar Hypothesis - when a star collapses, rather than collapsing to a singularity the matter in it instead undergoes a "phase transition" into an as yet unseen form of matter whose gravitational energy behaves similar to certain properties that we have observed here on Earth in Bose-Einstein condensates. This appears as an interior of vaccum surrounded a hard matter shell where the event horizon would be in a classical black hole (imagine a bubble). Outwardly, these have all the same properties as required (i.e. they look the same as a black hole would) but the inner workings are very different. The long and the short of it is that this formulation solves a lot of the traditional issues with black holes, i.e the conceptual difficulty with event horizons, the information paradox, the issue with a collapse to a singularity creating almost infinite entropy e.t.c. However, the recent detections by LIGO of gravitational waves has thrown a spanner in the works. Both gravastars and classical black holes would produce waves in a collision, however models have suggested that gravastars have a very slightly different characteristic tail-off of these waves (or ringdown from the phys.org article) than a classical black hole. The analysis of the LIGO results did not find that this difference to the expected outcome, meaning the Gravastar Hypothesis takes a big hit.

The only issue being they'll all crash trying to get there

It's not a lot if we're talking antimatter production. Also I'm pretty sure a lot of labs will spend more than this having their equipment calibrated each year.

The thing that worries me about this is that it doesn't seem to say (from my quick skim read) anywhere what the money is going to be used for... well, that and the fact that $200,000 will get you precisely nowhere with a project of this scale

Launch pushed back by 5 minutes

BEGIN SIDE NOTE: I would argue that using pets as example of how nice we are is a bit counter-productive. Modern day pets are quite literally the results of centuries of inbreeding and eugenics that turned wild animals into our possessions, because people saw wolves and big cats and said "Hey, those look cool, I want to own one and be its master". There is very little that's nice about that! END SIDE NOTE

Yeah the "literally skipping" part is wrong. What people tend to mean in this case is that if you're too shallow you'll not decelerate nearly enough and so it may take several passes to slow down to a sub-orbital velocity. If you look at it from a purely height-from-the-ground point of view though, this does look like you are skipping as you'll reach a minimum altitude and then climb up again.

Also, water is an amazing radiation shield

Very true, but considering very few people other than NASA can get hypersonic anything these days, this may be a while off

Well that seems a shame. I really like what they were trying to achieve and the whole air-launch concept as a whole. My best guess would be that that their aircraft may be able to go higher(?) and faster (???) that the L1011, giving the Pegusus a little more capability? Also,I suppose if the company can stay afloat (which might be stretch, considering currently the Pegasus on the old plane has two launches planned in the next two years) this is a good way to test their aircraft with a proven rocket.

Based on those illustrations, Titan is just about the worst place to be in the whole system!

Ref: Belbruno & Topputo, http://arxiv.org/abs/1410.8856 So as far as I can see, the manoeuvre exploits the dynamics of the Mars-Earth-Sun system. It's a weak stability boundary (WSB) transfer (which are a horrible set of things to have to try and come to terms with fully, having spent much of the past half-day trawling papers on them) which involves a set of stable points around Lagrange points as far as I can tell. Basically, the transfer is performed in such a way such that the burn to insert into the desired orbit (point xc in the diagram above) will have lower dV requirements (in some cases) that the burn that you would have to perform to shed excess hyperbolic velocity if you were doing a Hohmann transfer. These transfers have the advantage that they are not too sensitive to the relative position of the two planets - so you can transfer to Mars outside the ideal window for Hohmann transfers - and that in certain cases they can save dV. If you're trying to rationalise these orbits in terms of what you know from KSP, then don't. These transfers cannot be done in a 2-body regime because these orbits exploit features that don't exist in those regimes, so you'll just give yourself a headache for nothing

Realistically, if as much effort was put into the safe handling of Peroxide as, say, UDMH, Liquid Hydrogen, hydrazine or any of those other fun propellants there would not really be a problem with handling large quantities. Unfortunately, it just never happened.

While I agree on your premise, I think 2050 is a little pessimistic. If they're actively developing components now there no reason (unless the design is completely infeasible) why there can't be an expendable prototype launch vehicle in the next 10 years

Holy ambition Batman! 4 years for an experimental flight!

I guess their analysis suggest that the performance gains offset the extra mass.