PB666

Barges are big, go sit along the intercoastal at freeport you'll see quite a few monoliths pass. I've seen double wides @ double and triple longs. Some barges have tugboat at the back and a robotic pilot at the front, so having a four engine football field size barge with four pilot boat engines on it is not rocket science unique. When i saw OCISLU it looked like just a low drafting barge with some accessories on the ends. .

Yes, because, like, telephone poles are much better at landing on barges out in the Atlantic, . The rocket is emptied of most of its contents, the engines are the most dense part of the craft, it has landing stuts to move the tipover point further away from the center. Its a little bit better than a telephone pole at staying upright. using magnets would only be valid if the landing struts have iron in them, otherwise you would have to add magnet. I like the maget idea, the problem is that you would have to have a programmable array of electromagnets embedded in the barges deck, which might weaken the deck to the forces of landing. Electromagnets might fail in a storm.

Zephod! Back with both heads intact. Never saw this version of HHGTTG. Do you notice one inconsistency, Zephod doesn't carry a towel, he needs to be all panicky.

The dark side of the moon is not dark, because the moon is tidally locked, the distal surfaces are always distal relative to Earths surface, you could build a laser on these surfaces and accelerate an object from the surface of the moon using lasers. To do this you would have to have the capacity to generation 100 gigawatts of power in say the 15 days in which the moon faces the sun and store it. That creates three problems in addition to the Earth problem (4) 1. You would have to have be able to the capacity to generate 141 Gigawatts at peak insolance/15 days. Assuming storage at 90% efficiency that is roughly 10 GW per day, divided by 86130 seconds is 115 kw of power generation. That is roughly 400 meter ^ 2 of solar panels. 2. The battery capacity of a lithium ion battery is 900000j/kg and so if we take this as weight it about 110,000kg of lithium ion battery. Since this firing would likely be at the end of that lunar surfaces daylight cycle, the batteries could just passively dissipate the heat they generate in a full discharge, however it limits the size of the batteries to thin wafers, and this causes a problem during the full day cycle because of heat, they could be placed however under the solar panels. BTW you are not likely to get all 900000 in 100 seconds of operation, so that the battery should be considerably larger, say 3 or 4 times larger that its maximum capacity. 3. Since the craft would naturally launch from the moon (or meters above the surface) it would be influenced by gravity, whereas the Earth orbit launch would be at GSO, or close to it. The presumption here is that you could have an inclined orbit in which the craft is directly about Earth bound lasers, so when fired travel strait away from earth. Taking off from the lunar surface, the lasers would have to compensate for the ~1.5 m/s gravity of the moon some of which would be along the x and z axes. If the vessel is launched strait up, the effect of gravity would have negligible effect on course, but alpha-centauri does not pass over the moons equator, it would be in the southern hemisphere, which means that insolance is lower. The acceleration in the first few milliseconds would have the most profound effect. If we argue that once the satellite is 10 lunar radii above the moon that gravity is no longer consequential. If the radius is 1737000 km and 10 radii is 17.37E6 km then the distance traveled = 1/2 600,000 T^2 = 7.5 seconds. If the X-Z deflection is then say .707*1.5 then X-Z deflection is less than 49 meters. But to know for certain exactly how much you have to run the integral of the gravity versus time function. My guess it would be about 24 meters, over the total 100 second course it would be off by <1km. 4. although devoid of atmosphere it still rotates at 0.00013' per second, and since the lasers would fire over 100 seconds means that they travel 0.013 degrees, much less than earth, but still represent an off delta target at endpoint of about 1500 km perpendicular to the motion of travel without tracking. In addition the moons gravity which can be compensated for by the craft will tend to also deflect the craft. Being at the physical lunar pole offers on major advantage, you could place all the lasers on a giant rotating disk that is support by superconducting magnets. The disk could be a carbon fiber and filled with lunar sand at the periphery, once spun the disk would maintain the angular velocity of the moon, thus this tracking problem all but disappears. The conclusion here is that targeting from the moon is easier because 1. There is no atmospheric or particulate interference. 2. The change of surface angle relative to infinity is about 29 fold less, thus tracking will be more reliable. 3 While there would be an effect of surface gravity, it would be fractional relative to earths rotation. The problem of the moon is landing 1000 tonnes of lithium Ion batteries and posting >400 meters of solar panels, and a few 1000 lasers. Therefore the dark side of the moon is a valid option. Another valid option it the lunar pole, because putting the lithium ion batteries in a polar sink avoid the heating problem and optimizes cooling in the post launch period. The lunar poles could still target the earth, from the southern hemisphere there would not be many good targets on earth, Mr. Evil Genius could target the Antarctic ice cap and an attempt to melt it. Would not do as much damage as a 1 PPM rise in CO2. No more damage can be done than the number of solar panels. However Mr. Genius could melt the canyon hold int the West antarctic glaciers, allowing the inflow of salt water that would accelerate the melting of Antarctic glaciers. This could result in flooding major cities like Shanghai, Bombay, New Orleans, Miami, parts of New York city, parts of London. But even at best it would take 25 years to happen. Under international control you could make sure the lasers are mounted in a canyon below the horizon, so that it could only target stuff well into the Southern Hemisphere but not Earth.

Could such a creature exist, we could be that creature, if the graviton proves to be true, and you could uncouple two quantum entangled and recouple many of them at once, then it could be possible to send a directional gravity pulse at a craft in space that tears it apart, much like a ship passing very close to the event horizon of a black hole. You would have to be in space, the device could be on a moon or asteroid, with some sort of pointing device. Like many things, it might be possible to show that you could do something on a very small scale, making it work on a grand scale, more difficult. Another way would be to send a very intense EM pulse, though this somewhat depends on the magnetic responses of the elements in the ship.

With water in a vacuum, I can only give empirical evidence. Lyophilization requires a vacuum below 100 microns to keep the water frozen, that means that the vacuum has to about 0.0001 Atm. of pressure for the vapor pressure of water at freezing to be 0.0001 ATM, although the process will generally be slow. To get something to freeze solid you need about 10 microns. Inside a space suit that has a small leak, the pressure differential suffices to keep the vapor pressure of water at the skin high enough that water evaporates but does not boil, but not so high that the water under the skin is boiling, and still fast enough as to create a dynamic pressure. If you space someone, that means the dynamic pressure has no buffer, and exists exactly at the surface of the skin. https://en.wikipedia.org/wiki/Soyuz_11

Position follows the areea rule (the area swept by an orbiting object per unit time does not change). The period is determined by u and a. You need an engineering addon like MechJeb to know the period. For transfers the time required for the transferring ship is about 1/2 the period, since dividing ellipse along the low and high points in an orbit creates two equal halves, and given the area rule, thus the area is swept in one period, half the area amounts to half the period. Once you know the transfer time, all you need is the period of the target orbit angle its angular velocity its going to cross 360 per period. Since you know the transfer time, you can calculate the number of degrees the target orbit sweeps in the transfer time. Since the ship transfers 180 degrees the target sweeps x degrees. There for the targets positions relative to the transfer ship should be 180-x degrees, in front of the ship if it is positive and behind the ship if it is negative. https://en.m.wikipedia.org/wiki/Orbital_mechanics Many of the equations are here in the link above. https://en.m.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion The are other pages that link to this page. u (greek mu) = celestials gravitation constant = universal gravitational constant * central bodies mass (for a small satellite) In the game the semi-major axis (a) is equal half the major axis, which is sum of the altitudes of the periapsis, apoapsis and central bodies diameter. e is the difference of the Apo and Pe divided by the major axis.

Luck, the good is they are not saying next year, or the year after, they are saying lets start assembling the chain of resources now and in twenty years enough stuff should be in place where it is doable, while i critique what there plan is today, theygive themselves a chance to modify it and evolve, as any such projects evolve. What i am keen on is that they say they will set intermediate goals, such as targets in our system, planet 9 as a potential example, so if they can do this in five or ten years, then we can see the progress and see what their self-critical process. The most important thing is the process not the exact details of the plan, the process as i see it is to take the most mass conscious technology and couple it to a based energy supply is one way to handle the problem, see other thread, you don't have to take the energy supply or the reaction mass with you. The bad news its only suitable for fly-bye. If they are going to pulse 100 ships, i would have it that first the ships were sent out and reported back at intervals, so that if there are problems in communication or viability they don't find out after the nanoprobes have traveled for 20 years.

The soviets lost two astronauts due to short term suffocation during reentry, but there were other symptoms. @KSK Its fine if they at least try, I think stargate universe was good in the point that they tried to at least have a credible drive system and at least show that popping in and out of luminal drive has costs. Basically star trek chars had god status, so the conflicts are rather silly in retrospect, here kirk is battling godzilla in one episode, couple of movies later and spock is being resurrected from the dead form a coffin that was torpedoed to a planet, really. And the Dr is carrying his soul, cause like spock knew this was going to happen after which he goes on to live 200 more years. I like star trek, TWoK was i think one of the finest sci fantasy movies, but some of the other stuff you are shaking you head.

You mean the flare after passing through its Mach related bow shock? They could have prevented that if they had designed the nose piece minimize boundary separation after bow shock. Would have increased the weight though and cost of nose piece. After seeing the docked video of the barge at Canaveral I realized that it was paint, you can still see the space X Logo on the bottom of the stage. According to Sears-haack shape, the rise in crosssectional area should taper and then recede, otherwise you get wave formation along the rest of the body, as speed increases the wave length proceeds down the body and then down the plume. My bad, did not realize, thought it was a H2 / O2, in-fact it uses kerosene, yep that bow shock caused the engines to soot it up. But on the bright side, having the engines under the boundary layer does increase the ISP, lol, funny because creating that separation costs more in Mach drag.

I see that each pulse is for a single ship, apparently pearch in an inclined geo orbit, fired upon by massive laser, since AC is in southern sky it woukd have to be a southern high altitude point. Better idea, move ISS into super GSO orbit mount laser on ISS, expand the solar arrays when retired, fill the iside with lithium ion batteries, and fire on ships from point blank range using say 10,000 g instead of 60,000 g. Alternative move the ISS to L1, easier to get to from earth lower omega, more stable targeting.

I had the same thought for a star ship many years ago, the idea of supplying energy from lasers. Thevproblem is getting sufficient acceleration within a window of time that would be relevant. They intent to accelerate at 600000 m/s using a powerful laser from earth, theoretically possible, technically difficult given the strenth snd bulk of materials required to sustain such forces. Carbon fiber and titanium rotors can sustain the force and could be test beds, but for tethering a PL to a sail.. The second problem is targeting from earths imperfect surface through an inperfect atmosphere to something that is moving at 0.1c at great distances, remember the ship is pulsed once a day, it travels 80 minutes between sun an earth about 120 minutes to mars, we are talking about targeting between Earth with a laser to kuiper belt objects as part of the final accelerations from the Earths surface through the atmosphere. Techically that is a pretty tall order.

How sure are we that this is dust, could be that the paint burnt off, the hydrolics on the legs looks like they have been through fire. The coloration looks to me like heat oxidized metal.

The justification of this thread follows a lines of conversation that basically starts a couple years ago in which there has been a consensus progression in this group with the realization that every means we have for space travel is basically unsuitable for interstellar travel, except theoretically, generational ships (falling under the assumption that with a source of fusion power and perfect recycling humans could manage to survive in some large volume for a long period of time). This being unsatisfactory for many folks here we have two basic miracle power systems, the blackhole drive and the antimatter drive. (Excluding warp drives because of the emperical absence of known materials needed to make such a drive) Theory. If you can completely convert your fuel to energy then you have the perfect energy supply. Its actually not so true, as we will see, but its very close. For probes this seems like a really great thing, but how fast can you actually go. https://en.wikipedia.org/wiki/Relativistic_rocket This page tells you all you need to know. I will add a table (PL = payload, EM = Energy mass, RM = reaction mass) PL EM RM c - flyby c-start-stop Efficiency 1 1 0.6 0.42 Idealized (see 1) 1 1 0.42 0.25 Cosine losses 1 1 1 0.692 0.43 Idealzed (see 2) The critical formula is the ISP formulations for mass ejecting setups are. the n variable is the fraction of the fuel mass which is converted into energy. The Isp here is ISPv not ISPg. ISPg has no relevance for any equation dealing with relativistic rockets. You can derive fraction of c below by simply removing c from the right side of the equation, however you might have to correct this based on efficiency of the photon lensing. for photonic rockets (row 1 in table) https://en.wikipedia.org/wiki/Photon_rocket If the rocket has dead weight, that is power units or antimatter storage containers that are not apart of the reaction mass but are simply discarded at the end of the trip these have to be included as part of the payload, which ultimately lowers the ISP. From the final row of idealized 0.69c the velocities only go down, by the time the reaction mass is 100 the maximum flyby speed is 0.14c and start stop is 0.09c. Basic problem is for idealized values. 1. Photon drives, antimatter driven or black hole drive. - unfocusable hv - both of these devices release photons that are difficult to focus using reflectors. The logic here is a reflector has a non-penetrating surface that forces photons to bounce back into space. High energy photons can penetrate just about everything, and they tend to do quite unpredictable things once they penetrate. Because of this if you beam HEhv at a plate, the best you are going to get is around 0.707 Ve in the -y. In this case the second entry takes account of this hv scattering cause by HEhv. Its actually worse than that. - Damaging hv, radiation or radiation products. Part of the operation of an interstellar trip is to keep black hole or antimatter stable, the problem is that both can be quite damaging. In the case of antimatter you need containment, but once is undergoes annihilation, a necessary part of its behavior, it produces other particles and may annihilate with parts of the vessel creating radioactivity. This means that shielding and damage over time may occur, requiring redundant space craft systems. Black hole drives have a similar problem, at the end of their life the frequency of photon they release and the power increase extremely rapidly. As a consequence a black hole at endlife would have to be released and the ship would have to have a means of propulsion to take it far enough away from the black hole to survive its final moments. One way to avoid the endlife scenario is to carry life extending mass on the ship and feed the black hole, this would then increase the payload, most of the energy would be returned, but not all due to cosine losses. 2. Ablation drives, antimatter driven and shielding for black hole drive. The uranium sail used for the antimatter drive is coated with a fissile material, such as U238 which then degrades into Palladium 111. The antimatter is 1AU and the composite palladium is 222 meaning that 239 - 222 = 17AU go unaccounted for, given that the recoil velocities are 13,900,000 m/s; this is not explained by gained velocity energy. These other products are composed of radioactive materials. In this case the energies and damage induced go unaccounted for, Once again the tethered payload is directly in the path of ejection mass travel, and even though its a small footprint, over the life of the sail kgs of material, some of it incredibly radioactive (including neutrons), are being ejected at the antimatter containment field and payload. This has two effects, 1 by absorbing the ejecta the ISP of the ship is lowered, second shielding to protect the Antimatter containment system is needed. The protective shielding becomes part of the PL weight because it is neither an accelerant or an energy source. The other problem with ablation, the models assume a focused pitting ablation in which the ejecta create by antimatter digs a deep well and then is ejected strain backwards (and strait backwards then hits the containment unit and PL). Thus, if such pits could be achieved, they are unwarranted, but shallow pits result in cosine losses. Consequently one does not expect ablation to have perfect efficiency and we are probably looking at ISPv on the order of 0.707*Ideal. As one can see with even some losses considered in the Ablation drive with minimal sail mass, we are already below 0.4c, even for a flyby, and the stated design is well below 0.1c. Caveot emptor. 3. Starting and stopping. The forth column in the table shows the effect of requiring a stopping point. This is the goal ultimately of robotized or manned interstellar missions. A flyby may give basic information such as hmm, that might be a habitable planet, a stop start robotized mission could stop, investigate, even add seeds to the planet (such as cyanobacterium) to kick start the planet from the long phase of evolution. The problem of start-stop with these sublight drive systems is now that we have sensitive equipment/living systems on board we have to protect them from ionizing radiation and antimatter. There are also limitations, for example, you really don't want to accelerate humans at 2+ g forces for a few months, then 0 forces for 3 years, the 2+ g forces at the end of the trip. Ideally you want constant acceleration and then deceleration as to provide a source of artificial gravity. 4. As previously discussed and not needed to discuss here, the energy requirements of either creating antimatter or blackholes. I provide this thread as a gauge, if you see a website advertising that they can go 0.4-0.9c to alpha centuari in 8 to 20 years, beware, the devil is in the details. The page may say potential, but these potentials assumes ideality when only some of the theoretical restrictions are considered. Both Antimatter drives and BlackHole drives have a considerable mass devoted to operation and shielding and both have losses that cannot be absolutely defined until tested in real-world situations. The next question that comes up is why can't we just reduce the payload and go faster. The Answer is that reducing payloads, or even assigning payloads (as in the table above) when the theoretical restrictions have not been applied only kicks the can down the road, because once the rocket is built to function, payload starts rising as a consequence of antimatter containment (blackhole shielding and endlife feeding or endlife separation), lensing systems, structural mass for the prementioned. Ideally these could be fractional to the mass of the energy mass and ejection mass, but more than likely these will be a high percentage of the payload mass. IOW payload has to have features that lend themselves to manipulating and stabilizing high energy systems. Other high energy systems include Nuclear reactors, high output power plants, high temperature chemical conversion plants - current experience with all of these is that their structures are usually massive, the fuel is often a small proportion of the mass, the higher the energy output, the more massive they become, low output nuclear power (such as TNGs) can be less massive. Examples of poorly contained but higher output energy generation systems include post-detonation nuclear weapons. Somewhere between these two types of systems is where modern technology stands. We can thing of ablaters for example as low energy cosmic ray generators, this is something delicate systems should avoid in space if at all possible. We can think of Antimatter annihilation and endlife blackholes as mostrous X-ray/gamma ray machines and we can think of antimatter containment and endlife black hole drives as very massive nuclear weapons. So that before we can go, the system has to be safely contained, and before we can go efficiently the output has to be managed. Increasing Energy means increased containment and management, and eventually the reward is not worth the risk/cost.

My biggest pet peeve in many, I have so many, biggest science pet peeve, hmmmm, lets see: 1. Current favorit, Inertial forces that would otherwise be lethal. 2. My classic favorite, drive systems based in fantasy. 3. Throwing out scientific words that have to do nothing with what you are observing (like tacheon particles making invisible things visible) 4. Treating the distance between stars like they are down the street turn left and travel 3 blocks. 5. Treating the distance between sentient bearing planets as they are found on every other star.

For hydrogen (assuming you electrically neutralized protons) at the radius of mercury about the sun it would take 134,000 years to collect 1 kg across a meter squared. Antimatter is created in major solar flares, about 1/2 a kilogram, this is versus 1E9kg of hydrogen per second, and so the amount of antimatter production is less that 1/1012 The amount of matter production. IOW if you sat at Mercuries orbit collecting everything the flew by a meter squared in a year you would collect less that 10-19 kg of antimatter. Making it 1 kg of antimatter would take 9 x 1016 joules of energy (with no manufacturing losses), about the daily human production of energy. http://www.nasa.gov/centers/goddard/news/topstory/2003/0903rhessi.html So how if you had a sail about Mercury how big would it have to be to collect a kg of antimatter in a year. The sail would need to be a square 3 million by 3 million kilometers assuming that you had several decent solar flares in that year.

Mars might have had a thin atmosphere during the beginning, the way I interpret this is that these planets had atmospheres thicker than venus, but because of the stellar dynamics they could not retain their atmospheres and were lost early on. It might be true that there is a critical mass to a gaseous planet whereby the gravity is high enough then you see a gas giant circling a star, but if not or the star has a powerful enough pulse stage, the planet can lose its atmosphere and become rocky.

http://www.bbc.com/news/science-environment-36016045 Well folks, it grabbled.

http://www.bbc.com/news/science-environment-36016748 Title says it all.

Here is an image of the illustrated device. A little more credible . . . . .ON my IPAD I see a different article that defines the weight of the sail as 100 kg of Uranium on carbon fiber. http://www.iflscience.com/space/antimatter-propulsion-could-sail-stars http://accelconf.web.cern.ch/accelconf/p03/PAPERS/FOAA005.PDF It says that the Uranium 238 undergoes antimatter-triggered to 2 palladium 111 the kinetic energy of the release they claim is 14,000,000 m/s The amount of hydrogen in 17 grams is equal to 6.0223E23 that is 1.02E25 atoms that would cause the release of that number of Uranium at 98%, basically 1E25 That means how much mass will be lost, It will lose ideally 3.97kg of depleted uranium (U238, plus trace 236 and 235). If we take them at their word on the palladium post-fission velocities, the delta-v generated will be 14,000,000 * ln(110/106) = 514,000 m/s (0.0017c). Note: the article does not state what c it might reach. We could try other scenarios, lets say it releases instead of 1 uranium, 2 uranium at 7/10ths the velocity (0.0024c), 4 results in (0.0036c), 8 results in (0.0054c), we place the logical stopping point once we have depleted more than half the sail. That is 12.36 uranium lost per antimatter collision, this results in (0.0054c) beyond which the antimatter would cause the degradation of the sail. But lets just assume that all the uranium was lost and none of the carbon fiber was lost, lets assume that the carbon fiber and tether weights were zero, that means we have 100kg of depleted uranium to ablate. The dV produced is 0.022c. That is 1/20th the velocity stated in the cash-farming article and 1/5 the velocity of the forbes article. Note that the following weight were not given in the article and not added to my calculations: In terms of the power supply, it would need to be nuclear (TNG) and it would need to produce enough power to store the gas in magnetically contained compartments. The antimatter containment is a hand-waving engineering project so that its mass cannot be estimated. In a perfect world were only that mass was lost the amount of thrust you can produce is N/300MW (i.e. N/300,000,000 the same value as the speed of light). If you have a 10kg payload and convert 17 grams of mass then you have 1.35E15 energy. You can benefit from mass loss via ejection, but only so much because you have to accelerate the mass. The actual dV produced is actually less than I stated because you have heat losses on the sheild and because the ejecta is not strait backwards (-y) there are |x| and |z| vectors. Summary: Don't believe everything you read in a magazines, particularly articles pandering for money. . . .Caveot emptor. Fact checking? There is no magic bullet that gets us to the speed of light. If you convert mass the energy you get was defined 100 years ago everyone knows it, no one can forget it, its E = mc2. If you have a ship that initially weight 110+ kg and you convert 0.017 kg of mass you cannot expect to get anywhere close to the speed of light, even if you shed 9/10ths of the ship mass in the process.

And to think this thread was about composition, not classification. Rather interesting since there is already an active thread open on classification.

Repeat again skin friction is do to the media the object is in not the object. Read the wiki's https://en.wikipedia.org/wiki/Viscosity#Dynamic_viscosity Reynolds number = pressure(density)* object velocity*Length / viscosity https://en.wikipedia.org/wiki/Parasitic_drag#Skin_friction Air has a viscosity of mu=0.00018.6 Pa*sec. IOW the OP should have said that the object had a zero crossectional area and was moving through as gas with no viscosity (a fictitious gas). Note also on the page as velocity increases, the moment of heat on the boundary layer air increases with objects relative speed and the viscosity increases. To restate, an object that has no form drag also had no cross sectional area, because its the reflections of the gas off the object that creates form drag, an object that has no skin drag has no length, because it the movement of gas along the length that creates skin friction. Therefore a frictionless object has no cross-sectional area and no length, which is to say an object with no volume. As I said originally. Take the limit of a mass with a fixed density and using the most efficient form, the Sears-Haack shape, and reduce the mass to zero along the limit, as you will see drag-acceleration will go to infinity as mass goes to zero. If you read the wiki pages there is nothing more to be said on the subject.

That doesn't seem correct, not unless the space craft total weight was 100 grams, payload would have to be under 50 grams, 25 if you intent to stop at a destination. If you go by e = mc^2 and half the ships weight was antimatter the most you could get was 0.7c, that would mean a ship weight of 34g. Don't forget the ejecta is either light at 300MW/newton or some form of matter with an ISP in the 1e7 range. Not a ejecta would be going -y so there would loses there. Is it possible to do a better job checking the sources math before we throw numbers like this out, i've seen highly optimistic quotes like this with the black hole drive that just don't pan out. A sense of realism here would also factor in the carrying weight of containment.

Or maybe its really " if you find it is it worth sending a new horizins like misiion there anytime soon". If they said it was an earth-like planet, or a brown dwarf, i would be concerned about the hype. As it stands it looks like a kuiper belt dust bin not really to much hype there.

Parasite drag consist of at least form drag and skin friction. Even if the form were to disappear the motion of a fluid over a surface causes skin drag. E Exceeding the speed of sound Cd increases, you can decrease CoD by decreasing the surface angle relative to the axis of motion, but if you hold volume constant this increases the surface area and eventually skin drag will supercede form drag. A sears-haack body. Note that form drag exists on the leading edge (choose bottom left or top right), skin drag exists in the central and lagging region. https://en.wikipedia.org/wiki/Reynolds_number For any given volume there is a Sears-Haack body that confroms to a most efficicient shape that optimizes the flow, reducing the form drag without creating excessive skin drag. Or to put it like this, if you shot a gas at 1ATM though a meter tube at 30,000 m/s and there was a pressure differential, then there is skin drag. Skin drag is not dependent on the surface, its dependent on the gas and the pressure of the gas, in this particular case since a bow shock is created there will be a pressure well between the skin of the aircraft and the shockwave, the only way to reduce this is to make length longer which increases skin drag. The volume of such a body is V = LRmax3pi^2/16. Length(L) is going to be somewhat a function of velocity. Skin drag is going to be a trade off to reduce form drag created by a larger radius(R). CoD = 24V/L3