en-us http://www.intensedebate.com/users/562387 Comments by jedswift http://www.thespacereview.com/article/1938/1#IDComment204545720 In a word, yes. The purpose of the &quot;smart grid&quot; is to tie all the producers and consumers in the US, perhaps North America, together with an adaptive system to efficiently route power. This is going to be very important as we are incorporating intermittent power producers, as with wind and ground solar. If you have a rectenna system near each large concentration of users, a large connective infrastructure would be unneeded as one, or more GEO systems could simultaneously supply base load to the ground infrastructures. A much less capable grid may be needed to supply power to low density areas; likely that the current system could be adapted for this purpose. Fri, 7 Oct 2011 22:49:13 +0000 http://www.thespacereview.com/article/1938/1#IDComment204545720 http://www.thespacereview.com/article/1938/1#IDComment204410018 Two other benefits/considerations; SBSP would eliminate the need to rebuild our entire aging electrical infrastructure backbone with a cost estimated in the trillions as the production would be placed relatively close to the consumption; the second is the cost, land and effort required to build the rectenna or LASER receiver systems. The cost of the ground facilities could rival or exceed the cost of the space based infrastructure. Fri, 7 Oct 2011 15:56:40 +0000 http://www.thespacereview.com/article/1938/1#IDComment204410018 http://www.thespacereview.com/article/1934/1#IDComment199862277 Or Frederick Pohl&#039;s novel Gateway, the first of the Heechee series published in 1977. The idea of finding an alien artifact close by is both very powerful and flexible boundary condition for a story with a great deal of room for original development. I&#039;ll have to pick up a copy of this one as well. Tue, 27 Sep 2011 15:17:05 +0000 http://www.thespacereview.com/article/1934/1#IDComment199862277 http://www.thespacereview.com/article/1902/1#IDComment181314209 I would say that it would be much more like the automated Mars landings that have been demonstrated a number of times. No aero-effects though (both good and bad), but with only a 3 second time delay, which would likely preclude direct control, but could allow for some kind of directed behavior i.e. &quot;move target area 20 m out and 10 m left&quot; to miss the inconveniently placed bolder. Mon, 8 Aug 2011 19:39:33 +0000 http://www.thespacereview.com/article/1902/1#IDComment181314209 http://www.thespacereview.com/article/1897/1#IDComment180130736 To complete the thought; Third, it&#039;s even hard to make a living building spaceships... Thu, 4 Aug 2011 17:36:55 +0000 http://www.thespacereview.com/article/1897/1#IDComment180130736 http://www.thespacereview.com/article/1881/1#IDComment173104600 The technological solution has to match the economic situation. Perhaps Elon has the right idea; time will tell if his demonstrated expendable vehicle evolves to a salvageable system to bootstrap additional market to justify greater investment in advanced systems. In the studies I&rsquo;ve participated in and read, Including the Commercial Space Transportation Study cited by Dr. Andrews, the space market is remarkably flat; it will take a very large decrease in cost to generate a positive total market value. The field of dreams is a tough sell on Wall Street. Wed, 13 Jul 2011 15:47:47 +0000 http://www.thespacereview.com/article/1881/1#IDComment173104600 http://www.thespacereview.com/article/1881/1#IDComment173103642 Regressing and accepting your $B5 - $B10, we can make a quick, optimistic assessment of minimum possible initial price. Just assume that the vehicle system was developed instantaneously, runs itself with zero propellant costs without wear or failure. Assume a 20% return on investment and that the entire Earth&rsquo;s market of ~50 flights/year is instantly captured. $B1 to $B2/year are then required to pay the investors, or $M20 -$M40 per flight. This is only 1/2 to 1/3 the cost of currently available services. Now add the upper stage required for GEO access as most of the current market is going there, ground facilities procurement, development and operation, staff, and consumables. Development time of even just five years will cost an additional $2B to $B5. We can see why the investors or very leery a present. Wed, 13 Jul 2011 15:44:44 +0000 http://www.thespacereview.com/article/1881/1#IDComment173103642 http://www.thespacereview.com/article/1881/1#IDComment173103528 Noting that the mass fraction required for orbital performance will drive all systems, structural, propulsion, flight controls, environmental controls etc. etc., the cost per pound combined with the marginal payload fraction will conspire to make this system expensive. Using multi-stage system to gain relief for the mass fraction is paid for by the development of two (or more) flight systems and the operational costs and complexity of pre-flight integration. Multi-staging was employed by some early trans-Atlantic long range aircraft too, and was an economic failure. Going SSTO will save of the number of systems and operations (with some caveats), but will place a premium on the costs due to the on the edge performance required from all systems, especially propulsion, thermal protection and structures. Wed, 13 Jul 2011 15:44:22 +0000 http://www.thespacereview.com/article/1881/1#IDComment173103528 http://www.thespacereview.com/article/1881/1#IDComment173103351 Looking at past technology expanding and not so technology expanding programs I would stand on my comment &ldquo;tens of billions&rdquo; the 280 klb dry/500 klb wet XB-70 cost ~$B12 ($B1.1 in 1965). The 300 klb dry/ 500 klb wet Boeing 777 cost ~ $B7.5 in 1994 (my understanding from being there at the time that the real number was much higher to including an engine and an elaborate passenger accommodations/entertainment system development). As for the 787 no one is even talking. The X-15, similar in performance to a reusable first stage required $B2 &ndash; $B 2.8 for the 56 klb wet vehicle and 199 flight test program. Scale that up by an order of magnitude perhaps to account for the multi-million pound system needed to launch commercially viable masses. Wed, 13 Jul 2011 15:43:52 +0000 http://www.thespacereview.com/article/1881/1#IDComment173103351 http://www.thespacereview.com/article/1881/1#IDComment172659287 I can only wish that we had to worry over the environmental effects of those &quot;thousands, let alone millions, of rocket flights each day...&quot; Those numbers would make the tens of billions of dollars required to develop a RLV economically amortizable. Tue, 12 Jul 2011 14:23:20 +0000 http://www.thespacereview.com/article/1881/1#IDComment172659287 http://thespacereview.com/article/1867/1#IDComment165822150 The Zorgons are comming! Where is your towel? Thu, 23 Jun 2011 15:06:11 +0000 http://thespacereview.com/article/1867/1#IDComment165822150 http://www.thespacereview.com/article/1856/1#IDComment159706039 Anyone read &quot;Voyage&quot; by Stephen Baxter? The premise begins with whoever shot Kennedy having less acute aim than what was demonstrated and kills Jackie instead. Mr. Baxter postulates that we end up executing a Mars mission in 1986, after many twists, turns, and the development of the Saturn N. Certainly a fun read and doesn&#039;t violate physics as so much fiction does today. <a href="http://ebookstore.sony.com/ebook/stephen-baxter/voyage/_/R-400000000000000377062?in_merch=Global_SubjectLanding_New%20Arrivals" target="_blank">http://ebookstore.sony.com/ebook/stephen-baxter/v...</a> Sun, 5 Jun 2011 21:15:22 +0000 http://www.thespacereview.com/article/1856/1#IDComment159706039 http://www.thespacereview.com/article/1844/1#IDComment153686533 Ms. Jane, To expand on Jim&rsquo;s note: One test that science uses is to push a concept or hypothesis to the absurd and see if the basic tenant still makes sense. Take creationalism&rsquo;s basic tenant; &ldquo;there is no reason for science, all that we do not know is explained by God, i.e. &ldquo;God&rsquo;s will.&rdquo; Thus, we do not need, indeed are not even capable of understanding&rdquo; to the logical extreme. If we, the few of us that would exist, started and continued living to this philosophy would still be sitting in a cold cave biting the head off of a lizard to stay alive while shivering in fear and making up stories of God&rsquo;s wrath to explain the bright flashes and loud noises emanating from the clouds to this day. The basic tenant of science is that all observed phenomena IS explainable, predictable and understandable by People, i.e. the universe is rational. Now, you may observe that this tenant is just as un-provable as creationism&#039;s tenant is, indeed both are acts of faith, science&rsquo;s faith is a faith in our own capabilities, tenacity and intelligence. You can read K. Eric Drexler&rsquo;s &ldquo;Engines of Creation&rdquo; for the end state of one possible logical extreme enabled by this faith. Just using nature to the limits of our current understanding of physics sure beats cold and raw lizard dinners. We are, and I hope we continue to test, define and expand those limits. Thu, 19 May 2011 01:54:06 +0000 http://www.thespacereview.com/article/1844/1#IDComment153686533 http://www.thespacereview.com/article/1846/1#IDComment153681291 To continue... Thus the internal pressure of the outer tanks would have to be 85 to 95 psi with obvious impacts to the vehicle weights. The other option is to use pumps, where finding power, dealing with additional failure modes, and costs are all issues. The fuel will have similar issues although with a lower density (~40 lbs/ft^3), longer tank (?) and a lower propensity to boil at low pressures. Option 1 has shorter plumbing, base of the outer tank to the inlet of the inlet manifold, operation at the same pressures, and no additional pumps, but there is that pesky, undemonstrated and difficult to ground test tank switch required&hellip; Thu, 19 May 2011 01:39:10 +0000 http://www.thespacereview.com/article/1846/1#IDComment153681291 http://www.thespacereview.com/article/1846/1#IDComment153681016 Roderick has defined the possible configurations. Although #2 does appear simpler from a dynamics and engine interaction standpoint, it has a fatal flaw. To illustrate lets imagine the situation as the vehicle nears the staging point. The outside LOX tanks are nearing depletion, the center LOX tank is still full (as intended), and the vehicle is accelerating at over 3 g&#039;s (~2/3rds of the initial mass has been ejected out of the engines). Judging by the SpaceX drawings, the LOX tank is roughly 2.5 times the diameter or ~25 feet long. LOX has a density of ~70lbs/ft^3. Putting these three facts together indicates that 6,130 psf or 43 psi over the internal pressure of the center tank will be required to push the fluid to the top of the tank. Nominal tank pressures are generally in the 25 to 35 psi to inhibit boiling, suppress pump cavitation and provide structural rigidity to the tanks. Oh, you want the fluid to move? Assuming a flow velocity of 50 ft/sec, a typical flow velocity, the high density of LOX adds another 20 psi. There is also viscous pressure losses in the feed tube which will add additional pressure required. Bill K. might have some reasonable numbers for velocities and flow pressure losses. He also brought up the geysering issue, where LOX ascending up a pipe experiencing a decreasing pressure, if not at a low enough temperature will start to boil. This will cause an interesting (and destructive) effect not unlike what happens in your percolator. Thu, 19 May 2011 01:38:22 +0000 http://www.thespacereview.com/article/1846/1#IDComment153681016 http://www.thespacereview.com/article/1846/1#IDComment152667707 One of the reasons for the F9H&rsquo;s extraordinary performance is also one of its greatest technical risks; cross feeding the center module&#039;s engines from the outer module&#039;s tanks. More specifically, the risk is switching tanks on a running rocket engine, an event that must take place just prior to separating the outer modules. Rockets have a demonstrated reputation of being very sensitive to propellant inlet conditions. Technically the Shuttle cross feeds from the ET, but the engine is shut down prior to jettisoning. Pogo and pump instabilities are recurring issues flying large systems. The second flight of the Soviet Union&#039;s N2 failed just short of the first - second staging due to a propellant flow induced pressure fluctuation pogo event due to the programmed staged shutdown of some of the vehicle&#039;s numerous first stage engines. I trust that Elon&#039;s propulsion engineers have read their history and plan some serious tests and attempt to simulate this pre-staging event, however I don&#039;t think that it can be fully tested due to the high acceleration and jerks that will be a part of the flight environments. I wish them good fortune pushing into this so far undemonstrated technological advancement. Mon, 16 May 2011 16:02:07 +0000 http://www.thespacereview.com/article/1846/1#IDComment152667707 http://www.thespacereview.com/article/1807/1#IDComment138384930 The term &ldquo;deorbit&rdquo; was used a number of times misleadingly. Unlike aircraft, spacecraft do not fall to Earth&rsquo;s surface or fly away to interplanetary space when broken up or destroyed. Mr. Lister correctly discusses the issues with his overview of the long lived debris cloud that would result from the destruction of RITSAT-2. Orbital debris in militarily and commercially valuable orbits is becoming serious and will likely become more so as the larger pieces of debris are broken up by smaller bits, resulting in a very slow motion chain reaction that is on-going now. Another tale from the tragedy of the commons will be playing out. It is interesting that the US is currently loosening ITAR restrictions with India. There is likely things going on that the public is not or just dimly aware of. Tue, 29 Mar 2011 15:44:17 +0000 http://www.thespacereview.com/article/1807/1#IDComment138384930 http://www.thespacereview.com/article/1805/1#IDComment136907477 I enjoyed the article, despite a few minor fact errors. It was interesting to read about a project that I had participated in. The reusable Propulsion Avionics (PA) module is a classic Boeing concept that has its roots back to the 1970&#039;s, with many design iterations for both booster (suborbital recovery) and upper stages (orbital recovery). Marine recovery systems were designed and demonstrated, land recovery using airbags were designed and subscale testing programs executed. All this was before my involvement with the pre-MD Boeing EELV proposal. My part was to design and expedite the construction of a set of struts to dynamically replicate the hydraulically locked TVC actuators and a tow line/sea anchor deployment device. A boat yard in New Orleans built the &quot;crab pot&quot; using conventional welded aluminum construction methods, sized for a single SSME. Dover built the deployable spray shield/environmental cover. The operational version was to use two SSMEs in an elliptically shaped PA module for the ballistically recovered composite structure. There were a number of drop tests from a crane and a helicopter to simulate various wind speeds and water impact orientations into the canal off the Pearl River at Stennis. The final test was from the helicopter, over the Gulf were the PA module test unit was dropped, the three parachutes extracted, the inflatable spray shield/environmental cover deployed, a smooth water landing demonstrated, the towline/sea anchor deployed, and the system recovered and towed back to Stennis. The test SSME was subsequently successfully run on the test stand. Although technically very feasible, I am still ambivalent over the practicality and economy of the concept. I also was tasked to develop a &ldquo;low cost&rdquo; upper stage intended to reduce the expensive LOX/LH2 version that added significantly to the launch cost. This exercise brought home the futility of having a very high performance first stage with a moderate performance upper stage compounded by a very constrained staging Mach due to range limitations; Africa is very inconveniently placed for this concept. If anyone is interested I still have some pictures of the system and key shots of the tests. Wed, 23 Mar 2011 03:08:05 +0000 http://www.thespacereview.com/article/1805/1#IDComment136907477 http://www.thespacereview.com/article/1784/1#IDComment130005655 Your paper &quot;Cost Estimates...&quot; was very interesting and postulating a development cost between $20B and $70B likely brackets a commercial effort to achieve the stated TSTO fully reusable 20klb LEO access capability. I would say the price would trend toward the high end due to the requirement for two flight vehicles, and that Boeing currently requires about $20B to develop a subsonic airliner; something they should already know how to do. The one major cost element that seemed to be omitted in your paper is the cost of money, generally estimated between 10% and 20%/year. Unless Uncle Sam jumps in and pays for the development through meeting milestones or some other mechanism the money will have to come from banks and investors. These entities will want their money back, with interest. Going to the logical extreme, assume that the system costs $45B, takes two years to develop at a constant burn rate, operates with no additional funding, pays back money at 15% and generates 10 missions/year. Just to tread water on the loans, each flight must generate $675M. This is a fundamental issue; the substantial investment required combined with the very limited marked is a deal killer. Recall that the popular B-737, but just one model of airliner accounts for an operation (one take off/landing) every 5 seconds. 24/7. They fly off an entire year of business in less than a minute. For economical space launch we need hundreds not dozens of operations per year. Wed, 23 Feb 2011 04:58:25 +0000 http://www.thespacereview.com/article/1784/1#IDComment130005655 http://www.thespacereview.com/article/1760/1#IDComment122328694 The activities you are describing are called architecture studies. I was involved in a number of them for both NASA and the Air Force beginning in the mid 1980&rsquo;s. At that time is was apparent that these studies had been going on for some time. The answer one gets from these is dependent on what is asked, that is, what the end goal is and what the constraints are. They are then rated for mass launched, timing of launch requirements, technology development required, estimated risk, cost and burn rates (how much money to who&rsquo;s Congressional districts) etc. There are literally 40+ years of this kind of activity. NASA is a master of it, to the point of forgoing doing anything beyond the next study. My experience is that they always seem disappointed when they ask the same question with the same constraints and get the same answer. The problem is in what is what the goal is and what the constraints are. Wed, 19 Jan 2011 17:52:02 +0000 http://www.thespacereview.com/article/1760/1#IDComment122328694