Impaler

Northstar1989 : An airospace cost estimate before something is done is hardly worth anything, they are routinely off by orders of magnitude. And frankly NASA would be completely negligent to accept someone else cost estimate for ANYTHING. From what I've been able to find these costs estimates assumed absurd launch rates of nearly a million tons a year and partial reuse. These seem to be the studies. http://neverworld.net/truax/Sea_Dragon_Concept_Volume_1.pdf http://neverworld.net/truax/Sea_Dragon_Concept_Volume_3.pdf Stage propellent fractions are 88% on both the first and second stage, that's terrible. ISP claims are 242 for the first stage using Kero/LoX 409 for second stage Hydro/Lox, both of which are utterly absurd at the time, they are basically saying their pressure fed engine first stage engine would be just 18 sec lower ISP then the F-1 on the Saturn V and the second stage engine would be only 9 seconds less then the J-2. And all of this is done with chamber pressures that are an order of magnitude lower then what a pump-fed engine produces. I don't think these ISP numbers for pressure-fed were remotely achievable in that day and are probably not achievable now, this is why every nation has abandoned pressure-fed engines and move to pump-fed when they go beyond small sounding rockets. Your point about Russian rockets is dead wrong. Russian KeroLox rocketry has THE HIGHEST ISP performance in the world among Hydrocarbon rockets that is why we are BUYING THEM. An American made HydroLox rocket dose achieve a higher ISP because of it's fuels molecular weight but at enormous costs. The Russians and SpaceX rightly decided that it is not worth the cost. Russian/SpaceX style rockets are absolutely NOT big Dumb Boosters, anyone trying to claim their success as somehow retroactively validating SeaDragon has their head up their ass. These rockets are not high tolerance low performance 'dumb' things, they are LOW tolerance HIGH performance, they are made in large NUMBERS to bring manufacturing costs down. This is exactly the opposite approach from what Sea Dragon would have employed with one huge engine. As for your throwing out bunch of other unrelated propulsion concepts and challenging me that I must some how be opposed to them as well simply because they are 'advanced' is typical space-cadet thinking, aka anyone who disagrees with you is a defeatist and must think that no technology is worth pursuing. SeaDragon is just a bad DESIGN, the things it claims will save costs are not remotely likely to do so, like operating at Sea, anyone who knows anything about logistics can tell you that for for the same size logistical task the sea is many times more expensive. In SeaDragon they are just UNABLE to do it on land and then claim the sea is 'cheap', possible things are always going to look cheap compared to impossible things. The question is if the launch costs of SeaDragon at Sea would be cheaper then a non-dumb rocket on land, considering that SeaDragon was going to need a Nuclear Aircraft Carrier to make it's fuel and oxidizer onsite I can hardly call that cheap. The only pieces of infrastructure your replacing in the ocean area he concrete pad and the vehicle crawler, everything else that's part of a launch complex now has to be done from logistical ships at 10x the costs.

My solution was aimed at a Venus which is still just barely being visited by humans. If permanent habitation aka cities exist then that substantially alters the analysis and your multiple balloon rendezvous scenario becomes much more feasible. I still do not see how one could avoid mooring the vehicles together at some point. If the lower decent blimp is restricted to staying within it's allotted height bands then they will inevitably be swept downwind of the city when not in use and can't be reused until they complete one whole revolution more then city per the relative ground speed difference between them and the city. It seems that it has to get moored to the city by cable even if it is many km below the city and acting like an anchor. The key factors in making this scenario work are the amount of vertical range each balloon can accommodate as well as giving it horizontal cross range so it can accommodate for being blown downwind when at low altitude. Blimp like balloons need to keep their shape and inflation and are going to have less vertical range, but weather balloons can expand or contract radically for huge vertical range, but they don't have much ability to push themselves around horizontally. Crew transfer may also be ticky at the 35km height, that's not a survivable temperature at that height?

This BDB nonsense is the stuff that know-nothing space cadets like to 'discover' and then think they know rocket science and can thumb their nose at NASA and justify why reality is not like science-fiction "It's some politicians/bureaucrats fault for canceling technology X". Nuclear rockets often serve the same role. The BDB concept was for a PRESSURE FED engine, thouse things are abysmally low in ISP compared to tubo-pump engines which are NOT dumb. The BDB was never more then the fever dream of some engineer told to think outside the box, their is zero evidence that such a vehicle would deliver ANY payload to orbit let alone what it would cost. Remember getting to orbit is only just BARELY possible on Earth using chemical propulsion, if you 'dumb' down the rocket you sacrifice payload fraction, if you sacrifice it ALL it dose not matter how cheap the system is because it's doing nothing. This is why SpaceX is on the right path, they are making the rocket higher performance and the manufacturing process as lean as possible so they have a good expendable rocket. But if they can get a high enough performance (the kind the Russians have had for decades) then they can sacrifice some of the performance to get the stages back and reuse them.

I've altually been doing some thinking about what WOULD be necessary to get a 'flag and footprints' event on the Venus surface. I'm looking at half hour 2 man landing, grab rocks and go. Rocketry is not remotely feasible, but I think something more like a deep-sea dive via cable is conceivable all though HIGHLY challenging. First off you start with an entire second dirigible comparable in size to the HAVOC one, this one carries only a massive spool of cable, a 'cage' attached to the cable and an anchor on a short cable under the cage with winch. The cage has room for two massive rigid-body suits capable of withstanding the Venus pressure, the suits will need to be super insulated, likely by utilizing a double layer thermos type structure as well as active cooling, the suit will be impossible to move by human muscle power so it will be hydraulically powered by a kind of exoskeleton. Hydraulic fluid and active coolant (possibly the same fluid) will be supplied by a umbilical line no more then 100 m long connected to a large compressor/cooler unit in the cage. The compressor will be powered electrically by electrical lines embedded in the cable up to the dirigible. This is ofcourse a crazy inefficient arrangement for actual mobility and practical exploration, it would be vastly easier to just lower a 'submarine/tank' vehicle that the crew never leaves on the cable, but then no footprints, and a flag stuck in the ground by a robot arm is hardly very glorious. So in the interests of pure melodrama and the realization that Venus surface is a location we will go to initially only FOR such drama I'm proposing suits at the end of the cable. Operationally the scenario would involve the manned HAVOC blimp mooring in mid-air with the decent equipped blimp, the decent blimp with be forward with respect to the wind to create a in-line configuration that minimizes wind drag. This is necessary because once the whole cage/cable/blimp must come to zero velocity with the Venus surface and any thing NOT attached to that line and also at zero velocity is going to be hundreds of miles down range by the time the sortie is completed and separating the crew from their return rocket is a bad idea even if it is temporary. The crew will transfer to the decent blimp by zip-line while wearing oxygen masks, enter the suits by rear hatches and begin being lowered on the cable. As the cable descends into lower denser and slower winds it will act as a air-anchor and begin to be pulled at an angle from the blimp while also slowing the blimp. This will be accentuated by use of a parachute or para-foil deployed from the cage. By the time the cage is just above the Venus surface it will be moving only a few m/s relative to surface and the Blimp far above will be in nearly full 100 m/s winds which will be putting huge tension on the cable (far in excess of the weight of the cage), this force will want to bring the blimp down so it may be necessary for large air-foils on the blimps to generate more lift, much like a kite. Contact with the surface is made by lowering the anchor from the cage and hooking it to the Venus surface, then the cage is winched down onto the anchor and pinions are drilled into the surface to fully secure everything. The cable nessary to perform this mission looks to be the largest engineering challenge. Zylon plastic is our highest specific strength material and could easily handle the total distance without breaking under it's own or the cables weight, but it can only do some of the upper portion of the cable because it losses too much strength above ~200C. A series of materials with progressively higher temperature tolerances would be needed, with some kind of metal alloy like titanium or steal being used at the lowest portion, carbon fiber might be good for the middle section. The suits may need to be made of Inconel, a nickel based super alloy that can take the full heat of Venus surface and not lose a bit of strength.

I think that is perfectly feasible in the sense that the 'bucket' (I'm more imagining something shaped like a jet engine filled with screens) is going to cause drag. If it is not enough on it's own then having the chute dragging behind it would be fine and would keep the thing pointed into the wind. Their might be some conflict in which altitude is optimal for each device though, the maximum acidity level for the collector is unlikely to be the ideal location for a parachute, the chute is going to need to be very acid proof if it lives at that altitude. Still that seems better then trying to have two separate things dangling under the blimp, the inevitable tangle is just so obvious. The Acid solution naturally decays back into water vapor and Sulfur-Trioxide when it's heated in the lower atmosphere to 300C, perhaps this is all that needs to be done. I think I also read somewhere that CO might do the job, would steal an O atom leaving sulfur dioxide and water, can anyone else confirm?

Starship Troopers by Heinlein has something like this, they use a ablative heat-shield-shell and some kind of jet-pack for touch-down.

Much simpler to have a single wider Torus with two adjacent counter-rotating wheels inside it, the wheels are in contact with rails, motors and brake-shoes between each other to spin up and spin down. The rotating wheels are not pressure vessels, just thin walled habitat space that can be opened up to get access to the space between the wheels and the space between the wheels and the outer torus shaped pressure vessel. To access the no rotating parts of the ship or move between the who wheels when they are rotating you get into a small elevator car which is 'on top' (aka closer to the center of rotation) of one of the wheels, it is on rails and accelerates opposite the wheel it is on to an opposite be equal speed bringing it to rest with respect to the hub (your now weightless). An identical car doing the same thing on the other wheel comes alongside and you go though the aligned open doors like an elevator. Or if your going to the hub a sleeve extends down around the car and it locks into an vertical railing that allows it to ascend an elevator shaft to the hub, the same sleeve then deposits it back onto the rails when going back. All the rails and wheels are like thouse on roller coasters, double wheels that grip the rail and can't be knocked off, they must be made to 'let go' by active command likely some kind of electromagnet.

The usage of kites to counter the relative poleward and equatorial winds on Venus sound interesting, but I'm concerned that these kites would be delicate, likely to tangle in the wind or with each other and would be impossible to untangle. Would not simply lowering a static parachute into deeper air with lower relative wind speed be an adequate 'air anchor' without relying on complex active control. A drawstring on the chute should allow it to be expanded and collapsed for differing the amount of drag produced as well as allow it to be fully reeled back into the craft if needed. The low density of H2/O2 propellent makes rockets very puffy and increases atmospheric drag, on Earth for launching from the ground they often end up being no better then hydrocarbon rockets. Add in the extreme cooling requirements for the Hydrogen which we basically can't even do on Earth (the hydrogen is allowed to boil inside the rocket on the pad) and I think that propellent choice is out. The traditional Methane/LoX combo from Mars would just optimal for Venus as well. As ISPP is considered a must have for human landings on Mars I think it is perfectly valid to incorporate the same technology on Venus.

Double checking my numbers the density of acid droplets in Venus clouds can't be as high as I had thought, that was probably the vapor density I was looking at, the numbers are hard to get but most of what I'm reading is saying the density of droplets is comparable to Earthly fog and around 0.1 grams/m^3 at the densest cloud layer. This would mean that Venus has more like 100 kg of droplets per million m^3. Still this is quite viable to harvest, just increase the air-intake rate, it may not even require a fan if your getting differential winds at altitude, a scoop with a 10 m^2 area will bring in a huge amount each day. Also the expected air-speed of the Blimp is expected to be in the range of 5 m/s so this would translate to 50 m^3/s going into a collector, which would produce around 430 kg a day.

AngelLestat: Thx for the PDF, I had been wondering if their was one for this mission. I like your Hydrogen blimp concept as you have made it serve double duty as an energy storage mechanism, if it were just for marginal buoyancy over Helium it would not be worth the difficulty but by replacing batteries the savings in mass can be considerable and the ship will have good nigh-time power. Leakage of Hydrogen during the cloud-level portion of the mission dose not look to be much of a concern, the duration is just too short and if more lifting gas were needed then a secondary Nitrogen balloon can be inflated inside the blimp to supplement it, it is common for blimps today to have secondary interior balloons of denser gass at the for and aft to control trim and N2 balloons could serve this purpose. What kind of total energy storage would you get under your proposals, and how much mass is saved vs assumption of best-of-breed Lithium Ion battery storage? One nitpick, get rid of AC/DC inverter and just use DC motor for propeller, lower mass by a lot. The transport of Hydrogen during the trip to Venus would be the primary problem, but again this is a challenge that a Mars mission is generally believed to have as well. Though in the Mars case I believe that extracting moisture from the Mars atmosphere will prove to be superior to stored hydrogen brought from Earth. Like-wise the collection of the SulfuricAcid droplets on Venus will be more practical then transporting it from Earth, but this is not viable for the initial inflation of a blimp, the Hydrogen must be on board the ship at the time it makes atmospheric entry. From numbers I found the peak density of Acid droplets is a 45 km altitude, a mere 7-10 km below the operational altitude and within the tensile and thermal capability of things like a Zylon cable the density is 25 mt per Million m^3 of atmosphere (note that this is 5% of the density of an Earthly cloud). If this atmosphere is drawn in at a rate of just 1 m^3 a second (a very low rate) then the droplets are condensed out by passing the atmosphere through a fine screen (of gold so no it will not be destroyed by the acid, for that matter plate everything in gold, it's ridiculously cheap and easy to do) then over 2 mt of acid would be collected a day. The acid mix is thought to be 25% water, we might simply separate that out and dump the acid, or if it were deemed worth the effort water extraction could be raised to ~40% of gross droplet weight by chemically converting the acids hydrogen content. So water availability on Venus seems to be no problem when one actually looks at the numbers that are relevant (cloud density not overall atmospheric density). I would imagine that a specialized blimp-ship for doing this would be developed a 'cloud trawler' vessel that would dangle the collector unit on the end of a tether with the vessel equipped with radar to find and navigating around searching for the thickest clouds to optimize collection rates. The acid mix would be stored in the collector and perhaps once ever day or two the collector is hauled up and the acid transferred to a tank in the blimp gondola. When the Trawler itself is full, in perhaps a week or two it dose a fairly standard mid-air-refueling style transfer to another vessel (it extends a hose with a cone, other vessel inserts a probe), with the other vessel housing the equipment to process or use the water or acid mixture.

You would never try to land cargo on a platform directly from orbit, we don't do that here on Earth YET because of the precision it requires, rather we land in the ocean. And when and if it becomes practical to do so here on Earth the reason we do it is that salt-water is corrosive to a space capsule and air is not, and we live on land and not in the ocean. But on Venus everywhere is equally corrosive and we would be living in the same cloud layer that is everywhere else. Thus their is no detriment to the capsule or it's cargo to have it enter and float in the air a good distance (100 km) away from the city/crew/delicate-stuff and simply send out a tow-blimp to pick it up, even at slow blimp air speeds this would only take a few hours to tow in while avoiding all the danger and expense of a landing pad.

I'm speaking in this thread as an arm-chair engineer giving my opinion of the relative challenge of engineering for two competing destinations, not as an advocate for missions in general or even for a mission to the destination that is in my judgement more feasible. I never said Venus should be the next destination either, just that it can come before Mars for both an initial visitation mission and for a just about any kind of foreseeable colonization effort. It's difficulty over Mars has been grossly exaggerated by a number of posters here and I'm correcting that. The shorter 6 month asteroid visits would proceed either Venus or Mars and Moon return is likely to proceed even that. I am fully aware of the need to validate and use robotic fore-runners, and generally build up gradually, 2020's is an optimistic date for return to the moon in my opinion with visiting planets decades after that. I am not a Zubrinist who thinks everything can be done in 10 years and spits on every intermediate destination or development effort. On a broader note I think your a bit inconsistent on manned space-flight, it has never been about science, if it was we would call it 'Manned Science'. If your an advocate of manned space-flight then your an advocate for a goal which is not scientific. THAT IS OK we have a separate budget line for science and I don't believe it is a zero-sum game. The closest thing we have to Manned Science is the ISS, where human labor is used to run a laboratory doing lots of unglamorous research, but manned-space-flight people HATE ISS, I think at some level they know that the point of HSF is to get glory by going higher and farther and anything which is 'routine' lacks glory, even though it may be necessary to do the next glorious mission, fortunately less short-sighted people actually get to make most of the decisions. Personally I'm rather indifferent to human-space-flight, at least at the current costs, funds should be directed to technology development until the ongoing costs of these missions and campaigns fit within the current budgets for HSF.

I'd been discussing the NASA HAVOC mission and the general concepts around habitation of Venus over on the New Mars forums. Generally I think people highly OVER-RATE the hard-surface of Mars (or elsewhere ware in space), for any kind of initial settlement mission it provides only two thing, normal force and radiation shielding if you can get under it. On Venus the lack of normal force means you need to hang under a buoyant balloon, this is a well established technology and simply means that every habitat must carry some parasitic mass fraction of balloon and lifting gas, it is likely to be less then the parasitic fraction to land things on Mars. The radiation issue is moot for Venus as you have Earth-surface levels of radiation in the clouds due to the atmosphere above, to match that on Mars the habitat has too be buried which requires Regolith moving equipment. It is not practical initially to mine any body for any kind of raw metal that would be usable for building, that takes enormous equipment, infrastructure that is nearly global in scale and lots of fossil-fuel energy here on Earth utilizing the optimum ore deposits discovered over centuries of prospecting. Rocks are simply not a good feedstock, here on Earth EVERY industrial process benefits from operating on a gas or liquid rather then a solid, given that it is inevitable that atmosphere will be the only effective feedstock for industry on both Mars and Venus until populations are into the tens of thousands. Both atmospheres are broadly similar in composition and have CHON elements in similar ratios, Venus atmosphere has 2 orders of magnitude higher density and it's Hydrogen is concentrated in a defined layer which will make collecting it somewhat easier. In addition Sulfur and Chlorine can be obtained in the Venus atmosphere at trace levels which have industrial uses. Overall the extraction of water and breathable air, and plastic feed-stocks looks to be broadly similar on both planets. The presence of acidity is negative for Venus but it is again a highly OVER-RATED, conventional materials on Earth hold acids of the concentrations found on Venus all the time as part of our normal routine industrial processes. Simple Polyethylene plastic is highly resistant and should serve adequately as a skin-coat on every exposed surface. A person exposed to Venus atmosphere at the tops of the cloud layers would need to have a respirator mask both for breathing and to protect the mucus membranes from irritation, but the skin is not immediately burned by such diffuse droplets as some people wildly speculate. A plastic bunny-suit would be desirable for longer term work, this is comparable to the level of protection needed when spray-painting a car here on Earth and it pails in comparison to the equipment needed to go out on to the surface of Mars. Temperature and Pressure being at life-sustaining, and indeed life-optimum levels at the target altitude on Venus removes HUGE difficulties in the design, construction and maintenance of the habitation spaces being contemplated for Venus as compared to Mars. On Venus in the event of fire it would be practical to sound an alarm don small breathing-masks littered all over the habitat at WWI speed and vent the atmosphere, a move which would kill every person not in a space-suit on a Mars colony. In all likelyhood the construction of new habitats on Venus by simply building a scaffolding between two existing habitats and tenting it over with plastic and breathable air would be comparable to building suspension bridges or high-rise buildings here on Earth, safety nets and safty lines are all thats needed and the fact that your 55km above Venus matters not a bit. The high difficulty of Mars Entry-Decent and Landing which promise to eat up large mass fractions even if they can be scaled up to the sizes necessary to get reasonable sized habitats to the surface. Venus with it's higher atmospheric scale height, lower gravity and lack of a solid surface is by far the Easiest EDL in the inner solar system, and that includes Earth. On Venus an inflatable decelerator will bring a vehicle down to sub-sonic speeds well above the target altitude at which point balloon inflation will halt the decent, decelerators can be deployed before entry has been committed too so this leaves only one simple system that is life-critical, Martian EDL requires a half dozen critical systems to work during EDL, up to and including not putting the landing-legs on excessively large rocks at the last second. The largest detriments for Mars colonization are the long transit times and radiation experienced in transit, this is really the Mars Akilles-heel, we do not have ANY mitigation or control of GCR and the dosages will be too high on a Martian mission. Transit in space is the worst for GRC, but Mars surface continues to expose crea to half the in space dosage. Venus clouds bring dosages down to nearly Earth-surface levels leaving only the transits as windows of radiation exposure. Take these two fairly representative trajectories from NASA http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Venus&mission_class=roundtrip&mission_type=rendezvous&LD1=2015&LD2=2025&maxDT=2&DTunit=yrs&maxDV=9.0&min=DV&wdw_width=-1&submit=Search#a_load_results http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2015&LD2=2030&maxDT=4&DTunit=yrs&maxDV=7.0&min=DV&wdw_width=-1&submit=Search#a_load_results The Delta-V is nearly identical for purposes of apples-2-apples comparisons so same initial mass of rockets in LEO to get transit vehicles their and back again, we expect to go down to the planets in some other mission-specialized vehicle and return in a small capsule to get back in the transit vehicle and return to Earth. For Venus we have 128 and 96 day outbound and inbound transits, total 224 day. But on Mars the outbound transit is bigger then the whole combined Venus transit at 336, and then the inbound is 320, total 656 days! Worse the 336 day surface stay on Mars will effectively expose crew to 168 days equivalent GRC dosage bringing the total up to 824 days equivalent, a multiple of 3.67 over the Venus mission. In addition the total mission duration for Mars is almost exactly 1 whole year longer at 2.72 vs 1.88 that's a whole years worth of food and supplies needed. NASA is only now looking to look at do 1 year stays on the ISS now that 6 months has become operationally routine. Outside the radiation belts they are willing to do 6-month flights to things like NEA and that is the edge of the envelope right now. Venus would be the next step after that, as the radiation dosage would be only a modest increase over the Asteroid. The Biggest downside to missions to Venus is return to orbit from the cloud level. This is not a complex problem though, it is one that is simply concurred with mass as we already know how to do this on Earth and the Venus assent is comparable. Considering that many hard-core Mars advocates now don't even want to bother bringing people back from Mars this would by their own logic not be necessary on Venus either and the largest down-side to Venus would be off the table. Not that I support that kind of one-way silliness mind you.