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The HL-20 weighs only 17 tonnes, putting it in the range of a Delta-IV medium. Further, the eight-crew requirement only allows for astronauts sitting upright. Orbital Sciences has modified the design to accomodate a flight crew of two and three astronauts, allowing the astronauts to recline to a horizontal position as they return from a long-duration space mission.
The human body has a certain volume. Only that volume is required for the crew compartment. That volume can be accommodated in various configurations, upright and supine, but the volume does not change. A design that provides for 5 astronauts when it used to accommodate 10 in the same volume is just inefficient.
The Delta IV Medium can lift 8.6 tonnes to a 185km orbit at 28.5? inclination. I interpolate that to 5.1 tonnes to a 407km orbit at 51.6? inclination. This is much lower than 17 tonnes. The Delta IV Medium+(4,2) can lift 11.7 tonnes to 185km orbit at 28.5?, the Delta IV Medium+(5,2) can lift 10.3 tonnes to that same orbit, and the Delta IV Medium+(5,4) can lift 13.6 tonnes to 185km orbit. The Delta IV Large can lift 25.8 tonnes to 185km orbit at 28.5? inclination but I interpolate that to 17 tonnes to 407km orbit at 51.6? inclination. The Atlas V 551 can lift 20.050 tonnes to 185km orbit at 28.5?. That means you need a Delta IV Large to lift the HL-20 to the ISS.
An efficient and cost effective OSP will keep operational cost to a minimum. We don't need yet another white elephant. The Atlas V 401 can lift 12.5 tonnes to 185km orbit at 28.5? inclination, which I interpolated to 8.25 tonnes to an ISS orbit. That must be retained as the limitation. Remember that an Atlas V 401 cost $77 million in 1998 dollars. The Soyuz-TMA spacecraft can carry 3 cosmonauts to the ISS and the Soyuz FG launch vehicle only costs $50 million in 1999 dollars. Cost effectiveness and competitiveness demands it.
The Soyuz-TM masses 7.150 tonnes and can accommodate 3 crew for 2.3833 tonnes per crew member, the Soyuz-TMA masses 7.250 tonnes for 2.4167 tonnes per crew member. These have 14 days of life support and are made with metal hulls and tanks. You should be able to fit a 4-crew OSP with composite materials and 48 hours life support on an Atlas V 401.
The X-38 was developed from the HL-20 as a smaller version. NASA could pay for construction of a still smaller one. NASA's requires do state it "shall provide rescue capability for no fewer than four ISS crew". The HL-20 specifications accommodate 2 flight crew plus 8 passengers for a total of 10 astronauts onboard. The HL-20 is way too big. Since it would require a Delta IV Large to launch it, the launch vehicle would cost $170 million per launch. That makes it way too expensive. You are also falling into the trap of believing that if it hasn't already been done, it can't be done.
The Leonardo Multipupose Logistics Module masses 4 tonnes and can carry up to 9 tonnes of cargo packed into 16 standard space station equipment racks. That is a total of 13 tonnes launch weight. The 2-crew cockpit version of MAKS can carry 7.0 tonnes to the ISS or 3.6 tonnes if the airlock is carried. Perhaps it is simpler to carry fewer equipment racks per launch. The maximum the Shuttle can carry to the ISS is 16.050 tonnes, so anything that tries to carry the current logistics module would be about as large as the current Shuttle. Adapting to a smaller shuttle means fewer equipment racks per launch and more launches.
Progress-M can carry 1.340 tonnes of equipment and supplies, and 1.200 tonnes space station propellant. Progress-M1 can carry 2.230 tonnes of cargo of which a maximum of 1.800 tonnes is equipment and supplies and a maximum of 1.950 tonnes of propellant.
Ending Soyuz/Progress production might be a blessing for the Russians, too. More funding can be transferred from production to R&D ... More R&D is needed before we can proceed with a MAKS / Spacecab
Good point. Once MAKS is operational then Soyuz/Progress could be retired. I still think it is a good idea to maintain crew and cargo transport with at least 2 different systems in different countries, but Russia only needs one. Once OSP, the last EELV, and the European cargo craft are operational, as well as MAKS, then the American Shuttle can be retired. Retiring the Shuttle could direct finds into an America medium size shuttle of the size of MAKS.
we need an American Soyuz and Progress.
My suggestion is for an American OSP to provide an alternative to the Russian Soyuz, but encourage the Russians (possibly with European assistance) to continue Soyuz as well. I think Columbia has demonstrated the need for second system as a redundant backup, and the Russians want something independent of America. The OSP could provide some small cargo transport capability by removing seats, but not on the scale of a dedicated cargo craft like Progress. Let Europe provide the alternate cargo craft. The current NASA requirements to call for a cargo craft, possibly built as a second vehicle, but I am asking why America should do it all itself when Europe wants to get in the game and provide major launch capability to service ISS. Europe has even started development of an Apollo-style capsule as a manned vehicle. I think we don't need more than two systems to meet each requirement: let Russia and America provide crew transport, Europe and Russia provide cargo. Modules can be delivered via Proton, Atlas V and Delta IV.
There's got to be a better system than democracy! This short-term, near-sighted, to-hell-with-it-as-long-as-I-get-back-into-office-next-election kind of mentality is the scourge of today's society. It's remarkable that such a system has produced any progress at all since it replaced monarchies in the western world!
So pardon me if I hold you the American voter accountable for the actions of your elected officials. It is up to you to continue to push them to do the right thing.
*Shaun is Australian.
--Cindy
I apologize for the rant. I didn't realize Shaun was Australian. I shouldn't criticize American voters when the person calling for an alternative to democracy isn't an American. Still, average citizens can make a difference. I heard it said that democracy is advanced citizenship. You do have to get involved.
Part of the reason my education proposal was listened to was that I was a member of the chamber of commerce, a member of the chamber's federal-provincial finance committee (which produces the chamber's critique of government budgets), a former instructor at the local college that the current governing party likes to support, and a member of the local resident's association. I was later elected president of the associated community organization, the one which receives funding. I also live in a riding that always elects a representative for that party. These things tend to get politicians' attention. One reason I submitted my education idea was that the premier made an election promise to reduce post-secondary tuition, but didn't say how he would do that. It turned out he wanted to raid the surplus from the government owned insurance company to subsidize universities and colleges. Since that insurance company has a legislated monopoly on personal vehicle insurance in this province, the voters screamed "no". My idea gave him an alternative without costing any money at a time when he was scrambling for a way out.
My letter to the federal government included the education plan and how the provincial government was implementing it, so that showed my suggestions are successful. Politicians like individuals who are successful with politics. But another reason was that I sent a printed letter, not an email. It takes more effort to hit the print button and put it in an envelope that just to send an email. Very few people bother to write to their representative or senator. Consequently politicians take written letters very seriously.
tim_perdue, I was quite serious. I would want to push members to write their congressmen more so than to advocate a particular point of view. However, to be more effective we should have a unified message. The steering committee would want to decide any official Mars Society position, but we on this board could decide what we want to do. Perhaps we should debate a good over-all plan.
I would argue that as long as the ISS is international, and includes Europe and Russia, then the American plan should fit with and complement assets of the ESA and Rosaviakosmos. That means maintaining Soyuz and Progress spacecraft, and ESA producing a large expendable cargo spacecraft to be launched by Ariane 5. America should complete and maintain the EELV launch vehicles (Atlas V and Delta IV), build a 4-person Orbital Space Plane, and proceed with Project Prometheus. If Russia builds MAKS then the current Shuttle can be retired. For the long-term we need a fully reusable launch vehicle, but perhaps only something the size of MAKS; large cargo can be lifted with an expendable launch vehicle. We need to go efficient before we go big. Continued research into hypersonic air travel will help, even if only to produce a mothership for something like Bristol Spaceplane's Spacebus.
There's got to be a better system than democracy! This short-term, near-sighted, to-hell-with-it-as-long-as-I-get-back-into-office-next-election kind of mentality is the scourge of today's society. It's remarkable that such a system has produced any progress at all since it replaced monarchies in the western world!
I am in favour of democracy. Although I advocate an international system that permits and tolerates diversity in national governments, I am proud that Canada is a democracy. After all, it is part of the principles of democracy to permit the people who live in a country to decide what values and systems they want to establish to govern themselves. If they choose a bad system, it is not up to the citizens of some other country to bail them out. We can advise and suggest, but in the end the citizens of any country must live with the decisions they make. A dictatorship is an easy and potentially efficient system of government. It can make quick decisions and doesn't have to pay for a congress or parliament with the salaries and expenses of all its representatives not to mention their pork barrel projects. However, the citizens literally risk their lives on the benevolence of the dictator they select. Then how do you get rid of him/her if the dictator turns out to be a tyrant. It's a high-stakes game with the lives of the citizens.
Furthermore, the citizens don't have to think or make decisions with a dictatorship, so it's easy. Unfortunately many people in a representative democracy think they don't have to think either. Surprise! You do. I blame the voters who put a bad representative in office. Many people in Canada are apathetic and feel they can't do anything. I receive a letter every fall from a Member of Parliament asking me what the focus for the federal government should be from a Western Canada point of view. It is a form letter he sends to all constituents who bother to correspond with him. This year I sent a long, multi-page letter. One of the points was to keep the focus on the budget, maintain the surplus and pay off the debt, don't give billions of dollars to municipal governments but focus on national projects, and don't give federal money to post-secondary education. I included a copy of the letter I sent to the provincial education minister which detailed how to reduce tuition cost without costing tax dollars, and pointed out how most of the points of that letter are being implemented. I also wanted the GST rebate system replaced with a reduction in personal income tax. I made a big deal of holding elected representatives accountable to the voters, and wanted municipal bills paid for by municipal taxes so voters could hold municipal officials accountable at election time. The same for provincial bills. Not everything in my letter was done, but there was no new federal money for the education system, the promised hand-out to municipalities was cancelled, and the budget made a big deal of making the government accountable to voters. A group of MP's of which my representative is a member pushed for cancellation of the GST rebate system, although they didn't succeed. Although there was a total of 25 billion dollars in new federal spending over 2 years, it's not as bad as it was going to be. My letter did have an impact on the federal budget for this country.
By the way, when I sent my letter to the provincial education minister a couple years ago, his executive assistant said he had all the deputy ministers do a formal study of my letter. Then I got a very pretty letter from the minister himself thanking me for the letter and stating which points he intended to implement. One of those points was included in the premier's State of the Province address that year. Nobody mentioned me, the elected officials are taking credit for my ideas, but the important thing is that it's getting done.
So pardon me if I hold you the American voter accountable for the actions of your elected officials. It is up to you to continue to push them to do the right thing. If your senator or representative starts pushing for short-term, near-sighted projects then give him hell. If he doesn't listen to you then raise hell in your constituency. Representatives can get panicky at demonstrations and rallies in their own riding regarding a position they hold on a bill. Send a written letter to your representative and senator asking what they are doing to ensure NASA builds a good replacement for the space shuttle; one that is safe, permits frequent visits to space, and has a low operational cost. Ask them whether they intend congress to pay for the up-front cost of such a reliable system. If they don't reply then you can start by raising hell on this message board, but you will have to get more involved locally.
I doubt that chlorine bleach is the best choice for regolith simulant. Some chlorine and sodium probably combine to form salt. However, some chlorine will be tied up in the mineral chlorapatite, and sodium in albite (a constituent of feldspar). There may be a small quantity of sodium in a type of clay called corrensite, an iron form of smectite.
I would point you to the soil page on the Winnipeg chapter web site to see the results I have so far of my analysis of Mars regolith. However, it doesn't include clay and published results from the TES instrument on MGS indicate roughly 12% clay. Clay is a much more complex mineral than something like feldspar so the CIPW analysis is more difficult. I am still hoping to get a local geology professor to help me with that.
I kind of chuckled at your discussion of temperature. It has gotten as cold as -40?C outdoors here in Winnipeg, on the coldest day of the year and only once every few years. Right now it is -23?C and the weather channel predicts a high of -18?C (0?F). That's real temperature, not wind chill.
There are several factors the author of this article has left out. First and foremost is the fact that shuttle development was started in the early 1970's. This was the end of the Apollo program. Only 8 years had passed from John F. Kennedy's speech, at which time Mercury astronauts were flying on top of Redstone ICBM's, to men walking on the Moon. People honestly believed that the core of the international space station would be an upgraded Skylab module. The timeline was construction of a moon base during the 1970's and 1980's, a space shuttle and space station by 1980, and manned mission to Mars by 1990, latest. The great advances in technology from a humble Redstone to a Saturn V brought the expectation of highly efficient and routine rockets for the next generation vehicle. I remember seeing NASA's announced contenders for space shuttle designs. The leading design was a two stage to orbit, fully reusable launch vehicle. The booster stage would be a lifting body with wings, a single pilot and jet engines for a powered landing. The orbiter would be a pure lifting body. Although this design had greatest safety and the lowest operation cost, its development cost was more than congress was willing to pay.
NASA then decided to develop a simple space taxi. This would carry astronauts and just a little luggage to a space station. This small spacecraft was called the space shuttle, but congress cut funding to NASA again. NASA then had to get funding from the military. The military wanted a vehicle to service their new K7 spy satellite. The crew taxi was expanded to include a cargo bay designed to surround the K7; that created the space shuttle we know today.
Maintenance cost of the current shuttle was never supposed to be as high as they are now. It was designed to fly 100 missions per orbiter, with a total of 400 missions by 1990. The shuttle was supposed to be retired at that time and a second generation shuttle would replace it. The engines were not supposed to be serviced as often as they are now. It was intended to fly with minimal maintenance between flights; that was the point of a reusable spacecraft.
The point of replacing the F1 with SSME engines was not a slight against Werner Von Braun, it was an attempt to replace the giant Saturn V with something new, modern, efficient, and more compact. At the time the final shuttle design was announced it was a great disappointment for (then young) space fans such as myself. It was the design with the lowest development cost short of plopping an OSP on top of an expendable rocket, and it was the least safe. No one I know of considered use of solid rockets safe for human flight, much less a segmented rocket strapped to the side of a liquid hydrogen tank. Recovery of the SRBs was clumsy and expensive, the shuttle was supposed to get away from ocean recovery. Worst of all, the external tank was not reusable.
A critical view with today's knowledge would say that a double pointed external tank such as the Russian MAKS is much better than a cylindrical tank because it positions the main engines directly beneath the center of gravity. The asymmetry of thrust vector is also a good point (SRBs pointing in a slightly different direction than the SSMEs), and the single engine system of the MAKS does resolve that. The innovative use of kerosene/LOX or LH2/LOX by a single RD-701 engine is a remarkable achievement, but just wasn't available when the shuttle was designed. MAKS was designed in the late 1980's.
Finally, don't blame NASA for developing a single launch vehicle that is jack of all trades and master of none. They originally intended a space plane that would carry astronauts to the space station. Cargo would be delivered by a separate single-stage-to-orbit rocket that would splash down in a custom built circular pool at the cape.
Actually, you don't have the same amount of matter. Fusion, and even fission, convert a small fraction of the mass of atomic nuclei into energy. This can be reversed. Fermilab has a giant cyclotron call the Tevatron (Terra-Electron-Volt cycloTRON). They accelerate protons to a fraction of the speed of light so there is more energy in their motion than their mass, and then they slam the protons into a tungsten foil. The protons punch through, although their path is deflected a bit; the straight beam becomes a cone. However, they are slowed by the impact and the energy of their motion is instantaneously converted into a new subatomic particle. There is no control over which particle is created; any particle that requires that much energy may form. They use magnetic fields to sort the resulting particles and keep the antiprotons.
There is a second means of converting energy into mass. Focus a very high energy laser on an electron stream as it impacts a tungsten foil. It will create an electron-positron pair. The energy from a single photon from the laser plus the energy of the electron's motion must be enough for the mass of both the electron and positron created. Focusing the laser on an electron is not enough; the energy to mass conversion can only occur in the nucleus of an atom. Focusing a laser that intense on a nucleus without the electron tends to cause fission. A proton could emit a positron becoming a neutron, or a neutron could emit an electron becoming a proton. Either way, that changes the atom to a different element. Would the new element be stable, or undergo radioactive decay?
You will notice with each of these matter- to-energy conversions, charge is maintained. You either move a static charge or create both positive and negative at the same time. The total mass-energy of the system is also maintained, but energy is converted to mass using E=Mc^2. The input energy required is slightly larger than the energy to create mass; for example if you use the laser and electron method to create an electron-positron pair then the new particles must have enough energy to get out of the nucleus or they will just fall back in and be destroyed. That means the new electron and positron will have high speed. This means the energy-to-mass conversion is less than 100% efficient, and tends to increase entropy.
That is a very intriguing offer. However, any salaried job is based on the work done for that salary, not any work done prior to hire. That means if I just give my idea away to your company then I would not get a secure, well paid job. Furthermore, as you said the process to manufacture the chip MAY be available. I would be a fool to just give away my idea without any secure method of compensation. As for the schematic; my idea deals with the transceiver. I still need a communications engineer to work with me to interface this to a cell phone or cordless phone. That sounds like another excuse to avoid paying me for the invention. If there is some way to get your employer to sign a non-disclosure then I would jump at the chance. I would give them first right to purchase the rights to the device. I would offer to pay for custom chip manufacture, but I expect it would cost more than I can afford.
Interesting idea, and Bristol Spaceplanes has very ambitious plans. Their Spacecab is supposed to carry a total of 6 people: 2 crew plus 4 passengers. Its mothership would fly on turbojets to Mach 2, then rockets to Mach 4 before separation. However, their Spacebus would have 50 seats and its mothership would fly on turbo-ramjet engines to Mach 4, then accelerate on rockets to Mach 6 before separation.
In the 1970's I heard the SR-71 could fly at Mach 3.6 but today they are saying it can fly "in excess of Mach 3" and aren't saying exactly how fast it can go. The XB-70 Valkyrie was supposed to fly Mach 3 and it was a bomber with 450 tonne loaded take-off weight. The Spacebus mothership would have a 400 tonne take-off weight. The double-delta wing design looks more like a Concord than a Valkyrie, but the Concord cruises at Mach 2.2 and has a maximum take-off weight of 185 tonnes. I call the Spacebus Booster quite ambitious.
Then again, the Valkyrie was developed 4 decades ago.
This is a curious article, with Russia providing the US with nuclear fuel, and this is for Plutonium-238. I know Uranium-238 is depleted Uranium, so the question was what is Plutonium-238. The answer is it's used for radio-isotope batteries, not a nuclear reactor. I found the original ITAR-TASS news article in English.
Perhaps you're right. I was saying the same thing until the announcement about Prometheus. However, that initiative is focusing on nuclear electric propulsion for interplanetary spacecraft.
I am also interested in Mars regolith simulant. I have ignored the question of life, and left that for others to debate. My interest is what the mineral composition of Mars regolith is so I can make a simulant. I have been working on a CIPW analysis, and trying to get geology professors to help me. However, one of the papers I have accumulated includes creation of the superoxides by exposing regolith simulant to UV light under Mars atmospheric conditions. The superoxides are created. Does it explain everything in the biology experiments? I don't know and that isn't my concern. My concern is to identify the minerals with sufficient confidence to create a simulant that can be used by someone wanting to build a Mars rover test facility, or a Mars Garden.
Shaun, could you send to me a copy of the papers you are referencing?
I have an elemental comparison of results from Viking Lander's X-ray fluorescence and Mars Pathfinder's APXS instrument, against JSC Mars-1 and Santiam Mars-2. The last simulant is volcanic cinders from a Mars Society member. The simulants are too high in aluminum and titanium, too low in iron and magnesium, and are missing sulphur and chlorine. JSC Mars-1 has too little sodium; Santiam Mars-2 has too little potassium and phosphorus. I would post the results, however I can't see how to post a table.
I believe the manned OSP can remove small articles, such as single rack-mount tray. Remember I suggested 1, 2, or 3 seats of the 4-astronaut OSP could be replaced with cargo for launch or return. The current shuttle would be needed to replace an entire rack frame. NASA's current plan is 3 fold: maintain the remaining shuttles, build an OSP as soon as possible, and develop a replacement for the shuttle. The Russian MAKS-OS is a medium size shuttle that could replace an entire rack from the Science module, although not an entire station module. The number of flights required for a medium size shuttle would be so low that there is no need for 2 such systems. In fact, with a manned OSP that has the ability to carry 4 astronauts or small quantities of cargo up and down, an expendable cargo supply ship, medium lift (now called heavy) expendable launch vehicles, and just one medium size shuttle, there would no longer be a need for a full-size shuttle. For me that is sad because I would truly like to see Shuttle-C as a true heavy lift launch vehicle, and it is only economical as long as you maintain shuttle infrastructure.
Orbital Space Plane Program Level ? One Requirements Mission Needs Statement
The vehicle(s) and associated systems will support U.S. ISS requirements for crew rescue, crew transport, and cargo.Requirements
1. The system, which may include multiple vehicles, shall provide rescue* capability for no fewer than four ISS crew as soon as practical but no later than 2010.
Not to worry, these requirements do include cargo but permit multiple vehicles. Since the ISS is the *INTERNATIONAL* Space Station, I would simply let Russia continue to provide Progress cargo spececraft, and let the European Space Agency provide the new one. However, the OSP requirements do include a cargo spacecraft.
I would suggest an expendable vehicle that can be launched by another ELV, say another Atlas V 401, then dock with the ISS. There is no need for the cargo craft to be reusable, or have redundant control systems. It could use a commercial off the shelf radiation hardened single board computer. It would need a pressure vessel to hold its cargo, and a docking hatch compatible with the ISS. It would require maneuvering thrusters and propellant tanks, a targetting radar system, and communications with the ground. That is all, it wouldn't need life support or any form of re-entry system.
Here are some statistics for you:
The final proposed configuration of X-38 would have used the same Thermal Protection System as the Shuttle, would have carried 7 astronauts and no cargo, and would have had a total mass including its expendable de-orbit module of 14 tonnes. That is 2 tonnes per astronaut. Soyuz-TM has a mass of 7.15 tonnes, includes 14 days of life support, has propellant for a total delta-V of 360 m/s, and carries 3 cosmonauts. That is 2.38 tonnes per cosmonaut.
This means a new OSP to carry 4 astronauts should have a total launch mass of 2 tonnes per astronaut. Expect it to fit within 8.25 tonnes including a small suitcase per astronaut. Airlines permit a carry-on bag to be 23cm x 40cm x 55cm (9"x15.75"x21.65") and mass 10kg (22 pounds). One such carry-on bag per astronaut would mass a total of 0.04 tonnes. I think this is quite reasonable. The Atlas V 401 can lift 8.25 tonnes to ISS.
Marcus Lindroos has a scathing review of the economics of OSP.
Marcus Lindroos' criticisms of OSP are based on reduced cargo capacity. But why would you want to send cargo on a manned vehicle? Food and personal hygiene products are consumable, and waste can be de-orbited and burned up in an expended cargo vehicle. Cargo can be delivered via a high acceleration vehicle that is more propellant efficient but would turn astronauts into spam-in-a-can. Cargo does not require as much redundancy: if you have a loss rate of 1 vehicle in 50, while backup systems would improve survivability at a cost of say 25% reduction in cargo mass, then you would be better off letting the 1 in 50 vehicles be destroyed and simply replace it with another launch. You can't afford to do that with a manned vehicle. That means you are better off separating cargo from crew. Build the OSP to carry 4 astronauts and 1 suitcase of personal items each; that is all. Send food, water, spare parts, tools, scientific supplies, etc, on a separate cargo vessel. Keep EVA equipment on the space station.
If an entire equipment rack needs to be swapped out we still have the current space shuttle. No one said the shuttle is completely obsolete. We need a fleet of different vehicles for different purposes. A dedicated space taxi to transport crew will reduce cost and permit a greater number of crew rotations, and hopefully a greater number of crew at one time on the station. A dedicated expendable cargo vessel such as the Russian Progress will keep the station supplied at an affordable cost. New modules can be delivered via expendable rockets such as Proton, Angara 5, Atlas V 551, or Delta IV Large. The shuttle can be used for the rare times we need to swap an entire scientific rack, or use CanadArm for assembly or maintenance work that the station's CanadArm2 cannot reach.
MAKS-OS is capable of lifting 7.0 tonnes in its basic manned configuration to an altitude of 400km at an inclination of 51?. It is able to lift 8.2 tonnes to the same orbit if unmanned. The manned configuration has a 2-seat cockpit and no docking unit. MAKS-OS/TMS-1 has a docking unit and pressurized module with 4 more seats. MAKS-OS/TMS-2 has the docking unit but the remainder of the cargo bay empty for cargo; useful for re-supply missions, it can carry 3.6 tonnes.
MAKS-M can only carry 3.5 tonnes to the same orbit, and that is with no crew capability at all. The significantly reduced cargo capacity and inability to carry crew make it appear much less valuable than MAKS-OS. You have to look at the cost per tonne to orbit. Two flights of MAKS-M are required to match the lift capability of MAKS-OS, so would saving an expendable external tank reduce cost by as much as the total for a second launch?
In fact, for cargo you should look at the MAKS-T. Replacing the reusable orbiter with an entirely expendable second stage lifts 17.4 tonnes of payload to the same orbit. Disposing of engines, avionics, etc, would increase the per launch cost, but would the increased lift capacity be worth it? What matters is the cost per tonne to orbit.
I found some information on Thermal Protection Systems. The Shuttle uses a combination of systems; the grey areas on the tip of the nose and leading edges of the wings are reinforced carbon-carbon. These can withstand 2960?F heat and are extremely durable, but heavy. The black tiles are LI-900, also know as Reusable Surface Insulation or RSI tiles. They can withstand a maximum of 2300?F, but they are silica fiber foam coated with black glass glazing and glued to Nomex felt which is glued to the aluminum skin. White tiles have a white glass glazing and can withstand up to 1200?F. Low temperature upper areas have quartz fiber quilts for up to 1500?F, or elastomer (plastic) coated Nomex felt for up to 750?F.
The super alloy honeycomb (SA/HC) metallic Thermal Protection System (TPS) intended for X-33 was an Inconel metal honeycomb sandwich top plate held away from the skin with titanium stand-offs, and a folded foil bag of insulation. Inconel is a nickel alloy: 44.5% nickel, 20-24% chromium, 10-15% cobalt, 8-10% molybdenum, 3% iron, and some trace metals. It is heavy and its melting temperature is lower than titanium, but it retains its strength at high temperature. SA/HC metallic TPS tiles made with Inconel have a maximum operational temperature of 2000?F.
The Advanced Metallic Honeycomb (AMHC) thermal protection system uses PM2000 metal honeycomb sandwich top plate and Internal Multiscreen Insulation (IMI) with a thin titanium facesheet on the bottom. PM2000 is a form of stainless steel called Oxide Dispersion-Strengthened (ODS) alloy: 73.5% iron, 20% chromium, 5.5% aluminum, 0.5% titanium, 0.5% Y2O3 (yttrium oxide). AMHC tiles have a maximum operational temperature of 2200?F.
AMHC can operate almost as high as the black silica tiles on Shuttle. This permits reasonable operation and safety during re-entry. The greater durability of a stainless steel outer skin that is attached with metal fasteners rather than fragile silica fiber foam glued on felt means the heat shield will stay on. LI-900 tiles are typically 6"x6" in size, and AMHC was designed for 12"x12" tiles. However, I feel large panels would be far safer and more economical. Each gap between tiles is a potential entry point for hot plasma, and potential breaking point to lose a tile. Small tiles would only have one Allen screw or boss with quick release spring at each corner. A large panel could have multiple fasteners over its surface. If one fastener breaks loose on a large panel the remaining fasteners can keep it in place. Furthermore, each AMHC tile require a PM2000 side wall and a strip of Nomex felt between the tile and aluminum skin at the tile edges. Large panels reduce the number of edges, therefore reduce the quantity of sidewalls and felt strips; this reduces weight. Don't you love it when a weight reduction increases safety? Large panels also mean fewer panels to manufacture and install, so less labour which translates to lower cost.
There are 3 U.S. supplied pressurized mating adapters in the final configuration, one that connects the Zarya to Unity, the other 2 are docking ports. Those are just the U.S. docking ports, the Russian part of the ISS has 2 more: one at the end of Zvezda (intended for a Progress cargo craft), and the other on a Docking and Stowage module that is connected to Zarya. The last module is the docking port for Soyuz spacecraft, which will replace the current Docking Compartment. I don't know if the Docking Compartment can be used as a 5th docking port once it is moved to the Universal Docking Module. The bottom line is that 2 OSPs and a cargo craft are well provided for.
By the way, the European Space Agency had made a big deal at one point of developing a cargo craft to be launched on an Ariane 5 rocket. I assume they're still working on it.
Remember that the Atlas V 401 in 1998 dollars has a launch cost of $77 million. The Delta IV Large costs $170 per launch in 1999 dollars. If you can launch two 4-crew OSP vehicles for $154 million plus OSP processing and mission control, as apposed to one 7-crew OSP vehicle for $170 million plus the same OSP processing and mission control costs, then which is better? Let's see: 8 astronauts for $154 million vs 7 astronauts for $170 million. Even if the bottom line cost were the same, then the smaller vehicle gives you the flexibility of sending just a small crew, or rotating just 4 astronauts at a time.
By the way, NASA may want a completely independent crew transport capability, but Europe and Russia may want something else. In fact, Europe and Russia both want a transport capability completely independent of the United States. That is why ESA is talking about launching Soyuz spacecraft from Kourou. (SpaceDaily)
I support the OSP. A 4-crew vehicle would be an excellent addition to the ISS. Remember, the European Space Agency is working with Russia to maintain Soyuz. With both a Soyuz capsule and a 4 astronaut OSP that provides a total crew compliment of 7; which is the original design for ISS. Furthermore, a well designed 4-astronaut OSP could be launched on an Atlas V 401 at a cost of $77 million per launch for the rocket. A reasonable estimate for a 7-astronaut OSP would be the last design for X-38 with its de-orbit module, which would require a Delta V Large to lift it at a cost of $170 million for the rocket. A 4-crew OSP would be a very economical design. Furthermore, a vehicle designed to carry just 4 astronauts and no cargo at all could have 1-3 seats removed and replaced with duffle bags to carry cargo. That would fulfill the cargo requirement.