RECYCLING ROCKET EXHAUST

This is a concept for lunar industrial development.

Concept description

It seems technologically possible to produce a space based solar power (SBSP) system for Earth from lunar materials, but the economics cause difficult constraints and the current geopolitical situation is very difficult.

• Investment in costly infrastructure is necessary to take full advantage of the potential low cost of achieving orbit from the moon. Many launches to orbit for a large customer are necessary to pay for the infrastructure. So, committing to infrastructure for launching to orbit and the building of SBSP should be a package deal. One or the other by itself or half-way measures do not make much sense.
• Industrial production of oxygen on the moon with depot storage should be a first step. Then depots orbiting the Earth and moon. This technology is difficult, possible, and certainly possible to get wrong. Then there is the recycling of rocket exhaust into rocket fuel by having the acceleration to orbit on Luna occur in a tube that is horizontal along the equator with the tube in a semicircular cross section ditch in the lunar regolith with an air-lock door at the downrange end of the tube. The air-lock door must be closed after the rocket leaves the tube to allow the rocket exhaust to be captured by vacuum pumps. The regolith on which the tube rests should be built up enough so the craft exiting the acceleration tube misses any landscape features. The rocket flies free down the center of the tube with guidance from RFID tags mounted on the walls. The guidance of a free flying rocket would need to have about the accuracy that is achieved in acrobatic formation flying of jet airplanes. Jet airplanes have routinely flown as close as three feet from wing-tip to wing-tip while in formation flying. This suggests that three feet clearance between the rocket and the tube walls can provide room in which the rocket can maneuver to avoid hitting the walls. The choice between rocket-sled cargo launching and free flying rocket is a matter of which technology is most easily verified by development of models on Earth.
• If acceleration in the tube averages about 30 meters per second squared then the tube on Luna needs to be about 48.3 kilometers (30 miles) long. I find "30 meters per second squared for 30 miles for orbital speed" easy to remember. A rocket-sled can use one of various deceleration techniques to use fuel recycling. A free flying rocket continues on in orbit to an orbiting depot where another tube would exist for providing delta v to deorbit and return to the moon with the deceleration rocket exhaust recycled to rocket fuel on the depot. For orbital stabilization the orbiting depot would need large, high specific impulse electric thrusters with low thrust to weight ratio which are possible with various technologies. The mystery to me is why these technologies have not been already employed, since they were all available since 1985. The low thrust to weight ratio for the orbital maintenance thrusters on the orbiting fuel depot would not be something people would strive to achieve. It would be a natural result of releasing a weight constraint in design and using every means possible to increase exhaust velocity.
• The horizontal acceleration of a rocket in a tube should start with electric acceleration of a movable launching pad for the first 4% or so of orbital velocity. The moving start of the rocket prevents the rocket exhaust from having too much erosive effect on the tube, prevents excessive pressure build-up behind the rocket, prevents the rocket from flying in its own exhaust, provides ullage thrust for the start of the rocket engines and a portion of mission delta v. A larger diameter section of tube to collect exhaust behind the launch spot may also be desired. Six feet larger in diameter than the rocket should be about the minimum diameter for the launching tube to provide the clearance to avoid the rocket smashing into the tube wall. Rocket scientists can calculate whether the tube needs to be larger at some parts of the tube to accommodate the volume of exhaust. As the rocket continues down the tube at increasing speed, the mass of exhaust gas deposited in the tube per unit length decreases. So, the diameter of tube needed to accommodate the exhaust gas decreases with distance traveled in the tube to where it is less than the diameter needed to avoid crashes into the tube wall.
• Recycling rocket exhaust provides a way of storing the electrical energy needed for launch of a cargo carrying rocket. The energy is stored as rocket propellant. That compares to the use of that amount of energy as electricity in the short time that it takes a rocket to accelerate to orbital speed, a task that is undemonstrated and, I feel quite confidant, would require much more expensive infrastructure.

Mining the building materials

Of course, remotely controlled equipment would be necessary to mine the moon; separate oxygen which is 44 percent of the moon's regolith; store oxygen in tanks; separate the regolith into constituents by electrolysis in a bath of calcium chloride, potassium chloride or potassium fluoride, with the potassium and chlorine or fluorine recycled; take the iron sponge from the anode of the electrolysis bath and purify it by a carbonyl process; form the iron and aluminum into pigs, alloys, and bar and sheet stock; form sifted regolith into sintered brick and fiber glass; build buildings, the orbital acceleration tubes, sheltered and shaded East-West roads and North-South roads, each type by its proper techniques; make the solar cells and ship products out. Astronauts doing any of those things on the moon by any means other than remote control simply could not be economically competitive. This is not a new idea. "THE MOON : Resources, Future Development, and Settlement" described remotely controlled equipment doing industrial tasks before astronauts arrive on the moon before I did and did a better job of it than I can. Eventually there should be enough infrastructure built up to be able to support human workers on the moon doing tasks suitable for human beings in vehicles with suitable life support systems and in buildings with recycling life support systems; not in space suits. When people come to the moon they should be called passengers, not astronauts.

• The carbonyl process: The reason for the carbonyl process in purifying (and perhaps extracting) iron is that it can separate the iron from the nickel that is naturally in lunar iron that comes largely from meteorites. Nickel carbonyl and iron carbonyl plate out of vapor at different temperatures. The nickel is needed to put a corrosion resistant coating on the inside of the corrugated silicon steel tube that catches the rocket exhaust.
• A zeroth step in building a SBSP system is verifying the technologies. Step 0.1 is committing to all that is necessary for the whole chain of steps to work and finally start producing revenue. Within step 0.1 there are agreements among nations to share the financing, engineering, hardware building, electrical power sales arrangements, and revenue.
• For high specific impulse, large, thrusters for orbital stabilization of the moon orbiting fuel depot, the reaction mass should be oxygen plasma since oxygen is readily available on the moon.
• Transportation: For East-west roads on the moon the pavement could be graded regolith or sintered and perhaps glazed bricks separated by sifted regolith. There could be an East-West awning over the road held up by a row of pillars and made of aluminum sheet or aluminized glass sheet or material of suitable alloy containing some proportions of aluminum, silicon, magnesium, calcium, titanium or whatever available material is found to be most economic for the use. The pillars would separate the Northern lane from the Southern lane. There could be solar cells for charging batteries or recharging fuel cells that are swapped, spent for charged, by passing vehicles.
• The vehicles might be walking vehicles (four or more legged) that wear space suits holding one percent of an Earth atmosphere pressure of nitrogen thus eliminating the need for a gas tight rotary seal around wheel axles that would otherwise be necessary to prevent wheel lubricant (and all other lubricants inside the space suit) from evaporating into the vacuum.
• Alternatively, wheels could be outside of the pressure containing suit and supported by magnetic bearings, instead of a typical greased axle bearing, with only electric wire connections to the inside of the vehicle. The key to economic remote controlled equipment on the moon is long-lived equipment.
• The North-South roads could be sometimes two lane roads with a wall between the lanes and an awning hanging out over the lanes on both sides of the wall and sometimes a three lane road with two walls separating the center lane from the Eastern lane and the Western lane. The two walls would support an awning covering all lanes. When the sunlight comes from the East, the Western lane would be used. When sunlight comes from the West the Eastern lane would be used. Where three lane stretches meet two lane stretches there is a provision for cross over as necessary to stay in a shady lane. Spurs going off to the East or West under Awnings would provide the battery exchange stations where the spent batteries are charged.
• Roads can be involved with bringing necessities to the tube construction area, such as sulfur to aid in sintering in a sulfur dioxide atmosphere. It would be possible to construct a solar power grid active in lunar day and lunar night by connecting distant spots on or near the 87th latitude North or South. Electric power by wire could flow from this grid following a road to where a fuel recycling depot is being built. If nuclear power is available at the construction site, a polar electric connection might not be necessary. Road construction could be delayed until necessary. If it is found to be most expedient to build the polar power grid and forgo nuclear power, then for three circumpolar points with always one of the three in sunlight, a road to connect point A to point B and point B to point C would be about 240 miles long. Nuclear power or no nuclear power there would be much construction activity before a 48.3 kilometer (30 mile) long tube to collect the exhaust of a rocket launch to orbit could be built.

Impacts of mining on the Moon

People have complained that so much industrial development would ruin the pristine nature of the moon but people need to dig to get the scientific truth of the moon's composition. Where there is soil dug up and pushed around for industrial development, it will be first photographed then analyzed as much as is necessary to get a good idea of the moon's nature. The opportunity for exploration will not be missed. There are more than 9,370,000 square kilometers of lunar surface. A few hundred thousand square kilometers reserved as parks here and there might be reasonable, but not the whole 9,370,000 square kilometers.

Political context

It is essential that peaceful use of the moon be guaranteed with treaties forbidding any weapon based on the moon or in space that would reasonably have potential for damaging targets on Earth. Treaties must include a means of verification by inspection with robots for the inspecting nation given access to a reasonable environment and electrical power sold at rates equivalent to what it costs the operator of an industrial establishment to provide this for its own robots. The plans for industrial establishments on the moon must not be allowed to be secret. It would be nice to get Russia and China to a situation in which they would cooperate with an international group of nations to everyone's advantage. There is precedent for the cooperation of enemies in the numerous treaties the U.S. signed with the U.S.S.R. and China in the past referring to the launching of satellites, the sharing of radio broadcast frequencies and the elimination of smallpox.

• With a war going on between Russia and Ukraine, there must be peace before we can have cooperation from these countries in providing SBSP to Earth. President Volodymyr Zelenski has been quoted as saying that Russia should not receive control of the Crimean peninsula in a negotiated peace. That is a proper negotiating position to start from but it seems unlikely that there will be a quick settlement that fails to leave Russia controlling Crimea. The administrative assignment of Crimea to the Ukraine Soviet Socialist Republic by the USSR would indicate that Crimea should be part of Ukraine. The history of Russian military forces fighting to control Crimea, the considerable number of ethnic Russians living in Crimea and the Russian military occupation of Crimea since February 2014 tend to suggest that it should be Russian territory. The Russian invasion of Ukraine is inexcusable and terrible. There have been terrible elements of Ukraine's response which is more likely to be excused because of Ukrainians defending their home territory. The significant point is that both sides need to stop fighting without regard to assigning blame.
• We have a situation in which Russia and Ukraine are enemies. It did not need to be this way but we cannot change history. Both Russia and Ukraine have Christian backgrounds and Christian teaching favors dealing charitably with enemies when possible. Proverbs 25:21 states: "If your enemies are hungry, give them food to eat..." Mathew 5:44 states: "But I say to you, love your enemies..." Romans 12:19 states: "Beloved, do not look for revenge but leave room for the wrath; for it is written, 'Vengence is mine'..."
• It may be difficult for people in Ukraine and Russia to imagine cooperating peacefully after the harm and destruction that has been done but if all that can be imagined is continuing war, war will go on for a long time.
• One does not need to believe Christian teaching to see that it could be a basis for these countries with a history of Christianity to reach a peace agreement acceptable to many of their people. Scriptures respected by the Jews predate the exclusively Christian scriptures on this point so Zelenski should pay attention as well.
• Things that a peace treaty might include would be: 1) an agreement to not seek prosecution for war crimes that may have occured in this invasion by Russia and defense by Ukraine 2) a return to their orriginal countries of anyone captured or deported to another place who is willing to return 3) interviews with any persons unwilling return, which interviews are to be monitored by neutral parties 4) provisions allowing international trade with reasonable cross border shipping procedures to help both countries to return to economic productivity. There is some potential use to be made of Putin. He can carry the blame for "Putin's war". Leave him under house arrest in his dacha outside Moscow with the Kremlin controlling who does or does not visit him. It does not matter if ruling class in Russia forced this war on Putin or not. Only Russians can determine if this is practical or not.
• Other nations trying to assist in peace making will have the task of making reasonable analysis of the likelihood of Russia and Ukraine abiding by terms reached at any stage of negotiations and advising negotiations to bring about a successful end to fighting.
• Ukraine's help in setting up SBSP is desirable but Russia's help is especially needed because the international treaties needed for SBSP should be written to work with enemies being parties to the treaty forswearing use of the technologies for warlike purposes and verifying each other's compliance. Unfortunately the attitude of Putin and the Russian leadership make cooperation with a good enemy and the whole notion of industrialization of the moon seem unlikely. We should not quit without an attempt.
• China requires a different approach. A big concern of the People's Republic is that factions of the population take the opinion that the communist party government is illegitimate and even occasionally voice that opinion. The communist party leadership correctly interpreted the Tiananmen protests as a the first step in a change of government if they were to have done nothing. The nationalist Chinese on Taiwan could offer to help stabilize dissident groups by encouraging them to diplomatically word their grievances and plead for practical relief while acknowledging the legitimacy of the current government. They could do this with trained teams of diplomats visiting groups in the People's Republic and promoting the benefit of a stable government as opposed to the chaos that can be expected in a violent change of government, acceptance of the devil one knows rather than the unknown devil to come. Teams of two trained Taiwanese with PLA armed guards and a logistics support crew could be convincing. The idea that even the Taiwanese oppose violent overthrow of the communist government would make quite an impression. In return the People's Republic would agree to no invasion of Taiwan or use of violence to take over Taiwan. The People's Republic could become the best authoritarian government that it can be. The population of mainland China would have more of its needs met. Taiwan would still be safe behind the navies of the USA and Australia. The People's Republic suspects the nationalists on Taiwan of fomenting rebellion on the mainland. Another rbellion on the mainland would not only hurt the mainland population, it would hurt the world economy. We do not need to know if the communist party's suspicians are justified. Openly and actively oposing rebellion would answer such suspicians. Give peace a chance.
• I hope and pray enough talented people of good will will be able to bring some sort of solution to our political troubles.

Some alternate ideas

• As an alternative, a rocket upper stage or rocket-sled payload could leave the acceleration tube at orbital velocity leaving the first rocket stage or the rocket-sled to proceed to a deceleration track. This could accomplish a special purpose but it would introduce extra engineering considerations to be dealt with.
• Sintered brick reinforced with fiberglass cables is a possible material for building a tube to recycle rocket exhaust on the moon. A nickel coated corrugated silicon steel inner tube would be held in place by the outer sintered brick tube. It might be decided that an all metal tube is better.
• After the acceleration tube and fuel depot on the lunar surface are completed they can be helpful in constructing the exhaust collecting deceleration tube for the lunar orbiting fuel depot.
• People who were intent on using mass drivers to build space habitats as suggested in "THE HIGH FRONTIER" by Gerard K. O'Neill need not give up hope. Recycling rocket exhaust to make it possible to build SBSP and space habitats does not preclude perfecting better mass drivers for space transportation. The more that extraterrestrial resources become available, the more they can be used to develop more advanced technology.
• If the rocket for which exhaust should be recycled burned liquid methane and liquid oxygen, then the Sabatier reaction could be used to add hydrogen to the carbon dioxide at the proper temperature with a proper catalyst to produce methane and water. That water along with the exhaust water could then be subjected to hydrolysis to recover the amount hydrogen added previously and the amount oxygen that originally burned the fuel. As a side benefit the lower exhaust velocity of a methane/lox rocket as compared to a hydrogen/lox rocket would result in cooler gas to collect and recycle.
• oxygen gas could be used as a heat transport fluid for taking the heat from the captured hot exhaust and transferring it to shaded radiators extending from east to west along with the launch tube. Oxygen is not the best heat transfer fluid on Earth but on the moon we might take what we can get most cheaply and there is plenty of oxygen available.

Military Considerations

• An important point is that a desirable industrial infrastructure on the moon would be quite vulnerable to attack from Earth. A rocket with small warhead consisting of metal grains surrounding small explosive could ruin industrial equipment on the moon over a considerable area. The velocity of any rocket capable of reaching the moon would be sufficient to impart to metal grains in the warhead sufficient destructive potential to ruin photo-voltaic cells, electrically conductive wire, or gas filled tubes for radiation of waste heat. The explosive charge in the warhead would spread the grains out over the target area. Since there is considerable potential to use the moon for military purposes, an enemy of the United States (for example) could claim that if the United States is involved with its allies in industrial development of the moon it must allow examination of that industrial development to insure its non-military nature. Failure to allow such examination could be taken as evidence that the idustrial development is military in nature and so require its destruction.

Building industrial infrastructure resistant to such simple attack would likely make the industrial development prohibitively expensive. The more reasonable policy would be for the United States to include enemies in industrial development of the moon so that all can mutually benefit as with the treaties mentioned above.

Security Classification of Lunar Development Information

Since there is potential military application for the industrial development of the moon, should the study of such development be classified? What would we gain from such classification? There are some techniques of using the moon for millitary purposes that are so simple that any halfway decent training in an engineering field make them obvious. No one can prevent the Americans or Russians from understanding some military potentials by classifying them secret. No one can prevent suspicion that industrial development will serve a military purpose by refusing to discuss such development with enemies. Rather, engaging in some industrial development on the moon without demonstrating what it is, provokes suspicion on the part of enemies that it is military development.

It would be better to have a policy of "trust but verify" that idustrial development is nonmilitary. Verification can be accomplished with robots acting on behalf of enemies of the operators of the industrial facility and on behalf of neutral parties. Just who operates which robots is a matter to be determined by treaty.

As for myself, I can discuss the use of lunar industry for military purposes, nuclear fission weapons, thermonuclear fusion weapons, or advanced aircraft with secret features all without any restraint because I do not have an active security clearance. I have never been exposed to classified documents on any of these topics. It cannot be made illegal to discuss nuclear fusion weapons, the laws of nature that make them possible, the means by which and places from which they might be deployed. It is only illegal to reveal the contents of classified documents or discuss classified activities of and locations of the military about which a person has come to know by virtue of employment requiring access to such documents and knowledge of such activities and locations. I have no access to any classified documents, activities or locations. So I can discuss them all. If some military official cannot understand the need for some information to be openly demonstrated, that one might reasonably consider other employment.

However, if officials in charge of classifying documents related to lunar industrial development, for reasons known to themselves, insist on making such development sectet and making open discussion by professionals in the field impossible, I must accept their decissions. I cannot even learn of their decissions.

What goes on now

I have noticed several people simultaneously becoming reluctant to discuss lunar development. I suspect there may have been a decision that studies of such potential development should be classified. So, people who might have access to official discussion of such development can no longer openly discuss it. What can be done while keeping lunar industrial development secret? Technology verification experiments can be done. A rocket can fly through a two mile long tube made of chicken wire and mounting RFID tags. Scientists can learn how the output of inetial sensors for inertial guidence and data read from RFID tags correlate with maneuvering controls for the rocket. They learn how the data is a measurement of how straight and level the tube is in order to use such measurements for the tube to be built to actually collect rocket exhaust on the moon. They can measure the effectiveness of heat transfer by oxygen gas pumped from a storage tank to a heat source and on to a radiator and back to storage with the whole system being in a vacuum tank simulating the moon. They can test remote controlled devices to assemble a liquid oxygen storage tank, devices to produce oxygen from simulated lunar regolith and store it, devices to haul liquid oxygen to a rocket on a simulated lunar surface and make fluid transfer. They can test instrument landing systems and ground navigation aids for the rockets that will bring equipment to a lunar base construction site.

However, if they actually start to build something on the moon, there will be people who will want to know what the plans are.

THE MOON : Resources, Future Development, and Settlement; Second Edition (C) Praxis Publishing Ltd Chichester, UK, 2008; by David Schrunk, Burton Sharpe, Bonnie Cooper, Madhu Thangavelu