Monday, 30 April 2012

We have 55 years space flight history today, but we are still here, near Earth. Dreams on exploitation of other planets, asteroids, stars are as far as 55 years ago. Prospective programs of all space agencies do not include real plans for human mission far space. Only talks, talks, talks. Why? Why are we anchored on Earth? Why do we only dream about other planets and make movies?

The Moon is the nearest celestial body to our Earth. Man first visited the Moon in 1969. Why it was stopped? You say, it is too expensive?

No. The problem is that we can do nothing there: in space, on Moon, on Mars. Look our “modern” spaceships. Could you live in “fish-box” some years? Could you develop mining on asteroid if your “home” is 3x6x6 meters, where you can take out your hermetic spacesuit?

No. We need large construction in space. In order for long-term human missions to be possible, large pressurized construction is needed.

Let’s look what we have and what do we plan now. The 6.65 m3 pressurized crew compartment volume realized in Apollo program. MIR space station had 350 m3 pressurised volume. Completed ISS after  more than 10 years of building has 109 m length and total volume of 837 m3.

What do we need for real long-term space mission? Hundreds of cubic meters for one crewmember are required for living area, working area, greenhouse with sufficient plants and animals for food, air and water recovery and storage. We cannot go further without significant improvement of living space in space.

It is real barrier for space programs, space missions, space industry, space exploitation. No way further without breakage of this barrier.

The projects discussing such large metal constructions delivered from Earth were proposed since the first flight on Moon. However, this method is not realistic: such large construction cannot be launched from Earth (too big mass and size). Large construction cannot be landed on the Moon (too big inertia). Such large constructions should be extremely durable to survive under huge accelerations at start and at landing (if landing on Moon or Mars). Building of large construction in space requires a long presence of workers (workers need pressurized cabins, life support system, water, food, that needs large construction to deliver and to keep it), delivering of separate blocks to one place with landing rockets (accuracy of landing in some meters is too complicate, or it needs Moon’s/Mar’s tracks to collect all landed blocks). Experience with building of ISS (International Space Station) showed, that the module building is extremely expensive, need much more launches and time and resources, than planned before, it takes years to finish. But the volume of whole ISS is enough only for 1 crewmember for far space mission!

You can say: robots will build the construction. Yes. Sure. I agree, in next 100 or more years. No one house has been built by robots on Earth by now. No one man lives in such house. It is too complicate. But space environment is much more complicate, than your smooth land with developed communications, roads, suppliers.

Therefore, a large construction in space should be built it-self.

There is only one way to get sufficient volume of the pressurized crew compartment: an inflatable construction. The soft shell of inflatable construction can be prepared on Earth, folded and transported in small container to space. Then the shell is inflated to a sufficiently bigger volume than the container. The shell materials should be soft to unfold easy and light to provide low mass.

Space agencies have an extensive experience in inflatable constructions. The history of inflatable space structures started from the "Echo", "Explorer", "Big Shot" and "Dash" balloon satellites in the 1960s. Based on success of the balloon satellite flights new projects utilizing inflatable structures for antennas, reflectors, Lunar and Mars houses and bases, airlocks, modules based on light polymer films were proposed from that time. Some of inflatable structures based on new materials were successfully (and sometimes unsuccessfully) tested in real space flight.

However, inflatable structures haven’t had a wide application in space exploration because of high risk of damage of the soft inflatable shell. Of course, the shell could be made of thick multilayers (Spacehab project), but the shell becomes heavy and the advantages of inflatable construction disappear.

The use of inflatable construction in space environment needs a rigidization of the construction wall after inflating. Since the first inflatable constructions flights, several methods of rigidization have been discussed: rigidization due to chemical reaction of a soft polymer matrix by thermal initiation of reaction, by UV-light initiation and by inflation of gas reaction; mechanical rigidization due to a stressed aluminum layer in the deployed shell; foam inflation; passive cooling below Tg of material; evaporation of liquid from gel. In some cases a combination of hard and rigidizable structures was developed. All of these methods were tested in Earth laboratory experiments. Only one real mechanism of rigidization was successfully tested in real space conditions - Aluminum stressed layers. However, this method is not suitable for large space construction.

The best way of rigidization is a chemical reaction in polymer matrix impregnated by fiber filler, which gives a durable composite material. These materials were tested under superior conditions including real space flight experiments. These materials are used for a wide number of space constructions now on Low Earth Orbits (LEO) and Geostationary Earth Orbits (GEO). These materials have long life-time (up to 20 years) under free space conditions and certified in all space agencies. Therefore, the chemical reaction rigidization process is the best method to be used!

For the creation of the construction frame, the fabric impregnated with a long-life matrix (prepreg) is prepared in terrestrial conditions, which, after folding, can be shipped in a space ship to the Earth orbit, Moon, Mars or other planet. The curing process should be slow to keep the prepreg soft. In space the prepreg is carried out and unfolded by, for example, inflating an internal bag. Next the chemical reaction of matrix curing should be initiated. The reaction can be initiated with high temperature or UV light irradiation. The required temperature for the chemical reaction can be achieved with Sun light irradiation or with internal heaters inserted in the prepreg. If the curing reaction requires UV light for the initiation, the sun light or UV lamps can be used to illuminate the prepreg. After complete curing the construction can be pressurised, fitted out with the apparatus and life support systems.

However, the curing technology of the composite material in space is not yet developed. The curing process in terrestrial environment is different than it will be in space. The prepreg cannot be placed in thermobox for precise temperature cycle, as it is used on Earth. The prepreg cannot be kept at Earth atmospheric pressure to prevent evaporation of active components. The composite material cannot be tested after curing to be sure in strength and exploitation characteristics of the material as it is usually done for construction materials on Earth. The curing technology in space will use different principles of composition, curing, testing as on Earth. It should be well developed and proved.

The main factors of space environment are high vacuum, space plasma (different kinds of irradiation, cosmic rays, Sun wind, atomic oxygen flux on Low Earth Orbit), sharp variation of temperature, microgravity (in orbit flight). All these factors influence on the curing process.

We have investigated the curing process in different compositions: under high vacuum, plasma and ion beams, in wide temperature variations. We found curable compositions for space environment. We found, that space plasma will help us to cure the construction wall. We tested mechanicals strength of the materials, that were cured under simulated free space conditions. It works! 

Conclusion: a curing in space is possible.

What is now? We need to test our composition in real space flight and then we can build large construction in space. A building of 10 m diameter and 80 m length after one launch is enough for your space factory?