The Hotel on TK7, L4: The Next International Space Station

 

TK₇ is an asteroid that was discovered in 2010 by the NEOWISE team of astronomers using the WISE space telescope. It is about 300 Meters in diameter and is a part of the world’s most valuable real estate! Why? It is easier to reach than the moon, leave alone Mars. It’s orbit round the Sun is close to that of the earth and is gravitationally synchronized to the L4 location of the earth. It is astronomical convention to call asteroids at the L4 and L5 points associated with a planet Trojans. So, technically, TK₇ is a Trojan.

The mathematician and physicist Leonhard Euler had shown in 1750 that there are three points L1, L2 and L3, associated with a planet circling a central body like the Sun. The scientist cum mathematician Joseph-Louis Lagrange had shown in 1772 that there are two more points L4 and L5. Objects at or near these points are relatively stable there. Visit What are Lagrange Points?

We have L4 and L5 points on the earth’s orbit around the Sun.

A spacecraft headed to TK₇ will need much less fuel than one headed to Mars. A spaceship going to Mars would have to fire its rockets and burn a lot of fuel to do a soft landing on Mars. A spaceship headed to L4 or L5 would not need to fight any strong gravity. Gravitational force exerted by the Sun near L4 or L5 is only 6 mm/sec²! Synchronizing a spacecraft’s orbit with that of TK7 would not require huge amounts of energy.

The return to Earth from TK₇ will also require much less fuel than a return from Mars. Gravity at its surface is twenty thousand times weaker than that of the earth’s gravity we live in.

Why is 300 M diameter rock a valuable real estate? Because, living on it would be much easier and safer than living in the current International Space Station. You can live, say, 10 meters below TK₇’s surface, very well protected against cosmic radiation and micrometeorites. Temperature management would be a lot easier. Space available for living and for work would be a lot larger.

Who would want to live there? Scientists interested in studying the universe, for instance. They have had the James Webb Telescope working from July 2022 at the Lagrange Point L1 in the earth’s shadow. It is a very complex telescope, and if some part of it fails, there is no way to repair it. On the other hand, if a telescope is built on TK₇ a resident crew could repair it easily.

The 300-meter diameter TK₇ would have a surface area of about 60 acres if it is a smooth sphere though it is unlikely to be a sphere. However, gravity on its surface is so weak that we should have no trouble building big structures all around it. In course of time, we could even give it a 400 Meter diameter outer shell in the form of a smooth sphere! Building materials that weigh a ton on earth would weigh a mere 100 grams on TK₇! Elevators, if any, would need power mainly to cope with inertia, as weight would be negligible.  

Other possibilities are of modifying the rotation of TK₇, so that one side always faces the Sun and generates huge amounts of solar power. The other part could always face away from the Sun and can house big telescopes to study the universe at various wavelengths. Of course, there would be a need for radio telescopes as well on TK₇, provided we have tight control on electromagnetic noise.

How about air and water? Recycling them, monitoring them, and keeping them unpolluted, will be major challenges. Water and air will also escape the meager gravity of TK₇ if there are any leaks.

Building and operating a station on TK₇ would require international cooperation. This would be a unique project which would require states of the world to cooperate on a huge and expensive high technology project.

Would the scientific value of such a project alone persuade member states of the UN to contribute its cost? Would the project be sustainable without a source of revenue?

One option for a revenue stream would be to allow a certain percentage of facilities on the trojan to serve tourists for a few weeks each. That is why this article is titled “The Hotel on TK₇”. Wikipedia mentions 56 million as the number of millionaires in the world. Perhaps one could attract 10,000 of them per year to visit “The Hotel on TK₇”. If they stayed for an average of 7 days each, we would need about 200 bunks on TK₇. If they paid 2 to 3 million dollars each for the trip, they would contribute a reasonable amount. Would the astronomers want this crowd around?

Mining for rare elements is another possibility, but mining on TK₇ may not be compatible with other activities on it. Is there a sufficient tonnage of asteroids orbiting the L4 point to support mining activity? Ideally, mining should be coupled with manufacturing. This would make it worthwhile to mine even not-so-rare metals such as iron. To go lower down in sophistication, we can even manufacture prefabricated hollow blocks for use in constructing buildings on Mars. The manufactured products should be exported to Mars rather than to earth. The low cost of transportation from L4 would make Mars a very attractive destination for goods manufactured around L4.

It is possible to create a semi-permanent facility for asteroid mining to be located around L4, but not on TK₇. Potentially interesting asteroids could be brought to this facility by automated asteroid lassoing spacecraft. The miners who run these activities could be based on TK₇; they would make trips to the mining facility whenever necessary. However, human effort involved in space-based mining and manufacture should be minimized. Processes should be automated as far as possible because human presence in space is so expensive.

The biggest attraction of building a station on TK₇ is that it would be a valuable steppingstone to a permanent station on Mars. The scale of the effort would be smaller, and the costs and risks involved would be much lower.  

TK₇ is not the only trojan that we should consider. The earth has a larger trojan linked to its L4, 2020 XL5, designated as a minor planet. It is 1.3 KM in diameter, making it much heavier than TK₇. XL5 may not be as attractive as TK₇ for staging Mars expeditions, as its orbit takes it well away from Mars. In its nearest approach to the Sun, it gets closer to the Sun than Venus. Chances of finding water on it may be low.

There are several trojans in Mars’ orbit, and two are big: 5261 Eureka, trailing Mars in its orbit is 1.3 KM in diameter. 2011 UN63, also trailing Mars, is 560 KM in diameter. Setting up a base on one of these would be easier than setting it up on Mars.

Careful study and analysis may show the advantages and disadvantages of these trojans for staging a Mars expedition. Ultimately, I suspect that “local” resources would matter a lot. For instance, the presence of a thousand tons of water or ice would be a big attraction.  

We would need a new breed of robotic spacecraft to do the necessary investigations of several trojan asteroids. The Japanese have established a lead in creating such exploration spacecraft. Visit the Hayabusa Page

Srinivasan Ramani