NASA is building a space station on a strange orbit. here's why


Representatives of SpaceX, Blue Origin and United Launch Alliance participated in a forum organized last week by NASA to determine the future of humans on the moon. It's not just how they will live, how long they will stay, or what they will do; no, it's much more interesting: this is how humans will move from a lunar orbit to the moon's surface. The future of the next generation of lunar landers is being determined.

The current plan is totally different from Apollo, who sent a pair of spaceships into orbit around the moon, sent one to the surface, and then returned to the mother ship for the return trip to Earth. Instead of something quite simple, the next era of lunar exploration will take place from a footbridge orbiting in cis – lunar space. What makes this situation so amazing is how strange the orbit is and the reasons behind it.

It's the orbit it's special

Now, most of us should know how the Apollo missions went. The Saturn V took off, skirted the Earth for an orbit, and then turned on its engine to send it back to the Moon. After a three-day trip, the Apollo control module entered an almost equatorial orbit, sent the lunar lander on its way, waited a day or two or three, docked, and then was quickly returned to Earth. The Equator is the easiest place to land on the Moon and the first three Apollo missions to do so – Apollo 11, 12 and 14 – have all landed a few degrees from the lunar equator. Subsequent missions have ventured further north, but only so far: Apollo 15 has landed at 26 degrees north latitude. Of course, we explored the moon, but it's like saying you've explored the Earth if you've only been to northern Florida. There are interesting things in more temperate climates, and especially on the moon: there is ice under the craters on the lunar poles.

Possible landing sites of Apollo, highlighted. Apollo could not land at mid-latitudes with the Low Earth on the horizon. Also shown: landing sites for inhabited Apollo missions

Part of that was due to technology at the time. Apollo could theoretically land at the poles. He could also land at the equator. Middle latitudes were difficult; To reach these latitudes, the control module should orbit at an inclination as far from 0 as it is from 90. Of course, you could bring an Apollo lunar lander to the Moon at 45 ° North, with the Earth down to the horizon but to go back, it would be necessary to go to the control module. That too could happen, but then you would be stuck. Apollo was simply not built to land at mid-latitudes with the Earth on the horizon.

That's for sure, it's rocket science, but we also play with Kerbal Space Program. With the Kerbal Space Center at the equator and the Mun in an orbit at a zero-degree inclination, you do not need to think too far to go to Mun. If you want to travel to latitudes other than the Armstrong Memorial or the Munar Arc located just north of the East Crater, you will need a little more work.

Note that the same applies to potential landing sites for Apollo missions. When Harrison Schmitt suggested landing on the other side of the moon using a relay satellite to send emissions of several thousand kilometers of rocks, he suggested landing near the moon. ; equator. This never happened, but the possible Apollo landing sites were based on the capabilities of the Apollo spacecraft.

A new orbit and a bridge

NASA's new plan for future voyages on the moon does not go directly to the moon. Instead, future moon walkers will first visit a 'Moon Bridge' in a near-straight Halo orbit. What is an almost straight halo orbit (NRHO)? It takes a bit to decompress, but the benefits are worth it.

There are stable co-orbits in a three-body system, and there are already hundreds of objects in the solar system in such a configuration. As a thought experiment, imagine yourself on the surface of the sun. Jupiter is right above you, at about five AU. If you had to draw an equilateral triangle with legs five AU long, you would find a group of lagging asteroids and the leader, Jupiter. These are the Trojan asteroids and, thanks to Jupiter's huge mass, these asteroids are in an extremely stable orbit. They are also in orbit around a Lagrange point, in this case L4 (orbiting before Jupiter) and L5 (after Jupiter). There are three other stable points in any orbit, but the most important ones are L1 and L2. In the Sun-Earth system, these points are reserved for solar surveillance satellites and, eventually, the James Webb space telescope will hang around L2 Earth-Sun or in the shadow of the Earth, at about one million kilometers of distance.

The almost-straight orbit of Halo, centered on the moon. Image credit

Even if there is a mathematical reality of the points of Lagrange, it is in practice much easier to orbit them. This is exactly what the Moon Bridge will do. The almost-straight orbit of Halo is a special case of the Earth-Moon orbit L2 which, at first sight, seems to be a strange polar orbit of the moon, an orbit taking between 6 and 8 days.

From a simplistic point of view, the NRHO looks like an extremely eccentric polar orbit around the moon, with a distance of about 2,000 miles and an apoapsis about ten times greater. This orbit, however, is not a lunar orbit. Mathematically, it is always an orbit around the point L2 Earth-Moon. It takes a little more energy to get to a lunar orbit, but it does provide fantastic benefits. It is easy to access launchers in flight or test, it is well placed for observations of the Earth, the Sun and deep space and to communicate with the Earth. NRHO orbits can be used as relay stations for remote operations. side.

Since it is an orbit around L2 Earth-Moon, it is inherently unstable and will require some fuel to maintain the orbit. It's a problem, but as the Apollo scientific programs reveal, almost all the orbits around the moon are unstable and would need fuel to stay in orbit.

Source of the image

Soon, a space station will orbit around the moon. It's not really in lunar orbit, though if you look at it long enough, it may seem like it is. It is this orbit that will be the first point of passage on the way to the moon. Unlike the Apollo missions, this lunar bridge will take us anywhere, whether in the ice water trapped under the poles, far away. from the moon, or back to the historical sites of the Apollo and Surveyor landing sites.


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