Órbits
In order to understand the space industry and business opportunities in space, one must understand the playing field: orbits, how they are defined and what ventures are suitable for each orbit.
The main orbits are as follows:
Sub-orbital
Sub-orbital launches are those whose payload generally reaches a maximum altitude of 100-150 kilometers and then falls in a matter of minutes. The edge of space is located at 100 kilometers from the Earth’s surface.
These launches serve a primarily scientific purpose; experiments are conducted and technology is tested. NASA has tested the parachutes for the next vehicle that will send to Mars’ surface.
This is also the orbit in which companies are working to commercialize space tourism for the first time on a large scale–to the extent that you can create a large market for tickets of upwards of $100,000. Jeff Bezos’ Blue Origin and Richard Branson’s Virgin Galactic are conducting test flights with their respective spacecraft. Perhaps we will see the first instances of commercial space travel in 2021.
This orbit may also be leveraged in high speed, inter-continental travel–a 90-minute trip from Europe to Australia, for example. Though this possibility has been discussed–and Elon Musk says that the rocket his company is designing could serve this purpose–one thing is certain: in this field, no real bets have been placed to date.
Low Earth Orbit - LEO
This is the first step in leaving Earth and remaining in space. LEOs have an altitude that ranges anywhere from 200–2,000 kilometers above the Earth’s surface. They do not have to be circular, but typically they are or are near circular.
The large majority of satellites in space, no matter their purpose, are found in this orbit. The ISS and its predecessors have all been located in LEO. The only humans to have ever left lander were those aboard the Apollo 8 through Apollo 17 missions to the Moon. However, they never landed there.
Aside from orbital altitude, one must also consider orbital inclination. They span from zero degrees (following the path of the Equator) to polar orbits that are near 90º and, as their name indicates, extend from pole to pole. Inclination dictates which parts of Earth fall under an orbit.
The altitude, and therefore velocity, of a satellite determine the time it takes for a satellite to orbit Earth and return to a set point. The greater the altitude, the slower the satellite. This time period is now as the satellite revisit period. This is an important metric to take into consideration when building a satellite that measures, for instance, air pollution. Systems of two or more satellites are often employed in the same orbit to reduce the revisit period. This metric plays a key role in the construction of satellites that are designed to transmit voice and data communications across Earth. In LEO, many satellites (tens, hundreds or even thousands) are needed to ensure constant coverage.
Altitude also has a significant impact on the quality of data collected by Earth observation satellites. The closer a satellite is located to Earth’s surface, the better the image quality of whatever the satellite is measuring at the time. However, a lower altitude means greater atmospheric friction and, therefore, a shorter life for the satellite, as it is drawn ever close to the Earth’s atmosphere and ultimately consumed by it. Satellites use their motors to counteract the effects of atmospheric friction and maintain altitude. Yet when they run out of fuel, they inevitably fall. In fact, once or twice a month, the International Space Station uses its motors or those of any vessel docked to it to increase the altitude of its orbit. Even at 500 kilometers above the Earth’s surface, atmospheric friction causes the ISS to drop roughly one kilometer per month. If it weren't for these maneuvers, the ISS would have burned up in Earth’s atmosphere a long time ago.
Due to the popularity of this orbit, it is extremely important that space debris reduction strategies be employed and that satellites possess enough fuel to leave their orbits ad safely return to Earth’s atmosphere to be destroyed.
Medium Earth Orbit - MEO
This orbit is roughly above 2,000 kilometers and just shy of the 36,000 kilometers altitude of geostationary orbits.
Telecommunications and navigation satellites typically occupy this orbit. Common examples are the Beidou systems satellites, GPS, Galileo, Glonass and India’s IRNSS. Geotdetic satellites and those that measure space weather also occupy MEO. Depending on a satellite’s altitude, its revisit period can range anywhere from 2 to 24 hours. Telstar 1 was the first commercial, telecommunications satellite and was launched into MEO. Its minimum altitude is 952 kilometers and its maximum is 5,933 kilometers. It orbits at Earth at 45-degrees and has a revisit period of 2 hours and 37 minutes.
Geostationary and Geosynchronous Orbits - GEO
The two terms are often confused even though, technically, they are different. For all intents and purposes, satellites in geostationary orbit remained fixed above a specific location on Earth's Equator and from down on Earth, they appear to be fixed in the sky. Satellites in geosynchronous orbit appear to be in motion even though they never lose site of a specific point on Earth. These orbits are ideal for telecommunications because they allow telecomm satellites to provide a specific geographic location with constant coverage. They are also useful for Earth observation satellites, such as the famous European Meteosat satellites, because they allow for permanent observation of a specific location on Earth.
Given Earth's rotational velocity, these types of satellites must be located at an altitude of 35,786 kilometers. Furthermore, to prevent interference, these satellites cannot be too close together. That is why every launch must be approved by the International Telecommunication Union.
Today, there are slightly less than 450 satellites in these orbits, though some are inactive. Ideally, a satellite in GEO should have enough fuel to ensure that it can be sent into a higher, graveyard orbit upon completing its mission and that it will not interfere with other satellites once it stops operating.
High Earth Orbit - HEO.
Simply put, these orbits are found at a higher altitude than GEOs. Their defining characteristic is that their orbits exceed 24 hours and the part of Earth that they observe moves westward. In reality, HEO is rarely used.
Out of Orbit
Objects in this category do not revolve around Earth. They may be heading to the Moon, Mars, a different celestial body or any of the Lagrange points in the Earth-Sun or Earth-Moon systems.
These five points occur because the competing gravitational forces of the Sun and Earth or the Moon and Earth essentially counteract each other and immobilize small objects, such as space observatories or probes. These objects do not need to consume fuel. Lagrange points can occur between any two celestial bodies of substantial size. For example, the ESA-NASA Solar Heliospheric Observatory is located at the L1 Lagrange point. The Gaia observatory is at L2, and the James Webb Space Telescope will also be located there someday. Recently, China has placed the Quequiao satellite at the Earth-Moon L2 point so it can relay communications from the Chang’e 4 mission, the first landing on the far side of the Moon.
For now, the Moon, Mars and other celestial bodies have been the furthest destinations that we have reached. The New Horizons probe broke its own record, having already studied Pluto during a flyover on July 14, 2014; the probe visited Ultima Thule (an object located in the Kuiper Belt) on January 1, 2019.
New Horizons does not posses fuel to enter into orbit around Pluto, Ultima Thule or any other target. In terms of fuel consumption, each orbit is more costly than the last. Regarding the trip to Pluto, scientists needed to strike a balance between a reasonable time frame (9 years after launch) and fuel consumption. Without the right amount of fuel, the probe would have traveled so slowly that many of those involved in the mission would have died before the probe reached its destination.
In discussing commercial space exploration, asteroids of the asteroid belt are an attractive destination. Hypothetically, they could be an almost unlimited source for certain raw materials. Yet for now, we do not possess the technology for building a ship with the carrying capacity that would make such a trip worthwhile. We neither have the robots that would be capable of carrying out the mining project nor the manned ships that would transport miners.
For now, space remains the realm of science, and there are few opportunities for commercialization, apart from those that may be derived from the data collected by probes, rovers and space observatories.
