Propulsion

Propulsion is anything that helps a rocket (or any other object) move forward. Nearly all rockets use chemical propellants, though a few specific applications use other methods. In chemical propulsion, fuel alone isn’t enough — it needs oxygen to burn, which is scarce at high altitudes. That’s why rockets carry an oxidiser to supply oxygen for combustion. Together, the fuel and oxidiser make up the propulsion system.

Chemical Propulsion

Chemical propulsion is broadly classified into three types: solid, liquid, and hybrid. Many rockets use a combination of two or more of these in different stages.

Solid Propulsion

In solid propulsion, the fuel and oxidiser are mixed with a chemical called a binder, which acts like glue and also serves as fuel. This mixture is cast into a solid cylinder called a grain, with carefully designed gaps in the centre. These gaps control how much fuel is exposed at any given time, allowing the rocket’s thrust to be preprogrammed and, in turn, influencing its motion and direction.

Solid propellants have one major downside: They cannot be controlled or shut off at all after ignition. This is why it is often used for raw power and not for tasks that require high precision or efficiency. This makes them perfect for the lower stages of a rocket (though some still use liquid propulsion) or strap-on boosters. Solid fuels are used because they are relatively simple, last for long periods of storage, are low-cost, and are less sensitive.

Liquid Propulsion

As the name suggests, in such cases, the propellants are stored as liquids in separate tanks and are fed into a combustion chamber where they burn to produce thrust. Liquid propulsion allows scientists to control thrust during the flight using the valves and pumps. They can be shut off and re-ignited as necessary. They are also much more efficient and are used for high-precision tasks in the upper stages of a rocket.

Monopropellant Engines

In such engines, there is only one liquid propellant. It releases energy when it flows out of the tank and touches another chemical called a catalyst. They are very simple and reliable, but are low in efficiency. They are usually used for satellite propulsion and not for rockets

Bipropellant Engines

Such engines have two tanks – one for the fuel and one for the oxidiser. They are both released into the combustion chamber and either ignite on touching or are ignited by the engine to produce thrust.

Tripropellant Engines

Such engines are extremely rare or experimental. They have two fuels and one oxidiser tank. It uses the more powerful fuel first and later switches to the higher efficiency one.

Liquid propellants need to enter the combustion chamber at very high pressures. This is often done using a pump or by storing the fuel in high-pressure tanks. Some of them need to be ignited on entering the chamber, so ignition systems are often needed. Some high-efficiency fuels and oxidisers like liquid hydrogen or liquid oxygen need to be stored at very low temperatures. Such engines are called cryogenic engines. All these features start to increase the complexity of such engines.

Hybrid Propulsion

In hybrid propulsion engines, the oxidiser is stored as a liquid in a tank while the fuel is a solid grain, similar to solid propulsion systems. Cutting off the oxidiser allows the engine to be shut down and provides limited thrust control. Because the fuel and oxidiser are stored separately and avoid very high-performance solid fuels, these engines are safer and less prone to violent burning. They are simpler than full liquid propulsion systems, but are less efficient and cannot produce very high thrust.

Non-Chemical Propulsion

Here we deviate slightly from what most people would call a “rocket.” So far, we’ve only looked at propellants used in launch vehicles, but spacecraft, satellites, and deep-space probes also need propulsion. This is not to stay in orbit or to just move forward on its path, but to change orbits or speeds. Most of them do not use chemical propulsion, as it is expensive and heavy. Non-chemical propulsion greatly reduces spacecraft mass, making them easier to launch.

Electric Propulsion

This kind of propulsion is heavily used by spacecraft today. Nearly all satellites, spacecraft, probes, etc. have solar panels attached to them that help them generate electricity for not just their own functions but also for propulsion.

It works by ionising a propellant gas (usually xenon) – this means the particles become charged. These charged ions are then ejected out the back using electric or magnetic fields, and this moves the craft forward. Instead of shooting hot gases out the back like chemical propellants, they shoot out ionised particles.

Some experimental engines produce plasma (a big mixture of ions, positive particles, etc) which is shot out the back, similar to the ion propulsion.

Solar Sails

On Earth, a sail uses the wind hitting it to move a boat forward. Similarly, in space, some very light experimental satellites currently use solar sails for propulsion. As light particles from the sun hit these thin sails, it pushes the craft forward. This effect is tiny, but it builds up over time. Solar sails are extremely simple and don’t rely too much on complex technology.

Nuclear Propulsion

This was extensively researched in the 1960s but eventually shut down due to political and safety concerns. It applied not only to satellites and probes but also to high-power launch vehicles. It worked by using a nuclear source to heat up liquid hydrogen and make it expand. This gas was then pushed out through nozzles at high speed to propel the craft/rocket. Today this idea is being revisited for future Mars missions.

There are many more theoretical and experimental methods to propel rockets and spacecraft that are being researched today. Some sound like they are straight from sci-fi, like space-tethers or beamed energy propulsion, each of which would have to be given its own article. Considering that humans launched the first satellite only 70 years ago, who knows what the space industry will look like in another few decades?

What does it take to reach orbit?

A common way to explain this concept is through Newton’s Cannonball, a thought experiment proposed by Isaac Newton. He imagined firing a cannonball horizontally from a very tall mountain. A slow shot would land nearby, while a faster one would land farther away. If the cannonball were fired fast enough, it would keep falling around the Earth indefinitely, because the Earth is curved and the ground drops away beneath it as it moves forward.

The same idea applies to a rocket. Here we encounter another common misconception that rockets go straight up into space to launch a satellite. If this were the case, it would fall back down the second the engines shut off. This is why rockets mostly go sideways like Newton’s cannonball. Calculations have estimated the required speed (orbital velocity) to be about 7.8 km/s or 28,000 km/ hr to reach Low Earth Orbit. Any rocket that cannot achieve such speeds will not make it to orbit.

To escape Earth’s gravity entirely for missions to other planets or moons, an object needs to go at even higher speeds of 11.2 km/s (escape velocity). Many rockets cannot achieve escape velocity, but can achieve orbital velocity, so they instead initially put their payloads in low orbits and gradually increase the size of the orbit until it escapes completely. This is what missions like Chandrayaan-3 did.

Single Stage (Sounding Rockets)

Sounding Rockets are simple and inexpensive rockets designed to carry science instruments to high altitudes to study the upper atmosphere, space weather and so on. They have a very short flight time – usually just a few minutes, after which they drop back down to the Earth. No single-stage rocket today is capable of putting a satellite in orbit, as they cannot achieve orbital velocity. They can reach areas where weather balloons can’t, while being cheaper than satellites.

Double-Stage Rockets

These are the most common types of rockets used today. They are much more efficient and necessary for putting a payload into orbit.

First Stage:

This stage contains the core rocket engines, a large fuel tank and in some cases additional strap-on boosters. They provide thrust during liftoff and get the rocket through most of the thick atmosphere. Since this requires a massive amount of thrust, the first stage is the most powerful stage of any rocket. The strap-on boosters are optional and quickly detach after providing the initial thrust. However, they are still considered part of the first stage and not as a separate stage.

Second Stage:

This stage is crucial to getting the payload into orbit. While the first stage is optimised for raw power, the second stage is optimised for efficiency and precision since it operates in a near vacuum without much air resistance. It performs precise, controlled burns, shutting down and restarting its engines as required to reach orbit. A small misfire can completely change the payload’s orbit.

Triple-stage rockets

A two-stage rocket can get you into low Earth orbit, but for satellites in Geostationary Orbit (above 35,785 km from Earth) or interplanetary missions, you sometimes need more powerful three-stage rockets.

First stage:

Has the same function in any rocket.

Second stage:

Gets the payload into a temporary orbit or a parking orbit and provides most of the orbital velocity. It has medium thrust, high efficiency and good precision.

Third stage:

This stage has low thrust as most of it was provided by the second stage. It has a very high efficiency as it operates in an almost complete vacuum. It also needs extreme precision to inject the payload into a ‘transfer orbit’ from where the payload will make its way to the final orbit using its own propulsion.

Four or more stage rockets

Rockets with four or more stages are very niche today, but were more commonly used historically when engines were much less efficient and heavy. They would be used to launch payloads into high-energy orbits. The main goal of the extra stages was to provide additional acceleration. Most of these stages were small and fired only for a short period of time, called ‘kick stages’. Such four-stage rockets also have their own issues, like higher chances of failure. They can also only be used to launch small payloads, as a higher mass makes it harder for the kick stages to speed up the craft much. Today, rocket engines have gotten more efficient, and much lighter materials are used to build them, thus largely eliminating the need for more than three stages. No modern heavy-lift launch vehicles use four or more stages, while a few small-to-medium lift rockets, such as PSLV, still do.

What are Inflatable Habitats?

Inflatable Habitats, as the name suggests, are space habitats that can be launched into space in a compressed state and inflated and used by astronauts. They are made from extremely strong and flexible materials to survive space debris and the other harsh conditions of space. They occupy significantly less space during launch and offer much more volume than regular habitats. One of the earliest and most ambitious attempts was TransHab.

TransHab

In the 1990s, NASA’s Johnson Space Centre developed TransHab, an inflatable crew habitat for the International Space Station. It functioned like a balloon. It could be inflated and used in space, so it wouldn’t take up space on the rocket and could easily withstand the stress of the launch. The Transhab module provided 3 times as much space inside as rigid modules.

Structure

Outer layer:

• Insulates the habitat from extreme temperatures of space.

• Protects it from highly reactive atomic oxygen (single atoms of O) found in low earth orbit.

• Made of Layers of refelctive material to reflect sunlight.

Impact Shield:

• Protects habitat from micrometeoroids and small space debris.

• Slows down and breaks debris apart before it can reach the inner layer

• Made of strong fabrics with foam between them and Kevlar backing.

*Kevlar is frequently found in bullet-proof vests.

Structural layer:

• Maintains the shape of the habitat.

• Made of straps of Kevlar or Vectran.

Inner layer:

• Holds inner air and maintains pressure.

• Made of fireproof fabric + multiple bladders.

Project death

TransHab showed promising results during impact testing to make sure it was safe in the event of debris strikes. However, in the year 2000, the project was terminated due to high cost, complexity, and integration challenges.

Revival?

Today, these inflatable habitats could make a comeback as we have developed stronger, lighter, and more flexible materials like Vectran and Nextel. Robotic assembly and deployment, and 3D-printed complex structures could also help bring this to reality.

BEAM

BEAM, short for Bigelow Expandable Activity Module, was a direct descendant of the TransHab. It was developed by Bigelow Aerospace and launched to the International Space Station in 2016, making it the first ever inflatable habitat to be attached to a crewed spacecraft. Though its initial life was only supposed to be 2 years, it is still functioning as a storage module today. BEAM was an excellent proof of concept for inflatable habitats and showed that it is a viable option for space missions.

LIFE

The Large Integrated Flexible Environment (LIFE) is an inflatable habitat currently being developed by a company called Sierra Space. It aims to be used in Blue Origin’s Orbital Reef space station, which is planned for the future.

Others

Many space agencies and private companies are working on building inflatable habitats today. These include Lockheed Martin, Sierra Space. and more. Even NASA has proposed inflatable habitats for its Artemis program.

In the 1990s, TransHab was an ambitious project, perhaps a bit ahead of its time. Nearly 25 years after it was abandoned, technology has advanced rapidly, and proof of concepts like BEAM have performed exceedingly well. There is no doubt that we will see more of these habitats soon. Maybe even sooner than you think.

Space Tethers or in this case, Electrodynamic Tethers were a concept explored by NASA and the Italian Space Agency (ASI) in its Tethered Satellite System (TSS) experiments in the 1990s. These tethers were long wires suspended from satellites that could generate electricity by interacting with the Earth’s magnetic field.

The current flowing through the wire would interact with the Earth’s magnetic field and provide a gentle push to the satellite, so it could also be used to change a satellite’s orbit without using fuel.

What did it look like?

These wires were more than 20 km long and thinner than a shoelace. The wire was spooled up inside the Space Shuttle orbiter and deployed in orbit. The other end of the wire was attached to the ‘satellite’, a small sphere with antennas and sensors. The wire was not slack like a rope on Earth. Instead, it was under tension due to the difference in gravitational force on the ends of the wire.

Mission Death

TSS-1 was cancelled due to mechanical issues, but TSS-1R successfully deployed almost 20 km of cable before the cable unfortunately snapped. Despite proving the physics of Electrodynamic Tethers, the tech demonstration project was discontinued.

If a broken tether hit any important satellites or the ISS, it could cause devastating damage. The tether itself was vulnerable to micrometeoroid strikes, not to mention snags during deployment.

Revival?

Today these these Electrodynamic Tethers could be brought back using stronger engineered materials, and precision reel systems could help make this possible. However, it might have limited uses, like deorbiting dead satellites that have run out of fuel. However, it is still risky and very unreliable, which begs the question - should it be revived?.

Drag Tethers

While electrodynamic tethers may have their issues, a different kind of tether is in use today - a drag tether. These have been used on small cubesats like the ESTCube-1 and Aalto-1. Unlike electrodynamic tethers, these tethers are non-conductive and much shorter. They work by increasing the friction with the air molecules, causing ‘drag’ to slow the satellite down so that it eventually burns up in the atmosphere. These drag tethers only work on small satellites in Low Earth Orbit, as they are only passive systems. Electrodynamic tethers, on the other hand, can be used for larger satellites in higher orbits.

Let us take a look at popular sci-fi technology from ‘Far Fetched’ to ‘Hypothetically Plausible’ to ‘Nearly in Sight’

Far Fetched

Teleportation:

Teleportation is commonly seen in movies, like Star Trek’s transporter. Since we can’t physically send a body through the air, teleportation would require scanning every single atom of a person down to its exact position and behaviour (which breaks most theorums), beam the yottabytes (that’s a trillion terabytes. More than all the data ever created on Earth so far) of data across to a different place (which could take decades) and then reconstruct its exact arrangement again (which we currently can’t even do for basic molecules). Since this creates a clone of the person, the original will have to be killed, or there will be 2 copies, making the idea of teleportation very far-fetched.

Faster than light travel:

Many space sci-fi movies involve travelling to planets outside our solar system, which even light would take years to reach, so the starships use faster-than-light travel. Now, nothing can travel faster than light, at least not in the regular way. So, the starships in the movies use complex ideas like hyperspace travel, warp drives and wormholes to travel to higher dimensions or bend space and time itself. Some methods would even require theoretical exotic matter (matter with negative mass). While they may be based on scientific theories, we don’t even know enough to say if it is possible.

Hypothetically Plausible

Space Elevators:

As seen in various movies like Star Wars or Halo, Space elevators are massive cables that connect an orbiting spacecraft like the ISS to the Earth, so that supplies can be carried to space by a climbing elevator instead of using expensive rockets. This is a great idea that obeys the laws of physics and could be possible in the future. NASA and other space agencies have studied it seriously, but they just haven’t found the right materials for such a tough cable.

Dyson Swarms:

Unlike a Dyson sphere (a far-fetched idea) that requires a solid shell around a star, Dyson swarms are massive collections of satellites that orbit a star to harness its energy. We already have solar panel technology, so having a swarm around the sun that beams back energy to Earth could be possible in the future. The number of satellites required would be so massive that you would need to mine other planets for the materials to build them. Their orbits would also have to be managed so that they don’t collide. These satellites could beam back the energy to Earth using microwaves. Dyson swarms can harness energy 24 hours a day, from all angles of the sun and beam it back. A tiny swarm could capture more power than all of the Earth’s surface combined.

Nearly in Sight

Ion Propulsion:

In movies like Star Wars and WALL-E, some ships use ion engines to travel at ultra-high speeds (still slower than light, though). Unlike regular engines that burn fuel, Ion engines use electricity to blast out charged atoms to propel themselves forward. While these engines start slow, they can build up massive speeds over time. This means they are more suited for deep-space missions than liftoff from Earth. “Ion propulsion is already in use by space agencies worldwide. It has powered missions like NASA’s Psyche, Japan’s Hayabusa, and Europe’s BepiColombo en route to Mercury.”

Solar Sails:

Solar Sails are massive sails attached to spacecraft that use the force of the Sun’s photons hitting it to move forward. It’s a sail that uses light instead of wind. Such sails are seen in Star Trek, Star Wars and more. Such sails have even been used in real-life spacecraft like IKAROS, ACS3, NEA Scout, LightSail and more. While solar sail technology isn’t nearly as powerful right now to carry humans, it offers a no-fuel alternative for small crafts. There are even proposed missions that plan to use Earth-based high-power lasers to power the sail so that it can reach 20% speed of light.

Science fiction is never short of imagination. We can never say for certain if an idea is impossible, for we never know what the future holds. But we can be sure that some of the wildest space tech is much closer to reality than we imagined.

So what are FRBs? FRBs stand for Fast Radio Bursts. They are powerful bursts of radio waves that occur for incredibly short durations of time. FRBs can release as much energy as the sun does in an entire day, in a few milliseconds. They were earlier thought to be a rare phenomenon, but with advancements in technology, more and more of these bursts are being detected. However, what causes them is still a mystery.

Origins

FRBs have been traced to certain vicinities and sometimes even specific objects like black holes, but we still don’t have a complete understanding of what processes and reactions caused them. We know where it came from, but we don’t know why. Here are a few objects that FRBs have been traced to (or are believed to come from) -

Neutron stars: One theory is that they come from the collisions of neutron stars - incredibly dense objects composed entirely of neutrons, formed after the death of a star. When the 2 neutron stars merge, they release a lot of energy. This energy is believed to cause FRBs.

Magnetars: Another possible source of FRBs could be magnetars. Magnetars are a type of neutron star, which have extremely powerful magnetic fields. These magnetic fields cause all sorts of intense phenomena on the star, like magnetic flares (sudden release of electromagnetic radiation). Radio waves are also a form of electromagnetic radiation. This has led experts to believe that magnetars are also one of the sources of FRBs

Black holes: When a star gets too close to a black hole, it can get ripped apart and consumed by it. This process releases a lot of energy and could be a possible source of FRBs.

Galaxy Mergers: Galaxy mergers are also believed to be the main causes of FRBs. Even recently an extremely powerful FRB was detected. It released as much energy as the sun would in 30 years in just 1 millisecond. This FRB is believed to have been caused by a distant galaxy merger. You can read more about that FRB here.

Aliens: While this is a very unlikely idea, there are some who believe that FRBs may be deliberate communication signals sent by intelligent extraterrestrial beings. However, this is just a theory and has no proof behind it.

Classification -

FRBs are completely unpredictable. They can occur at any time and anywhere. They are classified into 2 types -

Repeaters: These FRBs continuously repeat themselves after periods of time. These time periods are often unpredictable and keep changing. Some could repeat every hour, some every day or maybe more. Some FRBs that repeat after a very long time may get classified as non-repeaters due to a break-off in observation. FRBs may continue to repeat for months or years or sometimes they could stop repeating in a short time. However, it is hard to be completely sure if an FRB has stopped repeating as the time intervals can largely vary. It could repeat again after the observations stop.

Non-Repeaters: Just like the name suggests, they occur only once for an extremely brief moment and then disappear. They don’t repeat themselves. However, many FRBs could have been falsely classified as non-repeaters due to a cut-off in observation.

Technology advancements in detecting FRBs

Since FRBs occur only for a few milliseconds, discovering an FRB by simply scanning a tiny portion of the sky would take a very large amount of luck. This is why new and advanced telescopes with a wide field of view and high sensitivity play a large role in their detection. Some examples are the CHIME Telescope in Canada, the ASKAP Telescope in Australia and the world’s largest single-dish radio telescope: FAST located in China. Such telescopes with their advanced technology are the main reason behind the increase in FRB detection over the past few years.

How are they located?

Since FRBs occur only for a few milliseconds at most, it is extremely difficult to capture them let alone get enough data to pinpoint their location. Here is how it is done -

Most radio telescopes have multiple antennas. These antennas can be placed in different locations around the world, forming a telescope array. In this case, each antenna is like a telescope of its own, working together to form one massive telescope. Another type of telescope has one massive structure with multiple antennas positioned on it, like the FAST single-dish telescope.

When an FRB enters the atmosphere, it gets detected by one of the antennas. Then it gets detected by the next one and then the next. Precise technology is used to measure the amount of time the FRB took to reach each antenna, and the time difference is calculated.

The data from all the antennas are put together and the patterns in the radio waves, help find the direction from which the wave originated. You can also find out the location from which it originated.

What can FRBs tell us?

When FRBs travel through space, they interact with the matter on their path and get dispersed. Once these FRBs reach the earth, scientists measure the amount of dispersion in the FRB and can tell how much matter was present in the path taken by the FRB. This technique helps us map how matter is spread out in the universe.

An FRB can also tell us more about the extreme conditions in space and the objects that it encountered on its path like neutron stars and powerful magnetic fields.

FRBs that come from billions of light-years away can be studied to understand the universe’s past. This is because since they came from millions of light-years away, they would have been travelling in space for a billion years before they reached us. Using previously mentioned techniques, scientists can study what the early universe was like.

Some believe that FRBs could be a signal sent by intelligent alien life. While this is unlikely, it could be one of the sources of FRBs. This makes some of them of great importance to the Search for Extraterrestrial Intelligence (SETI).

There are 2 types of rockets classified based on reusability: Expendable Launch Vehicles (ELVs) and Reusable Launch Vehicles (RLVs)

ELVs

Not all rockets are reusable. Most are Expendable Launch Vehicles or ELVs. These rockets can be used only once and are discarded once their fuel is exhausted. They either fall back into the oceans, burn up in the earth’s atmosphere or are simply discarded in space. ELVs are of 2 types -

Single-stage-rockets:

These rockets consist of a single stage or section. Once they run out of fuel, they separate from the payload and are discarded. These rockets are very rare and are not used much.

Multistage rockets:

These rockets are made up of multiple stages. Each stage has its own fuel tank and engine. Once the fuel in one section is used up, that section is discarded and the next stage comes into play. Every time the rocket discards one of its stages, it loses more weight and thus the fuel needed decreases. This makes it efficient and thus preferred more.

RLVs

Reusable Launch Vehicles or RLVs can either be completely or partially reused. This means they can be refilled with fuel and used for more missions.

Partially reusable rockets -

Only a few parts of the rockets are reusable. The other parts are discarded either in space or in the oceans. The parts that are usually reusable are -

1st Stage:

This is often the main target for reuse. This is the heaviest part of the rocket and the most powerful. The main use of this stage is to initiate liftoff and boost the rocket through most of the lower atmosphere. Reusing this stage significantly cuts the cost of the mission as it is one of the most expensive parts of a rocket. Usually, these stages drop down into the ocean after their use and are then recovered by boats. Some however can land safely on the ground like the ones developed by SpaceX. The components of the first stage include the boosters and propellant tanks.

Boosters:

The boosters are a part of the first stage of a rocket. A rocket booster is defined as a propulsion component that provides additional thrust during the initial phase of a rocket's ascent (first stage). There are many types of boosters like Solid Rocket Boosters (uses solid fuel), Liquid Rocket Boosters (uses liquid fuel), Strap-on Boosters (boosters that can be strapped onto special rockets) etc. The main engine of a rocket is also a booster. Boosters are usually recovered along with the first stage of a rocket, but sometimes they are recovered separately like in the case of a space shuttle(shown below).

Payload fairings:

These are the components designed to protect the payload (the object the rocket is carrying) during the launch. They stop the payload from being damaged by the harsh conditions of the launch and the atmosphere. Fairings are usually found at the tip of a rocket and have a highly streamlined shape to reduce air resistance. Once the rocket has reached a height where the atmosphere is so thin that it does not pose a threat to the payload, the fairings are jettisoned to reduce mass. The fairings may be equipped with parachutes or thrusters to slow down their descent enabling them to be recovered later.

Fully reusable rockets -

All the stages of these rockets are meant to be reusable. However, there are no fully reusable rockets functioning currently. It is still just a theory as organisations and startups are still trying to develop such a rocket. SpaceX’s Starship system aims to be fully reusable in the future but is currently still in a testing phase.

The International Space Station (ISS) is a habitable laboratory in space. This space station orbits the Earth at a distance of 420 km. It acts as a home to astronauts from all over the world and is responsible for conducting experiments and research that can only be done in space.

Brief history

The original ISS was a collaboration between 2 countries: Russia and the USA. Over time, other space agencies, including the ESA, JAXA, CSA, and others also joined the project, contributing modules, resources, and personnel to the ISS.

It all started when Russia launched its Zarya module into space, it was designed to be a solo mission and orbit in space by itself. The same year, the US launched its Unity module with the same intentions. This was when both countries had the idea to join both of the modules together to make a bigger space station. Thus the ISS began to form.

Over the years both countries started contributing modules and adding to the ISS’ size. Other countries like Japan and space agencies like ESA started to collaborate too. This is how the space station formed.

Why decommission the ISS?

The ISS has continuously been inhabited by humans ever since November 2000. This makes it the only space station to be uninterruptedly inhabited for this long. This also means that the ISS is getting old. Some warnings have popped up that some of the systems have passed their expiry date and small cracks have started to appear in the Zarya module. Even a few air leaks have been reported in the living quarters of the crew. While most of these problems have been handled, it shows that the days of the ISS are numbered. This is why the space station is being decommissioned and deorbitted by 2031. This is going to be done by the proposed transition plan.

The International Space Station Transition Plan

The International Space Station Transition Plan is the proposed plan for deorbiting the ISS. A total of 5 national space agencies are responsible for this including NASA, CSA, ESA, JAXA, and ROSCOSMOS. This is how it is going to be done -

• The ISS will slowly decrease its orbiting altitude using its own propellants, bringing it closer and closer to the Earth.

• A new and modified spacecraft called the U.S. Deorbit Vehicle (USDV) will be launched to the ISS.

• The spacecraft will then adjust the space station’s trajectory such that when it falls to the Earth, it does not cause any damage. This will happen in the final re-entry maneuver.

• The earth’s gravity and atmospheric drag will be used as much as possible to lower the orbit.

• After all the crew have safely returned to the earth, a few small and final maneuvers will be done to line up the station over the intended landing area over the sea.

• Space station operators will command a large re-entry burn, providing the final push to ensure safe atmospheric entry.

• Most of the ISS will burn up in the atmosphere and the rest of it will land at an isolated point in the Pacific Ocean far away from any human settlements.

What after ISS?

The ISS still has quite a bit of life left in it, but NASA is already planning for what will come next. It is working closely with a few privately-owned companies to make new space stations. Axiom Space already has received a contract from NASA to build its own habitable module on the ISS. After launch, it will remain attached to the space station for a few years and plans to split up and form its own space station just before it is decommissioned. Another company: Space Entertainment Enterprise, is working with Axiom Space to make a studio for filming movies in space.

Other space stations

Many other countries are also trying to build their own space stations. China’s Tiangong space station is already in orbit around the Earth and is carrying astronauts right now. The ISS is still the largest space station in orbit currently.

Sources- nasa.gov, sciencefocus.com

First-ever landing on the moon

The first mission to touch the lunar surface was Russia’s Luna-2 mission in 1959. However, this mission was not designed to soft-land on the moon. It was created to be an impact mission. The craft was intentionally meant only to crash onto the moon. The first-ever soft landing was done by the Luna-9 mission.

Luna missions

After the Luna 2, several other Luna missions were launched like orbiter, sample return, impact, and lander. For a few years after the Luna 2 mission, several other impact missions were executed successfully like Russia’s Luna 5 and Luna 6.

The first-ever soft landing on the moon was done by Russia’s Luna 9 which landed on the 3rd of February 1966. After this, several lunar orbiter missions were also launched like the Luna 10, Luna 11, and 12 etc.

Since 1970, five Russian lunar missions successfully landed on the moon. This includes The Luna 16, 17, 20, 21, and 24.

Luna 16 was the first-ever lunar mission to successfully return a sample from the moon to the Earth. Luna 20 and the Luna 24 were also successful in returning samples.

Luna 17 was the first to deploy a robotic rover onto the moon.

Luna 24 launched in 1976 was the last time Russia landed on the moon. The recent attempt at Luna 25 was not successful as the craft, unfortunately, crashed onto the moon.

The Ranger missions

After the success of Russia’s Luna 2 mission, the US also attempted several impact missions onto the moon called the ‘Ranger’ missions. There were a total of three successful ranger missions: the Ranger 7, Ranger 8, and Ranger 9. Even though they were designed to crash, they were still useful in transmitting important data about the moon in the few minutes before the crash.

The Surveyor missions

The American Surveyor 1 mission was the first American craft to soft-land on the moon. The mission landed on the 1st of June in 1966 less than four months after the successful Luna 9 soft landing.

After the success of the Surveyor 1, four other Surveyor missions landed on the moon: The Surveyor 3, 5, 6, and 7.

The Apollo missions

The first ever Apollo mission to land on the moon was the Legendary Apollo 11 which put a human on the moon for the first time.

The Apollo 11 mission was not the only manned landing on the moon, six Apollo missions have successfully landed humans on the moon including Apollo 11 all the way to Apollo 17 the only exception being for Apollo 13. Though these missions were successful, the names of the astronauts are not well known.

The Chang’e missions

The Chang’e missions launched by China are one of the recent soft landings on the moon. The first Chinese craft to land on the moon was the Chang’e 3 lander craft in 2013.

After the success of this mission, 2 other Chang’e missions have been launched by China: the Chang’e 4 and Chang’e 5. The Chang’e 5 was a sample return mission and it returned the samples back to the Earth in 2020.

The Chandrayaan missions

The Chandrayaan mission launched by India is another addition to this list. Chandrayaan 1 launched in 2008, was an orbiter mission, and the Chandrayaan 2 mission in 2019 that attempted to land on the moon crashed just before landing. The Chandrayaan 3 mission however successfully managed to soft land on the moon recently. This soft landing made history a few days ago on 23rd August 2023 and has put India among the top 4 countries to have soft-landed on the moon.

Orbit Raising Maneuver

The Chandrayaan-3 spacecraft doesn’t directly go to the Moon and land, it goes through many complex maneuvers. Before the craft goes to the Moon, it rotates around the Earth for a couple of days while gradually increasing its orbit height. When an orbit height is increased, it is called an orbit-raising maneuver. This is done to take advantage of the Earth’s gravity and use it to catapult the craft toward the Moon. It is like a hammer thrower spinning the heavy hammer faster and faster before suddenly releasing it. Chandrayaan-3 has 5 orbits around the Earth, taking 17 days for all 5 orbits at varying levels. The 5th and final orbit is called the lunar transfer orbit.

Trans Lunar Injection (TLI)

This is the maneuver where the spacecraft is injected into a path toward the Moon from the Earth orbit, after completing all its orbit-raising maneuvers. During this maneuver, the craft is injected into the Lunar Transfer Trajectory (see next). It is important to keep in mind that this does not mean that the craft is entering the lunar orbit.

Lunar Transfer Trajectory (LTT)

After completing all the orbit-raising maneuvers, the path taken by the craft from the Earth to the Moon is called the Lunar Transfer Trajectory. The craft enters into the lunar orbit from the lunar transfer trajectory. This maneuver is called the Lunar Orbit Insertion (see next).

Lunar Orbit Insertion

In this maneuver where the spacecraft is inserted into the lunar orbit from the LTT. The craft will then keep orbiting for a few days so that it can perform a successful soft landing on the Moon. This maneuver requires slowing down the spacecraft and waiting for the Moon to pull it into lunar orbit. There are a total of 5-6 different orbits, each successive orbit gets closer to the Moon.

Apolune and Perilune

Apoclause and periclase are 2 general terms for the farthest and nearest point in the orbit of a body. For specific planets and moons, we use different terms. For example, for Earth, we call it the apogee and perigee but for lunar orbit, we call it apolune and perilune.

The apolune is the point farthest from the Moon during an orbit and the perilune is the point in its orbit when it is closest to the Moon. These 2 points play an important role in the orbit correction of the spacecraft. When orbiting around the Moon, the spacecraft fires its thrusters in the opposite direction to decrease the orbiting altitude. This is called retrofiring, similar to pushing a moving shopping cart in the opposite direction to slow it down. Retrofiring is typically done when the spacecraft is at the perilunar point. When a spacecraft does this, it is called an orbit reduction maneuver.

Orbit Reduction Manuever

This maneuver is performed by the craft in the lunar orbit. This is similar to the orbit-raising maneuver except that it is when the spacecraft is orbiting the Moon. Just like the spacecraft orbits the Earth before launching itself towards the Moon, it also orbits around the Moon before finally landing on it. This time, instead of going farther and farther, it goes closer and closer to the Moon. There are about 5-6 lunar orbits in total and when the spacecraft shifts to each orbit, it is called an orbit reduction maneuver.

Lander Descent Phase

This refers to the stage where the lander (called Vikram), carrying scientific instruments and equipment, begins its controlled descent from its lunar orbit to safely land on the Moon's surface.

Soft Landing

Soft landing involves carefully controlling the lander's descent to ensure it touches down gently on the lunar surface, avoiding damage to the spacecraft and its scientific instruments. This process is completely automated. This means that nobody can do much to help the craft at this phase. It has to fire the thrusters at the precise second, make an accurate scan of the lunar surface, and gently land on the Moon. This is why it is referred to by experts as the “15 minutes of terror” where anything could go wrong at any second.

Lunar Surface Operations

After landing, this phase involves deploying the rover (Pragyaan) and other scientific equipment to explore and conduct experiments on the Moon's surface.

Hope this post has helped you finally understand the complex Chandrayaan-3 mission terms. Here is the overall view of the path taken by Chandrayaan from its launch till the landing on the Moon:

Galaxies are large clusters of stars, planets, dust, and other cosmic objects bound together by gravity. They are one of the largest cosmic objects in the universe and can contain billions or trillions of stars. There are estimated to be over 100 billion galaxies in the observable universe

Types of galaxies

Galaxies come in various different shapes and sizes into which they are classified. These are the main types of galaxies.

#1 Spiral Galaxies

Spiral galaxies are like galactic disks with arms that spiral around the central bulge of the galaxy. Our galaxy, the Milky Way is one such example of a spiral galaxy.

#2 Elliptical Galaxies

These galaxies are more rounded or elliptical in shape compared to spiral ones. They lack the distinctive spiral arms that a spiral galaxy has. These galaxies often are made up of old stars and generally have less gas and dust in them. They are the most common type of galaxy in the universe.

#3 Lenticular Galaxies

A lenticular galaxy is a type of galaxy that shares characteristics of both spiral and elliptical galaxies. It has a disk-like structure similar to a spiral galaxy but has no spiral arms. Like elliptical ones, these galaxies have fewer ongoing star formations and gas and dust in them.

#4 Irregular Galaxies

Irregular galaxies don’t have any particular shape. The shapes of these galaxies are irregular and chaotic. They usually have a lot of ongoing star formation inside them and contain a lot of gas and dust.

These 4 are the broadest categories of galaxies. There are many subcategories under these 4 like barred spiral galaxies and ring galaxies. The study of galaxy classification is known as galactic morphology.

Galaxy clusters

Galaxy clusters are huge cosmic structures made of a group of galaxies bound together by immense gravitational forces. They can contain anything between a dozen to thousands of galaxies. Galaxy clusters are often surrounded by very hot gas which helps hold the cluster together.

Gravitational lensing

Gravitational lensing is a phenomenon caused by galaxy clusters when their gravity is so strong that it bends light coming from other galaxies which causes a distorted effect in space. Scientists often use this to their advantage as the gravitational lensing effect creates a powerful natural telescope in space that lets them see cosmic objects extremely far away.

Intercluster Medium

The Intercluster Medium (ICM) is a very hot gas that fills the space between 2 galaxies in a cluster. The temperature of the ICM can reach up to millions of degrees celsius. For comparison, the temperature of the sun is approximately 5,000 degrees celsius and the temperature of an average lightning bolt is 30,000 degrees celsius.

In conclusion, galaxies are fascinating structures and an example of the complexity and grandeur of the universe.

Black holes are the most dense objects in space with gravitational fields so strong that nothing, not even light, can escape from them. This is why they are called black. They form when massive stars collapse in on themselves, and they can continue to grow in size by consuming other matter and merging with other black holes.

The Event Horizon

The Event Horizon or the “point of no return” is the boundary of a black hole beyond which nothing including light can escape. Once an object crosses the event horizon, it is trapped inside the blackholes gravitational pull and cannot escape. The more matter the blackhole asserts, the larger it gets.

Types of black holes

There are 3 main types of black holes which are classified based on their mass. The three types are Stellar, Intermediate, and Supermassive black holes.

Stellar black holes are the most common type of black holes in the universe. Their masses can be up to 100 times that of the sun.

Intermediate black holes’ masses can be anything between 100 to 100,000 times the mass of our sun.

Supermassive black holes are the largest type of black holes. They are usually located at the center of a galaxy. Their mass ranges between millions to billions of times the mass of our sun.

Black holes don’t suck everything up

Contrary to common belief, black holes are not like cosmic vacuum cleaners. They only pull in matter that gets too close to their gravitational pull. They don’t actively search and consume everything in their surrounding.

Hawking Radiation

Hawking Radiation is a theoretical concept first proposed by Stephen Hawking a theoretical physicist in 1974. He proposed that black holes can emit radiation, due to quantum effects near the event horizon. It is believed that this radiation can cause black holes to slowly lose mass over time.

What is inside a black hole?

We know close to nothing about what is inside a black hole since it does not let any light escape. There are however many theories about it. Here are a few interesting ones.

#1 Singularity

One of the most popular theories is that a black hole contains a singularity, which is a point of infinite density and zero volume at the center of the black hole. All mater that falls into the black hole gets compressed into that singularity.

#2 Wormholes

This theory states that the blackholes could act as a tunnel to completly different part of the universe or maybe even another universe. These are called wormholes.

#3 A tiny universe

Some beleive that black holes could contain a whole new universe inside itself. A universe that is completly different from ours and has a completly different history. Our universe could be inside a blackhole right now.

It is important to note that all these are just theories. We know close to nothing about blackholes. Black holes are one of the greatest mysteries of the universe and its up to us to solve it!

Fiction: There is no gravity on the International Space Station (ISS).

Fact: Your ISS does not escape the gravity of the Earth. We just feel the sensation of weightlessness because the ISS and everything are constantly falling toward the earth at approximately the same speed while moving forward at a high speed. As the ISS falls, the Earth curves away from it. So the ISS “falls” around the planet. This environment is called microgravity.

Light

Fiction: Space is completely dark

Fact: There is light in space, including sunlight and starlight, but it can be difficult to see due to the lack of atmosphere.

Temperature

Fiction: Space is always freezing cold.

Fact: Space can either be extremely hot or extremely cold based on the exposure of a region to direct sunlight. During spacewalks, temperatures can range from -150°C to +120°C based on the location of the spacewalk.

Dark side of the moon

Fiction: The moon has a dark side that never sees the sun.

Fact: The moon has a “far side” that is not visible from the Earth but it does receive sunlight. In fact, several missions like Soviet Union's Luna 3 mission and the Chinese Chang'e 4 mission have managed to land rovers on the far side of the moon and have proved that it does receive sunlight.

Asteroids

Fiction: All asteroids are made of solid rock.

Fact: While some asteroids are made of solid rock, many are made of ice and other materials

Aging

Fiction: Astronauts don’t age on the ISS

Fact: Astronauts do age on the ISS but they age slower than the people on Earth due to the high speeds of the space station. The aging difference is still very less though. If astronauts spend 6 months in the ISS they would only be younger by 0.005 seconds.

Protostar

A Protostar is a dense collapsing cloud of gas and dust in the early stages of star formation. They are formed by the gravitational collapse of a molecular cloud. A molecular cloud is a large, cold, and dense cloud of gas and dust in space mainly composed of hydrogen, helium, and carbon monoxide. As a protostar forms, it begins to contract and heat up until it reaches a temperature where nuclear fusion begins. Nuclear fusion releases a huge amount of energy. Thus a star is formed.

Main Sequence Stars

Main sequence stars are stars that are young and full of fuel and energy. They fuse hydrogen in their core to produce energy. These stars are the most common type of stars in the universe. Our sun is a main sequence star. Main sequences can be larger or smaller than our sun. They generally are however larger than dwarf stars and smaller than giant stars.

Blue giant stars

Blue giants are very massive and luminous stars that have high surface temperatures and emit most of their energy in the ultraviolet part of the spectrum, which gives them a blue-white color. Like the main sequence stars, blue giants also fuse hydrogen to produce energy but the main difference is that unlike the main sequence stars, their hydrogen is running out.

Red giant stars

Red giant stars are stars that have run out of hydrogen and have started to fuse helium or heavier elements to produce energy. This causes their cores to contract and their outer layers to expand. This makes it larger and brighter than other stars. Despite being bright, the red giants have relatively low temperatures.

Supernova

When a star reaches the end of its life, it completely runs out of fuel and begins to collapse. This causes the star to become extremely dense and hot. This triggers a massive explosion that can outshine an entire galaxy. The explosion releases a large amount of heavy elements into the surrounding. This plays a large role in the formation of other stars. The supernova stage happens only to stars that are 8-20 times the mass of our sun. Smaller stars like our sun, will turn into white dwarfs

White Dwarfs

White dwarfs are extremely dense remains of stars. After a small or medium size star exhausts its fuel, it sheds its outer layers to become a white dwarf. In this process, the star becomes extremely small. Mass-wise, it would be like compressing a watermelon into the size of its seed. In this state, the electrons in the white dwarf are so densely compressed that they refuse to compress further. This state of matter is called electron-degenerate matter.

Neutron Stars

Once a star undergoes its supernova stage, it crushes protons and electrons together to form neutrons. It becomes an incredibly dense object composed entirely of neutrons. Neutron stars are even denser than white dwarfs. While they are typically only 10-20 km wide their mass can be greater than the sun. They are the second most dense objects in the universe other than black holes.

#5 SpaceX

The annual budget of this private space agency is $2bn. With that amount of money, you can buy 2.5 million iPhone 14s.

#4 ROSCOSMOS

The annual budget of the Russian Federal Space Agency is $2.9bn. That is about 3.7 million iPhone14s.

#3 ESA

The annual funding of the European Space Agency is $7bn. That amount is enough to buy 8.7 million iPhones.

#2 CNSA

The annual budget of The China National Space Administration, $8.9bn is enough to buy 11 million iPhone 14s.

#1 NASA

The current annual budget of the National Aeronautics and Space Administration is $20bn. With that amount of money, you could buy about 25 Million iPhone 14s.

You might have heard about the Perseverance rover by NASA. It is a rover designed to explore the Jezero crater on Mars which is an ancient lake on Mars believed to have dried up. And when we say ancient we mean billions of years old. Perseverance has collected 11 rock samples and one atmospheric sample.

Scientists believe that these samples could hold a clue about whether life previously existed on the red planet. Although the rover has a vast variety of scientific instruments, it is not enough to test these samples. Scientists prefer to properly test these precious samples back on Earth. This is why they plan to return these samples to the Earth.

How will the samples be returned?

This mission will be a collaborative effort between two space agencies: NASA and ESA. Two launches are needed to return the samples. A mars orbiter called the Earth Return Orbiter, made by NASA and a Sample Retrieval Lander made by ESA are going to be launched to mars. The orbiter will be launched by 2027 and the lander by 2028. Let us look at what the lander’s role is.

Originally it was decided that there would be a separate rover that would collect the samples from the Perseverance rover and then take them back to the lander. But Perseverance is more than capable of delivering the samples itself. This led to a change in decisions. The rover will take the samples to the lander itself and the lander’s robotic arm will transfer the samples. As a precaution, the lander will also have two sample retrieval helicopters, which will fly over to the rover and collect the samples and fly back to the lander, if the rover is not able to do the job on its own.

The lander will also have a small rocket inside of it called the Mars Ascent Vehicle. It will launch from the martian surface with the samples inside. Now comes the role of the Earth Return Orbiter mentioned earlier. The ascent vehicle will meet with the orbiter, which will collect the samples from it while orbiting the planet. The orbiter will then return to Earth. Once it nears the atmosphere, it will release the Earth Entry Vehicle which will contain the samples. Finally, the Earth Return vehicle will touch down on Earth.

It will take 11 years to engineer these landers and orbiters and bring the samples to Earth. The samples will return to Earth by 2033.

Sources: NASA and CNN

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Kayhan Space is a startup that makes sure your satellite doesn’t crash into another. How does it do this? Let us find out.

This space startup monitors all the space debris more than 10 centimeters. It then uses computers to predict the path of this debris. When the two paths of different debris are predicted to collide, it is called a conjunction. When the computer predicts a conjunction, it warns the satellite owners about it.

More and more space missions are being launched. Thus resulting in more space debris. Kayhan space plans to make space a safer place for satellites, telescopes, space stations, and other missions.

It is incredibly fast

The International space station travels at the speed of 28,000 km/h. That is eight times the speed of a bullet.

Astronauts age lesser

Astronauts in the space station age lesser than they do on earth because of the high speeds of the ISS, time slows down for them. The aging difference is still very less though. If astronauts spend 6 months in the ISS they would only be younger by 0.005 seconds.

Lots of sunrises

In just 24 hours the space station makes 16 orbits around the earth. It thus experiences 16 sunrises and sunsets.

There is a lot of wiring

If you took out all the wires and cables aboard the International space station and laid them in a straight line, it would be eight miles long.

Lots of parking space

6 spaceships can dock on to the ISS at any given point

50+ computers

More than 50 computers control all the systems on the station

It’s really heavy

The ISS weighs a whopping 420,000kg - that's about the same as 320 cars.

Explore the space station yourself using google street view

What are the different types of exoplanets?

There are four types of exoplanets:

• Terrestrial - Rocky planets like the earth which have a solid surface and are small.

• Gas Giants - Planets like Jupiter, which have no solid surface and are made of gas. They are very large.

• Super-Earths - Planets that can be gassy or rocky. They are Bigger than Terrestrial planets but smaller than Gas Giants.

• Neptune-like - Gassy planets that are larger than Super-Earths, but smaller than gas giants.

Thus we can line up the types in their ascending order of size:

Terrestrial < Super Earth < Neptune Like < Gas Giants

Lots of exoplanets continue to be discovered every month. Therefore, it is hard to give an exact count of the number of exoplanets discovered so far. This table shows the number of exoplanets discovered up until May 2022.

Neptune-like: 1760

Super Earth: 1569

Gas Giant: 1500

Terrestrial: 187

Unknown: 5

The above table has been converted into a graph for better understanding.

OBSERVATIONS

• The most common type of exoplanet is Neptune-like. This makes them bigger than Super-Earths but smaller than Gas-Giants.

• The least common types of exoplanets are Terrestrial. There are 5 unknown exoplanets.

Now that we are familiar with the types of exoplanets, let us now look at the ways in which exoplanets are discovered.

One such method is the Transit method. When an exoplanet passes in front of a star while revolving, it blocks the light of the star or dims the light of the star. This method looks for such cases.

Another method is the Radial Velocity method. This method relies on the fact that if a planet is big enough, its gravity tugs on its star causing the star to wobble. This method looks for such wobbling stars.

A third method is the Microlensing method. When a planet is big enough, it starts to bend its star’s light. This method looks for such scenarios.

The last method is the Imaging method. Astronomers take pictures of places where there might be exoplanets and analyze the photos to find exoplanets.

Here is a graph that shows the percentage of exoplanets found using the above methods.

Transit - 76.70% Microlensing - 2.60%

Radial Velocity - 18.40% Imaging - 1.20%

Other methods. - 1.10%

OBSERVATIONS

• 1.1% of the exoplanets were found using other methods

• The Transit method is the most effective.

• The imaging method is not that effective

• Radial velocity is the second most effective

The first exoplanets were discovered using the pulsar timing method. Later, in 1995 an exoplanet was discovered using the Radial Velocity method for the first time. Immediately the next year 6 other planets were discovered using the same method. Since then scientists started discovering more and more exoplanets using that method. Only in 2002 was an exoplanet discovered using the Transit method for the first time. Even still, the Radial Velocity method was used more. Later, in 2006 an exoplanet was discovered using the imaging method for the first time. After that, the transit method started rapidly discovering more and more exoplanets. In 2014 a huge number of exoplanets started to be discovered using the transit method. Soon by 2022 most of the exoplanets had been discovered by the Transit method.

All this data was obtained from NASA’s dashboard for exoplanets: https://exoplanets.nasa.gov/discovery/discoveries-dashboard/

Try scrolling down to the exoplanet census and playing around with the slider bar below.

Try going to the exoplanet catalog and selecting any planet of your choice. Try to find out all you can about the planet. It has almost all the information you need.

for example:

The planet 2MASS J01225093-2439505 b

It is 110 lightyears away from the Earth.

It is a gas giant.

It was discovered in 2013 by direct imaging methods.

It looks very similar to Jupiter

Even though its size is the same as Jupiter's its mass is 24.5 times the mass of Jupiter.

This exercise was inspired by this article at ScienceNewsExplores.

Do you know anything more about exoplanets? Share with us in the comments.

On September 27th (Indian Standard Time) NASA plans to test its Double Asteroid Redirection Test rocket (DART) which will do just that. Don’t worry this time the asteroid is no threat to Earth. It will just be used as a test subject for the mission. The asteroid’s name is Dimorphos. For more information check https://www.space.com/dart-asteroid-mission-on-track-for-impact

You can watch the mission here live: