On 28th February'21, ISRO's PSLV-C51 will launch the Amazonia-1 satellite along with 18 co-passenger satellites. Pixxel's Anand satellite was one of the co-passenger satellites. On 23rd February, Pixxel's Twitter handle shared an image stating that it would not launch on the PSLV-C51 mission.

Anand Satellite Launch Scrub

Due to certain software issues that surfaced during the final satellite testing, we have decided not to proceed with our launch on the PSLV C51 mission scheduled for the 28th of this month. Given the time and effort that has gone into making the satellite, it did not make sense to rush a satellite to launch in which we do not have complete confidence at this time. We have thus decided to push our launch by a few weeks, reevaluate the satellite software, and test it rigorously over the next few weeks as we look for the next closest launch opportunity.

We would like to specially thank the ISRO, IN-SPACe and NSIL teams for the immense support they have been to us during this entire endeavour. From making testing facilities available to our satellite to providing support over the entire launch campaign, the help has been very encouraging to see. We wish the PSLV C51 mission the absolute best as it takes off on 28th Feb, 2021, albeit without us.

We'll keep you posted as we gear up for the launch.

The text in the image posted on their Twitter reads.

Pixxel's CEO, Awais Ahmed, also tweeted the same image while adding some information. According to him, "the HILS and the thermovac tests went beautifully without hiccups." Simultaneously, the company CTO Kshitij mentioned that they are currently aiming to get their SILS in line.

Understanding the Space Terms

To understand what went wrong, we need to know some of the terms used by Pixxel leaders.

SILS: SILS stands for the Software-In-Loop-Simulation. In simple terms, the satellite software is tested in a framework that imitates the environment. In this case, a dummy system is carrying out the test. It is not the actual hardware that will fly on the satellite.

HILS: Some of you may have guessed it. The 'H' here stands for Hardware. The rest of the abbreviation is the same as SILS. In HILS, the same software tested on a dummy system is now tested on the actual space hardware. The central computer, called the OBC, is connected to all other devices such as the sensors. Generally, the satellite is also fully integrated for this testing. A simulator makes the satellite believe that it is actually in Space. The software and the hardware are hence tested.

Thermovac: The SILS was a software test, while the HILS was a hardware cum software test. Thermovac is a little different. In thermovac, we place the integrated satellite into a vacuum chamber. The temperature inside the chamber is controlled to imitate the space environment. Therefore, here the satellite's thermal and vacuum properties are tested.

Understanding what when wrong

In an ideal scenario, SILS is followed by HILS. In contrast, the Thermovac can be performed before or after SILS. But the tweets of Pixxel indicate that the HILS and Thermovac completed nominally while SILS detected some issue.

• There could be multiple reasons behind this. The primary point to understand is that we can perform these tests multiple times.

• Therefore, I believe that a SILS test must be performed before the HILS and thermovac. Before the satellite's final integration with the launch vehicle, another SILS may have been tried. It is because SILS is one of the few tests which can be performed without any hardware.

• This recent SILS test must have indicated some issue that was enough to scrub the launch.

All this is pretty normal in a space mission. Once a satellite is in space, there is very little that can be done to repair it. Therefore, it is necessary to test as much on the Earth. Let it fail on Earth so that it doesn't fail in Space.

Pixxel team has taken a courageous decision to scrub the Anand satellite launch. I hope they come back stronger and launch their satellite within a few months.

Edit: Awais and Kshitij confirmed the reasoning

Both Awais and Kshitij replied to my tweets and confirmed my theory. The SILS was performed before shipping the satellite to Sriharikota where some issue was observed. Due to a tight schedule, the Pixxel team decided to perform the hardware tests parallel to the SILS on a makeshift test jig. While this may sound as wrong. They made sure to appropriately write the test cases and success criteria for the test.

Definitions: 

• The test cases are various scenarios for which the test is performed.

• Success criteria are pre-known conditions that, when achieved, mean that the test is passed.

• CG + MOI is a test to calculate the center of gravity and moment of inertia of the satellite.

Ham Radio Club IIT Bombay Team

While there are four primary members, the whole satellite team of 40+ students help in the various activities of the club.

What is Ham Radio? How did the Satellite Team start Ham Radio Club IIT Bombay?

Amateur Radio (ham radio) is a popular hobby and service that brings people, electronics, and communication together. It is mostly used for non-commercial uses like networking with like-minded strangers, experimentation, communication during natural disasters, and receiving signals from space. Ham Radio operators are also called hams or amateur radio operators.

The IIT Bombay Student Satellite Program is dedicated to the vision of making IITB a center of excellence in space technology. With the launch of their first satellite Pratham in 2016, a ground station was set up to communicate with the satellite. The services of ham communication were required for the same. Ham Radio Club IIT Bombay, a part of the Institute Technical Council, was brought under the Satellite team’s purview due to a better understanding of satellites and communication.

• Satellite Tracking (Albeit Rains)

• Antenna Making Sessions

• Theory Lectures

• YouTube Live

What are the intricacies involved in being a Ham Radio Operator?

To perform most of the ham radio activities, one needs to be a licensed ham radio operator. The domain of activities that do not need an individual to be licensed mostly contain receiving and processing signals. A ham radio license enables an enthusiast to transmit signals of a fixed power range for a multitude of purposes. Different types of ham radio licenses exist in different regions with different allowances, but associated with every license is a unique callsign, a unique identification number assigned to a ham radio operator.

An individual needs to pass one or more exams of different formats to acquire their license. The number of exams and their structure is slightly different for different countries. Although all the exams, irrespective of the region, test the individual’s knowledge in radio communication theory and ham radio rules & regulations.

In India, the ham radio license exam is organized regularly by the Wireless Planning and Coordination Wing of the Department of Telecommunication, GoI. The ham radio license has 2 ‘grades,’ namely the restricted grade and the general grade. To get a restricted grade, one needs to pass a theory exam based on radio communication theory and ham radio rules & regulation. To get a general grade license, one needs to pass a practical morse code receiving + transmitting exam along with the theory exam mentioned before. Anyone above the age of 12 is eligible to apply for any of the licenses mentioned. The two grades differ in allowances transmissions of signals in terms of frequency bands and power transmitted.

More Details:

A restricted grade ham license holder is allowed to transmit signal of power up to 10W in the UHF & VHF band and 25W in the HF band, whereas a general grade license holder, is permitted to transmit signal of power up to 25W in the UHF & VHF band and 400W in the HF band.

You recently received images from the International Space Station. I believe you received pictures earlier as well. How was it different this time?

Amateur Radio on the International Space Station(ARISS) transmits SSTV images for a few days to Earth twice or thrice every year to promote ham radio. Receiving & decoding these SSTV images has been a regular activity in our club. In normal times, we used our own portable ground station and equipment to receive the signals transmitted from ISS whenever it passed from over our sky.

Due to the pandemic and lack of access to our ground station and equipment, we decided to widen our scope and explore webSDRs. WebSDR is an online network of numerous ground stations set-up around the world. Any of these ground stations can be accessed and used by anyone with an internet connection through this network. It can be called Virtual tracking, much like the virtual world we are going through at present.

During the Christmas of 2020, ARISS celebrated its 20th anniversary by holding one more SSTV transmission event. This time, instead of using our own ground station, we accessed some freely available webSDRs located in the Netherlands and South Africa to receive signals. Our team was awarded the ‘ARISS SSTV Award’ for successfully receiving and decoding these images with the webSDRs.

What is the vision for HRC-IITB, and what are the upcoming plans?

Ham Radio Club IIT Bombay has the vision to foster and grow the Amateur Radio community in IIT Bombay and beyond. We aim to set up a full-fledged autonomous ground station with advanced and updated technology while attaining numerous ham radio licenses.

HRC-IITB has been organizing multiple theory and hands-on sessions in the lockdown and made them available on our YouTube channel. The pandemic gave us an opportunity to spread our online presence as much as possible and reach people whom we could have never met. Having started our own Instagram page last year, we have been conducting interactive activities like quizzes, learning the Morse Code. Our blog Stories of a Naive Radio (SNR) consists of a plethora of information on ham radio and wireless communication.

Upcoming is our flagship event, ‘Ground Station Workshop 2021’, a one-day long free of cost workshop. We are also planning multiple new Instagram series and blogs.

Can you detail a little bit on the upcoming Ground Station Workshop?

We are conducting our flagship event, The Ground Station Workshop, on 24th January 2021 in the virtual mode. It will be a full-day event held on an interactive online platform. The event will be held on a combination of YouTube Live and Discord. More details will be shared with the registered individuals soon.

It is majorly aimed at educating engineering college students from across India (and maybe this time the world) about ground stations so they could set-up ground stations or initiate space and ham-related projects in their campuses. It can also be a beneficial event for all the ham enthusiasts out there. Even after being technically oriented, the workshop will cover some talks on managerial aspects of team building and cost analysis of a ground station.

All the details regarding the event, from registration to timings, can be found on our social media handles.

Facebook: Ham Radio Club IIT Bombay

Instagram: @hrc.iitb

YouTube: Ham Radio Club IIT Bombay

Registration link: https://forms.gle/iB16d7qyQKT9cVVb9

Go follow Ham Radio Club IIT Bombay everywhere guys! The series I love the most is Morse Mania on Instagram. Learning Morse code was never this easy before!

X-33 Reusable Launch Vehicle

Case Study

X-33 was a reusable launch vehicle program started in 1996. The program had many objectives. Because America had last invested in a new launch vehicle technology during the shuttle design, to catch-up, they set to reach for new technology in every subsystem. One major technical challenge was the linear aerospike rocket engine. The team had alternate designs in case it faced development or testing problems. Though it was good to have alternates in your pocket, it was not possible to have equivalent alternatives to each and every subsystem. It was assumed that ground tests would have failures. Ultimately, one of the other subsystems failed in a test. The reached far, but the program was cancelled in 2001.

Learnings

• Estimate all resources from the start.

  While the initial design strategy was to set up new technology in every subsystem, an estimate of resources, money and facilities should be made.

• A constant vision and persistence, even in times of failure, is needed.

  The vision to achieve new technology in every subsystem was challenging to sustain with increasing costs and delays.

Hubble Space Telescope

Case Study

A team was tasked to design and develop a backup system for the primary fine guidance sensor that would work on different principles. There were many "eye-opening" problems identified by this team.

• People working on solar arrays were not coordinating with people working on the control system.

  "Therefore, as the solar would swing and out of sunlight, they would irrevocably excite the satellite in return, and there was no image motion compensation or effective correction in the control loop."

• The electronics, which were planned to be used, had launch-vehicle heritage rather than spacecraft which generally operated for much longer mission life.

• Finally, there was no end-to-end test of the telescope.

Despite all this, every contractor could prove their design met the requirement given to them.

Learnings

• Communication is the key to a sophisticated design.

  All the different teams should be able to communicate their ever-changing requirements with each other. The designs are often evolving, and therefore a constant communication is needed.

• Despite every individual subsystem proving the requirements set onto it, an end-to-end test is of utmost importance. There are hundreds of interfaces between different subsystems which are tested only in integrated trials.

Delta 180 Powered Space Interceptor

Case Study

The Delta 190 was a success. It was late after the launch when someone discovered a problem with the control system. The simulations had not modelled stiction, a friction force in the radar homing device. This oversight resulted in a slight lag of control which produced an error of a few feet in the trajectory. Fortunately, the interceptor technology was not good enough, resulting in a very big design. The Delta 180 still ended in a hit-to-kill blow. Three separate teams worked independently on the simulations, followed by a meeting to discuss the simulations. The launch was approved only when consolidated results were within 0.5 m error probables. Everyone missed the importance of stiction in the vacuum.

Learnings

• Despite an overall success, all the intricate subsystems parameters should be reviewed.

Summary

While the learnings presented above are based on my own understanding of systems engineering, the paper also offers a few essential learnings.

• Failure is an option

  Going against the famous words of Apollo 13, the panellists mentioned that failure should always be an option. In examples, only X-33 failed at the final level. Hubble had failures right until the 1993 servicing mission, but it still became the icon of space exploration.

• Process is not the solution

  In the case of Delta 180, every process was done right. Multiple independent teams worked and checked the simulations, and it still resulted in an oversight. The solution to failures in systems engineering is not increasing process. While the process is essential, teams which don't understand the system or the process fail. A simple example stated was that giving a checklist to fly an aeroplane cannot make everyone a pilot. Process, in the end, is just a tool. Humans and their creativity and intuition, along with the leadership, are what sets apart a great systems engineering team.

As we saw in the last lessons learnt article, it was humans who found creative solutions to the problems. Leadership and human resources management are, therefore, essential aspects of any program.

If you know about any other systems engineering failures, do let me know and I'll cover them in my subsequent posts.

The two astronauts, Douglas G. Hurley and Robert L. Behnken will crew the Crew Dragon on this spaceflight. Behnken has flown on the shuttle twice, has spacewalk experience and worked as Airforce Flight Test Engineer with a doctorate in Mechanical Engineering. Doug is an expert pilot with more than 5500 flight hours on more than 25 aircraft. He has also piloted two shuttle missions one being the final Atlantis STS-135.

While the astronauts have gotten a lot of coverage and press interviews, there are many personnel working behind the scenes. In a recent Houston, We have a Podcast, Podcast series, NASA's Lead Flight Director for the Crew Dragon Demo-2 mission, Zebulon Scoville, gave an interview. Zebulon Scoville, also known as Zeb, started in the EVA operations team and was also the lead EVA officer for astronaut Bob's first flight on STS-123. He has a Mechanical and Aerospace Engineering Background from Stanford University.

Zebulon talks about his early experiences with NASA and recent experience of collaborating with SpaceX for commercial crew program. He also explains the full in-flight operations which will take place once the Crew Dragon is launched by the Falcon-9 rocket from the Kennedy Space Center. A summary of the same is as follows (not exhaustive):

• Verify

  • Did everything survive and work throughout the launch?

  • If the navigation system is established with a good lock on the GPS?

  • The communication pathway via TDRSS satellites is established?

While the Crew Dragon is autonomous, they will be testing the manual flight of the vehicle.

• Manual Testing

  • The crew is going to take manual control in the far-field of ISS.

  • They'll be able to control the roll, the pitch and the yaw through their touchscreen displays.

  • They can do finite thruster input through those inputs to be able to get a clean rotational axis.

  • They might manoeuvre to realign the spacecraft with the local vertical, local horizontal reference frame.

• Sleep for the Crew

  • The crew dragon can dock with Space Station within 6 hours, but this time we are looking for about 19 hours. So the astronauts will have time to sleep.

  • The crew can put some window shades on the cabin and some earbuds. The crew dragon can provide some white noise which lets them go to sleep.

  • While the crew sleeps (ideally for eight hours) the Dragon and crew on the ground will continue to monitor all the parameters. They'll try their best not to have any thruster burns while they sleep, as they make a sound.

• Waking up and Operations

  • Will the crew wake up with music? (Shuttle Tradition) We will need to watch.

  • Have a meal and get vehicle status.

  • Wear there suits on again, as they get closer to ISS.

• Docking

  • There are a number of intricate procedures which will lead upto docking.

  • Another manual testing will be done around 170-220 meters from the space station.

• Welcoming Ceremony

  • The hatch will open, and the ISS crew will come and meet the Demo-2 crew.

• Onboard Operations

  • There are many tests to be performed while crew dragon is docked with ISS and is essentially a module of the space station.

  • Establish excellent communication from Dragon down through the U.S. segment, through the Russian segment to Soyuz.

  • Russian crew will be in Soyuz with a crew in Dragon and they'll make sure that audio signal is strong.

  • "That's important if there was an emergency on ISS. Both crew members will go back to their own respective vehicles and then prepare for responding to the emergency."

  • Check good data connection on Crew Dragon from the space station using space station laptops and I-pads.

  • They may have some ISS crew come over for a sleepover to check Crew Dragon capabilities. (It is designed for more than two humans)

So there are a series of tests and a lot of exciting science and technology set up for the next few days. The launch is scheduled at 20:33:33 UTC tonight (27th May 2020). Do tune into NASA TV or many other channels on YouTube which will be broadcasting this event live.

UPDATE: The launch was scrubbed due to Weather red flag. The next launch attempt will be at 3:22 p.m. EDT on Saturday, May 30 (12:52 a.m. IST Sunday, May 31), from Launch Complex 39A at NASA’s Kennedy Space Center in Florida. Hope we will be able to see the Crew Dragon Demo-2 mission launch soon.

I'll put the link of the podcast here and let you hear the details of the points listed above.

Jupiter Missile

The Jupiter was the First nuclear-tipped, medium-range ballistic missile (MRBM) of the United States Air Force (USAF). It used RP-1 and LOX as liquid fuel for the single Rocketdyne LR79-NA (model S-3D) rocket engine.

The Jupiter missile might be overlooked today, but without it, there would have been no Army Ballistic Missile Agency (ABMA), no Explorer I, no Saturn launch vehicle, and no Marshall Space Flight Center. Without Jupiter, U.S. astronauts would not have walked on the Moon in 1969.

Ed Kyle, Space Launch Report

Problem

On March 1st 1957, the first Jupiter missile AM-1A was launched from the Launch Complex-5 at Cape Canaveral. The vehicle broke up at T+73 seconds after control failed around the 50 seconds mark. The second Jupiter Launch, on April 26th, went as planned until T+70 seconds. The rocket then broke up at T+93 seconds due to instabilities related to Propellant Sloshing. The first problem was attributed to the burning of control wiring by turbopump exhaust. Therefore extra insulation was added in all subsequent flights. Though, the second problem, related to Propellant sloshing dynamics coupling with the control system was not easy to solve. Hence required more creativity.

Physics

We all have experience liquid sloshing in our lives. We have spilt liquids such as water, tea, coffee and juices when trying to go fast while a filled cup. What happens is that the liquid starts resonating with our movements, and it makes the control of the cup difficult. We tend to slow down to stop this sloshing or put a lid over the container.

Similarly, rockets filled with liquid propellants also experience this sloshing. While we have the option of slowing down and stop the sloshing rockets can't reduce their speeds. And even with closed containers, the problem is not spilling but causing instabilities to both combustion and control. Therefore, it is essential to understand this slosh dynamics. There are many good books on slosh dynamics which tackle this through an analytical point of view. But this theory is reasonably recent and did not exist in the year 1957.

Solution

While NASA had a team studying slosh dynamics using both analytical and experimental techniques, Jupiter 3 had to be launched within a month. The engineers took the Jupiter LOX tank, filled it with water and put it on an empty railroad car. Using a movie camera, they recorded the motion of water when the railroad car bumped against the spur railroad stop. They derived an equivalent slosh mass and frequency to be used in a control feedback simulation. This creative empirical technique would now help them test their control systems with a better environment.

But this was not the solution to the sloshing problem. As the phenomenon was still not well understood, the sloshing could be very different for the launch. It was at this point that human experience and creativity combined to help design a new device. An engineer remembered something from when he was back in farms. To haul water in steel drums in a wagon, he floated pieces of lumber on the surface to keep it from spilling. But a missile cannot of lumber floating in its fuel tanks! Therefore they designed a perforated cylinder truncated with cones and had a commode float inside to make it float. These new devices were called "Beer Cans". The whole fuel tank surface was covered with these devices, and Jupiter 3 was successful.

Later, through analysis and sub-scale testing, "Baffles" were developed. These were structures included in all subsequent liquid engines to prevent sloshing of liquid. The following link has information about the F-1 engine Baffles.

"The basic lesson is that we must reward all forms of creative actions of our people and start development of processes to remove inhibitors which suppress the creative actions of its people."

NASA Report

The Soviet Union launched Sputnik-1 on October 4 1957. The United States, once again, got left behind in the Space race. The government gave US Navy the go-ahead launch a satellite. Vanguard TV-3 attempted to launch US' first satellite on December 6, 1957, from Cape Canaveral. After lift-off and reaching only 1.2 m height it exploded on the launch pad. The Eisenhower administration then gave the go-ahead US army and JPL. The Jet Propulsion Laboratory designed and built the satellite within 90 days. On January 31, 1958, at 22:48 EST, the US Army Ballistic Missile Agency launched Explorer 1 using its Jupiter C rocket developed under the direction of Dr Wernher von Braun. Here is a small 5-minute documentary video on Explorer-1.

The Problem

Any satellite in orbit needs to be oriented in a particular direction for many reasons. One simple one is to turn the antennas so that they radiate towards the Earth. Explorer-1 utilised spin-stabilisation technique to accomplish this. A rotation around the longitudinal axis was provided to the satellite. But within a few orbits, the spacecraft changed its rotation axis. This phenomenon was very new for scientists and engineers of that era. Let us try to understand what went wrong through simple physics.

The Science

Many of us have studied the law of conservation of angular momentum for a torque-free rigid body. All of the discussion will revolve around this principle now.

Intermediate Axis Theorem

The Intermediate Axis Theorem states that the rotation of a rigid body around the maximum and minimum principal moment of inertia axis is stable. This principle can be seen in action in the following video. Also known as the Tennis Racket Theorem, this medium article explains it quite well. The post explains it using Euler's equations of motion.

Coming back to Explorer-1, the satellite was rotated about the least moment of inertia axis. Therefore, being stable it should have remained rotating about the same axis.

So, did the intermediate axis theorem fail?

The answer lies within the statement of the theorem. Explorer-1 had four flexible whip antennae sticking out of the spacecraft. Therefore, the assumption that 'the satellite is a rigid body' didn't apply. These antennae dissipated energy and led to a destabilising effect which resulted in a flat spin about the maximum moment of inertia axis.

We know that because there are no external torques, Angular Momentum is conserved.

Momentum:

• H=Iω (constant)

While we can also write the kinetic energy of the satellite as

Energy:

• E=½ Iω2

• Emin=½ (Imaxωmin)ωmin =½ Hωmin

• EMAX=½ (Iminωmax)ωmax =½ Hωmax

Where:

• H = momentum

• E = energy

• ω = spacecraft angular velocity

• I = momentum of inertia

With kinetic energy losing, satellite eventually went into the Emin state. Therefore, it started rotating about the maximum moment of inertia axis.

The following statement can be made:

If a spinning object has internal energy dissipation, it will orient itself so that the spin is about the axis of maximum moment of inertia (e.g., a long cylindrical object will flip into a flat spin).

Satellites with fuels will exhibit the same phenomenon as the rotating fluids will convert the kinetic energy to heat energy, much like the flexible antennae. Many experiments have been conducted onboard the International Space Station.

Solution

We know there are many satellites which contain fuel onboard. If one of them needs to be rotated like the Explorer-1, what should be done to mitigate the problem?

The engineers at JPL solved the problem quite simply for subsequent explorer satellites. Two fibreglass slot antennae replaced the original flexible antennae. Now, the Explorer-3 spacecraft indeed was a rigid body. Therefore, thanks to Intermediate Axis Theorem, the rotation about the minimum moment of inertia axis was stable.

But for satellites with fuel, we are still to solve the problem. The solution for this is also simple enough. The difficulty arises due to the dissipation of kinetic energy. If we could somehow impart energy to the spacecraft, the problem would again be solved. Hence the engineering solution, Reaction Wheels came into existence. Reaction wheels are a large moment of inertia bodies which can be rotated by converting electrical energy (motors).

Summary

In summary, a rigid body rotating about the highest or least moment of inertia axis is stable. If it starts losing Kinetic Energy through internal dissipation (Angular Momentum is conserved), the body will tend to rotate about the maximum moment of inertia axis only.

The following video by Veritasium explains this whole phenomenon quite well.

Different aerospace departments at various engineering institutes have different terms. In general, the following focus areas constitute Aerospace Engineering.

• Aerodynamics

• Propulsion

• Structures

• Dynamics and Control

• Design and Systems Engineering

Aerodynamics

The study of the movement of air around bodies such as aircraft or spacecraft. In turn, there are two classes based on speed, Subsonic and Supersonic. Subsonic deals with bodies moving at speeds less than that of sound, while Supersonic deals with rates higher than the speed of sound. Dealing with Aerodynamics needs a good understanding of fluid mechanics, calculus and programming.

"How a bird or an aeroplane flies?", if you have asked this question, the answer lies within Aerodynamics. Not only aeroplanes, a launch vehicle blasting to space, a racing car on the track or a kite flying, but all these objects are also affected by Aerodynamics.

You may find aerodynamics experts working day-night on a computer screen working on computational fluid dynamics (CFD) models or one may have his/her head inside a wind tunnel, fixing a model for testing. If you are lucky, you may also see the rarer ones, trying to work out Navier Stokes problem or creating a new model.

Structures

Structures is the easiest to describe. "Will your mobile phone survive a 10 ft (one floor) fall?". Its build, along with the material, represents this answer. Build depends on the shape and the placement of different joining elements such as nuts and bolts and the manufacturing process determines the material properties. In the end, all the above details are designed to ensure the mobile sustains various forces applied to it.

Similarly, aerospace structures are lightweight structures used for aerospace applications. Aerospace applications have a unique element to them; once deployed, they are tough to be repaired. Therefore, there is a history of various choices which are consistently made in Aerospace Structures. For example, the shape of an aeroplane has changed little in the last several years.

Along with the various details discussed above, Structures experts also design the mechanisms for different purposes such as Solar Panel Deployment.

Propulsion

You must have seen birds flapping their wings. Aeroplane, on the other hand, has fixed wings. Birds don't flap wings to generate upward force (lift) but to produce the forward force (thrust). This is evident if you watch a bird flying at high altitude. With high flowing wind, birds don't require flapping. The study of the generation of this forward force is propulsion.

Propulsion experts work on different techniques to generate propulsive forces. The engines range from air-breathing ones such as Jet Engine, RamJet, ScramJet and non-air-breathing ones like Rocket engines.

Propulsion itself is a very diverse field. For air-breathing engines, both fluid mechanics and thermodynamics are essential. Thermodynamics and Shock Theory is needed for ScramJet and Rocket engines. The propeller blades used for jet engines need aerodynamic studies. The high temperatures encountered have to be accounted for in the structural design. Slowly, the complexity of Aerospace Systems is coming into light.

Controls and Dynamics

An aeroplane takes off with nose up, cruises with wings level and takes a turn with body rotated. All these manoeuvres require the pilot to control the aircraft. To design the control system, we need to understand the dynamics of the aircraft. Similarly, all aerospace systems need guidance, navigation and control (GNC) systems. You need a strong mathematical background for GNC expertise.

Controls and dynamics need to account for all the forces being applied to the body. Aerodynamics provide the forces due to flow of air, propulsion provides the propulsive forces and internal forces due mechanisms are given through structural simulations. Along with this, there are many structural, thermal and dynamic constraints. The GNC system has to be able to account for all of the above details.

Design and Systems Engineering

With four of the fields understood, we recognise the complexity in the design of the Aerospace Systems. Design and Systems Engineering connects it all together. To design an aerospace system, experts from all the fours domains need to come together. Systems engineer ensures smooth workflow of information between the different subsystems defined by distinctive fields.

Design and Systems engineer also ensure that the mission of the Aerospace design is being met. Generally, that means an optimisation problem is solved. For example, we may be designing lightest parachute. This exercise would need all divisions to work. Therefore, design engineer, communicate with experts from different fields and create mathematical models with their assistance. These models are then utilised to solve the optimisation problem.

In the end, all the five divisions together design an Aerospace System.

I hope you gained a little understanding of Aerospace Engineering. I'll urge you to let me know about other topics and questions you have related to aerospace engineering through the following form or you can leave a comment. I'll make sure to cover them in next few Monday Mentoring posts.

Let us start this article by debunking another one: "Want to work in Space, Take Aerospace Engineering". Aerospace engineering is the discipline that gives the overall understanding of space technology. However, it is the era of interdisciplinary science and technology. With the ever increase in knowledge database of humanity, it is not possible for only a set of individuals. Everyone from different background needs to come together and develop new technology. Therefore, I answer "How Other Engineering Disciplines can contribute to Space Industry?" in this article.

Biosciences and Bioengineering

You may remember "Mark Watney" from the movie (or book) The Martian. For humans to survive in space, we require many systems such as Life Support System and Spacesuits. Not only these systems, for long-duration human spaceflight psychological and social (Humanities) aspects of astronauts become essential as well. Along with medicine and anthropology, bio-engineers also work on microorganisms studies, to understand the evolution of life. With the possibility of microbial life on moons of Jovian planets, these studies would prove essential.

Chemical Engineering

This one can be explained in simple words as "Rockets require fuel." Chemical engineering is the branch which designs 'chemical processes' to manufacture chemicals in large quantities and efficiently as required by the industry. Chemical engineering is essential for inventing new processes for green fuels for both rocket motors and small thrusters for spacecraft.

Civil Engineering

It may not be very intuitional how civil engineers can contribute. But it is one of the crucial disciplines for future space settlements on moon and mars. Various structures to be built would face the challenges of low gravity, pressurised internal environment and protection for space radiation. Civil engineering researches on innovating structures to be built from the materials available on site at these planetary bodies (In-Situ Utilisation). Not only this, one of the significant satellite applications: remote sensing is also a division studied under Civil engineering.

Computer Science and Engineering

With the advent of computers, every field studied on this earth utilises computer science for studying more complex problems. "Space doesn't give a second chance", and "Testing area technology is hard", these two sentences explain the need of performing hundreds of simulations before flying space hardware. All these simulations require a lot of computing power.

Along with simulations, the spacecraft needs to be autonomous. With machine learning and artificial intelligence, we may have a supercomputer like "Hal 9000" from 2001: A Space Odyssey in the future. Though, I do hope the AIs of the future don't end humanity as with almost all Hollywood movies.

Electrical Engineering

Another engineering discipline with applications over many domains. Spacecrafts require intricate electronics which can survive the hard space environment while working on meagre power resources. It is the job of electrical engineers to design hardware capable of overcoming the challenges of space radiation and severe temperatures while consuming less power. Not only this, but they also need to have less weight and small size.

Energy Science and Engineering

As discussed above, spacecraft is limited in energy resources. Energy science, along with electrical engineering develops better solar panels to convert a maximum of the solar energy to usable power. Future space colonies would require energy scientists and engineers to develop energy methods to sustain hundreds and thousands of humans.

Engineering Physics

Engineering physics is an amalgamation of physics and electrical engineering. They are responsible for understanding multi-body dynamics simulations which further help in determining the position of various celestial bodies. Physicists also develop various astronomy and micro-gravity payloads. Physicists develop even the optics required for remote sensing applications.

Mechanical Engineering

Mechanical is the closest branch to Aerospace engineering. Almost all aspects of mechanical can be extended to space applications. I would discuss the domains, I know. Structural and thermal design of the spacecraft and rocket is essential. It requires new innovative methodologies such as honeycomb plates for structure or origami mechanisms for solar panel deployment. Mechanical engineers can work on any of the four divisions of aerospace (Structures, Propulsion, Aerodynamics, GNC) based on their expertise.

Metallurgical Engineering & Materials Science

You may have heard about Space Elevators. One of the major roadblocks towards making one is material. We don't have materials to sustain high forces. It is not limited to this. We have almost reached the summit of launch vehicles with present technology. With breakthroughs in either propulsion or advanced materials only, we can have large growths in future. Satellites are slowly shifting to using 3D printing or composite materials instead of aluminium. Basically, from cryogenic engines to re-entry vehicles and even electric propulsion, all require a breakthrough in material science.

In summary, all engineering disciplines can contribute to space technology. Therefore, choosing an engineering branch should be based on the curriculum. Find what is interesting to you. Later, one can apply the knowledge to a space domain.

Aerospace Engineering

Now, it may seem, that aerospace engineering as a separate branch is not essential. Aerospace engineers make sure that all these different experts come and work together. Aerospace engineers, therefore, need to understand the essence of all engineering domains to be able to integrate the different subsystems into a functioning complex space system.

I hope a lot of your opinions changed after reading this article and you got much more informed. I'll urge you let me know about other topics and questions you have related to aerospace engineering though the following form or you can leave a comment. I'll make sure to cover them in next few Monday Mentoring posts.

I'll use the term aerospace for aerospace engineering throughout this article.

"It is Rocket Science, hence very tough."

Aerospace is many times colloquially termed as "Rocket Science". The term Rocket Science is used in both written and audiovisual media to convey extremely difficult scenarios or tasks. Though aerospace engineers are cool enough to garner attention, the field itself is not much different from other branches of engineering. It uses the basic concepts of physics and applies a lot of mathematics to make aeroplanes, rockets, and satellites. I know a few of you may get intimidated by my use of "a lot of maths", but that is true of all engineering branches.

Rocket science is cool and comfortable enough if you are good with mathematics.

"You won't get jobs, take CS, the packages are very high."

Many interested candidates would receive advice not to take aerospace because of job scarcity in the core sector and the lack of high-paid salaries. First of all, these are two separate issues, let us tackle them one by one.

Yes, there indeed are very few core aerospace jobs around the world. With the industry run by the government for more than 60 years, all significant recruiters are government-run organisations. In India, with Make in India and Startup India, private players are slowly coming in. Therefore, the jobs within the private sector would increase. For ISRO, DRDO, HAL, and NAL, the jobs are limited. Generally, the vacancies are filled through nation-wide tests where the government is still to upgrade to aerospace based vacancy instead of mechanical or electrical. Globally though both private and public sectors exist, the job profiles are limited to the citizens only. Also, in general, the number of jobs is limited: for every job.

You can overcome this barrier of less jobs. :P Even though not easy, generally aerospace engineers become passionate and patient in the four to six years of study.

High-paid salaries in computer science and electrical are very few. The average of CS-Elec may be a little higher at around 12-15 lakhs per annum but Aero-Mech core jobs are also at 8-11 lakhs per annum only. The dream of getting a high-paying job gets fulfilled for the only maximum of 2-5% people in a batch. (Rough statistics)

There are some other aspects as well. Engineering requires you to choose even before knowing what you are getting into. Picking CS just because it pays well, might not work out for you in the long run.

Job scarcity? Correct but passion, patience and friendships take you there. High-paid jobs, only 2% such jobs.

"You are interested in stars, take Aerospace."

In my three years as an Aerospace senior (the second year doesn't count, sorry sophomores, but you don't know much), I have come across many students mixing the two branches: Aerospace and Astrophysics.

Astrophysics is a branch of space science that applies the laws of physics and chemistry to explain the birth, life and death of stars, planets, galaxies, nebulae and other objects in the universe. It has two sibling sciences, astronomy and cosmology, and the lines between them blur.

As per space.com

Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering.

According to Wikipedia

Note, astrophysics is space science while aerospace deals with designing and making the technology to assist astrophysicists. Looking at the night sky and wondering about how stars came into existence: astrophysics. Looking at the night sky and wondering how to get to the moon: Aerospace. Though aerospace deals with the technology aspect, it is not possible without the help of physicists. To make an object as complex as satellite, many people come together.

How the stars formed? Astrophysics. How to reach stars? Aerospace.

"Aerospace is a restricted branch, take mechanical you'll still learn everything."

Yes, aerospace is a restricted branch while mechanical is a broader one. However, that doesn't imply that aerospace can be studied in the mechanical curriculum. To understand this better, it'll take a full post. I'll try to describe it a little here. First, let me inform you about the five sub-divisions of aerospace engineering.

Structures: This may be the closest subdivision to mechanical. The only caveat here is the weight of the vehicle. Aerospace applications require light-weight objects. Also, mechanisms have been known to fail a lot in space.

Propulsion: Deals with rocket engines and hypersonic flows while in mechanical very different car engines are studied.

Aerodynamics: Deals with the flow of fluids around aeroplane and helicopters. It also deals with the re-entry of space vehicles. Two fundamental differences with Fluid Mechanics (same underlying physics) taught in Mechanical Engineering: Aerodynamics majorly deals with the external flow and velocities are much higher.

Guidance, Navigation and Control (GNC): This sub-division helps in guiding and controlling the position and orientation of aircraft and spacecraft. Though the underlying mathematics is the same, the application of aerodynamic, elastic, and propulsive forces on the aerospace vehicles makes it essential to be studied under aerospace.

Systems Engineering: As understood, aerospace engineering while having the same underlying physics and maths as mechanical become very different due to its challenging applications. Here comes, the field of systems engineering, which makes sure the four of the above divisions work together. It also deals with operations and mission design, such as Airport schedule.

Another closely related sub-division is Avionics, but it is usually not studied under aerospace which is good for the Electrical Engineers who want to get into Aerospace.

"Mechanical and Aerospace are different branches due to different applications. Choose based on curriculums available of the websites of the universities."

"I want to become an astronaut. Hence I am taking aerospace."

I once read an answer by a NASA astronaut on Quora, that Astronaut is a second profession. There is no need to be an aerospace engineer to become an astronaut. Astronauts are all kinds of people, ranging from geologists to medical practitioners. You have to excel in your first job with a knack of doing adventurous stuff (also excellent physical and mental health) to get selected as an astronaut.

"Study and excel in the field you are interested in. Once, you are on top, apply for the astronaut programme."

I hope a lot of your opinions changed after reading this article and you got much more informed. I'll urge you let me know about other topics and questions you have related to aerospace engineering though the following form or you can leave a comment. I'll make sure to cover them in next few Monday Mentoring posts.