Archive of answers: Ask An Aerospace Engineer!

How many fields of knowledge (physics, mechanical engineering, electrical engineering, etc.) does an Aerospace Engineering Degree entail?

Answer: At least six fields. Aerospace engineering has a lot in common with mechanical engineering, except there's much more emphasis on fluid dynamics. Any engineering degree will require you to take several physics classes, math, and at least some introductory computer science and chemistry. Very little electrical engineering is covered in a mechanical or aerospace engineering degree. Keep in mind that for a bachelor's degree in any type of STEM (science, technology, engineering, or math) discipline, you will get a broad education in many subjects. It's typical for only the final year of classes to really specialize between different majors. I'd recommend you select the major that interests you the most.

- Sean Montgomery

Full Archive of Questions:

Q. If a craft is orbiting the earth, i.g. the space shuttle, and its orbit degrades, is it possible to safely re-enter without compromising the integrity of the craft?
-The craft has has wings to create lift.
-It enters at inside the re-entry corridor.
-It has attitude correction capabilities, but no forward thrust.
-It is traveling at the speed just under that to retain orbit.
A. The big question here is can the Shuttle enter safely. I assume that means landing on a runway that is adequate for the Shuttle. In a normal re-entry an entry interface (EI) point is selected about 4,000 miles from the landing site. That point is at 400,000 feet and is considered to be at the top of the atmosphere. Since the Shuttle may be orbiting at 200 nautical miles (a nautical mile {NM} is 6080 feet as compared to the miles we are used to which are 5280 feet) its trajectory must be modified to arrive at the entry interface point at the correct angle of descent and of course be at the correct location. If the Shuttle is in an orbit at 200 nautical miles that is equivalent to 1,216,000 feet. The Shuttle fires the Orbiting Maneuvering Engines (OMS) to get on the new orbit that will arrive at the desired entry interface point with the desired conditions.

At EI minus five minutes you are approximately 4,400 NM from the landing site. Once you are past EI the Shuttle follows a prescribed trajectory to land at the landing site. That trajectory has to fit within the heating constraints, the G constraints, and of course land in the correct place. There is some capability to change where you are to land and that is called the landing footprint. As an example, at the entry interface point you could change the lateral position of landing out of the plane of the orbit by about 1200 NM. As you fly the entry trajectory that number gets to be less and less until at touchdown there is no capability to change where you are going to land.

In your question the problem is getting to the entry interface point with all the correct conditions. If the Shuttle is in a decaying orbit it will be coming down quite slowly and estimating where it might come close to the entry interface point is very difficult, and controlling that is probably impossible. Your EI point is in the plane of the orbit and there is no reason the plane of the orbit and the correct altitude would all line up at the correct time. I’m sure you have heard on the news that some satellite may be going to re-enter and they estimate an area of thousands of miles where it may land. They just can’t predict where the satellite will have enough drag to cause it to plunge into the atmosphere.

On the Shuttle there are two OMS engines, each of which could do the de-orbit burn. There is also a set of Reaction Control Engines which could do the de-orbit burn. We practice the de-orbit burn many times, with all sorts of complicating problems, but I never practiced a decay re-entry. I believe you would probably run out of oxygen to breath, or hydrogen and oxygen to provide power, before you would do a decay re-entry.

Given all that I think it would be fun to play on the simulator and see if a procedure could be developed to solve this problem. For more information go to: http://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/

-Karol “Bo” Bobko
Pilot , STS-6 / Commander, STS-51D , STS-51J

Q. How did you get into a career in aerospace engineering?
A. I've always been interested in NASA's space program. A career in aerospace engineering typically begins with curiosity and personal motivation to be involved with aerospace vehicles.

Q. What are your main tasks or responsibilities at work?
A. As a simulation engineer for the Vertical Motion Simulator (VMS), my primary task is to integrate simulation models and other necessary software and hardware into the VMS real-time simulator environment to allow researchers and designers to evaluate vehicle models, control systems, and procedures using realistic piloted simulation.

Main responsibilities:
- Support existing research and experiment requirements
- Develop solutions aimed at solving problems related to the specific field being studied (vehicle performance, air traffic systems, and simulator design)
- Figure things out

Q. What kind of education, training, or other preparation do you need to get into your career?
A. Typically, a 4-year college education and/or advanced degrees in science or engineering are needed to communicate effectively with others during a project. Having a broad and grounded background in science, engineering, and mathematics makes it easier to convey ideas among a highly technical staff.

Schools may or may not offer as part of their curriculum additional skills useful to prepare you for this career (programming, CAD/drafting, presentations, engineering processes, etc.). It will be up to you to figure out how to obtain these additional skills in order to compete in the technical job market.

Aerospace tends to have a larger breadth of courses (math, physics, chemistry, propulsion, materials, aerodynamics, computing, electrical/electronic systems, orbital mechanics, engineering principles, etc.). Don't let the list scare you -- it's actually all very interesting!

Q. What personal characteristics are required for someone to be successful in your career?
Answers:
a) Patience in order to be able to zoom out and see a problem from a high-level point of view; dogged determination in order to be able to drill down and see a problem at the pixel or 16th-decimal-place-level.
b) Ability to be congenial and collegiate in order to work well with a diverse group of staff, engineers, and researchers.
c) Technical aptitude such that you can understand concepts from engineering, mathematics, and computer science.
d) Logical aptitude such that you can differentiate between cause, effect, and incidentals in order to more efficiently solve problems.
e) Most importantly, creative ability such that you can understand and formulate tangible descriptions of problems and find solutions.

To make any project a success, an organization must address and utilize the full gamut of individual characteristics. NASA employs many individuals with varying characteristics. Of these characteristics, the one that is used daily is personal drive and passion to solve the engineering problem. A little tenacity, a bit of ingenuity, and experience with duct-tape make an engineer.

Q. What is the future of research in hypersonic flow and which are the subjects I need to take for my masters to pursue a career in this field?
A. The future research in hypersonic flow will be focused on development of better CFD tools and physics-based models to support hypersonic air-breathing and planetary entry vehicle technologies. A combination of ground testing and occasional flight testing will provide opportunities to demonstrate these technologies as well as to validate analysis tools. The recommended subjects in masters would depend on the areas of interest. However, it is a good idea to take courses on fluid mechanics, physical chemistry, combustion, numerical methods in CFD, basic materials science, aerospace vehicle design, systems analysis and engineering, etc.

Q. What kind of subjects do I need to study in high school to become an aerospace engineer?
A. All subjects are useful, but you should especially concentrate on algebra, calculus, chemistry, computer programming, physics...and grammar/writing skills. Communication is an essential part of being a good engineer!

Q. How do airplanes fly?
A. There are four forces that act on an airplane: thrust, weight, lift, and drag. Airplane wings are shaped in a special way, so that when the engines create vehicle thrust and the wings slip through the air, there is an area of lower pressure on the top of the wing than on the bottom; this creates lift. As the airplane increases in speed, the lift increases until eventually, it overcomes the downward force of gravity (weight), and the airplane takes flight. The air itself creates drag, so the engine thrust must overcome this drag to keep the vehicle aloft.