Table 1: Direct Access
to the Sub-Disciplines of Aerospace Engineering
DESIGN-CENTERED INTRODUCTION TO AEROSPACE
ENGINEERING
2. Today's Dreams in Various
Speed Ranges.
Here are some dreams to consider: some are a lot closer than the others.
In each case, try writing out a mission specification, and a typical mission
profile, and then maybe you'll keep going, and figure out the detailed
design. Someone will, sooner or later, and most of these things will get
much closer to reality within the careers of today's students. Consider
that when today's professors were born, no human had ever reached orbit
(well, excluding anyone kidnapped by green-costumed visitors from the Andromeda
Galaxy..)
There are many kinds of flying vehicles today:
helicopters, balloons, fixed-wing aircraft (the X-29 is shown), and the
Space Shuttle are examples of designs which look drastically different
from each other, and are designed for very different missions.
Table
2: Today's Dreams
| Dream |
Technical
Requirements |
| Fly
like a bird |
0
- 100mph; land anywhere, hover, cross mountains & rivers |
| Commute
by air |
Garage
to parking lot to garage. 1 million cars per day above I-85, 300mph, all-weather,
safety & traffic management |
| City-city,
doorstep service |
400mph;
VTOL with mild downblast and noise |
| Cross
the world in a day |
Mach
3, approximately 1800 mph + range of 10,000 miles. |
| Visit
low earth orbit |
18000
mph; re-usuable spaceliner; comfortable takeoff, acceleration, re-entry
and landing. Cheaper than $50 /lb. |
| Visit
nearby planets |
36,000
to 500,000 mph; months of endurance. |
| Visit
nearby star systems |
Proxima
Centauri, 6 light-years: 5.7E14 km |
| Deep
space travel |
Millions
of light-years. |
| Nano-probes |
10E-9
meters size. Numerous applications. |
National Aerospace Plane (NASP) hypersonic airbreathing vehicle concept
from NASA, presented along with President Reagan's call for "the Orient
Express", a vehicle which can fly across the Pacific Ocean in less
time than it takes to get from Atlanta suburbs to the Atlanta airport.
The Space Shuttle is certainly a hypersonic vehicle, except that it takes
a whole army to get it ready for each flight, and several weeks to turn
it around for the next flight, and it uses rocket propulsion, where all
the fuel and the "working fluid" has to be carried on-board from ground
level. Picking up the oxygen-laden air en-route should make hypersonic
flight much cheaper, if this can be figured out completely: this is called
"airbreathing propulsion". One difficulty with a hypersonic passenger
craft is that the acceleration and deceleration phases would be quite "interesting"
for most passengers if one flies a direct route. This can be made
less stressful by going around the earth once, which would add another
2 hours or so to the flight time, but would require going to an even higher
speed and altitude. It might also raise the expectations of the passengers
with respect to the food service (the direct route will have a very short
cruise segment, which only merits peanuts/pretzels by today's standards).
Another interesting statistic (Aerospace America, Oct. 1998) is that roughly
75% of astronauts, who are all superbly fit and trained professionals,
get various symptoms of motion sickness during space missions, despite
medical precautions. So it is likely that the initial hypersonic "airbreathing"
vehicles to be revealed will in fact be (or already are) missiles, uninhabited
bombers, and perhaps later, some missions flown by military pilots. The
"Orient Express" that President Reagan described is still a few years away,
and will probably be replaced by a High Speed Civil transport flying at
lower supersonic Mach numbers (1.7 to 3.5). Yet another interesting
issue (one of very many) is that the surface temperatures generated during
high-speed flight might make it difficult to open the doors for some extended
duration after landing, so people might get very tired standing up in the
aisles with their hand-baggage after the "fasten seat-belt" light goes
out at the airport gate.
Of course these are not unprecedented problems: flight on the venerable
DC-3 Dakota airliner , which was the best option available to many of us
when we were younger, also used to make many people sick from the continuous
buffeting, and caused piercing ear-aches, partly from the pressure changes,
and partly from the pleasure of sitting for hours close to something
that sounded like five diesel locomotives at full power.
Next Section: 3. Designing a Flight Vehicle:
Route Map of Disciplines
Previous Section: 1. Course Organization