IEEE Electrification - December 2021 - 72

Depending on the size of a hyperloop's cargo and pas1,200
300
600
900
Route
Figure
5. A daily flight from Delhi to Ahmedabad, India (900 km),
spends less than 70% of the time cruising.
10
15
20
25
30
35
40
5
Taxi Out Takeoff Climb Cruise Descent Approach
and Land
Figure 6. The power required for a generic, 150-passenger, short-haul aircraft designed for a maximum
range of 3,000 nautical miles and a 1,000-nautical-mile (1,800-km) mission.
senger cabin, the mass air flow that the electric turbofan
takes in may have to be compressed beyond the desired
pressure ratio for propulsion efficiency. For such cases,
regeneration through an air turbine is required to achieve
high-efficiency values. Hyperloop vehicles must have very
high overall efficiency, otherwise, energy that is not used
for propulsion will be introduced into the track environment,
altering the optimum operating conditions. From a
safety and reliability point of view,
higher pressures facilitate these
systems with confidence at 10 kPa.
The Concorde proved that pressurized
cabins and turbofan engines
could operate at pressures lower
than 10 kPa (Figure 7). The technology
for operating at those pressures
has a high level of maturity,
which guarantees its use for passenger
and cargo transportation.
Below these pressures, the inefficiencies
of turbomachinery are
well studied, and a method to
avoid the piston effect is required.
From a turbomachinery and
Taxi In
Sea Level
1,000
100
10
1
Aircraft
Commercial
Concorde
Supersonic
Commercial
Aircraft
Zeleros
Hyperloop
High-Pressure
Concepts
SR-71
Military
Aircraft
Balloon
Red Bull
Stratos
Hyperloop
Low-Pressure
Concepts
Figure 7. The operating pressures for different vehicles. (Sources: SR-71 Online and Red Bull.)
Armstrong's Limit
1
2
3
4
5
6
Paris-Frankfurt
600 km
Boston-Baltimore
700 km
New Delhi-Ahmedabad
900 km
Figure 8. Point-to-point times for different transport modes. (Sources: SNFC, Deutsche Bahn,
Indian Railways, Amtrak, and Flight Aware.)
72
IEEE Electrification Magazine / DECEMBER 2021
pressurized cabin point of view, the
Concorde's roof could be established
for passenger and cargo transportation
as a certified limit. In terms of
safety, a boundary could be established
at the Armstrong limit of
6.26 kPa. Operating at vacuum levels
lower than the Armstrong limit is
potentially beneficial for energy
consumption, given the almost complete
mitigation of adverse aerodynamic
effects. However, cabins
certified to operate at those pressures
have specific and restrictive
safety protocols that may be unfeasible
for massive passenger transportation
systems. Currently, vehicles
operating below the Armstrong limit
cannot ensure survivability in the
event of depressurization, making
this approach riskier. Typically, the
threat is mitigated using space suits,
such as those for high-altitude
flights, that provide military pilots
and astronauts a unipersonal breathing
environment.
All hyperloop systems will benefit
from progress in electrical technology
to offer a zero-direct-emission
system. They will be designed from
their foundations to provide green
Total Travel Time (h)
Pressure (mbar)
Peak Power Required (MW)
Speed (km/h)

IEEE Electrification - December 2021

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