ROOM
61
Astronautics
supersonic Concorde, taking off from and landing on
conventional runways.
In this scenario the cost per seat to orbit is about
one thousand times less than it is today (a few tens
of thousands of dollars compared with a few tens
of millions) so that middle-income people prepared
to save can even afford to visit space hotels in orbit
round Earth. Cargo versions would launch satellites
and space platforms at greatly reduced costs.
The future possibilities for science, the
environment, human endeavour and leisure are
immeasurably vast and this new space age could be
achieved at low technical risk within 15 years, given a
change in our approach to space transportation.
Rocket science
In order to understand the argument, a little
knowledge is required of the various types of trajectory,
the need for staging, and some design logic.
Launching a spacecraft into orbit requires
climbing to space altitude - about 100 km (62 miles)
or higher - and then accelerating horizontally to
satellite speed, which is about 7.8 km per second for
low Earth orbits (LEO) of around 90 minutes. It is the
acceleration to satellite speed that requires most of
the energy - just climbing to space altitude requires
far less. A so-called suborbital flight, up and down
again with just a few minutes in space, requires a
maximum speed of about 1 km per second, or about
eight times less (see diagram below right).
Suborbital rockets, or ‘sounding rockets’, have
been used for many years for various kinds of
scientific research. They are far smaller and less
expensive than orbital launchers, but of course
only provide a few minutes in space. Two reusable
suborbital aeroplanes have already flown, and new
ones are being developed to provide suborbital space
experience flights. These will be useful stepping-
stones to orbital spaceplanes.
Staging
To achieve such a goal as soon as possible, we need
to use existing technology as far as is practical
and this will require the use of two stages. This is
analogous to the in-flight refuelling used to extend
the range of military aeroplanes. It adds complexity
to a mission but enables it to be achieved with
existing technology.
The amount of fuel needed for a flight to orbit
using a single-stage vehicle with existing rocket
engines, measured as a fraction of take-off weight,
is about 87 percent. This is roughly equivalent to the
amount needed to fly an aeroplane one-and-a-half
times round the world non-stop. The present record,
held by the Virgin Galactic Voyager, is just once.
To fly one-and-a-half times around the world
without in-flight refuelling would need either very
advanced technology or the use of two stages - a
large aeroplane carrying a specialised very long-
range aeroplane part of the way.
This analogy explains why flying to orbit with
existing technology needs two stages. The lower
stage boosts the upper stage to a speed such that it
requires a practicable fuel fraction to continue on
to orbit, and the two stages separate at this speed.
Single-stagers are clearly preferable in the long
term, but these will need very advanced new engines.
Design logic
An airliner capable of flying to LEO would transform
spaceflight by providing vastly lower costs and
improved safety. The essential design features
of the first such vehicle can be derived from
straightforward design logic.
The most important design requirement is greatly
improved safety. To date, human spaceflight has
The Anglo-French
supersonic Concorde of
the 1970s could have been
a precursor to the first
spaceplanes.
Orbital and suborbital
launch trajectories.
To Orbit, 7.8 km/sec @ 200 km height
Trajectories
Suborbital
= 1 km/sec max speed
SPACE
AIR
Airliner
100 km
