| Article: 64609
From: [email protected]
Newsgroups: sci.space
Subject: Skylon: A new spaceplane concept from Alan Bond
Date: 7 Jun 93 17:48:51 +0930
Organization: University of South Australia
There's an excellent article on the new Skylon spaceplane in
Spaceflight magazine (from the British Interplanetary Society) in its
May 1993 issue. Skylon is the next generation of the HOTOL Single
Stage to Orbit (SSTO) that was developed by Alan Bond, British
Aerospace, and Rolls Royce. The article is by Richard Varvill and Alan
Bond of Reaction Engines, Ltd.
Skylon has similar aims to HOTOL, to deliver 10,000 kg into Low Earth
Orbit (LEO) in the most cost effective manner as possible (very
similar to the aims of McDonald Douglas' Delta Clipper (DC) program).
Unlike DC, Skylon uses air breathing rockets in the lower atmosphere
to utilise the available oxygen and greatly increase the vehicle's
performance. The air breathing rockets change over to normal rockets
after leaving the atmosphere.
The Skylon looks like a cross between HOTOL and the SR-71 Blackbird
spyplane. The main difference between Skylon and HOTOL is that the
rear engine has been moved to a new type of engine on each wingtip
(the wings are now almost centrally located). The engines are called
SABRE (Synergetic Air-Breathing and Rocket Engine) and look similar to
the SR-71 engines, except that there are four rocket chambers at the
back. The reason for doing this is to minimise the mass of each
component of the spaceplane.
Although not specifically mentioned, it appears that Skylon does not
need a launch trolly (as did HOTOL). Skylon instead starts in rocket
mode (RATO or Rocket Assisted Take Off) for the initial acceleration
from the runway. Skylon is airborne after 7 seconds and a distance of
650 metres. The vehicle is uncrewed (but could be crew rated) and uses
liquid hydrogen and liquid oxygen propellants. Quoting from the
article the flight profile is:
"The SABRE performs its start transient in rocket mode, transferring
to air- breathing mode immediately that mainstage combustion is
initiated. The engine operates in air-breathing mode during an optimum
ascent to an altitude of 26 km at Mach 5. The vehicle then performs a
programmed dive followed by a pull-up in order to maximise the climb
angle at the start of rocket ascent. At this point, the engine
transitions to rocket mode, while continuing to operate, in order to
complete the ascent to transfer orbit injection at about 80 km. The
air inlets are closed throughout the rest of the mission including
re-entry."
Here are some specifications of Skylon (taken from the article):
Mass at Launch 275 t (1 t = 1000 kg)
Mass at RATO cut-off 262 t
Mass at Rocket Transition 224 t
Mass at Transfer Orbit 55.7 t
Payload 10 t (300 km circular, 5 deg inclination)
7.7 t (460 km circular, 28.5 deg inclination)
Length 82 m
Max Diameter 6.25 m
Span (over nacelles) 27 m
Max Gross Air-Breathing Thrust 2950 kN
Max Gross Rocket Thrust 2950 kN
I couldn't find the exact specifications for DC, but Henry Spencer
mentions in his (Semi-)Technical Aspects of SSTO article a vehicle
weighing 363 t at launch and 45 t in orbit (including payload).
There is also an excellent article on the engines that were going to
be used on HOTOL. The engine is a modification of the Liquid Air Cycle
Engine (LACE). Instead of liquifying the air, the air is compressed
and cooled to just above liquification. This reduces the amount of
cryogenic liquid hydrogen needed to cool the air. The compressed and
cooled air is passed directly into the rocket chamber where it is
burnt with the heated hydrogen. Surprisingly, 2/3 of the hydrogen is
dumped overboard during air-breathing mode. Only 1/3 is used in the
rocket chamber. Some specifications on the engine (called the RB545) are:
Mass (less intake/spill) 2.5 t
Nozzle expansion ratio 100:1
Nozzle exit diameter 1.82 m
Airbreathing Rocket
(Mach 5 at 26 km) (Vacuum)
Thrust (kN) 340* 735
Chamber Pressure (bar) 100 150
Chamber Temperature (K) 2700 3400
Hydrogen flow (kg/s) 23 23.3
Air flow (kg/s) 240 -
LOX flow (kg/s) - 140
Specific Impulse (m/s) 14,780* 4500
* Nett, i.e., ignoring momentum drag.
--
Steven S. Pietrobon, Australian Space Centre for Signal Processing
Signal Processing Research Institute, University of South Australia
The Levels, SA 5095, Australia. [email protected]
|
| re .3
Yep. If only they would build it!
Is this the Alan Bond of America's Cup fame? Isn't he currently "at her
majesty's pleasure"? If so, interesting the things people do with their
spare time...
re .2
> Airbreathing Rocket
> (Mach 5 at 26 km) (Vacuum)
>Thrust (kN) 340* 735
>Hydrogen flow (kg/s) 23 23.3
>Air flow (kg/s) 240 -
>LOX flow (kg/s) - 140
>Specific Impulse (m/s) 14,780* 4500
In case anyone saw that specific impulse figure and was surprised at
how high it is (as I was), I should point out that it has been calculated
using the Hydrogen propellant flow only. This is of course legitimate
from the point of view of design (since the air comes free) but one should
not compare this directly with non-air-breathing engines in terms of
performance.
|
| >>Is this the Alan Bond of America's Cup Fame?
Don't think so; he is a rich (well he was rich) Aussie businessman.
The Alan Bond in .2 is, I believe, a British aerospace engineer.
>> If only they would build it!
Sigh. If only.... There is absolutely zero prospect of the UK
government funding it in the forseeable future, not with a projected
PSBR (Public Sector Borrowing Requirement, ie deficit) of more than
50 billion pounds this year, and probably for several years to come.
The chances of any future government doing so are equally slim; even if
they manage to reduce their borrowings, they will be much more interested
in reducing taxes and/or increasing handouts for the voters than in
funding space ventures. If the UK government did try to build it, the
chances are (based on their past performance when meddling in technical
and industrial matters) that the result would in any case either be
a)a commercial disaster or b)a technical disaster, and quite possibly
both. The best that might emerge would be another solid gold albatross,
or Concorde as it is also known.
British Aerospace are no more likely to try to do it without a
government handout than I am to walk on the moon. (sigh again 8*{)
Tho HOTOL concept is purely a design exercise, I don't think any hardware
(apart from maybe a few models) has actually been built. They may have
done some wind tunnel tests on models.
Ken
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