Getting us into Space
I think there are relatively few who would argue that there is no reason to physically explore space. Most seem to understand that given the
opportunity, space exploration, and even habitation, would go far in helping us conserve our planet, especially if we mine resources, develop new
technologies, and extend the area which we humans can use, thus reducing our consumption of resources at home.
However, we seem caught in a foolish quandary; namely, that we can't "afford" to improve our lot.
One of the major obstacles in realizing the full potential of our space-faring capabilities is getting off the planet.
The two major players in moving people and materials into space are the United States and Russia (perhaps the former Soviet Union more so, since they
were willing to nearly bankrupt themselves competing for the potential prize.)
HOTOL was intended to be a single-stage-to-orbit (SSTO) craft that could take off from a normal runway, and reach altitudes that would allow it to
achieve Earth orbit.
Such a reusable craft would save space exploration billions over time, and would make the entire vehicle reusable, unlike modern rocket and booster
platforms that are expended once they have been used.
Until now, both have relied on heavy-lift multi-stage rocketry to get vehicles into orbit and beyond.
But there is a very real effort to make that a thing of the past.
Enter an ESA (European Space Agency) project 3 decades in the making. I offer a brief look into a future which includes no more titanic rocket thrusts
into space, but instead, a smooth takeoff and landing vehicle which our friends in the UK have been developing...
It started in in the early 1980s (does that seem so long ago?) with a project known as the Horizontal Take-Off and Landing (HOTOL) concept.
Aircraft manufacturers have always struggled to reach the highest possible altitude, and towards that end a few trivial facts;
The altitude record for a propeller-driven aircraft was just over 17,000 meters by Italian pilot Mario Pezzi in 1938.
This limit had to do with ‘lift
’ and the thinness of the atmosphere at that height.
There’s only so much thrust and lift a mechanical system can achieve lacking enough soupy atmosphere to swim through.
The equivalent ‘official’ record for an “air-breathing” jet aircraft was reached by Soviet pilot Alexandr Fedotov in a MIG-25M in 1977,
peaking at over 37,500 meters. A jet engine enclosure can generate much more thrust than a propeller; due to the higher compression such engines are
designed to create.
But in the end, without air with which to burn fuel and generate lift and thrust; these solutions can only get us so high and no further. For us, it
seems the issue is about steadfastly being married to the concept of ‘combustion’ to create the energies necessary to reach orbit and ‘slip the
surly bonds of earth.’
Bear in mind that in order to reach a true ‘orbit’ of our planet, you have to reach an altitude considerably higher than 100,000 meters. In order
to stay in orbit around Earth, an object must also have a certain amount of momentum; otherwise gravity will pull the object down into the atmosphere.
The more massive the object is, the more that pull has to be counteracted against by increased speed to stay in orbit. But also, the further away the
object is from the Earth the less momentum it will need to stay in orbit. The balance between object mass, and speed gives us the momentum needed to
achieve and maintain orbit.
Our International Space station, for example, orbits the Earth once every 90 minutes, at an altitude of around 350,000 meters … (that’s moving
about 27.7 kilometers per hour) although the orbit ‘decays’ about 2,000 meters a month. Interestingly, as we add more modules and equipment to
the station, the orbit will require recalculation… the last time I checked its mass was approximately 417,000 kg.
Reaching the upper atmosphere, where oxygen is lacking, poses a problem for our combustion-centric technology to overcome. This is something that only
certain kind of craft can do. …. enter rocket powered craft.
Lacking the abundance of oxygen to combust at that altitude, only rocket-propelled aircraft have reached true orbital height; the current ‘rocket
aircraft’ record, is just shy of 112,000 meters reached by Brian Binnie in the Scaled Composites SpaceShipOne in 2004. SpaceShipOne was an
experimental craft used to test new materials and composites; it was lighter ship design with commercial aims in mind, as opposed to military
applications. In fact, the next generation of this craft, the SpaceShipTwo, is expected to carry up to 6 passengers into low orbit.
The previous record holder for rocket planes had been the X-15’s 107,000 meter climb by Joseph A. Walker in 1963.
The X-15 was primarily a military test-bed, meant to determine the limits of aerospace technology. This aircraft reached a speed of Mach 6.7 and was
the pride of the US aerospace research industry, as it frequently dipped in and out of ‘space.’ Many early test pilots, including Neil Armstrong
(the first man to walk on the moon) earned their astronaut ‘wings’ in the X-15.
But both the X-15 and SpaceShipOne altitude records had been achieved after being released in flight. Since these are rocket driven aircraft, the
most efficient way to test them was by loading them onto a launch aircraft and releasing them in-flight. While the X-15 was eventually outfitted to be
able to perform runway takeoff, it was clears that outside of experimental research applications, this aircraft was not going to take us into
The reason rockets are capable of getting us into the orbital zone is because they carry their own fuels and oxidants, as opposed to planes and jets
which require the presence of an atmosphere to combust their fuel.
A simple diagram shows the basic concepts behind the applied science of rocketry:
Many rockets use liquid fuel. This kind of engine allows us to control the fuels burn rate. This is the kind of rocket used in most manned space
mission flights (although many use auxiliary solid rocket fuel boosters to assist in the early launch phases). Of course, there’s the inconvenience
of having to fuel up (a technically dangerous affair) and the delicacy of maintaining ‘plumbing’ for the engine, but it remains the mainstay of
the ‘heavy lift’ application.
Solid fuel rockets carry both the fuel and the oxidizer chemically combined into a solid mass. These kinds of rockets, once ignited, cannot be
stopped (much like a match head, once ignited, it exhausts itself), so the benefit of stability and long term storage are offset by their one time
use. These are commonly used in missile systems for military applications.
Back to the HOTOL
The design of this vehicle was meant to overcome the difficulties we had designing a craft that could efficiently and effectively be used (and reused)
to reach orbit, without having to blast off on rockets.
Towards that end, the HOTOL concept included a unique engine design which was patented in 1983. Known as the “RB545 air breathing rocket engine
concept”, it eliminated the need to carry any oxidizer aboard the vehicle in the early portions of flight.
Instead, the RB545 would use oxygen from the atmosphere, to combust the liquid hydrogen fuel it carried on board; once it reached a height where that
was no longer possible, it would switch to use an on-board supply of liquid oxygen and operate like a conventional rocket.
It was fortunate timing that brought this new engine design together with a new Rolls Royce airframe design which could accommodate the liquid fuel in
the rear (which incidentally made the aircraft heavy in the aft section (the rear of the aircraft) making for a design with a peculiar and distinct
pitch.) The aircraft’s center of gravity became a serious concern to contend with.
While an in-flight launch was certainly an option, it was also explored to launch this vehicle with a form of detached take-off gear, which would fall
away as the plane lifted itself.
Sadly, the HOTOL project funding dried up, and aside from a short-lived flirtation with the idea of teaming up with the Soviet Union to continue
development (which would have replaced the RB545 with Soviet standard rocket engines) ; the concept stalled for quite a few years.
Never Say Die
The aerospace industry has a real need for a surface launched aircraft that can reach orbit, and then subsequently, land safely for a relatively quick
turn -around time to launch again.
The progenitors of the HOTOL were not done.
If we are ever to ‘arrive’ as a space faring people, we are going to have to develop the means to get in and out of space without the monumentally
complex operations inherent with multistage rocketry and national-level investments. The first step to towards that goal is best represented in the
collective efforts to develop a space plane.
Skylon, a new aircraft design based upon the HOTOL concept is being fervently pursued by Reaction Engines Ltd. They have developed an improved version
of the RB545 engine called the SABRE (Synergic Air Breathing Engine).
Notice the gentle curve (7 degrees) of the engine nacelle. I suspect it harkens back to the ‘center of gravity conundrum’ faced by the early
The new more compact design of this engine leaped beyond several problems simultaneously, it made possible a new placement of twin engines on either
side of a fuselage (notice the similarity between the Skylon profile and the SR-71 of old). These engines can propel the Skylon from Earth to orbit,
reaching Mach 25 once outside the atmosphere.
Compare the SR71 frame above with the Skylon frame below....
Skylon’s Sabre engine smartly avoids the need to cool and compress air to a liquid form, taking it only to a ‘vapor’ state which reduces the
need for high fuel flow. It also eliminates the need for hardware associated with compression and condensation in typical liquid-fueled rocket
I have chosen the Skylon as the most promising design to come along in quite some time (unless we consider wholly theoretical designs and as of yet
unsubstantiated capabilities we may hear about.)
Skylon, is unfortunately still lacking in funding; but given the advanced concept and the dire need for a realistic reusable single stage orbiter, I
would expect this technology to become in demand quite soon.
edit on 3-6-2011 by Maxmars because: (no reason given)