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HOTOL: Britain’s Spaceplane
by
Dan Sharp

Now available for pre-order here:
HOTOL: Britain's Spaceplane

Tempest Books
ISBN: 9781911704294
Format: Hardback
Pages: 300

The start of Space Shuttle operations in 1981 marked a new era in spaceflight – with the five orbiters launching numerous satellites, interplanetary probes and the Hubble Space Telescope. But Shuttle was only partially reusable, its external fuel tank being expendable and its solid rocket boosters having to be recovered from the ocean and refurbished. Putting a satellite into orbit using a rocket was even more wasteful – with boosters such as Ariane being one-shot only. The costs were astronomical.

So when rocket scientist Alan Bond and aerospace engineer Bob Parkinson attended a British Interplanetary Society lecture on the proposed non-reusable Ariane 5 rocket in 1982, they began to discuss possible alternatives and concluded that the best solution was… an aerospaceplane.

The concept was deceptively simple – a vehicle able to take off from a conventional runway using airbreathing engines, switch to pure rocket propulsion at high altitude, fly up into space, complete its mission, then fly back down and land. Bond and Parkinson believed it could be done and HOTOL – HOrizontal Take-Off and Landing – was born.

By 1983 both British Aerospace and Rolls-Royce were backing the project. A broadcast on ITN’s New at Ten in 1984 made HOTOL famous overnight, with the whole nation now aware of its existence. The Government agreed to match-fund the companies’ financial commitment in 1985 and the work ramped up into high gear, with some of Britain’s best engineers engaged in making this remarkable vehicle a reality.

Two years later, Minister of State of Trade and Industry Kenneth Clarke declined to renew the project's funding – signalling the beginning of the end of HOTOL. Attempts to continue the project as an air-launched vehicle using the An-225 as its carrier continued into the early 1990s.

HOTOL: Britain’s Spaceplane by Dan Sharp covers the full story of HOTOL’s development in detail from beginning to end, drawing on the BAE Systems archive, the personal archives of the project’s creators and extensive interviews with those involved. It includes new artwork plus hundreds of contemporary diagrams and illustrations, ranging from full colour brochures and publicity material – both used and unused – to previously unseen diagrams and schematics of HOTOL’s numerous configurations and their associated components and technologies.

British Aerospace logo cover.jpg
 
It would be nice to see a Mortons reprint/new version of your Crecy BSP5 with Mustard written prominently on the cover as a companion volume to Hotol, not that you are busy or anything!

The rights to the Mustard book have now reverted back to me, since Crecy had 12 months (now expired) to reprint it or lose them, so a new Mortons-published version isn't impossible. However, the Hotol book would have to demonstrate first that such a thing would be viable.
Incidentally, work on Hotol is progressing rapidly...
 
Strange that only Ariane is mentionned as an exemple of expendable launcher amongst literally a myriad of them?
 
Strange that only Ariane is mentionned as an exemple of expendable launcher amongst literally a myriad of them?

Hotol was created as a direct response to Ariane 5/Hermes. And throughout its existence, it was in competition with that particular system.
 
This make perfect sense.
So, the end of Hermes did triggered the end of Hotol also?

In short: no. But the story is a lot more complicated than that. The British government decided not to continue funding Hotol during the late summer of 1987, but British Aerospace continued paying for the project itself. Then Rolls-Royce declined to continue funding the engine. BAe then switched to Interim Hotol, a pure rocket vehicle which used the An-225 to substitute for the RB.545's airbreathing stage. Then BAe Stevenage, which was leading the Interim Hotol effort (BAe Warton had led the original Hotol project) ran out of money because Hughes kept underbidding it for its main source of income - communications satellites. The Interim Hotol team were mostly laid off. The work continued with just a handful of staff members for a while, but eventually stopped because no further sources of funding were available.
Hermes did come to an end at a similar time, I think, but for unrelated reasons.
 
Hermes died at the ESA council meeting in Granada, Spain: 11/1991.
Skylon started in 1989
Interim Hotol died by 1992
HOTOL never had CNES ESA support but TBH it was more interesting - and risky - than Hermes AR5.
Also Saenger II on the german front.
Overall: a total mess. And nothing was built in the end.
 
I'm sure Sharp's book will be very informative, personally I at least know that *some* study work on Interim HOTOL continued under the ESA WLS (Winged Launcher Study) program up to Mid-1994, so on that front it at least outlived Hermes by a bit.
 
I wonder how much of the book will have previously classified data and information? Considering that it was a UK MOD project to begin with.
 
Thanks Dan, I suppose there is only so far that you can go with the scope of the book that you had planned.
 
Thanks Dan, I suppose there is only so far that you can go with the scope of the book that you had planned.

Maybe you misunderstand me. This book is going to cover everything in excruciating detail - probably more detail than anyone (except me) could want. I cover the whole project blow by blow, almost day by day, who said/did what and when, based on the primary sources courtesy of BAE Systems.
The issue of exactly how closely the Hotol project was associated with the MoD is addressed, I can assure you (it seems like you might be disappointed by what the documents reveal).
What you might be shocked by is the way the vehicle evolved over time and the incredible variety of different configurations looked at. How about a version with 10 engines built into its wings or one with a lifting body fuselage - or a nose intake?
 
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Eagerly looking forward to this book! Though on the other hand a bit terrified on how much I'll have to rework my HOTOL model (which tries to represent a circa 1987 configuration) if we get more accurate diagrams :D

HOTOL_101.jpg
 

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Eagerly looking forward to this book! Though on the other hand a bit terrified on how much I'll have to rework my HOTOL model (which tries to represent a circa 1987 configuration) if we get more accurate diagrams :D

View attachment 728117

Hotol's major configurations each had a letter in alphabetical order. This one is Configuration F, which was first devised in mid-March 1986 and officially became the new baseline design at the beginning of July 1986. A new variant, Configuration G, became the next baseline design at the end of June 1987.
 
Why have the hassle of all that editing when you can just make a new one from scratch and then you won't forget which parts you've edited and which you haven't?
;)
Well, I used "rework" as a generic term ranging from minor adjustments to a completely new model.
Hotol's major configurations each had a letter in alphabetical order. This one is Configuration F, which was first devised in mid-March 1986 and officially became the new baseline design at the beginning of July 1986. A new variant, Configuration G, became the next baseline design at the end of June 1987.
Thanks! I knew about the alphabetical designations but not which one this was. Looks like 'K' may have been the final HOTOL iteration?
Interestingly Skylon seems to have adopted a similar system with additional suffix numbers (eg. C2, D1, LAPCAT A2...)
 

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Yes - Configuration K was the last of the airbreathing line. I have a 1992 drawing somewhere of Interim Hotol with 'Hotol M' in the description box, but that designation doesn't seem to have stuck.

The nine main iterations were: A, B, C, D, F, G, H, J and K. There was no 'E' and no 'I'. And within those nine, there were further subdivisions - G3 for example. Many of the design proposals and changes didn't get a specific designation.
 
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Interim HOTOL work with Roc from Stratolaunch?

In the drawing above, the air breathing part was pictured "detached" to show how omitting air breathing reduces length.

But an actual detaching block parachuting down--that ever looked at?

(Simpler than spacejet...just a ramjet for this use unlike full sized HOTOL's engine.)
 
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Interim HOTOL work with Roc from Stratolaunch?

In the drawing above, the air breathing part was pictured "detached" to show how omitting air breathing reduces length.

But an actual detaching block parachuting down--that ever looked at?

(Simpler than spacejet...just a ramjet for this use unlike full sized HOTOL's engine.)

Brief investigations were made into retractable, shielded and jettisonable intake pods - yes (during August 1986). But according to Hotol project manager Sandy Burns, "these alternatives appear to involve more penalties than benefits".
 
Pure rocketry offers simplicity.
I fondly recall a decades ago conversation with a fellow German aerospace engineer called Johannes Spies from then ERNO, who in the 1980's worked on a German HOTOL reverse engineering effort called LART (referenced on this forum). That effort eventually resulted in a purely rocket powered version like Interim Hotol, the moniker of which escapes me at the present, because, as Johannes dryly stated at the time, when they ran an integrated design simulation to determine the optimum switching condition from airbreathing to rocket propulsion, the result was Mach 0...
 
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That’s about right.

If anti-gravity was real, the field effect would probably be only two feet wide with the mechanism needing to be in LEO anyway to turn it on…

I have no problem with airbreathing on return, with small jets just to have a powered landing—but I get my head bitten off if I mention it.
 
I fondly recall a decades ago conversation with a fellow German aerospace engineer called Johannes Spies from then ERNO, who in the 1980's worked on a German HOTOL reverse engineering effort called LART (referenced on this forum). That effort eventually resulted in a purely rocket powered version like Interim Hotol, the moniker of which escapes me at the present, because, as Johannes dryly stated at the time, when they ran an integrated design simulation to determine the optimum switching condition from airbreathing to rocket propulsion, the result was Mach 0...

Interesting. Is this related to the exponential nature of the rocket equation ? the "classic SSTO theory" is that airbreathing to Mach 1, Mach 3 is not worth it. It starts being worthy around Mach 6 (Skylon) - and after that: scramjet.

Since orbital velocity is Mach 24, Mach 6 should cover 25% of the tally - but it doesn't work that way. Not at all. It is much worse than that. Besides delta-v, the big deal is the energy to orbit and there, the exponential nature of the rocket equation hits severely. Reducing Mach 6 to much less than 25% of the whole effort... peanuts.

That's my modest understanding of the whole shebang of going to orbit...
 
Interesting. Is this related to the exponential nature of the rocket equation ? the "classic SSTO theory" is that airbreathing to Mach 1, Mach 3 is not worth it. It starts being worthy around Mach 6 (Skylon) - and after that: scramjet.

Since orbital velocity is Mach 24, Mach 6 should cover 25% of the tally - but it doesn't work that way. Not at all. It is much worse than that. Besides delta-v, the big deal is the energy to orbit and there, the exponential nature of the rocket equation hits severely. Reducing Mach 6 to much less than 25% of the whole effort... peanuts.

That's my modest understanding of the whole shebang of going to orbit...
To use a physics trope, the rocket equation is strictly only valid for a spherical cow, see https://en.wikipedia.org/wiki/Spherical_cow, because it neglects the influence of any external forces such as gravity or atmosphere(s) and is only strictly valid for a constant specific impulse. For airbreathers I therefore recommend to follow the approach I outlined in https://www.secretprojects.co.uk/th...ing-ascent-launch-vehicle-trajectories.38550/. The basic issue of airbreathing launch vehicles is that they are based on replacing cheap LOX with complex machinery and associated design and operational requirements and ascent flight path constraints. I drank that particular cool-aid for a while myself...
 
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as Johannes dryly stated at the time, when they ran an integrated design simulation to determine the optimum switching condition from airbreathing to rocket propulsion, the result was Mach 0...
Magnets have gotten better:

With SpaceLiner using deep cryogens might a sled allow for a HTOHL approach easier on ground crew and passengers?

SS/SH may be a pain in the neck, literally.

While kerosene makes more sense as a first stage fuel, I think ease of handling should come first.

A very cold hydrolox filled first stage gives a maglev something to bite into, field effect wise.

A kerolox (maybe tri-propellant?) winged upper stage might have simple jets so that—after re-entry—it’s just another jet plane.

I have this image in my head of a forklift driving up to the back engine compartment and sliding out the engine block in one piece and sliding a new one in…such that refurbishment takes place indoors…maybe in a pit…like operating theatres of old. Here, you look down…almost a giant glovebox, but with waldos manipulating things. The big booster pumps propellant into the upper stage and it can return as a drone…dead-stick.

While Musk is interested in typical rocketry—perhaps a better approach would be “how would an MRO worker design a spaceplane?”

If I were a plumber, I would have a kitchen a half-floor above an exterior service corridor—there, all pipes are at head level…

That kind of thing. A Mike Rowe approach.
 
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Magnets have gotten better:

Did I miss it?

None of the references claim improvement to magnetic flux density.

Two related to levitation, one of which must reduce the flux density (although they neglect to say it…. “2/10 must try harder)” and two more wildly impractical LH2 superconducting schemes….. don’t they have any idea of H2 liquidfaction energy demand, leakage, GWP multiple, flammability? …. Sorry just mentioned the unmentionable.
 
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This looks pretty stout;

Don’t know about this:

I do seem to remember permanent magnet advancements…

For space

The key is to replace the airbreathing with an initial source of acceleration the rocket plane doesn’t have to be encumbered with.
 
Publiusr
1 - A pinnacle of human achievement He supercooled electro magnet - yes wow, but the cost to build/operate? Have you seen the supporting ITER supercooling plant required to supply it with LHe?

2 - a five year old patent for magnetic invention that would change the world, only it hasn’t. You do know patents require no validation proof, …..patents have been granted for time machines.

3 - a magnetic gearbox - My very own fingers spun one of those about 15 years ago (Magnamatics Ltd), magnetic gears might have been around prior to this….a very expensive solution looking for a problem to solve that’s easy to solve by cheaper alternatives.

The key metric for the performance potential for practical magnetic application is flux density and that hasn’t improved for 25 years.

I’m not sure how any of this gets you to a low cost launching system.
 
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I was thinking that...if the space plane was filled with supercooled liquid hydrogen, then somehow the magsled track could get away being more primitive?

This is perhaps the one time a first stage having a deep cryogen makes sense.

Lands on normal runway empty.
 

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