Author Topic: The Reaction Engines Skylon Master Thread (1)  (Read 321445 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread
« Reply #1100 on: 10/29/2012 06:55 PM »
Talk of crash scenarios applies just as well to regular airliners, which SKYLON plans to be certified as, so anyone with that kind of imagination should live somewhere that airliners don't overfly or take medication for their nervous condition.  :)
Agreed. I think it's part of that *deeply* pervasive "artillery/missile" mindset versus an aircraft that will take *long* time to change.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline hkultala

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Re: The Reaction Engines Skylon Master Thread
« Reply #1101 on: 10/30/2012 07:00 AM »
It's a robotic aircraft with a ridiculously high GTOW percentage of which is liquid H2.
High certainly. I think you'll find it's no worse than the plane Steve Fosset was flying on his solo round the world flight.
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In fact, since it uses O2 from the atmosphere when in plane mode, the amount of H2 is huge. Please remember that it's as or more heavy than an A380.
Starting its takeoff roll yes. A chunk of that will go during the takeoff and climb out. Technically you could say that *all* of Skylons flight plan (it's an aircraft, not a missile) will be climb out (to orbit  :) )
as a robot a 45 deg takeoff slope is possible so 60kft downrange Skylon would be above *all* FAA jurisdiction. So if your runway is >12 statute miles from your countries border that would normally put it above most countries civil aviation oversight authority. 

I don't think it has the T/W to do a 45 climb initially, and doing it would anyway cost too much fuel, as with low speeds it would not have enough lift on high altitudes.

So it has to rise with shallower angle, gaining both speed and altitude simultaneously.


But I don't see any problem with this anyway. Chemical explosion on air is not dangerous on ground unless one is very close.

And skylon with lots of H2 but not much O2 would mean the explosion would be of "airburst" type, longer-burning, causing more heat but not so big pressure wave and not so high velocities for debris. Dangerous in closed place, not so dangerous in open space(high on air).


Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1102 on: 10/30/2012 11:55 AM »
SKYLON ascent trajectory:

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread
« Reply #1103 on: 10/30/2012 05:05 PM »
SKYLON ascent trajectory:

Nice graph. I used 45deg because 1 unit of length gives 1 unit of altitude rise and I was being lazy.

IIRC normal climb angle for airliners is about 7 deg (felt a hell of a lot more out of Newark. Like a roller coaster :) )
That's roughly 1 in 8 climb out so you'd need to be about 147Km from the border in your launch direction to be above the 60k ft level and outside controlled airspace (at least if you were flying over the US. I'm *guessing* most other countries rules are pretty similar). By that point it would be a mostly *empty* flying propellant tank, giving the same sort of explosion hazard as *any* other large aircraft.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline baldusi

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Re: The Reaction Engines Skylon Master Thread
« Reply #1104 on: 10/30/2012 05:16 PM »
SKYLON ascent trajectory:

Nice graph. I used 45deg because 1 unit of length gives 1 unit of altitude rise and I was being lazy.

IIRC normal climb angle for airliners is about 7 deg (felt a hell of a lot more out of Newark. Like a roller coaster :) )
That's roughly 1 in 8 climb out so you'd need to be about 147Km from the border in your launch direction to be above the 60k ft level and outside controlled airspace (at least if you were flying over the US. I'm *guessing* most other countries rules are pretty similar). By that point it would be a mostly *empty* flying propellant tank, giving the same sort of explosion hazard as *any* other large aircraft.
60k ft is not the limit of controlled airspace. 100Km is. The fact that the country might not even have a way to control it doesn't means it's not sovereign airspace. I.e you need their permission. You don't once you are in space.
In any case, Ecuador is a ridiculous location that solves a non problem. The number one consideration is a legal one, and Ecuador is the third worst location on the whole Americas. The second is to have some sort of tracking assets downrange, and you can't unless you ask Brazil. Whom already have a nice place with some interesting tracking assets. So, Alcantara is not bad, but overall Kourou is better. If you don't got to an equatorial launch, KSC or even Vandemberg are as good if not better.

Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1105 on: 10/30/2012 05:51 PM »
The best sites for freight operations may be islands in the Atlantic, Indian and/or Pacific Oceans, assuming an equatorial orbit destination. But, if you ran cargo or passenger SKYLON flights to a resort hotel in a polar, sun-synchronous orbit (which has advantages from the point of view of visitors always having a view of the Earth lit up in daylight), a launch site nearer the poles wouldn't be unreasonable as there would be no advantage to an equatorial spaceport for such a mission. Your passenger traffic is likely to be European, American, Chinese, Korean, Arabian and Indian. Europeans and Americans might find a spaceport on an island in the Atlantic more convenient, while the Asian nations would probably like to use an island in the Pacific. Indians and Arabs would prefer a site either in some remote location within their countries or an island in the Indian Ocean.

Probably the bigger consideration is noise from the takeoff, as Hempsell has pointed out numerous times, which argues for sparsely-populated island locations for siting launch facilities.

Landing is an entirely different matter as SKYLON can land at virtually any aircraft landing strip as Hempsell has also pointed out.

Online simonbp

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Re: The Reaction Engines Skylon Master Thread
« Reply #1106 on: 10/30/2012 06:12 PM »
But, if you ran cargo or passenger SKYLON flights to a resort hotel in a polar, sun-synchronous orbit (which has advantages from the point of view of visitors always having a view of the Earth lit up in daylight), a launch site nearer the poles wouldn't be unreasonable as there would be no advantage to an equatorial spaceport for such a mission.

Or always seeing sunset and sunrise; that would be quite spectacular. Also, useful power-wise.

Really, there are three different basic conops; single sats to GEO, cargo to a depot, and passengers to a station. Single GEO launches make sense to be equatorial, tourist stations will probably high inclination, and depots probably at 23-28 degrees (ecliptic aligned). The single GEO launches make sense to be equatorial, and so the first real Skylon base will probably be there. But if it works and is economical, I could imagine a proliferation of other launch sites in Europe and North America.

Offline Warren Platts

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Re: The Reaction Engines Skylon Master Thread
« Reply #1107 on: 10/30/2012 06:51 PM »
@ Bob, thanks for the graph. Looking at it, it looks like right after takeoff, there is a relatively flat trajectory where it gains speed, I assume, before beginning its climb. It then takes about 2 minutes to make the climb to 5 km, which is the height of a potential air field in the Andes. Thus, this 2 minutes could be eliminated from the flight profile. Over the 950 seconds on the graph, that's a 12% savings in fuel, assuming the engines are going full throttle the whole time. Of course, the graph probably peters out before it reaches orbit (or does it?), so the real savings would be much smaller, but a few percent savings is still a few percent.

@ baldusi: What have you got against Ecuador? You're from South America, so tell us what's wrong with the place. It looks like a fairly modern country to me. It's got good port facilities and railroads that link Quito with the coast. They use the US dollar for their currency, so, unlike Argentina, they cannot deflate their currency even if they wanted to. Also, the weather can't be beat: 70 degrees average daytime high; 50 degrees average night time low. All year round. Kourou on the other hand, is a hot, humid, malarial swamp. A place that's no fun to live.
"Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.--Leonardo Da Vinci

Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1108 on: 10/30/2012 07:34 PM »
@Warren: Here's how the SKYLON User Manual describes takeoff:

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With the vehicle stationary the engines are ignited in air-breathing mode, burning hydrogen fuel with pre-cooled compressed air. When nominal performance has been verified the brakes are released and the vehicle begins its take-off roll. The vehicle takes off from the runway in the same manner as a high performance jet aircraft with a take-off speed close to Mach 0.5. Following takeoff the vehicle jettisons around 3 tonnes of water, which would have been required by the boiling water braking system for a rejected take-off, should a malfunction have occurred.

After take-off the vehicle climbs and accelerates on its predetermined trajectory for 694 seconds (approx 11 1⁄2 minutes), by which time it has reached an altitude of 28.5 km and a speed of Mach 5.2. The vehicle is now 620 km downrange from the launch site.

From that description, the high-altitude takeoff wouldn't be affected by the appxoximately 50% less dense oxygen at that elevation. However, lift would be diminished somewhat (I don't know just how much). It certainly looks more viable from the compressed air perspective. It looks like a mathematical model will be required to determine just how feasible such a high-altitude takeoff would actually be. I suspect REL has done an exercise like this, so maybe Hempsell will show up to comment on the possibility, hopefully.

Offline 93143

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Re: The Reaction Engines Skylon Master Thread
« Reply #1109 on: 10/30/2012 08:50 PM »
The precooling and compressing are done by the precooler and compressor in the engine.  There's not a separate facility for this or anything; hot and high still applies.

@Warren:  The vehicle is supersonic before reaching 5 km, and most of the acceleration is done during the climb phase.  You can't just subtract the altitude off.

Offline Warren Platts

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Re: The Reaction Engines Skylon Master Thread
« Reply #1110 on: 10/31/2012 06:24 PM »
@ Bob: I agree a numerical simulation is the only way to settle the issue, and that they've probably actually looked at that. Next time Mr. Hempsell pops in, hopefully, he can weigh in on the issue. Not that it's a big deal, but I'd like a little input before I go buying any land on that big plateau east of Quito I found on Google Earth! ;)

@ 93413: I agree you can't just subtract the altitude--the savings is marginal--less than 5% no doubt, yet its real and maybe worth taking into account, other things being equal. One thing, if you're starting from 5 km up already, the drag you're going to experience as you accelerate to supersonic speeds is going to be significantly less.
"Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.--Leonardo Da Vinci

Offline 93143

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Re: The Reaction Engines Skylon Master Thread
« Reply #1111 on: 11/01/2012 07:11 PM »
One thing, if you're starting from 5 km up already, the drag you're going to experience as you accelerate to supersonic speeds is going to be significantly less.

The thrust will be significantly less too.  The flight profile is tailored to produce optimal engine performance over the substantial range of airspeeds seen by the intake.  Start the thing cold at the altitude at which it expects Mach 1.2 and you may be disappointed with the results.

I agree, of course, that an actual answer would require an actual analysis (or at least a response from someone sufficiently expert to genuinely see the answer as obvious, if such a person exists).

Offline MP99

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Re: The Reaction Engines Skylon Master Thread
« Reply #1112 on: 11/01/2012 07:38 PM »
But, if you ran cargo or passenger SKYLON flights to a resort hotel in a polar, sun-synchronous orbit (which has advantages from the point of view of visitors always having a view of the Earth lit up in daylight)

Night views from ISS seem spectacular. Would be disappointing to go to orbit and not see that.

cheers, Martin

Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1113 on: 11/01/2012 09:04 PM »
But, if you ran cargo or passenger SKYLON flights to a resort hotel in a polar, sun-synchronous orbit (which has advantages from the point of view of visitors always having a view of the Earth lit up in daylight)

Night views from ISS seem spectacular. Would be disappointing to go to orbit and not see that.

cheers, Martin

How about an orbit that follows the terminator? Very spectacular. If it were the sunset terminator, you would see afternoon to the left and evening to the right as the Earth sweeps below.

Online douglas100

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Re: The Reaction Engines Skylon Master Thread
« Reply #1114 on: 11/01/2012 10:05 PM »
Higher radiation exposure in a polar orbit.
Douglas Clark

Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1115 on: 11/01/2012 11:34 PM »
Higher radiation exposure in a polar orbit.

Do you have a quantitative comparison (or link to one)? Would it be comparable to passing through the http://en.wikipedia.org/wiki/South_Atlantic_Anomaly ?

Offline baldusi

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Re: The Reaction Engines Skylon Master Thread
« Reply #1116 on: 11/02/2012 04:30 PM »
Look at the profile:

for certain altitudes, as long as you don't stray too far from the Equator, you can get below the worst part of the Belt. But if you go in an exactly polar orbit, you'll be crossing the worst part four times per orbit!

Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1117 on: 11/02/2012 05:44 PM »
Thanks for the chart. I'm afraid we've wandered off-topic here. But, we have to deal with radiation if we're ever going to leave LEO.  :)

If we can't, then we're doomed as a species.

Offline baldusi

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Re: The Reaction Engines Skylon Master Thread
« Reply #1118 on: 11/02/2012 06:00 PM »
Thanks for the chart. I'm afraid we've wandered off-topic here. But, we have to deal with radiation if we're ever going to leave LEO.  :)
Not really off-topic. The SSO launches are a significant part of the launches market. If Skylon pretends to compete, it will have to be hardened for thousand of passes through the Van Allen belt. Luckily, for a vehicle of its size, it shouldn't be such a problem.
The other issue is one of performance. Will Skylon be able to put any significant payload on the 800km~600km altitude of the normal SSO or will it need an US?

Offline BobCarver

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Re: The Reaction Engines Skylon Master Thread
« Reply #1119 on: 11/02/2012 06:16 PM »
Bond talked about the initial SKYLON being analogous to a DC-3, with follow-on 747 and successive models to come in the future. I have no doubt that much higher orbits will be reached at some model level:

« Last Edit: 11/02/2012 06:24 PM by BobCarver »

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