Discussion A REAL Delta Glider (well, almost)

[T.Neo]

because of knowed reasons.

Let me guess: OMG-nuclear-its-bad-do-not-want-NIMBY-NIMBY-NIMBY!

I reconfigured the Resolve to an NTR/LANTR craft last days, it flys great! Needs no boosters or extra tanks. With a refill in LEO it flys to mars alone and glides dreamfull through mars's atmosphere. The hovers are chemical but very strong, for a landing without runway. Should not be unrealistic. I set Isp to 8800m/s and Fuel mass to 540 mT. Thats lesser than a STS-ET (720mT), and this size you can easy hide inside this big bird, without using the payload bay for it!

Sounds great. Again, hovers on a spaceplane are stupid... it's a spaceplane for a reason.

If we start to freak out about possibility of reactor core sinking to the ocean bottom then we should also immediatly ban all oil tankers because there is possibility of oil spill and thousands of tons of oil can do far more environmental damage than sunken few dozen kg of solid nuclear fuel.

Exactly. And considering that staged rockets currently need to overfly ocean (unless you overfly some uninhabited Russian/Mongolian wilderness), it should not be too limiting.

The nuclear fuel... I certainly wouldn't worry if it ended up on the bottom of the ocean. The potential for worry is almost nonexistant, if it is landing in a radiation shield 3 kilometers deep.

 

[Wishbone]

There is a free MS Excel viewer at the Microoosoooft site, I'm told.

 

[Hielor]

There is a free MS Excel viewer at the Microoosoooft site, I'm told.

Try http://www.officelive.com/

 

[T.Neo]

First mass breakdown iteration.

As you can see, I only have 8.2 tons left for my OMS/RCS, power supply, auxilliary systems AND main support structure!

Guess I'll just have to add 10 tons or so and lose a km/s of dV. :dry:

EDIT:

Next time I post, I must attach the image the first time. :facepalm: :lol:

 

[Hielor]

First mass breakdown iteration.

As you can see, I only have 8.2 tons left for my OMS/RCS, power supply, auxilliary systems AND main support structure!

Guess I'll just have to add 10 tons or so and lose a km/s of dV. :dry:

EDIT:

Next time I post, I must attach the image the first time. :facepalm: :lol:

Those are some pretty darn beefy landing gear...

 

[Axel]

@ T.Neo
Hovers are not stupid! Ok for a pure LEO-Taxi not needed, because earth is full of runways. And you want only this kind of spaceplane, thats ok.

But why not extend its tasks for moon and mars? With 10km/s dV it could easy land AND takeoff at these planets without refueling, when we use a plasma rocket transfer stage. And we can use the fuel at both vessels, a plasma rocket can run by hydrogen and your realistic DG can run by argon too, a NTR eats nearly all :thumbup:.
If we refuel at target, then we would not need a transfer stage! But this would only be practicable for moon, mars transit would spent 9 month.
Or the ship flys automaticly to mars, because a station/base there needs a shuttle.

 

[Wishbone]

The original design requirement stated LEO. It is quite tempting to add one requirement after another, and this is the very reason configuration control boards exist - to prevent feature/requirement creep.

 

[T.Neo]

@ T.Neo
Hovers are not stupid! Ok for a pure LEO-Taxi not needed, because earth is full of runways. And you want only this kind of spaceplane, thats ok.

But why not extend its tasks for moon and mars? With 10km/s dV it could easy land AND takeoff at these planets without refueling, when we use a plasma rocket transfer stage. And we can use the fuel at both vessels, a plasma rocket can run by hydrogen and your realistic DG can run by argon too, a NTR eats nearly all .
If we refuel at target, then we would not need a transfer stage! But this would only be practicable for moon, mars transit would spent 9 month.
Or the ship flys automaticly to mars, because a station/base there needs a shuttle.

No. For two reasons;

1. As you said, Earth is full of runways. You're not going to be launching this thing from the African wilderness either, rather, you will be launching it from a spaceport with considerable infrastructure present. That would presumably include an adequate runway for takeoff and landing.

2. Such a craft is totally and utterly impractical for interplanetary travel. Starting with the fact that the cabin is far too small for a month's travel, let alone 9 months (it really depends on how adequate your propulsion system is).

Secondly, regardless of that, the spacecraft is actually pretty specialised for what it does; taking off and landing on runways, and reentering through Earth's atmosphere.

This means that it has features (TPS, wings, etc) that just become parasitic mass on the Moon or Mars; indeed, they become parasitic mass anywhere outside of LEO. It means you're lugging around a good deal of stuff you don't need.

Thirdly, stuffing hovers into the spacecraft is not possible, due to the mass constraints. Even tilting the rear engines, and having only one parasitic engine, incurs too much mass; the engines are designed for thrust vectoring but tilting them that far is a whole different problem. This is why spacecraft don't have mains and hovers at the same time; they either land on their tail (or with a -y pointing main engine, like on the LM) or they don't land at all (or they land on a runway, like STS and this thing).

Installing an extra propulsion system is not an option. Power supply onboard will be far too limited for that. Even a low thrust electric engine requires far too much power, and it would take far too long to get anywhere.

Yes, a solid-core nuke can run on "almost anything". But argon is a bad choice; even though it is monatomic, it is a heavy particle and not as good to use as propellant as a lighter particle, such as, say, hydrogen. Argon also isn't that abundant, which makes obtaining it problematic.

I am unfortunately no longer using hydrogen in my engines; I've settled on methane (for now), because even with slush hydrogen, the volume needed as immense...

The original design requirement stated LEO. It is quite tempting to add one requirement after another, and this is the very reason configuration control boards exist - to prevent feature/requirement creep.

Exactly.

 

[Hielor]

T.Neo, why 4 tons for landing gear? That seems kind of over-the-top...

 

[T.Neo]

Ah, yes, I was getting to that...

Truth be told, I have no idea whatsoever about landing gear on aircraft, so I snipped the landing gear off of Orbiter's STS, calculated their volume with MeshWizard, and then multiplied that with the density of a modern warship- 0.5 tons/m^3 (I know it sounds like an extremely odd example, but still...).

That's how I got to that figure. Maybe it had something to do with including the landing gear doors with the actual gear itself. :shifty:

I'm not sure how durable the gear would have to be... obviously it has to withstand a 60-70 ton craft landing at high speed, but I'm also concerned about the need to land in an emergency with propellant tanks full, which would require landing a nearly 400 ton craft. Either way, they still have to withstand the takeoff of a 400 ton craft.

By all means though, if I can cut down on the mass of my landing gear, I'll jump at the chance.

Considering that you have far more knowledge of aviation than I do, Hielor, what would you suggest as a sensible mass for the landing gear of this spacecraft?

 

[Wishbone]

1. Re: emergency landing. Why not provide for an emergency dump of CH4 into the poor atmosphere (remember, you're the benevolent dictator and pay the global warming tax out of your dictatorial salary).

2. Also, I assume abort modes more or less correspond to those of the STS, so no extra mass for catapults/LES towers.

3. What are the requirements on reactor shutdown time and coolant needed (this would make you leave some CH4 even during an emergency)?

 

[T.Neo]

1. Re: emergency landing. Why not provide for an emergency dump of CH4 into the poor atmosphere (remember, you're the benevolent dictator and pay the global warming tax out of your dictatorial salary).

I'm primarily worried about being able to dump the methane fast enough.

Something tells me that ~300 tons of methane being released in the unlikely event of a launch abort isn't that bad, if the amount of methane released each year from seabeds and permafrost regions is half a million tons per year

2. Also, I assume abort modes more or less correspond to those of the STS, so no extra mass for catapults/LES towers.

They would correspond to STS, roughly, including RTLS, TAL (or at least, downrange landing), AOA, and ATO (where practical).

The difference here is that hopefully in the first two minutes of launch, you have the capability of saving the crew. You aren't riding a pair of 45 meter tall firecrackers.

3. What are the requirements on reactor shutdown time and coolant needed (this would make you leave some CH4 even during an emergency)?

Potentially, SCRAM-ing the reactor would involve inserting control rods and continuation of propellant flow until the reactor is cooled sufficiently.

But I am no nuclear engineer so I don't know how sound a process that would be, and actually implementing it in Orbiter is a totally different matter...

 

[Sky Captain]

Have you considered drop tanks like on jet fighter to increase propellant load without the need for oversized internal tanks? Even if drop tanks allowed only to reach high subsonic speed and some altitude they would save a lot of internal volume because taking off and initial climb would be the most inefficient regarding propellant usage.

 

[Axel]

I never wanted an internal plasma rocket engine, i ment an extra transfer vessel, like VASIMR to dock or another. But thats not relevant anymore, because you want a pure LEO taxi.

But why you speak about 300 t methan??? I think you want a DG style vessel in size?

 

[Hielor]

Ah, yes, I was getting to that...

Truth be told, I have no idea whatsoever about landing gear on aircraft, so I snipped the landing gear off of Orbiter's STS, calculated their volume with MeshWizard, and then multiplied that with the density of a modern warship- 0.5 tons/m^3 (I know it sounds like an extremely odd example, but still...).

That's how I got to that figure. Maybe it had something to do with including the landing gear doors with the actual gear itself. :shifty:

Landing gear doors will probably need to be of a different material than the landing gear itself, especially considering that they will need to have a TPS on them.

One option you might consider would be assuming landing gear weight as a percentage of vehicle weight--this page suggests that 3% or so of total vehicle weight is a good first-order estimate.

As a more specific look at the shuttle's gear, I'll use the following pictures for reference:

One thing you'll note is that a whole lot of the volume of the landing gear assembly is in the tires, which are mostly air, with some rubber holding the whole thing together. I'm not sure how thick the tires would be. There might be data out there on airplane tires for heavy aircraft that you could look into in order to figure out how dense that rubber is and how much of it is actually air.

From the first image, you can see that a lot of the structural components are fairly thin pieces--an I-beam of whatever they're made of is quite strong for its weight.

From the second image, you can see the cylinder in the middle (which probably makes up the second-biggest contribution to volume, after the tires) is a hydraulic system designed to cushion the impact of landing--there's probably a lot of hollow-ness there. Again, not sure what that looks like in cutaway or how much it masses, but there might be data out there somewhere for similar devices.

There also seems to be a whole book on the subject--chapter 8 applies to landing gear weight, book starts here, other chapters/appendices available by looking at the index of that directory. Looks like it could be an interesting read...

I'm not sure how durable the gear would have to be... obviously it has to withstand a 60-70 ton craft landing at high speed, but I'm also concerned about the need to land in an emergency with propellant tanks full, which would require landing a nearly 400 ton craft. Either way, they still have to withstand the takeoff of a 400 ton craft.

It's fairly common for aircraft to need to land at a lighter weight than they took off at, which is why that A380 which experienced engine failure a couple months ago spent a few hours circling and dumping fuel. The shuttle also dumps fuel during an abort maneuver (RTLS I know for sure, haven't read as much about the others), so I think that's a perfectly reasonable thing to be able to do.

Consider also what kinds of emergencies you're planning to handle. Presumably you'll have more than one engine onboard--Will your craft be able to fly on only one engine? Real multi-engine aircraft are capable of continuing flight with an engine missing. For your craft, if you had a single engine fail shortly after takeoff, what would you do? Seems to me that "fly in circles over/near the landing site and burn off fuel to reduce weight using the remaining engines" is a reasonable course of action, and then you don't really have to design the thing to handle a max-gross landing.

As for the extreme case "just took off, all engines failed," there's not really much use for a strong landing gear there, either--at that point you're probably looking at an off-airport landing (in the Hudson, maybe?) and in that case landing gear is either useless (for a water landing) or just used as additional padding (for a ground landing).

 

[Grover]

the B747 can run well on only 3 engines, but thats only 1/4 loss (and a bit of negative feedback due to the engines air resistance)

but will your DG have only two engines? of so thats 1/2 power loss, twice that of a 747 (despite having no increased drag factor), not to mention the power-yaw generated when the net thrust vector is off-plane with the COG, creating massive tourque when you have high thrust space engines. coupled with the evident lack of rudder surface on most spaceplanes, that will make it unflyable, even if it does have enough power. (imagine trying to land with 45* bank )

best bet: dont bother with super landing gear, theres no reason you cant just eject all your fuel at once, especially if you cant use it anyway, and if you can, theres no reason why you cant just circle for a few loops of the field, high fuel rate means that your tank wont last long.

-="negative, its going in the hudson"=-

 

[T.Neo]

Have you considered drop tanks like on jet fighter to increase propellant load without the need for oversized internal tanks? Even if drop tanks allowed only to reach high subsonic speed and some altitude they would save a lot of internal volume because taking off and initial climb would be the most inefficient regarding propellant usage.

I've thought about it a bit, but that adds seperate components... maybe suitably sized drop tanks could be a performance booster, of sorts.

Stuffing the prohibitative LH2 volume into a drop tank doesn't help much, aside from keeping the tank outside of the TPS (which means, less mass for the TPS). But it still ends up being very bulky and the size of the drop tank prevents the craft from being a practical runway-launched vehicle.

I never wanted an internal plasma rocket engine, i ment an extra transfer vessel, like VASIMR to dock or another. But thats not relevant anymore, because you want a pure LEO taxi.

I want a pure LEO taxi, because it is only practical as a pure LEO taxi.

If you dock the thing with a VASIMR propulsion unit or whatever, why don't you leave it and all it's parasitic mass at home, and instead use a dedicated landing vehicle?

But why you speak about 300 t methan??? I think you want a DG style vessel in size?

Yes, of course. But there are things that prevent me from having such a small craft; for one, my engines have a far lower exhaust velocity.

I've settled for a 70 ton spacecraft mass, I have no idea how primitive that is. But it is better than the DG, which is less dense than the shuttle, for it's size.

One option you might consider would be assuming landing gear weight as a percentage of vehicle weight--this page suggests that 3% or so of total vehicle weight is a good first-order estimate.

That gives a value of 2.1 tons for a 70 ton vehicle, which sounds far better.

As a more specific look at the shuttle's gear, I'll use the following pictures for reference:

I feel like an utter moron now. :facepalm:

Thanks for the description, Hielor. :tiphat:

As for the extreme case "just took off, all engines failed," there's not really much use for a strong landing gear there, either--at that point you're probably looking at an off-airport landing (in the Hudson, maybe?) and in that case landing gear is either useless (for a water landing) or just used as additional padding (for a ground landing).

Well, in that case, ditching the craft is probably going to be extremely dangerous. For that reason, I'd just bail out (if possible) and leave the thing to crash. Ditching a craft with 400 tons of methane fuel aboard would probably not be pretty.

In the instance of a partial engine failure, engine gimballing could potentially be used to prevent instability (along with use of control surfaces, of course).

Circling the runway would probably be the best course of action, it's only 8 or so minutes till the propellant depletes, and that isn't with an extra fuel dump going on as well.

The engine failure rates would (hopefully) be low enough to make such an event unlikely; at least, the oppurtunity to circle the launch site and return to it relatively safely, is an ability that is sorely missing from STS.

 

[Sky Captain]

The engine failure rates would (hopefully) be low enough to make such an event unlikely; at least, the oppurtunity to circle the launch site and return to it relatively safely, is an ability that is sorely missing from STS.

The biggest danger probably would be turbopump failure when engine is running at high power because when propellant stops flowing an engine overheating and meltdown could happen in seconds. Two turbopumps per engine likely would be needed for redundancy.

 

[Axel]

@T.Neo
To the special Lander:
I dont want to mutch vessels for a mission!
Today we would need 4 vessels: 1. HLV 2.support shuttle(your DG) 3.interplanetary transfer vessel 4.Lander
That makes missions very complex and expensive.
But with some progresses in drive technologys we can remove 1 or 2 vessels, in a very distant future we only need 1 vessel. Your vessel would have the capability to play the roll as support shuttle and lander. Pure support shuttles we have enough at orbithangar, which are allready realistic. ITs parasitic mass would not be that mutch for a VASIMR, which has some hundrets km/s of dV and some hundrets tonnes of payload capacity. I pushed a Resolve-Shuttle (with 120mT own fuel inside) easy to mars by VASIMR. We would save some fuel and money at start because a lander has extra to be developed,launched and needs servicing! Its not unlimited resusable. But a service in LEO is very complicated or impossible. To bring it home to earth to expensive. They would build new landers for nearly every mission. The next thing is, an incoming crew from mars or moon had to wait for a LEO taxi, because special landers can only land at their destinations and not at earth. With your DG the crew could return to earth instantly. If you not implement the Hover i will do itself in every case, like i did it for the DGEX and Starclipper.

To the fuel mass:
If you really want 400mt fuel and 70mT empty mass, wheres then the sense for a pure LEO taxi and the big difference to Skylon? :facepalm:
You sayed that Skylon is big and slow, but now yours is mutch bigger! A pure LEO taxi job will do Skylon better without nuclear engine:

Skylon :thumbup:
------------------------------------
Length 83.3 m
Fuselage diameter 6.75 m
Wingspan 25.4 m
Empty mass 53 tonnes
Propellant mass 277 tonnes
Nominal take-off mass 345 tonnes
Maximum air-breathing thrust 2 x 1350 kN
Maximum thrust in rocket mode 2 x 1800 kN
Payload mass 15 tonnes

So i see the only adavantage in your design in a MUTCH higher payload capability(maybe?) for a pure LEO taxi.
Maybe 50mT payload? I can to some calculations, this could remove the HLV from mission profil .

To fix the engine problem at emergency abort, you can set one engine above the other:thumbup:
You would not need any engine tilting or any massiv rudder surface attacks.

But i guees, all my ideas will be wrong for you again :download:

 

[Wishbone]

Axel, your input is very valuable. We're always faced with tradeoffs between universal and specific/specialist vehicles, sometimes the balance tilts towards the former, sometimes towards the latter. The real limitation here is available energy/dV, which is also incidentally why Apollo was modular.