Idea Delta Glider Zero

[T.Neo]

I wonder if the SSME would be able to run for even more than a second, with an amount of fuel that the DG could carry. :lol:

 

[TMac3000]

It is possible to build a DG.

It's size would make the Space Shuttle look like a paper airplane.
It's cost would make the entire U.S. space program from 1960 onward look like peanuts.
It could not reach orbit.

In short, it would be a bureaucrat's best friend.

 

[T.Neo]

Hey... you could make a nuclear spaceplane that could reach orbit and be roughly the same size as STS, though without the payload capability.

The only problem is that you'd have to throw the engines away after each flight, since they become... radioactive and trying to refurbish them, would mean killing the maintainance crew.

 

[Tacolev]

Yeeks! Well this thread certainly has become a bigger thing than I'd thought it would.

It seems like something like the MAKS orbiter might still be the closest thing here to minimizing infrastructure, namely through the advantages of an air-launch in sidestepping a lot of the unique flight modalities that effect the rocket for all of one minute in the lower atmosphere.

At the same time, the one advantage to a payload shuttle is that it is agnostic to low-orbit or high-orbit missions. OMS engines can equally be orbital insertion engines for a light stack or deorbit engines for a heavy high orbit stack. Those engines will be vacuum engines the whole way through.

If there was just some economical way to have a dual-use engine good for either launch or orbital maneuvering... I suppose if you have to refit an SSME after every flight anyway you could have an OMS package designed for a common mounting and make a given mission's engines change with the application but then you're just recreating the space shuttle's problems for no good reason.

 

[T.Neo]

If you want to launch and manuver on-orbit, why not just have two engine systems? STS does it...

If you wanted to badly enough, you might even be able to use RCS clusters for orbital manuvering...

 

[RGClark]

That is no longer any DeltaGlider, it is now just a variation on Hermes, HL-20, Prometheus, heck, even the X-20 to an extent. It is just a payload on a rocket and no matter how hard you try to make it its own commercially viable package or whatever, it will still be just that: a payload on a rocket.

Even my 50+ meter long, 100 ton (impossible!) SSTO is more of a DeltaGlider, than a winged payload on a rocket.

Actually the Hermes spaceplane could be a VTHL SSTO if you remove the requirement it has to carry payload, and just regard it as a crew transport vehicle to orbit. For then you can fill the entire fuselage aside from the cockpit with propellant.
It would just have the appearance of a fighter jet. Indeed it has been likened to a Mirage 2000. See the info and diagrams here to estimate how much propellant you could fit in the fuselage:

http://translate.google.com/transla...siers/espace_europeen/hermes/1985.htm&act=url
[Google Translate used to translate from the original French version.]


Bob Clark

 

[Loru]

Not DG 0 but idea of small shuttle

PS

@ RGCLark

You can't just stick rocket propellant in the fuselage of a vehicle. A lot of space will be used by internal systems and vechicle structure itself. It's not an empty shell to fill with fuel and engine on one end.

 

[RGClark]

Not DG 0 but idea of small shuttle

PS

@ RGCLark

You can't just stick rocket propellant in the fuselage of a vehicle. A lot of space will be used by internal systems and vechicle structure itself. It's not an empty shell to fill with fuel and engine on one end.

Yes you can because the original design was for this to be empty space since it was to have a payload bay.

Bob Clark

 

[Urwumpe]

Yes you can because the original design was for this to be empty space since it was to have a payload bay.

So, lets start at the 50 € question: What is the tank head for your main engine(s)?

 

[Loru]

@ RGClark

quote from second page of website you've provided:
" The hold has a volume of 35 cubic meters, a diameter of 3 meters and a length of 5 meters."

let's add another 20 cubic meters of volume (rear section and wings).

With avarge 1.3 g/cm3 propellant density (kerosene/lox) 55 cubic meters gives us ~70 tons of propellant.

With empty weight of 12,100 kg!

Total dV is 6343 m/s not counting gravity losses
With 1MN engine we have around 5km/s dV.

Go figure yourself...

 

[Urwumpe]

And these 55 cubic meters don't include the tiny detail, that you need a higher pressure inside the tanks for delivering the fuel from the tank to the engines. Especially for high performance engines, you need still a pretty high tank head to prevent your turbopumps from cavitating, or force you to add mass for low pressure pumps that pump from the minimal tank head to the pressure needed for the high pressure pumps and heat exchangers.

If you have a tank head of 4 bar, this means your tank walls still need to contain a 4 times higher pressure as the crew cabin, and the crew cabin is already a heavy structural element. That is why you can't make tanks in any shape for spaceflight applications.

 

[T.Neo]

Ok, let's see now.

The stock DG in Orbiter masses 11 tons. I am not sure, but this might be considered to be unrealistically light for a vessel of this size.

Let's assume a mass ratio of 8.5: enough for 9.5 km/s of dV at SSME vacuum performance levels. This means a wet mass of roughly 94 tons, or a propellant mass of 83 tons.

Under SSME-like mixture ratio, LH2 makes up about 15% of the propellant mass, LOX 85%. So that is roughly 12.5 tons of LH2 and 70.6 tons of LOX.

Assuming a liquid oxygen density of 1 141 kg/m^3 and a liquid hydrogen density of 67.8 kg/m^3, and assuming ullage volume of 5%, that is a volume of ~65 m^3 and 193 m^3 of LOX and LH2, respectively.

If we assume the LOX tank is a sphere, and the LH2 tank is a cylinder which spherical end-caps, the comparison to the DG looks something like this:

Oops.

If we assume that both of these tanks have 2 mm wall thickness, then they may weigh maybe 1.4 tons. But this is not including internal stringers, insulation, piping, or other requirements.

The Delta IV upper stage has a mass ratio of between 8 and 9, and the Centaur (pressure-supported, collapses without stretch or internal pressure) is maybe between 10 and 11. These stages are also maybe a bit smaller than this, but not by much.

Also, it is quite likely that the wings required to lift that propellant would be a good deal bigger than those on the DG. It is certain that the resultant vehicle will weigh more than 11 tons.

And if you have ever put the DG next to the Shuttle in Orbiter, you would get pretty scared... because the DG is quite physically large already.

Now you are transitioning from the realm of "private jet" or "fighter aircraft" sized vehicles, into the realm of airliner-sized vehicles... and soon you can reach the realm of 747/An-225/A380/C-5 sized vehicles.

Maybe I have represented tanks a bit too wide here, but if you thin them down, your vehicle will get longer as well. Maybe better aerodynamics for ascent and reentry, but it doesn't help the whole physics problem much.

 

[N_Molson]

:thumbup:

This is an excellent way to design credible space vehicles. I use it for making rockets : starting by the tanks, then building the LV around.

 

[RGClark]

Ok, let's see now.
The stock DG in Orbiter masses 11 tons. I am not sure, but this might be considered to be unrealistically light for a vessel of this size.
Let's assume a mass ratio of 8.5: enough for 9.5 km/s of dV at SSME vacuum performance levels. This means a wet mass of roughly 94 tons, or a propellant mass of 83 tons.
Under SSME-like mixture ratio, LH2 makes up about 15% of the propellant mass, LOX 85%. So that is roughly 12.5 tons of LH2 and 70.6 tons of LOX.
Assuming a liquid oxygen density of 1 141 kg/m^3 and a liquid hydrogen density of 67.8 kg/m^3, and assuming ullage volume of 5%, that is a volume of ~65 m^3 and 193 m^3 of LOX and LH2, respectively.
If we assume the LOX tank is a sphere, and the LH2 tank is a cylinder which spherical end-caps, the comparison to the DG looks something like this:
...
Oops.
If we assume that both of these tanks have 2 mm wall thickness, then they may weigh maybe 1.4 tons. But this is not including internal stringers, insulation, piping, or other requirements.
The Delta IV upper stage has a mass ratio of between 8 and 9, and the Centaur (pressure-supported, collapses without stretch or internal pressure) is maybe between 10 and 11. These stages are also maybe a bit smaller than this, but not by much.
Also, it is quite likely that the wings required to lift that propellant would be a good deal bigger than those on the DG. It is certain that the resultant vehicle will weigh more than 11 tons.
And if you have ever put the DG next to the Shuttle in Orbiter, you would get pretty scared... because the DG is quite physically large already.
Now you are transitioning from the realm of "private jet" or "fighter aircraft" sized vehicles, into the realm of airliner-sized vehicles... and soon you can reach the realm of 747/An-225/A380/C-5 sized vehicles.
Maybe I have represented tanks a bit too wide here, but if you thin them down, your vehicle will get longer as well. Maybe better aerodynamics for ascent and reentry, but it doesn't help the whole physics problem much.

That is why it has been argued that an SSTO can be made smaller using dense propellants.

Bob Clark

 

[T.Neo]

It will be made smaller- maybe.

It will also be made heavier and this has an effect on performance. It might not be able to reach orbit at all if it uses dense propellants.

Already ~83 tons of propellant is bad enough.

 

[RGClark]

@ RGClark
quote from second page of website you've provided:
" The hold has a volume of 35 cubic meters, a diameter of 3 meters and a length of 5 meters."
let's add another 20 cubic meters of volume (rear section and wings).
With avarge 1.3 g/cm3 propellant density (kerosene/lox) 55 cubic meters gives us ~70 tons of propellant.
With empty weight of 12,100 kg!
Total dV is 6343 m/s not counting gravity losses
With 1MN engine we have around 5km/s dV.
Go figure yourself...

Thanks for taking the time to do the calculation. That web page is a nice resource on the different proposals for the Hermes over the years.
As you said the specifications I was using were actually on the second page describing the plans for the Hermes as of 1985:

http://translate.googleusercontent....ossiers/espace_europeen/hermes/1985_part2.htm

I reached the same conclusions you did; with the listed payload and crew cabin volume amounts, it wasn't enough. I had to use the entire cylindrical fuselage and then subtract off a smaller crew cabin volume, which I took to be the same as the Dragon's habitable volume at 10 m^3.
I'll show the calculations under the thread An SSTO as "God and Robert Heinlein intended".


Bob Clark

 

[Loru]

:thumbup:

This is an excellent way to design credible space vehicles. I use it for making rockets : starting by the tanks, then building the LV around.

Aye. Themis LV was done that way - for my shuttles I haven't used this method because they use small fraction of their's internal volumes as tanks.

...but they're not SSTOs

---------- Post added at 07:24 AM ---------- Previous post was at 07:19 AM ----------

I reached the same conclusions you did; with the listed payload and crew cabin volume amounts, it wasn't enough. I had to use the entire cylindrical fuselage and then subtract off a smaller crew cabin volume, which I took to be the same as the Dragon's habitable volume at 10 m^3.
I'll show the calculations under the thread An SSTO as "God and Robert Heinlein intended".


Bob Clark

Whole thing is very very easy. Calculating internal volume is simple math and for mass, dV and thrust I use my rocket calculator sheet which makes those calculations in no time. Sure, there are better tools but on that one I have all numbers in one sheet.

[ame="http://www.orbithangar.com/searchid.php?ID=5240"]http://www.orbithangar.com/searchid.php?ID=5240[/ame]

Try it first and do some calculations before claimng something.

 

[n0mad23]

The rocket calculator sheet, plus a few mesh layouts as shown by T. Neo above really is the way to go - imo. Internal space in these kinds of kinds of projects really is a premium, and it doesn't take long to exceed what's physically there.

In trying to increase the fuel capacity in my X-37B hack, I ended up switching the placement of my kerosene and H202 tanks (on paper, as there was no need to do so in the mesh work), as the H202 tank size was the one that grew the most. Physically creating the tanks and placing them into the X-37B mesh at the beginning was a good move as it really illustrated what space was left. Needless to say the little cargo bay got a whole lot smaller (now only 1 m long).

Years ago, back in my incarnation as a corporate paralegal I was involved with a design-build contract dispute over a WWII oil barge turned into a Surimi factory processing vessel. The engineers involved had really poor inter-dept. communication skills and many areas ended up with hugely conflicting design elements. Electrical systems needed to go where extensive pipework and mechanical systems had been designed to go. Behind it all it was glaringly obvious that when you're dealing with limited space you've got to make sure that it's all really utilized. Right down to the last square millimeter.

Must be a nightmare to try to service things though, aye?

 

[RGClark]

And these 55 cubic meters don't include the tiny detail, that you need a higher pressure inside the tanks for delivering the fuel from the tank to the engines. Especially for high performance engines, you need still a pretty high tank head to prevent your turbopumps from cavitating, or force you to add mass for low pressure pumps that pump from the minimal tank head to the pressure needed for the high pressure pumps and heat exchangers.
If you have a tank head of 4 bar, this means your tank walls still need to contain a 4 times higher pressure as the crew cabin, and the crew cabin is already a heavy structural element. That is why you can't make tanks in any shape for spaceflight applications.

Correct. I'll have to add on the mass of the pressurized fuel tanks and of the engines.

Bob Clark

---------- Post added at 03:23 PM ---------- Previous post was at 02:19 PM ----------

...
http://www.orbithangar.com/searchid.php?ID=5240

Try it first and do some calculations before claimng something.

I did the calculation. For a SSTO, every scrap of internal volume is worth its weight in gold to hold propellant. For all the proposals I made on this forum the entire internal volume of the vehicle was converted to hold propellant. I usually suggested any crew capsules or payloads be carried on top of the vehicle, a la the later proposals for the VentureStar:

10 Space Shuttles which never flew
BY ADMIN – MAY 12, 2011

Lockheed Venturestar: this is the final configuration of the vehicle which no longer looked much like the X-33. (Image credit: Lockheed Martin Corp)
http://www.armaghplanet.com/blog/10-shuttles-which-never-flew.html

However, for this I found you could have sufficient propellant using the cylindrical portion of the fuselage to have an internal crew cabin the size of the Dragon capsules habitable volume.
BTW, you could have even better payload if you used the wings to hold propellant as is done with all modern aircraft. However, the amount is harder to calculate as they are non-cylindrical so their volume is harder to calculate and because being non-cylindrical it is harder to calculate what would be the needed tankage mass.


Bob Clark

 

[T.Neo]

RGClark, I am very tired of explaining this.

What part of "rocket propellant tanks need to be a dedicated structure as there are dedicated demands on them" and "you can't just fill the internal volume with propellant" do you not understand?

This has been explained multiple times over and over again.

Your only option is to try and make a dedicated propellant tank that is light enough for your needs, inside a vehicle that is light enough for your needs. And this is of course very difficult, but that is how the game goes.