Discussion A REAL Delta Glider (well, almost)

[walsjona]

Would the Fission rockets be used in the atmospheric stage and if so would they be safe? I don't know that much about them but there must be some sort of radiation cocerns linked to them

 

[Hielor]

Nuclear nuclear NIMBY NIMBY NIMBY!

also, I think a shorter name might be good

 

[T.Neo]

Would the Fission rockets be used in the atmospheric stage and if so would they be safe? I don't know that much about them but there must be some sort of radiation cocerns linked to them

The airbreathing engines are entirely seperate from the main (fission) engines, save for that they use the same propellant resource. They would probably best resemble the Reaction Engines Scimitar engines, but running on methane rather than (far less dense) liquid hydrogen.

Radioactive fallout (i.e. shedding or emission radioactive material or debris) should not occur with the engine, due to the uranium being encased in resistant materials and the whole design of the fuel elements and engine itself being durable in terms of temperature, corrosion and transmutation. Similarly this durability would prevent radioactive dispertion in the event of an accident.

Actual radiation from the operation of the engines is mitigated by both shielding on the engine structure, and the some 14 tons of polyethylene neutron shielding surrounding the engines. Most of that mass is in front of the engines (between the engines and the crew/payload) as a "shadow shield" to minimise radiation, whereas the thinner side shielding only provides minimal support, to prevent damage and transmutation of infrastructure around the engines (including OMS and RCS components, etc).

Radiation from the engines is further decreased by the presence of hundreds of tons of propellant between the engines and the crew, and also by the vessel structure, as well as the distance between the crew and the engines. For this reason, radiation exposure to the crew can be regarded as minimal.

Igniting the main engines only at altitude also eliminates any possibility of radiation exposure to people on the ground, as well as allowing more launch flexibility by isolating launch effects from airport structures and suchlike.

Nuclear nuclear NIMBY NIMBY NIMBY!

:lol:

also, I think a shorter name might be good

Well, it does shorten to "ROCS", but I agree... it is quite cumbersome.

Does anyone have a better suggestion for a catchy acronym?

 

[Wishbone]

ROCS is fine. BLAST is another fine acronym

 

[Fabri91]

I've read through the .pdf file, and it looks like this project is going on strongly.
I'm trying to imagine how big this thing is going to be...marginally smaller than an XR5 maybe? And also the gear is going to be quite massive, since the ROCS (doesn't sound bad!) has wet mass slightly higher than a 747-400's maximum take-off weight.

 

[T.Neo]

ROCS is fine. BLAST is another fine acronym

Maybe, but what does it stand for?

I've read through the .pdf file, and it looks like this project is going on strongly.
I'm trying to imagine how big this thing is going to be...marginally smaller than an XR5 maybe? And also the gear is going to be quite massive, since the ROCS (doesn't sound bad!) has wet mass slightly higher than a 747-400's maximum take-off weight.

Overall length is 53 meters, height with vertical stabiliser and gear deployed might be just under 20 meters, I'm entirely unsure of wingspan as of yet, but it'll probably be around 30 meters.

That compares to Endeavour's length of 37.4 meters, height of 17.79 meters, and wingspan of 23.25 meters. The XR5 is 60.34 meters long, and has a 76.67 meter wingspan.

When figuring out the dimensions for the propellant tanks, I had to decide between short and fat, or long and thin, and I chose long and thin, because the extra distance from the engines lowers radiation dosage to the crew, and reduces the profile of the vehicle.

You make a good point with the landing gear; I'm running on the assumption that it doesn't have to be as massive to withstand takeoff as it does landing, so my mass figure is higher than 3% of the dry mass, but lower than 3% of the wet mass.

In the event of an emergency landing, launch propellant would have to be dumped.

 

[Wishbone]

Best LEO Atomic Space Transporter?

 

[Axel]

Best LEO Atomic Space Transporter?

Is the ESA Nerva Shuttle :lol:.
Ok im joking, i never used it. Buts its actual only downloadable/usable, so its automaticly the number one.
But i guess/hope T.Neos will beat it.

 

[Cairan]

I love this website: http://www.projectrho.com/rocket/enginelist.php#LANTR

I've been reading it on and off for the past few weeks...

 

[T.Neo]

Indeed, Atomic Rockets is awesome, certainly a must-read.

I considered LANTR in the very beginning, but I don't really need it since I have enough thrust and I don't want to lose ISP.

 

[Wishbone]

Re: OMS/RCS fuel selection in your preliminary outline. Would suggest going back to the trusty Aerozine/UDMH/MMH + N2O4 combination since you're guaranteed ignition with them. It may get pretty embarrassing if OMS fails to ignite (igniter is also extra mass). For RCS, this BTW means another delay in the loop and please multiply ignition system mass by 22 (20 RCS + 2 OMS).

EDIT: Re: The reactor itself. What reactor fuel are you going to use? Uranium dioxide, or uranium carbide? TRISO or something else? Please consider that there'll be no throttling of the reactor thermal output. How many cycles are you planning to fly on a single reactor fuel load? What to do with carbon deposits (in the reactor or in the nozzle)?

 

[T.Neo]

I don't know, hypergolic propellants are really nasty, toxic chemicals, as well as (I would imagine) being expensive to produce. I think that far outweighs the added complexity and mass of an ignition system.

There are many engines that use non hypergolic propellants, and they do just fine. There have even been proposals to replace the hypergolics on the shuttle with LOX and alchohol, and the GOX/Sintin system obviously worked for Buran (which my system is inspired by).

Hypergolics are tried and trusted, they're very familiar, but I look at this spacecraft, with it's futuristic propulsion system, and I figure, that a little greener secondary propellant couldn't hurt.

Nevertheless, I am unsure of my propellants as I have them now, and I have other concepts as well:

GOX/CH4: Advantageous because fuel is shared with main propellant. Crossfeeding on-orbit would probably be impractical, but it could simplify ground handling. Advantageous because gaseous methane removes the need for secondary pressurant for the fuel, but gaseous methane will be less dense than sintin.

H2O2/Hydrocarbon: A mixture of hydrocarbons (ethylene/propane, etc) is self pressurising, and pressurises liquid high concentration H2O2 via means of a collapsable membrane (as per this study). No secondary pressurant is required, and with the inclusion of a catalyst, hydrocarbon/H2O2 is hypergolic (Bristol Siddely Gamma is an example of this sort of system). H2O2 does not have the toxicity of hypergolic propellants, but it is a very strong oxidiser and could prove to be unstable.

H2O2/Sintin: Similar to current option, but with GOX replaced with H2O2. Both propellants would need to be pressurised by secondary gas sources, although peroxide decomposition removes the need for an ignition system.

 

[Cairan]

As for where to dump the heat, you could have a set of large radiators that deploy in orbit from the wings... imagine something looking like very large spoilers and flaps on the wings, which would deploy from both the upper and lower surface of the wing and be perpendicular to the wings and the fuselage, and hence presenting a minimum aspect towards the ship... I don't know the power output of your reactor at idle, but you could circulate liquid sodium in the core to carry the heat away to high temperature (ie. glowing hot) radiators while the core power downs to a warm standby temperature...

 

[T.Neo]

I'm going to try to keep doors on the underside of the vehicle to a minimum, so no large doors there. A door on the upper side of the wing would be better as that is only FRSI insulation or similar.

My reactors aren't operating on orbit, they're there solely for propulsion and have no electrical power generation potential- for that I use solar power.

I still have to remove residual heat from the engines though, and unless that can just be done by letting the heat diffuse into the rest of the vehicle and slowly radiate through the main radiators, it would presumably be required to use some sort of expendable coolant, or even left over methane propellant.

I don't know what I'm going to do about the radiators that remove the general system waste heat, they're quite large on STS and on this vehicle I'm not really sure as to where they can go.

 

[Cairan]

Your reactor is probably going to be warm enough to provide power through thermoelectric coupling, just like an RTG... how long is your endurance on orbit going to be? You might do without solar panels all together using the residual heat of your reactor to power equipment...

 

[T.Neo]

Planned orbital endurance is 20 days, as stated in the PDF.

I don't like the idea of using the reactors on-orbit, for one they would need to be redesigned to run continuously, as well as have some sort of cooling system for on-orbit operation, which will require larger radiator area. As far as I can understand, thermocouples are pretty inefficient and that would mean a lot of waste heat.

Getting an engine to produce ten megawatts of power and getting a reactor to produce at most, ten kilowatts of power, are two very different things, to achieve that at all you'd need to engineer the engine especially for that sort of multirole aspect.

Mind you if there's considerable energy from the radioactive decay alone, it might be worth it to tap into that for a little extra power, but in that case it'd be more of implementing a system to utilise something that's already there, than specifically designing the engines to be bimodal.

 

[Cairan]

I'd think that if you run your reactor at full power for the orbital insertion, you are going to have considerable waste heat on shutdown to dispose of... For precise orbit insertion, you'll need to cut the propellant flow very quickly, which would result in a bad heat spike which could damage the solid fuel elements if it is a solid core reactor. So you'll probably have to carry enough extra propellant to quench it while it basically scrams with some sort of neutron poison (ie. boron) added in the mix to really get it subcritical really fast, while venting the vaporised propellant from opposite vents, probably on the sides of your ship...

Even then, it will still carry quite a bit of waste heat, specially during the early days with the daughter isotopes undergoing energetic decay... This is some good reading: http://decay-heat.tripod.com/

Typically, the amount of decay heat that will be present in the reactor immediately following shutdown will be roughly 7% of the power level that the reactor operated at prior shutdown. A reactor operating at 3600 MW will produce 252 MW of decay heat immediately after shutdown; this demonstrates the importance of decay heat if no cooling is present. The amount of decay heat produced in the reactor will exponentially decrease as more and more of the radioactive material decays to some stable forms. Decay heat may decrease to about 2% of the pre-shutdown power level within the first hour after shutdown and to 1% within the first day. Decay heat will continue to decrease, but it will decrease at a much slower rate. Decay heat will be significant weeks and even months after the reactor is shut down.

With your figure of 17 GW output for the reactor, you'd end up with 1,2 GW immediately after MECO, with 340 MW of decay heat after 1 hour, 170 MW after 1 day and slowly decreasing to maybe half of that after 3 weeks, depending on decay products... I'm pretty sure you'd be able to tap-off all that waste heat. So even with a thermocouple operating at an abyssal 5% efficiency, and a 30-ish% efficiency for the heat transport system, you'd have, in theory, 18 MW of power at MECO, 5 MW after an hour and 2.5 MW after a day...

Which brings the point that with so much waste heat, you might be much more interested in having a Sterling generator, with an efficiency more into the 30-40% range, and manoeuver in orbit using a electric propulsion system (electromagnetic tether, ion engine), you'd have a LOT of power to spare.

 

[T.Neo]

Ok, you've definitely convinced me now. :thumbup:

I can chuck out the solar panels, they're not needed at all anymore. My problem is no longer power, not at all... it's now... getting rid of waste heat.

I hate waste heat. :dry:

Even with the thermocouples I have more power than I know what to do with, and I have to get rid of most of it as well, which entails pretty big radiators. That have to fold out, and not rip off, and not hit anything. And not weigh anything.

Let's say I have 100 kW available, and I want to run a resistojet with an exhaust velocity of 10 000 m/s. Such a device might be 25% efficient, and I end up with a grand thrust at the end of... 5 newtons. Utilising the power from a Sterling generator gives maybe 1.7 kN. Maybe dropping the specific impulse would help, in the end I could end up with a relatively low specific impulse that's still far better than that of my chemical OMS.

Maybe it would make sense to inject the neutron poison in with the final amount of propellant before cooling down the reactor with extra (non-propulsive) propellant, to save mass.

But I still don't have a clue of what I'm going to do with all that waste heat. Maybe yet another of my projects will be sunk by waste heat. :dry:

 

[Cairan]

You could always downsize the reactor and use a different profile to orbit... I don't have much time to run the math on it, but the whole upper surface of the wings could be radiators themselves...

Let's say the upper surface of the wings are actually folded radiator panels protected by an isolation layer. There is a pivot point at the wing tips, and the latches are at the wing root. The upper surface, containing radiator elements, would unlock and deploy, pivoting 180 degrees longitudinally around the wing tip. The isolation layer itself could also rotate 90 degrees more, which would bring it perpendicular to the bottom side of the wing. You'd have 3 times as much radiator area, with the original surface of the upper wing and both sides of the deployed additional radiator panel.


... is void space

Before deployment, port wing, top view:
../==|
./===| Ship
/====|
------
Wing

From behind

......x====| Ship
.......Wing

After deployment, port wing, top view:

|==\..../==|
|===\../===| Ship
|====\/====|
------------

From behind:

Radiators exposed
=====x====| Ship
.....|.....
.....|.<- Protective panel
.....|.....


Another idea, more structurally sound, but which I lack the ASCII skills to render, is to deploy the radiators along the wing leading edge instead of a single-point pivot at the wing tip... That way it would be much more sturdy.

 

[T.Neo]

I'm skeptical that it would work, my test (that of deploying a single panel off the leading edge) shows that a radiator on the wing, and on a similarly-sized flap off of the wing, would only be able to radiate about 24 megawatts (the outer side of the panel, that is presumably covered with something like FRSI, doesn't radiate so well). In addition, the radiator in the wing is also radiating back into the vehicle structure. And heating on the structure can't be a good thing. This is with 500 degree C radiators (773 K).

The more panels that are deployed, the flimsier the system gets. And it would weigh a ton- figuratively of course. My guess is that it'd probably mass 20 tons or more, and that effectively murders my orbital capability.