OHM NTR core propulsion stage

[OrbitHangar]

Author: wishbone

NTR core propulsion stage (Aug.21, 2011, build 8) by wishbone
This is the notional core propulsion stage from Mars DRA 5.0.

Acknowledgements

Martin Schweiger for the Orbiter simulation environment, HST and ShuttlePB boilerplates which I (ab)used.
http://www.orbiter-forum.com dwellers for ideas and suggestions, and of course for the desire to see the dream of a manned Mars mission come true.
BrianJ for on-screen display code, and sun tracking (with RussH).
Space Shuttle Ultra team for PID control and thrust vectoring code.
Moach for suggesting the dummy thruster idea.
T.Neo for staunch defense of nuclear propulsion that made me curious.
NMolson for convincing me that animations are not that difficult.
NASA, SAIC and all Mars mission planners.
Anatoly S. Koroteev and his researchers for the wealth of theoretical and experimental data.
Joshua Clough from UMD for his Ph.D. thesis on bi-modal NTRs.
Chris Knestrick and Tim Blaxland (for insights into attitude control).
R.G.Ross and his colleagues for the Cryocoolers 11 proceedings.
David G. Gilmore and other authors for "Spacecraft Thermal Control Handbook" (2002).
Donald Rapp for cryoformulae from "Transporting hydrogen to the Moon or Mars and storing it there" (2006). ArtLav for solar panel texture.

 All errors are mine. The code (insofar as it is written by me and not anybody else) is public, see notes attached to code snippets for extra limitations. This is work in progress, so some things may not always go as planned. Formulas are common knowledge…

Changelog Build 8: June 18, 2011
Added loadable command scripts. Enhanced set of commands available through Alt-C. First attempt to texture the NTR core stage. When attitude autopilots are active, time acceleration is limited to 10x.

Installation and requirements

Installation is simple: just un-zip the archive into your Orbiter 2010 directory.

Technical data are in the docs



DOWNLOAD

 

[markp]

Looks interesting. I'll give a test run soon to Mars.

 

[mc_]

Looks good, i'll test it :thumbup:

Tried to build something like this myself, but stuck with textures. Anyway, dll-based NTR is better, then spasecraft3 barrel of UDMH with a huge engine behind.

//mayde offtopic, but i need to say this: why all addons of this kind (stages, boosters, tugs, etc) are missing proper description at the site? So, you have to download (or even install) it to figure out empty/gross mass, thrust, dimensions and other stuff necessary to build a stack.

 

[Wishbone]

mc_, point taken. Will update the description and the dox. There are missing elements for the stack - in-line tank, drop tank for the crew, and of course the habitat, will get to them as schedule permits. BTW, the mesh source (in 3DS format) is included with the pack.

 

[Tacolev]

Since you still haven't nailed everything down you might also consider including a version with 110 kN engines for the piloted jupiter system reference mission. Apart from an extra in-line tank bolted to the front all depictions of this element of the two architectures have been identical.

 

[Wishbone]

Will look into it. AFAIR drop tanks should empty first, am using clbkGeneric to poll docked vessels for info on drawdown sequence (assuming they understand the messages). Another known bug: RCS thrusters' coordinates are not aligned with the stage, since they come directly from ShuttlePB.

For Isp to change realistically with exhaust temperature, I need dependence of the latter on reactor power, after that should amend the algorithm for calculation of the "final dV".

EDIT: Thanks go to SSU folks, in the working version have borrowed TVC code, the engines can be manually gimballed. Also implemented pumping fuel from first tanks in all docked and attached vessels without relying on Fuel Transfer MFD, and of course, the auto-cutoff function.

 

[mc_]

Hmm... with a gross weight less than 100 tons it looks like Energia can handle this thing.

:thumbup:

 

[Wishbone]

Re: Energia. Please bear in mind that the stage has v.large diameter, and has to be carried to 470 km circular orbit...

Tacolev was right, BTW. The thrust of 66 kN is way too small, I mangled my unit conversion badly... Will uprate to 111 kN in the next build.

 

[anemazoso]

Nice work. Love where you are going with this.

 

[mc_]

Tried several launches with Energia. Looks like the payload fits well (still needs a nose cone and some cover for engines, though), but a few seconds after liftoff strange thing happens: NTR just disappears from simulation (checked with ScnEditor).

 

[Wishbone]

Ummm... mea culpa, my fault entirely, which I'll fix in the next build. To avoid reentries, and to simulate "destruction" in the upper atmosphere, I put in a check for DNP<1 kPa. Must have thought about adding that to the manual, but it somehow slipped past me.

 

[mc_]

How should i launch it to space then?

Dreaming about a full mission "from pad to %PlanetName%", and NTR looks like the proper engine...

 

[Wishbone]

Updated to build 4

Update to build 4 is now at OHM, with some problems (hopefully) fixed.

 

[mc_]

Energia launch is still problematic: payload needs a little boost after separation, othervise it will fall back to atmosphere.
But we still can catch it on a half way down:



It's a quite tricky maneuver (less then 15 min for everything), maybe, i should dump part of fuel and attach DM-2 to NTR... Just wanted to feel i'm "крутой космонавт" :thumbup:

Problems found:

• Something wrong with NTR mesh visibility when docking to it. I had similar ones with my Spacecraft3-UDMH booster, fixed adjusting "size" parameter;
• Camera in "glass cockpit" is close to the center of the craft, so we can see some elements of the construction "inside out". Looks weird;
• BTW: How to retract solar panels in launch mode?

 

[Wishbone]

NTR mesh visibility - acknowledged, thanks for the "size" hint.
Camera location - will put near the top.
Retract panels - K key. I suppose this is a bug, will be investigated.

Thanks for testing!
Currently in the development version: fixed the DAP during powered flight, one can set pitch and yaw rates instead of directly operating the TVC gimbals. This is a high-priority item since the stage must cope with one engine out gracefully (no loss-of-mission) and two engines out (no loss of attitude control).

 

[Urwumpe]

Energia launch is still problematic: payload needs a little boost after separation, othervise it will fall back to atmosphere.
But we still can catch it on a half way down:

Add a few small RCS modules to it, you would need them anyway: For settling the propellant at the manifold (called "ullage") before the nuclear engines could even be started.

 

[Wishbone]

Urwumpe: thanks, yes, current RCS config is a problem, need more (Orbiter-wise) +Z thrusters. Am wondering about the length of ullage burn: how long should it be and does it depend on the amount of fuel left?

EDIT: re - circularization. AFAIR all design documents state bluntly that circularization burn will not be required, ergo all the RCS propellant is for LEO rendezvous, cruise attitude control and MCCs.

 

[mc_]

Retract panels - K key. I suppose this is a bug, will be investigated.

I suppose this bug is called RTFM :facepalm:

 

[Urwumpe]

Urwumpe: thanks, yes, current RCS config is a problem, need more (Orbiter-wise) +Z thrusters. Am wondering about the length of ullage burn: how long should it be and does it depend on the amount of fuel left?

Depends on the tank design, but generally yes, you need to burn long enough that even in the worst case (all propellant concentrated at the opposite end of the tank), enough of the propellant without pressurant gas bubbles concentrates at the siphon. That includes of course tank geometry, and the acceleration of the RCS. If you have rather weak thrusters, this can mean easily a minute or more of ullage.

 

[Wishbone]

Okay, now is the time for looking up the formulae in the handbook...

mc_: if you cannot find the key in the screen it is MY fault as the designer, no kidding. It is also my responsibility to ensure that all animations are in their right positions in all modes. Please remember that K key will not be tied to that particular animation forever.