OHM NTR core propulsion stage

[markp]

Nice work Wishbone. Had a play with trying to get to Mars but it's little more complicated than I thought. I think several repeat burns need to be done before it's possible to escape from orbit around Earth? Need to give it a bit more thought.

 

[Wishbone]

Yes, two burns are in order. You would need extra propellant, so a fuel-tank only module with two docking ports should be used. Boiloff losses for the current state-of-the-art "zero-boiloff" insulation will be included later.

 

[markp]

Ah ok, that makes sense now, thanks. Look forward to future developments!

 

[Wishbone]

Build 5 uploaded. Ullage burn is only 20 seconds, no dependence on fuel quantity though.

Major changes to the DAP. First, it is rate-based, with arrow keys to set required rates in pitch and yaw, and Insert/Delete keys (NOT numpad!) to set roll rate. Second, it _should_ work with a stack of several vessels docked (shameless self-citation, code nicked from Precession MFD). Third, you can change DAP gains after pressing Ctrl-Y.
Fourth, pitch yaw roll channels for the DAP are individually selectable (Ctrl 1 2 3 respectively to turn them off and on).
Fifth, DAP works with RCS for pitch and yaw when engines are off, and TVC for pitch and yaw when on. Roll control is always (for now at least) provided by RCS.

EDIT:

Possible next major steps:
1. Ramp up and shutdown the three NTR sisters separately, with gimballing and possibly RCS nulling out residual torque.
2. Back-of-the-envelope qualitative FMEA (failure mode and effect analysis). What happens if a control drum pair is stuck? What's the probability of that occurring? How should the user designate abort boundaries during powered flight? Shall we consider a stuck gimbal as a possible failure? What is the worst-case scenario if a turbopump blows up? Will the fragments kill two other engines? (to be honest, I was considering adding a kevlar screen between the turbopumps on adjacent engines )
3. Electrical systems, which should be easier on this spacecraft than anywhere else (no crew, no ECLSS).

 

[LuckyHendrix]

Just discovred this addon,and it is very nice.:thumbup:
But i'm having problems for keeping my attitude during burns. Before the burn I activate the DAP and align for the burn and then I set all the rotation rates to 0. But when the are started up , they start to gimbal and the propulsion stage start to spin in a totaly uncontrolled manner. Am i doing something wrong ?

 

[Wishbone]

I discovered that it is due to excessive gains. In the current build I fixed the defaults, but you can do the following:
Alt-C
TVC Pitch Prop 5
Alt-C
TVC Yaw Prop 5
Alt-C
RCS Pitch Prop 5
Alt-C
RCS Yaw Prop 5
Alt-C
RCS Roll Prop 5

Sorry for the inconvenience, I'm going through exams (at least my students are...)

 

[LuckyHendrix]

thanks for the quick reply, it works perfectly :thumbup:

 

[PeterRoss]

Nice one, Wishbone! Tried it yesterday, planning to have a test flight to moon in the nearest time. Not a big request - could you please modify your mesh for solars to be folded by default? I've used Quasar 471 to launch that baby into orbit and it looks weird when foldings goes off and the solars appears sticking out of it Quasar is a spacecraft3/multistage based vessel, so it uses payload mesh in its default state to depict it before separation.

 

[Wishbone]

Hope I can do it. The good news is, the exams are over, and it is only the re-sits that remain. In the meantime I have meshed and coded a fuel tank, and the next released build will allow stacking the train together with some payload. Am tweaking the fuel tank's RCS (I assume it will use boiloff gas for attitude control after LEO insertion until assembly).

 

[Wishbone]

Build 6 released, haven't got to fixing the solar arrays yet (mesh changes should be co-ordinated with code ripple in 1 or 2 places). No textures as of now. DAP needs some tweaking for heavy stacks.

EDIT: (so as not to up the post count) I really need to add rate deadbands, not just attitude deadbands, plus, the spherical trig stuff would have to be revised to let the DAP run optimally.

 

[Wishbone]

A major fix as Work-in-progress, for the propulsion stage only.

DAP re-written with code from Apollo Colossus.
Boiloff, heat loads and cryocooler implemented. Solar power and battery recharge done.

Installation: extract the NTR_test.dll to the Modules directory.

 

[Wishbone]

Okay, build 7 uploaded.

 

[Wishbone]

A word of caution: rendezvous with the orbiting hydrogen tank using only forward RCS of the NTR core stage requires a VERY VERY gradual approach (burns of 1-2 m/s each, quite unlike the usual routine). By the way, I have done some lousy texturing on the core stage, as soon as I port the boiloff etc. code from the core to the tank, this stuff will be uploaded to OHM.

 

[Tacolev]

So I've been playing with your rocket lately, Wishbone and it's terrific. I have a request though involving fuel management.

I've been using docked radial drop tanks and the NTR reaches into them one at a time once the IL tank is empty. This leads to some obvious CoG problems. Do you think you could let the user configure the tank-draw order and allow for retrieval in parallel for just this sort of situation?

Also here's a shot of your stack in action. Thanks again for a great add-on!

 

[Wishbone]

Thank you for your kind words. Added to the punch stack, together with fixing default animations, as per previous request by PeterRoss. I'll be also simplifying large powered turns (it ain't that fun to hit the right arrow for XXXX times).

 

[Wishbone]

A small update: am finetuning multistage guidance for Ares V ([ame="http://www.orbithangar.com/searchid.php?ID=4584"]Ares V v1.5[/ame]), since there are very few super heavy vehicles to carry this stuff into LEO... Files are attached...

Re: drawdown sequence (parallelizing etc.). Did only the display of the current sequence. Other things will have to wait a bit.

EDIT: When you fire the scenario up, don't laugh too hard, the NTR stage mesh indeed has "ears" of solar arrays... Please note that in the currently publicly available NTR_test.dll one has to use Scenario Editor to fill both tanks of the stage after separation from the Ares; the multistage bug will be circumvented in the next release.

 

[QuentinT]

Hi !

Great Addons, good job !
But I got a question : I want to perform a fly to Mars and use the aerocapture like the NASA's reference mission, but after some test, the NTR is destroy...

I read somethings about a launch mode who can bring the resistance of the NTR to 7G, but I don't find how to switch between checkout mode and launch mode...

Anybody can help me ?

PS : Sorry for the really bad english :thumbsdown:

 

[Wishbone]

NTR stage is not designed for aerocapture or any other violent atmospheric maneuvers, and it will self-destroy after dynamic pressure builds up to something like 0.5 kPa, which makes sense since the thermal insulation works only in vacuum. Re: launch mode - in the scenario, insert line LAUNCH_MODE, and delete line CHECKOUT_MODE (if present).

EDIT: if you want to aerobrake/aerocapture (with MarkP's DRM 1.0 cargo craft, for instance), the routine would be to discard the propulsion stage to fly in the space so that it would have very low chances (say, 1 in a billion) of hitting Earth or Mars in the next million (AFAIR) years. Propulsive capture is so far the best option for manned MOI if nuclear propulsion is involved.

 

[QuentinT]

Thanks for answer, in fact I would like uses the NTR for perform the Mars to Earth return HTO, so I have to use the propulsion capture for MOI...

I have to add more propellant to the tanks :lol:

 

[Wishbone]

Did a quick update, the core stage now accepts command scripts from an external file. Only the core stage is textured and has boiloff implemented, though.