General Question Most realistic XR2 settings?

[EnDSchultz]

I've always been trying to make my flights with the most realistic ISP and fuel quantity possible, and I was wondering what would be most plausible for the XR2. In the config file it has options for a "realistic" ISP and max thrust, but I was wondering about fuel capacity. Would it be more realistic for it to need extra tanks in the cargo bay to reach the default fuel weight? Or is that option there just for extra challenge? I guess I just find it a little hard to believe that on "realistic" fuel consumption and thrust settings it would have enough fuel aboard to reach low earth orbit without any external boosters whatsoever.

Of course, the vessel isn't designed to be totally realistic, but I'd like to get it into the ballpark of plausibility.

 

[N_Molson]

The first thing to begin with is : what kind of fuel does it burns ?

Here you can choose your poison

http://www.astronautix.com/props/index.htm

The second thing is to estimate how much fuel can be stored in the XR2 tanks. Also consider that most cryogenic fuels takes a lot of volume.

For realistic settings, my best guess would be : an external booster for reaching the orbit (like the DG-launchers ), then a N2O4/MMH mixture for orbital manoeuvers, like the Space Shuttle. You could also try N2O4/UDMH, there's plenty of choice there !

Or you can consider the XR2 as a suborbital spaceplane, and give it just enough rocket fuel to lit the scramjets.

 

[FuzzyLogic]

There's a modification by skycaptain/River Crab that makes the XR2 a lot more realistic. She's way more fragile and requires boosters (or Kulch's winged tug) to achieve scram speeds.

Link here, hope it helps

[ame="http://www.orbithangar.com/searchid.php?ID=4219"]Realistic settings for XR2 Ravenstar[/ame]

Edit: Credit goes where its due :tiphat:

 

[River Crab]

Well, in the case of XR2, such vessel is by design not going to be SSTO-capable with known materials science (debatable, but that's beside the point). You can get something plausible, though, by using the config cheatcodes to directly edit the vessel's properties. This is something I've been playing with: Realistic settings for XR2 Ravenstar
Very challenging; it puts the XR2 atop a booster (Either the XL70 or an SRB) to reach SCRAM speed and altitude. Pretty close in terms of realism, and the result is AWESOME.

Edit: :ninja:

 

[Shinrar]

This was something I was very interested in doing as well, though I ran into a few conflicts with the numbers I was getting - vs the numbers that the "realistic" settings were using (the aforementioned mod).

I don't have my numbers here (and I think they've been trashed, so I'd have to research them all again. Doi), but if I recall correctly:

The fuel seemed to work out well if you assumed the vessel had no cargo space (and the entire cargo volume was dedicated to fuel), if you used a very dense fuel. However, the values for fuel using SCRAM were - sadly - way out of the ballpark. If I recall, I was getting numbers that said the amount of fuel the mod was giving was more than the volume of the spacecraft in total... Then again, I might of been doing the math using the incorrect fuel.

However, after all my math and work, I never got the add-on to work with the XR2 sitting atop of the XL70, so I sort of moved on without figuring out where my math was wrong... Now you're sparked interest in it again. :lol:

That being said - if you assume the cargo space becomes fuel space - what is the XR2 beyond a very high altitude airliner?

Edit:
Also, this thread is the prelude to his add-on, where he got a lot of opinions on how best to do it.

 

[EnDSchultz]

Well, that's a darn shame. I had hoped the XR2 would at least have a little more oomph than the Space Shuttle...Is the only really advantage of conventional takeoff to supersonic, SCRAM to hypersonic, and then rockets to orbital velocity that it overall requires less fuel than a traditional rockets-only ascent because the atmosphere acts as the oxidizer for a good portion of it?

Also, I suppose using the "cargo bay tanks required for max fuel capacity" option in the config file would also be appropriate.

 

[Shinrar]

Well, that's a darn shame. I had hoped the XR2 would at least have a little more oomph than the Space Shuttle...Is the only really advantage of conventional takeoff to supersonic, SCRAM to hypersonic, and then rockets to orbital velocity that it overall requires less fuel than a traditional rockets-only ascent because the atmosphere acts as the oxidizer for a good portion of it?

Also, I suppose using the "cargo bay tanks required for max fuel capacity" option in the config file would also be appropriate.

Firstly, apoligies for bad spelling. Typing from a cellphone, lol.
Regarding the using the cargo bank tanks for max fuel - I agree it would be appropriate. I'd have to number crunch how those work though.... Without looking into it, I think they may have a fixed mass of fuel (and thus density, as the volume is fixed as well). Making a mental note to check that when I get home.

As far as advantages - if you utilize a transport like the XL70 to bring it to SCRAM speed, the advantage over the shuttle is one of cost per flight. Everything is reusuable, vs having to make a new ET for every flight on the shuttle.

 

[Sky Captain]

IIRC my assumption behind realistic XR2 addon was that cargo bay volume is used to store fuel. There is supposed to be ~70 m3 of methane for SCRAM and ~25 m3 of main engine fuel. As far as I was able to guestimate volume it should fit if cargo bay is used.

 

[Shinrar]

Hrm. What's the estimates (or actual?) volume of the CargoBay..?

 

[T.Neo]

The engines of the XR2 actually fit into the range of closed-core gas nuclear thermal engines, but the mass and the appearance of the hardware isn't modelled. The major problem is the lack of volume for propellant.

 

[Sky Captain]

Hrm. What's the estimates (or actual?) volume of the CargoBay..?

XR2 manual says cargo bay has volume of 30 m3. I assume fuel is stored also inside the wings and in the space behind and below cargo bay. Keep in mind XR2 is fairly large, nearly as big as Space Shuttle so there should be a space for ~95 m3 of fuel.

 

[N_Molson]

Is it possible to store fuel in the wings in a spaceplane ? The reentry puts a lot of physical on thermical stress on those, which seems hardly compatible with fuel tanks. Also, in reality, rocket fuel tanks are always more or less spherical (I guess it's a matter of pressurization), so a lot of space is "lost".

 

[T.Neo]

Spherical... cylindrical... it's easier that way. Imagine a cubic propellant tank. You'd waste plenty of mass on reinforcing it, and mass matters more than wasted space, most of the time anyway.

If the XR2 had 65m^3 of fuel (removing the 30m^3 for the payload bay), it would be able to carry around 4 tons of liquid hydrogen, and around 6 tons with the volume of the payload bay included. If that was methane, it could carry over 25 tons in the body alone. Of course the problem with methane is that it'll give you a lower exhaust velocity than hydrogen...

 

[Rtyh-12]

So does that help us in our quest to build a SSTO XR2 spaceplane?

 

[N_Molson]

If you want to use existing technologies (and realistic mass settings), I fear that a SSTO XR2 isn't possible.

 

[River Crab]

With the help of a large, very high speed mass driver, maybe you could get an SSTO XR2 in the realm of possibility (if the mass driver doesn't count as a stage). Even if such a method were employed, it would be still be difficult with the small size of the vessel, and would likely not be used for a vessel shaped like the XR2, but rather something larger that maximizes volume. There's also the problem of heat shielding, I'm inclined to just say "nanotechnology"...
As well as some more minor problems, like the opening nose cone (good for playability and cool factor, not so much realism), large curved cockpit glass, small protrusions from the AF control surfaces, etc.
It's been discussed before in more detail, so I'd rather not go into that. I haven't delved too deep into the number-crunching to make it work, so you'd be better off taking it from someone who has.

Anyway, I can certainly appreciate the Ravenstar for what she is, a beautiful addon. :tiphat:




Now...
For anyone who wants to play with the realistic settings, here is a bit of an easier rendezvous scenario (made for SkyCaptain's config) using Siriusfett's Ess (I know, not exactly realistic, but it's better than Mir). It's only easier; hard, but not lunatic (due to the advantageous launch site). There are lots of tips in the description, hopefully not too long as it includes the links to required addons; I might script it as a challenge when I learn how.

The first time I tried it without jettisoning the bay tanks, I docked with no main fuel and less than 30% RCS fuel left!

XL70 and XR2 Ravenstar Ess rendezvous.scn

BEGIN_DESC
This scenario is meant for SkyCaptain's realistic
 settings for XR2 Ravenstar config. You should have a joystick, and be familiar with operation of XR2 and XL70.


--------------------------------------------------------


REQUIRMENTS:


XR2 Ravenstar (Doug Beachy and Steve 'Coolhand' Tyler): 
  http://alteaaerospace.com/index-3.html


Realistic
 settings for XR2 Ravenstar config (SkyCaptain): 
  http://orbithangar.com/searchid.php?ID=4219


S3 Hyperdart/XL70 (Cigdriver): 
  http://www.orbiter-forum.com/showpost.php?p=38399


Universal Cargo Deck (Yuri Kulchitsky): 
  http://orbithangar.com/searchid.php?ID=3262


Ess station (Siriusfett): 
  http://www.orbiterfrancophone.com/index.php?disp=addons&id=12


Wideawake International (wehaveaproblem): 
  http://www.orbithangar.com/searchid.php?ID=3666


And, optionally, the X-15 skin for XR2 (Astrosammy): 
  http://www.orbithangar.com/searchid.php?ID=3957


--------------------------------------------------------


MISSION: 


Take off from Wideawake and rendezvous with the Ess (in a low inclination LEO) to deliver a fresh crew and supplies to the station. Be gentle on the ship 

and the crew; they are both delicate and valuable.


--------------------------------------------------------


MISSION DETAIL: 


Your XL-XR stack is on the runway at Wideawake; the Ess is passing over the US west coast. 


Take off immediately and climb in the XL70, maintaining your current heading; the runway is almost perfectly aligned with your launch azimuth. Lower the 

wingtips (key W) as you reach mach 1; use CoG shift and trim to compensate for your large payload. As you approach 25 km, power up the Ravenstar's APU 

and open the SCRAM doors. Release while coasting to the top of a parabolic trajectory reaching 25 km alt at a speed approaching 1191 m/s (Mach 3.5). You 

are nearing the limit the XL70 is rated for. 


Bonus 1: After release, you can delete the XL70 from the scenario, but if you wish for an added challenge, you can try to fly it back to base.


The XR's SCRAM engines should be able to autostart- pitch into a shallow climb and cruise on SCRAM power at about 0.3 G acceleration. Keep an eye on hull 

temps, keeping vertical speed at a minimum to take advantage of the air. Align planes in flight for little fuel cost. Do NOT use attitude hold autopilot; 

it will waste your RCS fuel during ascent. This is the longest part of the ascent, and efficiency here will save you precious main fuel later. 

Unfortunately, the SCRAM TSFC gauge does not work with the realistic config settings (it's always at maximum).


When you run out of SCRAM fuel, activate rotational RCS, close the SCRAM doors, and engage the mains. Perform your intercept burn immediately after 

insertion to save fuel, and go for rendezvous at intercept 2 (bonus 2: use TransX). Open the radiator as soon as possible; your coolant temperature is 

likely to trigger a warning at this point. To save Delta-V, you can release the now-empty bay tanks before your intercept burn, as they are on a path to 

re-enter in the Atlantic Ocean (you decide whether this is realistic or not). Bonus 3: Don't jettison the bay tanks.


Circularisation and docking are fairly straightforward; however, try to conserve RCS fuel, as it depletes faster than it would with normal settings. You 

may have to use cross-feed if you are very low on fuel.


If you do all this efficiently, you can make it with some fuel left.
Congratulations, you've delivered a fresh crew and a hab module full of supplies (and possibly some empty fuel tanks) to the station!


Bonus 4: You will pass over Wideawake again in a few orbits. Why don't you transfer the crew, refuel, and try reentering?




~Scenario 2010 River Crab~
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 60247.4237563888
END_ENVIRONMENT

BEGIN_FOCUS
  Ship XL70
END_FOCUS

BEGIN_CAMERA
  TARGET XL70
  MODE Extern
  POS 309.19 -4.53 -17.27
  TRACKMODE Ground Earth
  GROUNDLOCATION -14.41586 -7.97234 253.44
  FOV 40.00
  BEGIN_PRESET
    Ground:XL70:40.00:Earth -14.41586 -7.97234 253.44
    Ground:XL70:10.00:Earth -14.99780 -8.15162 22665.62
  END_PRESET
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE Surface
  SPDMODE 1
END_MFD

BEGIN_MFD Right
  TYPE Map
  REF Earth
  OTARGET Ess
  POS 0.00 0.00
END_MFD

BEGIN_VC
END_VC

BEGIN_SHIPS
Ess:Ess
  STATUS Orbiting Earth
  RPOS 1491234.04 483568.40 6477266.12
  RVEL -7488.762 -789.327 1784.801
  AROT -11.23 64.81 -19.51
  AFCMODE 7
  IDS 0:109 100 1:110 100 2:111 100 3:112 100 4:113 100 5:114 100
  NAVFREQ 0 0
  XPDR 484
  roue 3 0.0732
  ant 3 0.0965
  pant 3 0.3219
  currentdock 5
  KillAngularRotation 1
  UMMUCREW Ast-Yvan_Dumaine-34-65-64
  UMMUCREW Capt-Franck_Solo-26-67-65
  UMMUCREW Spe-Daniel_Leprince-40-70-70
  UMMUCREW APhy-Isabelle_Tomasi-25-70-70
  UMMUCREW Eng-John_Dudertre-20-70-63
  UMMUCREW Bio-Thierry_Jehan-35-70-70
  UMMUCREW Doc-Severine_Blard-35-70-70
  UMMUCREW Geo-Marc_Gandin-40-70-70
  UMMUCREW Ast-Sylvain_Tessier-34-65-64
  UMMUCREW Spe-Sebastien_Irisee-36-70-70
  UMMUCREW Tech-Francois_Varinot-30-70-70
  UMMUCREW Min-Isis_Valle-45-70-70
  UMMUCREW Eng-Alain_Weill-32-70-70
  UMMUCREW Chem-Christopher_Kleine-48-70-70
  UMMUCREW APhy-Arnaud_Pavon-40-70-70
END
XR2-01:XR2Ravenstar
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 118.08
  ATTACHED 0:0,CargoDeck
  RCSMODE 0
  PRPLEVEL 0:1.000000 1:1.000000 2:1.000000
  IDS 0:199 100
  NAVFREQ 94 524 84 114
  XPDR 193
  SECONDARY_HUD 3
  LAST_ACTIVE_SECONDARY_HUD 0
  ADCTRL_MODE 0
  TAKEOFF_LANDING_CALLOUTS 0.000000 -899.437003 -899.423003 0.000000 0.000000
  APU_FUEL_QTY 0.977287
  LOX_QTY 1.000000
  CABIN_O2_LEVEL 0.209000
  CREW_STATE 0
  INTERNAL_SYSTEMS_FAILURE 0
  COGSHIFT_MODES 0 0 0
  MWS_ACTIVE 0
  COOLANT_TEMP 36.986765
  DMG_0 1.000000 Left Wing
  DMG_1 1.000000 Right Wing
  DMG_2 1.000000 Left Aileron
  DMG_3 1.000000 Right Aileron
  DMG_4 1.000000 Landing Gear
  DMG_5 1.000000 Nosecone
  DMG_6 1.000000 Retro Doors
  DMG_7 1.000000 Top Hatch
  DMG_8 1.000000 Radiator
  DMG_9 1.000000 Airbrake
  DMG_10 1.000000 Left Main Engine
  DMG_11 1.000000 Right Main Engine
  DMG_12 1.000000 Left SCRAM Engine
  DMG_13 1.000000 Right SCRAM Engine
  DMG_14 1.000000 Fore Hover Engine
  DMG_15 1.000000 Aft Hover Engine
  DMG_16 1.000000 Left Retro Engine
  DMG_17 1.000000 Right Retro Engine
  DMG_18 1.000000 Forward Lower RCS
  DMG_19 1.000000 Aft Upper RCS
  DMG_20 1.000000 Forward Upper RCS
  DMG_21 1.000000 Aft Lower RCS
  DMG_22 1.000000 Forward Star. RCS
  DMG_23 1.000000 Aft Port RCS
  DMG_24 1.000000 Forward Port RCS
  DMG_25 1.000000 Aft Star. RCS
  DMG_26 1.000000 Outboard Upper Port RCS
  DMG_27 1.000000 Outboard Lower Star. RCS
  DMG_28 1.000000 Outboard Upper Star. RCS
  DMG_29 1.000000 Outboard Lower Port RCS
  DMG_30 1.000000 Aft RCS
  DMG_31 1.000000 Forward RCS
  DMG_32 1.000000 Bay Doors
  IS_CRASHED 0
  MET_STARTING_MJD 60247.427331
  INTERVAL1_ELAPSED_TIME -1.000000
  INTERVAL2_ELAPSED_TIME -1.000000
  MET_RUNNING 1
  INTERVAL1_RUNNING 0
  INTERVAL2_RUNNING 0
  ACTIVE_MDM 3
  TEMP_SCALE 2
  CUSTOM_AUTOPILOT_MODE 0
  AIRSPEED_HOLD_ENGAGED 0
  SCRAM0DIR 0.000000 0.000000 1.000000
  SCRAM1DIR 0.000000 0.000000 1.000000
  HOVER_BALANCE 0.000000
  MAIN0DIR 0.000000 0.000000 1.000000
  MAIN1DIR 0.000000 0.000000 1.000000
  GIMBAL_BUTTON_STATES 0 0 0 0 0 0
  ATTITUDE_HOLD_DATA 0.000000 0.000000 0 0 0.000000
  DESCENT_HOLD_DATA 0.000000 -3.000000 0
  AIRSPEED_HOLD_DATA 0.000000
  OVERRIDE_INTERLOCKS 0 0
  TERTIARY_HUD_ON 1
  CREW_DISPLAY_INDEX 0
  GEAR 0 0.0000
  RCOVER 0 0.0000
  NOSECONE 0 0.0000
  AIRLOCK 0 0.0000
  IAIRLOCK 0 0.0000
  CHAMBER 0 0.0000
  AIRBRAKE 0 0.0000
  RADIATOR 0 0.0000
  HATCH 0 0.0000
  SCRAM_DOORS 0 0.0000
  HOVER_DOORS 0 0.0000
  BAY_DOORS 0 0.0000
  APU_STATUS 0
  EXTCOOLING_STATUS 0
  TRIM 0.000000
  SKIN X_15
  LIGHTS 0 0 0
  XRUMMU_CREW_DATA_VALID 1
  UMMUCREW XI0-Moritika_Rinnosuke-32-65-78
  UMMUCREW XI1-Marisa_Kirisame-17-65-55
  UMMUCREW Sci-Reimu_Hakurei-17-67-54
  UMMUCREW XI2-Sakuya_Izayoi-18-64-57
  UMMUCREW Tech-Sanae_Kotiya-16-68-53
  UMMUCREW XI4-Patchouli_Knowledge-19-66-50
  UMMUCREW Sci-Kurenai_Misuzu-18-67-59
  PAYLOAD_SCREENS_DATA 0.0 0 1 0
END
XL70:xl70
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 118.08
  AFCMODE 7
  PRPLEVEL 0:1.000000
  NAVFREQ 0 0
  GEAR 1 1.0000
  WING 1 1.0000
  TEMP 374.325425
  COG -2.000000
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 118.08
  AFCMODE 7
  PRPLEVEL 0:1.000000
  NAVFREQ 0 0
  UMMUCREW Capt-Peter_Falcon-41-65-74
  UMMUCREW Eng-Fanny_Gorgeous-27-67-55
END
CargoDeck:UCargoDeck
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 118.08
  ATTACHED 0:2,XL70
  AFCMODE 7
  NAVFREQ 0 0
  XPDR 0
  CORE_NAME XL70
  JETTISONSPEED 24.00
  JETTISONINT 5.00
  ALLOW_SEND_FOCUS 1
  DEF_ATT_PARAMS 0.000 0.000 0.000 0.00000 0.00000 1.00000 0.00000 1.00000 0.00000
  PL_DESCRIPTION XR2-01 0.000 4.000 0.000 -0.0000 -0.0000 -1.0000 0.0000 1.0000 0.0000 0
  IN_JETTISON 0 0
  J_MARKER 0.00
END
XR2-01_Bay:XRPayloadBay
  STATUS Landed Earth
  POS -14.4280539 -7.9609872
  HEADING 118.08
  ATTACHED 0:3,XR2-01
  AFCMODE 7
END
XR2PayloadMainFuel-03-1:XR2PayloadMainFuel
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 294.18
  ATTACHED 0:2,XR2-01
  AFCMODE 7
  PRPLEVEL 0:1.000000
  NAVFREQ 0 0
END
XR2PayloadCHM-01-1:XR2PayloadCHM
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 294.18
  ATTACHED 0:0,XR2-01
  AFCMODE 7
  NAVFREQ 0 0
END
XR2PayloadSCRAMFuel-02-1:XR2PayloadSCRAMFuel
  STATUS Landed Earth
  POS -14.4280300 -7.9609998
  HEADING 294.18
  ATTACHED 0:1,XR2-01
  AFCMODE 7
  PRPLEVEL 1:1.000000
  NAVFREQ 0 0
END
END_SHIPS

BEGIN_ExtMFD
END

For 's sake, please take care of my beloved UMmus...

Edit:

There's a modification by skycaptain/River Crab that makes the XR2 a lot more realistic.
...

Eh? No, no, I didn't make the config, just the scenario right here!

 

[Shinrar]

Now...
For anyone who wants to play with the realistic settings, here is a bit of an easier rendezvous scenario (made for SkyCaptain's config) using Siriusfett's Ess (I know, not exactly realistic, but it's better than Mir). It's only easier; hard, but not lunatic (due to the advantageous launch site). There are lots of tips in the description, hopefully not too long as it includes the links to required addons; I might script it as a challenge when I learn how.

Okay. Having a blast, but very much failing at getting the XR into orbit, lol.

I've made four attempts at it. The first time, I stalled out the XL-70, and ... yeah. That was a little hilarious actually. I tried to save the XR2, but wound up only slamming into the ground (Ocean) at -25 m/s , which is still pretty horrible.

Second time I broke my left wing. Somehow. Stack plunged into the ocean.

Third and Fourth time, I got into orbit altitudes, but not with enough velocity to have orbit speeds.

I'm getting better! Though I'm wondering if it'd be easier with a joystick at this point.

Thanks for the scenario, though!

EDIT:
-Update-
I don't know if I was just trying to rush earlier, or what. But... Fifth time was the charm! I'm presently docked with the ESS, in orbit, with 20% mail fuel and 46% RCS fuel remaining (0% SCRAM fuel - used it all up during ascent). I DID change the crew slightly, to match me and my mis-fit friends (we collectively weight less), and I DID dumb the empty tanks during my glide from engine shutoff to 150km ApA before circularizing my parking orbit in preparation to Sync Orbits. I figured that'd be the most realistic time to do it, even though jettisoning them doesn't make 'realistic' sense to begin with. But I was running out of fuel...

On my future attempts, I'll need to find some way to adjust the separation so that the XR2 doesn't collide with the XL-70. As I was watching separation, the XR2 lifted, and then sank right into the XL-70 (Likely a combination of the XL-70 suddenly having more lift with less weight, and the XR-2 not being at a good AoA to lift itself). As of right now, that's fine - no collision detection - but I can see it being a problem as orbiter continues to evolve...!!

Now all that is left to do, is Land...! Ahh... Reentry, my nemesis... Time to land this brick..!