Challenge XR2 to ISS & back - Isp limit breaking

[hribek]

1. Use the default XR2 to ISS scenario in Orbiter 2010. (KSC, with CHM, 14 crew aboard).
2. Before launch, add two fuel tanks to the empty bay slots (2 and 3)
3. launch and dock with the ISS and return to KSC within 48 hours (safe landing on RWY 33/15).

MainFuelIsp is set via CHEATCODE to a specific value. No other cheatcodes are used. The following part of the config file covers remaining important settings.

[GENERAL]

#--------------------------------------------------------------------------
#  Number of crew members to add to the ship if there is no UMMu data in  the scenario file,
# or if there is no scenario file (for example,  when spawning an XR2 via the scenario editor).
# Crew will be added  starting at [PASSENGER0].
#
# The default is 14 ( [PASSENGER0]  through [PASSENGER13] )
#--------------------------------------------------------------------------
DefaultCrewComplement  = 14

#--------------------------------------------------------------------------
#  Enable or disable the altitude and vertical speed indicators on the  surface mode HUD.
#
# The default is 1 (enabled).
#--------------------------------------------------------------------------
ShowAltitudeAndVerticalSpeedOnHUD  = 1

#--------------------------------------------------------------------------
#  If enabled, either the Commander or Pilot must be 
# on board in  order to control the ship; otherwise, the ship's controls will 
# be  disabled until either the Commander or Pilot reenter the ship.  The
#  Commander and Pilot are determined by the crew member's rank as defined  
# in the PASSENGER sections.
#
# 0 = Any crew member on board  can pilot the ship.
# 1 = Only the Commander or Pilot can pilot the  ship.
#
# The default is 0, meaning that any crew member on board  can pilot the ship.
#--------------------------------------------------------------------------
RequirePilotForShipControl=0

#--------------------------------------------------------------------------
#  Defines whether payload bay fuel tanks are necessary in order to 
#  reach normal fuel capacity.  Options are:
#
# 0 = No bay fuel  tanks necessary to reach normal fuel capacity.  (default)
# 1 = One  MAIN fuel bay tank and one bay SCRAM fuel bay tank required to reach  normal fuel capacity.
# 2 = Two MAIN fuel bay tanks and one bay SCRAM  fuel bay tank required to reach normal fuel capacity.
#
# Fuel  tanks may only be attached in bay slots 2 and 3.  Note that with 
#  setting '2' you will not be able to reach normal capacities for both  MAIN and SCRAM fuel
# simultaneously; in that case, you will need to  either: 
#   a) Use two main fuel bay tanks and no SCRAM bay tank, in  which case you will have 
#      100% main fuel capacity and 0%  SCRAM fuel capacity.
#      ...or...
#   b) Use one main and one  SCRAM fuel bay tank, in which case you will have 75% main fuel capacity
#       and 100% SCRAM fuel capacity.
#
# This setting is designed for  advanced pilots who want the added challenge of having to
# use  payload bay fuel tanks in order to reach normal fuel capacity. 
# 
#  Internally, here is what each setting does:
#
# 0 = Internal fuel  tanks are sized at 100% of normal capacity.  (default)
# 1 = There  is no internal SCRAM tank, and main tanks are sized to only 75% of  normal capacity.
# 2 = There is no internal SCRAM tank, and main  tanks are sized to only 50% of normal capacity.
#
# The default  value is 0 (no bay tanks required).  
#--------------------------------------------------------------------------
RequirePayloadBayFuelTanks=0

#--------------------------------------------------------------------------
#  Enable optional "dual performance" mode for AF Ctrl.  If this
#  setting is enabled, different AFCtrlPerformanceModifier values will be  applied to
# elevator performance depending on whether AF Ctrl is set  to 'Pitch' or 'On'.
#
# If you enable this setting, be sure to  set AF Ctrl=Pitch when taking off 
# in an atmosphere; otherwise it  will be difficult to rotate the ship at takeoff.
# Then after you are  airborne, set AF Ctrl=On to switch the elevators to a 
#  lower-performance mode for smooth handling.
#
# 0 = AF Ctrl normal  mode (AFCtrlPerformanceModifier disabled)
# 1 = AF Ctrl  "dual-performance" mode (AFCtrlPerformanceModifier enabled)
# 
#  The default setting is 0 (AFCtrlPerformanceModifier disabled).
#--------------------------------------------------------------------------
EnableAFCtrlPerformanceModifier=0

#--------------------------------------------------------------------------
#  Determines the performance of the ship's elevators when "dual  performance"
# AF Ctrl mode is enabled.  
#
# The first number  is used for 'AF Ctrl=Pitch' mode.
# The second number is 'AF Ctrl=On'  mode.
#
# The default values are: 1.30 0.70  (increases elevator  performance to 130% 
# of normal in "Pitch" mode, decreases elevator  performance to 70% of normal
# in "On" mode.)  
#
# Each value  is limited to between 0.2 and 5.0.  1.0 = "no change".
#
# NOTE:  these values have no effect unless 'EnableAFCtrlPerformanceModifier' 
#  is set to '1' above.
#--------------------------------------------------------------------------
AFCtrlPerformanceModifier=1.30  0.70

#--------------------------------------------------------------------------
#  Main Fuel ISP ("Specific Impulse") setting.  This determines how much 
#  main/hover/rcs fuel is burned each second for a given thrust level.
#  Higher settings allow longer flights without refueling.  Remember to 
#  update the 'LOXLoadout' value later in this file as well so the crew  will
# have enough oxygen for the mission!
#
# NOTE: The  'Expert' setting (0) is tuned so that you will need to use your SCRAM  engines
# efficiently during ascent to LEO ("Low Earth Orbit").
#  ISP values for each level are shown in [brackets].
#   0 = Expert     (ISS Only w/expert use of SCRAM engines and expert deorbit/landing)   [13943]
#   1 = Realistic (ISS Only)                [20914]
#   2 =  Default   (ISS and Moon)            [25962]
#   3 = Medium    (ISS  and Moon w/reserve)  [32981]
#   4 = Stock DG  (Moon w/large reserve;  this is the original stock DG setting)  [40000]
#   5 = Big        (Mars)                    [52922]
#   6 = Huge       (Jupiter+)                [366251]
#   7 = Massive   (Jupiter+ w/full  payload) [476127]
#
# The default value is 2 (ISS and Moon).
#--------------------------------------------------------------------------
MainFuelISP=0

#--------------------------------------------------------------------------
#  SCRAM Fuel ISP ("Specific Impulse") setting.  This determines how much 
#  SCRAM fuel is burned each second for a given thrust level.  Higher  settings
# allow longer flights without refueling.
#   0 =  Realistic 
#   1 = 1.5x normal
#   2 = 3x normal
#   3 = 6x  normal
#   4 = 10x normal
#
# The default value is 0  (Realistic).
#--------------------------------------------------------------------------
SCRAMFuelISP=0

#--------------------------------------------------------------------------
#  LOX (Liquid Oxygen) loadout setting.  This determines the maximum  duration of a mission without 
# replenishing the LOX tanks.  Times  listed assume a full crew (14 crew members); reducing the 
# number  of crew members will increase the maximum mission duration accordingly.
#
#  Increasing this value will increase the LOX loaded into the ship.  The  mass value
# displayed for each setting assumes a LOXConsumptionRate  (the parameter following this one)
# of 4 (realistic: 100% of  normal).  To reduce the LOX mass required for a long mission,
# leave  LOXConsumptionRate set to its default value of -1 (AUTO), or set it it 0  (OFF) or 1 (very low).
#
# Valid options (duration assumes full  crew of 14):
#   0 = 7 days          (  182 kg)
#   1 = 14  days         (  364 kg)
#   2 = one month       (  792 kg)
#   3 =  three months    ( 2374 kg)
#   4 = six months      ( 4746 kg)
#    5 = one year        ( 9489 kg)
#   6 = two years       (18975 kg)
#    7 = three years     (28462 kg)
#   8 = four years      (37948 kg)
#    9 = five years      (47438 kg)
#
# The default value is 1 (14  days).
#--------------------------------------------------------------------------
LOXLoadout=1

#--------------------------------------------------------------------------
#  LOX (Liquid Oxygen) consumption setting.  This determines how much  oxygen is consumed
# by the crew for a given length of time.  This  setting determines the LOX mass required for a 
# given mission  duration; i.e.,
#
#       LOX mass loaded = LOXLoadout x  LOXConsumptionRate
#       
# WARNING: setting this value to other  than 0 (AUTO) or 1 (very low) may result in a significant mass increase  
# when LOXLoadout is set for a long mission duration (e.g., one  year or longer).
#
# For example, with a LOXLoadout of 5 (one  year), the actual LOX loaded would be:
#       4 (realistic) = 3389  kg (100% of normal)
#       3 (medium)    = 2542 kg (75% of normal)
#        2 (low)       = 1695 kg (50% of normal)
#       1 (very low)  =  848  kg (25% of normal)
#       0 (OFF)       =  100 kg (mass is fixed)
#       -1 (AUTO)      =  848 kg (varies between 100% and 12.5% of normal  depending on LOXLoadout.)
#
# Valid options are:
#  -1 =  AUTO      (Recommended; varies between 100% and 12.5% of normal  depending on LOXLoadout.)
#   0 = NONE      (oxygen consumption  DISABLED)
#   1 = very low  (25% of normal)
#   2 = low       (50%  of normal)
#   3 = medium    (75% of normal)
#   4 = realistic  (100% of normal)
#
# The default value is -1 (AUTO).
#--------------------------------------------------------------------------
LOXConsumptionRate=4

#--------------------------------------------------------------------------
#  Modifies the default crew oxygen consumpation rate.
#
# For  example, a value of 2.5 would mean that the crew would consume oxygen
#  at 2.5 times the normal rate.  Note that the crew's normal O2  consumption rate assumes
# that the ship's CO2 scrubbers are 100%  efficient so that no oxygen is wasted.  This setting, 
# however,  allows you to simulate wasted oxygen that is not reclaimed from CO2 by  the scrubbers.
#
# Valid values are between 1.0 and 10.0.  
#  The default value is 1.0 (normal consumption rate).
#--------------------------------------------------------------------------
LOXConsumptionMultiplier=1.0

#--------------------------------------------------------------------------
#  Maximum main engine thrust, per engine (x2 for total):
#   0 = 240  kN (easy)
#   1 = 192 kN (realistic)
#--------------------------------------------------------------------------
MainEngineThrust=1

#--------------------------------------------------------------------------
#  Maximum hover engine thrust, per engine (x2 for total):
#   0 = 168  kN (easy)
#   1 = 132 kN (realistic)
#--------------------------------------------------------------------------
HoverEngineThrust=1

#--------------------------------------------------------------------------
#  SCRAM Fuel Heating Value (FHV): this is the amount of heat energy  generated 
# from burning one kg of propellant.  This affects SCRAM  thrust for a given
# fuel flow level.
#   0 = 4.2e8 (easy)
#   1  = 2.4e7 (realistic)
#--------------------------------------------------------------------------
SCRAMfhv=1

#--------------------------------------------------------------------------
#  SCRAM Max Fuel Flow Rate (DMF): this is the maximum amount of fuel that  can
# be burned in kg/sec; this affects the maximum thrust that the  SCRAM engines
# can produce.  Note that this value will be adjusted  to compensate for the
# 'SCRAMFuelISP' setting, so the actual maximum  flow rate may vary from the 
# numbers below.
#   0 = 9.0 kg/sec  (easy)
#   1 = 6.0 kg/sec (realistic)
#--------------------------------------------------------------------------
SCRAMdmf=1

#--------------------------------------------------------------------------
#  APU Fuel Burn Rate : this is the rate at which APU fuel is burned in  kg/sec.
# The Auxiliary Power Unit (APU) provides hydraulic power to  the ship.
#   0 = unlimited : (runs indefinitely)
#   1 = very  low  : 0.90718474 kg/minute (2 lb/minute)    (3.7 hours runtime)
#   2  = low       : 1.81436948 kg/minute (4 lb/minute)    (110 minutes  runtime)
#   3 = moderate  : 2.72155422 kg/minute (6 lb/minute)     (74 minutes runtime)
#   4 = realistic : 4.08233134 kg/minute (9  lb/minute)    (49 minutes runtime)
#   5 = expert    : 6.12349701  kg/minute (13.5 lb/minute) (33 minutes runtime)
#
# The default  value is 2 (low: 110 minutes runtime).
#--------------------------------------------------------------------------
APUFuelBurnRate=4

#--------------------------------------------------------------------------
#  APU Idle Runtime Callouts : this is the "idle time" threshold in  seconds 
# above which a voice callout will sound when the APU is  running but without load.
#
# Valid range is 0 seconds (callouts  disabled), or between 5 and 600 seconds.
#
# NOTE: if  APUFuelBurnRate=0 (unlimited), this value is ignored since callouts 
#  will be automatically disabled.
#
# The default value is 60  seconds.
#--------------------------------------------------------------------------
APUIdleRuntimeCallouts=30

#--------------------------------------------------------------------------
#  Enable or disable auto-shutdown of the APU when the pilot switches  vessel
# focus; this is a safety feature designed to prevent the  pilot from
# accidentally leaving the APU on and running out of APU  fuel while the
# focus is switched to another vessel.
#
# The  default value is 1 (APU auto-shutdown ENABLED)
#
#   0 = APU  auto-shutdown disabled
#   1 = APU auto-shutdown enabled  (recommended)
#--------------------------------------------------------------------------
APUAutoShutdown=0

#--------------------------------------------------------------------------
#  Enable autostart of the APU when the ship's autopilot or automated  flight
# control systems need to shift the ship's center of gravity  (this is ncessary
# during reentry).  If you are an experienced pilot  and want to always manage 
# the APU yourself, set this to option to  0 (disabled).
#
# The default value is 1 (APU auto-startup  ENABLED)
#
#   0 = APU auto-startup for COG-shift disabled
#   1  = APU auto-startup for COG-shift enabled 
#--------------------------------------------------------------------------
APUAutostartForCOGShift=1

#--------------------------------------------------------------------------
#  Enable or disable ship damage due to wing stress, hull heating, hard  landings,
# crashes, excessive dynamic pressure, and SCRAM engine  overheat.
#   0 = damage disabled
#   1 = damage enabled
#--------------------------------------------------------------------------
WingStressDamageEnabled=1
HullHeatingDamageEnabled=1
HardLandingsDamageEnabled=1
CrashDamageEnabled=1
DoorStressDamageEnabled=1
ScramEngineOverheatDamageEnabled=1
EnableDamageWhileDocked=1

#--------------------------------------------------------------------------
#  Enable or disable reduction in thrust due to atmospheric pressure.
#    0 = easy (no reduction)
#   1 = realistic (reduction)
#--------------------------------------------------------------------------
EnableATMThrustReduction=1

My own attempts:

6500: Perfect landing with 500kg fuel left.
6400: all went well, re-entering with RCS tank at 90%, all great until I accidentally set AoA and bank to zero. Following that, I tore off the right aileron, but still somehow managed to hit the runway at 4.56m/s vertical speed and stop right at the edge of the RWY 33 overrun end, nosewheel about 3 metres in the grass.

That was an unnecessarily close call. I think that this might be doable with Isp = 6000. Will you break the limit?

---------- Post added at 01:47 PM ---------- Previous post was at 09:06 AM ----------

MainFuelISP=6000.0
25.6kg fuel remaining, flight time 23 hours 18 minutes.
about 30% of total fuel capacity (with tanks) was remaining on MECO 1 when I started SCRAM ascent. less than 100kg SCRAM fuel remaining on door close, and something like 10% fuel after MECO2, apoapsis 230km. Radiator opening, I got rid of half a metric ton of empty tanks, and had about 2% int tank left on docking, 80% RCS. 35% RCS tank only on deorbit.

 

[dgatsoulis]

:hmm: Why did it take you 48 hours to do something that can be done in less than 2 hours?
It's possible, even with an ISP setting of 6250, to dock with the ISS and land (deadstick) back at Canaveral, in a single orbit.
I'll attach the playback here.

 

[insanity]

:hmm: Why did it take you 48 hours to do something that can be done in less than 2 hours?
It's possible, even with an ISP setting of 6250, to dock with the ISS and land (deadstick) back at Canaveral, in a single orbit.
I'll attach the playback here.

Dgat, I must say I love your videos and playbacks mate.

 

[Izack]

We just can't keep up!

:hail:

 

[dgatsoulis]

@Insanity: Thank you. Glad you like them.

@hribek: Hadn't seen your edit about the 6000 ISP 23 hours 18minutes flight.

Here is another playback: ISP setting: 5950, time: 1 hour 58 minutes.

The only different setting i had in the XR2prefs config file, is that i used an expert setting for the APUFuelBurnRate (5 instead of 4).

Nice idea, interesting challenge. Just change the time limit from 2 days to 2 hours. :lol:

 

[hribek]

First of all, the goal is to increase realism. I'll change the limit to 24 hours, so that you get some 2 reasonable landing opportunities. But then again, this isn't a race. So the time does not matter all that much.

:hmm: Why did it take you 48 hours to do something that can be done in less than 2 hours?
It's possible, even with an ISP setting of 6250, to dock with the ISS and land (deadstick) back at Canaveral, in a single orbit.
I'll attach the playback here.

Oh, nice work there.

Except that I mentioned a safe landing, that's why I wouldn't count that borked attempt of my own, even.


I have seen your 6200 playback. If you did that in a DGIV that has the functionality, the crew would die. The vertical acceleration values in your playback are over 5 Gs for several minutes, twice peaking at +8G.

Maybe that's the reason why I think it's nice to hug the ISS crew for a few hours, pose for the TV, and land in daylight on the next day.

Even if your crew survived, I think the first thing on their mind after they got out of hospital would be to kill you. Be nice to your crew

 

[hribek]

View attachment XR2 ISP 5900.zip

Here is a scenario for Isp 5900, landed in something like 23 hours. I've been trying to fly it like the shuttle, i.e. holding a high AoA for high mach numbers to avoid melting the windshield. I didn't do a lot of banking, though. I was low on RCS fuel and landed with something like 12kg of it. MaxG is about 3 during the transition to low AoA atmospheric flight (roughly one second in duration).

Known bugs:
- the gear isn't retracted on launch, I pulled it up too soon, not realizing that the Orbiter's playback position integration algorithm will cause the glider to go underground. Use scenario editor to retract gear after the "on ground, can't retract gear" message appears.
- the playback does not support fuel tank cross-feed, so the deorbit burn appears to be done with an empty main tank, and landing occurs with plenty of RCS fuel, while actually I was almost dry.

Personal note:
The rendezvous operations aren't anywhere near optimal, and the ascent could have been flown better as well. I think somebody might manage Isp=5500 or so in the future. Basically if you have like 30% fuel left when you switch to SCRAM engines, you're "go".

 

[hribek]

View attachment XR2 ISP 5700.zip

MainFuelIsp=5700

Fixed time steps used to record the playback, not sure if it helped a lot. The ascent is kinda funny, I think there's always a lot of room for improvement. With a good autopilot or with a stick, you might be able to do a good enough launch with a lower Isp. Gear goes up properly this time. The entry is a bit suboptimal, reaching 3-4Gs here or there (I used a lower AoA to turn more, but I did it too early and went in too shallow, with small descent rate. So I had to brake it hard - back to 40deg AoA or so, and then the atmo flight with banks was kinda bumpier than normal, but reasonably good) The deorbit burn was done partly with RCS translation so that I wouldn't have to crossfeed at all. I don't think I had any fuel at all on landing, entered atmosphere with about 32% RCS.

 

[RisingFury]

:hmm: Why did it take you 48 hours to do something that can be done in less than 2 hours?
It's possible, even with an ISP setting of 6250, to dock with the ISS and land (deadstick) back at Canaveral, in a single orbit.
I'll attach the playback here.

Pwned!

 

[hribek]

Pwned!

What's your personal record?

 

[Usquanigo]

dga, I tried your first playback, but it crashes my Orbiter. What version was it recorded for (& does that matter)?

---------- Post added at 09:19 PM ---------- Previous post was at 08:48 PM ----------

It's my XR-2 it seems. Just tried a few different scenarios with it (on the ground, in space, etc) and it always crashes. Nothing helpful in the log files that I can see either. And it's the O-2010 model.

---------- Post added at 11:59 PM ---------- Previous post was at 09:19 PM ----------

Ok, the XR-2 problem was the install. The downloaded archive did not work with the Orbiter Addon Installation System v1.1 that I use, so I unzipped it, then re-zipped it, and the OAIS worked with it. However, it didn't install right for some reason.

When I simply extracted the original archive to the Orbiter install directory, the XR-2 now works.

But, when I try to watch the "xr2 isp 5700" track, it loads everything, starts playing some sound effects, but only shows a white screen, then a few moments later, Orbiter crashes.

Any thoughts? I tried several XR-2 scenarios and they all work.

 

[dbeachy1]

As a test, please try viewing the playback in a clean Orbiter installation with only UMMu, OrbiterSound, and the XR2 installed. It is likely that another add-on is corrupting memory, causing the crash.

 

[hribek]

I think that another challenge might be doing an entry with lowest MaxG possible. (Though, the XR2 doesn't record this like the DGIV does.)