Hello
I haven't tried the SLS addon and related scenario but the description caught my attention:
If you would like to add some realism, F3 to the Orion, extend the solar panels with 'S' and F3 back to the iCPS. Be aware, switching vessels clears any MFD settings.
Keep the second stage (iCPS) attached, it will be handy for midcourse maneuvers and can even insert you into an elliptical lunar orbit.
As usual, what follows is only being written in a spirit of constructive feedback
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I. SLS + iCPS + Orion
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If using:
a) an optimistic ISP of 465s for iCPS (instead of the ~459s that I believe, from feedback of people who know better, may be closer to the actual average performance of RL-10B-2)
b) and if assuming a low mass for that stage / departure stack (I remind readers that ~>1t of extra mass also needs to be accounted somewhere to represent the iCPS-to-SM interface + Orion's SM bottom adapter and that the iCPS is also slightly heavier – dry mass - than the usual stage used on Delta IV Heavy)
c) and also if assuming full tanks load (~27.2t), which is not true because iCPS would need to raise the perigee for stable Earth orbit insertion, before TLI happens (and there is also the problem of boil-off and using the stage beyond more than a few hours, if using it for middle course corrections and any kind of lunar proximity ops, days ahead!...)
d) and last but not least, if assuming a low mass for Orion, for example, 15t (which, under current assumptions, would practically mean an empty - zero main prop. load - Orion or else, a very specific Orion variant with a lighter CM + SM configuration and a much smaller main prop. load)
Like I was saying, if assuming all these very (and I mean VERY) optimistic assumptions plus if burning all iCPS propellants down to zero (which is not realistic and would do nasty things to the engine), I get, from the rocket equation:
465*9.807*ln((3.5+27.2+15)/(3.5+27.2*0.00+15)) = 4124 m/s
This seems a good number for a TLI (and LOI) but...
Yes, if making the simulation based on official info, the departure would be from ~185x1800 km orbit (which helps to cut down a little the dV for TLI) but... even then, the above great dV estimation quickly starts decreasing by hundreds of m/s if assuming:
- 459s ISP,
- ~4.2t for ICPS related masses,
- ~>25t or so if wishing to represent a full Orion (plus do not forget the SM bottom adapter)
- and if assuming less than 27.2t at the start of the TLI burn (because of raising perigee to 185 km from the the suborbital value required for SLS core disposal).
- This TLI is also a loooooong burn (with low T/W), with some gravity losses associated.
As mentioned, note that the prop. load assumed at the start of the ICPS burn depends of SLS perigee parameters (a burn of 35m/s up to 80m/s may be required, depending of simulation specificities) and of boil-off simulation. This could then mean an iCPS prop. amount, at the start of TLI, at anywhere between 26.7 to 26t or so.
Only as example, and
using more realistic assumptions to feed new numbers to the rocket equation plus based on a past custom simulation, the impulse provided by the iCPS could be ~2700m/s up to 2800 m/s or so, if also taking in consideration gravity losses and if keeping a prop. margin somewhere between ~1% up to 2% (of the initial iCPS prop. load) at the end of TLI (for stage disposal burns, performance reserves, residuals, etc).
All the above only to say that if realism is a concern, then the assumption of using iCPS after the TLI moment may not be a very realistic one, at least from the way I'm doing the math and also based on past custom simulation work + available official information (but maybe I'm missing something related with the overall launcher configuration being specifically linked in the scenario)
Just to be clear, we are talking about SLS block1 (4 RS-25, 2 x 5 seg. SRB) with something on top which would be similar to the stage used on Delta IV Heavy, correct?
If the answer is yes, I would find a lot more plausible to only assume Orion SM burns and no iCPS burns after TLI.
Another factor that enters in these brainstorms is how much time the virtual astronauts wish to spend on the way to the Moon (and back): if wishing relatively fast transfers (similar to Apollo, ~3d) then the TLI burn may need a little of extra help from Orion's SM (or else, the departure trajectory may need to be wider = take more days for the spacecraft to reach the Moon).
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II. About Orion, Quick Feedback
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Thanks for the '06' files, much appreciated!
The main engine parameters seem to be a little on the high side: during Constellation the SM's engine was expected to have a longer nozzle and an ISP of ~326s. The current MPCV design is apparently assuming something without such extension and an almost 'drop-in' utilization of Shuttle's OME, with an ISP of ~316s or so.
The '06' files are assuming an ISP of ~347s, which already starts to enter the realm of something burning methane-lox: no problems here, I think that it was a mistake to abandon methane for Orion's SM (and Altair's Ascent Module) and, for these 'higher mass Orion simulations', methane-lox could bring some balance to the Force (and provide greater playability)
Just for completeness, quick and simplistic dV estimation, assuming 3% margin (to account for RCS, performance reserves, non-nominal scenarios, non-used prop, etc, etc):
326*9.807*ln((10.3+5.2+9.2)/(10.3+5.2+9.2*0.03)) = 1433 m/s (Constellation's hypergolic, optim. nozzle)
316*9.807*ln((10.3+5.2+9.2)/(10.3+5.2+9.2*0.03)) = 1389 m/s (ESA SM using Shuttle's OME)
347*9.807*ln((10.3+5.2+9.2)/(10.3+5.2+9.2*0.03)) = 1526 m/s (methane-lox /
playability tweak?)
and then, if using an high-end methane-lox (this would probably need a slightly longer nozzle or other assumptions):
365*9.807*ln((10.3+5.2+9.2)/(10.3+5.2+9.2*0.03)) = 1605 m/s
Note: the above assuming that the 5.2t mass of the SM would protect for all these different configurations, which may or may not be true. Another suggestion: if not using the hypergolics numbers, maybe the documentation could include a small note about the 'playability tweak', just to let people know that they are getting greater performance from Orion than what is baselined.
About the solar panels swivel, accordingly with documentation, the panels have canting angles of -60º for TLI (ex: with iCPS) and +55º for LOI/TEI (when just using SM). As a suggestion, perhaps it would be interesting to also implement the -60º setup
Thanks for all,
Happy flights and Merry Christmas!
António Maia