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/r/spaceflight
To clarify I am an amateur space flight fan, so I am not well verse in the technical details. But I been trying to figure out what would be the smallest possible manned spacecraft capable of lunar landing. Specifically, I am focusing on mass.
Looking over previous ideas, the closest I seen was one proposed here for Lunar Gemini that uses either two titan 3C launches or a single launch with a Saturn C-3. Which implies something along the range of 26,200-36,300kg launched into low earth orbit.
This would be in range of some heavy lift rockets, rather than super heavy lift rockets. I find myself wondering if something even smaller could be used, like a spacecraft for just one man.
I'd like to work with GMAT for a student project and need to import CCSDS-OEM files to simulate spacecraft trajectories. I'm not sure if GMAT supports direct import of CCSDS-OEM files, and if it does, how to properly set it up. Any guidance, examples, or resources would be greatly appreciated!
Thanks in advance for any help!
You know the drill, discuss why we should do both. Convince me! (hint, I like one and not so much the other)
Prior to the 2010s on the Soyuz TMA and TMA-M they carried the TP-82 . However now in the MS descent module what firearm do they carry in the survival gear?
Ignore anything physiological related to g forces because I don't know if this would inherently require g forces humans couldn't tolerate.
I'm really disappointed when I see a person I like saying that we shouldn't/can't go to Mars. Bill Burr is an example of that. I like him as a comedian and think he's funny but when he starts talking about the plans to go to Mars he's like there's no way we can go there, and why should we even try etc. to me this is the most exciting endeavor humanity has ever tried. I don't care that much if it's SpaceX or NASA or someone else, I just want humanity to take that leap. And a lot of times it seems that people's opinion of going to Mars is a result of their feelings about Elon musk. And the classic shit of "we have so many problems here, we should spend money trying to fix them and not leave the planet" "We only have one earth " " the billionaires are gonna go to mars and leave us here to die" and all of that stupid shit that doesn't have any real merit as arguments. It feels like I'm on a football match and half the people on the stadium think that football is stupid and shouldn't be a sport. Half the people don't get it
Edit: I'm not talking only about Mars but human space travel in general. And as far Mars is concerned I'm talking about visiting. I think colonizing Mars should wait for a couple of decades
based on aerodynamics simulation of the fall at terminal velocity near the end starship weighed about 176 tons just before landing burn
assuming very limited fuel reserves based on its deceleration during the landing burn, time spent tilting, item spent hovering and typical fuel header about 20 tons of that are probably fuel making hte empty weight about 156.2 tons
either way, starship when coming back from orbit was still 176.2 tons
but it does mean that of the 1200 tons of fuel everything else can only use up to 1180 tons
when separating from the booster starship has a speed of about 1457m/s at a 30° angle making its lateral speed 1262m/s
it passes a total speed of 3000m/s tilted at about 20° making its lateral speed about 2820 m/s
thats 1558m/s of lateral acceleration with an average angle of 25° so we'll use an efficiency of cos25° meaning 1719m/s of delta v used
drag is already pretty insignificant at that latitude, probably only costing somethign around 0.02m/s delta V at any point after booster separation
we'll also assume that booster separation doesn't change much with a paylaod since its a relatively small mass compared to fully fuelled starship
at 5000m/s the ship is going at an angle of about 9° so thats 4938m/s lateral
assuming an average angualr efficiency of cos(15°) over that section we get about 2193m/s delta V again adding up to 3912
the sea levle and vacuum engines running together have an average isp of 3455m/s assuming they have the same fuel flow rate meaning more thrust comes from the higher isp vacuum engines
so IF we assumed the ship was 1350tons in the beginning it would now be at about 435 tons according to rocket equation (just a momentary estiamte, no final calculation) and going at a speed where due to centrifugal force you only have to lift about 1/2 your weight to maintain altitude and the vacuum raptor engines alone have a thrust of about 800 tons and the ship is still moving up so we'll be optimistic and assume that at this point you could diverge from the IFT trajectory, turn off the sealevel engiens and use only the raptor engines with no significnat further gravity losses
so to account for different isps we'll add up deltav/isp bits rather tha nadding up delta v and dividing in the end
so far we've used 3912m/s at 3455m/s so 1,13227 isps worth of delta v
we're going at 4938m/s lateral and driftingto a height of 160km
a 160kmx160km circular orbit has a speed of about 7807m/s
the webcast has it at 7344m/s, thats the earths rotatio ncause they track groundspeed
assuming you don't go into a very loe inclination orbit but not quite ap olar orbit either you'd need closer to 7510m/s
thats another 2572m/s at 3700m/s isp or 0,69513 isps worth adding up to 1,8274
from that circular orbit raising the apogee to say 240km would be another 24m/s
raising the perigee after another 24
lets be optimsitic and put in only an extra 20 for coruse correction AND safety margins, thats tight
thats another 68m/s or 0,018378 isps so now we're at 1,8457
now paylaod separates so lets take the rest the other way round
takes another 50m/s to deorbit plus another 10 for course adjustments so 176.2*e^60/3700=179.1 tons of ship plus fuel are left when the paylaod separates
minus 156.2 tons of empty weight thats 22.88 tons of fuel still left so we could use up to 1200-22.88=1177.12 tons so far
e^(deltav/isp) is the wet to dry mass ratio so that minus 1 is the fuel to dry mass ratio so if we can use 1177.12 tons of fuel for 1,8457 isps worth of delta v then total mass at paylaod deployment can be 220,74 tons
minus 179.1 tons of ship plus fuel thats 41.64 tons
thats with a very optimsitic calculations, assumign the booster is not affected by the extra 40 tons, no safety margins, no gimbal losses, very little course correction, switching to vacuum only engines as soon as posisble ,neglecting further gravity losses...
realistically, the extra mass is gonna take about 30m/s delta V from the booster so we need to add another 30m/s of delta V early on at 3455m/s isp or 0,00868 isps to 1,85438
we'll probably have about 1% gravity losses during the last boost so thats an extra 0,0069 to 1,8613
probably lost ab it to rounding errors so make that 1,862
probably gonna be another 30m/s lost to engine startup/shutdown inefficiencies so 1,87
might need a bit more course adjustments and safety margin so realistically 1,88
that gets us 211.9 tons at payload deployment or 32.86 tons of payload
and since thats only about 1/7 of the mass at this point compared to falcon 9 or atlas v upperstages where the empty first stage is soemthing liek 1/5 or 1/4 of the paylaod capacity any higher orbit or steeper inclination or other delta v expenditure is going ot hit hte payload in a more extreme way because if you need a bti of dleta v meaning your mass to target goes down by 1% thats 1% of the ship plus payload plus landing fuel or about 7% of the payload wehreas with a falcon 9 or atlas v thats 1% of the payload plus upperstage or 1.2% of the payload
empty weight was already supposed to drop down from 200 to 120 tons 5 years ago going form hopper testbeds to stacked flight test hardware
also at higher inclinations you're gonna need a bit of extra delta v left at the end to adjust the starships course and get it back on track ot the landing site because of earths rotation
thats gonna add another 15 tons of fuel to the ship on paylaod deployment reducing payload capacity to 17.86 tons if you want the ship back immediately rather htan waiting for a day for it to line up again
to iss orbit with the ship returning immediately you would have that plus more orbit raising/lowering plus steeper inclination less rotational boost would leave you with about 12 tons of payload capacity
the upside is that since the reentry weight is about 1.14 times the empty weight due to landing fuel and since terminal velocity goes down with a lighter ship you can probably increase paylaod capacity by about 1.2 tons for every ton of empty weight removed
so to get 100 tons to an iss like orbit you'd need to scrape off only 73 tons, cutting hte empty weight down to 83 tons
minus enignes that would be 70 tons left
minus heatshield about 58
skins about 62 tons
so you have a whole -4 tons of mass budget for electronics, actuators, structural reinforcements other than the skin, fuel management, power supply, orbtial thermal regulation, rcs, catch hardpoints, etc
we'll leave out basic fuel tank and structural mass because the skin already does that and skin thickness plus stiffeners is already the limitingfactor
2 tons if you assume they cut the weight of the next raptor generation in half
you'll need at least 1 ton for... the rest
so thats 1ton for all the structural reinforcements inside plus the flap hinges
well the inner structural reinforcements are gonna be at least half hte skin weight
and the tanks need liek front walls and rear walls and baffles
optimistically but remotely realistically, a stripped down starship might be able to get 55 tons to an iss like orbit at best
anything more and you have to use completely different materails or a completely different rocket concept
peopel throw aroudn numbers like 5-10 million operationa lcost for falcon 9 without the second stage
scaling that up by a factor 10 for around 20 tons payload would give us costs of 3750$/kg
from waht little leaked financial data we have it seems like falcon9 is barely makign a profit though, even reusably
scaling that up by a factor of 10 and you get 35000$/kg for 20 ton payloads and 8750$/kg for 80 tons
a falcon 9 scaled up by a factor of 10 really simplistically would have about 176 tons paylaod capacity with first stage reuse, 130 with rtls but due to size, materialsand second stage reuse their mass fraction drops and drops
with a 12 ton payload it would at least have a paylaod capacity optimzied for market demands but you could do the same with a falcon 9 with droneship reused and scaled DOWN 33% making it actually cheaper
had to run the aerodynamics sim to get a good current mass estimate and wait for ift 6 trajectory first though
also did a pretty precise graph on reentry laods over ift testflights and a lnar reentry profile
bit disappointed that the supposed "more agressive reentry" they wanted ot test was about the smae minus the little hump