SpaceX Starship can return from Mars without surface refilling

this video is sponsored by surfsharkvpn hey hey marcus house with you here and today we want to explore the logistics for the very first possible mars returns missions with starship we will look into how and why that we can tackle this before situ resource utilization or refueling on mars has even been established we'll also get up to speed with the expected performance of starship and assess the overall requirements for such a mission yes while we think in situ resource utilization or isru for short is vital we are pretty sure that the initial missions to mars with starship won't have to be one-way missions despite isru not being ready at first why is that the case though well we need to explore the delta v requirements for flying to and from mars in the moon shot video we already dived into the basics of rocket science and explained isp and delta v a bit it could be worth watching that one appearing here in the top right before watching this in short though if you want to get somewhere in space you need a specific velocity relative to the celestial bodies usually you are either going to be moving too fast or too slow relative to where you want to go so we need to change our velocity sometimes quite significantly this change in velocity is usually called delta v as in delta for change and v for velocity and we achieve this velocity by firing up our rocket engines with chemical rocket engines like spacex's raptor engine the burn lasts usually a matter of seconds up to a few minutes not the most efficient method but simpler and faster compared to the other modes of propulsion for this we need propellant and ideally as little of it as possible here the specific impulse or isp is the measure of how much propellant is needed for a specific amount of thrust and therefore the change of velocity the raptor engine designed for the use in the vacuum of space also called the rvac has about 378 seconds of isp so this means that with one kilogram of propellant it can produce 378 seconds of thrust equaling one kilogram of force now today i also want to tackle a weird thing called c3 now c3 or characteristic energy is the square of the velocity needed after having left the influence of a celestial body and the unit is usually kilometers squared per second squared now this might sound a little confusing so let's see what this is good for just take a look at this image we see that if we want to get from earth to mars we need to fly along this elliptical orbit around the sun which connects the orbits of earth and mars together true there tends to be a slight inclination change involved too but just to keep it simple here we'll stay on the same plane and imagine that the orbits match perfectly now basically this is a homan transfer the most efficient way to change orbits but for this we need to accelerate here at earth relative to the sun so much that we can raise our orbit to intercept the orbit of mars while doing this of course the gravity of earth is still pulling the spacecraft back therefore we need to not only achieve the required velocity for the transfer but additionally we need quite a bit to escape from earth's sphere of influence luckily for the fuel requirements we don't need to add these velocities together so getting to mars needs a c3 of about 15 kilometers squared per second squared meaning about 3.9 kilometers per second additional to the speed of the earth traveling around the sun and that is roughly 30 kilometers per second now to derive the delta v requirements from low earth orbit we can do this simply by the square root of the c3 value plus the escape velocity squared then from that we subtract the velocity that we have in low earth orbit the escape velocity from earth is about 11 kilometers per second that squared is 121. to that we add the c3 value of 15. the square root of the 136 is 11.66 and from that we subtract the velocity in low earth orbit so 7.8 kilometers per second so this gives us a result of 3.86 kilometers per second so this is the delta v that we additionally need after we achieve orbit around the earth to enable a transfer to mars now what you might find interesting is that this is just 0.66 more than the difference between the escape velocity and low earth orbit velocity which we'd need to leave the earth regardless there is some nice orbital mechanic shenanigans at work there such as the oberth effect so let's just round up a little to 3.9 kilometers per second to send our starship out on a mars transfer arriving at mars we now have two options either flying right into the atmosphere to land at the target location or we could also get into a mars orbit first with a direct landing starship would utilize the mars atmosphere anyway but even when getting into low mars orbit we can simply skim through the atmosphere and drop most of the velocity needed there to save that valuable propellant now this is called an aero capture or aero braking and this is possible because we have a huge heat shield anyway for landing there and here on earth in order to place ourselves into a stable low mars orbit we would need just a little propellant to slightly raise our perigee so that we don't have our ship continuing to re-enter the atmosphere on each orbit and then being slowed down too much so yes we need a little propellant to at least do this and typically there would also be some slight inclination adjustments to do as well keeping a bit of propellant for that does make sense the cool thing about this is that we can just dip into the atmosphere on that first pass just enough so that we end up on a highly elliptical orbit if done just right you only need a tiny bit of propellant to correct the inclination at apogee where the vehicle is moving the slowest after that spacex could slowly lower the apogee by making many passes through the upper mars atmosphere to drop down to a low mars orbit over time this is all very efficient as it's using the atmosphere to do the vast majority of the work without using the atmosphere a powered orbit injection would require about 2.3 kilometers per second but with aero capture we can easily get away with around half a kilometer per second just for these small adjustments after all this of course we still need to land on earth the delta v requirements are pretty low due to the dense atmosphere slowing anything down very nicely but on mars the atmosphere is much much thinner now anaes here working with me has once again done some calculations to give us a rough estimate the mars atmosphere density measured in kilograms per cubic meter is around 0.02 close to the surface here on earth at sea level we have around 1.2 kilograms per cubic meter now as you can see here we've used 0.01 for the calculation of mars atmosphere and this is because we need to consider the atmosphere slightly higher above the ground because we still need time to engage the engines to reduce the terminal velocity to zero with a reasonable deceleration if we didn't do that we'd be smashing into the mast surface with velocities up to several times the speed of sound that's really going to ruin your day now this calculation considers a ship weighing 110 metric tons carrying 175 tons of cargo and enough propellant to land with reasonable margin we're talking about 1.3 kilometers per second of delta v that we're going to need to touch down safely okay so now we know the total amount of delta v that we're going to need so it's time to go back to low earth orbit to see how much propellant we actually require for this if you check out this table here this shows the calculations for the refilling flights and the mars cargo ships delta v requirements in fact you might remember those tables from the moon shot video as much as we currently know about the numbers that we get for super heavy starship and the engines we think that spacex calculates quite conservatively when they're talking about 100 to 150 metric tons to low earth orbit engaging the launch trajectory model 170 plus metric tons looks possible considering the usage of the upcoming second generation of raptor depending of course on the ship variant used so when that's the case just five additional refilling flights are needed to get over 900 metric tons of propellant into low earth orbit to refill the cargo ship and have it land on mars with sufficient uncrewed margin the dry mass of the cargo ship we predict will weigh 10 tonnes more than the tankers and this is due to them not needing any of the zero boil off equipment if you're traveling to mars for eight to nine months you need good insulation and solar powered recondenses to stop the cryogenic oxygen and methane from boiling off now this is something by the way that still needs to be solved even before thinking about landing a starship on mars in fact it is also needed for a moon mission as well so as said at the start we're trying to see if we can get away without using any sort of refueling on mars via in-situ resource utilization systems that's of course all about generating the liquid oxygen and the liquid methane direct from mars so that a starship can refuel and return to earth now don't get me wrong here of course at some point this makes the most sense i'm certainly not saying that i'm against isru systems for mars because mid to long term it's essential for a successful self-sufficient mars colony saying all that though it is a colossal effort to establish that required infrastructure initially okay so roughly speaking a starship with a reasonable amount of payload needs around 1 000 tons of propellant to not only launch from mars but also to put itself on a trajectory all the way back to earth with the fuel margin to land back at home again those 1000 metric tons of propellant will consist of around 220 tons of methane and 780 tons of oxygen to create both electrolysis and the sabatia process are required if we want to use the resources from mars the oxygen is merely a by-product in those processes so that's covered but for methane we need around 165 tonnes of carbon and 55 tonnes of hydrogen on top of that we need a whopping 5 gigawatt hours of electricity to generate it that is enough by the way to drive your standard tesla about 40 times the distance to the moon and back while the carbon is present everywhere on mars since the atmosphere is around 96 carbon dioxide water is needed for hydrogen luckily this is abundant with scientists estimating that there could be at least 5 million cubic kilometers of it existing on mars much of it though is in the form of dirty ice it needs to be extracted and the infrastructure just for that could be very extensive we'll talk more about that in just a moment but first a massive thank you to surfsharkvpn for sponsoring this video a virtual private network or vpn is a service that both hides your ip address and encrypts your data as methods for phishing and cyber attacks become more sophisticated it is becoming more important to add an extra level of security to your online presence and surfshark is a perfect first port of call for this protection tired of pop-ups and potential malicious ads well surf shark's clean web feature will take care of that need privacy beyond a vpn well surfshark has you covered here too with real-time alerts if any of your emails or passwords are at risk of being hacked on top of that you also get to unlock all of the extra online content that would normally be geographically blocked from you maybe your favorite movie is just not available in your country yet just fire up your vpn and you can sort that out right away you just change the country you're accessing the internet from and the job is done refresh your browser and hey presto you will now have all of the selected regions content available to you another feature to note is that just having the one subscription will give you unlimited use so you can use the surfshark vpn service across all of your devices simultaneously if you would like to support my channel here and are considering a new vpn or even changing your existing vpn head to surfshark.deals marcus and use code markers to get 83 off and three extra months for free the link is in the description below so yes we sure would need a lot of water to process the propellants needed on mars to refill an entire starship there is plenty of that water resource there on mars more than enough to fill any feasible number of starships that we would ever want the issue though is that the water is not everywhere in useful quantities and it needs resource heavy farming and cleaning before it can be split with electrolysis the time frame for a mission between landing and then a mars to earth transfer window is somewhere in the ballpark of 400 earth days in that time we need to fully produce the propellant meaning around 550 kilograms of methane is required per day now this may not sound that much but it's going to need an electricity supply via nuclear reactors or solar arrays producing up to 520 kilowatts so let's look at the solar panel option while on a clear day at midday here on earth we receive around one kilowatt per square meter in raw solar energy on mars though it's just 0.59 of a kilowatt simply due to mars being further away from the sun unlike earth here though this value doesn't change a great deal during the evening or in the morning because mars's atmosphere is thinner by a factor of 60. this gives a few hidden benefits you may not expect if we remove night time of mars and take into account that we can generate more consistent energy throughout the martian day a good estimate on the average solar energy received at the ground would be around 0.2 of a kilowatt per square meter this is the raw energy though and photovoltaic cells at low temperature have an efficiency close to 20 therefore with one square meter of solar panels we can generate on average around 0.04 of a kilowatt geez that is not much and this all assumes the panels are not covered in dust or that there isn't some dust storm reducing that lower this is about as high as we can expect so given this we need at minimum around 13 000 square meters to fill one starship for its return after 400 earth days additionally we need to power the facilities and keep the cryogenic liquids cooled luckily on mars though with low atmospheric density and below zero temperatures this shouldn't be too much of a problem i mean here on earth we've perfected it quite well so the energy cost shouldn't be too significant in comparison so yes that is a load of panels that would weigh in at around 250 metric tons including the scaffolding wiring and all that sort of thing so yes for just the solar farm this is close to two fully loaded cargo starships and we would also need the machinery to convert the propellants with the sabatia process and electrolysis and then the crawler for digging around in the ice and cleaning facilities that is a lot of infrastructure to get sorted now this is all certainly doable with a few expendable starships but this is all yet untested in the martian environment especially for such a long time span the innovation and engineering that is going to be needed oh man it's going to be crazy i'm confident that we can work all this out at the end but i wouldn't put my trust in having any of this infrastructure really sorted for any of the initial missions just use the example of landing at a spot that doesn't quite have as much ice nearby as expected and then having to have the transportation system set up to transport all of that ice from kilometers away we'd also need to have backup systems to have redundancy for technical issues as well maybe general floors come up which can't be fixed with resources at hand all of this means that further earth mars transport cycles are going to be needed to bring in all of the additional improved equipment okay so one thing we know for sure is that a single starship mission with minimally useful cargo cannot land on mars and make it all the way back to land on earth a single ship in this case would require over 12 kilometers per second of delta v and this includes getting away from low earth orbit landing on mars with a huge amount of propellant left for the return to earth launching off mars into orbit and then the further trans earth injection finally then we need to land back here on earth even when utilizing highly elliptical refilling orbits around earth as we mentioned for lunar starship this would still leave a single ship with only nine kilometers per second to fly it by itself we are nowhere near obviously this whole problem is solved by refilling on mars well into the future but we can't do that for the early missions so how can we do a returning flight from mars without isru well actually you may be surprised how about using some tankers in mars orbit absurd you say well let's run the scenario we need the already mentioned zero boil off equipment for the regular starships so we'll just add that equipment to the tanker so that they can make the journey to mars and stay in mars orbit for years now in this scenario we're running here the crew starship would never land on mars but instead stay in orbit around it as well for surface to orbit transfer a separate shuttle starship would do the trick basically this would be the same design as the crude starship but with all of the mass excluded that is needed to keep the crew alive and entertained for eight to nine months while traveling to mars and back again we strip this all back with just the seats in the crew compartment in the front with only the necessary life support systems for a small trip for 10 astronauts perhaps just 20 tons of equipment should be enough which is then added to the mass of the 110 ton long duration starship now there's a lot of assumptions there but what do you think let me know your thoughts in the comments below this shuttle starship just needs to have enough propellant to land and then get back into orbit with the crew once again we will be wiping most of our velocity off by aero braking for this we need the 1.5 kilometers per second and then to get back into orbit another 3.8 totaling 5.3 and this could then be refilled for even more crude landings so the question is how much can a tanker bring to low mars orbit once again applying some math in this table provides us the answer 300 tonnes in low mars orbit that's actually not too bad the surface to orbit shuttle would need around 420 tonnes of propellant for the 5.3 kilometers per second remember as well that when the shuttle starship arrives at mars in the first place it won't be completely empty so just one refill might be sufficient to provide what is needed now before any of this would happen we would expect a lot of pre-landed starships that can be converted to housing and will be storage for consumables signs and other equipment now i wouldn't even say that these are expendable because that typically implies that they're going to be destroyed or just crashed into the surface these would be serving a real purpose as one-way vehicles that kick off the martian starbase besides them simply being used as housing and storage this also provides many many tons of very high quality steel for their use in the future but what about the starship that carries the crew all the way to mars in the first place well nasa luckily has us covered regarding the consumables there as well this study here shows that a complete mars cycle has a good 1 000 days in length this requires 12 metric tons of consumables for 4 people made up of water food oxygen clothing and that sort of thing unlike the moon mission shown here it assumes recycling to at least some degree to store all of this we need around 50 cubic meters of storage space so scaling this up to 10 people which i think is a reasonable number for initial missions means that there is 30 tonnes of supplies stored in 125 cubic meters starship's fairing has a volume of around 1 000 cubic meters so that is covered and we also want this starship to have enough propellant to get from earth orbit to mars orbit and then return to earth and land again that leaves us with a payload capacity of around 65 tons this is looking a little tight but still possible nearly half of that is already gone for suppliers and that leaves around 35 tonnes to provide crew compartments the flight deck and machinery to support comfortable living keep in mind as well that a further tanker to mars with another 300 tons of propellant available opens up some new possibilities to transfer added cargo from the surface and back to earth as well so there's all sorts of mission options that could exist if we are willing to expend a few more tankers in fact it could actually be possible to leave enough fuel in the tankers for them to then land on mars to become part of starbase after they're finished with their refilling exercise the options here become quite interesting and maybe we could cover a few of these in a future video so yes to summarize such a mission to explore without in-situ resource utilization on mars would consist of one crude starship for 10 astronauts one surface to orbit shuttle and two tankers for a crew return and shuttle topper so yes that is four separate starships total and prior to this of course we would see several single use cargo ships let's say four or five to comfortably oversupply the landing site initially now i think if we could have a few of those pre-supply missions going out by 2026 then it could be quite possible to be seeing tankers a starship shuttle and finally the crude starship on such an epic journey by the end of this decade i would love to know what you think let me know in the comments below and if you've enjoyed this content please do consider subscribing we love creating all of this content for you we make videos about starship progress every single saturday along with other exciting space updates such as these deeper dive videos that we really love making as well these videos in particular are made possible by our amazing patrons and youtube members and of course those of you picking up gear from our merch store including this shirt that you see here these links are all below and if you would like to help support what we do that would be most appreciated big thank you to the amazing production crew helping me here especially anaes adam and tiago for all of their help in this video in particular it has been a big team effort if you're interested in these topics and you would like to keep up to date remember you can follow here below and on twitter at marcus house as well in the tile in the bottom left today we have the moon shot video talking about the potential lunar mission options with starship if you enjoyed this video that is the next one to watch in the top right is my latest video and in the bottom right content youtube is selected from the channel just for you thank you sincerely everyone for watching all this way and we'll see you all in the next video

Channel: Marcus House

Views: 506,467

Keywords: elon musk spacex, spacex super heavy booster, Spacex starship, Spacex starship landing, spacex starship full stack, spacex news, Spacex starship progress, marcus house, Spacex, Spacex starship update, spacex elon musk, spacex boca chica, spacex launch, spacex launch tower catch, spacex mars mission, Elon musk, spacex mars plan, spacex mars gateway, in situ resource utilization, refilling on mars, Refueling in orbit, spacex mars, spacex moon, spacex starship

Id: u55zpE4r-_Y

Length: 21min 23sec (1283 seconds)

Published: Tue Oct 26 2021

Reddit Comments

[u/QVRedit]

Great video, very informative, good to see that SpaceX have several different solutions available to them.

This coming decade is going to be really interesting !

Even the next few years as SpaceX get Starship fully operational is going to be interesting too !

[u/[deleted]]

Most interesting idea here to me was the idea of keeping your interplanetary coast Starship in orbit and descending in a stripped down vehicle.

It's interesting how the flexibility of the Starship architecture makes "just send more Starships" into a halfway reasonable proposal for how to solve a crew return problem. I agree with Marcus that ISRU is a fantastic goal, but it's a hell of a long pole. Would be nice to get humans to mars to explore before that is ironed out.

[u/manicdee33]

TL;DR: haul your propellant around with you like some kind of primitive person using expendable rockets.

Slightly longer version: Marcus goes into just how many expendable rockets you have to haul your propellant around in, and whether those rockets are really expended.

Tune in if you like Marcus House, Starship animations, spreadsheets, or just thinking about the possibilities of getting humans to Mars.

[u/mr_robot_1984]

I really like Marcus, he goes really into detail on his videos.

[u/Reddit-runner]

Very interesting video.

But it took me by surprise that he went this conservative on the solar power system mass.

I get between 40 and 60 tons of solar panels to generate the fuel for a return trip over the course of 2 years.

[u/deadman1204]

This will have to be the way. Its gonna take awhile to get real isru setup, and will inevitably involve humans on the ground during construction.

[u/NoBodyLovesJoe]

If you could make the propellent plant less then 40 tons, you could just bring all the hydrogen you need for the first missions until the viability of ice mining on Mars is perfected, would also make it easier to test a return trip as I highly doubt SpaceX will send anyone to Mars unless they can prove they can get back.

[u/Decronym]

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
EDL	Entry/Descent/Landing
H2	Molecular hydrogen
	Second half of the year/month
HLS	Human Landing System (Artemis)
ISRU	In-Situ Resource Utilization
LEO	Low Earth Orbit (180-2000km)
	Law Enforcement Officer (most often mentioned during transport operations)
LOX	Liquid Oxygen

Jargon	Definition
Raptor	Methane-fueled rocket engine under development by SpaceX
Sabatier	Reaction between hydrogen and carbon dioxide at high temperature and pressure, with nickel as catalyst, yielding methane and water
electrolysis	Application of DC current to separate a solution into its constituents (for example, water to hydrogen and oxygen)
methalox	Portmanteau: methane fuel, liquid oxygen oxidizer

---

^{Decronym is a community product of r/SpaceX, implemented by request
10 acronyms in this thread; the most compressed thread commented on today has 20 acronyms.
[Thread #9183 for this sub, first seen 29th Oct 2021, 15:02] [FAQ] [Full list] [Contact] [Source code]}

[u/SalmonPL]

One more issue that the video doesn't address that might be a blocker for early return missions: preparing a lift-off surface.

Remember the static fire where the Raptor blew chunks of the concrete pad up into the engine and destroyed it? It's likely to be even worse on Mars.

The problem on landing isn't quite as bad because the ship is much lighter on landing, so it needs less thrust from the engine, and it can do a hoverslam that means it's not close to the ground for long. Plus, if the engine is damaged at the last moment on landing, you can still land safely. But on lift-off the vehicle needs to have a lot of propellant, so more thrust is needed, which probably means more engines and you need them to continue working immediately after lift-off.

Because preparing a hardened pad is so challenging, my guess is that the best solution for the first return mission would be to bring along a diassembled launch/landing stand in an early Starship, then assemble it on Mars and have the return ship land on the stand. Then when it lands and takes off it's on the stand quite a distance up from the ground. This seems to me like a significant challenge to do without humans on the ground.