Ol’ Musky Boi

That's quite a difficult thing to judge, considering that even Astronauts don't spend half their time having fun in microgravity or looking at the view, and even then the ISS doesn't have quite the same amount as open space as perhaps a Starship or a large space station would have (those windows in most of the Starship renderings are massive, I imagine that view would be pretty phenomenal compared to the Cupola). Until someone tries it of course we won't know, but I'd wager that people wouldn't get sick of it so easily. What seems most likely to me is that some may spend short ~1 week sorties in Starships, and then up to ~1 month stays in bigger space hotels (possibly longer, you may be an employee there who stays on board for months at a time), with artificial gravity to prevent muscle atrophy and to aid in many gravity adjusted tasks. I doubt you'll stay in space beyond that as a tourist, only if you were a researcher, employee, or permanent resident (of which there would likely be few). If we're talking Lunar or Martian tourism the travel times involved make longer stays more attractive, kinda like how some people might spend a couple of years abroad for a change of scenery.

I don't necessarily think there'd be a lack of entertainment if you stayed in space for a month, some people like to go on cruises for similar lengths of time, but I do think you're right that the limiting factor may be zero g exposure, so perhaps for an up and down Starship space trip a week would just about do the trick. Although once we start talking artificial gravity stations, where you might only spend a few hours a day in microgravity, longer stays do start to look more attractive. It's interesting to imagine what a Lunar cruise may be like, perhaps a 3 day journey there to spend 2 weeks on the surface during the lunar day (not much to see in the dark), then another 3 day journey back to LEO in some sort of cruiser, perhaps with changing gravity like in the Artemis book, where the centrifuge would slowly spin up or down to accustom the passengers to Lunar or Earth gravity during transit. Of course the cost of sending payloads to the Moon is about an order of magnitude more expensive than sending payloads to LEO, so ticket prices will be at least in the million dollar range for quite a while, at least if you're going for comfort.

I agree, I say as much in my post, I think a month is about the max any tourist would want to spend in orbit, since the majority of the cost will be that of launch (even with full reusability), the longer you stay in space and the more passengers there are the cheaper the tickets, somewhere in there there's a balance that people would want to pay for. Though when the ISS is eventually decommissioned sometime in the mid 2020s there will be a need for a new interim orbital research lab for operation and recovery of microgravity experiments. Starship fills this role pretty well, it has more pressurised volume than the ISS, and likely a similar power capacity (most recent numbers I can find are 300 kW for the ITS, so perhaps half that for the current iteration), one can imagine space agencies or even universities hiring out a Starship to do 6 months of research with. Heck, a Starship's propellant tanks probably make up an extra 1,400 m3 of pressurised volume at least (based on an O/F ratio of 3.8, and a propellant mass of 1200 tonnes), so a refurbished Starship "wet workshop" could feasibly increase crew capacity from 100 to 240, and if you dock two of them together now you've got a space station with a crew capacity of 500, add a couple more and it's 1000, and so on. Currently Musk says the cost of Raptor manufacture is $2 million per unit, which could drop to as low as $200 thousand per unit in future. Assuming that this is the majority of vehicles costs, with say an added 10% cost for the rest of the vehicle, each Starship could cost between $1.3 - $13 million. Meaning that you could theoretically build a space station of 1 million occupants for $5.4 - $54 billion. Why off Earth you would need such a station (pun intended, sorry not sorry), other than planetary invasion, I don't know, but it's an interesting idea nonetheless. Since there may also be an increasing demand for partial gravity research, we could also see Starships tethered together to make makeshift artificial gravity stations. Of course, I think by the time Starship production ramps up enough to make these kinds of things feasible it'll make far more sense to have dedicated stations for space tourism, instead of slap dash fuel tanks with cramped bunks and no windows. We could see the wet workshop concept being employed on Mars, since it does make a lot of sense to keep most of your Starships on Mars permanently to minimise load on the fuel production plant, and a nice roomy 2,400 m3 area I can imagine would be well received by initial crews, which will likely consist of perhaps only a dozen or so members.

Since so much Starship development has been happening lately, I think it's a good time to discuss it's capabilities in the realm of space tourism, and wether or not this could be a source of good income for SpaceX. I am no economist or business expert, but I've done my best to estimate a couple of ways this might work. LEO Tourism, How Might It Work? Musk recently said that Starship could cost as little as $2 million per launch. Which for a 150 tonne payload capability means an incredible $13/kg price tag, about 1000 times cheaper than a Delta IV Heavy, which still boggles my mind, based on that, and a stated passenger capacity of 100, launch cost per person (and 1.5 t associated hardware/consumables) could be as low as $20,000. Now, it's worth noting that Starship won't just be a big crew capsule, it's essentially a recoverable space station, with a pressurised volume of 1,000m3, each passenger could have 10m3 of space, which translates to a cubical about 2.15m on each side. That sounds small, but in space the floor, wall, and ceiling can all be useful spaces, whereas on Earth it's mostly just the floor (or rather, what we put on the floor), so you can imagine it'd be the equivalent useful surface area of a room 5.3m on each side, so I think it's reasonable to say that you could probably live in such a room fairly comfortably. So, with a 1.5 t mass allowance per passenger, how long could you reasonably spend in orbit? We can assume about 100 kg of that allowance will be made up by the passenger and whatever luggage they have brought, we can also assume that about 330 kg of that will be life support systems (the ISS life support system on the Zvezda module weighs 2.3 t, the ISS has a maximum capacity of 7 crew, therefore each crew has 330 kg of life support), and perhaps another 330kg of associated internal structures. All in all perhaps half of the mass allowance per passenger will be dedicated to life support and comfort. Effectively leaving 75 t of payload that can then be used for consumables that can't be recycled, like food. Let's say each passenger uses up 3 kg of these consumables per day, that means you could support 100 passengers for about 250 days, or about 8 months, of course in reality you'd want to have a good margin on that, so let's say you can keep them in space for 6 months, about the same as a trip to the ISS, so there's loads of relevant data. Now, assuming 10 of the passengers are actually employees of SpaceX, chefs, janitors, room service etc, and you pay them each, say, $20,000 on their 6 month stay, then your total cost is about $2.4 million. Say SpaceX operates at a profit margin of 100%, and each ticket for the other 90 passengers will cost about $53,000 dollars. At a rate of 20 launches a year, this amounts to a profit of around $48 million. Of course, this works under the assumption that people will want to spend 6 months in orbit in a small cabin, this seems unlikely if the destination is LEO. Rather I imagine passengers might want to spend perhaps a month in orbit in a much larger cabin, where microgravity activities and sports could provide an attractive source of entertainment, as well as sight seeing and perhaps even recreational EVAs. So instead let's say each launch consists of 25 passengers, perhaps 5 of them being members of staff (each payed perhaps $3,000 a month), in this scenario the total cost is $2.015 million, and ticket prices per passenger are (at a 100% profit margin) about $200,000 each, with each passenger having a much larger 40m3 of space, or a cubical 3.4m long per side. How many people would pay to experience such a holiday is a hard question to answer. But it'll probably have to be people earning at least more than $1 million a year. In America, that represents some 235,000 people, of which perhaps 1% would be interested in such a holiday. So let's say theres a market of 2,000 people a year who would pay for such a holiday, meaning that SpaceX could launch around 100 passenger Starships a year at a profit of $200 million. That market size may sound optimistic, but considering 600 people have already signed up for a few minutes of weightlessness on Virgin Galactic's SpaceShipTwo, for roughly the same price, I'd say it's a reasonable guess. Does Starship Necessitate Space Tourism? The Starship, if/when it flies, will be so capable it'll instantly dominate the global launch demand. There were only 111 rocket launches in 2018, perhaps a cumulative payload of a few hundred tonnes, and a single Starship could satisfy this demand by launching a handful of times a year, at a cost 2-3 orders of magnitude lower than the current competition. Clearly, another source of launches must be found to make Starship economical. SpaceX themselves are already creating one possible source of launches with their Starlink constellation, which may one day consist of up to 42,000 227 kg satellites, a total mass of 9500t. But even though that's over double what's currently in orbit, is still less than 70 Starship launches, even at SpaceX's current launch capability of 30 rockets a year, that only gives Starship a couple of years of work. It seems inevitable that SpaceX will have to branch off into services that, as of now, do not exist. Space tourism is one such service, and makes a good stepping stone for SpaceX to build up experience with human crew before committing to shipping massive colonies off to Mars, which is ultimately what Starship is designed for. I can't help but think that other launch providers, such as ULA or Blue Origin, will have to really up their reusability game to stay in business in the next decade. My personal hunch is that Blue Origin is already on it, and their mysterious "New Armstrong" vehicle is a fully reusable Starship analog. I'm not sure about ULA though. Any thoughts?

Ah, thanks for clearing that up. I did think 41.6N sounded a bit much, I've not studied fluid mechanics in my physics course yet so I'm basically learning all this stuff off the internet. Guess I'l have to redo the calculations then...

That's correct, I assumed the mass flow rate would be 38 g/s based on how long it took for one canister to empty. But it may be that when the engine is firing and under pressure the mass flow rate goes down somewhat, I'm not sure. A TWR of 33 would be amazing! You're right about the cameras, next time we'll set up some tripods and try to get a few different angles.

Here's some testing from last week, no ignition but I think we're pretty close, just need to get the burst disc the right thickness, we went too thin for 2 of the tests and too thick for the other, so the sweet spot must be somewhere in the middle. The fuse is a 20cm or so length of plastic ignitor cord (PIC), which is coiled up in a cavity under the burst disc, hopefully that'll serve to both melt the burst disc and to decompose the N2O. The injector piece was 3D printed by a friend (largely because I had no access to metal working tools at the time) who's been helping out with the project, and held up fairly well under the heat, although there is a little bit of wear. We're going to do some more testing this weekend probably, and see if we can achieve ignition. If all goes well we can start construction of a second prototype, where we will try to cut down on weight and fix any other issues (current design weighs 126g wet and 117g dry, so there's a lot of trimming to do). I've already done some preliminary nozzle calculations: Throat diameter: 3 mm Exit diameter: 7 mm Specific Impulse: 112 s Average thrust: 41.6 N Impulse: 10.4 Ns (D size motor) For the second motor we will likely switch to using acrylic fuel over paraffin, as paraffin wax has proven to be a right PITA. And we may switch from using 8g N2O cartridges to using 16g ones, which will give us double the burn time and impulse (current motor is about 5 Ns). But we're not certain yet, 16g cartridges are a lot more expensive.

I imagine a back-up parachute system would have a similar mass to a drogue + retrorocket system, if not slightly less. Based on this document the Apollo CM's parachute system had a mass of ~100kg (If I've interpreted the data right), so I still think that it would be a lighter way to go even accounting for that. You're right though, we are getting a little off-topic.

Great post, but it's worth noting that in the case of Dragon 2 the landing engines would have also been the LES, so that offsets some of the mass penalty. If we assume that an expendable LES would've been jettisoned at first stage separation (which occurred at ~1,900m/s for the DM-1 mission) and would've had a mass of 2,000 kg, then the payload penalty of bringing the LES to orbit (~7,500m/s) is about 1,600 kg, not 2,000 kg. So about 1,200 - 1,300 kg more massive than the drogue + retrorocket system. This doesn't change the picture much in terms of which is more lightweight though, the landing system you mentioned is still 4-5 times lighter. But I think using the LES as a landing system has an advantage in cost savings and reusability. As you'd still need an LES of some sort for any crew capsule, and if you wanted to re-use that LES (and re-use is half the reason you'd want to land with retrorockets anyway) you'd still need to bring that 2,000kg system back with you, in which case why wouldn't you use it to land with? I believe that's why SpaceX initially went with the latter system, as it actually saved mass, additionally, keeping your LES with you all the way to orbit gives you quite a lot of abort options. With all that being said, SpaceX still ditched the system, I imagine it was because of the safety issues you mentioned and the difficulty they would've had in getting that approved by NASA.

I can't blame him, I gave up on my hybrid rocket project for a year. I've restarted development though, should see a few more tests and the construction of a second prototype in the coming weeks (hopefully). Seeing everyone's work on this thread was a big inspiration.

How you had the patience to build this is beyond me.

I tried to build one about a year ago, could never get it to re-enter without spinning out. Maybe it's about time I try again...

Can we get an ETA on 1.8 by any chance? Or is it a done-when-it's done kinda thing?

I second this, 1.25 m and 2.5 m cargo bays are greatly needed!

That's a very nice spot for a base!