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Commercial Space Flight General / Re: Boeing Smallsat Constellation
« Last post by Sam Ho on Today at 05:20 AM »
Boeing's FCC filing is here:

Initial Deployment is 1396 satellites at 1200km, mostly at 45 degrees inclination with some at 55.  Final Deployment is a total of 2956 satellites adding more satellites at 55 degrees, and polar-orbit satellites at 88 degrees, 1000 km.  (p23)

They are planning cell sizes of 8-11 km on the ground. (p7)

On the orbital debris front, they are reserving 90% of their propellant to lower each satellite to an orbit below 500km and 5-year lifetime at end of mission. (p35)

There's no mention of any advanced debris mitigation, just the low disposal orbit and passive reentry.
People need to specify what phase of development they thing their solutions are good for.

Were not going to have water available in that kind of quantity on an initial human landing, any water that you can make will be going into fuel so you can actually return.  Building with water is a mid to long term concept usable only after a super abundance of water is available, and I'm very doubtful any such super abundance will ever be available.

We all agree that on the Mars surface you shield yourself using some kind of local derived material, this is a no brainier and not at all the difficult part of the problem and were just arguing over architectural and building material merits at this point and that can't be resolved without figuring out the entire ISRU scheme and the relative cost of different local materials.

In space transit is where better solutions are needed.  I'll throw out an idea, hibernation type sleep systems allowing passengers to be stacked into very tight well shielded spaces and then to accelerate them at a more modest speed.

Suppose a cylinder 6 m long and 7 m in diameter, internal volume is 230 m^3, covered in 30 cm of polyethylene and the dosage would be 1 mili sev/day in space at a mass 70 tons of shielding.  Yes that is a lot of shielding mass but it's not prohibitive considering the expected payload masses involved and if it is left in orbit to use during the return transit.  A 5 month transit time each way would thus yield an acceptable radiation dose without cranking up speed to things like 3 months which is likely to require a lot more then 70 tons of additional propellant to do.

Because both increasing propellant mass to shorten duration and adding shielding mass experience strong diminishing marginal utility the optimum solution for any desired radiation level is to mix speed and shielding strategies rather then relying on one exclusively.  The sweet spot between them always moves towards more shielding mass as the vehicle size and payload increase because the surface area to volume ratio makes shielding more efficient while propellant requirements scale linearly with total vehicle mass for any given DeltaV.  Hibernation makes the protected volume much smaller and likewise amplifies the efficiency of shielding, note that only the actual people in transit need to be shielded, life-support equipment and consumables can be outside the shielded zone.

In addition Hydrogenated Boron Nitride nanotubue fiber is being investigated as a material that could serve as both structure and shielding, it may be able to provide shielding very nearly equal to polyethylene and would make an excellent skin for an inflatable Hab.
Sorry for being late - I'm now scanning the various Chinese articles related to this launch, which contains info on the flight sequence, the upper stage and (some) of the various payloads on board. Gimme some time.....
SpaceX Mars / Re: Where will BFR launch from?
« Last post by the_other_Doug on Today at 04:37 AM »
Just thinking of bending loads, when seeing a Falcon 9 first stage transported. Long and slender, very lightweight. They just put wheels under both ends and transport it over the highway.

Well, to be honest, they connect the wheel trucks to handling rings (in the case of the road trucks, there are two sets of claw-like rings at each wheel truck, integral to the trucks), which are strategically connected to specially reinforced sections of the long, slender, lightweight stages, and I bet there are longitudinal stiffeners that run up and down the stages from those attach points.

In other words, it's not that simple rolled tubes of the aluminum-lithium alloy SpaceX uses for the Falcons are so strong they wouldn't show bending deformations without stiffeners.  Such stiffeners do add to the mass of the stage, but they also add strength and longitudinal stability, not just during transport and erection on the pad, but also in flight.  I'd be willing to bet that pretty much every airframe, for every type of aerospace vehicle, has such attach points connected to strengthened or reinforced sections of the airframe.

Besides, I seem to recall that SpaceX uses a chemically milled integral stiffening on the interiors of their vehicles, and tries to reclaim the material milled away from the etching chemicals.  Which means they can pattern the stiffeners and the attach points, both external and internal, into the metal using the milling process.  I believe the overall stiffening pattern is the grid pattern we can see in the internal views of the tanks.

I know that things like the Saturns had big metal stiffeners welded into their structures, though they became thinner and less massive the higher you got on the stack -- that staged rocket equation.  Maybe it was just an engineering intuition that was ultimately faulty, but back then, they worried about bending effects on rockets the size of the Saturn V, Nova -- and in this case, the BFR.  I figure that SpaceX thinks they have such things figured out, and aren't too worried about such effects with either FH or BFR, at this point.
SpaceX Mars / Re: Where will BFR launch from?
« Last post by envy887 on Today at 04:27 AM »
Transport is easier than standing in terms of bending, because the supports are very far apart. On the pad, the supports are close together, and the moment arm twice as long.
OCISLY drydock update:
She will also reportedly have her bottom plates numbered in order to make her eligible for the Coast Guard's UWILD (Underwater Inspection in Lieu of Drydock) program.

I wonder if there might be a similar reason that a commercial diver doing underwater construction in Louisiana later told his old girlfriend cutting my hair in Atlanta GA last month that he was working for SpaceX out in California. She didn't know exactly what he was doing for SpaceX and I couldn't figure it out at the time either, but maybe JRTI already has her numbers.
And if you mix the water with other ingrediants to form a slurry that freezes as it is applied such that the ice itself is both reinforced and in part self insulated.........

Like the Mars Ice House  :)
The Mars Ice House is supposed to be 3D printed with like little robots and also applying like an ETFE film to keep the ice from sublimating. I was talking about something different, where you can skip the 3D printing altogether just by using an inflatable design. A lot simpler. You can pack up the inflatable plastic in a very small, lightweight volume, then simply pump in water and wait for it to freeze.

I'm fond of inflatables for the simplicity - the first time I saw a inflatable shelter that has a concrete mix in the wall that hardens into a permanent building I fell in love with them.  I like 3d printing for buildings but the more i'd have to depend on machines not breaking down the better.

The Mars Ice House is an inflatable.

Inside the skin is a form that spirals up. The printer grips this form and spirals up accordingly while printing the wall.

Using a mix of fibre, aerogel & water creates a stronger better insulated wall.

Now if you could use a double skinned inflatable as you say, do away with the printer and still be able to pump in the water, aerogel & fibre mix without those ingrediants settling out, then perhaps you have the best of both worlds.

I believe pure water ice is less resilient than the water, aerogel & fibre ice.

I want resilience in case someone hits it with a Rover etc.  :)
SpaceX Mars / Re: Thoughts on SpaceX's next big steps
« Last post by guckyfan on Today at 04:17 AM »
No way, if a private enterprise is on the verge of landing on Mars and SLS is still a joke (or even making the meager progress they say it will make), it would be political suicide for any politician to propose outlawing private progress that is so efficient and economical and claiming that the government ought to be doing it with its boondoggle of a plan. That is outlandishly beyond possibility. Those few people you imply can try it now, but once MCT is flying, it will be beyond possible.

Of course the government would not make a law prohibiting Mars flights. But from somewhere grave concerns regarding planetary protection might come up. After a year or two of those becoming bigger and bigger with great regret a decision would be made that such flights cannot be allowed a private company. Only NASA can be trusted to be responsible enough.

I sure hope this won't happen but I see that possibility as the greatest threat to Elon Musks Mars plans.
SpaceX Mars / Re: Where will BFR launch from?
« Last post by guckyfan on Today at 04:12 AM »
Just thinking of bending loads, when seeing a Falcon 9 first stage transported. Long and slender, very lightweight. They just put wheels under both ends and transport it over the highway.
Some thoughts:

- For people with vaginas (note that this is not the same as "women"), the crotch problem in MCP suits can probably be solved with a water bladder.  Since water is incompressible this does not create the problems that an air-filled bladder would.
- For people with penises (again, not that this is not the same as "men"), the same solution probably works.
- The solution to the problem of the testicles may not be obvious, but it is extremely well known in the transgender community: force the testicles up into the inguinal canals.  This is surprisingly comfortable being able to remain in such a position for many hours on end is the norm, not the exception.  Look up "tucking transgender" for information on how it is done.
- Changes in peoples' builds WILL need to be dealt with.  At a minimum, this includes changes in stomach volume due to eating, changes in chest volume due to breathing, and changes in breast volume due to the menstrual cycle in people who have one.  The spacesuit MUST be able to be able to be adjusted to reflect changes in peoples' bodies or, even better, self-adjust.

I think that the last problem is the hardest to solve.  The spacesuit needs to be able to be adjusted substantially.  The volume changes due to breathing alone are ~5L.  Weight gain/loss and/or body fat/muscle redistribution (the latter being unavoidable and unpreventable) need to be dealt with.  Swelling due to injuries needs to be handled.  Finally, this all needs to be fail-safe: even if the suit loses all power, the suit must neither expand and become useless nor contract to the point of cutting off circulation, breathing, or movement.

My preferred solution is to have the rigid lines in the suit be tightenable by means of pull cords. Simple and works, and sensation is perfectly adequate to detect mis-tension.
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