Author Topic: Distributed Lift Readiness  (Read 1175 times)

Offline jebbo

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Distributed Lift Readiness
« on: 02/27/2018 12:08 PM »
Not sure if this is worth its own topic, but there has been scattered (distributed  :D ) talk of distributed lift.  It struck me that the SpaceX BFR/BFS vision for Mars relies heavily on this.

So really, I'm wondering if there are short term things that should be done ... for example, demonstrating on-orbit fuel transfer seems like a good first step. Similarly, i can imagine various on-orbit assembly tasks that might need development.

--- Tony

Offline Darkseraph

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Re: Distributed Lift Readiness
« Reply #1 on: 02/27/2018 12:57 PM »
It appears that Distributed Lift would require relatively fast turnaround of boosters to prevent excessive boil-off. Otherwise stages would require the extra weight of active and passive cooling equipment. SpaceX have so far been unable to demonstrate rapid turnaround or even regularly launching on time. Distributed Lift is technically feasible but it's not delay tolerant. I'll be more convinced when SpaceX achieve 5 flights in a row that are on schedule with Falcon 9.

Propellant Depots would be more delay tolerant. Because they are sent only once to orbit, fitting them out with tons of insulation and crycooler equipment is not onerous. Propellant can be sent months or years before an actual journey to the Moon or Mars is made, making the schedule more flexible.

An initial BFR depot could be a simplified version of the cargo ship. Two huge tanks making up most of the structural volume. No legs. No Header Tanks. Vacuum Raptors only. Outer surface covered in MLI. Deployable Sunshield in a small area in nose cone. Solar panels to run avionics and a crycooler. Because it would be flown with no payload or return propellant, it accommodate a stretch beyond BFS Cargo/Spaceship height.
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Online speedevil

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Re: Distributed Lift Readiness
« Reply #2 on: 02/27/2018 01:02 PM »
Not sure if this is worth its own topic, but there has been scattered (distributed  :D ) talk of distributed lift.  It struck me that the SpaceX BFR/BFS vision for Mars relies heavily on this.
It  doesn't, other than propellant transfer.

There is no cargo movement between vehicles, no on-orbit assembly, no docking of multiple things in a permanent manner, no assembly in other ways, no reactivating dormant vehicles, no inflation, no ...

There is plausible stuff that could be done that has not been done for no good reason other than strict adherence to the fact that it has never been done, therefore can't be risked.

https://forum.nasaspaceflight.com/index.php?topic=44127.msg1745345#msg1745345 - for example notes that BFS can carry 60m^3 or so of aluminium. This is 2400m^2 of aluminium, at one inch thick, if you were to make a tube 30m in diameter, and 200m long, you can do that with around ten launches of BFR. (atmospheric load is about 15% of yield, and yes, you would need lots more launches of shielding)

But, first, you need to prove that rivets work in space. (or bolts, or ...)
A cargo consisting, for example, of a dozen varying model industrial robots would be an interesting first cut on this - have them play around in zero G and with entirely commercial off-the-shelf fasteners, and see what works easily and rapidly.

Fail lots - fail fast, just try something..



Offline AncientU

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Re: Distributed Lift Readiness
« Reply #3 on: 02/27/2018 02:04 PM »
An early step would be to pick/use a fuel that has little boil-off tendency and won't freeze.  That leaves out hydrolox and kerlox, and obviously focuses on methlox.  (Hydrolox can come later, but is a much more difficult technology to begin the process.)

Next, we need refuel-able methlox spacecraft and/or second stages.  Engines for these are coming soon, and a variant of the RL-10 can burn methlox, I believe.

Finally, we need to start refueling second stages and/or spacecraft. 

Preparing a push for Europa Clipper would be a worthy first objective; the technology for this push could easily be ready before the spacecraft.
« Last Edit: 02/27/2018 02:06 PM by AncientU »
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Offline Jim

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Re: Distributed Lift Readiness
« Reply #4 on: 02/27/2018 02:30 PM »


Preparing a push for Europa Clipper would be a worthy first objective;

No, not with a nuke spacecraft or even a class A spacecraft.  Play around with GEO comsats first.

Offline Paul451

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Re: Distributed Lift Readiness
« Reply #5 on: 02/27/2018 02:46 PM »
there has been scattered (distributed  :D ) talk of distributed lift.
But, first, you need to prove that rivets work in space. (or bolts, or ...)

Are we talking about Distributed Lift, as in the ULA/LM concept, or just orbital structure assembly?

Online speedevil

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Re: Distributed Lift Readiness
« Reply #6 on: 02/27/2018 03:16 PM »
Preparing a push for Europa Clipper would be a worthy first objective; the technology for this push could easily be ready before the spacecraft.

Distributed launch is only one aspect of what needs to be worked on - how to do things beyond the traditional constants of spaceflight.
If BFS/Mars actually works in 2022, for the price of one expended BFS, you can throw over a hundred tons or so at Mercury, a little under a hundred at Jupiter. (or reusable, with a couple of high energy refuellings needing three tankers)

If it's delayed four years, fifty tons or so to Jupiter, with a saturn mission (or two in one) the same price.
2028, and a similar payload to Uranus.

There is a really nice earth-jupiter-uranus window in 2020, but that's probably too optimistic :)

Distributed lift is great, but you can't distribute lift at $200M per rocket very well, for obvious reasons and have much left over.

Offline Lar

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Re: Distributed Lift Readiness
« Reply #7 on: 02/27/2018 03:50 PM »
What launch company or organization has demonstrated 5 flights in a row without a single delay? Even if you discount weather delays, and why should you, I don't think anyone has.
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Online Kansan52

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Re: Distributed Lift Readiness
« Reply #8 on: 02/27/2018 04:00 PM »
Wouldn't DL benefit from a staging area, a really good space station design for serving such and operation? Or am I still living in a Disney/2001 world of stations in LEO for real work?

Online speedevil

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Re: Distributed Lift Readiness
« Reply #9 on: 02/27/2018 04:15 PM »
Wouldn't DL benefit from a staging area, a really good space station design for serving such and operation? Or am I still living in a Disney/2001 world of stations in LEO for real work?

There are many ways of doing everything! :)

A station is not an inherently bad way, especially if you can get it launched very cheaply.

Boiloff concerns can in principle be addressed on a spacecraft level.

Either active refrigeration, MLI, or even massive sun/earth shades (with gaps to radiate to cold space).

Weather and launch reliability concerns can be addressed statistically, with several launch sites and launch vehicles more tolerant of the weather.

Launch vehicle flexibility also - if you slow the BFR/BFS so that it takes an extra hundred seconds to get out of the weather, you have considerably reduced stress on the system, and retained a moderate amount of fuel to transfer over.


Offline jebbo

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Re: Distributed Lift Readiness
« Reply #10 on: 02/27/2018 04:29 PM »
Are we talking about Distributed Lift, as in the ULA/LM concept, or just orbital structure assembly?

I don't particularly mean the ULA specific idea. Really, I guess the topic is more about what will need to be done in-orbit to prepare for BEO missions(*) ... the concept of fuelling in-orbit is implied in the BFR presentations but they gloss over issues such as boil-off.  This alone leads to either a very rapid succession of tanker launches (which seems a stretch), or propellant depots. And you can rapidly expand to include no end of infrastructure

(*) Not specific to Mars. Feels like practising by going to the moon might be a step along the way, though clearly this can be done without this.

--- Tony

Online speedevil

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Re: Distributed Lift Readiness
« Reply #11 on: 02/27/2018 04:52 PM »
I don't particularly mean the ULA specific idea. Really, I guess the topic is more about what will need to be done in-orbit to prepare for BEO missions(*) ... the concept of fuelling in-orbit is implied in the BFR presentations but they gloss over issues such as boil-off.  This alone leads to either a very rapid succession of tanker launches (which seems a stretch), or propellant depots. And you can rapidly expand to include no end of infrastructure

Note that BFR is designed for multiple launches per day, per vehicle.
However, there are various options to avoid this, if it's a concern.

Extensive sun/earth shades are one, mentioned above, as are stations.
Boosting into a GTO-like orbit is another.
Earth-shading is hard in LEO, it's trivial for most of GTO, as is sun shading.

A BFS that gets to LEO with 150 tons payload can get about 70 tons fuel into GTO, and if launches are cheap, and boiloff is a bigger concern - why not?

(launch scheduling gets more problematic, and there are radiation issues)

As mentioned above, launcher flexibility can also play into it.
If you've got a launcher that absolutely requires perfect weather, then your availability is quite impacted by weather.

If your choice is not 'go, nogo', but 'meh', and you're able to do stupid things like launch and ascend at 55mph until you're at 5km, and then start accelerating, so you clear the weather, and still get to your desired orbit with half the nominal fuel load, that helps enormously.

The other approach to boiloff is that as long as you're topping it up faster than it's evaporating, that's fine too.

So, it takes eight launches not six - why do you care, if they're cheap.

« Last Edit: 02/27/2018 05:14 PM by speedevil »

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