SpaceX BFR Discussion.

[tater]

Yeah, with the min cost being the pro-rata cost of the vehicle (vehicle cost/uses + some dev amortization), then plus fuel (with profit margin built in).

[sevenperforce]

We should do the math...if an empty tanker is placed in low lunar orbit, could a fully-loaded crew vehicle leaving from LEO (no eccentric-orbit refueling) reach LLO, dump its return/landing propellant in the tanker, land, ascend, and then refuel for the homeward journey?

If they are really going to use orbital refueling for BLEO operations, they are going to need to be Scott-Manley-good at flying rendezvouses.

[Rakaydos]

On 2/24/2018 at 10:30 AM, sevenperforce said:

We should do the math...if an empty tanker is placed in low lunar orbit, could a fully-loaded crew vehicle leaving from LEO (no eccentric-orbit refueling) reach LLO, dump its return/landing propellant in the tanker, land, ascend, and then refuel for the homeward journey?

If they are really going to use orbital refueling for BLEO operations, they are going to need to be Scott-Manley-good at flying rendezvouses.

"scot manley good"

 

Did you know RL rendevus with the ISS arnt allowed to use RCS near the station? They line up the docking port (or at least the robot arm) entire orbits before rendevus, and just coast in.

[sevenperforce]

17 minutes ago, Rakaydos said:

"scot manley good"

Did you know RL rendevus with the ISS arnt allowed to use RCS near the station? They line up the docking port (or at least the robot arm) entire orbits before rendevus, and just coast in.

Is that for berthing only, or for docking as well?

[Rakaydos]

1 hour ago, sevenperforce said:

Is that for berthing only, or for docking as well?

As I understand it, it's avoiding toxic propellant impingement.

[daniel l.]

One thing that's nice about the BFR is that its interior is arranged into decks with floor-plans. This means the ship's interior can be quite comfortable in gravity.

Artificial gravity could be easily achieved by sending two BFR's to the destination and tethering them by the nose. This way they can use their RCS to pull the tether and spin themselves.

[DAL59]

On 2/24/2018 at 12:16 PM, NSEP said:

Combine This with BFR and im completely done fam.

Ok sure thing, they are both powerpoint slides.

Combine this with BFR. 

Nuclear SSTO plane.  

It could launch 20 of them, fully fueled, at once!  

What would happen if one of the BFR's engines was replaced with a NERVA?  

[sevenperforce]

19 minutes ago, DAL59 said:

What would happen if one of the BFR's engines was replaced with a NERVA?  

Nothing good.

[T-10a]

25 minutes ago, DAL59 said:

What would happen if one of the BFR's engines was replaced with a NERVA?  

!!SCIENCE!! would happen.

[Starman4308]

6 hours ago, Rakaydos said:

Did you know RL rendevus with the ISS arnt allowed to use RCS near the station? They line up the docking port (or at least the robot arm) entire orbits before rendevus, and just coast in.

I thought they were still permitted to use cold-gas thrusters?

3 hours ago, DAL59 said:

What would happen if one of the BFR's engines was replaced with a NERVA?  

Cost skyrockets as the safety concerns of using a live nuclear reactor require extensive design modifications and elaborate inspections, which describes a lot of the Space Shuttle's cost issues. There's also the issue of "how do you safely land something with a poorly shielded and fragile, lightly-built active nuclear reactor?".

[sevenperforce]

23 minutes ago, Starman4308 said:

I thought they were still permitted to use cold-gas thrusters?

Dragon has none.

23 minutes ago, Starman4308 said:

Cost skyrockets as the safety concerns of using a live nuclear reactor require extensive design modifications and elaborate inspections, which describes a lot of the Space Shuttle's cost issues. There's also the issue of "how do you safely land something with a poorly shielded and fragile, lightly-built active nuclear reactor?".

Not to mention that propellant transfer is right out.

[tater]

They use RCS around 3:30:

 

Its at like 30m away at that point

[StrandedonEarth]

59 minutes ago, tater said:

They use RCS around 3:30:

I thought so, I remembered seeing clips with thruster pulses from approaching craft. I just couldn't find an example during my quick search.

[kerbiloid]

First declare that you're going to

Spoiler

8 hours ago, DAL59 said:

. 

 

then:
Okay, okay, we will just

8 hours ago, DAL59 said:

one of the BFR's engines was replaced with a NERVA

Edited February 26, 2018 by kerbiloid

[NSEP]

 

[kerbiloid]

This cannot be. It's private and commercial, the first of its name.

P.S.
Sounds like the music from Mars series trailer was inspired by Terminator theme, while this one — by Rains of Castamere.

Edited March 2, 2018 by kerbiloid

[tater]

That video is idiotic. They might get some money (small amounts) from the USAF, maybe even NASA for some tech if NASA is interested, but as Shotwell said when asked about this, they’re building it anyway, regardless.

[DAL59]

On 2/25/2018 at 2:39 PM, WildLynx said:

suction caps, in space.

 

On 2/25/2018 at 2:39 PM, WildLynx said:

I followed the link and one of the first things I noticed is manipulators equipped with suction caps, in space.

They aren't suction cups, they are joints. 

[wumpus]

On 2/24/2018 at 1:30 PM, sevenperforce said:

We should do the math...if an empty tanker is placed in low lunar orbit, could a fully-loaded crew vehicle leaving from LEO (no eccentric-orbit refueling) reach LLO, dump its return/landing propellant in the tanker, land, ascend, and then refuel for the homeward journey?

If they are really going to use orbital refueling for BLEO operations, they are going to need to be Scott-Manley-good at flying rendezvouses.

By "refuel" I suspect you mean "dock with a complete rocket stage, ready to fire and be discarded", at least until this type of thing becomes commonplace.  The other catch is that such fuel pretty much needs to be non-cryogenic, and probably hypergolic as well, I'd strongly look into hybrid rockets (presumably pressure fed for the crew-rating, but I'd look into using turbopumped NO₂ as well) as they shouldn't need to vent.

Presumably this is how a two Falcon Heavy trip to the lunar surface would work.  Each docking would be "dock or die" which might scuttle the mission right there.

[Thor Wotansen]

7 minutes ago, wumpus said:

By "refuel" I suspect you mean "dock with a complete rocket stage, ready to fire and be discarded", at least until this type of thing becomes commonplace.  The other catch is that such fuel pretty much needs to be non-cryogenic, and probably hypergolic as well, I'd strongly look into hybrid rockets (presumably pressure fed for the crew-rating, but I'd look into using turbopumped NO₂ as well) as they shouldn't need to vent.

Presumably this is how a two Falcon Heavy trip to the lunar surface would work.  Each docking would be "dock or die" which might scuttle the mission right there.

Have you watched the video of Elon's talk at the IAC in Sydney?  He lays out the entire process pretty clear.  The regular LOX and liquid methane are transferred through the fuel connectors that are the same connectors that connect the first and second stages for fuel load on the ground.  The fuel is transferred by firing the RCS system, creating micro G forces and causing the fuel to flow 'down' into the other vehicle.  At any point either or both vessels could easily abort to land on Earth or whatever.  On paper it seems to be an elegant solution to the refuel in space problem, but will certainly need some testing.

[sevenperforce]

6 minutes ago, wumpus said:

By "refuel" I suspect you mean "dock with a complete rocket stage, ready to fire and be discarded", at least until this type of thing becomes commonplace.  The other catch is that such fuel pretty much needs to be non-cryogenic, and probably hypergolic as well, I'd strongly look into hybrid rockets (presumably pressure fed for the crew-rating, but I'd look into using turbopumped NO₂ as well) as they shouldn't need to vent.

Presumably this is how a two Falcon Heavy trip to the lunar surface would work.  Each docking would be "dock or die" which might scuttle the mission right there.

No, I meant for the BFR/BFS mission architecture.

The current BFS lunar mission profile involves launching numerous tankers to get two full tankers in LEO, sending both tankers and the crew ship into EEO, docking and transferring propellant from the tankers to the crew ship, sending both tankers back to Earth, and sending the crew ship on to a direct ascent mission at the moon.

If multiple missions were planned, however, placing a single, empty tanker in low lunar orbit would allow it to act as a propellant depot. A crew ship could launch into LEO, refuel, and then launch directly to TLI, without any need for refueling in EEO. Once in LLO, the crew ship could rendezvous with the empty tanker, transfer its TEI and EDL propellant into it, and then proceed to the lunar surface. By storing its TEI and EDL prop in the empty tanker, it should add enough margin that it would only need the LEO refuel rather than the EEO refuel. The tanker could hang out in LLO indefinitely, servicing multiple crew landers simultaneously, and then eventually heading home with its accumulated residuals.

Apollo was "dock or die" and the Constellation architecture would have been, too. 

BFS will have propellant management capabilities to allow long-duration stays on orbit, but the Falcon upper stage does not. A two-Falcon-Heavy moon mission would probably involve lofting a purpose-build lunar module and command module into LEO, already mated, then sending an empty Falcon Heavy up to dock nose-to-nose for the TLI burn. You'd need to send a Dragon 2 up first to transfer in crew and consumables.

[wumpus]

3 hours ago, Thor Wotansen said:

Have you watched the video of Elon's talk at the IAC in Sydney?  He lays out the entire process pretty clear.  The regular LOX and liquid methane are transferred through the fuel connectors that are the same connectors that connect the first and second stages for fuel load on the ground.  The fuel is transferred by firing the RCS system, creating micro G forces and causing the fuel to flow 'down' into the other vehicle.  At any point either or both vessels could easily abort to land on Earth or whatever.  On paper it seems to be an elegant solution to the refuel in space problem, but will certainly need some testing.

I'd still prefer just docking and firing if my life was on the line.  On the other hand, I'm pretty sure the ISS takes fuel to keep itself in orbit, so this appears to have been solved for at least some situations (I was expecting this to go the way of asparagus staging).

[PB666]

3 hours ago, Thor Wotansen said:

Have you watched the video of Elon's talk at the IAC in Sydney?  He lays out the entire process pretty clear.  The regular LOX and liquid methane are transferred through the fuel connectors that are the same connectors that connect the first and second stages for fuel load on the ground.  The fuel is transferred by firing the RCS system, creating micro G forces and causing the fuel to flow 'down' into the other vehicle.  At any point either or both vessels could easily abort to land on Earth or whatever.  On paper it seems to be an elegant solution to the refuel in space problem, but will certainly need some testing.

Since both fuels are cryogenic the moment of acceleration is simply to move the fuels to the transfer outlet. The pressure of the cryogenics will move the fuel, but also push the craft away from each other. Its not a robust fuel transfer system. To achieve an efficient transfer there needs to a condesation system in the recipient tank, otherwise  a vapor lock will occur and you will just that, push the craft away from each other. The recipient tanks need to be precooled and toward the end of the process transferred under pressure (as fuel flows from the first adiabatic cooling occurs and the second tank will warm, meaning fuel wants to flow backwards). 

A better way, to connect the tanks in such a way that there is centrifugal force operating. The force is pushing liquids down the tube in which the rate of flow is determined by the spin, the heat can be radiated from the recipient tank or the degassing liquid can be transferred back to the top of the source tank.

[sevenperforce]

23 minutes ago, PB666 said:

Since both fuels are cryogenic the moment of acceleration is simply to move the fuels to the transfer outlet. The pressure of the cryogenics will move the fuel, but also push the craft away from each other. Its not a robust fuel transfer system. To achieve an efficient transfer there needs to a condesation system in the recipient tank, otherwise  a vapor lock will occur and you will just that, push the craft away from each other. The recipient tanks need to be precooled and toward the end of the process transferred under pressure (as fuel flows from the first adiabatic cooling occurs and the second tank will warm, meaning fuel wants to flow backwards). 

A better way, to connect the tanks in such a way that there is centrifugal force operating. The force is pushing liquids down the tube in which the rate of flow is determined by the spin, the heat can be radiated from the recipient tank or the degassing liquid can be transferred back to the top of the source tank.

All tanks involved are autogenously pressurized. The docking/mating system is a secured hold that produces a load-bearing connection between the two vehicles. The micro-gee RCS acceleration is required only for propellant settling; once settled, simply varying tank pressure is all that's required to effect transfer.

This talk of propellant settling makes me wonder...the BFR RCS system is pressure-fed, but are they hot-gas thrusters, or are they methalox liquid thrusters? I suppose the latter is possible as long as the thrusters themselves use a tension propellant trap. Otherwise settling will be an issue.

[Elthy]

They dont need liquid fueled RCS, mixing the gases from the tank pressurisation and igniting them should provide more power than any RCS currently in operation...