Hi there,Has there been talks about the possibility to refuel BFB in Orbit? (from the videos it seems that in detaches only after reaching orbit).
Quote from: sleepy-martian on 04/24/2018 09:24 amHi there,Has there been talks about the possibility to refuel BFB in Orbit? (from the videos it seems that in detaches only after reaching orbit).It does not.It detaches at somewhere around 3km/s, not the 8km/s or so to orbit. Unfortunately, orbital mechanics isn't as simple as '3 times the thrust, 1/3 the delay'.At optimal launch periods, it takes about 4.5km/s to get a hundred day transit.At non-optimal launch periods, it needs about 300km/s. (cancel earths 30km/s velocity, accellerate to 5 times that velocity on a direct course, decellerate, and match velocity with Mars)200km/s is well outside the possibilities with chemical.I thought for a while about this a bit back, and couldn't come up with a reason to refuel the booster in orbit. The booster in principle can get to orbit with no payload, it's just there is no point - once you're refuelling anyway.(and of course, it can't get back from orbit, so you've thrown away the booster)
I'm pretty sure that the booster will get nowhere near orbital velocity. The animations may have misled you.
Quote from: darkenfast on 04/24/2018 09:28 amI'm pretty sure that the booster will get nowhere near orbital velocity. The animations may have misled you.Sure the booster alone couldn't do SSTO? With an assumed 150t dry and 640t + 2300t of propellant it should be able to just like BFS alone. Getting a BFB to Mars could be interesting for a number of things too.
Hi there,Has there been talks about the possibility to refuel BFB in Orbit? (from the videos it seems that in detaches only after reaching orbit).Now this would obviously required a lot of tanker trips, but given the amount of thrust it generates I imagine you could do the mars trip way quicker, or even outside of the Transfer Windows, which would allow faster response times in case of an emergency (unexpected equipment breakdown and the likes).Being able to bring stuff to, or evacuate people from Mars within a few months instead of in the worst case 2 years would definitely make the planet more accessible and alleviate some of the concerns of long isolation times.BFB is has sea level engines though, which AFAIK can fire in vacuum at full thrust, but really shouldn't. So might the only possibility to pull this off be a 3 Stage BFR with the second stage having vacuum engines?I could also image the BFR launching to LEO in the way we currently know it. And than another BFB bringing up the and mating the DS version of the booster.
Quote from: sleepy-martian on 04/24/2018 09:24 amHi there,Has there been talks about the possibility to refuel BFB in Orbit? (from the videos it seems that in detaches only after reaching orbit).Now this would obviously required a lot of tanker trips, but given the amount of thrust it generates I imagine you could do the mars trip way quicker, or even outside of the Transfer Windows, which would allow faster response times in case of an emergency (unexpected equipment breakdown and the likes).Being able to bring stuff to, or evacuate people from Mars within a few months instead of in the worst case 2 years would definitely make the planet more accessible and alleviate some of the concerns of long isolation times.BFB is has sea level engines though, which AFAIK can fire in vacuum at full thrust, but really shouldn't. So might the only possibility to pull this off be a 3 Stage BFR with the second stage having vacuum engines?I could also image the BFR launching to LEO in the way we currently know it. And than another BFB bringing up the and mating the DS version of the booster.There has been discussion here on NSF (not AFAIK by SpaceX) about the idea of using a BFS (cargo/Tanker) as a sort of deep space booster for BFS. This is basically just adapting a Tanker so it can mate nose to tail with a BFS and using other Tankers to fill both it and the BFS with propellant. The Tanker Booster would end up looping back earth and the BFS would have significant new performance options. This seems in line with what you had in mind.If this was going to be done repeatedly, the Tanker might be modified to optimize for the role as booster and left in orbit.
Quote from: Ludus on 04/26/2018 05:07 amQuote from: sleepy-martian on 04/24/2018 09:24 amHi there,Has there been talks about the possibility to refuel BFB in Orbit? (from the videos it seems that in detaches only after reaching orbit).Now this would obviously required a lot of tanker trips, but given the amount of thrust it generates I imagine you could do the mars trip way quicker, or even outside of the Transfer Windows, which would allow faster response times in case of an emergency (unexpected equipment breakdown and the likes).Being able to bring stuff to, or evacuate people from Mars within a few months instead of in the worst case 2 years would definitely make the planet more accessible and alleviate some of the concerns of long isolation times.BFB is has sea level engines though, which AFAIK can fire in vacuum at full thrust, but really shouldn't. So might the only possibility to pull this off be a 3 Stage BFR with the second stage having vacuum engines?I could also image the BFR launching to LEO in the way we currently know it. And than another BFB bringing up the and mating the DS version of the booster.There has been discussion here on NSF (not AFAIK by SpaceX) about the idea of using a BFS (cargo/Tanker) as a sort of deep space booster for BFS. This is basically just adapting a Tanker so it can mate nose to tail with a BFS and using other Tankers to fill both it and the BFS with propellant. The Tanker Booster would end up looping back earth and the BFS would have significant new performance options. This seems in line with what you had in mind.If this was going to be done repeatedly, the Tanker might be modified to optimize for the role as booster and left in orbit.Do two BFS stages give that much more dv? I calculated a full BFB giving a 3000m/s boost to a 1335t BFS and having 3250m/s left to return. For a BFS as a push stage the margins are much tighter.
Quote from: niwax on 04/27/2018 10:32 amQuote from: Ludus on 04/26/2018 05:07 amQuote from: sleepy-martian on 04/24/2018 09:24 amHi there,Has there been talks about the possibility to refuel BFB in Orbit? (from the videos it seems that in detaches only after reaching orbit).Now this would obviously required a lot of tanker trips, but given the amount of thrust it generates I imagine you could do the mars trip way quicker, or even outside of the Transfer Windows, which would allow faster response times in case of an emergency (unexpected equipment breakdown and the likes).Being able to bring stuff to, or evacuate people from Mars within a few months instead of in the worst case 2 years would definitely make the planet more accessible and alleviate some of the concerns of long isolation times.BFB is has sea level engines though, which AFAIK can fire in vacuum at full thrust, but really shouldn't. So might the only possibility to pull this off be a 3 Stage BFR with the second stage having vacuum engines?I could also image the BFR launching to LEO in the way we currently know it. And than another BFB bringing up the and mating the DS version of the booster.There has been discussion here on NSF (not AFAIK by SpaceX) about the idea of using a BFS (cargo/Tanker) as a sort of deep space booster for BFS. This is basically just adapting a Tanker so it can mate nose to tail with a BFS and using other Tankers to fill both it and the BFS with propellant. The Tanker Booster would end up looping back earth and the BFS would have significant new performance options. This seems in line with what you had in mind.If this was going to be done repeatedly, the Tanker might be modified to optimize for the role as booster and left in orbit.Do two BFS stages give that much more dv? I calculated a full BFB giving a 3000m/s boost to a 1335t BFS and having 3250m/s left to return. For a BFS as a push stage the margins are much tighter.I suppose that depends on where you want the booster BFS to end up. It would be in some very eccentric earth orbit returning on its own. Any Dv applied after the boost would be to adjust that orbit.
But if all you need is a large tank in orbit, make a dedicated one. It would likely be based on tanker-BFS.Unlike the regular tanker, which brings fuel from the surface to orbit, this orbital fuel depot never needs to reenter. So you can strip the sea level raptors, and maybe only gice it one single vacuum raptor. That shoild be enough to get it to orbit initially - and empty.In orbit it would be fuelled by regular tankers until.full.
Then u would attach it to a BFS in tandem combo, like the shuttles external tank, or if thats too complicated just accelerate in formation to the crewed BFS, then after the initial burn, transfer the fuel to the main BFS to replenish its tanks to maximum. Maybe in a very high earth orbit or slow escape trajectory.Then the BFS does the rest.of its burn.
The almost empty fuel tank would then decelerate just enough to remain in a HEO. It could lower its Periapsis to aerobrake its Apoapsis back to LEO then be refueled again.
.. and it could never reach earth surface for maintainance.Better to have atmospheric-capable BFS-tanker which can be brought back to earth for maintainance.
Better to use ordinary BFS-tanker for this.
Quote from: hkultala on 06/13/2018 05:36 amBetter to use ordinary BFS-tanker for this.From a performance point of view, incorrect. It makes sense only because using an"ordinary" BFST (Big falcon spacetanker) avoids the complexity of needing yet another version, which for SpaceX is a biggy.
The fact that you can surface land it is a nice bonus, but its also possible to do maintenance in orbit, so that is by no means a neccesity Once the ship needs "dry dock" to repair u might as well scrap it and build a new one. ( remove the engines and utilities/avionics, store them.on a spacestation. Reenter the crippled empty hull)
The downside is that you will always drag along dead weight such as sealevel engines. For the suggested mission where the tanker stays in Jupiter orbit, this really is a waste.
But hey, if you have orbital maintenance facilities, you could also launch a BFS with sea level engines, then remove them for a deep space mission