Is there an advantage to a single booster instead of two, assuming you're reusing everything?You could put a couple Merlin vacs on a Falcon Heavy core stage, mate the payload right on top of the core stage, and accomplish the same thing with more margins and no oddly located centers of mass or thrust.
There's a whole lot of things to swing a comment at here but the largest it seems to me is that we more or less know the maximum re-entry speed is what SES-9 did, and that's right on the edge of what's possible. So all of the dV to get from orbital speed down to SES-9's re-entry speed has to be done by burning fuel. That would be a lot of fuel. Looking at the webcast of the SES-9 launch I see MECO 1 at 8250 kph, this is more or less the speed you'd need to get down to before reentry. You'd need to do that from (in the case of SES-9) a SECO of 26,980 kph. That's a lot when you're accelerating a whole first stage and the fuel.While the originally proposed concept has a lot of interesting tails to chase around and may make for a long thread I think the proposal above to put some Mvacs on a FH center core may be the one that we want to put some of our R&D time into.
I guess it depends on whether they can burn through re-entry to produce an exhaust shield.
The assumption that you can go one orbit and land in the same place is a bit flawed unless that place is two places or unless that one orbit has more orbits.
Quote from: sevenperforce on 04/07/2016 03:39 pmI guess it depends on whether they can burn through re-entry to produce an exhaust shield.Sorry. But unless you have the math that says otherwise, this is not likely to work. You would be taking the weight of the legs and grid fins almost all the way to orbit. Cross feed plumbing will weigh more too. As others have said, slowing down again would take a lot of fuel. Thus, if it comes from the booster, that booster could not provide the delta-V itself and still have enough propellant for return.
An apogee burn to define re-entry, combined with the re-entry burn and the grid fin control, should permit enough crossrange for RTLS on any launches reasonably close to the equatorial plane.
mvac bells are paper thin. exposure to atmosphere at any sort of velocity (up or down) will tear them to bits.
Source?
twice the thickness of a soda can at the end
Quote from: sevenperforce on 04/08/2016 02:30 pmSource? Source is SpaceX. Quotetwice the thickness of a soda can at the end http://www.spacex.com/press/2012/12/19/update-cots-demo-1-launch-activities
This is more speculative than anything else, and there's no evidence SpaceX is considering anything like this......but if they wanted to try pulling off 100% stage reuse for Falcon 9, I have an idea for how they could.First of all, replace two of the Merlin 1D engines on a standard Falcon 9 first stage with Merlin 1D Vacuum engines (I think they would fit, though it might be tight):
I'd need to do a bit of math to get a general notion of how much margin you'd get with one booster vs two.
I don't think you need to get down to the SES-9 MECO speed before re-entry. The problem with re-entry for SES-9 was not re-entry; it came through re-entry beautifully and headed straight for OCISLY (well, straight for the poor barge's corner).
Remember, the delta-V to get back to a landing from orbit is equal to the delta-V to get to orbit. So orbit and back requires twice the delta-V to get to orbit. Some of that you get from drag, but not too much or your vehicle burns up.
This is more speculative than anything else, and there's no evidence SpaceX is considering anything like this......but if they wanted to try pulling off 100% stage reuse for Falcon 9, I have an idea for how they could.First of all, replace two of the Merlin 1D engines on a standard Falcon 9 first stage with Merlin 1D Vacuum engines (I think they would fit, though it might be tight):Then strap on a Falcon Heavy style booster with crossfeed and put your payload on top:I'm sure you can see where this is going. Launch with all nine engines on the side booster and the seven SL-optimized engines on the payload booster. Once you're past maxQ, ignite and throttle up the two vacuum engines while throttling down the seven SL engines on the core booster; allow the side booster to burn down to its landing reserves and then separate. With the higher specific impulse and thrust of the vacuum engines, plus additional fuel from crossfeed, the payload booster should have enough dV to enter orbit, deliver the payload, and then burn off enough velocity to re-enter on a RTLS trajectory after a single orbit.The challenges would be making sure the SL engine exhaust doesn't damage the extended vacuum engine, figuring out center of thrust and center of mass due to the unbalanced launcher, and determining whether crossfeed would work. But if all that worked, then you'd have a parallel-staged fully-reusable launch system.