Talk-Polywell.org

I guess it deepends on the downrange needs verses the ability on the unit to translate back uprange. I don't think it gets orbital, so it can't make a single loop return. I am not clear on how the profile works in real terms.

ladajo wrote:I guess it deepends on the downrange needs verses the ability on the unit to translate back uprange. I don't think it gets orbital, so it can't make a single loop return. I am not clear on how the profile works in real terms.

I was wondering about this too... Not sure if it could make it to Africa, but even if it did, it seems the cost to return it would outweigh the benefit. Likewise wouldn't getting back up range too much fuel to make it practical? Confused about how this will work....

EDIT: Musk estimated that saving the fuel to perform a controlled landing on water requires sacrificing 15 percent of the potential payload; returning to land will take a 30 percent cut

Still doesn't say where that land is, though.

If the first stage was landed across the Atlantic from the launch site, the easiest way to get it back home might be to fuel it up and have it fly itself back. But self ferry reduces the number of launches a stage can make.

If you had the needed hoist at both ends, a cargo ship could transport it, but that's slow.

Even if engineering considerations close, I'd be wary of recovery in Africa on account of local unstable politics.

Looks like touch down accuracy is excellent, what about a used oil rig platform converted to just a pad?

mvanwink5 wrote:Looks like touch down accuracy is excellent, what about a used oil rig platform converted to just a pad?

But what, then, is the advantage vs just landing in the ocean? A little less wear?

Also, if landing in the ocean, why not just use parachutes ala the shuttle SRBs? Is the spacex first stage fast enough the it would burn on re-entry?

Maui wrote:But what, then, is the advantage vs just landing in the ocean? A little less wear?

Landing in the ocean, via chute or engines, means dropping the stage and its expensive engines into salt water... for hours.

And the F9R 1st stage is meant to return to the launch site. Launchers spend most of the boost stage getting out of the lower atmosphere before arcing over and accelerating into orbit.

So if you're going to land a first stage then you might as well land it where it started from... which is also where all of the support gear is.

zapkitty wrote:

Maui wrote:But what, then, is the advantage vs just landing in the ocean? A little less wear?

Landing in the ocean, via chute or engines, means dropping the stage and its expensive engines into salt water... for hours.

And the F9R 1st stage is meant to return to the launch site. Launchers spend most of the boost stage getting out of the lower atmosphere before arcing over and accelerating into orbit.

So if you're going to land a first stage then you might as well land it where it started from... which is also where all of the support gear is.

Exactly. Also the goal is to refly it with minimal processing inbetween flights.

So, the question remains, what is the actual flight profile to include lateral translation of the first stage?
How much pitch over and down range does it do? Even the shuttle boosters got out to sea a ways.

And 30% fuel is a lot of lift.

I don't think it is so viable to land at the same launch site.

I do like the idea of an offshore platform on the continental shelf. Or even a large landing barge, if the rocket is stable enough when empty for small pitch and roll.
If it is accurate enough, the barge pad could even be gimbled with some sort of landing clamp stabilization system.

Just thinking craziness out loud here.

Russia would sure like to have a SpaceX recovery system!

Maui wrote:Also, if landing in the ocean, why not just use parachutes ala the shuttle SRBs? Is the spacex first stage fast enough the it would burn on re-entry?

He's practicing for landing on the Moon and Mars.

ladajo wrote:I do like the idea of an offshore platform on the continental shelf. Or even a large landing barge, if the rocket is stable enough when empty for small pitch and roll..

That's what SeaLaunch does. . .erm. . .without the landing part.

The Zenit costs even less than the Falcon, but it's old Russian tech and can't compete so far as the efficiency needed to tail land. I think the costs of launch on land and sea will dictate where to launch from and so far, it looks like land. FL is closer to the equator so there's some real benefit there if one can find an empty enough area. The more equatorial the launch, the more home grown horizontal V.

That's what SeaLaunch does. . .erm. . .without the landing part.

Yes, I know. And the platform they use is not so conducive for landings.

ladajo wrote:So, the question remains, what is the actual flight profile to include lateral translation of the first stage?
How much pitch over and down range does it do? Even the shuttle boosters got out to sea a ways.

And 30% fuel is a lot of lift.

I don't think it is so viable to land at the same launch site.

I do like the idea of an offshore platform on the continental shelf. Or even a large landing barge, if the rocket is stable enough when empty for small pitch and roll.
If it is accurate enough, the barge pad could even be gimbled with some sort of landing clamp stabilization system.

Just thinking craziness out loud here.

It is not just the fuel that took a lot of payload, but also the legs and the improved structure. The stage is pretty much empty and there is no second stage and payload on it. It also does not have to fight gravity on the way back. Essentially it is still coasting upwards and all you have to do is brake and turn around and fly back. The braking part is something you have to do whether you return to the launch site or whether you land somewhere downrange. That is what they tested this time together with the landing burn, which is also something you have to do when you land down range. So the only additional fuel you need is for the burn that flies you back. So the difference is not that huge.
There was a lot of discussion on various forums about why RTLS is better than landing downrange and it all comes down to cost of operation. For an RLV performance is secondary to the cost of operating the LV. The shuttle was an example where this was completely neglected and that is why it was extremely expensive to operate with long maintenance hours between flights. Musk wants the exact opposite and that is a good thing. He essentially wants 24 hours turn around for a first stage. So you fly back, do a very superficial inspection, add the second stage and the payload, retank the stage and then fly again 24 hours later. If you can not keep the operating cost down, RLVs make no sense.
Landing downrange, especially on a floating platform opens a whole can of worms. First of all, you need a stable platform, even at 20 foot waves (like they had this time). That means it has to be big, very big. You need the platform. You need the staff to operate the platform. The platform needs to be able to move to the location the stage will be landing at, depending on the inclination and it has to do so quickly to not cause delays between launches. So it either has to be towed, or be capable of moving on its own. Then the stage has to be transported back to the launch site, which can take days (ships are slow). All the while the crew on the platform needs to be paid.
RTLS is much simpler, all it costs is fuel and that is extremely cheap compared to the rest of the launch costs (Musk once said about 200k USD for a launch). The fuel you need for RTLS barely makes for a rounding error compared to the total launch costs.

I need to find something that no shit talks about the proposed flight profile.

Not just some shiny Power Point Graphic that doesn't tell you dick.

Whole lot of hand waving going on right now. We need some facts to chew on.

Skipjack wrote: RTLS is much simpler, all it costs is fuel and that is extremely cheap compared to the rest of the launch costs (Musk once said about 200k USD for a launch).

I don't think anyone questions that RTLS is ideal if you can do it. My question, at least, is HOW is this done.

Skipjack wrote: So the only additional fuel you need is for the burn that flies you back. So the difference is not that huge.

This is the part I'm having a hard time with... if I had to guess, by the time the first stage separates, I'd think ~90% of the momentum is along the x-axis. Gravity, in this case, doesn't help you much in getting back to the launch site. Reversing course (even on an empty 1st stage) strikes me as impractical/impossible... though I'm certainly open to the fact that my hunch is wrong. Someone earlier suggested it might be easier to actually accelerate further to make it once around... this strikes me as somewhat more possible. Even then, still surprised it only means sacrificing 30% payload, though.

EDIT: Indeed, my hunch was wrong-- the plan is to turn around:

If the technology is used on a reusable Falcon 9 rocket, the first stage separation would occur at a velocity of approximately 2.0 km/s (6,500 km/h; 4,100 mph; Mach 6) rather than the 3.4 km/s (11,000 km/h; 7,000 mph; Mach 10) for an expendable Falcon 9, to provide the residual fuel necessary for the deceleration and turnaround maneuver and the controlled descent and landing.

http://en.wikipedia.org/wiki/SpaceX_reu ... nt_program
http://www.popularmechanics.com/science ... ns-6653023