Falcon 9 flight trajectory

[imspacy]

And without RTLS forget about recycling the rocket in a matter of hours or days.

I beg to disagree...
Suppose SpaceX has a floating barge somewhere downrange, supporting booster landing and some refuel capability....
The booster can then use atmospheric aero drag to reduce both vertical and horizontal speed, no need to eliminate horizontal speed much less get a return component.... so only minimal delta-v is needed to minimally reduce/control speed to avoid reentry damage, and for a high-gee landing..
Then fuel it up enough to RTLS, send it back... if the booster is designed for re-use, this shouldn't be a problem.
Of course, a slow boat back is not a problem either... so what if it takes a few days for the boat trip back.. a trivial expense ($10k?) compared to throwing away a $50 million vehicle.

We all have to readjust our mindset for reusability... for example, so what if the booster airframe needs to be twice as big for the same payload, when you save 96% of the cost (airframe) and only spend on fuel (4%)..

[pagheca]

I fully agree with you on the need to develop reusability.

What doesn't seem right is:

1) if you do not RTLS you cannot, as Elon Musk claimed several time, relaunch in a matter of hours. Musk never mentioned a barge. He mentioned a real RTSL.
2) a 30% fee on the payload seems to me extremely optimistic for RTLS. I'm not talking qualitatively. I just did my homework and the numbers show we are completely out of the game with a Falcon 9 v1.1, even in the most optimistic scenario.

Again: I'm not saying Elon Musk is wrong. He is clearly on top of that. What I mean is which flight profile may allow an RTLS.

Again 2: powered descent is clearly feasible. RTSL seem a completely different business and would require much more powerful rocket and engines.

cheers

[Jcc]

While landing on a barge may be possible, and would allow more payload, it is apparently a lot more complicated than landing on land and more prone to failure, so that is not the first choice. A landing platform that is big enough and stable enough to be reliable would also be quite expensive to buy and maintain.

[pagheca]

just to point out how good the aerodynamic drag on the first stage can be, I just noticed that the dry to wet ratio of the 1st stage of a Falcon is not that different from the one of a 330 ml beer can (ok, the height to diameter ratio is not).

Falcon 9 v1.1 1st stage: 18000/390000 = 4.6% (other sources give a dry mass slightly higher)
330 ml beer can: 14/(330+14) = 4.1%

This gives an idea of how much sophisticated must be the design and material used here, considering a beer can doens't features 9 engines so far as I know , and must not survive to a Max Q and the stresses of a launch. Amazing...

[gospacex]

Going to a steeper launch profile is simply a waste of fuel. Yes it would result in less fuel to return to launch site, but at the expense of not achieving orbital velocity and having your satellite crash back to earth.

Wrong.
It's far from being pointless for first stage to throw second stage way above atmosphere with significant vertical velocity component.
It allows second stage to fire more horizontally, having less gravity losses.

[ArbitraryConstant]

What really matters is the delta-v in rocket propulsion. Specially when the gravitational drag must not be taken in account (and we are talking about the horizontal velocity). So, in terms of propellant to be used for such a maneuver, it doesn't matter if you build up speed slowly or not or if you have more or less time.

As the first stage is moving downrange prior to relight, acceleration does matter since total displacement downrange will be increasing with time.

[Avron]

Whatever calcs are made, leave some margin on landing, as you want to shut the center engine down in a controlled manner and not have a RUD on landing, that will defeat the purpose

[meekGee]

And without RTLS forget about recycling the rocket in a matter of hours or days.

I beg to disagree...
Suppose SpaceX has a floating barge somewhere downrange, supporting booster landing and some refuel capability....
The booster can then use atmospheric aero drag to reduce both vertical and horizontal speed, no need to eliminate horizontal speed much less get a return component.... so only minimal delta-v is needed to minimally reduce/control speed to avoid reentry damage, and for a high-gee landing..
Then fuel it up enough to RTLS, send it back... if the booster is designed for re-use, this shouldn't be a problem.
Of course, a slow boat back is not a problem either... so what if it takes a few days for the boat trip back.. a trivial expense ($10k?) compared to throwing away a $50 million vehicle.

We all have to readjust our mindset for reusability... for example, so what if the booster airframe needs to be twice as big for the same payload, when you save 96% of the cost (airframe) and only spend on fuel (4%)..

"real" RTLS is of course preferable, but it's not an absolute.

The land-and-fly-back concept might win for the center core.  It is still RTLS in that there is no transport of the rocket by other means, and the time span can be measure in < 1 hour.  Once it lands, it join the regular flow as if there was no refueling.

For Mars launches from TX, the location of the refueling pad is pretty much fixed, which further simplifies things.

[TrevorMonty]

They have priced F9 launches based on fact it is expendable, recovery is optional.  There is a lot of unknowns in recovery but you can be assured they will apply all knowledge gained to any LV the Raptor is used in.

[pagheca]

They have priced F9 launches based on fact it is expendable, recovery is optional.  There is a lot of unknowns in recovery but you can be assured they will apply all knowledge gained to any LV the Raptor is used in.

Actually Musk is committed to make F9 a resuable vehicle. He mentioned several time this is the real aim of SpaceX. All the rest is a mean to reach this goal (and actually allow a human mission to Mars). He stated he would consider a failure in doing so a personal failure.

F9 is designed to become reusable. What I question is if a RTSL is practical or not. Anyway, Blue Origin is doing the same, with an even more larger in diameter first stage (that would allow much larger aerodynamic drag to help).

[CuddlyRocket]

They have priced F9 launches based on fact it is expendable, recovery is optional.  There is a lot of unknowns in recovery but you can be assured they will apply all knowledge gained to any LV the Raptor is used in.

Actually Musk is committed to make F9 a resuable vehicle. He mentioned several time this is the real aim of SpaceX. All the rest is a mean to reach this goal (and actually allow a human mission to Mars). He stated he would consider a failure in doing so a personal failure.

Musk being committed to F9 reusability does not mean that the F9 isn't priced based on costs incurred if it were to always be an expendable rocket. Reusability is not guaranteed (although I personally think they will make it work) and it therefore makes sense for prices at present to be based on expendability. Once reusability is demonstrated prices can be adjusted (hopefully down! ).

Also, F9 is IMO a self-financing development vehicle - they are using it to develop the knowledge and techniques required for reusability whilst pulling in the funds. But I'd be surprised if they weren't already planning its successor; with methalox engines etc (though it might turn out that it's cost effective to keep the F9 for smaller payload missions).

[pagheca]

Whatever calcs are made, leave some margin on landing, as you want to shut the center engine down in a controlled manner and not have a RUD on landing, that will defeat the purpose

What RUD means? I couldn't find that acronym over the internet.
Thanks

[Lee Jay]

Whatever calcs are made, leave some margin on landing, as you want to shut the center engine down in a controlled manner and not have a RUD on landing, that will defeat the purpose

What RUD means? I couldn't find that acronym over the internet.
Thanks

Rapid Unplanned Disassembly.

[guckyfan]

What RUD means? I couldn't find that acronym over the internet.
Thanks

Rapid Unscheduled Disassembly.

Some rude people call it an explosion.

[pagheca]

Ok, thanks.

One more question: is someone aware of how far downrange was exactly the landing site for the latest Falcon 9 v1.1 flight?

[pagheca]

really no one is able to answer the question I asked in my previous message?

Sorry to insist, but I need it for my simulations.

Thanks

[neoforce]

really no one is able to answer the question I asked in my previous message?

Sorry to insist, but I need it for my simulations.

Thanks

I'm pretty sure that answer isn't publicly available.  As stated in the post SES-8 article at http://www.nasaspaceflight.com/2013/12/ses-8-success-trajectory-future-spacex-possibilities/:

sources note there was also a boost back test during the SES-8 mission, or at least the restart of the first stage post staging.

So, we don't even know when the restart of the first stage happened.  SpaceX keeps some things close to their vest and releases things when it suits them. 

If you are insisting on information from SpaceX, you should always remember what the Man in Black said:  "Get used to disappointment."

[pagheca]

"Nobody knows" is actually an answer to my question... Thanks! I will try put this as an unknown in my simulation.

p.s. My plan is to wrote an extended simulator in MathCAD rather than excel or google drive spreadsheet. It doesn't allow me to solve the general equations of motion to minimize propellant usage, but I may iterate onto a few free parameters to see which obtains the best result. I'm now including an atmospheric model into it and would like to do the same using a reasonable model of the Merlin 1D throttle. Once I have a working testbed I will convert everything to python.

[starsilk]

really no one is able to answer the question I asked in my previous message?

Sorry to insist, but I need it for my simulations.

Thanks

try looking for the location of the 'american islander'.

[Lobo]

Going to a steeper launch profile is simply a waste of fuel. Yes it would result in less fuel to return to launch site, but at the expense of not achieving orbital velocity and having your satellite crash back to earth.

Wrong.
It's far from being pointless for first stage to throw second stage way above atmosphere with significant vertical velocity component.
It allows second stage to fire more horizontally, having less gravity losses.

Yea...

Is there a reason that F9 couldn't ascend mostly vertical and then the 2nd stage pitches and adds the additional required dV to get to orbital velocity?  That would prevent the F9 booster for getting very far down range and would essentially fall right back to the launch pad, needing only course corrections, and maybe a retro burn prior to getting too far in the atmosphere to slow down so it doesn't hit the atmosphere too fast.  Basically what the Shuttle SRB's did, and would have done if SRB Sep had been before the Shuttle started it's pitch.  Of course, you don't want burnt out SRB's crashing back down onto a populated area.  ;-)
So they really probably did want them to be jettisoned after the Shuttle pitched away from the Florida coast.  With a "smart" booster like F9, couldn't you keep mostly vertical until staging?
Maybe you'd still want to be 10-20 miles off the coast in case of a problem, the stage would fall into the ocean off the Florida coast, rather than risk falling into the populated coast.  F9's RCS system and engines could then guide it back to a landing site at the Cape if everything is operating properly.