SpaceX News

[D Tibbets]

The only other alternative I know of is the tentative ULA proposal to separate the expensive rocket engine assembly from the rest of the first stage and snag it in the air as it is falling under parachutes. A single stage to orbit or Shuttle approach allows for a wide choice of landing sites, but implementation has proven to be a disaster for SSTO and a cost disaster for the Shuttle.
Dan Tibbets

We are talking about snagging more weight than a C-130J can carry. twice the weight of a CH53-E can carry for the first stage. I do not know what the motors weight is
It would be very sporty at best; then there would be landing.
I don't know of anything on the other side of the fence that could work. Anyone?

It is the weight of the two(?) rocket engines and associated base plate structure of the first stage alone, the rest of the stage is sheared off. I don't know what this residual weight in relation to the first stage empty weight is.

[D Tibbets]

I'm thinking more of a Falcon 9 Enhanced. The returnable F9s have three landing legs, why not have three tuned F1s that are strapped on to, or between, the legs but transfer no thrust. They go along for the ride and are equiped to fly back. All they do is transfer fuel. Unless of course it is easier to actually transfer the thrust.

Having strap on fuel tanks that are ejected befor the first stage exaustion is a way to increase fuel to structure weight, but it is dependent on adequate thrust from the active first stage. Falcon 9 first stage has about 1.2+ million pounds of thrust. And the stack weight is (guess) about 1 million pounds. If you had two strap on fuel tanks, each with perhaps 500,000 lbs of fuel, the stack weight would be ~ 2.0 million pounds or more. Upon mission ignition the rocket would go nowhere until 800,000 pounds of propellant was burned off. Then the rocket would slowly begin to climb with initially dismal efficiency. If you add weight, you have to add available thrust, unless you already have lots of surplus thrust capacity. This is what Falcon heavy does by having the two strap on "Fuel tanks" that have their own rocket engines. This maintains, or probably actually mildly improves the overall thrust to weight ratio. You are wasting less of your fuel for just balancing out the Earth's gravity. You may also achieve some advantage by transferring some of the fuel from the strap on powered "fuel tanks" so that the primary first stage has more fuel on board upon "tank" separation than it would otherwise.

Dan Tibbets

[ladajo]

Looks like the barge is home. No gurgle. Almost though, nice hole in the deck top left of photo...

[Giorgio]

Funny, the debris seems to be evenly spread in middle of landing area while the hole is in top left.... Maybe they already moved the debris by the time they took the picture, but I am now very curious to see the on-board video to clarify the crash dynamics.

[krenshala]

I'm thinking more of a Falcon 9 Enhanced. The returnable F9s have three landing legs, why not have three tuned F1s that are strapped on to, or between, the legs but transfer no thrust. They go along for the ride and are equiped to fly back. All they do is transfer fuel. Unless of course it is easier to actually transfer the thrust.

Having strap on fuel tanks that are ejected befor the first stage exaustion is a way to increase fuel to structure weight, but it is dependent on adequate thrust from the active first stage. Falcon 9 first stage has about 1.2+ million pounds of thrust. And the stack weight is (guess) about 1 million pounds. If you had two strap on fuel tanks, each with perhaps 500,000 lbs of fuel, the stack weight would be ~ 2.0 million pounds or more. Upon mission ignition the rocket would go nowhere until 800,000 pounds of propellant was burned off. Then the rocket would slowly begin to climb with initially dismal efficiency. If you add weight, you have to add available thrust, unless you already have lots of surplus thrust capacity. This is what Falcon heavy does by having the two strap on "Fuel tanks" that have their own rocket engines. This maintains, or probably actually mildly improves the overall thrust to weight ratio. You are wasting less of your fuel for just balancing out the Earth's gravity. You may also achieve some advantage by transferring some of the fuel from the strap on powered "fuel tanks" so that the primary first stage has more fuel on board upon "tank" separation than it would otherwise.

Dan Tibbets

You want your strap on fuel tanks to have engines, though, or all you are doing is decreasing your TWR, and thus increasing your ∆v losses due to gravity. Up to a point you can still go farther (higher overall ∆v) with just more tanks, but not by much.

If SpaceX can get fuel crossfeed working reliably between the outer two cores and the center, however, they are going to get significant improvements in capabilities since the net result is the central core "launching" at a high velocity and altitude, still with a full load of fuel. In KSP, its trivial to do fuel crossfeed and see the benefits. In real life, getting the fuel crossfeed to work is difficult at best (from what I understand), and reverting to the launchpad isn't an option.

[ladajo]

This was the model the STS used with the external tank feeding the SMEs. In addition, they added the solid core recoverable boosters to makeup for the added external tank/fuel weight. The math/cost worked out that the external tank was a throw-away. Shame, it was not cheap to build.
The boosters were a wet landing, but given the simplicity of design and material, it was relatively cheap and easy to blast them clean, repaint, reload with solid fuel, and fly again. I am not sure how many cycles they got out of them.
There may be some benefit for SpaceX to consider strap-on wet recovery solid core boosters to account for the super-heavy/GEO pushes. Dry land the main liquid core, wet land the solid fuel boosters. A hybrid machine, like STS.

[paperburn1]

Space is hard, space is harder to go fast.

Reading the comments about the boosters and a strap on tanks I think we forget the original plan. Is not to get more weight to orbit but to get weight to orbit cheaply. If Elon musk succeeds just to recycle the rockets three times before he must throw them away than he is essentially dropped his costs in half. This is far cheaper per payload kilo than anyone out there currently. At this rate it would only make sense to copy his design and get on the bandwagon.

Everybody's been watching this has been saying he should be able to get 6 to 10 launches out of every first stage. If this is a case than he has lowered the cost orbit two point where the return on the investment is such that it doesn't matter.

While it's fun to speculate on different modes of getting more weight orbit I don't believe this is his plan it all and if everything goes according to what he wishes we are talking 200 to $300 a kilo to low Earth orbit and maybe only $400 a kilo to geosynchronous orbit and perhaps $500 a kilo to lunar insertion.

The future's so bright we got to wear shades

[D Tibbets]

This was the model the STS used with the external tank feeding the SMEs. In addition, they added the solid core recoverable boosters to makeup for the added external tank/fuel weight. The math/cost worked out that the external tank was a throw-away. Shame, it was not cheap to build.
The boosters were a wet landing, but given the simplicity of design and material, it was relatively cheap and easy to blast them clean, repaint, reload with solid fuel, and fly again. I am not sure how many cycles they got out of them.
There may be some benefit for SpaceX to consider strap-on wet recovery solid core boosters to account for the super-heavy/GEO pushes. Dry land the main liquid core, wet land the solid fuel boosters. A hybrid machine, like STS.

I think the solid boosters in the STS were warped by the internal pressures and/ or smacking into the water at parachute speeds. They had to add machinery to round up the sections and perhaps stretch one side or the other so that they would join together appropriately. This added cost and I presume shortened the anticipated lifetime. Another area where the mostly reusable shuttle deviated from early cost saving estimates. I assume that the Space X first stages-one to threeon the launch vehicle, will need little effort to prepare for the next flight, if as advertised, they might be used only a few days later. Weather this optimistic scenario plays out or additional costs creep in is probably as important as the recovery itself.

Dan Tibbets

[D Tibbets]

Space is hard, space is harder to go fast.

Reading the comments about the boosters and a strap on tanks I think we forget the original plan. Is not to get more weight to orbit but to get weight to orbit cheaply. If Elon musk succeeds just to recycle the rockets three times before he must throw them away than he is essentially dropped his costs in half. This is far cheaper per payload kilo than anyone out there currently. At this rate it would only make sense to copy his design and get on the bandwagon.
...


The future's so bright we got to wear shades

Space is hard, space is harder to go fast.

Reading the comments about the boosters and a strap on tanks I think we forget the original plan. Is not to get more weight to orbit but to get weight to orbit cheaply. If Elon musk succeeds just to recycle the rockets three times before he must throw them away than he is essentially dropped his costs in half. This is far cheaper per payload kilo than anyone out there currently. At this rate it would only make sense to copy his design and get on the bandwagon.
....

The future's so bright we got to wear shades

Certainly, light system weight is a very important starting position. From that point the choices become more convoluted.

Cheap is a relative term. Launching a 10,000 lb payload to LEO with a launch system costs twice as much as lofting 20,000 lbs with the same system. Or, launching two satellites for the launch cost of one is almost always preferable. A Falcon heavy might cost twice as much per launch, but if it lofts 3 times the payload, the cost per pound is decreased.
This also implies that good planning and matching the launch system capacity to the commercial users needs is important. If you have a rocket that has a launch capacity of 40,000 pounds, but most missions only carry 20,000 lbs, you are only utilizing only 50% of the name plate capacity and costs per pound would approach twice the advertised cost. The percent of non payload weight to orbit or some component towards orbit is also important for final cost. The Shuttle failed miserably, probably mostly due to this consideration. The empty Shuttle weighed ~ 180,000 pounds and the external tank about 40-50,000 pounds. Space X has low system weight and this makes it significantly easier to offer lower costs to customers. Of course they have to incorporate reliable performance of the system. Re usability of portions of the system can also lower costs provided recovery is reliable and refurbishment is cheep, and launch reliability is maintained. And, if the re usability weight penalties are acceptable.

The Falcon heavy will have greater margins (um... well, at least potentially) so that associated re usability is easier and payload is improved. And the increased payload is essential for launching the Crewed Dragon, and may allow for more efficiency with multiple payloads. A simple example would be launching three satellites instead of two. The cost of the deployment system, and shroud would be less per satellite. It is not just a weight consideration.

Rocket science is complicated, so is balancing various considerations from a business perspective.

Dan Tibbets

[ladajo]

Okay Dan, fair point, but also note that in reality the shuttle was a soft recoverable space station. This gave it capabilities that have never been matched.

[paperburn1]

Side note, the shuttle external tank was originally intend to be taken to orbit for industrial civilian use but due to a lot of factors this never panned out.
http://www.permanent.com/ext-tank.htm

[ladajo]

I vaguely remember that now. Thanks for the link and mental refresh. Too bad we wasted all that.

[D Tibbets]

Side note, the shuttle external tank was originally intend to be taken to orbit for industrial civilian use but due to a lot of factors this never panned out.
http://www.permanent.com/ext-tank.htm

I also am reminded. There was also a proposal to use a highly modified Shuttle as the basis for a new station. The cost sharing with the Russians that already had an advanced design implementation for their next station after MIR made more sense (I suppose). The Shuttle had some impressive capabilities, but compromises, mission creep, and Air Force abandonment contributed to the cost escalation. As a pure shuttle it was grossly expensive. Mismanagement compromised safety and reliability, and politics didn't help either.

It is perhaps ironic that the Air Force abandoned the Shuttle at least in part due to cost, but eventually ended up paying ULA enough for two Shuttle launches per year for the privilege of paying more for actual launch services. Talk about mismanagement (read as theft!). The private service for set cost approach seems to be a very important aspect of a good management approach. This may be as important as any engineering considerations.
Of course the graft continues- like the new funds for ULA for rocket development. I am amused, enlightened and dismayed that this condition is not limited to only space access.

Dan Tibbets

[kunkmiester]

I seem to remember most rockets burn a surprising amount of fuel on the pad before they even begin to move.

If cross linking works, what would be the savings of hooking the rocket to the tower and burnING land based fuel until take off?

[ladajo]

That is an interesting question. Of course there could be significant risk for the gantry lines and the engine plume. Wouldn't be cost effective to detonate your launch pad with each boost.

I bet it could be engineered. But from a physics standpoint, the argument sees counterintuitive.
Although, it would seem getting over that initial inertia hump could save a good amount of "go juice".